Gold Recovery from Cyanide-Based Leach Solutions Using Zinc Cementation: A Case of Small-scale Gold Mining in Zimbabwe

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 2<sup>3</sup> 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.