Beneficiation of a low grade limestone sample

Pilot scale column flotation studies were conducted on a low grade siliceous limestone ore. Silica content was reduced to less than 1% in the concentrate so that it became satisfactory for use in the paper or rubber industries. The limestone sample was crystalline and constituted primarily of calcite that contained quartz, feldspar, pyroxene, and biotite as gangue minerals. Quartz is the major silicate gangue whereas feldspar, pyroxene, and biotite exist in minor to trace quantities. Traces of pyrite were also observed within the sample. A reverse flotation process was adopted where the silicate gangue minerals were floated using two different commercial cationic collectors: Chem-750 F or Floatamine-D. The studies clearly suggest it is possible to produce a limestone concentrate assaying around 96–97% CaCO₃ containing less than 1% SiO₂. The effect of feed flow rate, percent solids, froth depth, and wash water on the grade and recovery of the CaCO₃ concentrate is discussed.