Settling rates of nickel-laterite clay-rich residues from high-temperature acid leaching

摘要

Treatment of a clay rich fraction from a Western Australian nickeliferous laterite by high temperature acid leaching results in hematite-silica residues. Decantation of these siliceous residues has proven difficult, due to slow settling rates and low under-flow densities. In this study, leach temperature, agitation, time and acid concentration were varied in order to improve settling rates. Measurement of the electrophoretic mobility of leach residues suggests variations in surface chemistry account for the differences in settling performance. However changes in operating practice can have a significant effect. Acid addition at 150 deg C is recommended prior to nickel extraction at 250 deg C to optimise silica precipitation. It is shown that saline process water leads to jarosite formation and higher under-flow volumnes. The effect of Eh and Cr(VI) on settling rates of these clay rich ores requires further investigation.