IntroductionThe complexity of lithium iron phosphate waste sources dictates the intricate composition of the solution after acid leaching. Particularly during the pretreatment process, lithium iron phosphate waste can become mixed with anode materials and may contain trace amounts of nickel, cobalt, and manganese. Therefore, in addition to the characteristic impurities of lithium iron phosphate, such as iron, aluminum, and phosphate, the acid leach solution obtained from lithium iron phosphate waste through high-pressure oxidation leaching is typically accompanied by small amounts of copper, nickel, cobalt, manganese, fluorine, and other impurity elements. On one hand, regarding product purity, if these impurity elements are not adequately removed, they may lead to the deterioration of lithium carbonate quality, adversely affecting subsequent processing. On the other hand, considering recycling value, metals like copper, nickel, and cobalt have significant market value, necessitating their recovery to improve the economic viability of the entire process.MethodsRemove Cu, Fe, Al, P, Ni, Co, Mn and other impurities by chemical method. Removal of calcium impurities by HP4040 resin. The adsorption process of Ca²⁺ was correlated using kinetic equations, confirming that the adsorption process of HP4040 resin for calcium removal aligns more closely with a pseudo-second-order kinetic model. This indicates that the adsorption reaction between calcium ions and the resin is predominantly governed by chemical adsorption. Thermodynamic analysis revealed that the adsorption process of calcium ions on the resin conforms to the Langmuir isotherm model. Removal of fluorine impurities by modification of MgO-modified β-spodumene, both pseudo-first-order and pseudo-second-order kinetic equations were employed to describe the adsorption of fluoride ions onto the adsorbent. The fitting results suggest that the fluoride adsorption process largely adheres to the pseudo-second-order kinetic model. Thermodynamic analysis further indicated that the adsorption of fluoride by the defluorination agent aligns better with the Langmuir model, suggesting a preference for monolayer adsorption.Results and discussionThe main conclusions of this study are summarized as follows. This research systematically investigates the purification and decontamination processes of waste LiFePO₄ lithium-containing leach solutions, focusing on the reduction and removal of copper, neutralization of iron, aluminum, and phosphorus, alkalization for nickel, cobalt, and manganese removal, resin-based calcium removal, and adsorption for fluoride removal. The distribution of impurity ions in the acid leach solution, including Fe, Al, Cu, Ni, Co, Mn, Ca, and F, has been analyzed throughout the decontamination process, and the entire flow of acid leach solution decontamination has been experimentally validated. The findings are as follows: To effectively reduce and remove copper, the optimal addition of iron powder is 1.1 times the theoretical amount, achieving a recovery rate of 99.95% and a copper sponge purity of 95.02%. For neutralization to remove iron, aluminum, and phosphorus, the optimal reaction conditions are a temperature of 30 ℃, an endpoint pH value of 4, and a reaction time of 30 min. Under these conditions, the impurity elements Fe, Al, and P are predominantly removed, while the loss of valuable metals like Ni, Co, and Mn is minimal. In the alkalization process for removing Ni, Co, and Mn, precipitation occurs at pH 12, with precipitation rates exceeding 99.5% for all target metals. The resin-based calcium removal process studies and compares the advantages of three commercially available calcium removal resins, ultimately selecting HP4040 resin, which demonstrates a maximum adsorption capacity of 35.28 mg/g for calcium, achieving over 91.6% single-stage calcium adsorption. Meanwhile, the synthesized MgO-modified β- spodumene adsorbent material achieves a single-stage adsorption rate of over 85.8% for fluoride, providing a pathway for developing low-cost deep fluoride removal materials.ConclusionsThis study systematically investigates the purification and decontamination process for waste LiFePO₄ lithium leach solutions. After the reduction to remove copper, neutralization to eliminate iron, aluminum, and phosphorus, alkalization for nickel, cobalt, manganese removal, resin-based calcium removal, and adsorption for fluoride removal, the purification of the liquid obtained allows for lithium carbonate recovery.