Deep Purification And Enrichment Of Cobalt In Zinc Hydrometallurgy System

The antimony salt purification method is the most used impurity removal process in the current zinc hydrometallurgy system.However,this process has problems such as insufficient impurity removal depth,large consumption of zinc powder,and low utilization rate of cobalt resources.In view of this situation,the hydrothermal purification method was carried out to remove impurities in the first stage purified liquid and the supernatant,and to separate and enrich cobalt in the cadmium-depleted liquid.It is of great practical significance to investigate the removal effect of cobalt by process conditions,to find out the removal and enrichment rules of impurities by hydrothermal purification,and to provide technical support for the improvement of the quality and efficiency of the hydrothermal zinc smelting purification process.Based on the impurity removal mechanism and process characteristics of antimony salt purification method,a study on the removal of cobalt from typical hydrothermal zinc smelting solution by zinc powder hydrothermal purification method is proposed.With the help of the Zn-Me-H₂O potential-p H diagram in the hydrothermal system,the thermodynamic reaction trend of the monometallic Me-H₂O or multi-metal water system was analyzed,the mechanism of the hydrothermal purification of zinc powder was revealed,and the process characteristics of the hydrothermal purification reaction were mastered through single-factor experiments,to obtain the optimal conditions for hydrothermal purification to remove and enrich cobalt in typical solutions containing cobalt in zinc hydrometallurgy.After systematic experimental research,the following conclusions are obtained:（1）According to the Zn-Me-H₂O potential-p H diagram in the hydrothermal system,with the increase of temperature,the precipitation potential corresponding to the chemical reaction in the stable region increases,indicating that high temperature is more conducive to the occurrence of the reaction and the reaction kinetics conditions are more favorable.With the increase of hydrogen partial pressure,the cobalt stable region moves to the positive potential direction,and the cobalt stable region increases,indicating that the replacement effect of zinc on cobalt is improved,and the trend of hydrogen evolution reaction is reduced.（2）The hydrothermal purification method can realize the deep removal of cobalt in the liquid after one stage of purification.The hydrothermal temperature,the ratio of antimony to cobalt and the concentration of copper ions have significant effects on the removal of cobalt.With the increase of hydrothermal temperature,the purification efficiency of zinc powder increases.When the temperature exceeds 110℃,the cobalt in the solution can be reduced to below 0.2 mg/L after 60 min of reaction.With the increase of antimony-cobalt ratio and copper ion concentration,the removal effect of zinc powder on cobalt first increased and then decreased.When the antimony-cobalt ratio exceeded 0.05 and the copper ion concentration exceeded 200 mg/L,the dissolution rate of zinc powder accelerated.Excessive consumption of zinc powder leads to the conversion of the zinc-cobalt-antimony primary battery into a cobalt-antimony primary battery,and the cobalt as the anode is obviously re-dissolved,which reduces the removal rate of cobalt.（3）The hydrothermal purification method can realize the one-step removal of copper,cadmium,nickel and cobalt in the supernatant,and the ratio of antimony to cobalt and the hydrothermal temperature have a significant effect on the removal of impurities.Compared with copper,cadmium and nickel,the removal of cobalt is larger.As the ratio of antimony to cobalt increases,the replacement efficiency of cobalt and zinc powder increases.When the antimony-cobalt concentration ratio increased from 0.05 to 1.0,the replacement efficiency of cobalt and zinc gradually increased,and the cobalt removal rate increased from 73.41%to97.80%;when the antimony-cobalt ratio further increased,the cobalt removal rate decreased.The deposited cobalt begins to dissolve back.The purification efficiency of cobalt increases with the increase of the hydrothermal temperature,and the higher the temperature,the less time it takes to achieve the best impurity removal effect.When the temperature is 110°C,the cobalt concentration can be reduced from 11 mg/L to about 0.6 mg/L after a reaction time of30 min,which can fully meet the technical requirements of zinc electrowinning.（4）The separation and enrichment of cadmium and cobalt in the cadmium-depleted solution can be achieved by the medium temperature-hydrothermal zinc powder replacement method.When the hydrothermal temperature increased from 100℃to 140℃,the cobalt ion concentration in the reaction solution decreased from 139.0 mg/L to 27.7 mg/L.When the hydrothermal temperature was further increased,the cobalt ion concentration in the reaction solution began to increase instead.At 50°C,when the amount of zinc powder is 3 times,the cadmium removal rate is close to 100%,while the removal of cobalt is less than 10%,and the cadmium content in the obtained cadmium removal slag exceeds 72%.After removing cadmium,the liquid is hydrothermally purified to obtain purified slag,and its cobalt content is as high as 4%,which is more than 4 times higher than that of the conventional zinc powder replacement process,and the enrichment of cobalt is better achieved.