Enhancement mechanism of ammonium polyphosphate on flotation separation of pyrite from fine serpentine

Serpentine slime coating significantly deteriorates the flotation performance of sulfide minerals due to electrostatic attraction under weakly alkaline conditions. To address this issue and develop a low-toxicity reagent regime, this study introduced ammonium polyphosphate (APP), specifically with varying molecular weights, as a novel depressant to achieve the efficient separation of pyrite from serpentine. Single-mineral and artificial mixed ore flotation tests demonstrated that APP with a medium degree of polymerization (APP-2) exhibited the best performance. At pH 8.5 and an APP-2 dosage of 80 mg/L, the recovery of pyrite reached 93.17 % with significant rejection of serpentine. APP-2 chemically adsorbs onto the serpentine surface through the formation of stable P-O-Mg bonds, reversing its surface charge from positive to negative, while having negligible interaction with pyrite. This effectively eliminates the heterocoagulation between the two minerals. Despite these promising laboratory results, the complexity of mineral textures in run-of-mine ores remains a challenge for industrial translation. Future perspectives focus on evaluating the pilot-scale performance of APP and further exploring phosphate-based green reagents to facilitate cleaner production in sulfide flotation.