A new mixture of anionic collectors for improvement of apatite floatability

Flotation is the most essential method for the concentration of phosphate reserves and, hence, the production of apatite concentrate. With the reduction of high-grade reserves and the necessity of exploiting low-grade phosphate ores, many efforts have been made to use different chemical reagents alone and their combinations as collectors for apatite flotation and achieving high-quality concentrates for preparing phosphoric acid and fertilizers. This work focuses on applying direct apatite flotation by employing a novel mixture of fatty acid collectors to optimize the apatite processing plants. Extensive experiments using tall oil fatty acid (TOFA) and oleic acid polyethylene glycol ester 6 mol (OAPEGE6) alone and their mixture in different ratios were conducted in micro-flotation, bench flotation, and plant flotation scales. The micro-flotation experiments showed that using OAPEGE6 and TOFA, the flotation recovery of apatite at a pH of 9.5 is 46% and 86%, respectively. However, by mixing TOFA and OAPEGE6 in a weight ratio of 70% to 30%, the flotation recovery of apatite increases to 95%. At this weight ratio of TOFA and OAPEGE6 using a 600 $g/t$ mixed collector, an apatite concentrate containing 23.2% $P_2{O}_5$ with a recovery of 90.4% is achieved by rougher stage bench flotation in laboratory experiments. Finally, using the mixed collector with the formulation mentioned above on a plant-scale, an apatite concentrate with almost 33% $P_2{O}_5$ and 59% recovery is obtained through rougher and cleaner stages of the flotation process. FTIR analysis and zeta potential measurements show that the simultaneous presence of TOFA and OAPEGE6 with a synergetic effect can strengthen the chemisorption of oleate active species on the apatite surface. As confirmed by contact angle measurements, this improved the formation of an insoluble hydrophobic layer on the apatite surface and resulted in its flotation recovery.