Low/no-corrosion leaching of spent lithium-ion battery cathode materials in hydrothermal water using amino acid or mixed organic acids as the leachant

采用流动体系，以柠檬酸和甘氨酸的混合物（10%/90%，简称酸X）为浸出剂，成功地实现了废LiNixCoyMn1-x-yO2 （NCM）正极材料的连续水热浸出。原料料浆加料50 min后，Li、Co、Ni、Mn的浸出效率达到90%以上，所得浸出液pH值保持在6.5左右。首次通过高效、低/无酸腐蚀的绿色工艺，实现了废NCM正极材料的连续酸浸。采用收缩未反应核模型，对废NCM正极材料在酸X作用下的水热浸出动力学进行了研究。发现产物层内的扩散是浸出Li， Co， Ni和Mn的限速步骤。根据测定的反应速率和Arrhenius方程，计算了浸出Li、Co、Ni和Mn的活化能。利用柠檬酸对LiCoO2/LiNiO2 （LCO/LNO）正极材料进行水热浸出，并利用一系列沉淀剂对所得浸出液中的金属组分进行了顺序分离。最终，Ni、Co、Li的回收率分别为97.2、96.1、94.1%，相应沉淀物中Ni、Co、Li的纯度分别为96.3、96.2、99.9%。此次试验成功后，一种由热液浸出和沉淀分离步骤组成的升级湿法冶金方法正式投入使用，并有待进一步开发。

Continuous hydrothermal leaching of spent LiNixCoyMn1-x-yO2 (NCM) cathode materials was successfully achieved employing a flow system and using a mixture of citric acid and glycine (10%/90%, referred to as acid X) as the leaching agent. After feeding the slurry of raw materials for 50 mins, the leaching efficiencies of Li, Co, Ni, and Mn achieved >90% and the pH value of the obtained leachate was kept at around 6.5. That was the first time to realize the continuous acid leaching of spent NCM cathode materials through a green process with high efficiency and low/no acid corrosion.A kinetic study for hydrothermal leaching of spent NCM cathode materials with acid X was conducted using a shrinking unreacted core model. Diffusion within the product layer was found to be the rate-limiting step for leaching Li, Co, Ni, and Mn. According to the determined reaction rates and Arrhenius equations, the activation energies for leaching Li, Co, Ni, and Mn were calculated.Furthermore, hydrothermal leaching of LiCoO2/LiNiO2 (LCO/LNO) cathode materials with citric acid was performed and the metal components in the obtained leachate were separated in order using a series of precipitants. Finally, the recovery rates of Ni, Co, and Li were 97.2, 96.1, and 94.1%, respectively, with the purities of Ni, Co, and Li in the corresponding precipitate being 96.3, 96.2, and 99.9%, respectively. With this success, an upgraded hydrometallurgical method, composed of hydrothermal leaching and precipitation separation steps, was officially launched for LIB recycling and is subject to further development.