| In recent years,under the background of green environmental protection,China’s new energy vehicle industry has developed rapidly and has become the largest new energy vehicle market in the world.However,the service life of power lithium batteries(LIBs)used in new energy vehicles is generally five to eight years,and is about to enter a large-scale scrap period.The failure ternary LIBs contain abundant high-value metals and a variety of toxic pollutants.The clean recycling of failure ternary LIBs is of great significance both for protecting the environment and solving the dilemma of artificially controlled resources.However,the traditional hydrometallurgical process has problems such as low lithium recovery rate,large consumption of chemical reagents,complicated purification of leachate,long separation process of valuable metals,and the production of a large amount of highly salty organic wastewater and various hazardous waste residues.The technical issues of traditional hydrometallurgical process were studied,and a new efficient recovery process for failure ternary LIBs was developed,and related basic research was carried out.The main contents are as follows.A combined process of self-reduction roasting with graphite,carbonation water leaching and ammonia leaching was proposed to recover failure ternary LIBs materials after pretreatment and sorting.Firstly,the effects of roasting temperature,graphite content and roasting time on the phase transformation and leaching of valuable metals were investigated.The results show that the cathode materials can be completely dissociated and reduced to lithium carbonate,elemental nickel,elemental cobalt and manganese monoxide after self-reduction roasting(roasting temperature:750℃,mass ratio of graphite to cathode materials:22.5 wt.%,roasting time:2.5 h).It was found that aluminum in the failure ternary LIBs materials easily reacts with lithium carbonate at high temperature to form waterinsoluble lithium aluminate,thereby reducing the leaching efficiency of lithium during the carbonation water leaching process.The aluminum content in the failure ternary LIBs materials should be controlled below 3.0 wt.%.The phase transformation mechanism of the cathode materials during the self-reduction roasting was clarified by XRD,SEM-EDS and XPS.92.8% of lithium can be selectively and efficiently recovered from the roasted product through carbonation water leaching,and the lithium-containing leaching solution can be purified and simple thermally decomposed to prepare battery-grade lithium carbonate products.The effects of different ammonia leaching conditions on the leaching efficiency of valuable metals in the carbonation water leaching residue were studied.Under the optimal leaching parameters of ammonium carbonate concentration of 2.5 mol/L,ammonia concentration of 10 mol/L,liquidsolid ratio of 8 mL/g,temperature of 25℃,time of 6 h,and oxygen as oxidant,the leaching efficiency of nickel and cobalt both reach more than 98%,and other elements such as manganese,aluminum,and iron are not leached at all.The results show that ammonium leaching has selective leaching characteristics for target metals(nickel and cobalt)and non-target metals(manganese,aluminum,iron,etc.).The kinetics of ammonia leaching process indicate that the leaching rates of nickel and cobalt are controlled by chemical reactions.On the basis of small-scale experiments,the extensive experimental study on the recovery of failure ternary LIBs materials by the combined process of self-reduction roasting,carbonation water leaching and ammonia leaching was carried out.Next,the research on the separation of nickel and cobalt by solvent extraction was carried out using Mextral 984H as extractant.The results show that the cobalt is not extracted at all during the nickel extraction,but some ammonia is co-extracted.The optimal operating parameters of nickel extraction are extraction agent concentration of 30 vol.%,ratio of 3.5:1 and time of 3 min.The optimal operating parameters of ammonia scrubbing are sulfuric acid concentration of 10 g/L,ratio of 1:1 and time of 3 min.After two-stage extraction,two-stage scrubbing and threestage stripping,more than 99%of nickel is recovered to prepare high-purity nickel sulfate products.The cobalt in the raffinate is precipitated by the reductive ammonia distillation process,and more than 90%of the cobalt can be precipitated by only evaporating about 35 vol.%of the water.The cobalt precipitate is roasted to prepare tricobalt tetroxide products.Volatile ammonia,decomposition products of ammonium carbonate and residual liquid in the ammonia distillation can be recovered and returned to the ammonia leaching process for recycling.The trend of fluorine and phosphorus in the reduction roasting,leaching process and the product preparation process was studied.The results show that the amount of fluorine and phosphorus entering the final product is low enough to affect the quality.The object of the above recycling process is the failure ternary LIBs materials after pretreatment and sorting.Aiming at the serious mutual inclusion of copper,aluminum foil and active materials caused by the pretreatment sorting process,a process for recovering entire failure ternary LIBs without pre-sorting was proposed.The entire failure ternary LIBs were roasted at 600℃ and starch dosage of 17.5 wt.%for 0.5 h,the cathode materials can be dissociated and reduced to lithium carbonate,elemental nickel,elemental cobalt and manganese monoxide.Copper and aluminum foil do not participate in reactions.Graphite and organics such as separators and electrolytes that are difficult to recover economically can also be used as reducing agents during reduction roasting.82%of lithium can be preferentially leached through carbonation water leaching,and over 98%of nickel,copper and cobalt can be leached from leaching residue through ammonia leaching.Nickel,copper and cobalt in the ammonia leaching solution were effectively separated by solvent extraction,and the ammonia leaching residue was screened to separate aluminum foil and manganese-rich graphite residue.The process simplifies the pretreatment process and improves the comprehensive recovery rate of valuable metals.Compared with the traditional hydrometallurgy and pyrometallurgical processes of failed ternary LIBs,the combined process of reduction roasting,carbonation water leaching and ammonia leaching has the advantages such as high recovery rate of valuable metals,high added value of products,green environmental protection,low output of three wastes and low recovery cost,which conforms to the basic idea of atomic economy and has good promotion and application prospects. |
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