Abstract:
The dramatic increase in hydrometallurgical extraction of gold from arsenic bearing gold ores has inevitably resulted in the
release of arsenic into the environment worldwide. Residual arsenic minerals in tailings storage facilities can be oxidised and
mobilise arsenic into the environment. This can contaminate soils, ground and surface waters and eventually biota. In spite of
well-established technologies and recent advances in arsenic remediation, there are limited knowledge and understanding of
the iron oxide substrate (goethite, hematite and magnetite) mineralogy and the fate of arsenic on the surface charge of these
iron oxide substrates in an aqueous media during adsorption. The aim of the present study was to investigate the influence of
interfacial chemistry on arsenic adsorption onto selected iron oxide particles to assist in developing a better understanding and
new knowledge in arsenic removal from contaminated waters. Bulk mineralogy and partial chemical composition of selected
iron oxide minerals were obtained using quantitative x-ray diffractometry (QXRD) and acid digestion followed by metal
determination using inductively coupled plasma optical emission spectrometry (ICP-OES) respectively. Zeta Potential
measurements involving iron oxide particles as arsenic adsorbents were carried out to elucidate the influence of interfacial
chemistry on the adsorption behavior of arsenic from solution. The study confirmed that the iron oxide minerals were
predominantly hematite, magnetite and goethite with goethite containing significant amounts of quartz. Arsenic adsorption
was pH dependent and strongly influenced the zeta potential and isoelectric point (IEP) of the iron oxide particles. The zeta
potential of all substrates studied was strongly positive at pH 2 but indicated a reversal at pH ~ > 9. The interaction between
substrates, arsenic and its hydrolysable products resulted in significant decrease in the magnitude of zeta potential and change
in IEP indicating specific adsorption.