Selective flocculation and recovery of chrome from plant slimes using starch and sodium oleate as flocculants

Abstract

A steady global decline in the grade of chromite ores is causing an increase in the mining of low grade and complex ores. The processing of such low grade and finely disseminated ores results in the increased production of primary and secondary slimes. Slimes have very poor recovery performance in most conventional technology and are usually disposed of into tailings storage facilities (TSF). The historic slimes in the TSFs and those arising from most chrome production processes constitute potential recoverable chrome resources. In this study, the selective flocculation of slimes from a chrome processing plant in the north west province of South Africa was conducted using raw corn starch and sodium oleate as flocculants and sodium silicate a dispersant was applied on. Limited work has been reported on the flocculation of non-synthetic chrome slimes. The results showed that a slime sample with a chrome (Cr2 O3) head grade of 22.92% was upgraded to a maximum concentrate grade of 42.55% at a sodium oleate dosage of 88 g/tonslurry, a sodium silicate dosage of 44 g/tonslurry, 39.61% at a starch dosage of 106 g/tonslurry and sodium silicate dosage of 62 g/tonslurry. The cor-responding recoveries using sodium oleate as a flocculent were between 80–89% and 73–79% for starch. Sodium oleate showed a better performance than starch in terms of both grade and recovery. Decantation washing tests showed that the chrome (Cr2 O3) grade of the concentrate can be further increased to above 44%. These results are very encouraging as they indicate that selective flocculation can achieve satisfactory upgrade ratios and recovery when processing chrome ultrafine or slime material.