Abstract
Froth flotation is a multifaceted complex process which is water intensive. The use of recycled water as an alternative source of water to meet water demands of the process may introduce deleterious inorganic ions that affect the mineral surface, pulp chemistry, and reagent action, hence the need to establish whether threshold ion concentrations exist beyond which flotation performance will be adversely affected. This is of paramount importance in informing appropriate recycle streams and allowing simple, cost-effective water treatment methods to be applied. Here we report that increasing ionic strengths of synthetic plant water (SPW); 3, 5, and 10 SPW respectively, resulted in an increase in water recovery in the order 0.073 mol·dm−3 (3 SPW) < 0.121 mol·dm−3 (5 SPW) < 0.242 mol·dm−3 (10 SPW), indicating an increase in froth stability as higher water recoveries are linked to increased froth stabilities. This behavior is linked to the action of inorganic electrolytes on bubble coalescence which is reported in literature. There was, however, no significant effect on the valuable mineral recovery. Spiking 3 SPW to 400 mg/L Ca2+ resulted in higher copper and nickel grades compared to 3 SPW, 5 SPW, and 10 SPW and was deemed to be the Ca2+ ion threshold concentration for this study since 3 SPW spiked with further Ca2+ to a concentration of 800 mg/L resulted in a decrease in the concentrate grade. The spiking of 3 SPW with Mg2+ resulted in higher copper and nickel grades compared to all other synthetic plant water conditions tested in this study.
Highlights
In froth flotation, reagents are added to a milled ore slurry so as to manipulate the physicochemical nature of minerals present in the ore
Laskowski and Castro [11] suggested in a later study that Ca2+ and Mg2+ should be removed prior to flotation by precipitates decantation method, as high saline environments at alkaline conditions promote the formation of precipitates that deposit onto the valuable mineral surface. These concerns have led to the proposed novel spiking method used in this study which aims at ascertaining the impact that individually selected ions have on flotation performance, while maintaining a complex water chemistry background as would be found on site
Water recovery increases with increase in Ca2+ spiking concentration and follows the order: 10 synthetic plant water (SPW) > 800 mg/L Ca2+ > 400 mg/L Ca2+
Summary
Reagents are added to a milled ore slurry so as to manipulate the physicochemical nature of minerals present in the ore. These reagents are added to enhance the differences in hydrophobicity between valuable minerals and gangue [1,2,3]. Different ores bear different minerals and behave differently in the presence of chemical reagents. This understanding led Bradshaw et al [4] to assert that it is difficult to isolate and quantify the interaction of each reagent with minerals present in an ore. The question of how process water constituents such as ions will affect reagent–mineral interactions and flotation is often barely addressed when new reagents are developed
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