Acidulation

From crushing & grinding, the slurry proceeds to thickening to remove excess water, increasing percentage solids from 40% to 53%. The water is removed because autoclaving is a high temperature process (210ºC), requiring heat to raise the temperature from 25ºC. Reducing the water content reporting to the autoclave substantially reduces heating costs. Excess water is returned to the grinding for re-use.

Prior to entering the autoclaving circuit, excess carbonates in the ore are removed to a maximum level of 2% CO₃ by the addition of sulphuric acid. Carbonate levels are between 3% and 6% in the ore. This pre-treatment improves the efficiency of the autoclave both from operations and maintenance aspects. From acidulation the slurry moves forward to autoclaving.