| Battery-grade lithium carbonate is a major material of the lithium-ion batteries. With the continuous development of new materials and energy, the demand for lithium carbonate is increasing sharply. There is an abundant of Li resource in the Xitaijinaier Salt Lake, with the reserves of LiCl about 3.08 Mt. Till now, as the Xitaijinaier Salt Lake brine raw materials, the production of industrial-grade Li2CO3 has been prepared. In order to improve product additional value and extend industry chain, the research on the preparation technology of battery-grade Li2CO3 is necessary. In this paper, the battery-grade Li2CO3 was produced from the mixed salt of lithium and magnesium using the coupling technique of hydrogenation decomposition and ion exchange. Meanwhile, the effecting conditions in the different process of preparation technology of battery-grade Li2CO3 were studied using the single factor method.Quantitative analyses and identification showed that the composition and mass fraction of mixed salt were MgO= 35.09%, Mg(OH)2= 22.10%, MgCl2·6H2O= 18.39%, LiCl·H2O=22.07%, KCl=1.37%, K2SO4=0.73%, and CaSO4=0.25%. The optimum technological conditions of lithium solution preparation process were: the mixed salt was crushed and sieved to +20 mesh, added distilled water (solid-liquid ratio was 1:3) continuously to dissolve 20 min and placed at 25℃. The dissolve rate of Li+ reached 94.18%. The removing impurity experiment showed that the total removal rate of Mg2+ and Ca2+ was 99.71% and 97.18% respectively by adding NaOH and H2C2O4.The industrial-grade Li2CO3 was prepared by Na2CO3 precipitation method. The effect of conditions, such as feeding method, reaction temperature, feeding rate, stirring speed, and seed addition was investigated. The optimum reaction conditions were:reverse feeding flow rate was 16.7 mL/min, stirring speed was 400 r/min, add seed quality percentage was 0.5, reaction temperature was 85℃. The purity of industrial-grade Li2CO3 that prepared under the optimum condition was 99.45% and reached national secondary standard. The recovery rate was 89.75%.The effect of hydrogenation conditions, such as reaction temperature, stirring speed, solid-liquid ratio, reaction time, and gas pressure was investigated respectively. The optimum conditions were:the industrial-grade Li2CO3 and distilled water was mixed by 1:3 and placed at 25℃, blew CO2 consecutively and stirring speed was 800 r/min to react for 60 min. The 001×7(732) sodium form cation exchange resin was used to remove impurity. Research showed that 30 BV/h of flowing speed was appropriate for the ion exchange process and the dynamic saturated exchange capacity was 1.03 mmol/mL. The removal rate of Mg2+, Ca2+, and K+ was reached to 38.8%,46.77%, and 17.44% respectively. The effect of decomposition conditions, such as decomposition temperature, stirring speed, and loss percentage of water was investigated respectively. The optimum decomposition conditions were:placed the solution at 85℃, stirring speed was 500 r/min and react until the evaporation rate of water reached 56.39%. The purity of product that prepared under these conditions was 99.83% and the recovery was 95.38%.Three times of reproducibility tests showed that the purity of product prepared under the optimum conditions was reached the national industry standard of battery-grade Li2CO3 and the standard of FMC lithium. The total recovery rate of Li+ was 89.75%. The cost and economic benefit of the optimum technology conditions were accounted. Data indicated that the cost of battery-grade Li2CO3 prepared under the optimum condition was 26462 RMB/t which was lower than existing method. The market price of battery-grade Li2CO3 is 47000～50000 RMB/t. It means that this technology has a high economic benefit and application prospect. |
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