Recovery of fine particles of activated carbon with gold by the electrocoagulation process using a Taguchi experimental design

Abstract

The high efficiency of gold recovery via the industrial metallurgical process is increasingly relevant because gold is present at low concentrations in mineral bodies and is difficult to extract. In the mining–metallurgical industry, gold adsorption on activated carbon (AC) includes stages that compromise the structural integrity of the particle. In particular, carbon is an organic material that tends to wear and break down in recovery systems, causing fine particles losses of up to 41% of the average consumption (40 g/t of AC). Carbon-in-columns (CIC) for gold recovery systems lacks on a measure to prevent losses of particles <0.040 mm. Electrocoagulation (EC) technology is an option to improve AC particles recovery from CIC systems, thus increasing the recovery efficiency of ultra-fine particles of AC without requiring additional chemicals. To find the optimal working parameters of gold recovery by EC, the present study conducts laboratory-scale, batch-type EC experiments on AC particles of different sizes (0.106 and 0.053 mm) using different electrodes (iron and aluminum). The EC process was performed in synthetic aqueous medium with an AC particle concentration of 0.80 g/L. The experimental design and results were carried on using the Taguchi statistical method. Scanning electron microscopy images of the filtered and recovered elecrocoagulated product revealed partially coated AC and aggregates of various AC particles with gold. The EC process with the aluminum electrode more effectively recovered the 0.106-mm-sized AC particles, with a more uniform coating, than EC with the iron electrode. Small particles tended to aggregate into larger particles with aluminum hydroxide species, enabling extremely fine AC particle recovery by EC. When used with the aluminum and iron electrodes, the gold–AC recoveries of the EC process exceeded 96% and 88%, respectively.