Mining has advanced primarily through the use of two strategies: pyrometallurgy and hydrometallurgy. Both have been used successfully to extract valuable metals from ore deposits. These strategies, without a doubt, harm the environment. Furthermore, due to decades of excessive mining, there has been a global decline in high-grade ores. This has resulted in a decrease in valuable metal supply, which has prompted a reconsideration of these traditional strategies, as the industry faces the current challenge of accessing the highly sought-after valuable metals from low-grade ores. This review outlines these challenges in detail, provides insights into metal recovery issues, and describes technological advances being made to address the issues associated with dealing with low-grade metals. It also discusses the pragmatic paradigm shift that necessitates the use of biotechnological solutions provided by bioleaching, particularly its environmental friendliness. However, it goes on to criticize the shortcomings of bioleaching while highlighting the potential solutions provided by a bespoke approach that integrates research applications from omics technologies and their applications in the adaptation of bioleaching microorganisms and their interaction with the harsh environments associated with metal ore degradation.

The ball mill is a rotating cylindrical vessel with grinding media inside, which is responsible for breaking the ore particles. Grinding media play an important role in the comminution of mineral ores in these mills. This work reviews the application of balls in mineral processing as a function of the materials used to manufacture them and the mass loss, as influenced by three basic wear mechanisms: impact, abrasion, and corrosion. The effect of grinding media geometries and density on the mill performance was also reviewed to determine what the research has recommended as the most suitable grinding media for different grinding applications. Although considerable work has been carried out in that area, the influence of grinding media shape on the liberation of minerals, as well as the effect of various mill conditions on the performance of mixed grinding media shapes, are still poorly understood. Thus, the review opens up opportunities for further research to improve the grinding processes, especially considering that even a slight improvement in the process efficiency significantly reduces the production costs.

Engineers face increasing pressure to manage and utilize waste (whether of animal, human or municipal origin) in a sustainable way. We suggest that a solution to the problem of organic waste in rural communities lies in their being able to convert it to biogas technology. This would offer smallholders and farmers a long-term, cheap and sustainable energy source that is independent of the national electricity grid. However, although the technology involved in making biogas from waste has already been fully developed, there are obstacles impeding its adoption. First, there is a general ignorance about this source of energy among the very people who can most benefit from using it. Second, at present, South Africa has no regulatory framework to support the installation of biodigesters. The research focused on the current gap between knowledge and need. The two objectives were raising general awareness of the many and varied benefits that biodigestion can offer, especially to rural communities, and demonstrating how it works. Using science events as a platform, the team introduced the concept of biodigestion, its functioning and uses, to their audiences, and then invited informal responses, which were recorded. The second stage, the case study, entailed the setting up of a small-scale (10 m3) household biodigester in the Muldersdrift community in Gauteng, South Africa. It was put into operation, using fresh cow dung as the feed. Members of the community were invited to watch every step of the process and afterwards were asked to participate in a more formal survey, which sought their opinions on whether biodigestion offers a power source the individual farmer could (and would) use. The results presented in this paper were derived from a comparison of the ‘before-and-after-installation’ responses of the persons interviewed. We found that the members of the Muldersdrift community who had been involved in both phases of the case study (explanation followed by experience of a hands-on educational example) had become more willing to adopt the technology. The results justified our contention that, to ensure a greater adoption of biogas technology in South Africa, it is necessary to provide targeted communities with educational programmes and exposure to pilot plants.