Research On The Enrichment Of Gold, Silver And Tellurium From Lead Anode Mud By Vacuum Volatilizatio

Lead anode slime（LAS）is an important resource for obtaining gold,silver,tellurium,and other rare and precious metals,and the silver extracted from LAS accounts for 57%of the total amount of mineral silver in China.The traditional treatment process of LAS mainly adopts the reduction smelting-oxidation blowing method,which has the disadvantages of long process flow,high energy consumption,low metal recovery rate,and dispersion of rare and precious metals.The clean and efficient extraction of rare and precious metals has become a common problem and urgent task faced by the lead smelting industry.This paper proposed an innovative idea of"selecting oxidation-vacuum volatilization"to enrich gold,silver,and tellurium,successfully enhancing the separation of heavy metals from rare and precious metals,and the green and efficient extraction of gold,silver,and tellurium in the form of high gold-silver alloy and high tellurium concentrate were achieved.This dissertation focused on the thread of"selecting oxidation-vacuum volatilization".Theoretical studies were systematically conducted on the occurrence state of elements in lead anode slime,vacuum volatilization characteristics,and thermodynamics of selective oxidation.The mechanism study on direct vacuum volatilization and selective oxidation-vacuum volatilization were developed.The main research conclusions are as follows:The occurrence characteristics of gold,silver,and tellurium in LAS were revealed by means of XRD,XPS,SEM-EDS,and EPMA.The results show that the noble metals gold and silver mainly exist in the forms of simple substances and intermetallic compound Ag₃Sb in LAS,and the rare metal tellurium has only one phase Pb Te.Using classical thermodynamic methods,thermodynamic laws including the saturated vapor pressure of pure substances,separation coefficient of binary alloys,and thermal stability of compounds were systematically analyzed.The average molecular free path,maximum volatilization rate,and condensation rate of substances were calculated to clarify the volatilization characteristics of substances under vacuum conditions.The saturated vapor pressure of heavy metals in LAS differs greatly from that of precious metals,the separation coefficient of binary system Ag-i and Au-i is far less than 1,and the volatilization rates of As₂O₃,Sb₂O₃,Te O₂,Pb Te,Pb O,Sb,Pb,and Bi₂O₃are at least 4 orders of magnitude higher than those of gold and silver.Direct vacuum volatilization can be used to separate gold and silver from heavy metals.However,the intermetallic compounds Ag₃Sb,Cu₃As,and Pb Te are difficult to decompose under vacuum conditions,affecting the separation and enrichment of rare and precious metals.The study of vacuum volatilization characteristics of LAS provides important scientific enlightenment for enriching rare and precious metals using vacuum volatilization technology.The mechanism of direct vacuum volatilization of lead anode slime was studied,and the volatilization behavior and enrichment rules of gold,silver,and tellurium were discussed.A residue with an Ag content of 15.02%and an Au content of 1010 g/t was obtained under the conditions of a distillation temperature of 1173 K and a distillation time of 45 min.The direct recovery efficiencies of Ag and Au were 89.11%and95.03%,respectively.The intermetallic compound Ag₃Sb did not decompose,and part of silver in the form of Ag₃Sb volatilized together with arsenic and antimony into the gas phase,resulting in the volatilization of silver.The low-temperature vacuum volatilization was performed at a distillation temperature of 723 K and a distillation time of 45 min,tellurium volatilized with arsenic in the form of Pb Te into the gas phase,and a volatile with a Te content of 5.01%was obtained.The direct recovery efficiency of Te reached 93.89%,but the separation of Te from As was not achieved.The direct vacuum volatilization of LAS achieved green,efficient,and short-process enrichment of rare and precious metals to a certain extent.However,due to the volatilization of silver,the separation of silver from antimony,and tellurium from arsenic was not thorough,and subsequent extraction of silver and tellurium is difficult.To reach efficient separation and enrichment of rare and precious metals,LAS was regulated by selective oxidation to achieve phase transition of intermetallic compounds Ag₃Sb,Cu₃As,and Pb Te before volatilization.The selective oxidation of LAS was theoretically analyzed,and the thermodynamic laws of oxidation of elements and compounds were discussed.The bond energy of Au-Me,Ag-Me,and Te-Me is smaller than that of the Me-O bond.In these intermetallic compounds,the element Me bound to gold,silver,and tellurium can be oxidized.By comparing the oxygen potential of various oxides and calculating the Gibbs free energy values of the reaction of intermetallic compounds（formed between As,Sb,Pb,and Ag,Au,Cu,Te）oxidized by Pb O₂and Pb₃O₄,it can be seen that under the temperature of 653 K,Pb O₂and Pb₃O₄can oxidize arsenic,antimony,lead,and tellurium,while the noble metals silver and gold can remain in a simple state.The high valence oxides Sb₂O₅,Pb O₂,and Te O₃that may exist in the selective oxidation product of LAS can be decomposed into low valence oxides at high temperature,according to the phase diagram of the Me-O binary system,while the low valence oxides Sb₂O₃,Bi₂O₃,Pb O,and Te O₂all have a high saturated vapor pressure.Thermodynamic analysis of vacuum reduction reactions of high gold and silver residue shows that the Gibbs free energy values of carbothermal reduction reactions are less than 0 when the temperature is higher than 523 K and the system pressure is kept at 5 Pa,and the carbothermal reduction reactions are easy and complete.With waste lead acid battery lead paste as raw material,based on analyzing the chemical reaction of the mixed solution system of Pb-SO₄^2--CO₃^2--H₂O,and the decomposition reaction rules of Pb CO₃,through desulfurization and calcination,a calcined product containing Pb₂O₃,Pb₃O₄,and Pb O₂,was obtained,and the calcined product was used as an oxidant for selective oxidation of LAS.The mechanism of selective oxidation-vacuum volatilization of LAS was studied,and the effects of different conditions on the enrichment of gold,silver,and tellurium were systematically investigated.The phase transitions including selective oxidation of LAS,vacuum pyrolysis and volatilization of oxidation product,and vacuum reduction of high gold and silver residue during the enrichment of rare and precious metals were analyzed.Under the conditions of an oxidant ratio of 0.45,an oxidation temperature of653 K,and an oxidation time of 120 min,the oxidation regulation of intermetallic compounds Ag₃Sb,Cu₃As,and Pb Te was achieved,silver was converted into elemental Ag,and tellurium was converted into Te O₂.Then vacuum volatilization of oxidation product was conducted under a distillation temperature of 1123 K,and a distillation time of 90 min,a residue containing 14.18%Ag and 893.8 g/t Au were obtained,and tellurium entered the volatile as Te O₂.To further enrich precious metals,the residue of high gold and silver was subjected to vacuum reduction.Under the conditions of a reduction temperature of 1073 K and a reduction time of 90 min,the oxides of lead and antimony were reduced and efficiently separated,and gold and silver were enriched in the form of an alloy.The Ag content in the alloy was 67.58%,the Au content was 4287g/t,silver and gold were enriched 7.59 and 7.64 times,respectively.The tellurium-containing volatile from the selective oxidation-vacuum volatilization of LAS was distilled.The high tellurium concentrate with 0.78%Te content was obtained under the conditions of a distillation temperature of 623 K and a distillation time of 60 min,and tellurium was enriched 2.69 times as Te O₂in which high tellurium concentrate.Arsenic was separated from tellurium and volatilized as As₂O₃.In this new process,the direct recovery efficencies of Au,Ag,and Te in LAS were 99.91%,99.25%,and 97.67%,respectively.The significant improvement in the direct recovery efficencies of Au,Ag,and Te were attributed to the successful regulation of LAS by selective oxidation.The new technology of selective oxidation-vacuum volatilization of LAS developed in this research has achieved green and efficient separation of gold,silver,and tellurium from metals including arsenic,antimony,and lead.An alloy with an Ag content of 67.58%and an Au content of 4287 g/t and a high tellurium concentrate with a Te content of 0.78%were obtained.The new process does not produce high arsenic dust and soda residue,which neither consumes fossil fuels,acid,and alkali reagents,nor sulfur-containing auxiliary materials.The problems of the low direct recovery efficiency of rare and precious metals and tellurium dispersion can be solve,achieving a win-win situation of efficient utilization of rare and precious metal resources and environmental protection.At the same time,it has fundamentally solved the arsenic pollution problem that has plagued the development of the lead industry.In summary,this technology has favorable industrial application prospects.