Abstract

Gold and silver have diversified demand, ranging from jewelry and luxury goods to technology. Today in Mexico, the preferred method for silver and gold recovery has long been the zinc dust Merrill-Crowe process. However, the metallurgical plant’s operations must optimize every step of the precious metals recovery to remain profitable in all market conditions. The operation analysis in these plants shows that after the precious metals are precipitated with zinc dust in the filter press, the resulting cake that contain the precious metals often requires extra leaching treatment to control the accumulation of mercury, copper, lead, cadmium, and iron impurities in the final Dore product. Also, the use of cyanide in gold mining operation requires the careful handling and storage of cyanide rich tailing. Due to these operational metallurgical problems, which yields low-quality Dore (90%), along with the lengthy seven-day operation time required to obtain the precious precipitation metals cake in the filter press, high reagent costs, and prolonged treatment in the induction furnace. Recently, the Hermetic Hybrid Electrocoagulation (EC) process, is a promising alternative to achieve high-quality Dore and also attenuation between the tailings pond and the receiving environments. The EC technology requires no chemical additions for the recovery of precious metals.

Furthermore, in this study, by using air injection in the bottom of the EC reactor to remove the HCN gas and recovery simultaneously gold/silver in a Hermetic EC process and also in a separate steel reactor tank can be used to regenerate NaCN by bubbling HCN gas into liquid sodium hydroxide allowing it to be recycled back to the cyanidation leach process as a free cyanide. The optimized operational conditions voltage, current, pH, and temperature of 15V, 10A, 8, and 25 °C, respectively, the EC process yields a 98% Dore product quality within one day, compared with 7 days for the popular method, Merrill-Crowe process and recovery of cyanide of 80%. Finally, the results suggest that magnetite particles and amorphous iron oxyhydroxides present in EC remove gold and silver with an efficiency of more than 98% at an operating time of no more than 20 minutes, through magnetite species and amorphous iron oxyhydroxides generated inside the Hermetic air injection EC reactor.

Keywords:Hybrid hermetic electrocoagulation; Merrill-crowe zinc cementation process; Cyanide recovery