Gold reduction in batch and column experiments using silica gel derivates and seaweed biomass

• Gold recovery from aqueous solution through colloid nanoparticle formation.
• No effect of pH or presence of other metal over gold recovery.
• A plausible mechanism was suggested for the reduction process.
• FTIR and SEM provided decisive evidence supporting the mechanism.

Gold recovery from aqueous solution was studied in the present work. Two synthetic materials composed of immobilized chelating agent on silica gel, and the brown seaweed Sargassum muticum were used as reducing agents inducing gold colloid nanoparticles formation. The results showed that there is no pH effect and no interference on gold recovery by the presence of other metals in solution, such as Co, Ni, and Cr(VI). A strong complexing reagent for gold leaching, such as thiourea, was able to recover a significant amount of the gold previously reduced over the surface of the materials. The investigated synthetic materials presented much faster rate than the algae for gold recovery. A first order model with respect to the oxidizable groups and gold concentrations accuracy described the entire kinetic process. The rate constant of the reaction and the concentration of oxidizable groups per gram of material were obtained from kinetic data fit. Column studies were conducted varying the flow rate and the quantity of material used. Under favourable conditions of flow rate (1 mL/min) and quantity of material in the column (⩾0.2 g), more than 95% of the gold was recovery from the inlet solution. A mechanism based on the experimental evidences was proposed. FTIR and SEM analysis supported the suggested mechanism. Based on the results showed it can be concluded that the gold removal from aqueous solution is mainly based on a reduction mechanism where gold colloid nanoparticles are produced.