The effect of citric acid in the flotation separation of bastnaesite from fluorite and calcite using mixed collectors

Abstract

Bastnaesite is a chief natural source of light rare earth elements (LREEs). The effective depression of Ca-containing minerals such as fluorite and calcite in bastnaesite flotation system is normally difficult, and it is imperative to exploit more environmentally-friendly depressants which can inhibit these gangue minerals simultaneously. Hence, we employ citric acid (H3Cit), a green, cheap and commonly available organic acid, to selectively depress the flotation of fluorite and calcite, and use octanohydroxamic acid (OHA) and sodium oleate (NaOL) with a molar ratio of 2:1 as mixed collectors. Micro-flotation results show that H3Cit decreases the recoveries of fluorite, calcite, and bastnaesite by 84.73%, 62.96%, and 9.23%, respectively at pH 8–9. The depression mechanism of H3Cit was investigated through zeta potential measurements, microcalorimetry measurements, solution chemistry and reaction thermodynamic analyses, and X-ray photoelectron spectroscopy (XPS) analyses. These further analyses at the minerals/water interfaces indicate that H3Cit preferentially adsorbs on the gangue mineral surfaces due to the positively charged fluorite and calcite surfaces which interact more easily with citrate ions (Cit3-), and the spontaneous interaction between Cit3- and Ca2+ on the surfaces. Accordingly, H3Cit is supposed to be a potential depressant for Ca-containing minerals in the flotation separation of bastnaesite.