Reduction of magnesia in nickel concentrates by modification of the froth zone in column flotation

The reduction of the magnesia (MgO) content in a nickel concentrate was investigated for a nickel sulphide ore from Western Australia. Tests were conducted using both a conventional flotation cell and a column flotation cell. The conventional flotation tests show that the use of magnesia depressants were effective in controlling the magnesia levels in the concentrate. Of the depressants tested carboxy-methyl cellulose (CMC) and guargum were found to be the most effective. All of the column flotation tests were performed using a 7.0 cm diameter column. Depression of magnesia was studied by modifying the froth phase chemistry of the column via the wash water system. This allowed large addition rates of flotation modifiers to be used economically compared to high dosages normally added to the pulp phase. The depressant dosages tested in the wash water were equivalent to 0.66, 2.6, 4.6 and 6.6 kg/t in the froth respectively. It was found that CMC is a more effective magnesia depressant than guargum when added to both the pulp and wash water. Excessive addition of CMC show no obvious effects on the nickel grade and recovery compared with guargum where further addition above the optimum dosage had a detrimental effect on nickel grade and recovery. It was also found that the wash water pH can have a positive effect on concentrate grade and recovery. (C) 1997 Published by Elsevier Science Ltd.