Evaluation of interaction mechanism for calcite and fluorapatite with phosphoric acid using electrochemical impedance spectroscopy

Abstract

Flotation separation of apatite from calcite is difficult due to their same active calcium atoms on the surface. Flotation is mainly used to separate calcite and apatite minerals from each other and this can be done by knowing the interaction mechanism for each which is our aim here. Phosphoric acid is used to separate apatite and calcite. The outcomes showed that phosphoric acid had a strong depression ability to apatite but it does not for calcite. Herein, the interaction mechanism between minerals like calcite (36–100 μm) and fluorapatite of two size fractions (36–100 μm) and (20–100 μm) with phosphoric acid on 316L stainless steel, at 25 °C, was studied. Both materials are easily available, natural product, cheap and environmentally acceptable. Each mineral works with a different mechanism and this is confirmed by changing the shape for both Nyquist and Tafel plots after adding each mineral to phosphoric acid. Electrochemical impedance spectroscopy (EIS) showed that calcite materials work with both diffusion and adsorption mechanism, however, fluorapatite interaction mechanism is controlled by adsorption. Also, the dissolution of calcite material is higher than fluorapatite as confirmed by EIS and potentiodynamic polarization techniques. Results show that either increasing in concentration of the phosphoric acid or immersion time or size of particles, decreases passivation for both materials.

Keywords

• Flotation
• Phosphoric acid
• Passive film
• 316L stainless steel
• Corrosion inhibitor
• EIS measurements