Abstract
The global demand for Platinum Group Metals (PGMs) is increasingly being met by processing secondary resources, such as historical tailings deposits. Middle Group (MG) chromite tailings represent a significant, yet underexploited, reservoir of PGMs. The primary obstacle to their exploitation is a complex and refractory mineralogy, characterized by finely disseminated PGM-sulphides embedded within an oxide matrix and contaminated by problematic gangue minerals, particularly talc and serpentine. These serpentines over-grind to form ultrafine, hydrophilic slimes that coat PGM particle surfaces, degrading their floatability. Consequently, conventional froth flotation methods, designed for primary sulphide ores, prove largely ineffective, leading to poor recovery (typically 20-30%), low-grade concentrates (~9 g/t), and substantial economic and environmental losses.
This thesis aimed to develop a novel and implementable beneficiation strategy to overcome these challenges through an integrated approach that couples comprehensive characterization with advanced surface reconditioning and predictive modelling. The research first established a detailed baseline through quantitative mineralogical and surface chemical analysis. Using QEMSCAN, XRD, and SEM-EDS, it was determined that the tailings are primarily composed of chromite (38.7%) and silicates (54.8%). Critically, while 65% of the PGMs were present as sulphides and 41.5% were fully liberated, the majority of these liberated grains were in the sub-3μm size fraction, presenting a fundamental recovery challenge. Furthermore, 20% of PGMs were locked within a chromite matrix. Surface chemistry analysis confirmed the presence of deleterious hydrophilic coatings, composed of iron and magnesium oxides.
Zeta potential analysis was pivotal in elucidating the separation mechanism. A significant electrostatic disparity was identified between the highly negative PGM minerals (-40 to -50 mV) and the less negative serpentine slimes (-16 to -19 mV) across a pH range of 2-12. This repulsion was insufficient to prevent slime coating. The use of sodium metabisulfite was shown to modulate the serpentine's zeta potential to a more negative value (-34 to -40 mV), enhancing repulsion, but this chemical approach alone was inadequate...