Considering the Ionic Strength and pH of Process Water on Bubble-Particle Attachment of Sulfide Minerals: Implications for Froth Flotation in Saline Water
October, Lisa Louise (1); Corin, Kirsten (1); Manono, Malibongwe (1); Schreithofer, Nora (2); Wiese, Jenny (1)
1: University of Cape Town, South Africa; 2: Aalto University, Finland
Due to the current climate of water scarcity in mining areas and the fact that water treatment is costly; the recirculation of process water seems to be a viable option in mineral processing. A consequence of the recirculation of water is the build-up of ions such as Ca2+, Mg2+, Na+, SO42- and NO3- as well as increases in pH. This study thus considers the combined effect of increasing ionic strength and pH of process water on the froth flotation process. These parameters are important to study simultaneously because complex water systems at high pH values, may result in the formation of various hydroxo complexes.
The attachment of hydrophobic (valuable) particles to air bubbles is critical in achieving the separation of value from non-value in froth flotation; therefore, this study uses a novel attachment timer housed at Aalto University as a way to investigate the effect of increasing ionic strength and pH on the fundamental bubble-particle attachment of sulphide minerals. Furthermore, these two variables were also investigated from a flotation perspective by means of microflotation tests. In an attempt to delve deeper and understand mechanistically what happens when the ionic strength and pH of process water is increased, zeta potential measurements and xanthate adsorption studies were carried out on sulfide minerals and these were related to the speciation of the process water.
Both fundamental bubble-particle attachment tests and microflotation show decreases in attachment and sulfide recovery as the pH is increased to 11. However, at the elevated pH the recovery increases as the ionic strength (water recycles) is increased. This could be due to the compression of the electrical double layer by the indifferent ions as seen by the zeta potential measurements. Zeta potential measurements also show steep increases in the potential of the sulphide minerals at pH 11 due to the presence of hydroxide complexes as shown by speciation diagrams. These hydroxide complexes may be responsible for the decreased adsorption of the collector reagent.
Although this work suggests that process water with a pH as high as 11 will result in decreased mineral recoveries, it has been shown that at increased levels of ionic strength (increased recirculation of process water) higher recoveries can be obtained. Thus, it can be concluded that if the pH of process water was to reach a pH of 11, the combined effect of recirculation of process water would not have detrimental effects on sulfides flotation performance.