The interactions of the biosurfactant surfactin in coal flotation

Abstract

Surfactin, a biosurfactant, has the potential to replace synthetic surfactants in froth flotation. This research investigates the surface interactions between surfactin and coal which determine whether surfactin has collecting or depressant characteristics on coal using electrokinetic, FTIR, and micro-flotation experiments. At concentrations of 5 mg/L, surfactin removes species on the surface of coal, especially in the alkaline pH range. At surfactin concentration of 15 mg/L adsorption of surfactin onto coal surfaces are indicated and likely to be due to hydrophobic physisorption between aliphatic groups of surfactin and the hydrophobic carbonaceous surface functional groups of coal. Hydrophobicity of coal was observed to be enhanced at pH 3,6 and 10 except the intermediate pH of 8. Micro-flotation tests showed that hydrophobicity of coal was most significantly enhanced by surfactin presence at pH 3 and 15 mg/L from 42.9% to 74%, and least impacted when surfactin concentration was 5 mg/L at a pH of 10. The collecting or depressant characteristics of surfactin on coal as a function of pH and surfactin concentration have been demonstrated for the potential use of this novel biosurfactant as a Green Chemistry substitute for synthetic surfactants.