Reducing the environmental impact of the flotation of sphalerite: An alternative reagent scheme

-Hydrocinnamoyl-N-phenylhydroxylamine (HCNPHA) was found to float sphalerite without activation by copper sulphate. However, concomitant flotation of sulphidic gangue minerals, such as pyrite, significantly reduced the grade. Adding 200 g/t of copper sulphate, which is approximately 80% reduction in the amount consumed in the xanthate reagent scheme currently used in the industry, improved the grade and the recovery. Batch flotation tests were conducted using 350 g and 1 kg ore samples to optimize the flotation variables (2.5 Lpm air flow rate; 200 g/t collector dosage; 80% passing through 63 mum particle size). Carboxymethylcellulose (CMC) and sodium silicate were added to suppress sulphidic and non-sulphidic gangue minerals. This improved the grade of sphalerite from 45.5% to 60.1%. CMC also helped regulate the frothing characteristics of HCNPHA, minimizing entrainment of gangue in the float concentrate (froth). Flotation kinetics studies confirmed the improved selectivity using the auxiliary chemicals CMC and sodium silicate. The selectivity index (SI) for sphalerite with respect to pyrite increased from 0.88 to 2.35 upon the addition of copper sulphate, and for non-sulphidic gangue it improved from 1.93 to 6.29 on adding CMC. With the combination of all auxiliary chemicals studied, the SI for sphalerite with respect to pyrite and non-sulphidic gangue further improved to 2.58 and 8.01, respectively. By using a drastically reduced amount of copper sulphate and adding two environmentally friendly auxiliary chemicals (CMC and sodium silicate), the mineral processing industry has the potential for savings of over...