Abstract:

Phosphorus iron slag is one of the by-products of the production of yellow phosphorus. It is often treated as solid waste due to its chemically stable, which not only pollutes the environment but also consumes a lot of manpower and material resources. How to rationally utilize the iron (Fe) and phosphorus (P) elements in iron phosphate slag is a problem that must be solved by phosphorus chemical enterprises. The traditional technology of preparing iron phosphate (FePO₄) from iron phosphate slag has the disadvantages of high energy consumption, large safety hazards of by-products and difficulty in industrialized production. Thus, this paper adopted iron phosphate slag, phosphoric acid, hydrochloric acid and ammonia as raw materials, and prepared battery-grade FePO₄ by a combination of high-temperature activated leaching-precipitation method. In the stage of high-temperature activated leaching, the correlation law between the leaching time, the leaching temperature, the concentration of hydrochloric acid, the liquid-solid ratio and the leaching ratio of iron phosphate slag was explored. The effects of reaction temperature, time, pH and feeding ratio on the performance of prepared FePO₄ were also investigated. The concentrations of Fe and P elements in the leaching solution and the crystal structure, morphology and particle size of FePO₄ were analyzed. The experimental results showed that the optimal conditions for the leaching of ferrophosphorus slag were: leaching time of 3h, leaching temperature of 90℃, hydrochloric acid concentration of 5.5mol/L and liquid-solid ratio of 20mL/g, under which the leaching rate of elemental Fe could be up to 93.55%, the rate of elemental P could be up to 82.21%, and the rate of solid slag leaching could be up to 90.06%. The optimal conditions of the precipitation reaction process were: reaction temperature 70℃, reaction time 2h, reaction pH=1.2 and Fe/P feeding ratio of 1. This condition of the preparation of iron phosphate (FePO₄) materials with high crystallinity, uniform morphology, good dispersion, a particle size of 100—200nm, iron and phosphorus ratio of 0.97 and the content of impurities was in full compliance with the industry standards. The lithium iron phosphate (LiFePO₄) cathode material synthesized in this way had good electrochemical performance, and the discharge specific capacity can reach 151.62mA·h/g at 1C multiplicity, indicating that the prepared FePO₄ fully met the requirements of the precursor of LiFePO₄ cathode material.

Key words: iron phosphate slag, activation, leach, precipitation method, battery-grade iron phosphate

摘要：

磷铁渣是黄磷生产的副产物之一，化学性质稳定，常作为固体废物处理，不仅污染环境，也消耗了大量人力物力。如何合理利用磷铁渣中铁（Fe）、磷（P）元素是磷化工企业必须解决的问题。以磷铁渣制备磷酸铁（FePO₄）的传统技术存在能耗大、副产物安全隐患大、难以实现工业化生产等缺点。有鉴于此，本文采用磷铁渣、磷酸、盐酸、氨水为原料，通过高温活化浸出-沉淀法制备了电池级FePO₄。在高温活化浸出阶段，探究了浸出时间、浸出温度、盐酸浓度、液固比与磷铁渣浸出率的关联规律。并研究了反应温度、时间、pH、投料比等条件对制备FePO₄性能的影响。对浸出液中Fe、P元素浓度和FePO₄晶体结构、形貌和粒度进行了分析。实验结果表明，磷铁渣浸出的最佳条件是：浸出时间3h、浸出温度90℃、盐酸浓度5.5mol/L、液固比20mL/g，在此浸出条件下Fe元素浸出率可达93.55%，P元素浸出率可达82.21%，固体渣浸出率可达90.06%。沉淀反应过程的最佳条件为：反应温度70℃、反应时间2h、反应pH=1.2、Fe/P投料比为1，此条件制备的磷酸铁（FePO₄）材料结晶度高，形貌均匀，分散性好，一次粒径为100~200nm，铁磷比为0.97，杂质含量完全符合行业标准。以此合成的磷酸铁锂（LiFePO₄）正极材料电化学性能较好，在1C倍率下，放电比容量可达到151.62mA·h/g，表明所制备的FePO₄完全满足LiFePO₄正极材料前体的要求。

关键词: 磷铁渣, 活化, 浸出, 沉淀法, 电池级磷酸铁