Kinetics and Energy Consumption for a Three-Stage Electrocoagulation Process for the Recovery of Au and Ag from Cyanide Leachates

Abstract

The most common processes used for the recovery of gold and silver from cyanide leachates are Merril-Crowe, activated carbon in pulp, and ion exchange resins; the process of electrocoagulation (EC) also is a promising new technique. EC is an electrochemical process whose mechanisms include oxidation, reduction, decomposition, deposition, coagulation, absorption, flotation, and precipitation. It has been used for the treatment of water and wastewater with different degrees of success. This study aimed to determine the kinetics of the reaction and the energy consumption at constant voltage, and at constant current using aluminum electrodes with two different distances between electrodes. EC was run in three stages for the removal of gold and silver from aqueous cyanide solutions from samples supplied by a Mexican mining company. Characterization of the sample showed initial concentrations of 49.48 and 383 mg/L of gold and silver, respectively. Results showed the effectiveness of the process by achieving removals up to 98.59% of gold and 99.43% of silver. Additionally, it was determined that the kinetics of the reaction is of zero order and that the lowest energy consumption can be achieved when working at constant voltage and with a separation of 0.8 cm between electrodes.

Keywords

• cyanidation
• electrocoagulation
• zero order reactions