The effect of surface contamination on the electrostatic separation of mineral sands

Dale Killeen

Electrostatic separation, a process governed by the conductivity and dielectric constants of particles, is susceptible to the influence of surface contaminants on mineral particles. These contaminants, either physiosorbed or chemisorbed, can lead to misreporting during the separation process. The Jacinth Ambrosia ore body, managed by Iluka, presents a significant challenge due to the surface contamination of its valuable heavy minerals. The contaminants, including ferruginous, saline, and siliceous coatings, compromise product quality, reduce plant recoveries and increase misreporting during separation. This thesis investigates the impact of these contaminants on mineral separation at the Iluka plant, focusing on their effect on electrostatic separation. The research will be conducted on a process stream currently rejected from the plant due to high contamination levels. The primary objectives are to identify the contaminants and develop effective treatment methods for their removal. The study incorporates ore characterization through various techniques to ascertain the mineralogy of a reject stream at the Narngulu Mineral Separation Plant. Numerous analyses were undertaken on the target minerals to identify surface contamination present. The ore characterisation and surface contaminant identification methods included scanning electron microscopy, X-ray diffraction, inductively coupled plasma, optical emission spectroscopy, X-ray fluorescence, magnetic separation, heavy liquid separation, and size-based chemical analysis. The thesis also evaluates several treatment techniques for their ability to enhance electrostatic separation efficiency by removing targeted contaminants. These treatments include attritioning, urea pre-treatment and subsequent attritioning, and washing with hydrochloric acid, sodium hydroxide, and sulphuric acid. The efficacy of each treatment method is measured by the separation efficiency of conductors and non-conductors following each treatment. The control sample demonstrated poor electrostatic separation, with only a 10% separation efficiency. However, attritioning and washing to remove salt coatings improved efficiency by 28%. Samples treated with urea before attritioning yielded a 29% efficiency, similar to water-washed samples. Sulphuric acid wash achieved a 45% efficiency, though secondary mineral formation inhibited further improvement. Sodium hydroxide wash reached a 64.5% efficiency, effectively removing silicates from kaolinite but less for iron oxides. Hydrochloric acid leach residue showed the most substantial improvement, achieving a 74% separation efficiency by effectively removing iron, salt, and silica contaminants. These treatments significantly improved separation efficiency by selectively targeting specific surface contaminants. The thesis also discusses innovative treatment methods that combine current on-site unit operations with the examined treatments.

The effect of surface contamination on the electrostatic separation of mineral sands

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