有色金属(冶炼部分)

磷酸锂作为合成磷酸铁锂的最佳锂源，其性能至关重要。目前，磷酸锂制备方法根据原料不同分为碳酸锂法、含锂溶液法、氢氧化锂法和粗磷酸锂提纯法。对比了电池级碳酸锂、99.99%/99.999%碳酸锂沉锂后母液、电池级单水氢氧化锂作为原料制备磷酸锂，开展原料加入顺序、原料浓度、反应温度、除杂剂用量、净化方式等对磷酸锂纯度、锂转化率、粒径等的影响。最终确定高纯磷酸锂制备最佳工艺为：向磷酸中滴加质量浓度为6%的二次纯化后氢氧化锂溶液，pH至6.5时停止，用氨水调节pH至7.5，搅拌1 h，过滤，冷水搅洗，得固体湿料，160℃干燥3 h，得到达到行业标准的磷酸锂产品。

With the rapid development of new energy vehicles, the performance requirements for lithium batteries have become increasingly demanding. Lithium iron phosphate(LiFePO₄) batteries, known for their long cycle life and excellent safety performance, are widely used as a cathode material. The performance of the synthesized LiFePO₄ depends critically on the quality of its lithium source. Lithium phosphate(Li_3PO₄) is one of the preferred lithium sources for synthesizing high-quality LiFePO₄. However, large particle size in Li_3PO₄ leads to low discharge capacity, poor cycling performance, accelerated capacity decay, and impurities can exacerbate side reactions, directly affect the structural integrity and electrochemical activity of LiFePO₄, potentially compromising battery safety.Currently, Li_3PO₄ preparation methods are categorized based on raw materials: the lithium carbonate method, the lithiumcontaining solution method, the lithium hydroxide method, and the crude lithium phosphate purification method. Nevertheless, these methods suffer from drawbacks such as small particle size, difficult solid-liquid separation, high impurity content, low conversion rate, high energy consumption, and operational complexity. Therefore, conducting a systematic review of Li_3PO₄ synthesis processes and identifying the optimal process for high-purity Li_3PO₄ production present an urgent challenge.This study compares the preparation of Li_3PO₄ using different raw materials: battery-grade lithium carbonate, 99.99%/99.999% lithium carbonate derived from lithium-deposition mother liquor, and battery-grade lithium hydroxide monohydrate. It determines that battery grade lithium hydroxide monohydrate is the best raw material for preparing lithium phosphate. The effects of the raw material addition sequence, raw material concentration, reaction temperature, impurity removal agent dosage, and purification methods on key parameters such as the Li_3PO₄ purity, lithium conversion rate, and particle size were investigated. The results show that larger Li_3PO₄ particle sizes facilitate solid-liquid separation and reduce production time. Adding a low-concentration lithium hydroxide solution to phosphoric acid can promote the formation of larger Li_3PO₄ particles. The addition of EDTA effectively reduces Fe and Ca impurities in Li_3PO₄, however, this comes at the expense of reduced particle size, increasing the difficulty of solid-liquid separation. Purifying the raw material lithium hydroxide can solve the problem of Fe and Ca enrichment and improves solid-liquid separation. Na impurities in Li_3PO₄ can be removed by washing with cold water. Through process optimization studies, the optimal process for preparing high-purity Li_3PO₄ is determined: a secondary purified lithium hydroxide solution with a mass concentration of 6% is added dropwise to phosphoric acid. Addition is stopped when the pH value reaches 6.5, and the pH value is then adjusted to 7.5 with ammonia water. After stirring for one hour, the mixture is filtered, and the solid is washed with cold water to obtain the wet product. Finally, the wet product is dryed at 160 ℃ for 3 hours, the Li_3PO₄ products are obtained that meet industry standards.