Dissolution Behavior Of Gold And Its Main Coexistent Sulfide Minerals In Acid Thiocyanate Solutions

Many researchers have been investigating the use of non-cyanide substances in gold leaching,to replace the use of cyanide,which is toxic.With its high efficiency and low toxicity,in recent years thiocyanate has been considered as a potential substitute for cyanide.Leaching gold under alkaline conditions is environmentally friendly,which is the trend of future research.But the leaching rate is low.Therefore,most of the current research is focused on the acid thiocyanate gold leaching system,which has high leaching rate and efficiency.But the theoretical study in the system of gold leaching is still not perfect.In this paper,the linear polarization was used to systematically study the electrochemical behavior of the dissolution of anodes occurring with Au or its associated minerals,as well as the effects of different thiocyanate concentration,Fe3+concentration and pH.The corrosion current and corrosion potential of gold in alkaline thiourea solutions thus calculating the kinetic parameters was studied with the Tafel test at different temperatures.The QCM-D measurements was used to study the effect of ions of main associated minerals such as chalcocite dissolved in acid thiocyanate system on gold leaching.In the acid thiocyanate system,the optimum thiocyanate concentration is 0.15mol/L,the optimum ferric ion concentration is 0.2g/L,and the optimum pH is 2.The Tafel curves showed that with the temperature increasing,the corrosion current of gold in acid thiocyanate solutions increased differently because Fe3+is added.The results showed that Fe3+ could increase the apparent activation energy,thus the gold leaching is controlled by electrochemical polarization.The corrosion voltage and corrosion current of gold and its associated minerals under different conditions are obtained by the Tafel curve.Without thiocyanate,Au,stibnite,galena,low iron sphalerite and high iron sphalerite hardly dissolve,and chalcocite,arsenopyrite and pyrite can dissolve.With the adding of thiocyanate,dissolution occurred on the gold surface,arsenopyrite and pyrite can dissolve,and the dissolution of chalcopyrite was inhibited compared with the condition without thiocyanate,arsenopyrite,galena,low iron sphalerite and high iron sphalerite hardly dissolved.The addition of Fe3+ increased the dissolution current of the associated minerals,but the absolute value of the dissolution currents of the associated minerals such as stibnite,galena,yellow sphalerite and black sphalerite were low.The chalcocite is suppressed by thiocyanate,after adding Fe3+,its current density is increased several times compared to the thiocyanate-free system.The apparent activation energy of chalcocite,arsenopyrite and pyrite was calculated from the Arrhenius equation,which was no more than 40 kJ/mol,thus the dissolution is controlled by diffusion.Without the addition of thiocyanate,chalcocite,arsenopyrite and pyrite as cathode reduction reaction occurs and promote the anode dissolution of gold,and galena as anode to inhibit the anode dissolution of gold;stibnite,low iron sphalerite and high iron sphalerite have almost no galvanic corrosion behavior with gold.The addition of thiocyanate changed the galvanic corrosion behavior of stibnite and low iron Sphalerite,which as anode inhibited the anodic dissolution of gold.The addition of Fe3+ can significantly promote the dissolution of gold,the dissolution of arsenopyrite is suppressed,the dissolution of chalcopyrite increases,and the dissolution behavior of other associated minerals does not change much.The QCM-D measurements showed that in the acid thiocyanate system,the ions of arsenopyrite,pyrite and chalcopyrite dissolved in the solution have an inhibitory effect on the dissolution of the Au chip surface.Among them,ions of chalcocite dissolved in the system have the most inhibitory effect on the dissolution of Au chip surface,as well as ions of arsenopyrite dissolved in the system have the least inhibitory effect on the dissolution of Au chip surface.The leaching experiments of practice pure minerals show that chalcocite and pyrite have the obvious influence on the gold leaching rate,that of arsenopyrite is lower.Stibnite almost has no effect on gold leaching rate,while galena and sphalerite have little effect on gold leaching rate.This is the comprehensive effect of the galvanic corrosion behavior of gold couple with associated minerals and the dissolution of associated minerals themselves.