Reduction of copper from dilute acid solutions by hydrolysis of wood carbohydrates

Abstract

Copper reduction to metallic copper from dilute acid solutions containing Cu⁺² was studied by means of sawdust from Radiata Pine as a reducing agent. Influence of the temperature, copper concentration and reaction time on the reduction of copper was investigated using an autoclave reactor. Furthermore, maximum reduction capacity of the sawdust was calculated through consecutive reductions. Results obtained show that diluted acid solutions containing Cu⁺² can be effectively reduced to metallic copper by sawdust from Radiata Pine above 120°C. For a 0.5 g L⁻¹ Cu⁺² solution at 120°C and in 60 min, close to 90% of the copper can be reduced to metallic copper, which crystalises on the surface of the wood particles. At 120°C and for 90 min reaction time up to 95% of the copper can be reduced, generating an effluent with 0.02 g L⁻¹ of copper. This value is similar to those obtained using activated carbon. Consecutive steps of reductions of the sawdust with fresh solutions with 0.5 g L⁻¹ Cu⁺² indicate that for 6 steps, the copper load of the sawdust is about 11.9 kg Cu/ton sawdust (dry basis) while for more concentrated solutions of 16.7 gL⁻¹ Cu⁺² the copper load reaches 15.0 kg Cu/ton sawdust. These results indicate that this process could be an alternative to conventional electrowinning.