Effect of calcium concentration on calcite flotation from apatite using carbonic gas

The flotation process currently considered for apatite concentration from the Santa Quitéria phosphate deposit (Brazil), involves bulk flotation of apatite and calcite with anionic collector at pH=10 followed by calcite flotation at pH=5.5, adjusted with H3PO4. Although this concept is efficient from the point of view of separation between apatite and calcite, the intensive use of inorganic acids causes ion accumulation in the process water, especially Ca2+ and PO4 2-, which leads to problems in the flotation stage as well as in the environment. CETEM has been studying a process for the separation of carbonate minerals and apatite that involves the use of carbonic gas injected into the bubble generation system of flotation machines instead of inorganic acids. The aim of this study was to evaluate the effect of Ca2+ ion concentration on the water during the calcite flotation stage of the Santa Quiteria phosphate ore, between 6 mg/L (standard test) and 670 mg/L (maximun concentration) on the flotation performance in terms of P2O5 grade and its loss and the CaO/P2O5 ratio (RCP). The results indicated a reduction in the selectivity on the flotation of calcite from apatite for Ca2+ concentrations from 6 mg/L to around 285 mg/L. Despite this, the results obtained in this study indicated that the process based on the application of CO2 for the separation of calcite and apatite may be a technical alternative that causes less impact in flotation performance for the phosphate concentration ores with carbonated gangue.