Assessing the potential of activated bagasse as gold adsorbent for gold–thiourea

This study was conducted to establish the potential of bagasse, the fibrous by-product of sugarcane milling operation, as a precursor for preparing adsorbents for gold–thiourea complex. It was also of interest to identify the carbon properties, which promotes adsorption. Bagasse was activated in this study by physical (gasification) and chemical techniques. It was found bagasse is more amenable to activation by physical techniques producing activated carbon with surface areas exceeding 1000 m2/g. Among the chemical activating agents, it was found that ZnCl2 was most effective in developing the surface structure of bagasse. Gold–thiourea adsorption was found to be favoured in carbon exhibiting high surface area. Finer pore sizes are developed with higher surface area. As such the extent to which the surface area could improve adsorption was limited by steric hindrance in the finer pore size. It was found that steric hindrance affected gold–thiourea adsorption in mean pore sizes less 20 Å. The effect was particularly significant when the carbon pH was greater than 7.0, where the alkaline nature of the carbon may have shifted the Tu/Au ratio to higher values such that the formation of the larger AuTu2+ and AuTu3+ are promoted. The greater development of physically activated bagasse favoured gold–thiourea adsorption. The optimum adsorption capacity by the physically activated bagasse was approximately 318 mg Au/g of adsorbent (ash free), achieved after 25 h of gasification in 15% CO2. This was comparable to adsorption capacities obtained from commercial activated carbon and resins of 197–321 mg Au/g adsorbent (ash free). These results are encouraging and confirm the potential of activated bagasse as gold–thiourea adsorbent.