Study On The New Technology Purification And Cobalt Removal In Zinc Hydrometallurgy

Hydrometallurgy zinc production accounts for more than80% of the world’s zinc production.Its process mainly includes roasting,leaching,purification,electrolysis,casting,and acid production.Most of the zinc hydrometallurgy adopts the three-stage reverse antimony-zinc powder replacement process,which is relatively practiced.However,there are many problems such as large consumption of zinc powder,high cost of steam,instability,re-dissolution of impurities,and difficult filtration.In order to solve these problems,this study puts forward a new reagent purification method for cobalt removal and efficient comprehensive recovery and purification technique from cobalt residue by conversion-two-stage oxidation leaching-washing.The main results are summarized as follows:(1)Single-factor experiment and industrial production experiment were used to verify the removal effect of cobalt by a new reagent.The optimum conditions for cobalt removal were the reaction temperature at80 ℃,p H range of4.8-5.2,2 times of theoretical amount for new reagent dosage,and 30:1 mass ratio of new reagent to sodium nitrite,and reaction time of1.5 h.This condition resulted in Co < 1 mg/L and Cd < 1mg/L in the electrolyte solution.(2)Residual cadmium and germanium can be removed by replacing zinc powder with zinc alloy powder.The cadmium ion was removed to less than 10 mg/L,with the removal rate of cadmium and germanium over 99% and 75% respectively,and the loss rate of cobalt within10%.The optimal control parameters were reaction temperature at 70 ℃,the reaction time of 60 min,and 3 times of zinc powder alloy.(3)A four-stage purification process combined with zinc powder and new reagents was proposed.The first stage is the removal of copper and cadmium using metal zinc powder at low temperatures.The second stage is to remove residual cadmium and germanium with zinc alloy powder at low temperatures.The third stage is to remove cobalt and nickel from cobalt slag in advance at a high temperature(80-85 ℃).The fourth stage is deeply removal of cobalt with new reagents at high temperatures(80-85 ℃).The residue with low cobalt from the fourth stage was returned to the third stage to further remove the cobalt and the slag from the three-stage reacted with the liquid with poverty cadmium to further remove cobalt.This method improved the utilization efficiency of new reagents and the purification efficiency,which optimized and upgraded the purification process.(4)A process of conversion-two-stage oxidation leaching-washing was proposed to recover and purify cobalt from residue.The optimal conversion conditions were theoretical addition amount of sodium sulfide,conversion temperature at 65 ℃,the reaction time of 120 min,and p H range from 6 to7.In the oxidation leaching process,ammonium persulfate was used as an oxidant.The optimal parameters for first stage oxidation leaching were that the addition amount of ammonium persulfate was 0.6times the theoretical value,the reaction temperature was 80℃,the reaction time was 4 hours,and the endpoint of p H was 2.5.The optimal parameters for second stage oxidation leaching were that ammonium persulfate was added according to 0.6 times the theoretical amount,the reaction temperature was 80 °C,and the reaction time was 4 hours.With the above method,the cobalt grade reached 10%,the slag rate of cobalt concentrate was 25-27%,the recovery efficiency of zinc is83.5%,and the recovery efficiency of cobalt is 81.3%.The advantage of this process is easy to operate,which achieved comprehensive recovery of valuable metals.