三元体系Li+, NH4+//SO42——H2O 298 K相平衡研究

四川甲基卡、李家沟等地锂辉石储量丰富，为下游锂电池储能材料等领域提供了重要的原料来源。传统锂辉石制碳酸锂工艺中，采用氢氧化钠中和法除去铁、铝等杂质，但是副产硫酸钠附加值低，导致生产成本较高，本论文研究了以氨气替代强氧化钠中和法除杂制碳酸锂工艺，发现在精制锂溶液沉淀结晶过程中存在LiNH₄SO₄复盐产生，影响了锂的收率和碳酸锂产品品质。为解决此问题，本论文采用等温溶解平衡法研究了三元体系Li+，NH₄+ //SO₄2--H₂O在298 K下的稳定相平衡关系，测定了平衡液相中各组分溶解度、密度和折光率数据，并绘制了该体系的相图、密度-组成图和折光率-组成图。结果表明该三元体系为复杂三元体系，有复盐LiNH₄SO₄形成；其稳定相图由3个固相结晶区，3条单变量曲线和2个共饱点组成，3个结晶区分别为（NH₄）₂SO₄，Li₂SO₄·H₂O和LiNH₄SO₄，且LiNH₄SO₄复盐的结晶区较大。研究结果表明，为了避免LiNH₄SO₄复盐的产生，需在锂辉石制工业级碳酸锂工艺前端通过钙离子沉淀法将锂溶液中锂硫比[Li₂SO₄·H₂O/（NH₄）₂SO₄]降到1.6以下，研究结果为四川锂辉石湿法冶金工艺中采用氨中和除杂提供了理论指导。 

Stable Phase Equilibrium of the Ternary System Li+,NH4+//SO42--H2O at 298 K

Sichuan Jiajika, Lijiagou and other places have rich spodumene reserves, it provides an important source of raw materials for downstream lithium battery energy storage materials and other fields.In the traditional spodumene production process of lithium carbonate, sodium hydroxide neutralization method is used to remove impurities such as iron and aluminum. However, the added value of by-product sodium sulfate is low, resulting in high production costs. This paper studies the process of replacing strong sodium oxide with ammonia gas to neutralize impurities to prepare lithium carbonate, it was found that LiNH₄SO₄ double salt was produced during the precipitation and crystallization process of refined lithium solution, which affected the yield of lithium and the quality of lithium carbonate products.In order to solve the problem, the stable phase equilibrium relationship of the ternary system Li+, NH₄+//SO₄2--H₂O at 298 K was studied by the isothermal dissolved equilibrium method. The solubility, density and refractive index data of each component of the equilibrium liquid phase were measured, and the phase diagram, density-composition diagram and refractive index composition diagram of the system were drawn. The results show that this system is a complex ternary system, with the formation of LiNH₄SO₄ double salt; its stable phase diagram consists of 3 solid phase crystallization regions, 3 univariate curves, 2 invariant points, 3 crystallization regions corresponding to (NH₄)₂SO₄, Li₂SO₄·H₂O and LiNH₄SO₄, And double salt LiNH₄SO₄ crystallization area is the largest.The research results show that in order to avoid the production of LiNH₄SO₄ double salt, It is necessary to reduce the lithium-sulfur ratio (w(Li₂SO₄)·H₂O/w(NH₄)₂SO₄) in the lithium solution to less than 1 through the calcium ion precipitation method at the front end of the spodumene-made industrial-grade lithium carbonate process, the research results provide theoretical guidance for the use of ammonia neutralization and impurity removal in the Sichuan spodumene hydrometallurgical process.