Simple and efficient method for purification and recovery of gypsum from phosphogypsum: Reverse-direct flotation and mechanism

A simple and efficient approach of high-speed stirring scrubbing, reverse flotation and direct flotation was adopted to the purification of phosphogypsum (PG), and KH and dodecylamine hydrochloride (DH) were first used as the collectors of reverse and direct flotation, respectively. X-ray diffractometer (XRD), thermal gravimetric analyser (TGA), X-ray photoelectron spectrometry (XPS), and Fourier transform infrared spectroscopy (FT-IR) were used to characterise the samples and analyse the mechanism. KH selectively reactes with organic matter, slime, quartz and pyrite via hydrogen bond and dehydration condensation between the –OH in silanol hydrolyzed by KH and –OH on the surface of quartz and pyrite, and –COOH in the organic matter. Furthermore, the direct flotation collector of DH exhibited superior selectivity of gypsum via electrostatic attraction, and increased the whiteness and purity of the gypsum concentrate to 69.2% and 97.24%, respectively, and the soluble phosphorus and fluorine contents decreased to 0.046% and 0.024%, respectively. The gypsum concentrate reached the first-grade national standard of PG in China (GB/T 23456-2018). Therefore, this study provided a new approach for the purification of PG, which has an important guiding significance for the resource utilisation of PG.