Abstract
Mine tailings spread across many countries with a long history of mining activities. One of such countries is South Africa. These abandoned tressures are usually rich in minerals like precious and industrially important metals. Nevertheless, due to lack of sufficient information and /or ‘supposedly vast ore deposits’ that are rapidly depleting, they are often left as wastes. This study investigated the use of plant-based technology called phytomining on a pilot scale to complement the existing traditional mining techniques; reclaimed these metals considered as wastes and applied the recovered bio-ore in catalysis technologies. Samples of cyanogen-rich high biomass plants native to African origin – Manihot esculenta and Acacia sieberiana were selected as hyperaccumulators that naturally are non-edible due to toxicity based on their hydrogen cyanide content, thereby not hampering food security. The plants were grown in the greenhouse for six months and after that contaminated with 500 mg/L solutions of nickel (Ni), palladium (Pd) and platinum (Pt) in each case for eight weeks. Subsequent to the eighth month pilot trial, the plants were harvested, cut into organs/parts (leaves, stems, and root), dried and ground to powder; the average concentrations of Ni, Pd and Pt as determined by flame atomic absorption spectrometry (FAAS) and inductively coupled plasma–optical emission spectrometry (ICP-OES) was highest in the adventitious roots with 898 ± 0.0023, 78 ± 0.047 and 1 276 ± 0.036 μg/g, respectively. To produce the catalysts, the biomass was calcinated, generating Ni@CassCat, Ni@AcaciaCat, Pd@CassCat, and Pt@CassCat bio-ore catalysts. The biocatalysts were then characterised using high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM) with energy dispersive X-ray (EDX), powder X-ray diffraction (pXRD), Ultraviolet-visible (UVVis) spectroscopy and surface area and pore size distribution measurement techniques...
Ph.D. (Chemistry)