Recover Lead And Silver From Lead-silver Slag By Low-temperature Alkaline Smelting

This paper discusses a low-temperature alkaline smelting method for the treatment of lead-silver slag,can be achieved by one step lead and silver recovery effectly and sulfur condenscend.This paper provides some references for the recovery of valuable metals in lead-silver slag as well as the new process.Through the quantitative analysis and the phase analysis,the content of the main elements of lead-silver slag and its formation state were determined.The lead content is 16.3%,the iron content is 16.17%,the zinc content is 11.95%and the silver content is 210 g/t.Lead is mainly existed in the form of PbSO₄,PbS and PbO,respectively.Silver mainly consists of silver oxide,silver sulfide,Most of the iron exists as Fe₃O₄and ZnFe₂O₄,while FeS exists as a small part of the iron.Most of the Zn exists as Zn Fe₂O₄,and a small amount of ZnSO₄ and Zn₂SiO₄.The thermodynamic analysis of the lead-silver slag was carried out.The results of gibbs free energy showed that the lead-silver slag was feasible by low-temperature alkaline smelting,It is recovered as crude lead,and the elemental sulfur is condenscended in the form of ZnS.Iron is present in the slag as Fe₃O₄.The reduction equilibrium diagrams of PbSO₄,PbS,PbO and Zn Fe₂O₄ are respectively made on the basis of the reduction equilibrium diagram of the iron-containing compounds.It is found that proper control of the mass fraction of PbS and ZnFe₂O₄ in the system can prevent the formation of crude lead while fixing sulfur The formation of metal iron.The mechanism of sulfur fixed was studied,that is:the sulfur compounds were reduced to metal oxides and sulfur oxides,and the sulfur oxides were absorbed by sodium carbonate to form Na₂S.The Na₂S was transformed into ZnS by Zn O.By considering the direct of lead and silver,residual rate and crude lead grade,the final optimal choice:mNaCl:mNa₂CO₃ is 4:6,the melting time is 1 h,the melting temperature is 900?,the dosage of added carbon powder as raw material 10%,Na₂CO₃ dosage of 1.215 times the raw material.Under these optimal conditions,the direct lead and silver yields were 85.28%and 86.19%,respectively.The residual lead-silver was 7.81%and 5.66%,respectively.The crude lead purity of the obtained product was 99.71%.Under the optimal experimental conditions,the iron in the leached residue mainly exists in the form of Fe₃O₄,while zinc exists mainly in the form of ZnS,which also corresponds to the thermodynamic study.Under the optimal conditions,the stability of the experiment was repeated,the vertical yield reached more than 84%,of which the average direct yield of lead reached 85.12%;the direct silver yield reached more than 85%;the average silver direct yield reached 87.52%;The residual rate of lead is less than 13%,the silver residual rate is less than 9%,and the average remaining lead-silver ratio is 11%and 7.83%respectively.