Process parameter optimization for natural graphite purification via composite molten salt method

WANG Bing; WANG Xiaofei; PENG Gang; YUAN Xiaoyan; LIU Dan; SHEN Xiangfeng; GUO Shouwu

doi:10.13732/j.issn.1008-5548.2025.05.016

Abstract：Objective To improve the performance of natural graphite raw materials and expand their application scope,a composite molten salt purification method is employed to purify the natural graphite raw materials,and the process parameters are optimized,aiming to improve production efficiency while reducing energy consumption and production costs. Methods The components of the natural graphite raw materials were analyzed.High-purity graphite was prepared at room temperature using a dilute hydrochloric acid leaching method,with NaOH,Na2CO3,Li2B4O7,Na2B4O7,and Li2CO3 serving as the molten salt components.The effects of inorganic salt types,composite molten salt formulations,calcination temperatures,and the mass of natural graphite raw materials on the purity of purified graphite were studied.Moreover,a comparative analysis of the microscopic morphologies of the natural graphite raw materials and the purified graphite was performed. Results and Discussion After two rounds of optimization experiments,NaOH,Na2CO3,and Na2B4O7 were selected as the formu-lation components of the composite molten salt.When the mass fraction of natural graphite raw material was 95.77％and the mass was set at 4 g,the respective masses of NaOH,Na2CO3,and Na2B4O7 were optimized to 1.0,0.5,and 1.0 g,with a calcination temperature of 700 ℃.Under these conditions,the mass fraction of purified graphite reached as high as 99.965％,with a mass ratio of NaOH to graphite of 1:5.5,and a composite molten salt to graphite mass ratio of 2.5:4.These parameters achieved an optimal balance between the equipment performance,production efficiency,and processing costs.The characteris-tic peaks in the X-ray diffraction(XRD)patterns of the purified graphite were highly consistent with the(002),(004),(100),and(110)crystal planes referenced in the graphite standard PDF card(PDF#41-1487),indicating that the composite molten salt method effectively removed impurities while preserving its crystalline structure.The purified graphite particles still maintained their ellipsoidal morphology,though with significantly diminished white substances on the particle surface and notably smoother surfaces,demonstrating the efficacy of the purification process in impurity elimination. Conclusion The composite molten salt method synergistically enhances the reaction with minerals by leveraging the advantages of individual salt components,effectively reducing alkali consumption while improving graphite purity.In terms of industrial production,this method simplifies the operational procedures,and its efficient alkali treatment process significantly reduces the difficulty of the subsequent acid treatment process.