INVESTIGATIONS ON THE SURFACE PROPERTIES OF ARSENIC AND BORON MINERALS AND THEIR FLOTATION SEPARATION
Film - Micro Flotation, Critical Surface Tension
Boron ores have distinct issues related to their sparingly soluble nature, resulting in the accumulation of undesirable levels of solubilized species spreading to the surrounding area and water contamination. The presence of arsenic sulphides such as realgar and orpiment can potentially cause even greater problems to the environment due to their toxicity. Arsenic contamination in water sources is a significant environmental issue in some regions, leading to adverse health impacts and requiring remediation measures. A detailed experimental investigation was conducted to study the fundamental surface properties of arsenic-bearing minerals. Based on the previous research on the relationship between native floatability and crystal structure, realgar and orpiment were known to be inherently hydrophobic. In this work, realgar is shown to be more hydrophobic than orpiment due to the additional role of its capacity to form elemental sulphur. Such differences were studied through the determination of wettability profiles from film-flotation experiments for arsenic-bearing minerals, but also other sulphide minerals. Although, it is an oxidation product from arsenic sulphides, arsenolite (As2O3) was found to be strongly hydrophobic, which was characterized with respect to pH and reactions with metal ions. A UV method was developed based on quantitative analysis of elemental sulphur from solvent extraction of sulphide minerals, which was correlated with their film-flotation profiles. Monoclinic pyrrhotite indicates much greater amounts of elemental sulphur on its surface than hexagonal pyrrhotite. FTIR studies provided additional support for the presence of elemental sulphur on sulphide minerals, but the quantitative correlation with film-floatability and UV studies was lacking, which was attributed to the much finer particle size range required in the KBr methodology. Micro-flotation experiments were carried out with single minerals and mixed minerals involving realgar-orpiment-arsenolite and colemanite. Micro-flotation results were in general agreement with film-flotation results. Both direct flotation and reverse flotation approaches were tested for the separation of arsenic minerals. The kerosene flotation system involving sodium silicate as a depressant for colemanite was found to be the best option for the removal of arsenic minerals.