Adsorption and depression mechanism of an eco-friendly depressant PBTCA on fluorite surface for the efficient separation of cassiterite from fluorite

Cassiterite is the most purist tin-containing mineral and plays a dominative role in the tin resources. Owing to the limited selectivity of conventional collectors, the efficient separation of cassiterite from fluorite is normally difficult. Herein, 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA) was employed as an eco-friendly depressant to selectively depress the flotation of fluorite. The flotation experiments were conducted to evaluate the separation efficiency of the two minerals, and the results showed that cassiterite and fluorite could be efficiently separated at the flotation reagent scheme of 15 mg/L PBTCA and 20 mg/L NaOL when pH was 8.04. Furthermore, a series of detection and simulation technologies including wettability analysis, zeta potential measurement, FTIR analysis, XPS analysis and DFT calculation were performed to uncover the underlying adsorption and depression mechanism of PBTCA on cassiterite and fluorite. These further analyses indicated that PBTCA could be chemisorbed on the fluorite surface through the interaction between the phosphate group in PBTCA and the calcium sites in fluorite. Moreover, the adsorption of PBTCA on fluorite surface would intensively inhibit the adsorption of NaOL. However, PBTCA was only weakly adsorbed on the cassiterite surface and could not affect the interaction between NaOL and cassiterite. Finally, a most likely adsorption model of PBTCA onto fluorite surface with the “mono-polar group” interaction was proposed by DFT calculations.