Linking molecular structures of yeast-derived biosurfactants with their foaming, interfacial, and flotation properties

Abstract

Yeast-derived bola amphiphiles have attracted growing attention in various industrial sectors as green reagents. However, their physico-chemical properties relevant to mineral separation by froth flotation are poorly explored. To bridge this gap, we studied the foaming, interfacial, and flotation properties of acidic sophorolipid (ASL), acidic glucolipid (GL) and alcoholic glucoside (GS) obtained from strain engineering of the yeast Candida bombicola by molecular editing of the headgroups. Bench-scale flotation testing of a copper sulfide ore showed that ASL can effectively separate copper sulfides (85% recovery at 20% grade), GL is less effective (ca. 60% recovery and 13% grade), while GS is a poor collector. To understand this trend, we studied the interfacial and foaming properties of these three biosurfactants. The surface tension study reveals that, contrary to GS, selfassembly of both ASL and GL at the air–water interface is pH-responsive, suggesting that both the biosurfactants acquire a Π-shape. The dependence of the foaming properties of all the three surfactants on pH and concentration does not correlate with the trends in the static surface tension, suggesting the critical roles of dynamic factors, interfacial elasticity and interfacial viscosity. Hydrophobicity of djurleite (a model copper sulphide) in the presence of the three surfactants was assessed using the contact angle and Hallimond flotation methods. ASL and GL only float the pure mineral at alkaline pH, which is consistent with the contact angle data. In contrast, even though GS does not have a significant effect on contact angle, it floats djurleite in a wide pH range, which is explained by the mechanical entrainment of hydrophilic mineral particles in rich GS foams. Overall, these results demonstrate the potential of carboxylic bola biosurfactants for the recovery of copper sulfides from ores. They also bring new insights into the interfacial and foaming properties of bola biosurfactants, which can assist their introduction into other industries.