NEUTRALIZED TAILINGS AND SULFATES - SETTLEMENT, DRYING AND CONSOLIDATION

At Ranger uranium mine it was proposed to calcine local magnesite and use it instead of imported lime to neutralize tailings. A pilot-scale study comparing a bed of tailings neutralized in this way with one neu tralized with lime showed that magnesite settled less and consolidated more slowly, resulting in an increased short-term storage requirement . To find out why, the relative humidities of solutions of calcium and magnesium sulphates and of samples from the beds dried to known water contents were determined. Other samples were dried intermittently in linear shrinkage moulds under a constant, low evaporative demand. Prec ipitation of magnesium sulphate eventually caused a skin to form on ma gnesite, greatly reducing the rate of drying. To explain the shrinkage patterns and low bulk densities of the slurries after oven-drying, it is suggested that the clay-sized particles present form a framework i n which the larger particles are held. It is deduced that the earlier results were due to the smaller clay content of lime and the lower rel ative humidity of magnesite at a given water content. With a large eva porative demand, a skin could increase the long-term drying rate of st ored tailings.