Basic knowledge of lead smelting

In recent years, China’s lead smelting industry has seen significant development. According to the 2000 \"Non-ferrous Metals Statistics,\" in 1999 the annual production of lead for electrical use was 918,400 tons (including lead recovered from recycling). Of this, 812,000 tons were mineral lead (including imported lead-containing materials). Domestic lead concentrate contained 501,000 tons of lead, yielding 486,000 tons of crude lead. The annual production is currently rising rapidly. There are over 800 lead smelting plants nationwide, including 66 state-owned enterprises, 606 collective enterprises, 14 joint-stock enterprises, 15 cooperative enterprises, 34 private enterprises, 21 foreign-invested enterprises, and 19 individual enterprises. Among these lead smelting plants, single leased lead smelting plants, single electrolytic refining plants, and integrated lead smelting plants that have both roughing and electrolytic refining processes account for roughly one-third each. In lead smelting plants, there are only 5 large enterprises with an annual crude aluminum production capacity of over 50,000 tons, namely Zhuzhou Smelting Plant, Shenyang Smelting Plant, Shaoguan Smelting Plant, Northwest Lead-Zinc Smelting Plant, and Yuguang Gold-Lead Group. There are a total of 16 plants with an annual crude lead production capacity of 10,000 to 40,000 tons. The rest are all below 10,000 tons. In recent years, the production and sales of lead in our country have been strong; in addition to meeting domestic market demand, a large amount of lead is also exported. Lead smelting enterprises generally achieve profits and enjoy good economic returns, making it a favorable sector within the non-ferrous metals industry. China’s lead smelting processes are less diverse than those for copper; all crude lead is produced through pyrometallurgical methods. For the refining of crude lead, only the Silver, Lead, and Zinc Plant has adopted a fully pyrometallurgical refining process; all others use electrolytic refining. For the smelting process of crude lead, the Baiyin Lead-Zinc Smelter has adopted the QSL method from German company Lurgi, the Jijie Smelter in Yunnan uses the pelletization and blast furnace smelting method, while the Guangdong Qianjin Smelter once used the electric furnace reduction smelting method for sintered blocks; all other lead smelters employ the sintering and blast furnace smelting method. Lead smelted in sintering blast furnaces accounts for over 95% of China’s total mineral lead production. A Sintering machines, sintering pots, and sintering trays are used for sintering. In the smelting process using blast furnaces, the concentrate is sintered; larger manufacturers use sintering machines for this purpose, while the vast majority of small and medium-sized enterprises employ sintering pots or sintering trays. The manufacturers that use sintering machines to process lead concentrate include: Zhuzhou Smelting Plant, Shenyang Smelting Plant, Huize Lead-Zinc Mine, Yuguang Gold-Lead Group, Anyang Tangyin Lead Smelting Plant, Shaoguan Smelting Plant, and Baiyin No. 3 Smelting Plant – a total of 7 companies. Among them, except for Huize Lead-Zinc Mine which uses suction sintering to process oxidized ore and the high-lead slag left over from traditional lead smelting, the other 6 plants all use blast sintering. Yuguang Jinlian Group and Anyang Tangyin Lead Smelting Plant have low-concentration SO2 acid production facilities for the flue gas from lead blast furnace sintering, with a sulfur recovery rate of approximately 80%. The Shaoguan Smelter and the Baiyin No. 3 Smelter process mixed lead-zinc concentrates, producing both lead and zinc using the ISP process; as the raw materials contain high levels of sulfur, double-turn double-suction systems are used instead of single-turn single-suction acid production units to manufacture sulfuric acid. The Zhuzhou Smelting Plant, the Shenyang Smelting Plant, and all other manufacturers that use sintering tables and sintering kettles to produce sintered pellets do not produce acid from their flue gases; these gases are simply released directly through chimneys. Approximately 0.6–0.7 tons of SO2 are produced per ton of mined lead. In 1999, 812,000 tons of lead were mined; the flue gases from factories such as Shaoguan Smelting Plant, Baiyin No. 3 Smelting Plant, Yuguang Smelting Plant, and Tangyin Smelting Plant were used to produce acid ； Smelting plants in Huize, Jijie, etc., process lead oxide ore ； Many smelters process some of the secondary lead materials they acquire on their own; in total, this amounts to about 250,000–300,000 tons of lead, and this does not cause SO2 pollution. Meanwhile, 500,000 tons per year of mineral lead generate 300,000–350,000 tons per year of SO2 emissions, which are released directly into the atmosphere and cause pollution at high altitudes. Lead sintering machine, sintering tray. The operation of the sintering furnace, as well as multi-stage regrinding, pose serious problems related to low-level pollution from lead dust and lead vapor; the working conditions are extremely harsh. Lead smelting is currently the sector in China’s non-ferrous metal production that has the worst working conditions and the most severe environmental pollution. Zhuzhou Smelting Plant is currently the largest plant in China that produces crude lead using sintering machines and blast furnaces for smelting. In 1999, 95,000 tons of lead for electricity production were produced. The main process is as follows: the sintered pellets produced by the sintering machine are sent to a blast furnace for smelting, and the resulting slag and lead are separated through sedimentation in an electric heating pre-bed. The slag is sent to a smelting furnace for treatment, to volatilize and recover the remaining lead and zinc. Crude lead is sent for electrolytic refining; the resulting electro-lead is cast to produce refined lead. The Third Smelting Plant of Hunan Shuikoushan Mining Bureau is the largest smelting plant in China that uses sintering furnaces and blast furnaces for melting, and it produced 50,500 tons of lead in 1999. Except that the materials are sintered in a sintering furnace, which differs from the Zhuye method, the overall process involves melting in a blast furnace, separating slag and lead using an electric heating pre-bed, electrolytic refining of crude lead, and the volatilization of residual lead and zinc in a slag flaring furnace for recovery. The Lancang Smelter was the first smelter in China to use sintering discs for sintering and blast furnaces for the reduction and melting of lead; in 1998, it produced 10,000 tons of refined lead. The plant originally processed the high-lead slag left over from local lead smelting, as well as some lead oxide ore. After sintering on sintering tables, the sintered material was melted in a blast furnace together with the old slag. The crude lead produced is sent to the original Kunming smelting plant for electrolytic refining; the sintering tables at that plant have been in use since the mid-1950s. The BQ, S, L process: In the 1980s, the Baiyin Northwest Lead-Zinc Plant introduced from the German company Ruhrkohle AG a lead smelting plant using the Q, S, L process, with an annual production capacity of 50,000 tons of refined lead; this plant began trial operation in 1995. During the trial operation, the daily processing capacity of the furnace charge reached 281.3, the vertical recovery rate was 93.9%, and the grade of crude lead was 99.25%. The flue gas contains 7.6% to 11% SO2. There were some local issues at the time of commissioning, and it has been shut down ever since. This plant was the first in the country to use a purely pyrometallurgical method for the production of refined lead; it was equipped with all necessary facilities. However, due to the shutdown of the roughing system, the pyrometallurgical refining process could not be operated effectively. The “Shuikoushan lead smelting method,” developed through joint efforts by 8 organizations including the Shuikoushan Mining Bureau and the Beijing Institute of Non-ferrous Metallurgy Design and Research, underwent semi-industrial trials in 1988, with additional tests conducted in 1998. The overall lead recovery rate was 97%, the grade of the crude lead was 98.4%, the desulfurization efficiency in the oxidation stage was 9**, the SO2 content in the flue gas exiting the furnace was 15%, and the lead precipitation rate in the oxidation stage was 40%. The treatment capacity of the oxidation section is 5 to 10 t/(m3·d), with a dust emission rate of 20%. The productivity of the blast furnace reduction melting bed (for high-lead slag) is 40 t/(m2•d); the lead recovery rate is 94%, the lead content in the slag is 3%–4%, the dust emission rate is 3%, and the SO2 content in the exhaust gases is less than 400×10^-6. The comprehensive energy consumption per ton of lead (in standard coal) is 655 kg/t, and the total processing cost is 10% lower compared to smelting using a sintering machine and a blast furnace. This process has been used for the renovation of the lead smelters at Chizhou Smelting Plant and Yu Guang Gold and Lead Group. D Secondary lead resource utilization: China ranks second in the world in terms of both lead production and consumption, but the recycling of secondary lead resources (recycled lead) is at a quite low level. According to statistics from 1991 to 1999, the production of recycled lead accounted for only 10% to 30% of the total production. In recent years, some local enterprises have introduced technologies for recovering lead from used batteries, as well as some key equipment, from the United States and Australia. For example, Jiangsu Chunxing Group introduced American technology and established three enterprises. Mechanical automatic battery disassembly is used to separately recover and process plastic, lead sulfate sludge, and metal fragments. The group’s processing capacity has reached 120,000 tons per year; in 2000 it produced 60,000 tons of lead, and it is now preparing to adopt foreign technologies in order to further expand its production capacity. Since 1985, Hubei Jinyang Co., Ltd. has introduced two patented technologies and taken the lead in researching and developing \"pollution-free recycled lead technology.\" It has now established a production base for recycled lead and lead alloys capable of processing 65,000 tons of used lead-acid batteries per year, producing 40,000 tons of recycled lead, 35,000 tons of lead-based alloys, 10,000 tons of electrolytic lead, and 1,500 tons of lead products. In addition, Shanghai Feihong Non-ferrous Metals Co., Ltd. has adopted Australian technology to establish a smelting plant capable of processing 50,000 tons of waste per year. The effective recovery of secondary lead has already begun. Overall, secondary lead recycling is mainly carried out by township enterprises and individual businesses across the country; these entities typically use manual methods to disassemble used batteries, allow the lead sludge to dry naturally, and combine it with other waste alloys and materials. Smelted in batches using a reverberatory furnace. These factories have a low recycling rate for pencils, poor environmental conditions, and waste gases, wastewater, and lead dust pose hazards to the workers and the surrounding environment ； It has a small scale, poor management levels, and no centralized department in charge; it operates in a state of laissez-faire. Summary: (l) China’s production of electric lead increased from 296,500 tons in 1990 to 918,400 tons in 1999, a tripling over 9 years with an average annual growth rate of 13.38%. It is the metal with the fastest growth rate among heavy non-ferrous metals. In addition to meeting domestic demand, lead is also exported in large quantities; in 1999, the total export volume of lead was 470,000 tons. Over the past five years, exports have been increasing at an average annual rate of 19.6%, making China the world’s second-largest producer of lead. (2) In China’s lead smelting industry, 100% of production relies on the sintering-blast furnace smelting process and electrolytic refining of crude lead. The Northwest Lead-Zinc Smelting Plant has adopted a new process that involves one-step lead smelting using Q, S, L methods, along with full-fire refining of crude lead; however, there are still some engineering issues, and production has not yet commenced ； Lead smelters operate on a small scale but in large numbers; the vast majority of them lack SO2 recovery systems, resulting in severe pollution both at high and low altitudes. It is the industry with the worst environmental conditions among those involved in the production of non-ferrous metals. (3) The recycling of secondary lead resources has not received adequate attention or focus from relevant authorities, remaining at a quite low level: the recovery rate of secondary lead is far below the world average of 50%. (4) The severity of pollution caused by lead smelting has drawn widespread attention from various levels of government in our country. Measures are being taken to shut down a number of small lead factories with severe pollution levels, and to introduce advanced technologies to establish large-scale factories instead ； Transforming existing small and medium-sized lead smelters using the bottom-blown single-blast furnace smelting process developed in our country ； Using Topso technology to produce acid from sintering plant flue gas ； Locally modify the Northwest Smelting Plant system to restore production of the Q, S, and L processes. After the implementation of the above measures, the environmental pollution caused by lead smelting in our country will see a fundamental improvement.

The current status of lead smelting technology over the past decade or so. The present situation of lead smelting technology in the recent ten years. China Enfi Nonferrous Engineering Co., Ltd., Wang Zhongshi. 1. The current status of lead smelting technology abroad. The current situation of world lead smelting technology. Traditional processes involving sintering and blast furnace reduction are still used for lead smelting abroad, and these methods account for the majority of production volumes. However, it has drawbacks such as high energy consumption, severe environmental pollution, and poor working conditions. Factory construction was rare in the late 20th century. Some research institutions began their studies in the late 1960s, aiming to develop a new direct smelting method that was technologically advanced, economically viable, characterized by high melting efficiency, continuous processing, and a combination of roasting and smelting, so as to achieve self-heating or essentially self-heating smelting of lead sulfide concentrate and thereby reduce or eliminate environmental pollution. Since lead and its sulfides and oxides have high vapor pressures at high temperatures and are prone to volatilization—especially lead sulfide, which has significant volatility characteristics—this posed considerable challenges to direct smelting and its flue gas systems. As a result, early technological development progressed slowly. It was not until the late 1980s, through extensive experimental and engineering research, that breakthroughs were achieved in suspension smelting and bath smelting technologies. These advancements also included research on the reduction control of lead slag, the development of new waste heat boilers, and improvements to furnace design and lining protection, enabling new lead smelting processes to move toward industrial application. To date, four such industrial methods are in use. 1.1 KICVET direct lead smelting process: KICVET—the direct lead smelting process. Experiments on this direct lead smelting process began in 1967 at the Research Institute of Non-ferrous Metallurgy in the former Soviet Union; intermediate tests were conducted using furnaces with a capacity of 5 t/d, and semi-industrial tests were carried out using furnaces with a capacity of 20 t/d to 25 t/d. Finally, industrial-scale continuous production was achieved in 1988. The main feature of this method is that it carries out processes such as the roasting of lead concentrate, reduction, and the volatilization of part of the zinc in the slag, all within a single Kiefel furnace. Lead concentrate, secondary materials, and finely ground fluxes are mixed and dried until their moisture content is below 1%; after that, they are crushed and screened before being sent to the silo in the smelting workshop. Coke particles of 15mm–20mm size are sent to another silo. The Kivset furnace consists of a nozzle, a heat-insulating fuel burner, a reaction tower, a melt pool, a partition wall, an electric furnace, a vertical flue in the melting area, an electric furnace area, and a rear combustion chamber. The charge and coke particles are fed in through the nozzle feed ports at the top of the reaction tower. Industrial oxygen (95% oxygen) is introduced at a tangent direction on the side of the nozzle, thereby spraying the feed material into the reaction tower. The oxygen-to-feed ratio is adjusted so that the feed material can be completely desulfurized; in this atmosphere of industrial oxygen, sulfides rapidly oxidize and release heat during suspension, melting, and slag formation. During the injection and descent process, about 10% of the coke particles burn up, and they quickly fall into the molten pool, forming a red-hot layer of coke on the surface of the pool (about 200 mm thick). As the melt falls into the molten pool, approximately 80% to 90% of the lead oxide is reduced to lead, which then sinks rapidly to the bottom of the pool. Oxide melt and lead liquid enter the electric furnace area from below the partition wall. The smelting flue gas, which contains high concentrations of sulfur dioxide and metal oxide dust, is sent through a vertical flue; after dust removal in a waste heat boiler and an electrostatic precipitator, it is directed to an acid plant where acid is produced using the double-contact process, ensuring that the exhaust gases are discharged in compliance with regulations. The electrical energy for the electric heating zone of the Kiefset furnace is supplied by carbon electrodes, to keep the melt in a molten state. Coke particles are added through a nitrogen-sealed feeding port at the roof of the furnace zone, to reduce zinc oxide and any remaining lead oxide in the melt. A siphon for lead drainage is installed at the bottom of the end wall in the electric furnace area, while a slag outlet is provided at the lower side for regular slag removal. To further recover the residual lead and zinc in the slag, a flue furnace is typically used to treat the slag. In the electric furnace area, the lead and zinc-containing vapors are drawn into the after-burning chamber where they are oxidized by air; thereafter, they pass through a waste heat boiler, heat exchangers, and bag filters for dust removal before being released. The hot air generated by the heat exchangers is used for drying the furnace charge. The Kivset furnace has a complex structure; to extend its service life, numerous copper water jackets are installed in areas such as the reaction tower, partition walls, and melt pool. The main operational parameters of the Kivset furnace are as follows: flame temperature in the reaction tower ranging from 1380°C to 1420°C, temperature of the slag layer in the melt pool between 1100°C and 1200°C, sulfur dioxide concentration in the smelting flue gas at 20% to 30%, flue gas temperature between 1200°C and 1300°C, desulfurization efficiency of 97%, zinc content in the zinc oxide-containing dust at 40% to 50%, lead recovery rate of approximately 96%, recycling rate of dust at 5%, lead content in the slag ranging from 3% to 5%, zinc content from 7% to 10%, oxygen consumption of 160 m3/t to 170 m3/t of feedstock, coke consumption of 45 kg/t of feedstock, and electricity consumption of 140 KWH/t of feedstock. Plant examples: (1) the Ust-Kamenogorsk lead-zinc plant in Kazakhstan: Lead smelting using the Kivcet process began in January 1986; the plant was designed to handle 340 t/d of feedstock. Following adjustments during production, it was modified in 1988, with the area of the electric heating section reduced by half and the reaction tower expanded, thereby increasing its processing capacity to 500 t/d. The main feature of this plant is that when processing charge with a copper content of over 2%, matte is produced; the layer of matte between the crude lead and the slag is about 100 mm thick, and the resulting matte is sent to a copper plant for further processing ； Using furnace slag instead of coke as a reducing agent, and adding 10%–12% of the furnace slag produced by zinc smelting volatilization kilns (containing about 25% carbon) as a reducing agent not only saves coke but also allows for the recovery of valuable metals from the slag ； A smelting furnace is used to further recover zinc and lead from the slag, in order to prevent excessive reduction of zinc oxide in the slag of the electric furnace area, which could lead to the reduction of iron oxides. (2) Italian lead smelter at Port of Visme (KSS): This plant was the first large-scale Kivcet process lead smelter to be successfully built (in February 1987) and put into operation outside the country where the process was invented; it has a designed capacity of 84,000 t/year of crude lead, with two nozzles installed at the top of the reaction tower for simultaneous feeding. After years of operation, the production capacity has reached 120,000 t/a of crude lead, with the equipment operation rate exceeding 96%. The main features of this plant are that it was developed through collaboration between the Italian companies Samim and Snamprogetti, building on patent technology from the former Soviet Union; significant improvements were made to the technical equipment used ； While processing domestic and imported lead concentrates, it also handles leaching residues, sludge from zinc electroplating plants, and battery sludge ； A siphon lead discharge outlet is provided on the end wall of the electric furnace area; the lead dam is 500 mm high, and gas nozzles are installed for insulation ； The side wall of the electric furnace area is equipped with five slag discharge ports at three different heights; under normal circumstances, the two ports at the middle height are used ； After water quenching, the slag is sent to a volatilization kiln for treatment or piled up at a slag yard. (3) Trellis Lead-Zinc Plant of Cominco Canada: The existing QSL lead smelting process was replaced with a Kivsite furnace; it came online in April 1997, with a production capacity of 120,000 t/year of crude lead. The Trelleborg lead-zinc plant is a integrated lead-zinc facility, with four logistics lines throughout the plant that connect the entire lead and zinc production process. The leaching residue from zinc plants is sent to lead plants for processing; the amount of such residue that needs to be processed accounts for about 45% to 50% of the raw materials used in Kivcet lead smelting. The zinc oxide powder produced by lead plants is sent to zinc plants for further processing, and this accounts for about 15% of the raw materials used in zinc smelting. The sulfur-containing flue gases from Kivcet furnaces are combined with those from zinc roasting furnaces to produce acid, while the wastewater from zinc electroplating plants is treated before being used as industrial water in lead plants. The Keminke Company’s Kivset furnace is equipped with four nozzles at the top of the reaction tower for simultaneous feeding; the feed rate is 70 t/h on a dry basis, and the feed consists of lead concentrate, leaching residue, flux, and coal. After drying and grinding, it is mixed with returned dust and granular coke, and then sprayed into a reaction tower for smelting. This plant has processed large amounts of leaching residues and other miscellaneous materials; as a result, the SO2 content in the smelting flue gas is slightly lower than that in the first two plants (14%–18%). To prevent the deposition of matte in the electric furnace, this plant requires a high temperature in the furnace in order to ensure that the lead containing a high amount of copper can be discharged from it. The slag discharged from the electric furnace area is processed in a smelting furnace, and both the zinc oxide powder recovered from the electric furnace area and that from the smelting furnace are sent to a zinc smelting plant for zinc production. The zinc content in the slag from the smelting furnace is less than 2.5%. This method is characterized by its ability to process raw materials with high copper content. Its disadvantages are high investment, high energy consumption, and high operating costs; production has been halted in Kazakhstan and Ust-Kamenogorsk. 1.2 QSL lead smelting process: The QSL process makes use of the principle of melting in a molten pool, along with the intense agitation provided by bottom-blown oxygen, to ensure thorough mixing of sulfide concentrates, lead-containing secondary materials, and fluxes within the molten pool of the reactor (smelting furnace). This facilitates rapid melting, oxidation, reactive interactions, and reduction, resulting in the formation of crude lead and slag. It is characterized by a high oxygen utilization rate (nearly 100%), a high desulfurization rate (greater than 9**%), and a high sulfur dioxide concentration in the flue gas (the sulfur dioxide concentration in the flue gas entering the waste heat boiler is approximately 8%–12%). It is suitable for acid production using the double-contact method, offering advantages such as simple operation, good working conditions, and low costs. In the 1980s, the Berzelius lead-zinc plant in Germany built a QSL pilot plant with a processing capacity of 10 t/h and conducted industrial trials, processing large amounts of lead concentrate and lead-containing leaching residues, thereby laying the foundation for the large-scale industrial application of the QSL lead smelting method. Since the 1990s, four plants have been built successively. Of these, aside from the QSL lead smelting plant in Trail, Canada, which was later converted to use the Kivcet process for lead smelting, the other three plants are the Northwest Lead-Zinc Plant in China, the Stobek plant in Germany, and the Unsan Smelter in South Korea – all of which are now in operation. The QSL lead smelting plant at the Northwest Lead-Zinc Factory in China underwent three trial productions; the last of these trials lasted for five months. Production was halted for various reasons and has not resumed to this day. The Stobek Lead Plant and the Wenshan Smelting Plant were established slightly later than the Northwest Lead-Zinc Plant. Some of the initial problems were resolved through modifications, enabling successful operation at full capacity; the production capacity has even exceeded the design level, with production metrics meeting or exceeding the design values. The lead recovery rate is 96%–97%, and the sulfur utilization rate in the flue gas is over 96%. This method effectively addresses the environmental pollution caused by lead smelting, and significantly improves the working conditions in the operation area. The QSL reactor is the core equipment of QSL, and it mainly consists of an oxidation zone and a reduction zone. A partition wall separates the two zones; the primary slag produced in the oxidation zone (lead-rich slag) flows into the reduction zone through a channel located at the bottom of the partition wall. The crude lead produced in both the oxidation and reduction zones is continuously discharged through siphon openings situated at the end of the oxidation zone, while the final slag is regularly removed through slag outlets built into the end wall of the reduction zone. The reactor is a rotatable cylinder lined with refractory bricks; the oxidation zone has a larger diameter, while the reduction section has a smaller diameter. It is installed at an inclination of 0.5% to facilitate the flow of crude lead toward the siphon outlet. 3 to 4 oxygen lances are installed at the bottom of the oxidation zone, while 7 pulverized coal reduction lances are installed at the bottom of the reduction zone. Fuel burners are installed at both the ends of the reduction zone and the oxidation zone to heat the reactor charge and melt it when necessary. At the upper part of the oxidation zone, there are 2 to 3 feeding ports and flue gas exhaust ports; the flue gas enters a vertical flue through a sealed smoke hood. This vertical flue, which is composed of membrane walls, constitutes the radiation section of the waste heat boiler. The sealing mechanism of the smoke hood ensures unrestricted rotation of the reactor, facilitating maintenance and replacement of the oxygen lance and reduction lance. Both the oxygen lance and the reduction lance are of special design and represent key components of the QSL reactor; they must ensure the reactor’s oxidation and reduction functions while also facilitating maintenance and disassembly. Typically, the lifespan of an oxygen lance is 2 to 3 weeks, while that of a reduction lance is 3 months. The concentrate, secondary materials, flux, dust, and solid fuel added when necessary are prepared by batching, mixing, and granulation before being fed into small silos. From there, they are supplied to the melt pool through a weighing belt feeder at the feeding port at the top of the oxidation section of the reactor. Oxygen is injected from the bottom via oxygen lances cooled by protective gases and misted water. The materials undergo oxidation, desulfurization, and melting at temperatures between 1050°C and 1150°C, resulting in the production of crude lead. The primary slag flows into the reduction section; the pulverized coal used in this section comes from the pulverized coal preparation workshop, is transported by pneumatic means to the pulverized coal silo in the melting workshop, and then is fed into each reduction gun through a metering silo, a compressed air delivery system, and a distributor. The reduction furnace features a three-tube structure: coal powder enters through the central tube, oxygen enters through the inner tube, while nitrogen and atomized water enter through the outer tube. The combustible substances in the flue gas generated by the reaction are further burned up by the air supplied from the upper part of the reactor. The reaction temperature in the reduction section is 1200°C. The reduced crude lead flows to the siphon at the oxidation section, while the reduced slag flows to the slag outlet at the end wall of the reduction section. The flow and discharge of the QSL reactor melt in these three factories are basically the same; the differences mainly lie in the types of raw materials processed, production capacity, reactor size, partition wall structure, and the subsequent equipment used for slag treatment. Plant examples: (1) Stobek Plant: The raw materials used are 60% lead concentrate, 37% lead-silver slag, with the remainder being lead dust from refineries. The designed production capacity is 80,000 tons per year of crude lead, with a feed rate of 500 tons per day; in reality, the plant currently produces 110,000 tons per year of crude lead. The total length of the reactor is 33 m, the diameter of the oxidation zone is 3.5 m, the length of the oxidation zone is 11 m, and the length of the reduction zone is 22 m. The structure of the partition walls is similar to that of the QSL reactors at the Northwest Lead-Zinc Plant in China. The flue gas treatment system is also similar to that used at the Northwest Lead-Zinc Plant. The slag resulting from the reaction contains 3%–5% lead; after water quenching, it is sent to a slag processing plant. (2) Unsan Smelter in South Korea: The raw materials processed include 52% lead concentrate, with the remainder being lead-silver slag, battery sludge, zinc filter residue, and gold-silver ore, etc. Its designed capacity is 60,000 t/year of crude lead, with a feed rate of 550 t/day; currently, the actual production volume exceeds 100,000 t/year of crude lead. The total length of the reactor is 41 m. The diameter of the oxidation zone is 4.5 m, with a length of 13 m; the diameter of the reduction zone is 4 m, with a length of 28 m. The upper part of the partition wall is closed, separating the flue gases from the oxidation zone from those from the reduction zone, with the flue gases being discharged respectively through the exhaust outlets at the upper part of the oxidation zone and those in the reduction zone. The sulfur dioxide content in the flue gas from the oxidation zone is higher than that at the Stobek plant; the flue gas cooling and dust collection processes are similar to those in the former plant. The flue gas from the reduction zone contains virtually no sulfur, and at 1200°C it is cooled and dust-free before being released. The final slag discharged from the QSL reactor contains less than 5% lead and 15% zinc; it is then sent to an Osmet furnace for flue gas treatment, which reduces the lead and zinc content in the slag to less than 1% and 3%, respectively. 1.3 Oxygen-enriched top-blown submerged melting method: The CSIRO top-blown submerged melting method is a melting technique that evolved from the top-blown submerged gun technology developed by the Commonwealth Scientific and Industrial Research Organization of Australia (CSIRO) in the early 1970s; it falls under the category of pool melting. In the late 1970s, Australia’s MIM collaborated with CSiRO to develop the Thilo smelting process for direct lead production, and secured a patent for the Isa lead smelting method. MIM conducted a pilot plant test using lead sulfide concentrate with a processing capacity of 5 t/h, and the results showed good performance. Subsequently, the Isa lead smelting plant with a processing capacity of 20 t/h and 60,000 t/year of crude lead was designed; it operated for four years before production came to an end, reportedly due to a shortage in raw material supply. Later, an Isa copper smelter with a capacity of 180,000 t/a was built, and production has since expanded to 250,000 t/a of crude copper. In the early 1980s, the inventor of the top-blown submerged spray gun technology founded Ausmeit Company and carried out development work on the spray gun as well as in some new application areas; as a result, both MIM and Ausmeit obtained the rights to use this technology. The main process in top-blown submerged melting involves directly injecting air or oxygen-enriched air and fuel into the molten pool through a lance inserted vertically into the slag layer, thereby vigorously stirring the molten pool and inducing intense physical and chemical reactions such as melting, oxidation, reduction, and slag formation in the feed material. The melting process is adjusted and controlled based on the amounts of gas, fuel, and carbonaceous reducing agent injected by the spray gun, thereby enabling the oxidation and reduction processes respectively. At the user’s request, oxidation melting, reduction melting, and even slag volatilization treatment can be carried out in stages within a single furnace. Continuous oxidation and melting, staged reduction and melting, as well as slag volatilization processes can also be carried out in two furnaces. That is, the high-lead slag produced by the first furnace is subjected to stepwise reduction smelting or volatilization in the second furnace. Phased operation of a single furnace helps to reduce the project’s investment, but the operational control is more complex. In particular, the flue gas acid production system must take necessary measures to ensure flexible control mechanisms that can meet the requirements for continuous operation of the acid plant, given the significant variations in SO2 concentration in the flue gas across different melting stages. The commonly used method: producing acid by mixing with other sulfur dioxide-containing flue gases ； The flue gas with a high SO2 concentration during the oxidation smelting stage is compressed and cooled to retain some of the SO2, which is then released into the flue gas system during the reduction smelting stage, ensuring that the flue gas in the reduction stage meets the requirements for acid production ； The flue gas is absorbed and decomposed by organic amines, and its composition is adjusted to meet the requirements of the acid production plant. Oxygen-enriched top-blown submerged melting places few requirements on the charge preparation system; lead concentrate, secondary lead-containing materials, return dust, flux, and coal fuel added when necessary are fed in through the top feeding port after being mixed and granulated, and the particle size and moisture content of these materials can vary over a wide range. The top-blown furnace is a vertical cylindrical furnace with a steel shell lined with magnesia-chromia bricks. The working conditions in the furnace walls are severe: the lower part is subjected to erosion and scouring by the vigorously agitated melt, while the upper part is affected by erosion from splashing slag and high-temperature flue gases. To protect the furnace walls, three different measures are typically employed: strict control of the furnace temperature to prevent large fluctuations that could cause the lining to peel off ； The outer surface of the furnace shell is cooled by water spraying ； A copper water jacket is installed between the brick and the furnace shell. By adopting the above measures, the lifespan of the furnace wall can reach one year or more. The spray gun is the core of this melting method; it is non-consumable and features a concentric tube structure. During normal operation, it is inserted about 200 mm into the melt. The splashing of the melt and slag is cooled by the airflow from the outer tube, resulting in the formation of a solid slag layer on the outer wall of the spray gun, which prevents the high-temperature melt from corroding the spray gun. The lower part of the spray gun, approximately 400 mm to 600 mm long, is the section that can be cut out and replaced; the lifespan of this section of the spray gun tube is usually 4 to 5 days. When necessary, it is replaced with a spare spray gun, while the damaged spray gun is repaired and kept as a spare. At different heights in the lower part of the top-blown furnace, there are outlets for releasing lead and slag; each outlet is equipped with a replaceable copper water jacket to enable regular removal of lead and slag. The main technical differences between MIM Company and Ausmeit Company lie in the structure of the spray gun, the design of the furnace roof, and the methods used for protecting the furnace walls. The spray guns of Ausmeit company consist of three tubes: the primary air carries fuel in from the inner tube, thereby regulating the reaction temperature inside the furnace; the secondary air is oxygen-enriched air that enters through the inner sleeve to supply the oxygen required for the reactions taking place in the furnace; the tertiary air is ordinary air that enters through the outer sleeve, serving to cool the exterior of the spray gun while also providing sufficient airflow at the upper part of the furnace to burn any combustible substances present in the flue gases. The furnace roof is an inclined refractory cast piece that connects to the radiation section of the waste heat boiler, namely the rising flue. The furnace top and furnace body are cooled by water spraying to ensure the lifespan of the refractory materials. The spray gun of the MIM company consists of two tubes: primary air and fuel are fed in through the central tube, while secondary air, which is oxygen-enriched air, is fed in through the outer tube; this provides the oxygen required for the reactions inside the furnace and simultaneously cools the outer surface of the spray gun. Tertiary air is supplied to the upper part of the furnace via a heat-retaining burner to burn any combustible substances in the flue gases. Only in emergency situations, when the main spray gun is raised above the liquid level, does the heat-retaining burner supply oil to maintain the temperature inside the furnace. In other words, both the heat-retaining burner and the spray gun are in operation during normal operation. The auxiliary fuel burner of Ausmeit Company does not enter the furnace when the spray gun is in operation; it only enters the furnace and becomes active when the furnace is shut down for insulation. The roof structure of the MIM furnace consists of horizontal membrane wall tube bundles; both this structure and the vertical flue are part of the waste heat boiler, which facilitates self-cleaning and cleaning by allowing splashes and dust to adhere to them. Based on its experience, MIM Company generally does not use water spray cooling for the furnace walls; instead, it relies on operational and technical management methods to control the furnace temperature in order to extend the service life of these walls. Practice has shown that the lifespan of the furnace wall has been significantly improved. Due to the flexibility of the top-blown submersion melting technology and its wide adaptability to various raw materials, it is used to process materials containing lead and zinc, as well as leaching residues, dust, slags, and waste battery sludge. To date, five production facilities using this technology for processing lead concentrate or integrating it into lead-containing secondary materials have been built (including the lead plant at the Qujing Non-ferrous Metals Base in China). Factory examples: (1) Shuimaike Lead Smelter in Namibia: In 1995, a lead smelter with a capacity of 30,000 t/year was built using the Ausmeit technology to replace 50% of the capacity of the sintering-blast furnace system. The plant was completed in 1997; it processes raw materials such as lead concentrate and secondary materials returned from copper plants, and it uses an Ausmeit furnace with a diameter of 4.4 m that operates in both oxidation and reduction stages. It has previously processed copper concentrates with high lead content to produce qualified matte. According to available reports, the factory ceased production in a very short period of time; the reason for its shutdown was corporate failure that led to bankruptcy. (2) Australian MIM Company’s lead smelting plant: The industrial development of the oxygen-enriched top-blown submerged melting technology went through a rigorous process. It started with test units of 0.5 t/h to 1 t/h, progressed to test units with a capacity of 50 kg/h, followed by semi-industrial tests at 200 kg/h to 300 kg/h, and then industrial tests at 1 t/h to 5 t/h, before eventually moving on to industrial application. In 1992, a cupola submerged lead smelting plant built by MIM Company at a cost of 65 million Australian dollars came online; it was designed to produce 60,000 t/year of crude lead, using the company’s own lead concentrate. The plant was originally designed to operate with two top-blown furnaces in sequence: the raw materials were mixed with flux and recycled dust, granulated, and then fed into the melting furnace for oxidative melting. The oxygen concentration in the oxygen-enriched air supplied to the nozzles was 27%, and the melting temperature was 1100°C. The SO2 concentration in the flue gas exiting the furnace was **%. The crude lead produced by the melting furnace, along with that produced by the reduction furnace, was sent to the lead refining plant. The lead-rich slag resulting from melting entered the second top-blown furnace directly for further reduction melting, with coal being fed through the central tube of the nozzles in the reduction furnace to facilitate reduction and heat supply. During the production process, production in the reduction section was halted due to a malfunction in the pulverized coal system; instead, the lead-rich slag was quenched with water and sent to the sintering system of the existing 180,000 t/a old lead plant to be used as return powder. The oxygen-enriched top-blown submerged melting furnace in that plant was in operation for four years, but production was halted due to changes in the company’s mineral resources, which prevented it from achieving the expected production capacity; as a result, the output of lead concentrate was insufficient to meet the needs of the smelting plant. (3) Nordhannen Lead Smelter in Germany: Initially, it used a sintering-blast furnace process. Due to environmental concerns and the need to handle large amounts of battery sludge, it was decided to transform the smelter by adopting Ausmeit’s oxygen-enriched top-blown submerged lead smelting method. A new lead smelter with an annual capacity of 90,000 tons was built in 1996. To reduce investment costs, only one top-blown furnace was installed to operate continuously. Since the lead concentrate and battery sludge mixture processed contained over 70% lead, the amount of lead-rich slag generated was low; as a result, 90% of the crude lead could be obtained directly, with only 10% of the lead ending up in the lead-rich slag. This slag contained approximately 45% lead. It was quenched with water and stored, before being subjected to reduction melting in the same furnace. When the plant began operations, there were problems with the feeding system and the circulating waste heat boiler; after modifications, it was able to operate successfully. However, the reduction melting of lead-rich slag has never been carried out. The reason for this is that the amount of slag is small, and it is more economical to use this furnace to process larger quantities of high-lead materials rather than reducing lead-rich slag. As a result, the plant grinds the water-quenched lead-rich slag and sells it externally. The Ausmeit furnace in this plant has an outer diameter of 4.2 m and a height of 9.5 m, with its steel shell cooled by external water spraying. The operation certificate of this plant shows that it offers significant environmental and energy-saving benefits compared to the old lead factory. (4) Hindustan Zinc Limited, India: In 2005, it built a lead bullion smelting plant using technology from Ausmeit Company. An oxygen-enriched top-blown furnace was employed, with lead concentrate as the feed material; the plant’s processing capacity is 85,000 tons per year of lead concentrate. The manufacturing process consists of three stages: oxidative smelting, reduction smelting of lead-rich slag, and slag volatilization. Melting stage ； Lead concentrate, flux, and dust are mixed according to predetermined proportions and then fed into the furnace. A controllable amount of oxygen-enriched gas is introduced into the furnace via nozzles to oxidize the lead and iron sulfides present in the concentrate. The iron oxide, together with silicon oxide, calcium oxide, and other components in the mixture, forms slag, resulting in a lead-rich slag containing 30% lead. Some of the produced crude lead settles at the bottom of the furnace and is removed periodically. Appropriate fuel is injected into the furnace through nozzles to supply the heat needed to sustain the reaction, keeping the temperature of the molten pool around 1150°C. Once the furnace reaches its maximum slag production capacity during the smelting phase, the lead-rich slag remains in the furnace, and the reduction phase begins. Reduction stage: The high-lead slag produced in the smelting stage is reduced to yield crude lead. During the reduction phase, the lead content in the slag will decrease from 30% to 5%. The ratio of gun air to fuel is adjusted to maintain the reduction conditions at the gun outlet. A small amount of lead concentrate is added during this phase, and its proportion can be controlled to ensure that the temperature rises and remains at 1200°C during the reduction process. The dust generated during reduction contains high levels of lead, and this dust is returned along with the dust produced during the melting phase to the feed mixture. When the lead content in the slag drops to 5%, the crude lead is extracted and sent for refining along with the crude lead produced during the melting phase. The reduced slag remains in the furnace for the third stage of smelting. Slag fumigation stage: Fumigating the low-lead, high-zinc slag produced in the reduction stage to generate waste slag. During the smelting stage, appropriate lump coal is added through the feed port at the top of the furnace, and the ratio of air to fuel supplied by the nozzles is adjusted to ensure the reducing conditions at the nozzle exit and to maintain a temperature of over 1250°C during this stage. This allows lead and zinc in the slag to be reduced and volatilized into the flue gases, where they are then burned and oxidized by the air supplied through the sleeves. The recovered zinc (lead) oxide dust is sold to zinc factories. The smoking stage reduces the lead content in the slag from 5% to below 1%, and reduces the zinc content to below 2%; the slag is then discarded after water quenching. The flue gas during the melting and reduction stages contains SO2, while it contains little to no SO2 during the smelting stage. In order to provide acid production plants with continuous and stable conditions for acid production, the flue gas is cooled and dust-separated first, after which it is absorbed, stored, and regenerated using organic amines. The regenerated SO2 gas is then sent to the existing acid production plants to be used in the acid production process. Although operating a single furnace in a three-stage cycle can significantly reduce investment, it causes many difficulties in operation management and sulfuric acid production from flue gas. The factory began operations in late 2005. It is said that one furnace operates in three stages, and there are also some technical issues; the factory plans to add another furnace to address the problems associated with the carbonization stage. 1.4 Caldo lead smelting process: Caldo’s technology, developed by the Swedish company Boliden Metal, is an application of oxygen metallurgy in top-blown converters and falls under the category of bath smelting. The first Carrod furnace used for the smelting of non-ferrous metals was developed at the Lonskog Smelter in northern Sweden in 1979; it was initially used to process lead-containing ash, and later Carrod furnaces for processing lead concentrate were put into operation. In 1982, the Paulson Company completed comprehensive smelting tests on various types of lead concentrates using Cardo furnaces, enabling the industrial application of oxygen top-blown Cardo converters for lead smelting. It is also used to process lead oxide concentrate, scrap copper, and materials containing precious metals. The Carido furnace consists of a barrel-shaped lower furnace chamber and a trumpet-shaped furnace mouth, both lined with magnesia-chromium bricks. Two large rims are fixed to the outer wall of the lower furnace chamber; they are secured within a frame structure using several sets of idler wheels, and during normal operation they can rotate along the axis of the furnace. Their rotation speed can be adjusted between 0 and 30 revolutions per minute. The furnace’s main frame, through those two larger rims as well as the two sets of idler wheels installed on the furnace base, allows the furnace to tilt as needed while maintaining its rotational motion, thereby facilitating the removal of slag and lead. At the section with the normal operating inclination, smoke hoods and flues are used to direct the furnace gases into the dust collection system. The combustion nozzles for delivering fuel and oxygen, as well as the feeding nozzles for supplying concentrate, are inserted obliquely into the furnace through these smoke hoods at the furnace mouth. The entire furnace, including the crude lead tank, slag tank, and their respective trolleys, is enclosed by a large ventilation hood; subsequently, a high-capacity exhaust fan is used to send the smoke and dust dispersed within it to a bag filter chamber for purification before discharge. The hearth of the Kaldo furnace at the Lonskog smelter has an outer diameter of 3.6 m and a height of 6.1 m, with an inclination angle of 28 degrees under normal operating conditions. The flue hood directs the reaction flue gas out, where it is cleaned by a venturi wet dust collector before being sent to the acid plant. The smoke, dust, and sludge are thickened and filtered under pressure; thereafter, together with the lead concentrate, they are dried and dehydrated to 0.5% before being fed into the furnace via feeding nozzles. The fuel spray gun provides the heat required for melting the material; the oxygen concentration in the oxygen-enriched air is 60%, while the flux and coke particles needed for the reduction process are added to the furnace through a water-cooled feed hopper. The operation of the furnace is intermittent. Oxidative smelting and reductive smelting are carried out in stages in one furnace, with reductive smelting requiring oil heating as supplementary heat. The melting cycle lasts between 4.5 hours and 5 hours. To address the severe fluctuations in SO2 concentration in the flue gas during the oxidation and reduction phases, the acid production system employs a flue gas compression and cooling system to store part of the SO2 present in the flue gas with high SO2 concentrations during the oxidation phase, and then release it into the flue gas during the reduction phase, thereby meeting the requirements for continuous acid production. To date, three lead smelting plants of the Kaldo type have been built. In addition to the Lonskog smelter operated by the Swedish company Boliden, there are also two plants owned by the Iranian Lead and Zinc Company and China Western Mining Corporation. At the plant belonging to the Iranian Lead and Zinc Company, the raw material processed in the Kaldo furnace is lead oxide ore, with fuel oil serving as the heat source. The Lonskall lead plant and the Western Mining and Metallurgy Lead Plant process lead sulfide concentrate as their raw material. The first two factories have been in operation for many years; the Western Mining and Metallurgy Lead Factory began operations in 2005. The main problems associated with this production process are periodic intermittent operation, complex operational procedures, large temperature differences, and difficulties in process control and management ； The service life of the furnace linings is short; it is known that the furnace linings at the Lonskar lead plant last for three months, while those at the Iranian lead plant last only 1–2 months. Due to low operational rates, the production capacity of crude lead has remained around 16,000 t/year for many years (with a designed capacity of 40,000 t/year of crude lead). The Western Mining and Metallurgy Company has been in operation for a short time, and currently its furnace linings last only 1 month. Furthermore, this process also has a higher energy consumption compared to the previous lead smelting processes. For reasons such as the above, the Cardo process for lead smelting has been used in industrial production since early on, but it has never been widely adopted. 2. The current status of lead smelting technology in China. Over the past decade, China’s lead smelting industry has developed rapidly, with production volumes increasing significantly, and considerable progress has been made in lead smelting processes and related technologies. The national production of refined lead was 706,200 tons in 1996, and it rose to 2.378 million tons in 2005, an increase of 1.6718 million tons; the average annual growth rate over those 10 years was 14.9%. During the same period, the world’s total lead production increased from 5.785 million tons in 1996 to 7.4688 million tons in 2005, an increase of only 1.6838 million tons. It is evident that over 99% of this increase in global lead production was achieved by China during that time. In terms of lead smelting processes, before 1995, the sintering-blast furnace process was used throughout the country; only the Shenyang Smelter and the Zhuzhou Smelter employed sintering using sintering machines (with the exception of the ISP lead-zinc hermetical blast furnace process), while the rest used sintering pots or sintering beds. All SO2 flue gases from lead smelters are discharged. Lead smelting was the industry with the most severe environmental pollution among non-ferrous metal smelting at that time. **Great emphasis has been placed on this matter, and relevant industrial policies have been introduced requiring the phasing out of outdated lead smelting processes such as sintering furnaces and sintering trays by the year 2000. At that time, the General Corporation of Non-ferrous Metals Industry and the Ministry of Science and Technology took corresponding measures. On the one hand, efforts are made to accelerate the research and development of new lead smelting processes; on the other hand, new foreign lead smelting processes and technological upgrades are actively introduced to improve the conditions in lead smelting. In the 1980s, the Shenyang Smelting Plant carried out expanded tests on wet lead smelting ； The Hunan Shuikoushan Mining Bureau carried out a semi-industrial trial of bottom-blown lead smelting ； Baiyin Company has adopted the QSL lead smelting process from the German company Lurgi ； The Shenyang Smelting Plant adopted the former Soviet Union’s unsteady-state acid production technology for lead sintering flue gas with low SO2 concentrations. The expanded tests on wet lead smelting at the Shenyang Smelter used a chloride-based system; it is technically feasible, but the processing costs are high, making it difficult to compete with fire-based lead smelting and thus unsuitable for industrial application. Semi-industrial trial of bottom-blown lead smelting at Shuikoushan: The high-lead slag produced by the bottom-blown furnace was directly reduced using pulverized coal injected into an electric furnace. Due to limitations in funding for the experiments, the coal powder preparation system was rudimentary, resulting in poor reduction effects and unsatisfactory outcomes. However, the aforementioned work laid a certain foundation for the development of lead smelting technology in China from 1995 to 2005. 3.1 Industrial application of the SKS lead smelting method: In 1998, the Beijing General Institute for Non-ferrous Metallurgy Design and Research took the lead in organizing a consortium that included units such as the Shuikoushan Mining Bureau and the Yuguang Gold and Lead Group. Together, they funded the use of the Shuikoushan bottom-blown lead smelting test workshop to carry out verification tests on oxygen bottom-blown melting combined with blast furnace reduction for lead smelting – namely, the SKS method. After more than two months of testing, it was proven that this process was reliable and its performance parameters were feasible. About half of the lead in the lead concentrate is obtained directly, while the other half is present in the high-lead slag; after being cast into blocks, it is sent to a blast furnace for reduction and melting, resulting in waste slag. It has made it possible to replace the sintering and recycled powder crushing steps in traditional lead smelting processes with bottom-blown melting. Due to the high SO2 concentration in the flue gas from bottom-blown furnaces, it is suitable for acid production; the sulfur recovery rate reaches 95–96%, while the sulfur capture rate is >99% ； At the same time, by eliminating the crushing of sintered return powder, SO2 and lead dust pollution has been completely eliminated. The bottom-blown melting process does not require additional fuel; it is fully self-heating and can utilize some of the waste heat to generate electricity, thereby saving energy. More importantly, during the bottom-blowing process, about 50% of the lead is converted directly into crude lead through interactive reactions. The high-lead slag that enters the blast furnace contains 40–45% lead, which is on par with the lead content in the sintered pellets. As a result, the amount of material required for melting in the blast furnace is reduced by approximately 50% compared to the sintering process. This leads to a significant decrease in coke consumption, thereby reducing the cost of lead production compared to traditional methods. Together with the profits from sulfuric acid, this results in good economic benefits. The perfect combination of new pool melting technologies with traditional blast furnace melting has resulted in a new lead smelting process that features low investment costs, reduced energy consumption, environmental friendliness, stable operation, high efficiency, and good economic returns. This process was rapidly adopted in China; by 2005, four production lines had been built and put into operation, with a designed capacity of 230,000 t/a of crude lead, while the actual production capacity had reached 360,000 t/a. In 2006, two more production lines were successfully put into operation. Currently, there are 10 more under construction or in the design phase for construction. The total actual production capacity of these 16 facilities once completed will reach 1.55 million tons per year, accounting for half of China’s lead production. The specific manufacturers are listed in Table 1. Table 1: List of oxygen bottom-blown melting projects that are in operation, under construction, or in the design phase. Company Name, Design Capacity (10,000 t/a), Date of Operation, Remarks: Henan Yuguang – 5, 2002.7; Actual production: 80,000 t/a. Anhui Chizhou – 3, 2002.8; Actual production: 60,000 t/a. Shuikoushan – 10, 2005.8; Actual production: 140,000 t/a; Maximum daily production: 540 t. Henan Yuguang – 5, 2005.3; Second production line has a capacity of 80,000 t/a. Lingbao Xinling – 5, 2006.9; Has reached design specifications. Xiangyun Feilong – 6, 2006.10; Has reached design specifications. Inner Mongolia Shuangyuan – 5, 2007; Under construction. Inner Mongolia Baiyinnuoer – 8, 2007; Under construction. Jiyuan Jinli – 8, 2007; Under construction. Inner Mongolia Xing’an – 8, 2007; Under construction. Jiyuan Wanyang – 8, 2007; Under construction. Chenzhou Yuteng – 6, 2007; Under construction. Guangxi Cangwu Non-ferrous Metals Company – 6, 2007; In design phase. Jiangxi Guyang Jiangzhi – 8, 2007; In design phase. Chenzhou Yinxing – 10, 2007; In design phase. Lingbao Zhishen – 10, 2008; In design phase. 2.2 Promotion of technologies for producing acid from low-concentration SO2 flue gas and for desulfurizing sulfur-containing exhaust gases. Application of the new technology: Many manufacturers have upgraded or built new sintering furnace-blast furnace lead reduction processes, equipping them with non-steady-state acid production facilities. With a flue gas SO2 concentration of 2–3%, self-heating can be maintained; the SO2 conversion rate is 90–92%, and the sulfur recovery rate is 80–85%. Some manufacturers install alkali washing or ammonia absorption systems for acid-producing exhaust gases, enabling the exhaust to be discharged in compliance with standards. Despite ongoing issues such as low quality of sulfuric acid, pollution from crushed lead dust resulting from sintering waste, etc., 3.3 To address the environmental problems associated with lead smelting, China has introduced a number of lead smelting technologies over the years. Importing lead smelting technology to address environmental problems: The lead-zinc plant of the aforementioned Baiyin Company adopted the QSL lead smelting process from German company Ruhrchemie; however, for various reasons, the lead smelting plant has been shut down to this day. Western Mining Company adopted Polytun’s Kaldo lead smelting method from Sweden; after it was put into operation, the life of the furnace was only about 30 days, and the desired results were not achieved. The Zhuzhou Smelting Plant has adopted Topsoe’s acid production process from Denmark to address the environmental issues associated with the flue gases from sintering machines. The acid production process works well, enabling the exhaust gases to be discharged in compliance with standards. The problem is the high cost of acid production, and some domestically produced equipment requires significant maintenance work. The Qujing Smelter in Yunnan has adopted the MIM top-blown melting–blast furnace reduction process for lead smelting, with a designed capacity of 80,000 tons per year. After tuning and over a year of operation, its production capacity has exceeded the designed level. However, compared to bottom-blown processes, it involves higher investment and energy consumption, as well as a slightly lower effective operating rate; it is considered one of the most successful cases of technology adoption in lead smelting. In addition, the lead electrolysis workshop at Qujing Smelting Plant has also introduced from Japanese company TDE Co., Ltd. a production line for casting lead anodes using vertical molds, an automatic sorting system for lead cathodes, a machine for manufacturing lead cathodes, and a DM casting machine for starting plates. The design incorporates a 150-ton lead melting pot, large electrolytic cells with 1.6 m2 of electrode area, as well as internationally advanced production processes and technical equipment such as low current density and long-cycle operation. These elements help to narrow the gap between China’s lead refining industry and world-leading standards in terms of technical equipment and process control, serving as an important model for lead refining production in China. These technologies introduced into the lead smelting industry have enriched China’s lead smelting process technologies. 2.4 In addition to the above major technical advancements in China, there are also various independently developed technological achievements: Some technological achievements in China. (1) The process of sintering lead concentrate using domestic sintering machines has seen significant improvements: parameters such as material particle size, moisture content, ignition temperature, air volume, layer height, and the type of binder used have been optimized, resulting in substantial improvements in indicators such as the layer height of the sintered material, its permeability, caking rate, and bed capacity. Some manufacturers use oxygen-enriched blast furnaces with an oxygen concentration of 23–24% for sintering, which reduces the rate of powder return by an average of 9% and increases the SO2 concentration in the flue gas by 1%. (2) The low-concentration sulfur dioxide flue gas treatment technology developed by a certain environmental protection equipment company utilizes calcium carbide slag, limestone, lime, or metal oxides (zinc oxide powder is commonly used in lead and zinc smelting plants today) to create a slurry for absorbing SO2 in flue gases with concentrations ranging from 1 to 80 g/m3, achieving a desulfurization rate of over 98%. Tailpipe emissions are basically up to standard. (3) For new lead smelting plants, especially regarding environmental protection issues, this traditional process is no longer used. Yunnan Metallurgical Group has applied blast furnace injection technology to traditional lead smelting blast furnaces. By injecting inexpensive fuels such as mixtures of pulverized bituminous coal, semi-coke, and lignite through the tuyeres into the blast furnaces, it is possible to reduce their coking ratio. Meanwhile, the waste heat from the blast furnace flue gas is utilized to preheat the blast air, resulting in an increase in the furnace bed capacity by over 10% and a reduction in the coking ratio by 15%, thereby lowering the costs associated with crude lead smelting. (4) New progress has been made in the comprehensive utilization of zinc-lead blast furnace slag through smelting ； The upper part of the furnace chamber in the flue gas treatment furnace is designed as a membrane wall radiant waste heat boiler, which recovers the waste heat from flue gas at 1200°C for power generation. The flue gas, cooled to 650°C by the waste heat boiler, enters a jet-type air exchanger to preheat the blast air for the lead blast furnace to 200–250°C, thereby making full use of the waste heat. Furthermore, through gravity feeding and continuous operation, the bed capacity is increased by more than 20%; the final slag contains less than 2% Zn, and its composition is that of iron-calcium-silicate slag, which can be used as a cement admixture for comprehensive utilization, thereby achieving zero waste residue in lead smelting plants. (5) For the control of lead vapor pollution from the melting lead pots used in the lead smelting process, by combining blowing jets with suction airflow, the direction of the polluted air flow is properly managed and exhaust ventilation is controlled, thereby effectively addressing the problem of lead dust pollution from these melting pots. (6) Henan Yuguang Gold and Lead Group, in collaboration with Central South University of Technology, conducted a semi-industrial trial involving the direct reduction of liquid high-lead slag produced by bottom-blown furnaces using an oxygen vortex furnace along with coke; this approach yielded slag with lower lead content. However, the furnace lining lasted only about a week. Further tests are being carried out on the liquid reduction of lead-rich slag using other types of furnaces. 2.5 Examples of new lead bullion processing technologies in China: Examples of new lead bullion processes in China (1) The Northwest Lead-Zinc QSL Lead Smelting Plant – This plant acquired the entire set of QSL lead smelting technologies and the main process equipment from the German company Ruhrchemie in 1986; these include disk granulators, QSL reactors, oxygen guns, reduction guns, waste heat boilers, electrostatic precipitators, high-temperature fans, as well as a coal powder metering system. The raw material processed is 100% lead concentrate, with a designed capacity of 50,000 t/year of crude lead, which corresponds to 430 t/day of lead concentrate being processed. The total length of the reactor is 30 m; the diameter of the oxidation zone is 3.5 m and its length is 10 m. The diameter of the reduction zone is 3 m and its length is 20 m. A gas passage is located at the upper part of the partition wall. The flue gas from the reduction zone enters the oxidation zone through this passage at the top of the partition wall, and together with the flue gas from the oxidation zone, it is discharged through the exhaust outlet into the vertical flue. Thereafter, it passes through a waste heat boiler and an electrostatic precipitator for dust removal, before being sent to the acid production plant using the double-contact process by a high-temperature exhaust fan. Crude lead is discharged through the siphon at the end of the oxidation section. After being cast into large ingots using a disk casting machine, they are sent to the fire refining workshop. The slag is intermittently discharged through the slag discharge port at the end of the reduction section to the electric heating pre-bed for further precipitation of lead in the slag. Liquid slag is also supplied to the carbonization furnace on a regular basis; the slag resulting from the volatilization process in the carbonization furnace is sent to a slag disposal site after water quenching. The zinc oxide dust recovered by the carbonization furnace is sent to a zinc smelting plant for the recovery of zinc and other valuable metals. The oxygen and protective nitrogen required for the oxygen lance and reduction lance at the bottom of the reactor are supplied by an oxygen production station and connected to the lances via hoses, to ensure that the reactor can rotate 90° during lance changes and in case of accidents. The plant was completed in 1991, and by October 1992, it had undergone three trial productions. The third trial production lasted five months, proving that the process was feasible and the workflow was seamless. Main problems during the trial production: the boiler’s capacity is low, and the temperature at the inlet of the electrostatic precipitator is high, which limits the processing capacity; only 60%–70% of the designed capacity can be achieved ； The Northwest Lead-Zinc Plant does not have a pulverized coal preparation system; the pulverized coal is loaded at the copper smelting plant’s pulverized coal station and transported to the QSL melting workshop. The pulverized coal has a high moisture content and coarse particle size, which causes frequent blockages in the pulverized coal distributor in the QSL reactor, resulting in uneven coal supply. Additionally, since the system is operated manually, it is difficult to adjust the amount of pulverized coal according to changes in the composition of the lead-rich slag, leading to unstable lead content in the final slag, which typically varies between 3% and 7%, and sometimes exceeds 10% ； Due to the significant variations in lead content in the final slag, its melting point also changes; as a result, the slag often freezes at the feed end of the electric heating preheater, disrupting the normal progress of subsequent processes. Based on the summaries of the above pilot production, the Northwest Lead-Zinc Plant formulated relevant rectification plans. However, due to a shortage of funds and low lead prices at the time, lead smelters faced difficulties and were unable to implement it for a long time. (2) SKS Lead Smelting Plant of Yuguang Gold and Lead Company. To promote the development of the company, Yuguang Gold and Lead Company aimed to address the environmental pollution issues associated with the traditional sintering-blast furnace lead smelting process. In May 2002, an SKS lead smelting plant with a capacity of 50,000 t/a of crude lead was built. It is also the first industrial production plant in our country to use a newly developed lead smelting process of domestic origin. The plant was successfully put into operation in July 2002, with results better than expected; within just three months, all technical and economic indicators reached or exceeded the design values. By the second year, the production capacity had exceeded 80,000 t/a of crude lead. Practice has shown that, compared with the traditional processes, it offers advantages such as lower energy consumption, better environmental conditions, higher sulfur utilization rate, shorter process duration, higher level of automation, simpler operation, and greater adaptability to various raw materials. Therefore, the plant built and put into operation a second SKS production line for 80,000 t/a of crude lead in March 2005; today, the combined actual capacity of the two SKS systems amounts to 180,000 t/a. The design of Chizhou Non-ferrous Metals Company’s 30,000 t/a SKS lead smelting plant was slightly later than that of Yuguang Gold and Lead Company’s SKS lead smelting plant. However, it was put into operation in July 2002, and the plant started working smoothly, reaching its designed capacity in the very month of commissioning; its current production capacity is 60,000 tons per year. The successful operation of these two plants laid the foundation for the widespread adoption of the SKS lead smelting process in China. After 2005, three more SKS plants were built and put into operation; the projects that are already in operation as well as those under construction are listed in the table below. List of Oxygen Bottom-Blast Lead Smelting Projects That Are in Operation, Under Construction, or in the Design Stage
Serial Number | Company Name | Designed Capacity (10,000 t/a) | Commissioning Date | Remarks
1 | Henan Yuguang | 5 | July 2002 | Actual output: 80,000 t/a
2 | Anhui Chizhou | 3 | July 2002 | Actual output: 60,000 t/a
3 | Shuikoushan | 10 | August 2005 | Actual output: 140,000 t/a; maximum daily output: 540 t
4 | Henan Yuguang | 5 | March 2005 | Actual output of the second production line: 80,000 t/a
5 | Lingbao Xinling | 8 | September 2006 | Has reached design specifications
6 | Xiangyun Feilong | 6 | October 2006 | Has reached design specifications
7 | Inner Mongolia Shuangyuan | 5 | 2007 | Under construction
8 | Inner Mongolia Baiyin Nuor | 8 | 2007 | Under construction
9 | Jiyuan Jinli | 8 | 2007 | Under construction
10 | Inner Mongolia Xing’an | 8 | 2007 | Under construction
11 | Jiyuan Wanyang | 8 | 2007 | Under construction
12 | Western Mining | 10 | 2008 | In design stage
13 | Chenzhou Yinxing | 10 | 2008 | In design stage
14 | Guangxi Cangwu Non-Ferrous Metals Company | 6 | 2008 | In design stage
15 | Chenzhou Yuteng | 6 | 2008 | In design stage
16 | Jiangxi Yiyang Jiangye | 8 | 2008 | In design stage
17 | Henan Luoyang Kunyu | 8 | 2008 | In design stage
18 | Gansu Chengzhou | 6 | 2008 | In design stage
19 | Chifeng Kunsteel Shuangqiang | 8 | 2008 | In design stage
20 | Yichun Jinlin | 8 | 2008 | In design stage
21 | Yunnan Zhadian | 8 | 2008 | In design stage
22 | Zhuzhou Smelting | 10 | 2008 | In design stage
23 | Yunnan Shadian | 6 | 2008 | In design stage

The production process for this technology involves: lead concentrates from various sources and with different grades being mixed together in the raw material processing area. After mixing, they are fed into the storage bins using grab cranes. The mixed ore in these bins, along with lead dust from the bottom-blown furnace, as well as lead-containing materials and fluxes from the raw material processing area, are measured according to specified composition ratios using nuclear scales located beneath the bins. After granulation, these materials are fed into the furnace through feed ports at the top of the furnace. Industrial oxygen is injected into the molten pool from oxygen nozzles at the bottom of the furnace, where it reacts with the lead melt to produce lead oxide. Under intense stirring, lead oxide reacts vigorously with lead sulfide present in the upper part of the melt, resulting in the formation of crude lead. After the separation of crude lead from lead oxide slag by precipitation, the crude lead is continuously discharged via siphoning, while the lead oxide slag is discharged intermittently. After being cast into ingots by an ingot casting machine, it is sent to a blast furnace for smelting to produce secondary crude lead. After being cooled in a waste heat boiler and cleaned of dust in an electrostatic precipitator, the flue gas is sent to the double-contact acid production system; the dust collected by the waste heat boiler and the electrostatic precipitator is directly used to synthesize and granulate the mixture. The bottom-blown melting furnace of Yuguang Jinlian Group is a horizontal, rotatable cylindrical furnace lined with steel-reinforced refractory bricks. A siphon lead discharge port is located at one end of the furnace, a slag discharge port at the other end, and the flue gas outlet is situated above the lead discharge port. To avoid affecting the rotation of the furnace, a banana-shaped sealed smoke hood is installed at the smoke outlet and connected to the vertical flue (i.e., the radiation section of the waste heat boiler). Two air-seal feeding ports are located above the part near the smoke outlet. The bottom-blown furnace operates under negative pressure, and the air that leaks in through the feeding ports can fully oxidize the volatile lead sulfide, preventing it from entering the waste heat boiler and causing post-combustion, which would hinder the proper operation of the waste heat boiler. There are 4 oxygen guns below the feeding port; industrial oxygen and protective nitrogen are supplied by an oxygen production station and connected to the oxygen guns via hoses. In case of gun replacement or malfunctions, the furnace can be rotated 90°. The oxygen lance is retracted above the liquid level to prevent clogging and allow for replacement. After the slag type is adjusted through flux addition, the lead-rich slag lumps and coke are weighed separately and then fed into a blast furnace for reduction melting. This blast furnace operates with a high material column, and its tuyeres and furnace belly differ slightly from those of blast furnaces used for sintered lumps in order to accommodate the reduction properties of the lead-rich slag lumps. The reduced secondary lead and the primary lead from the bottom-blown furnace are sent to the melting pot in the lead electrolysis plant for processing. Due to the low zinc content in the raw materials, no smelting system has been installed in the blast furnace workshop; however, room for expansion exists. After lead is further separated through sedimentation in a pre-bed, the blast furnace slag is quenched with water and then sent to the slag dump. Key technical and economic indicators from October to December 2002: Effective operating rate of the bottom-blown furnace was 90% ； Desulfurization rate: 98% ； Dust rate 14% ； The SO2 content in the flue gas exiting the furnace is 10% ； Lead-rich slag contains 40–45% lead ； Sulfur 0.3～0.4% ； Sulfur recovery rate: 95% ； Sulfur content in the acid treatment system: 3–4% ； Oxygen lance lifespan: 30–50 days ； Oxygen consumption per ton of lead: 215 m3 ； Nitrogen consumption: 17 m3 ； Power consumption: 95–100 Kwh ； Fuel consumption: 215 kg ； Lead recovery rate: 96% ； Gold and silver recovery rate ≥98% ； Blast furnace slag contains 3.6–3.85% lead. (3) Chihong Company’s lead smelting plant is located at the Jing Non-ferrous Metals Base and makes use of the oxygen-enriched top-blown submerged melting technology provided by the Australian company MIM. In July 2005, a plant with an annual capacity of 80,000 tons of crude lead was built there; the raw materials used are lead concentrate produced by the company itself as well as lead crude concentrate purchased from outside. MIM was responsible for the basic design of the electric arc furnace unit as well as the detailed design of the furnace itself. The waste heat boiler of the Essa furnace was designed by the German company Ossas. Except for the main spray gun, insulation burner, heating burner, slag opening machine, and the instrumentation control system for the Essa furnace, which are supplied by MIM Company, all other equipment was designed and purchased domestically. The lead smelting process consists of two stages of melting, namely oxygen-enriched top-blown submerged melting and blast furnace reduction melting. Oxygen-enriched top-blown smelting is a process in which, using oxygen-enriched air and at a melting temperature of 1050°C to 1100°C, the charge is oxidized and smelted to produce lead-rich slag and crude lead, which are discharged intermittently from the slag discharge port at the bottom of the furnace and the crude lead discharge port, respectively. The crude lead ingots are sent to the refining workshop, while the lead-rich slag is cast into blocks using a slag casting machine and then sent to the blast furnace workshop for reduction melting. The flue gas from the Aisa furnace is sent to the double-contact acid production plant after passing through a waste heat boiler and a dust collector. The Isa furnace is a vertical furnace with an outer diameter of 4 meters, and the total height from the furnace base to the furnace top is 11.95 meters. Both the furnace body and the furnace bottom consist of a steel shell lined with magnesia-chromia refractory bricks. The furnace top cover is composed of horizontal membrane tube walls and is a component of a waste heat boiler. The top cover is equipped with a spray gun port, a feeding port, a heat-insulated burner port, a probe rod port, and an interface for the vertical flue (i.e., the radiation section of the waste heat boiler). The main nozzle is a key component of the Essa furnace, and it is inserted into the melt during normal operation. When changing the gun, it needs to be raised outside the furnace top and then taken to the maintenance area. The main gun performs the aforementioned insertion, lifting, and gun replacement operations through a gun trolley, slide rails, a winch, and a top crane. The main nozzle consists of three concentric circular tubes. The innermost layer consists of a pressure regulation tube connected to an external pressure difference transmitter, which is used to measure the back pressure and determine the depth to which the spray gun is inserted into the melt. The second layer is the diesel channel, which is used to regulate the furnace temperature; when no fuel needs to be burned, only high-pressure air is passed through it. The outermost layer is oxygen-enriched air. The insulated burner is lifted by another winch. It is usually inserted above the furnace liquid level, with a small lifting height, so the lifting system is simple. It consists of two sleeves. The inner tube serves as the fuel passage, while the outer tube functions as the air passage. When the spray gun is replaced or the material level is adjusted, the heat-retaining burner supplies oil to maintain the temperature inside the furnace. When the spray gun is in normal operation, the heat-retaining burner stops supplying oil but continues to supply air for secondary combustion. The heating burner structure is similar to that of a heat-insulating burner. But it is equipped with an automatic ignition device and a system for automatically adjusting the amount of oil and gas. The heating burner is only inserted during furnace startup, to ensure that the furnace temperature follows the requirements of the baking curve precisely. The charge preparation system for the Isa furnace at Jingtan Lead Plant and the reduction system using lead-rich slag in a blast furnace are similar to those at Yuguang Lead Plant. However, the control system is of high quality; in the Isa furnace, the material preparation system uses cylinder granulators instead of disk granulators. Although cylinder granulators are less effective than disk granulators, practice has shown that there is no significant difference in dust emission between the two. The blast furnace for lead-rich slag at Qujing Lead Factory, like that at Yuguang Lead Factory, is also a blast furnace with double rows of air inlets covering an area of 8㎡. Since the raw materials used by the Qujing lead factory contain a high level of zinc, it was also taken into account that the raw materials used by the Qujing zinc factory have a high level of germanium as well. To recover zinc and germanium, based on the industrial tests conducted by Chihong Company in Huize, two 12㎡ flueing furnaces were installed in the blast furnace reduction workshop to process hot lead slag and leaching slag generated in the zinc production process. The zinc oxide dust produced by these furnaces is sent to Huize for germanium recovery; zinc and lead are also recovered in this process. For flue gas desulfurization furnaces over 4.5 meters in length, the membrane wall structure together with the vertical flue forms the radiation section of the waste heat boiler, while the horizontal convection section of the waste heat boiler follows the vertical flue. The gasification furnace has a conventional water jacket structure below 4.5 meters; the medium-pressure steam generated by the Aisa furnace’s waste heat boiler and the gasification furnace’s waste heat boiler is sent to the waste heat power generation unit to make full and efficient use of the waste heat. Since the calciner processes the leaching residues from zinc plants, the exhaust gas from the calciner contains SO2 in amounts exceeding the emission standards; therefore, a liquid ammonia absorption system has been installed. The main technical and economic indicators of the plant one year after its commissioning: the capacity of the Isa furnace to process lead concentrate increased from 500 t/a to 650 t/a for processing lead-containing materials (Pb55–60%) (including lead-silver slag and lead scum) ； Effective operation rate: 80–85% ； Essa furnace fuel coal <1% ； Oxygen concentration: 34% ； Dust and smoke rate: 13–15% ； The lead sinking rate is 40–60% per time ； The SO2 concentration in the flue gas exiting the furnace is 10–12% ； Lead-rich slag contains 35–45% lead ； Oxygen consumption per ton of lead: 140–180 m3 ； The service life of the brick lining in the first firing cycle is 16 months ； The spray gun needs to be repaired every 5–7 days ； The coke ratio of the blast furnace is 13.14% ； Blast furnace dust emission rate: 2.47% ； Blast furnace slag contains 3.5% lead ； Zinc content in slag < 11% ； The SO2 content in the flue gas from the blast furnace is <500 mg/m3.

:):):) It’s not the latest yet – the newest smelting method for three furnaces in one

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Very good material; I learned a lot from it. I hope there will be updates