Carbonate Content Reduction in Zinc Ore Concentrate

The hydrometallurgical zinc extraction from the willemite concentrate is impaired by the presence of high carbonate content. A stiff froth is produced causing zinc losses and acid consumption. A standard procedure was developed to define the acceptable froth layer height in a laboratory test. Froth layers shorter than 2 cm resulted from carbonate content in the concentrate below 10.8%. The feasibility of adding a carbonate flotation stage to the circuit was tested in laboratory and pilot scales. Among the collectors investigated, only those presenting a saponification degree above 189 mg KOH/mg were effective in the laboratory experiments. Oleine and rice bran oil soaps were selected for the pilot scale experiments. The final stage was a one month long industrial trial performed in a circuit consisting of three pneumatic cells G18. A comparison between the average results of the industrial trial including the carbonate flotation stage and data of the raw industrial concentrate indicated that the MgO content in the concentrate dropped from 3.7%–3%. Concurrently, the carbonate content in the concentrate dropped from 11%–10.6%, the zinc grade in the concentrate increased from 41.4%–42% and the zinc recovery increased from 86.6%–89.8%. The concentrate was processed in the hydrometallurgical plant with no frothing problems.