Principal Investigator: Thandazile Moyo

Status: Completed – 2022

More Details: https://pure.psu.edu/en/publications/a-study-on-the-applicability-of-agitated-cyanide-leaching-and-thi

Abstract:

Mercury amalgamation is the method of choice to recover gold in artisanal and small-scale gold mining (ASGM). However, despite the low cost and simplicity of this method, the use of mercury presents serious health and environmental risks, as well as low efficiency in gold extraction. This study investigates the application of cyanide and thiosulphate leaching as alternatives to mercury amalgamation. This investigation was undertaken by conducting leach experiments using cyanide at 1 g/L, 3 g/L, and 5 g/L, and ammonium thiosulphate at 0.1 M and 0.5 M, on three ore samples originating from an artisanal mining area in Zimbabwe. The operating conditions (T = 26 °C, solids loading: 30%, particle size: −300 + 150 µm) were selected to mimic as closely as possible the conditions of artisanal mining processes. It was found that cyanide leaching was the better performing technology compared to thiosulphate leaching, as it achieved gold extractions of 71.6%, 69.7%, and 67.8% for the three ore samples (Sample 1, Sample 2, and Sample 3, respectively), whereas thiosulphate leaching achieved gold extractions of 54.1%, 35.6%, and 38.0% for the three ores, respectively. Both methods outperformed mercury amalgamation, which typically achieves gold recoveries of 30%–50%. Studying the minerology of the ores, using XRF, XRD, QEMSCAN, SEM-EDS, and a diagnostic leach, revealed the presence of sulphide minerals hosting refractory gold which contributed to the low gold extractions observed. Besides achieving higher gold extraction, cyanide leaching proved to be a system that is easier to control compared to thiosulphate leaching, making it much more attractive to artisanal miners.

Principal Investigator: Olumide Ogunmodimu

Status: Completed 2021

More Details: https://oa.mg/work/10.1016/j.mineng.2020.106771

Abstract:

Screening is often applied to separate granulated ore materials into multiple particle size fractions. Therefore, achieving optimal efficiency in the screen performance becomes essential for improved downstream processing. Several techniques such as physical modelling, empirical modelling, mathematical modelling and the discrete element method (DEM) have been adopted by scientists and engineers to study granular flow on vibrating screens. However, advancement in the current state-of-the-art modelling of particle screening requires a mechanistic understanding of their motion along the screen. This necessitates the need to fully quantify the granular rheology determined by the depth of the particle bed along the screen, the solid concentration, and the average velocity of the granular avalanche on the screen. In this study, the concept of granular rheology is applied to study granular media on vibrating screens. This approach overcomes the extreme dependency on machine-specific empirical models for vibrating screens. The kinematic outputs from DEM simulations are used to formulate a visco-plastic model of the granular rheology along an inclined vibratory screen. This mechanistic screening model includes a description of the rheology of granular flow on a vibrating screen. The model captures the flow transition from a quasi-static phase to a dense-flow regime. The quasi-static regime transition occurs at the inertial I value of 0.018, the dense-like regime to a turbulence or gas-like regime at 0.018

Principal Investigator: Kwadwo Osseo-Asare

Status: Completed 2019

More Details: https://pure.psu.edu/en/publications/sequential-pretreatment-of-double-refractory-gold-ore-drgowith-a-

Abstract:

Double refractory gold ore was sequentially pretreated to oxidize sulfides by thermophilic archaeon Acidianus brierleyi and then to decompose carbonaceous matters using the cell-free spent medium (CFSM)from white-rot fungus Phanerochaete chrysosporium. The pretreatment by A. brierleyi significantly improved the gold recovery from 25% to 77%. Additionally, the crude lignin-degrading enzymes in the CFSM converted the carbonaceous matters into more easily degradable substances, which were removed by alkaline washing, leading to a final gold recovery of 92%. These mineralogical alterations were confirmed by differential thermogravimetric analysis and quantitative evaluation of minerals with scanning electron microscopy. Based on the results, gold grains were mostly liberated after bio-oxidation of sulfides, and in following CFSM treatment, large particles of carbonaceous aluminosilicate were formed from the aggregation of clay minerals, gold grains and with partially decomposed carbonaceous matters acting as binders.