An Investigation into the Applicability of Pyrolyzed Tyre Char and Tyre Crumb for the Recovery of Gold from Acidic Solutions

The present study has assessed the performance of pyrolytic tyre char and tyre crumb as cheap adsorbents for gold recovery from acidic solutions. The performances of the aforementioned cheap adsorbents, prior to and after undertaking demineralisation operations, were also investigated. Demineralisation of the adsorbents was undertaken via the application of 1 M sodium hydroxide and 1M nitric acid at a temperature of 90 °C for a duration of 24 h with changes in BET surface areas (SBETₛ) and adsorption performances, subsequently evaluated. Initial investigations established that the pH value of 2 constituted the preferred pH at which adsorption was enhanced, thus this pH was maintained while undertaking subsequent kinetic and equilibrium adsorption experiments. Based on the experimental investigations, it was demonstrated that the kinetics and adsorption of gold ions (Au³⁺) as AuCl₄⁻ anions from acidic solutions was best described using pseudo second order kinetic and Langmuir equilibrium isotherm models, respectively. Even though the demineralisation process resulted in a notable increase in BET surface areas (SBETₛ) for both char (23%) and crumb (984%), it was found to negatively influence adsorbent loading of Au³⁺ ions onto the adsorbents. It was therefore suggested that sulphur removal via demineralisation may explain the reduced adsorbent loading since there is typically an affinity of gold ions (Au³⁺) for localised elemental sulphur. This affinity causes sulphur to be oxidised into solution and the gold ions (Au³⁺) to be reduced to elemental gold on the adsorbent surface. The present study was therefore able to demonstrate the preference for untreated of pyrolytic tyre char and to a lesser extent, untreated crumb, as alternative low-cost adsorbents for gold recovery from acidic solutions.