Applied Foundational Research Of Selective Recovery Of Selenium,Silver And Gold From Copper Anode Slime

Copper anode slime is produced in the process of electrolytic refining of blister copper,which usually contains rare and precious metals such as Se,Au,and Ag.Therefore,the value of copper anode slime is rather high.Conventional pyrometallurgy processes are widely used in the treatment of anode slime by the large smelters.However,the drawbacks of large investment,low direct yield of silver and gold,and serious lead bearing smoke dust restrict its use in the small and medium smelter.As a comparison,the roast-wet leaching processes are more suitable for the current situation of China's copper anode slime treatment industry,of which the sulphatising roast-leaching process is the typical representative.Nevertheless,it still suffers the drawbacks of sever pollution,equipment corrosion,long recovery period,etc.Hence,the sustainable development of the copper anode slime industry urgently requires a more environmentally friendly,efficient and low-energy treatment process.Focusing on the efficient and green recovery of valuable elements from copper anode slime,the applied fundational research of selective recovery of selenium,silver and gold was studied in this paper.The main research contents and conclusions of the thesis are as follows:(1)H2SO4-MnO2 leaching system for the selective recovery of Se and Cu from copper anode slime.The Gibbs free energy criterion confirmed the thermodynamic feasibility of the leaching process,besides,basced on the analysis of Eh-pH diagram of Me-H2O system,the state changes of main metals in copper anode slime during leaching process were identified.Effects of leaching parameters on the recovery of Cu and Se were then explored.Under the optimal conditions of 60wt%(mass ratio of MnO2 to copper anode slime),1.0 mol/L H2SO4,rotating speed of 650 r/min and leaching solution of 80 ?,extraction rates of Se and Cu were both 100%.Mechanism of oxidative leaching Se with H2SO4-MnO2 system was:under strong acid conditions,the active center Mn(IV)in MnO2 crystal was released into solution,which then diffused to the surface of anode slime to conduct oxidation process.For the recovery of silver,selenium and copper in leaching solution,the Ag+ was firstly separated from the solution by adding NaCl to precipitate Ag+,then,copper powder was added to reduce selenium and Cu2+in residual solution was separated with extraction.The recovery rates of Ag,Se and Cu were 99.5%,94.8%and 95.5%,respectively.The cost-benefit analysis of the proposed process also confirmed its potential industrial application prospects.(2)Selective recovery of silver from copper anode slime with alkaline thiosulfate method.Aimed at the problems that Ag2Se and AgSbS2 in the unpretreated anode slime cannot dissolve in alkaline thiosulfate solution,and the dissolved silver in solution re-precipitated in the presence of Cu2S,the H2SO4-MnO2 leaching system was used to successfully convert the sulfide to SO42-,as well as the Ag2Se and AgSbS2 to readily leached Ag2SO4.The thermodynamic basis and leaching kinetics of selective recovery of Ag in pretreated residue by thiosulfate,sulfite and ammonia leaching were studied.It was found that when concentrations of S2O32-,SO32-and NH3 were 0.035 mol/L,0.4 mol/L and 1.4 mol/L,respectively,the corresponding silver extractions were 93.0,92.4 and 80.2,respectively,which indicated that the thiosulfate leaching had the advantage of low reagent consumption and high leaching rate compared with sulfite and ammonia leaching.Exploration of silver recovery from thiosulfate leaching solution with electrodeposition was also carried out.A 95.3%recovery rate was obtained by recycling the electrolyte for silver leaching,confirming the feasibility of recycling of lean liquid for silver leaching.(3)Solvent-free mechanochemistry for the recovery of gold from copper anode slime.Results of gold conversion with series of oxidant-NH4Cl combinations showed that only the KMnO4-NH4Cl combination worked.The presence of Cu2Se in anode slime hindered the gold conversion.The mechanism of gold conversion by mechanochemistry approach was revealed,involving the in situ generation of highly reactive,easily diffusible Cl2 gas by mechanical energy,which then diffused to the surface of gold to convert the elemental gold to water soluble AuCl3.Effects of NH4Cl addition,water content,mass ratio of ball-to-batch,rotating speed and milling time on gold conversion were also studied.Under the optimal conditions,the conversion rate of gold can reach 97.45%at 60 min.Assessment on the selectivity of mechanochemistry approach(MA)and hydrometallurgical processes demonstrated that the MA had excellent selectivity for gold,though contents of co-existing metals,including Sb,Ag,Cu and Ni,were 96.85,4.18,6.71 and 4.59 times higher than that of gold,respectively,extraction rates of co-existing metals were nearly zero,as a comparison,the gold extraction rate reached 80%.(4)Na2S2O3 leaching-Na2S2O4 reduction process for the silver recovery from de-gold anode slime-500 kg scale-up experiment.Results of the scale-up experiment confirmed the efficient recovery of silver by Na2S2O3 leaching,and the successful reduction of silver ions to elemental Ag by Na2S2O4 in leaching solution.After reduction,the solution was recycled to leaching and the silver extraction rate met the requirements enterprises.Compared with the ammonia leaching,N2H4 reduction process,the proposed process decreased the water consumption from 7 m3 to 1.45 m3 and reduced cost of processing 1000 kg anode slime by 42%,confirming the feasibility of the industry application of new process.