Polysaccharide-derived sulfur-containing mesoporous carbon materials for platinum group metal recovery

As cost effective and sustainable materials for the recovery of platinum and palladium we have investigated the potential of sulfur-containing porous carbon materials. Utilising the naturally abundant sulfur-containing κ-carrageenan, or by doping K2SO4 into alternative polysaccharides (i.e. alginic acid), the Starbon process provides a sustainable route to high surface area mesoporous materials without the need for templates or activating agents. X-ray diffraction, elemental analysis and X-ray photoelectron spectroscopy were used to elucidate the development of sulfur chemistry during pyrolysis so that conditions could be optimised to yield materials with significant quantities of reduced organic sulfur chemistry, considered most promising for platinum group metal adsorption. The resulting materials were found to exhibit large capacities for Pd(II) (156 mg g−1) and Pt(II) (246 mg g−1) as well as selectivity over the other platinum group metals and the common contaminant ions Cu(II), Ni(II) and Co(II) in large excess. Pd(II) and Pt(II) could be removed by elution in thiourea and the material reused, suggesting excellent potential for the application of these materials to the recovery of platinum and palladium from low grade feeds. Analysis of adsorbed palladium using X-ray photoelectron and X-ray absorption spectroscopies provides evidence for coordination to organic sulfur-containing groups on the Starbon surface.