Extraction Of Gold From Copper Anode Slime Leached By Chlorinated Solution For Removing Lead

It is very important to carry out efficient and comprehensive method to exploit copper anode slime,as copper anode slime is the main raw material for extracting precious metals and rare metals.Although many traditional fire treatments about copper anode slime have been researched,most of them have the disadvantages of low metal recovery,serious environmental pollution,producing toxic gases.So it is an urgent problem about how to deal with copper anode slime efficiently.In this paper,lead in the copper anode slime was leached by HCl and/or NaCl solution,the effect of lead to extraction of gold has been studied.The solution which contains dilute precious metals was recovered by the compound of Na₂S₂O₅,SO2 and N2H4,the reduction product was treated by controlling potential method to extract gold,which achieved a highly efficient non-polluting progress of extracting gold from copper anode slime.The existence of lead in chlorinated system was studied,thermodynamic and dynamic characteristics ofreducing dilute precious metals from mixed solution by Na₂S₂O₅ compound were analyzed.Lead in the copper anode slime was leached by HCl and/or NaCl solution,the appropriate experimental conditions of hydrochloric acid system were as follows: hydrochloric acid concentration of 30%,L/S= 6: 1,the reaction temperature of 55 %,the reaction time of 2 h.The appropriate experimental conditions of sodium chloride + hydrochloric acid system were as follows: the reaction temperature of 55 ?,the reaction time of 30 minutes,sodium chloride dosage of 200 g/L,L/S= 12: 1,hydrochloric acid concentration of 12%.And the appropriate experimental conditions of sodium chloride system were as follow:sodium chloride dosage of 340 g/L,the reaction temperature of 55 ?,the reaction time of 30 min,L/S= 8:1.The existence of lead in chlorinated system was analyzed,the results show that the Pb???mainly existed in form of PbCl42-in three different system.The experiment of removing lead from the off-copper anode was carried out under the appropriate conditions of sodium chloride system,the extraction rate of lead was 96.9% and the slime rate was 48.40%.The precious metals in the anodic mud were highly enriched,the Au in enriched anode slime were extracted by chlorinated solution with leaching rate of 99.80%,whereas the leaching rate of Au without removing lead was only 95.20%Dilute precious metals were recovered from mixed solution by the compound of Na₂S₂O₅.In order to determine the optimum process parameters,three main effect factors were investigated by an orthogonal experiment.The thermodynamic and dynamic characteristics of reducing precipitated gold solution by Na₂S₂O₅,SO2 and N2H4 compound was analyzed.The study shows that: the influence factors on reduction rate of Se and Te decrease in such an order: reaction time,the amount of Na₂S₂O₅,the amount of N2H4.When SO2 is bubbled to saturation,the amount of Na₂S₂O₅ is 30 g/L,the amount of N2H4 is1.5 mL/L,reaction temperature is 85 ?,SO2 is passed into solution intermittently,that is the time for SO2 passing into solution is 0.5 h after one hour per reaction,which flow rate is 0.4 L/min,reaction time is 9 h,the reduction rates of Au,Pt,Pd are 100%,the reduction rates of Se and Te are71.50% and 90.30% respectively.The reaction of Na₂S₂O₅ compound reducing Se and Te follows First-order kinetics.The apparent activation energy of reducing Se and Te which is controlled by chemical reaction is determined to be ESe=52.53 kJ/mol and ETe=70.83 kJ/mol.The analysis of thermodynamic characteristics shows that Se,Te,Au,Pd and Pt exit in the form of AuCl4-,PtCl42-,PdCl42-,H2SeO3 and TeCl62-,respectively.Sodium metabisulfite and SO2 exit mainly in the form of H₂SO₃,hydrazine hydrate exits in the form of N2H5+.The platinum and palladium concentrate obtained by complex reduction was used as raw material to study the removal of base metal and the extraction of gold by controlled potential method.The optimum reaction conditions were as follows: the L/S= 5:1,the reaction time of 3 h,the electrode potential of 500 mV,the hydrochloric acid concentration of 5mol/L,the reaction temperature of90 ?.Under this condition,tellurium removal rate was 43.00%,copper removal rate was 82.10%,gold,platinum,palladium was not leaching.After the impurity removal of the platinum and palladium concentrate,selenium was leached by Na₂SO₃ solution.Gold,platinum,palladium was highly enriched.The enriched platinum and palladium concentrate was dissolved at electrode potential of900 mV and the gold was reduced by controlled potential.The suitable conditions of reducing gold were as follows: 50 g/L Na₂S₂O₅ solution as the reducing agent,the electrode potential of 600 mV,the reaction temperature was60 ?,the reaction time was 2 h.Under this condition,the reduction rate of gold was 97.00%,the reduction rate of platinum was 7.10%,the reduction rate of palladium was 12.80%,the reduction rate of selenium was 13.40%,the reduction rate of tellurium was 19.45%.In the reduction product,gold content was 80%,platinum,palladium,selenium,tellurium,copper content were 2.53%,0.05%,0.03%,1.26%,0.06% respectively.