LiNi0.05Mn1.95O4的合成及其对Li+的离子交换热力学

以乙酸锂、乙酸锰和乙酸镍为原料, 采用溶胶-凝胶法合成出掺镍的尖晶石型锂锰氧化物LiNi0.05Mn1.95O4. 用0.5 mol·L-1的过硫酸铵对其进行酸改性后制得锂离子筛(记作LiNiMn-H). 经测定LiNi0.05Mn1.95O4在酸改性过程中Mn2+的溶出率仅为0.31%(w, 质量分数), LiNiMn-H对锂离子的饱和交换容量达5.29 mmol (36.72 mg) Li+/g 离子筛. 测定了15、25、35、45 ℃ LiNiMn-H 在H+-Li+体系吸附锂的离子交换等温线, 并利用Pitzer 电解质溶液理论计算出该离子交换体系的活度系数, 得到H+-Li+交换的平衡常数Ka, △Gm、△Hm和△Sm等热力学参数. 结果表明, Ka随温度的升高而降低, LiNiMn-H对Li+的选择性大于原来可交换阳离子(H+)的选择性, 吸附锂的过程是自发过程(△Gm<0), 该离子交换反应是放热反应.

Synthesis of LiNi0.05Mn1.95O4 and Its Ion-Exchange Thermodynamics for Li+

A spinel lithium manganese oxide doped with nickel (LiNi0.05Mn1.95O4) was prepared by a sol-gel method using acetic lithium, nickel and manganese as rawmaterials. The lithiumion-sieve (denoted as LiNiMn-H) was obtained by acidification of the obtained LiNi0.05Mn1.95O4 with 0.5 mol·L-1 (NH4)2S2O8. After testing, we found that the dissolution ratio of Mn2+ fromLiNi0.05Mn1.95O4 during the acid-modification process was only 0.31% (w, mass fraction) and the saturation ion-exchange capacity of LiNiMn-Hfor Li+ was 5.29 mmol (36.72 mg) Li+/g ion-sieve. The exchange isothermal curves of LiNiMn-H in the H+-Li+ system were measured at 15, 25, 35 and 45 ℃ and the average activity coefficients of the electrolyte were calculated using Pitzer electrolyte solution theory. Other thermodynamic constants, such as the equilibrium constants Ka, △Gm, △Hm, and △Sm, were calculated during the exchange process. We conclude that the equilibrium constants reduce with the increase in temperature and that the selectivity of LiNiMn-H for Li+ is higher than the original ionH+. The exchange process is exothermic and the adsorption process occurs spontaneously (△Gm<0).