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.
Highlights
IntroductionThe two conventional processes for the recovery of gold and silver from cyanide leachates are the activated carbon adsorption process and the Merril-Crowe process of cementation on zinc powder
The two conventional processes for the recovery of gold and silver from cyanide leachates are the activated carbon adsorption process and the Merril-Crowe process of cementation on zinc powder.In the carbon adsorption process, precious metals are adsorbed within the activated carbon granules; after they are adsorbed, gold is separated using a solution of caustic cyanide
This work is important because electrocoagulation might provide a simple and economic alternative for the removal of silver and gold from cyanide solutions
Summary
The two conventional processes for the recovery of gold and silver from cyanide leachates are the activated carbon adsorption process and the Merril-Crowe process of cementation on zinc powder. In the carbon adsorption process, precious metals are adsorbed within the activated carbon granules; after they are adsorbed, gold is separated using a solution of caustic cyanide. This solution is taken to an electrolytic cell in which gold and silver are deposited on steel fiber cathodes. In the Merril-Crowe process, which requires basic condition of deoxygenation using a vacuum tower, the product is a filtered zinc precipitated powder. The goals of this research are: (1) To determine the reaction order because EC is an electrochemical process that depends on thermodynamics and kinetics, and (2) To
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