Study On Selective Leaching And Separation Of Metals In Waste Ternary Lithium Ion Batteries

With the rapid increase in demand and production of lithium-ion batteries in recent years,the amount of waste lithium-ion batteries has also increased dramatically.Waste LIBs contain a large amount of valuable metals,but the organic electrolytes can cause serious environmental pollution and endanger human health.Traditional hydrometallurgical recycling process mainly focuses on the recovery of the pure cathode active materials,which is complex,prone to secondary pollution,and can not recover LIBs with complex composition.Therefore,it is great significance to conduct environmentally friendly and adaptable research on the recycling process of waste LIBs.This thesis takes the waste nickel-cobalt-manganese ternary LIBs as the object,systematically studies the selective leaching and separation behavior of valuable metals in the waste LIBs.This process can ensure the high recovery efficiencies of metals in the leaching solution,increases the added value of final products and the environmental friendliness.Besides,the whole recycling process provides a theoretical basis and approach to achieve green and efficient recycling of waste LIBs.For the leaching of waste ternary LIBs(LiNi_1/3Co_1/3Mn_1/3O₂),citric acid was employed as the leaching agent,and the effect of reaction temperature,time,citric acid concentration,solid/liquid（S/L）ratio,reductant addition on the leaching efficiency were investigated,and the selectivity over Cu and Al as well.In addition,the leaching kinetics of each metal was analyzed,the control of metals leaching and activation energy of each metal were clarified,and the promotion effect of the current collectors（metal Cu and Al foil）on the leaching of Li,Ni,Co,and Mn was discussed in combination with thermodynamic calculations.The results showed that about 91.0%Li,90.9%Co,94.1%Ni,89.1%Mn,19.5%Cu and 26.9%Al were leached under the optimum leaching conditions of 0.5 mol/L citric acid,S/L ratio of 80 g/L at 90°C for 80min in the absence of reductant.Ascorbic acid shows better leaching selectivity than H₂O₂,and the step-wise addition of reductants is more conducive to improving the leaching efficiency.The kinetic calculation results indicated that the leaching of Li,Co,Ni and Mn fitted best to the Avrami equation controlled by the surface chemical reaction,whilst the leaching of Cu and Al corresponded to the surface chemical-controlled reaction based on shrinking core model.The activation energies for leaching Li,Co,Ni,Mn,Cu,and Al were 44.12,56.33,48.25,55.71,39.04,and 40.37 k J/mol,respectively.The thermodynamic calculation results revealed that metal Cu can promote the leaching of Li,Co,Ni,and Mn,while metal Al has no effect on the leaching.The influence factors of separating the metals in the leaching solution with different precipitants were studied.The experimental results show that about 93.5%Cu is selectively reduced by ascorbic acid as the ultrafine metal Cu powder at a Cu/ascorbic acid molar ratio of 1:3.5,pH=6,80℃ for100 min.At a pH of 4,25℃,a precipitation time of 60 min,and a（Co+Ni）/KEX（potassium xanthate）molar ratio of 1:3 and 25℃,around 98%of Co²⁺and Ni²⁺are simultaneously precipitated.Under the conditions of pH=3,40℃and 60 min,90%of Mn²⁺can be precipitated into Mn C₂O₄·2H₂O by 0.25mol/L oxalic acid.Combined with Eh-pH theoretical calculations,about 92%Al³⁺and89%Li⁺can be precipitated by Na₃PO₄ at pH 5 and 11,respectively.The optimal precipitation conditions of Li are 0.4 mol/L Na₃PO₄,pH=11,2 h,and reaction temperature 25℃.Precipitation-solvent extraction mixing method for separation of metal elements in the leaching solution shows that Cu,Ni,Co,Mn,Al and Li can be effectively separated in sequence by the mixed method.Around 95%Cu can be extracted by 10 vol%LIX84-I,under the conditions of contact time of 5 min,pH=2.0,organic phase/liquid phase volume ratio（O/A）=1.0,25℃.Mc Cabe-Thiele diagram shows that after two-stage counter current extraction,the Cu extraction efficiency is 99.5%,and 99.9%Cu can be stripped from LIX 84-I by 2 mol/L H₂SO₄.Because Co and Ni cannot be effectively extracted from leaching solution by traditional extraction agents such as LIX 84-I,Cyanex 272,and D2EHPA.KEX was selected to recover Co and Ni.The optimal conditions for the extraction of Mn are:pH=3.5,O/A=1.0,pH=3.5,extraction time 120s and 20 vol%D2EHPA,the extraction efficiency of Mn is about 98%.Mc Cabe-Thiele diagram shows that after two-stage counter current extraction,99%Mn can be extracted under the optimum condotions.About 92.1%Al can be separated by 10 vol%D2EHPA under the conditions of extraction time of 5 min,pH=4.0,O/A=2.The extraction efficiency of Al by two-stage countercurrent extraction can reach 99.6%,and it can be stripped by 1 mol/L H₂SO₄.89%Li can be pricititated under the optimal conditions of 0.5mol/L Na₃PO₄,pH=11,25℃and 2 h.