Study On The Recovery Of Copper And Cyanide From Copper-cyanide Wastewater By Protective Electrodeposition

Gold is mainly extracted from its ores by cyanidation.However,due to the presence of associated minerals,a large amount of copper containing cyanide wastewater will be produced during the cyanidation process.The existence of numerous copper ions in cyanide leaching solution can significantly reduce the leaching rate of gold and increase the consumption of cyanide,which caused copper-cyanide wastewater can not be directly returned to cyanidation process.It can only be treated properly and discharged.The valuable metals(copper)and cyanide in the wastewater can not be recycled by the conventional purification techniques,which consuming large amount of chemical agents.Although the cyanide can be recycled effectively by acidification-volatilization-regeneration(AVR)technique from wastewater,there are still some defects such as high cost and the acidified wastewater can not be re-used directly,furthermore,the valuable metals in the waste water can not be used effectively.The traditional electrodeposition process is a useful method to recover valuable metal(copper),however,the recovery of valuable metals and cyanide can not be achieved simultaneously due to the serious oxidation of cyanide.In order to achieve comprehensive recovery of copper-cyanide wastewater,the protective electrodeposition technique which owns industrial application potentiality has been developed in this paper,in which the protective agent(sodium hypophosphite)was used to inhibit the oxidation of cyanide in the process of copper electrodeposition.On this basis,the simultaneous recovery of copper and cyanide in the low concentration copper containing cyanide wastewater was successfully achieved by solvent extraction-protective electrodeposition technique.Furthermore,the electrode reaction mechanisms of cyanide and hypophosphite in the wastewater were also studied in this paper.The coordination forms of copper-cyanide complex ions and the deposition potentials were studied in different conditions.The results showed that the form of copper-cyanide complex ion was mainly affected by the temperature and the molar ratio of cyanide to copper.The distribution of Cu(CN)32-complex ions increased with the increasing temperature or the decreasing molar ratio.The increasing temperature also reduce the deposition potential of Cu(CN)32-at the cathode,which could promote the electrodeposition of copper.The increasing molar ratio and pH value of solution had perverse effects on electrodeposition.The copper-cyanide wastewater was treated by electrodeposition with sodium hypophosphite used as a protective agent.The results showed that the hypophosphite could effectively inhibit the oxidation of cyanide in electrodeposition process,by which the recovery effect of cyanide was improved.The increasing temperature could also promote the recovery of cyanide,yet the current density and pH value had a tiny effect on the recovery of cyanide and copper.The ferricyanate in wastewater had an adverse effect on the electrodeposition recovery process.The decreasing current density could eliminate its negative influence.The wastewater could be directly reused for cyanide leaching after protective electrodeposition and the leaching rate of gold had no obvious change.The investigation of solvent extraction used for pretreating the low concentration copper containing cyanide wastewater was conducted.The results showed that 200 g/L Aliquat 336-20 vol%2-octanol-sulfonated kerosene was an effective extractant for enriching the copper-cyanide complex ions from the above wastewater.The maximum extraction capacity was higher than 13 g/L and the complex ions was mainly extracted as Cu(CN)32-into organic phase.The stripping efficiency of copper was over 96%after three-stage continuous countercurrent extraction using 1.5 mol/L NH4SCN.After countercurrent extraction,the copper and cyanide in stripping liquid could be effectively recycled by the protective electrodeposition.The raffinate after treatment could be used to leach gold and there was no obvious influence on the leaching rate.The mechanism of anodic reaction in the electrodeposition of copper cyanide wastewater was studied.The results indicated that the degradation of cyanide was mainly caused by Cu2+;the precipitation of Cu(OH)2 forming on the anode surface,which absorbed free cyanide and cause directly electrochemical oxidation of cyanide during electrodeposition.Hypophosphite could effectively inhibit the oxidation of cyanide by preferentially reacting with Cu2+ in protective electrodeposition process,which wasn't directly oxidized on the anode surface.On the base of anodic reaction mechanism of hypophosphite,the study of using carbon fiber as anode material was conducted.The results indicated that the process had a certain enhanced the inhibitory effect of phosphite and increase recovery of cyanide;however,the effect of anode sediment on the reaction process must be noted when dealing with actual wastewater.