氯化锂溶液磷酸盐沉淀法除镁的热力学分析  

Thermodynamic Study on Removal of Magnesium from Lithium Chloride Solutions Using Phosphate Precipitation Method

作　　者：肖超[1] 肖连生[1] 曾理[1] 高从堦[1] 

机构地区：[1]中南大学冶金与环境学院,湖南长沙410083

出　　处：《稀有金属》2016年第2期149-154,共6页Chinese Journal of Rare Metals

基　　金：人力资源与社会保障部中国博士后科学基金项目(2013M531809)资助

摘　　要：锂镁离子性质接近,锂镁分离是高纯氯化锂制备过程的关键问题。针对磷酸盐沉淀法除镁工艺进行热力学分析。根据平衡原理和质量守恒定律,分别绘制了298 K时Mg2＋-PO3-4-H2O,Li＋-Mg2＋-PO3-4-H2O,Li＋-Mg2＋-NH＋4-PO3-4-H2O系热力学平衡图,并考察了工艺参数对除镁的影响。研究结果表明：锂离子的存在不利于磷酸盐除镁,磷酸铵镁盐法除镁效果优于磷酸镁盐法,平衡镁含量随着溶液中总氮浓度升高、锂浓度降低而降低。当氯化锂溶液中[Li]T=1.00 mol·L-1,[N]T=0.03 mol·L-1,初始[Mg]T=0.01 mol·L-1,初始[P]T=0.03 mol·L-1时,p H范围为4.5～13.0时,The separation of magnesium from lithium chloride solution is the key point of pure Li Cl preparation for the similar chemical property between lithium and magnesium. Thermodynamic analysis was conducted on the removal of magnesium from lithium chloride solutions by phosphate precipitation method. The thermodynamic equilibrium diagrams of Mg2 ＋-PO3-4-H2 O,Li＋-Mg2 ＋-PO3-4-H2 O,Li＋-Mg2 ＋-NH＋4-PO3-4-H2 O system at 298 K were established based on the thermodynamic calculation,respectively. The effect of process parameters on the removal of magnesium was also investigated. The results showed that the presence of lithium ion was harmful to the removal of magnesium. The method of magnesium ammonium phosphate precipitation was better than phosphate magnesium precipitation on the separation of magnesium from lithium chloride solutions. Equilibrium concentration of magnesium decreased with the increase in total nitrogen concentration and the decrease in lithium concentration. There were four stable solid phase regions in p H range of 4. 5 ～ 13. 0 at [Li]T= 1. 00 mol·L- 1,[N]T= 0. 03 mol·L- 1,the original [Mg]= 0. 01 mol·L- 1,[P]= 0. 03 mol·L- 1in lithium chloride solutions,which were Mg HPO4（ 5. 9 〈p H 〈6. 6）,Mg NH4PO4（ 6. 6〈 p H 〈9. 6）,Mg（ OH）2（ 10. 0 〈p H 〈13. 0）and Li3PO4（ 6. 6 〈p H 〈1. 3）,respectively,and the corresponding magnesium concentration in Mg NH4PO4 stable solid phase regions was 1 × 10- 3. 5mol·L- 1,which satisfied the efficient removal of magnesium requirements. The demonstration test results showed that the concentrations of Li2 O and Mg were 14. 95 and 0. 45 g·L- 1,respectively,with ammonium phosphate trihydrate addition of 1. 35 times theoretical amount at p H 8. 0 and stirring at 25 ℃ for 4 h,the concentrations of residual magnesium and phosphorus were only 0. 011 and0. 004 g·L- 1,respectively,and magnesium removal rate was 97. 56%. Theoretical calculation and experimental results were consistent.

关 键 词：氯化锂 除镁 磷酸铵镁 热力学 

分 类 号：TQ124.4[化学工程—无机化工]