Copper recovery from copper(II) sulfate solutions by reduction with carbohydrates

Copper(II) in copper sulfate solutions can be reduced with various carbohydrates to obtain a copper powder. The favorable conditions for Cu2+ reduction are intertwined with favorable conditions for hydrolysis and degradation of carbohydrates. The effect of various parameters on these conditions was tested in a series of autoclave experiments, where the copper concentration (2–20 g/L), the temperature (150–250 °C), initial solution pH value (1.5–5), the time to heat to the set-point temperature (1–55 min) and the carbohydrate type were varied. Hemicellulose and the pentoses derived thereof appeared to be the more effective reductants at lower temperatures (170–200 °C) and initial acidities (0.01–0.1% w/w). The recovery of copper was limited due to (organic) acid build up and reactions of the degradation products and copper. By increasing the reductant concentration, total copper reduction could be increased by a few percent. Only by adjustment of the pH with NaOH could recoveries of >99% be obtained. Reduction times of less than 20 min were feasible at 185 °C by inserting the reductant in the autoclave at the set-point temperature. The characteristics of the recovered copper powder depended heavily on the experimental conditions.