The present study aimed to investigate the mineralogical and morphological properties of two South African clays, namely bentonite and kaolin. These clays are mined in specific regions of the country but have not been fully characterized in terms of their properties for potential application in a number of industries. Bentonite was found to have a larger specific surface area, pore size, and more interchangeable cations than kaolin. The bentonite was also identified as Na-bentonite due to the huge Na content present in the clay. The powder X-ray diffraction (PXRD) patterns revealed that both clays are crystalline, together with the Fourier-transform infrared (FTIR) spectrophotometer results; presumably, some impurities of quartz could be present in the clay materials. The most prevalent functional groups present include Al-OH, Si-O-Mg, Si-O, and Si-O-Al groups. The surface charge of bentonite was consistently negative across all pH values, indicating its potential for adsorption applications. On the other hand, kaolin exhibited a negative charge at pH values greater than 2.4. The scanning electron microscopy (SEM) images provided visual evidence of the presence of pores in the clay structures, which supported the Brunauer–Emmett–Teller (BET) results classifying both bentonite and kaolin as mesoporous and macroporous materials. The particle size analysis revealed a broad distribution for bentonite and a bimodal distribution for kaolin. Overall, the clays revealed interesting features that can be useful for application in several industries, for example, in the treatment of wastewater. Further research and development can explore their potential to address environmental challenges, particularly the application of bentonite and kaolin in water treatment processes to remove toxic metal ions.

Acid mine drainage (AMD) has always been a global environmental issue; particularly in countries with intensive mining activities due to the severity of its ecological, human health, and socio-economic effects. AMD is generated by both active and abandoned mines (particularly gold and coal) in countries with advanced and intensive mining industries. As such, research are still ongoing to prevent its formation. On the other hand, the already generated AMD is mostly treated using active and passive approaches, with the first being driven by chemical and energy inputs while the second is self-renewable approach but efficient to be used as a polishing step. The drawbacks associated with active and passive treatment methods have motivated the design and exploration of hybrid, integrated, and emerging technologies. Hybrid and integrated systems are promising and cleaner technologies since they can effectively treat AMD to required standards while recovering minerals and reclaiming water thereby ensuring zero liquid discharge (ZLD). Emerging technologies are cost-effective, however, they are slow and not eco-friendly in the case of nanoremediation. Herein, the body of knowledge on AMD treatment technologies is comprehensively reviewed and discussed, with a focus on their sustainability using life cycle assessment methodology (LCAM).

For the determination of 15 potentially toxic elements (V, Cr, Fe, Mn, Co, Ni, Cu, Zn, As, Se, Ag, Cd, Sn, Hg, and Pb) in plant and sediment samples of the Akaki River, Ethiopia, inductively coupled plasma–mass spectrometry, inductively coupled plasma–optical emission spectrometry, and a RA-915+ mercury analyzer were applied. Sediment and plant samples were mineralized using a closed-vessel microwave-assisted digestion system. The elemental concentrations varied considerably in plant and sediment samples. The minimum concentration was observed for known toxic elements (As, Hg, and Cd) while the highest concentration was observed for the elements of relatively low toxicity Zn, Mn, and Fe. The concentration of Cr, Fe, Pb, Zn, and As in Swiss chard surpassed the maximum permissible levels at specific sites. At some of the sites, the sediment quality guidelines are surpassed for Cu, Zn, and Pb.

In this study, the sequential extraction method was applied to extract selected potentially toxic elements (PTEs) (Cd, Cr, Cu, Fe, Ni, Pb and Zn) in river sediments collected from the Blood River situated in Seshego area, Limpopo Province, South Africa. The study aimed to assess a possible trend of mobilisation of these elements from sediment to water. The accuracy of the sequential extraction method was confirmed by analysing sediment-certified reference material, and quantitative percentage recoveries ranging from 86 to 119%, 81 to 111% and 77 to 119% were achieved for exchangeable, reducible and oxidisable fractions, respectively. The potential risk of the PTEs in sediments was evaluated. The calculated values of contamination factor (CF) as well as risk assessment code (RAC) for Cd, Cu, Ni and Pb revealed the mobility of these elements. The PTEs in river sediments are at a high toxicity-risk level and could therefore cause a threat to organisms dwelling in sediments and humans via consumption of crops irrigated with the polluted river water.

Precious metals accumulated to high concentration spread across tailing dumps, mineralised soil and at many metal-processing facilities across the African continent. Currently, about 71% of the world’s deposits of platinum group metals (PGMs) are found in South Africa. The country produces about 60% of the world’s output of three of these precious metals namely; platinum, palladium and rhodium. Traditional mining technology is grossly insufficient to quantitatively recover all metals economically. Therefore, low concentrations of these valuable metals are often wasted away as leftovers – posing environmental menace to the general ecosystem via dissolved ‘associated-toxic metal leaching’ and run-offs. In the past few decades, the concept of phytomining to recover low concentration precious metals from mine tailings, has been investigated by various researchers inMexico, New Zeeland, Caledonia, Canada, United Kingdom and Australia. This review presents a synopsis of the reported precious metal phytomining studies developed on the laboratory scale, and/or in greenhouse or pilot scale as well as in the field, in the last two and half decades. A summary of work done so far as relating to the techno-economic assessment of precious metal phytomining is also presented. We have also taken the opportunity to specifically discuss the applications of the phytoextracted plant-based metal in catalysis and related fields – an area with great potential to support the catalyst market and its adjacent chemicals and pharmaceutical industries but has been less explored for its possible coupling with phytomining activities so as to augment the economic prospects of this mining method.