Reduction of silica from complex calcite ore for use in seawater magnesia production

The amenability of a calcite-bearing ore to the reduction of silica to belo w 0.2% by physical beneficiation was studied. The objective was to use the are as a raw material for seawater magnesia production. The ore contains co mplex gangue minerals such as diopside, forsterite, phlogopite, clinohumite , graphite and quartz. These contribute to around 25% acid insolubles with 6% SiO2. Reverse-flotation studies using various cationic collectors with t annin as a depressant indicated the possibility of reducing the acid insolu bles to around 5%. Direct flotation of calcite with anionic sodium oleate i n the presence of sodium silicate and lactic acid as a depressant indicated the possibility of reducing the acid insolubles to below 3% and the SiO2 t o from 0.2% to 0.3%. Lactic acid was found to be an effective depressant of the complex gangue minerals in the ore.