Novel ethylbenzyl and hydroxyethyl quaternary ammonium collectors for co-reverse flotation desilication and impurity removal from phosphogypsum: Flotation performance and mechanism

In the reverse flotation process for desilication and impurity removal from phosphogypsum (PG), quaternary ammonium salts are commonly used as cationic collectors, but their selectivity and stability under strongly acidic conditions are limited. In this study, for the first time, dodecyl-dimethyl-ethyl benzyl ammonium chloride (DDEA) and dodecyl-bis(2-hydroxyethyl)-methyl ammonium chloride (2HEAC-12), were used as collectors for the PG co-reverse flotation desilication and impurity removal. Flotation experiments show that both DDEA and 2HEAC-12 collectors exhibit good desilication and impurity removal performance for PG, whereas DDEA shows superior selectivity for quartz than that of 2HEAC-12. When DDEA and 2HEAC-12 were used as collectors, the purity of dihydrate gypsum in obtained PG concentrates was 94.88% and 93.47%, respectively, meeting the first-grade standard for PG used as a building material (GB/T 23456–2018). Adsorption experiments indicate that the adsorption of both collectors on quartz and dihydrate gypsum follows the Langmuir model, suggesting monolayer physical adsorption. Both collectors exhibit a higher selectivity for quartz than dihydrate gypsum. The adsorption process was mainly accomplished by electrostatic interactions and hydrogen bonds. The adsorption process was mainly accomplished by electrostatic interactions and hydrogen bonds. This work provides a viable strategy for developing collectors for PG co-reverse flotation efficient desilication and impurity removal.