In the refining of crude lead , bismuth is the most difficult impurity to remove. Some foreign plants often use calcium and magnesium to remove bismuth. Since the lead is separated between calcium, magnesium and bismuth generated refractory metal compound to form a scum.
Fig. 1 is a state diagram of a Ca-Bi system. Calcium and strontium constitute two compounds: Ca 3 Bi 2 and CaBi 3 . Wherein Ca 3 Bi 2 contains 7.6 77.66% by weight, the melting point is not lower than 1200 ° C: and CaBi 3 decomposes at 507 ° C into Ca 7 Bi 4 .
Figure 1 Ca-Bi system state diagram
It can be seen from Fig. 1 that there are two eutectic crystals: the eutectic melting point of Ca 3 Bi 2 and yttrium is 270 ° C, the composition is close to pure lanthanum, and the eutectic melting point of Ca 3 Bi 2 and calcium is 786 ° C, containing 铋 12% (atoms) ) or contain 41.5% by weight. Since Ca-Bi constitutes the refractory intermetallic compound Ca 3 Bi 2 , it is used for the removal of crude lead.
Figure 2 depicts a Bi-Mg system state diagram.
Figure 2 Bi-Mg system state diagram
As can be seen from Fig. 2, bismuth and magnesium constitute the compound Bi 2 Mg 3 and have a melting point of 823 ° C. The eutectic point temperature of Bi 2 Mg 8 and Bi composition is 551 ° C, containing 14.3% (atoms) of Bi, and the eutectic point temperature of Bi 2 Mg 8 and Mg is 260 ° C, containing Ba 95.7% (atoms). И.И. Kirillov pointed out that strontium and magnesium constitute a finite solid solution, the solubility of magnesium in strontium is about 15.0% (atoms) at 300 ° C, about 30.0% (atoms) at 500 ° C; in magnesium The solubility of cerium was 0.18 atomic % at 400 ° C and 1.12% (atomic) at 551 ° C.
Here are a few examples:
(1) In the flame refining of crude lead in the Belen electric zinc plant in Belgium, the method of adding calcium and magnesium to remove slag is used to produce sorghum scum, and the process flow is shown in Figure 3.
Figure 3 Barron electric zinc plant recycling process
This process mainly includes three steps of melting, Pb-Bi electrolysis and chlorination refining: alkaline decalcification, magnesium and electrolysis are included in the melting to achieve separation of lead and antimony, and chlorination refining is to remove residual lead. In the pyrometallurgical refining of lead, impurities such as copper , arsenic , antimony , silver , and zinc have been removed before dislocation. Therefore, after the scum separates calcium, magnesium, and lead, fine sputum can be produced.
(2) The crude lead produced by the West Germany North German Lead Refinery is firstly denitrided by vacuum denitrification. After dezincification, the lead content is 0.05% to 3.5%, and the dezincification lead containing more than 3.5% is directly cast into the anode. Electrolysis, separation of bismuth and lead, and for dezincification of lead containing less than 3.5%, using calcium and magnesium removal methods, the sorghum slag is melted and alkaline refined, and the Pb-Bi anode produced contains 4% 铋~8%, copper 0.005%~0.01%, silver 50g/ton, separated by electrolysis, Pb70g/L in electrolyte, Cu<0.002g/L, Bi<0.002g/L, B188 in anode slime %～90%, Pb2%～4%, Cu0.06%, as the raw material for refining fine sputum, the process flow is shown in Fig. 4.
Figure 4 Process of recycling 北 in the North German lead refinery
This process is characterized by the use of electrolytic refining for dezincification lead with high bismuth (Bi>3.5%) and desulfurization of lead with low bismuth (Bi<3.5%) by pyrometallurgical refining from Pb-Bi electrolysis. Refined recovery of ruthenium in anode mud.
(3) The crude oil of the Burleyton smelter in Canada will be refined by the preliminary method of refining, adding calcium and magnesium, and the scum produced will contain 2% to 4% of scum. After alkaline enrichment, the Pb will be produced. -Bi alloy containing é“‹8% to 10%, directly using chlorine gas enriched ruthenium, enriched to Pb-Bi alloy containing yttrium higher than 65%, adding zinc to silver, chlorination dezincification, lead, and then alkaline Refined, producing the first fine. The process flow is shown in Figure 5.
Figure 5 Flow chart of the recycling process at the Burlington plant
The process is characterized by two times of chlorination and lead removal. The first chlorination acts to enrich bismuth (Bi>65%); the second chlorination removes the effect of residual lead.
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