Mechanism of phthalic acid collector in flotation separation of fluorite and rare earth

The mechanism of phthalic acid, a dicarboxylic acid collector, in flotation separation of fluorite and rare earth (RE) was studied in this paper. The experimental data of flotation show that phthalic acid, as the collector, can realize highly efficient separation of fluorite and rare earth under weakly acidic conditions. The adsorption mechanism of phthalic acid on the surface of fluorite and bastnaesite was analyzed in this paper by means of the zeta potential measurement, the Fourier transform infrared (FT-IR), the X-ray photoelectron spectroscopy (XPS) and the stability constant measurement of active metal ion and phthalic acid coordination complex. According to the zeta potential testing results, the surfaces of fluorite adsorb the collector phthalate ion with negative charge under weakly acidic conditions which, in turn, increases its electronegativity and results in the motion of its potential. After the reaction between phthalic acid and fluorite ores under weakly acidic conditions, the peak of the fluorite ores is found to have significant changes in the FT-IR results, indicating strong chemical adsorption on the surfaces of phthalic acid and fluorite ores. According to the XPS analysis, the peak of benzene ring of phthalic acid is as high as 2% on the surface of fluorite, while no obvious characteristic peak of benzene ring is found on the surface of bastnaesite. According to the pH potentiometric titration results, the stability constant Ktotal of calcium phthalate complex within the acid range is higher than the stability constant Ktotal' of cerium phthalate complex, indicating that the complex generated between phthalic acid and Ca2+ is more stable than the complex generated between phthalic acid and Ce3+. The possible reason is that Ca2+, with the highest reticular density, plays a prevailing role in the octahedron structure of fluorite amidst the acidic media. As the active point of flotation, Ca2+ works with the carboxyl groups of the collector phthalic acid (–C=O–) to form polycyclic calcium phthalate complex.