The use of galvanic interactions between zero-valent aluminum (ZVAl) and activated carbon (AC) to recover gold (Au) ions is a promising technique to overcome the challenges due to the poor recovery in ammonium thiosulfate systems, but the applicability to practical Au ore processing remains elusive so far. The present study describes (1) the recovery of Au ions from low Au concentrations, which are typical concentrations used in Au ore processing; and (2) an investigation into the effects of various coexisting base metal ions that can be present in pregnant ore-leached solutions. The results showed that high Au recovery (i.e., over 85%) was obtained even at low Au concentrations under the following conditions: 1:1 of 0.15 g of ZVAl and AC with 10 mL of ammonium thiosulfate solution containing 5 mg/L of Au ions at 25 °C for 1 h in an anoxic atmosphere. Selected coexisting metal ions (i.e., copper, iron, cobalt, nickel, and zinc) were studied to establish their effects on Au recovery, and the results showed that the Au recovery was enhanced (about 90%) when copper ions coexist in the solution with minimal effects from other competing base metal ions.

The enhanced cementation technique by galvanic interaction of aluminum (Al; electron donor) and activated carbon (AC; electron mediator) to recover gold (Au) ions from the ammonium thiosulfate solution is a promising technique to eliminate the challenges of poor recovery in the system. This study presents the kinetics of Au ion cementation in an ammonium thiosulfate lixiviant as functions of initial Au concentration, size/amount of Al and AC, temperature, and shaking speed. The recovery results basically followed first order kinetics and showed that the cementation rate increased with a higher initial concentration of Au, smaller electron donor size, greater both electron donor and mediator quantity, decrease in temperature, and higher shaking speed in the system, while size of electron mediator did not significantly affect Au recovery.

The small-scale gold mining sector (SSGM) in Zimbabwe is a significant contributor to the country’s economy, at 12% of total exports. Although official output figures are rising, the general belief is that most of the small-scale gold production is unaccounted for, as it only reports gold produced from amalgamation and carbon adsorption, which the Government monitors through Statutory Instruments. However, gold produced from unregulated methods often ends up in illicit gold trading, with Zinc cementation being one of the unregulated gold recovery methods that small-scale gold miners rampantly abuse due to its ease of filtration and low cost. Governing legislation or Statutory Instruments for control of Zinc cementation are non-existent, creating easy loopholes for abuse and strong links to illicit financial flows. This study investigates the feasibility of regularising Zinc cementation as a gold recovery method for small-scale operations in Zimbabwe, ensuring effective monitoring and surveillance. Optimum parameters for Zinc cementation were determined experimentally. The determination of optimum parameters for Zinc cementation was done using a 2³ fractional factorial design and gold deportment analysis was conducted using samples from a small-scale gold mine located on the early Precambrian, Bulawayan, andesitic and dacitic meta-volcanic geological formation in Zimbabwe’s Matabeleland mining region. The influence of free cyanide concentration, dissolved oxygen concentration and pH on gold recovery was evaluated. Experimental work showed the feasibility of using Zinc Cementation as a possible recovery route for gold in SSGM with optimum parameters of: - pH value 11.5, free cyanide concentration 0.05g/L and dissolved oxygen concentration of 0.5ppm. The analysis showed that pH and Oxygen concentration increase gold recovery by a factor of 40%, with pH having the most significant effect on gold recovery. The study concludes that Zinc Cementation for small-scale hydrometallurgical gold extraction is an effective recovery method and should be regularised by the Government through a Statutory Instrument for easier monitoring and surveillance. Further studies on various ores from different provinces are recommended to incorporate diverse mineralogical differences into the design. Additionally, setting up a pilot plant to refine the metallurgical plant requirements for controlling zinc cementation is suggested.