| Thiosulfate leaching is a hot topic at present.However,due to the large amount of reagent consumption,the nontoxic gold extraction technology of thiosulfate gold extraction has not been industrialized.Compared with the common Cu2+-NH3-S2O32-gold leaching system,the Cu2+-en-S2O32-gold leaching system has the characteristics of low reagent consumption,but it still lacks the technology of effective recovery.Cementation of gold from Cu2+-en-S2O32-leaching solution by zinc powder was studied in this paper.(1)The balance distribution of species in the gold leaching system and the electrode potential of the relative electric pair were calculated,the possible chemical reactions and their products in the process of zinc powder cementation were speculated.The results showed that in the range of ethylenediamine concentration of 0.001 mol·L-1-0.08 mol·L-1,the species of copper ethylenediamine complex in leaching solution was Cu(en)22+,and the main form of copper hydroxides was Cu(rH)2,the main products of zinc were Zn(en)32+ and Zn(OH)2.(2)The effect of the components of the solution and experimental condition on the cementation reaction were discussed:The optimum pH was at 9-11,and it would generate hydroxides higher than 12;high concentration of thiosulfate made insignificant effect on the whole;it had little negative effect on the recovery process when the ratio of copper to ethylenediamine was 1:2,1:1;1 g,L-1 zinc powder was enough for cementation reaction;The cementation rate of zinc powder in the simulated leaching solution was very fast under room temperature,cementation rate was close to completed in 10 min,the actual leaching solution was complex and the cementation rate of gold was lower than that in the simulated gold leaching solution,but the once gold cementation rate was still up to 80%in 15 min.(3)The copper ion in the leaching solution could be reduced.The copper co-reduction increased with the increase of pH,zinc powder,thiosulfate concentration and temperature.When the ratio of copper to ethylenediamine was 1:1 and 1:2,the degree of copper co-reduction was relatively low.(4)The electron microscopy analysis showed that the zinc powder changed from the original smooth and fine-grained ball to irregular particle after cementation reaction.The results of energy spectrum analysis showed that sulfur or sulfides on the surface of zinc powder,after cementation reaction.The consumption of zinc in the process of cementation was increased with the increase of reaction time,pH,zinc powder,ethylenediamine concentration.Thiosulfate concentration and the temperature had little effect on the consumption of zinc powder.(5)Although the thiosulfate was consumed continuously in the lean solution after the completion of the cementation,the cementation time was relatively short,which did not affect on recycling of solution.To sum up,zinc powder cementation has the characteristics of fast,high efficiency,simple process,and little influence on the consumption of reagent,it can be used for gold recovery in the Cu2+-en-S2O32-system leaching gold. |
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