After the lead-zinc plant is put into operation, gold and silver are produced from the lead anode mud produced in the electrolytic lead production process, and the process flow chart is shown in Figure 1.
In addition to high-grade silver, anode mud also contains 25%-40% bismuth metal, which is enriched into oxidized slag by more than 70% in the above process. With the rapid development of the industrial field, the demand for bismuth is expanding rapidly, and various fields are scrambling to buy bismuth and bismuth raw materials, resulting in the continuous rise of bismuth.
The bismuth content of the oxidized slag is 25-40%, which enters the precious lead in the reduction smelting process of the precious lead furnace, and the impurities of the precious lead are oxidized and removed with the difference of melting point and boiling point in the process of oxidation and refining in the silver separation furnace, and the oxidation process is mainly achieved by the air on the surface of the melt pool and the high-pressure wind blown in, when the low melting point impurities arsenic, antimony and lead are oxidized one after another, after being removed, the bismuth will be oxidized and become bismuth trioxide.
Because the melting point of bismuth is low 71o, and the boiling point is very high up to 1890, therefore, the furnace temperature of about 1000 is controlled in the production process to enrich the bismuth 8o in the precious lead as the raw material for the production of bismuth oxide slag, and bismuth trioxide and lead oxide constitute a very low melting point and good fluidity of the oxide slag. The main chemical composition of oxidation slag is shown in Table 1.
The smelting principle of oxidized slag.
In the production process, it can be seen that the oxidized slag contains other metals in addition to bismuth, such as gold, silver, copper, lead, antimony and other metals introduced in Table 1, which exist in the oxide form in the oxidized slag according to the phase analysis, as shown in Table 2.
The smelting of oxide slag is a reduction smelting process of the precious lead furnace, in the high temperature state of the actual production process, part of the metal with low melting point such as lead, arsenic and antimony volatilizes into the smoke and dust as oxides, and the other part reacts with the added sodium carbonate to form slag floating on the surface of the melt pool.
The reducing atmosphere in the furnace is strictly controlled during the smelting process, and if the atmosphere in the furnace is too strong, the production process will produce furnace knots, because of the treatment of oxidized slag, conclusion.
1) From the oxidation slag bismuth is a necessary way to produce bismuth and improve the efficiency of enterprises, this process is simple, easy to operate, no special requirements for fuel and flux, and the converter is treated separately, the construction investment cost is less, the productivity and the rate effect is obvious, the rate can reach more than 85. However, the problems arising in the production process still need the help of people from all walks of life to jointly study and solve.
2) There are still some problems in the melting process. Due to the old and old-fashioned equipment of MCC Huludao Nonferrous Metals Group, the dust collection bag is made of 208 silk fiber cloth bag, which has poor air permeability, resulting in the dust collection effect is not too good, and the environmental pollution is serious.