Study On Efficiency Separation Of Cobalt And Zinc In Zinc Plant Purification Residue

Cobalt is used in various industries because of its excellent physical and chemical properties.Recently,with the development of new energy vehicles and battery industries in China,the demand and consumption of cobalt have grown rapidly,and China has become the world's leading consumer of cobalt.Due to the lack of cobalt resources,Most of China's production was from partially refined cobalt imported from Congo?Kinshasa?.Therefore,while we investing the supplier,there is an urgent need to find new cobalt resources.Zinc plant purification residue is a by-product of zinc hydrometallurgy,and it's a good secondary resource of cobalt with abounding cobalts.However,its compositions are complex and it contains amounts of zinc,cobalt,lead,cadmium and other metal elements.It is difficult to separate zinc and cobalt,which limits the recycle of zinc plant purification residue.In this paper,alkali leaching process and oxidizing precipitation were combined to carry out an experimental investigation on the separation of zinc and cobalt.Moreover,the reaction mechanism was studied.Zinc plant purification residue in this paper was from a znic plant.It has analyzed by chemical composition analysis,XRD,SEM,and thermogravimetric analysis.The main component of ZPPR is zinc,which also contains lead,cadmium,and cobalt,which are 54.57%,1.68%,0.78%,and 0.18%respectively.Its main phase composition are zinc sulfate and hydroxide.The distributions of Pb,Cd and Co are concentrated.The effects of time,slurry pH,temperture,liquid-solid ratio and alkali concentration were investigated.The results showd that time of 40 min,temperature of30°C,reaction liquid-solid ratio of 20 m L/g,alkali concentration of 3 mol/L,and agitation speed of 300 rpm were the optimal flotation conditions.In these conditions,the leaching rates of zinc and cobalt were 96.14%and 5.68%,respectively.The leaching residue is constituted by loosely-packed,randomly distributed agglomerated particles The main components were Zn O and Zn?OH?₂ and ZnS,as well as a small amount of PbO,Cd?OH?₂ and Co SO₄·3H₂O;and the leaching solution contained Zn?OH?₄^2-/Zn O₂^2-.Therefore,the experiments of synthesis of nano-zinc were performed by using the leaching solution.The direct alkali leaching method has a good effect on separating Zn and Co,however,it costs lots of alkali.The potential?Eh?-pH diagram of Zn-Co-H₂O shows that the pH of Co³⁺and Zn²⁺is significantly different when they are hydrolyzed.Co?OH?₃ and Zn²⁺have obvious coexisting regions,indicating that oxidizing precipitation can separate cobalt and zinc in solution.The potential-pH diagrams of several oxidants were analyzed,and the oxidizing precipitation experiment was investigated by using sodium persulfate?Na₂S₂O₈?as the oxidant,and compared with H₂O₂.The results showed that Na₂S₂O₈is better.The optimal conditions are Na₂S₂O₈dosage of 10 times the theoretical equivalent,the temperature of 85oC,the liquid-solid ratio of 20 m L/g,and the sulfuric acid concentration of 0.26 mol/L,the agitation speed was 300 rpm,first leaching with sulfuric acid for 30 minutes,and then adding sodium persulfate to oxidize and precipitate for 25 minutes.Under these conditions,the leaching rates of zinc and cobalt were 92.14%and 0.15%,respectively,and the amount of ZPPR were reduced by about85%.The chemical component of leaching residues are zinc,lead and cobalt,the contents of which are 46.91%,5.50%and 0.48%respectively.The main phase composition is ZnSO₄·3Zn?OH?₂ and Pb SO₄.The response surface experiment was designed to conduct the alkali leaching experiment on the oxidizing precipitation resdiues.The optimal conditions were obtained through response surface analysis:the temperature of 40oC,the time of 30 minutes,the alkali concentration of 3.0 mol/L,and the leaching rate of zinc was close to 99%,cobalt is not leached.The significance test showed that the response surface model is reliable,the verification experiment results showed that the zinc leaching rate was 97.89%,and cobalt was not detected,which was close to the predicted result.That indicated that the obtained response surface model has a certain reliability.The chemical component of the oxidizing precipitation-alkali leaching residues are Zn,Pb,and Co,the contents of which are 19.31%,17.4%,and2.16%,respectively.The content of Co increased 12 times compared with the 0.18%of the ZPPR.And the mass of residues was about 1.35%of the ZPPR.Its main phases are ZnS and PbO,the particles were loose and porous.