Utilization ethylbenzyl quaternary ammonium salt as a selective collector for co-reverse flotation removal of silica, organic matter, and fluoride from phosphogypsum

Impurities such as silicon, organic matter and fluoride restrict the utilization of phosphogypsum (PG). In this study, dodecyl dimethyl ethylbenzyl ammonium chloride (DDEA) was used as the reverse flotation collector to remove impurities from PG. At the natural pH (2.3–2.5) of the slurry, with pine oil and DDEA dosages of 300 g/t, slurry concentration of 30 %, and aeration of 0.20 m³/h, the content of SiO₂, organic matter, and fluoride ions in PG can decreased from 6.87 wt%, 0.94 wt%, and 0.42 wt% to 1.90 wt%, 0.13 wt%, and 0.03 wt%, respectively, and the whiteness increased from 33.67 to 64.41 %. Correspondingly, the obtained CaSO₄·2H₂O purity is 94.44 %, meeting first grade standard of PG used as building materials (GB/T 23456–2018). Characterization analysis revealed that flotation primarily removed the quartz phase present in the fine particles. DDEA exhibited high selectivity for adsorption on the quartz surface by significantly affecting the electronegativity and hydrophobicity of the quartz surface. It was mainly adsorbed on the quartz surface through electrostatic attraction with Si-O^- and hydrogen bonding with Si-O bonds, without undergoing chemical reactions. Compared with traditional flotation methods, this process achieved the simultaneous removal of SiO₂, organic matter, and fluoride, which has potential industrial application prospects.