Abstract
Ores from open cast operations or near the surface have been altered by weathering and oxidation. using the traditional flotation method for sulphide minerals when processing the oxidised PGM ores, results in poor flotation performances (usually less than 50% recoveries). Therefore, it is necessary to create alternative processing methods that can economically handle low-grade and oxidised ores.
For a successful flotation, an understanding of the mineral surface, the right selection of the surfactant/reagent regimes, as well as their molecular chemistry and unique adsorption mechanisms, are required. The purpose of this research was to fully understand the particle surface properties, the mechanism of particle surface-reagent interaction, and the proper choice and dosage of the reagent to create the best selectivity conditions needed for a successful flotation.
The purpose of this study was to investigate the mineralogy and surface characteristics of an oxidized PGMs ore by examining how varying dosages of the chosen reagents affected the oxidised minerals' ability to float. XRF, XRD, SEM-EDS, and fire assaying were used to characterise the oxidized PGM ore. Zeta potential and contact angle techniques were used to study the surface characteristics of an oxidized PGM ore.
The ore was identified as a low-grade PGMs ore with an average of 3,28 g/t of the 4Es (Platinum, Palladium, Rhodium and Gold) by Fire assaying and ICP-OES characterization techniques. Nickel (0,12%) and Cobalt (0,01%) were the base-metals which were identified. Cr (27,03%), Fe (20,57) and Si (5,41%) presented the major elements which were present. Chromite, quartz, iron oxide minerals such magnesium/ferric iron, trevorite (nickel iron oxide) dominated the ore sample and secondary minerals such as covellite which is generally found in zones of secondary enrichment (supergene) of copper sulphide deposits were present as indicated by the characterization results.
The contact angle of minerals were determined by applying drops of water on the various spots of the pure minerals to measure their contact angles using a sessile drop technique. To investigate the effect of reagents on the contact angle of the minerals, Reagent suites (1-3) were added. Chromite was activated by the reagent suite 1, the angle changed to (15,76˚) from (13,72˚) when in water. Serpentine’s contact angle
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changed to (80˚) in reagent suite 1 from (38˚) when in water. Reagent suite 2 resulted in the contact angle of Serpentine being slightly above 90˚. Reagent suite 3 resulted in Chromite’s angle being lowered to 8˚, Serpentine reported a contact angle of 105˚in Reagent suite 3.
The zeta potentials of minerals with reagent suite 2 ranged between -50mV and -60mV at pH, significantly lower than those with suite 1, and slightly altered for Talc, chromite, and plagioclase, while serpentine showed a more negative potential. Reagent suite 3 resulted in serpentine becoming more negative with a zeta potential of -75mV, the lowest value among all suites, while Chromite's zeta potential decreased slightly.
Statical Analysis of the flotation data indicated that platinum recovery was improved by increasing dosages of SIBX and Lupramin. Since the PGMs ore studied was proved to be non-sulphide, Statical analyses suggested that it would be practical to adopt higher dosages of AM810 (60g/t) and lower dosages of SIBX (150g/t) to maximise the recovery of Pt. The SIBX, AM810 and lupramin interaction should be minimised for higher platinum recoveries.
Key words: Oxidized PGM ore; Surface properties; Contact Angle; Zeta potential; Flotation