Sustainable and Highly Selective Depression of Serpentine in Pyrite Separation Enabled by Phosphorylated Nanocellulose

Hetero-aggregation between serpentine and sulfide minerals represents a persistent challenge in the efficient recovery of valuable metals from complex ores, while most existing depressants suffer from limited selectivity, insufficient suppression efficiency, or environmental and toxicity concerns, restricting their application in sustainable mineral processing. Herein, we report for the first time the use of a phosphorylated nanocellulose biopolymer as a highly selective and environmentally benign depressant to overcome serpentine-induced interference in sulfide flotation, and elucidate the selective depression and interfacial mechanism. Phosphorylated cellulose nanofibers (P-CNF) and phosphorylated cellulose nanocrystals (P-CNC) were synthesized by introducing phosphate functional groups, resulting in a marked enhancement in pyrite flotation performance, with recoveries exceeding 88.0% and reaching 89.6% for P-CNF. The exceptional separation efficiency arises from the highly selective adsorption of phosphorylated cellulose on the serpentine MgOH plane, with a surface coverage of 96.32% on serpentine compared to only 0.28% on the pyrite surface. This pronounced selectivity induced a reversal of the serpentine surface charge, thereby transforming pyrite–serpentine interactions from electrostatic attraction to strong repulsion. Force-resolved atomic force microscopy measurements provided direct nanoscale evidence for this transition, revealing a dramatic reduction in adhesion forces from ∼9.81 mN m –1 to ∼1.25 mN m –1 (P-CNC) and ∼0.10 mN m –1 (P-CNF). Moreover, phosphorylated nanocellulose promoted the flocculation of fine serpentine particles via polymer-bridging effects, leading to the enlarged aggregates and effective suppression of mechanical entrainment. This work establishes phosphorylated nanocellulose as a novel green depressant platform and provides molecular insights into interfacial interactions governing complex mineral separation, thereby enabling the rational design of sustainable reagents and advancing resource-efficient environmentally interfacial responsible mineral processing.