| The battery-grade ferrous oxalate is the main raw material of lithium iron phosphate cathode for lithium-ion battery. Its performance is greatly determined by the purity and particle size of ferrous sulfate. Ferrous sulfate is one of the by-products in titanium dioxide production.It is difficult to be directly used due to the high impurities inside and serious environmental pollution it may cause. If the recycling for the ferrous sulfate byproduct can be associated with the preparation for battery-grade ferrous oxalate, it can not only solve the waste and pollution problems for the byproduct ferrous sulfate, but it can also meet the requirements of the lithium battery industry for quantity and quality of raw materials.In this paper, the resource and nature of by-product ferrous sulfate were firstly presented. Then the status quo of comprehensive utilization for by-product ferrous sulfate and the analyses for current states of preparating the battery-grade ferrous oxalate by detailed investigation were introduced. The by-product ferrous sulfate in titanium dioxide production was purified by cooling crystallization method. The processes of preparing battery-grade ferrous oxalate by liquid-phase precipitation method was studied.In the purification process, according to the impurity segmentation and mass transfer, a numerical more of crystal purity prediction used for the prediction of the impurity concentration after several times of crystallization was proposed on basis of the solid-liquid boundary layer theory of impurity diffusion. The proposed numerical model of crystal purity prediction could be used to predict the change of impurity concentration by repeatedly cooling crystallization experiments. The effect of the purification conditions on the by-product ferrous sulfate purification was further investigated. The best purification conditions, the crystallization temperature being 10℃, the crystallization times being 3 times, the pH being 2, the stirring speed being 300r/min were determined. The purity was 99.45% under above purification conditions.In the preparation of the battery-grade ferrous oxalate process by liquid phase precipitation, combined with the Plackett-Burrnan design (PBD) method, the single factor method, and the center composite design (CCD) method, the influences of reaction conditions, such as reaction temperature, ageing time, concentration of ferrous sulfate, on the purity and particle size of ferrous oxalate were screened and optimized. The experimental results indicated that the optimal reaction conditions were determined as the reaction temperature being 31.2℃, the aging time being 56min, the concentration of sulfate ferrous being 5%. At this optimal reaction conditions, the product of crystallization was used as raw material to synthetise the ferrous oxalate which reached the industry standard for battery grade ferrous oxalate by the purity bing 99.91% and the particle size being 3.57 μm. In addition, the surface active agent can not only control the morphology of the ferrous oxalate, but also can effectively improve the size of the particles.In this paper, the recovery for by-product ferrous sulfate of titanium dioxide and the preparation of raw materials for lithium ion battery were combined which solved many problems, such as environmental pollution and waste of resources, and also achieved effective use of the by-product ferrous sulfate of titanium dioxide. By further optimizing the preparation process of battery grade ferrous oxalate, it can provide the theoretical and experimental basis for improving the performance and quality for raw materials of lithium ion battery.
|
PDF Full Text Request