Browsing by Author "Schlebusch, Izak David"

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    The application of the lipopeptide Surfactin in heavy metal extraction from mine wastewater
    (2023-12) Schlebusch, Izak David; Tadie, Margreth; Pott, Robert William McClelland; Stellenbosch University. Faculty of Engineering. Dept. of Chemical Engineering. Process Engineering.
    ENGLISH ABSTRACT: Heavy metals (HMs) are a common contaminant present in wastewater generated by mining operations. HMs can be toxic and carcinogenic, and do not naturally degrade. They, therefore, tend to accumulate in environments where they are discharged. Conventional HM separation processes can be effective, however several drawbacks including poor selectivity, high process costs, or generation of secondary pollutants can limit their efficacy in industry. Surfactin is a lipopeptide biosurfactant which shows great promise for application in HM separation processes. Surfactin is capable of coordinating HM cations into stable complexes, and the mechanism of cation coordination is hypothesized to render the complex insoluble in aqueous solutions. These properties, in tandem with the environmentally benign nature of biosurfactants, makes surfactin an attractive alternative to synthetic reagents using in conventional separation processes. The aim of this dissertation is to determine which HM extraction methods can successfully utilise surfactin to extract HMs from aqueous solution and investigate the efficacy of these processes. Based on the hypothesis that surfactin forms insoluble complexes with HM ions, a chelating precipitation process was identified as one potential mode of HM extraction. The ability of surfactin to bind HMs into a hydrophobic complex also suggests that it may be functional as a collector in an ion flotation process. To test the potential of these processes, single ion copper, nickel, and cobalt solutions were used simple model contaminated wastewaters. The ability of surfactin to coordinate and precipitate the metal ions was first confirmed by mixing equimolar concentrations of surfactin with each respective copper, nickel, and cobalt solution. The precipitates that spontaneously formed were dried and analysed by FTIR spectroscopy to determine the binding sites which coordinated the HM ions. It was found that the carboxylate groups and the amide groups present in the hydrophilic cyclic heptapeptide moiety were both capable of coordination, and coordination of the HMs at these sites would decrease aqueous solubility of the complex. The extent of precipitation of copper, nickel, and cobalt by surfactin was then quantified to determine the efficacy of the precipitation process with surfactin as a precipitant. Up to 84% and 88% of nickel and cobalt respectively was extracted by the surfactin precipitation process, and up to 100% of copper was extracted by surfactin precipitation in conjunction with alkaline precipitation. Initial relative surfactin concentration and pH were shown to be key operating parameters that should be controlled in the surfactin-aided precipitation process. The value of the ion flotation process utilising a surfactin collector was investigated by determining how far the ion flotation process could lower the concentration of HMs in the residual solution. The reduction in copper, nickel, and cobalt concentrations in the residual solution was 67%, 82%, and 96% respectively. It was further found that the extent of ion extraction could be improved by optimisation of the flotation pH, air flowrate, and initial concentration of surfactin. Based on these results, it appears that precipitation and ion flotation have the potential to effectively utilise the promising properties of surfactin to treat HM contaminated wastewater.