Experimental and density functional theory studies of the effects and mechanisms of Cu2+ on flotation separation of cassiterite from fluorite

Cu 2+ was found to have intensive and selective depressing effects on fluorite in the flotation separation of cassiterite from fluorite using 2-carboxyethylphenylphosphinic acid (CEPPA) as a collector at pH 4.0. The depressing mechanism was investigated by flotation tests, zeta potential measurements, X-ray photoelectron spectroscopy (XPS) analyses and density functional theory (DFT) calculations. Flotation test results demonstrated that Cu 2+ selectively depressed the fluorite in an artificially mixed cassiterite-fluorite ore. Zeta potential measurement and XPS analysis results indicated that Cu 2+ could be anchored on cassiterite surface by adsorption or substitution but not on fluorite surface, and the adsorption of CEPPA on fluorite surface was cut off by Cu 2+ . DFT calculation results demonstrated that CEPPA had stronger affinity for Cu 2+ than for fluorite, and the adsorption or substitution of Cu 2+ on cassiterite (110) surface showed no negative effects on the adsorption of CEPPA monoanion on cassiterite (110) surface. Based on these results, the depressing mechanism of Cu 2+ on fluorite was that Cu 2+ consumed the collector CEPPA in solution, and little free CEPPA was left to be adsorbed on fluorite surface while the adsorption of CEPPA on cassiterite was normal. Thus, the floatation of fluorite was selectively and intensively weakened.