Direct lead smelting

4.3 Kivcet process for lead smelting: A direct lead smelting process that was developed by the Soviet Academy of Non-Ferrous Metals Sciences starting in the 1960s; it was put into use in large-scale industrial production in the 1980s. At the beginning of 1986, a lead smelting plant using the Kivcet process was built in Ust-Kamenogorsk, Kazakhstan. In 1986, the Italian company Samin acquired its patents and built a lead plant (KSS Plant) with a processing capacity of 600 t/d, which is still in operation today. At the end of 1996, Cominco’s Kivcett lead smelting plant with a capacity of 120,000 t/year of crude lead was successfully put into operation and is currently in use. The Kivcet process for lead smelting belongs to the flash melting-electrothermal reduction method (Kivcet process), with the reaction process primarily taking place in the reaction tower of the Kivcet furnace. Its equipment connection diagram is shown below: A. Advantages: 1. Strong adaptability to raw materials, capable of processing lead-zinc-containing slag ； 2. High recovery rate for major metals, with good overall recovery ； 3. Slag has low lead content, <2.0% ； 4. The dust content is low, at around 5%, allowing it to be directly returned to the furnace for smelting ； 5. Low production costs; the comprehensive energy consumption for crude lead is 0.35 tons of standard coal per ton ； 6. The furnace has a long service life, up to 3 years, resulting in reduced maintenance costs. B. Disadvantages: 1. The raw material needs to be dried to a moisture content of less than 1%. 2. The one-time investment is high. The Kifset lead smelting technology is a patent of the Kazakh Institute of Eastern Non-ferrous Metallurgy. At present, this technology is still under patent protection; in order to use it in China, it is necessary to purchase a patent license through technology introduction. Content to be introduced: 1 Purchase of patent license ； 2 Basic design and technical parameters for the drying and melting processes ； 3 On-site guidance and technical services during commissioning and trial operation ； 4 Nozzles specific for Kiefset furnaces. The quote is $4.2 million (for the first 3 items). C. Main technical and economic indicators: 1. Moisture content of the feedstock: <1%. 2. Drying strength: 35 kg/m3·h. 3. Drying recovery rate: 99%. 4. Feedstock volume in the Kivcet furnace: 1583.81 t/day. 5. Lead content in the feedstock: 24.17%. 6. Lead recovery rate: 96.96%. 7. Percentage of silver contained in the crude lead: 99.5%. 8. Percentage of gold contained in the crude lead: 98.06%. 9. Percentage of copper contained in the crude lead: 80%. 10. Percentage of zinc converted to zinc oxide: 50%. 11. Dust emission rate: 5–7%. 12. SO2 concentration in the flue gas from the vertical furnace: 18%. 13. Slag volume fraction: 49.5%. 14. Lead content in the slag: 2.10%. 15. SO2 recovery rate in the sulfuric acid purification process: 99.5%. 16. Total conversion rate of sulfuric acid: 99.75%. 17. Total sulfur recovery rate in the plant: 99.05%. 18. SO2 content in the exhaust gas: 870.16 mg/m3 (standard). 19. Operating schedule: 330 days per year, 24 hours per day. 1) During the production process, lead-containing materials, flux, and industrial oxygen (~95%) are injected into the vertical furnace. The reaction temperature ranges from 1573 to 1673 K. The lead sulfide ore undergoes oxidation and desulfurization as well as melting in a suspended state, resulting in the formation of crude lead, high-lead slag, and flue gas containing SO2, along with the release of large amounts of heat. Due to the injection speed of oxygen and concentrate being 100–120 m/s, the oxidation of the charge, its melting, and the formation of initial crude lead and slag melt are completed within just 2–3 seconds. As the coke passes through the space of the approximately 4m high reaction tower, it is heated by the hot flue gas; however, due to the fine particle size of the concentrate, its ignition temperature is low, allowing it to burn before the coke does. Only about 10% of the coke is burned as it falls through the reaction tower. Coke has a low density; when it falls on the settled melt at the bottom of the reaction tower, it forms a red-hot layer of coke. This is similar to the coke layer in the tuyere area of lead smelting blast furnaces, where it filters the melt containing primary lead and lead-rich slag, thereby reducing PbO in the lead-rich slag to metallic lead. Hence, it is called a coke filtration layer. Here, about 80% to 90% of the lead oxide is reduced. The equipment configuration of the Kivsett direct lead smelting system is shown in Figure 4-2, while the chemical reactions that occur in the reaction tower and carbon layer as well as the distribution of temperature changes along the cross-section are shown in Figure 4-3. Coke blocks are added to the sedimentation tank and float on the surface of the melt; the lead oxide melt is reduced as it passes through the layer of red-hot coke floating on the melt pool (the coke filter layer). Zinc oxide in the melt is also reduced and enters the dust. Products: crude lead, high-lead slag, crude zinc oxide, dust. 2) Advantages of the Kiefert process: ① Good working conditions ； ②It has strong adaptability to raw materials with Pb content of 20–70%, S content of 13.5%–28%, and Ag content of 100–8000 g/t ； ③Continuous operation: oxidation and reduction take place in the same furnace, resulting in fewer production steps ； ④High SO2 concentration in flue gas allows for direct acid production ； The amount of flue gas is low, so less heat is carried away; waste heat is utilized effectively, which results in smaller equipment for flue gas cooling and purification. The dust content is around 5%, and this dust can be directly returned to the furnace for further processing ； ⑤The main metal recovery rate is high (Pb recovery rate > 98%), and the lead content in the slag is low (

4.4 Oxygen Bottom Blowing Lead Smelting Method 4.4.1 QSL Method A direct lead smelting process developed by the German company Lurgi in the 1970s. The Stolberg lead smelter in Germany and the Unsan QSL plant in South Korea were built and put into operation in 1990 and 1992 respectively. In 1989, the QSL process lead smelter built by Cominco in Canada came online; however, due to issues with the process equipment, it was able to operate only for 3 months before having to shut down. In 1993, it was reconstructed using the Kivcet process ； The QSL technology introduced by a smelting plant in northwestern China in the 1980s was put into operation in 1992, but stopped operating shortly after due to certain reasons. 4.4.1.1 QSL Furnace – 3D Diagram of the QSL Furnace (1) Equipment: Reactor: a horizontal cylindrical converter lined with chromium-magnesium bricks and covered with steel plates; there is a partition wall inside the furnace (with connecting holes at its lower part and dual flue ducts), dividing it into an oxidation zone and a reduction zone. Feeding port: For adding lead concentrate or other lead-containing secondary materials. Nozzle: Oxygen is injected in the oxidation section ； Oxygen, pulverized coal, or natural gas is injected into the reduction section. The furnace is tilted 5% toward the oxidation section and can rotate 90 degrees. (2) Process: The depth of the melt pool is 1500 mm, and the depth of the lead liquid at the bottom of the furnace is 250 mm. Oxidation stage: After the charge is added, reactions occur within the slag-metal-gas emulsion melt to produce Pb and PbO, releasing heat that enables self-heating melting; at this stage the oxygen potential is relatively high, around 2.2. The initial lead contains 0.3-0.5% S, and the initial slag contains 40-45% lead. The temperature in the oxidation zone is 1050–1100°C. In the reduction zone, the coarse slag flows into this zone from beneath the partition wall. Coal dust (or natural gas) and oxygen are injected to produce CO and H2, thereby reducing the high-PbO slag at 1250°C. The oxygen potential in the reduction zone is low, around 0.2. The temperature is quite high, ranging from 1150°C to 1250°C. As the slag moves toward the slag discharge port on the end wall of the reduction zone, it is gradually reduced; the metal lead formed as a result of this reduction (secondary crude lead) sinks to the bottom of the furnace and merges with the primary crude lead (primary lead). Crude lead flows in the opposite direction to the slag and is discharged through the siphon outlet ； Slag is discharged continuously or intermittently from the slag outlet. Compared to the oxidation rate of sulfides in the oxidation zone, the reduction rate is slower, and the length of the reduction zone is approximately twice that of the oxidation zone. For raw materials with high zinc content, the final slag from the QSL method must be sent to a flue gas desulfurization furnace for further zinc volatilization. The depth of the reactor melt pool directly affects the degree of mixing between the melt and the charge. Operation with a shallow melt pool not only results in uneven mixing of the two components, but it also makes it easy for the airflow emitted by the spray gun to penetrate, thereby reducing the efficiency of oxygen or oxygen-coal dust utilization. Therefore, appropriately increasing the depth of the reactor melt pool is beneficial for reactor operation. Due to the characteristics of the melting process, it is necessary to maintain an adequate layer of lead at the bottom of the QSL reactor in order to keep the chemical potential and temperature within the molten pool reaction system relatively constant. In operation, to separate the slag layer from the siphon lead outlet and ensure smooth discharge of liquid lead, there must also be a sufficient layer of lead at the bottom. The thickness of the bottom lead layer is generally 200–400 mm, while the slag layer should be thin, at 100–150 mm. The depth of the molten pool in the oxidation zone of the reactor is large, typically ranging from 500 to 1000 mm. Practice has shown that by adding a retaining ring at the start of the reduction section, keeping a lead layer 200 mm thick in that section, it helps the lead beads reduced in the slag to settle, thereby reducing the lead content in the final slag ； Furthermore, reducing the liquid level in the reduction section results in a thinner slag layer there; this increases the intensity of mass transfer at the interface between the slag layer and the lead layer. At the same time, the intensity of eddies within the slag layer decreases, which facilitates the settlement of lead. The direct lead smelting process using the QSL method is shown in the figure: A. Advantages: ① Oxidative desulfurization and reduction are carried out continuously in one furnace ； ②Simple material preparation ； ③A low amount of return material helps to improve the production capacity of the equipment and reduce costs associated with factors such as energy and labor ； ④Oxygen enrichment reduces the amount of dust generated; the SO2 concentration in the smoke is high, allowing it to be used directly for acid production ； ⑤Using coal instead of coke results in lower costs. ⑥The recovery rate of major metals is high. B. Disadvantages: It is relatively difficult to control operating conditions ； High dust concentration (20–30%) ； The spray gun has a short service life ； The slag contains high levels of lead and requires further treatment.

4.4.2 Shuikoushan Method The Shuikoushan lead smelting method is an oxygen-bottom-blown direct lead smelting process developed independently in China. In the 1980s, after successful semi-industrial trials at the No. 3 Smelting Plant in Shuikoushan using an oxidation furnace with dimensions of Φ2234mm×7980mm, this technology was expanded and applied in the production processes of Henan Yuguang Gold and Lead Company and Anhui Chizhou Lead Factory, thereby giving rise to a new lead smelting process that involves oxygen bottom-blown melting followed by reduction of the lead oxide slag using a blast furnace. Production practice has shown that for the transformation of the traditional sintering-blast furnace lead smelting process currently used in China, the Shuikoushan method is a viable option that results in less pollution, lower investment costs, and faster benefits. The one-time lead yield in oxygen bottom-blown smelting is related to the grade of the lead concentrate; the higher the grade, the higher the yield of crude lead obtained in a single process. To meet the requirements of reduction in a blast furnace in the subsequent stage, the lead content in the oxide slag should be around 40%, which is slightly lower than that of the raw sintered masses used in traditional lead smelting methods. Accordingly, the yield of crude lead is generally between 35% and 40%, and the crude lead contains sulfur