Effect of Salinity on Nickel Laterite Processing

摘要

The effect of salinity on the processing of various nickel laterite ores is discussed. In particular, the presence of high concentrations chloride, sulphate, sodium, calcium and magnesium is addressed. Key unit process operations affected by these ions include ore preparation, pressure acid leaching, counter-current decantation and product purification and precipitation. Some of the process implications of these dissolved species are discussed in terms of rheology and process chemistry. Laterite slurries that display good natural flowability are less influenced by salinity, as the maximum decrease of yield stress ranges from 15% to about 20%. Heating these slurries to 120℃ and higher can however reduce the yield stress up to 98%. The yield stress of some laterite slurries that display poor rheology can be reduced by over 83% due to the presence of high concentrations of total dissolved solids, mainly as sodium chloride. The combined effect of temperature, i.e. over 130℃, and salinity can in fact render some of these slurries almost free flowable. Unfortunately, the presence of chloride ions in the downstream process intermediates can cause serious engineering problems such as corrosion, unmet product specifications and difficult water balance management. The use of high throughput continuous precipitators was found to improve chloride rejection. Test products assayed 0.02-0.07 wt.% Cl~- compared to 0.4-1 wt.% Cl~- in the conventional precipitation products.