Study On Preparation Of Lithium Carbonate By Microwave Assistend Pyrolysis

The demand for battery-grade lithium carbonate has gradually increased in recent years.In view of the high output of industrial-grade Li2CO3 and low production of battery-grade Li2CO3,the most of China's battery-grade Li2CO3 relies on imports.Therefore,purification technology of Li2CO3 has become one of research hotspots.Carbonization pyrolysis method has been investigated in recent years and is considered to be promising to produce high-grade Li2CO3 in batch scale.However,there still are some shortcomings,such as low heat transfer efficiency,uneven temperature distribution,and difficulty in scale-up.In view of these,rotating packed bed(RPB)and microwave heating technology were used to achieve rapid uniform heat transfer in the pyrolysis process and to improve energy efficiency and apparent reaction rate.In this paper,industrial grade Li2CO3 was used as raw material,and three pyrolysis processes,including water-bathing heating method(WHM)in stirring tank reactor(STR),microwave assisted in STR and microwave assisted high-gravity,were studied,respectively.The main conclusions are list below:(1)Pyrolysis process study of two heating methods in STRThe effects of LiHCO3 concentration,pyrolysis temperature,stirring rate and pyrolysis time on the composition and mean crystal size of Li2CO3 were investigated through single factor method in both water bath heating method and microwave heating method respectively.The kinetics of pyrolysis process was also investigated.The results showed that the pyrolysis conditions had the same effect on product concentration and yield in the both pyrolysis processes.the Li2CO3 concentration in the product first decreased and then increased with the increase of pyrolysis temperature,and first increased and then decreased with the increase of LiHC03 concentration and stirring rate.The yield increased with increasing the pyrolysis temperature and LiHCO3 concentration,and the stirring rate showed little effect.The optimum operation conditions using water-bathing heating method were:LiHCO3 concentration of 6.05 g/100gH2O,pyrolysis temperature of 90?,STR stirring speed of 400 rpm,and pyrolysis time of 120 min,and a high concentration of prismatic Li2C03 of 99.86%and mean crystal size of 11 ?m were obtained.The optimum operation conditions in microwave heating method were:LiHCO3 concentration of 6.80 g/100gH2O,pyrolysis temperature of 90?,STR stirring speed of 400 rpm,and pyrolysis time of 10 min,and a high concentration of prismatic Li2C03 of 99.81%and mean crystal size of 21 ?m were obtained.(2)Pyrolysis process study use microwave assisted high-gravityThe effects of LiHCO3 concentration,pyrolysis temperature and RPB speed on the composition and mean crystal size of Li2CO3 were investigated using single factor method.The results were compared with water-bathing heating method and microwave heating method in STR.The results showed that the mass concentration of lithium carbonate in the product first decreased and then increased with the increase of LiHC03 concentration and first increased and then decreased with increasing the pyrolysis temperature and RPB speed.Yield increased with increasing RPB speed,pyrolysis temperature,and LiHCO3 concentration.The optimum operation conditions in high-gravity microwave coupling heating method were:LiHC03 concentration of 7.56 g/100 gH20,pyrolysis temperature of 75?,and RPB speed of 400 rpm,and a high concentration of prismatic Li2C03 of 99.52%and mean crystal size of 26?m were obtained.Comparison results indicate that,the high-gravity microwave coupling heating method obtained the highest efficiency,and the water-bathing heating method obtained highest mass concentration of product.