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Oxidative leaching is an inexpensive alternative to using chemical cyanide extraction methods for gold from low-grade gold sulfide. Oxidation of finely ground gold-bearing ore by Acidithiobacillus ferrooxidans was evaluated in terms of cell density, pH, and leaching efficiency of Fe and Au in shake flask experiments. The compositional and elemental analyses of the beneficiated ore were analyzed using XRD and EDXRF spectroscopy. The ore’s primary constituents are gold (4.356 mg/L), silicon, iron, and sulfur (62.456, 15.441, and 7.912 wt%, respectively). XRD spectra, the main phases of the concentrated ore, showed that the major components of the ore were quartz, syn, silicon sulfide, pyrite, and polymetallic elements such as silderenrite, gismondine, siderenikite, hematite, and syn. The experimental results, with Acidithiobacillus ferrooxidans bacteria and blank, were evaluated. The pH of the blank remained nearly constant, and the pH of the bioleached was occasionally lowered. The A. ferrooxidans strain always grew better throughout the bioleaching process. For the A. ferrooxidans strain, the cell density of cells reached a maximum of 90.00 × 106 cells/mL after the 11th week and decreased to 87.00 × 106 cells/mL after the 12th week. The decrease in cell density may be due to the presence of polymetallic elements such as Al, Cr, Ti, and Ni, leading to reduced metal tolerance of the A. ferrooxidans strain. In the A. ferrooxidans leaching process, the maximum total iron and gold extraction reached 92.16% (14.23 mg/L) and 99.97% (4.355 ppm), respectively, after the 11th week, and leaching tends to decrease up to 14 weeks, which may be due to the formation of secondary minerals. More research will be performed to optimize the procedure and leaching kinetic, examine the impact of metal content, and take into account the potential for bioleaching process pollution in addition to the amount of gold recovered.

The objective of this study was to assess the levels of essential and toxic metals in leaf and stem of Rhamnus prinoides which are used for bitterness of local alcoholic beverages in Ethiopia and as traditional medicine in some African countries. Levels of essential metals (Ca, Mg, Cr, Mn, Fe, Co, Ni, Cu and Zn) and toxic metals (Cd and Pb) in the leaves and stems of Rhamnus prinoides (Gesho) cultivated in Ethiopia were determined by flame atomic absorption spectroscopy. Known weights (0.5 g) of dried samples were digested with the optimized mixture of HNO3, H2O2 and HClO4 on a Kjeldahl apparatus with a reflux condenser. The efficiency of the optimized procedure was validated by spiking experiment and the percentage recovery for all the metals was in the range of 92–103% for leaf samples and 91–103% for the stem samples. The levels (mg/kg) of the metals were found to be: Ca (6304–22236), Mg (3202–5706), Cr (5.08–20.6), Mn (8.12–17.9), Fe (47.9–187), Co (22.2–42.1), Ni (12.8–27.3), Cu (6.5–73.0), Zn (12.2–43), Cd (0.81–3.10), and Pb (17.7–25.0) in the leaf samples and Ca (3601–5675), Mg (2635–5528), Cr (ND–16.3), Mn (2.16–3.98), Fe (22.0–124), Co (18.7–91.7), Ni (9.68–19.2), Cu (16.8–233), Zn (17.4–28.2), and Cd (ND–1.56) in the stem samples. However, the levels of Cr and Cd in stem samples at one and two sample sites, respectively, and the levels of Pb in stem samples at all sample sites were below the method detection limit. This study showed that the leaf and stem of R. prinoides (Gesho) are good sources of essential minerals and virtually free from toxic metal Cd but not from Pb in the leaf.DOI: http://dx.doi.org/10.4314/bcse.v26i3.2

Oxidative leaching is an inexpensive alternative to using chemical cyanide extraction methods for gold from low-grade gold sulfide. Oxidation of finely ground gold-bearing ore by Acidithiobacillus ferrooxidans was evaluated in terms of cell density, pH, and leaching efficiency of Fe and Au in shake flask experiments. The compositional and elemental analyses of the beneficiated ore were analyzed using XRD and EDXRF spectroscopy. The ore's primary constituents are gold (4.356 mg/L), silicon, iron, and sulfur (62.456, 15.441, and 7.912 wt%, respectively). XRD spectra, the main phases of the concentrated ore, showed that the major components of the ore were quartz, syn, silicon sulfide, pyrite, and polymetallic elements such as silderenrite, gismondine, siderenikite, hematite, and syn. The experimental results, with Acidithiobacillus ferrooxidans bacteria and blank, were evaluated. The pH of the blank remained nearly constant, and the pH of the bioleached was occasionally lowered. The A. ferrooxidans strain always grew better throughout the bioleaching process. For the A. ferrooxidans strain, the cell density of cells reached a maximum of 90.00 × 106 cells/mL after the 11th week and decreased to 87.00 × 106 cells/mL after the 12th week. The decrease in cell density may be due to the presence of polymetallic elements such as Al, Cr, Ti, and Ni, leading to reduced metal tolerance of the A. ferrooxidans strain. In the A. ferrooxidans leaching process, the maximum total iron and gold extraction reached 92.16% (14.23 mg/L) and 99.97% (4.355 ppm), respectively, after the 11th week, and leaching tends to decrease up to 14 weeks, which may be due to the formation of secondary minerals. More research will be performed to optimize the procedure and leaching kinetic, examine the impact of metal content, and take into account the potential for bioleaching process pollution in addition to the amount of gold recovered. [ABSTRACT FROM AUTHOR]