Purification of natural amorphous graphite by flushing process

Abstract

Amorphous graphite slurries used in flushing operations were conditioned at pH4.2 in the presence of chelating and reducing agents both to release graphite and clayey particles and to enhance the hydrophobicity of the graphite surface. Graphite particles were first extracted from the aqueous slurry using a kerosene-based oil phase, while clayey impurities (including kaolinite, illite, chlorite and quartz) were left in the water phase. Then, the residual clayey impurities in the graphite particles were extracted from the oil phase using an aqueous solution containing the same reagents as used for making the raw slurries. The ash content of purified products proportionally decreased with increasing amount of dissolved iron component, indicating the existence of iron (III) hydroxide compounds which aggregate the constituent particles of raw graphite. Furthermore, the efficiency of removing the impurities became greater as the particle size of the pulverized raw graphite decreased because of the improvement in liberation of clayey impurities from graphite particles. In a graphite sample with a mean particle size of 2 μm, the ash content could be lowered from 8.4 to 2.8 mass %.