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The purpose of bottom-blown furnace melting is: (1) to oxidize the sulfides of lead and other metals in the charge to produce SO2 for the production of sulfuric acid； (2) Produce some crude lead while enriching it with gold and silver ； (3) React the slag-forming components with lead oxide to produce high-lead slag for reduction and smelting in a blast furnace ； (4) Enrich volatile associated metals such as thallium and cadmium in the dust to facilitate comprehensive recovery. In addition to melting lead concentrate, bottom-blown furnaces can also process various secondary lead materials such as used batteries. Basic principles of bottom-blown furnace melting: The oxygen bottom-blown furnace melting of lead sulfide concentrate, like the melting in a bath for other metal sulfides, is a multiphase reaction process involving interactions between the liquid phase and the gas phase, as well as between the liquid phase and solid phases and among liquid phases. Since each material has its own unique physicochemical properties, and concentrates are often composed of multiple minerals. Therefore, the melting process in a bottom-blown furnace is a highly complex physicochemical process, in which the behavior of various components during melting is the main factor affecting whether the melting process can proceed smoothly. Since lead concentrate is in powder form, it provides a large reaction area and results in a fast reaction rate, whereas limestone and quartz are in granular form with a smaller specific surface area; therefore, the reactions that primarily affect the reaction rate are the decomposition of limestone and the slag formation reaction. II: Material preparation for oxygen bottom-blown melting 1. Process flow: This process represents the preliminary preparation stage for oxidizing and melting the feed materials in a bottom-blown furnace. Its purpose is to continuously produce mixed granules with uniform and stable chemical compositions, as well as consistent particle size and strength, meeting the technical requirements of the bottom-blown furnace melting process. Lead concentrates with different compositions are fed in proportion to each other to form a mixed concentrate with uniform composition. This mixture is then combined, along with fluxes and heat supplements such as quartz stone, limestone, and crushed coal, in proportion using quantitative feeders. It is subsequently mixed with ash, moistened, and granulated to produce pellets with appropriate physical and chemical properties, which are then sent to the bottom-blown smelting process via quantitative feeders. 2. Several key process items: 1) The purpose of measuring the balls and materials is to accurately control the amount of material fed into the furnace, so that an appropriate amount of oxygen can be supplied to regulate the oxygen level inside the furnace. This, in turn, helps to control the rate of lead deposition and the grade of the slag with high lead content. If the measurement of balls and materials is inaccurate or subject to large fluctuations, it will also affect the stability of the operation of the bottom-blown furnace as well as its technical performance indicators. 2) Control of oxygen potential in bottom-blown furnaces: The logarithm of the percentage content of oxygen in the furnace relative to the oxygen feed rate is called the oxygen potential. If the oxygen potential is too high, the lead precipitation rate is low and the lead content in the slag is high; if the oxygen potential is too low, the lead precipitation rate is high, but the slag becomes sticky and the quality of the crude lead is poor. Therefore, selecting the optimal oxygen potential is key to controlling bottom-blown furnace production. The control of oxygen potential is primarily achieved by adjusting the oxygen-to-feed ratio, that is, the amount of oxygen consumed per unit amount of feed. This ratio can be adjusted either by changing the amount of feed or by changing the amount of oxygen supplied. 3. Properties of high-lead slag and its formation: High-lead slag is a mixture composed of various metallic and non-metallic materials. The properties that affect production include viscosity, melting point, density, and interfacial tension with lead. Among these, viscosity and melting point influence the fluidity of the slag and the furnace temperature, while density and interfacial tension affect the efficiency of slag-lead separation and the quality of crude lead. The chemical composition of high-lead slag mainly consists of FeO, SiO2, and CaO, as well as the level of PbO present in the slag; additionally, the amount of ZnO can also affect the properties of high-lead slag. 4. Operational practices for oxygen bottom-blown furnaces 1) Starting up the furnace: To start an oxygen bottom-blown furnace, it is first necessary to follow the furnace drying curve strictly. Once the temperature inside the furnace reaches the required level, slag is added; after the slag melts, lead is added. Once the lead has melted as well, the furnace can be put into normal operation. 2) Normal operation of a bottom-blown furnace involves mainly slag removal, lead removal, oxygen adjustment, control of the amount of balls and materials fed into the furnace, and maintenance of the feeding ports. The release of slag and lead should be balanced according to the conditions in the molten pool; excessive release of either one will affect the furnace operation and the lifespan of the oxygen lance. Adjusting the oxygen level and the amount of material fed into the furnace is primarily based on the results of tests regarding slag lead content and flue gas temperature, in order to achieve an appropriate lead content in the slag and maximize the processing capacity. 3) Shutdown of oxygen bottom-blown furnaces can be divided into short-term shutdowns and long-term shutdowns. During a short-term shutdown, it is sufficient to remove as much slag as possible from the furnace and maintain heat insulation during that time. In the event of a long-term shutdown, all slag and lead inside the furnace must be removed before restarting it again. 5. Judgment of normal operation of bottom-blown furnaces and main technical and economic indicators. When a bottom-blown furnace exhibits the following characteristics, it can be considered to be operating normally: A. Minimal splashing at the feeding port, with slight blockages; B. Good fluidity of the slag; C. Normal lead flow, little scum, and stable fluctuations; D. Stable oxygen and nitrogen flow rates and pressures in the oxygen lance; E. Stable slag temperature within the range of 1000–1100°C; F. Stable flue gas temperature within the required range. The main technical and economic indicators of a bottom-blown furnace include dust emission rate, processing capacity, lead precipitation rate, and the grade of slag containing high levels of lead. Factors affecting the soot yield include the grade of the pellets and feed, the oxygen-to-feed ratio, the slag line level, the amount of pellets and feed added, the type of slag, and the soot circulation time. The processing rate refers to the amount of pellets fed into the furnace per unit of time; the main factors affecting it are the dust emission rate and the calorific value of the pellets, while the cooling efficiency of the waste heat boiler also has a direct impact on this rate. The lead sinking rate refers to the ratio of the amount of lead produced to the amount of lead contained in the feed material. The main factors affecting the lead sinking rate are the grade of the feed material and the oxygen-to-material ratio. The main factor affecting the grade of high-lead slag is the oxygen-to-feed ratio. 6. Common faults in oxygen bottom-blown furnaces: A. Clogging is likely to occur after material feeding due to slag sticking. B. Poor slag fluidity and high viscosity, caused by low slag temperature, a low oxygen-to-material ratio, and an inappropriate slag type. C. Good slag fluidity and thin slag, (resulting from high slag temperature and a high oxygen-to-material ratio). D. Thick scum on the surface of the lead, (due to a low oxygen-to-material ratio). E. Little or no variation in lead level (either due to low amounts of lead in the furnace or siphon blockage). F. High flue gas temperature. G. High slag temperature, caused by an inappropriate slag type ； The calorific value of the pellets is relatively high