Abstract
The mining and mineral processing of Cu-Ni-PGM sulfide ores in South Africa occurs in semi-arid regions. The scarcity of water resources in these regions has become one of the biggest challenges faced by mineral concentrators. As a result, concentrators are forced to find ways through which they can manage and control their water usage. The recycling and re-use of process water in mineral concentration plants has therefore become a common practice. This practice is beneficial in that it reduces reliance on municipal water and harnesses compliance to stringent environmental regulations on freshwater usage. This approach also offers a better response to the Sustainable Development Goals (SDGs) for the mining industry, as water and its preservation form part of the SDGs. This practice could, however, be somewhat concerning to a process operator because recirculated water often has higher concentrations of ions compared to fresh or potable water. This is because an unintended change in the process water quality may affect critical aspects of flotation such as the stability of the froth. This issue has led to the need for both the mining industry and researchers in the field to find the ions in process water that have the greatest impact on froth stability. Thus, the authors of this study investigated the effects of various ions common in the process water of a typical Cu-Ni-PGM ore on froth stability using a 3 L bench scale flotation cell. Solids and water recoveries were used as proxies for froth stability. These were further complemented by bubble size, water recoveries, foam height, and dynamic foam stability from two-phase flotation systems. A two-phase foam study resulted in observations that supported findings from a three-phase study. Generally, single salt solutions containing Ca2+ and Mg2+ ions resulted in higher water recoveries both in the two-phase foam and three-phase froth studies, increases in foam heights and dynamic foam stability, and a decrease in bubble size compared to the solutions that contained Na+. SO42− also resulted in increased foam stability compared to Cl− and NO3−. These results showed that the divalent inorganic electrolytes—Ca2+, Mg2+, and SO42−—were more froth- and foam-stabilizing than the monovalent inorganic electrolytes—Cl−, NO3−, and Na+. This finding was in agreement with previous research. The findings of this study are deemed crucial in the development of a process water management protocol in sulfidic Cu-Ni-PGM ore concentrators. However, more comparative three-phase froth stability tests are needed as subjects of future investigative work to further ascertain specific ion effects on froth stability in sulfide ores.
Highlights
Development Goals (SDGs) for the mining industry, as water and its preservation form part of the Sustainable Development Goals (SDGs). This practice could, be somewhat concerning to a process operator because recirculated water often has higher concentrations of ions compared to fresh or potable water. This is because an unintended change in the process water quality may affect critical aspects of flotation such as the stability of the froth
This issue has led to the need for both the mining industry and researchers in the field to find the ions in process water that have the greatest impact on froth stability
Single salt solutions containing Ca2+ and Mg2+ ions resulted in higher water recoveries both in the two-phase foam and three-phase froth studies, increases in foam heights and dynamic foam stability, and a decrease in bubble size compared to the solutions that contained Na+
Summary
As a physicochemical separation process, consists of two distinct zones: the pulp zone where mineral recovery takes place and the froth zone where concentrated mineral particles are separated from the bulk [1]. There are, many parameters available to indicate froth stability; Farrokhpay [8] listed the following parameters for use as indicators for froth stability: froth half-life time [14,15], maximum froth equilibrium height [4,16,17], bubble growth across the froth phase [18], air recovery, amount of solids loaded onto the bubbles [17], froth velocity, and froth rise velocity [4,19]. Previous research has shown that the rupturing of rising bubbles results in the falling back of solid mineral particles and liquid film drainage, so the amount of water recovered in the flotation cell concentrate launder can be used to quantify froth stability. It is worth noting that at the equilibrium height, the rates of growth and bursting are equal This method was well-described by Barbian et al [4] and allows for the determination of, e.g., the dynamic foam stability factor, the froth rise rate, the froth rise velocity, and the froth retention time. The literature suggests that there are many other correlations and parameters that can be used to quantify froth stability, and these continue to be topics of future investigative research
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