Investigation into the Effect of Froth Flotation Process Variables for the Recovery of Residual PGMs from Mine Tailings

This project investigates the recovery of residual platinum-group metals (PGMs) from mine tailings by diagnosing froth-flotation constraints and defining a rigorous optimization pathway. Tailings from the PGM mining operation were sampled across the dam; the material was air-dried, crushed to ≤2 mm, riffle-split, and characterized for particle-size distribution. Mineralogical studies were conducted by XRD, and chemical composition was assayed by ICP-OES to inform the reagent strategy. The feed is ultra-fine, with a particle size of 78.6 % passing 75 µm. Baseline rougher flotation employed a 42 % w/w pulp with isobutyl xanthate as collector, X3-DEP as depressant, sodium silicate as dispersant, copper sulphate as activator, and X2-froth as frother under controlled aeration. Product streams were filtered, weighed, and assayed for PGMs and Cr₂O₃ to compute mass pull, grade, and recovery. Results show pronounced sensitivity to feed characteristics and operating variability. Across tests, increasing mass pull increased recovery but diluted concentrate grade, evidencing gangue entrainment; conversely, higher grades were obtained at lower mass pull with associated recovery penalties. Monitoring of Cr₂O₃ in the concentrate constrained mass pull to meet smelter compliance. These inverse grade–recovery responses are consistent with ultra-fine feeds, surface oxidation of PGM minerals, and froth drainage constraints. Performance differences were attributed to reagent dosage and pH control, conditioning and residence time, and hydrodynamics. The recommended pathway is a constrained operating window centered on ~42 % solids, with reagent set points and control loops for pH and dosing, explored via designed experiments spanning collector/frother dosages, air rate, and conditioning time. Feed-grade variability should be dampened by blending to stabilize head grade and mineralogy. Where mineralogical analysis confirms locked PGMs or oxide coatings, targeted ultrafine grinding in inert media and/or tertiary scavenging circuits may be justified on a cost-normalized metal basis. Consequently, the study confirms technical feasibility but emphasizes process-control rigor to achieve predictable recovery from tailings and to manage the grade–recovery–mass-pull variables.