Enhancing the efficiency of AuCl4 ion removal from aqueous solution using activated carbon and carbon nanomaterials

The removal of AuCl₄⁻ ion from acidic aqueous solutions is studied using a series of non-oxidized and surface oxidized carbon materials (activated carbon, carbon nanotubes, carbon-encapsulated iron nanoparticles and carbon black). The studied sorbents differ in crystallinity, porosity and morphology. In the case of non-oxidized carbon materials the maximum removal efficiency (74%) is found for activated carbon, whilst graphitized nanomaterials (i.e. carbon nanotubes and carbon-encapsulated iron nanoparticles) are able to remove 42–45% of gold ion from the solution. The oxidation in nitric acid significantly improves the removal efficiencies. The uptake of Au(III) increases two times (to 91–92%) for oxidized carbon nanotubes and carbon-encapsulated iron nanoparticles. The same oxidation procedure applied to activated carbon and carbon black moderately enhances the uptake efficiency to 88% and 55%, respectively. The observed substantially distinct uptakes are discussed in the frames of textural properties, morphology, surface chemistry characteristics and crystallinity of the studied carbon materials. Moreover, the possibility of a galvanic exchange reaction between AuCl₄⁻ and metallic Fe in the carbon encapsulate core is also evaluated.