At the regrind or secondary grinding stages of base metal ores, the concern about energy efficiency is usually extremely important. In general, the specific energy consumption at this stage is higher than during the primary grinding stages. In addition, a tendency of finer grinding has been observed in the new projects of metallic minerals, due to the finer mineral liberation, which leads to increasing capital and operational costs. At Vale’s new copper projects in Brazil, regrind sizes with a P80 of approximately 40 to 20 µm have been necessary. Conventional ball mills, adequate for primary grinding, usually bring about low energy efficiency with products below 50 µm. Vale is using the vertical mill on its copper projects – Sossego and Salobo, in order to optimize the regrind of rougher concentrates and reduce energy consumption.
This paper presents the results of industrial surveys carried out on the Vertical mill circuits of Sossego plant during its initial years of operation, and compares these results with the design criteria and laboratory regrind tests used for the mill scale up.
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Keywords: grinding, regrinding, copper, vertical mill, stirred mill