Calcite is considered a semi-soluble mineral in flotation. Its solubility in acids plays a major role in its floatability. In this study, micro-flotation experiments are conducted to investigate the interaction of calcite particles with potassium oleate (KOl). Potassium oxalate is used as a depressant in the presence of HC1 or H2SO4 as pH modifiers. Flotation experiments indicated that calcite behaves differently in the presence of HCl and H2SO4. The calcite floatability is higher in the case of HCl. The different behavior is more obvious in the presence of oxalate. The depressing effect of oxalate is more pronounced in the case of using H2SO4 as a pH modifier. In addition, the sensitivity of calcite flotation to pH goes back to the amount of free Ca-ions in the solution. Ionic equilibrium of the dissolved ionic species is proved to play a crucial role in either enhancing or reducing the oleate adsorption, which in turn affects the calcite floatability.