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Mining is a complex process involving activities that range from exploration through mine development, mineral beneficiation, metal extraction, smelting, refining, reclamation, and remediation (Bian et al., 2012; Ndlovu, Simate, and Matinde, 2017). In the process of extracting the metal values, these activities produce significant amounts of wastes, typically consisting of (1) solid wastes in the form of waste rock, dusts, sludges, and slags, (2) liquid wastes in the form of waste water and effluents, and (3) gaseous emissions. In South Africa, mining and metallurgical wastes constitute one of the biggest challenges to the environment. If not managed properly, the anthropogenic effects of these mining and metal extraction activities can result in irreversible damage to the environment and a hazard to humans. In South Africa, in particular, these types of wastes are usually disposed of in landfills, thereby creating serious environmental and health challenges for communities. Mitigating the effects of such mining, metallurgical, and metal manufacturing processes requires a holistic waste management approach that incorporates reduction in the amount of waste

This paper critically discusses the structure, properties and applications of ironmaking and steelmaking slags and their silicate-based variants as low-cost adsorbents for removing cations and anions from industrial effluents and wastewater. Undoubtedly, the performance of slag-based adsorbents depends on their physical, chemical and phase chemical properties. The presence of crystalline phases, for example, has a significant effect on the adsorption capacity. However, despite their low cost and ubiquity, their chemical and geometric heterogeneity significantly affects the performance and applications of slag-based adsorbents. These challenges notwithstanding, the efficacy of slag-based adsorbents can be significantly enhanced through purposeful activation to increase the specific surface area and density of adsorption sites on the surfaces of adsorbent particles. The synthesis of functionalised adsorbents such as geopolymers, zeolites and layered double hydroxides from silicate and aluminosilicate precursors can also significantly increase the performance of slag-based adsorbents. In addition, the ability to stabilise the dissolved and/or entrained toxic metal species in stable phases in slags, either through controlled post-process fluxing or crystallisation, can significantly enhance the environmental performance of slag-based adsorbents. Most critical in the design of future slag-based adsorbents is the integration of the engineered properties of molten and solidified slags to the recovery and stabilisation of dissolved and/or entrained metals.

The gasification process of phosphorus from municipal sewage sludge during carbothermic reduction process was investigated using a quadrupole mass spectrometer gas analysis and thermo-gravimetric analysis. Two types of sludge, with high and low Fe 2 O 3 content, were used to evaluate the possible effect of Fe 2 O 3 on the gasification behavior of phosphorus from sewage sludge during incineration processes. The gas species vaporized during the carbothermic reaction were measured by the quadrupole mass spectrometer with comparison to the ion currents for the respective molecular gas species. From the gas analysis, it was observed that PO and PO 2 gas species were dominantly vaporized around 1 073 K. Metallic phase phosphorus gas of P 2 vaporized in the 1 273-1 700 K temperature range. The evolution of another metallic phase phosphorus gas of P 4 was found to be negligibly small. Fe 2 O 3 in the sludge has an important role in the phosphorus emission from the sludge during carbothermic reduction reaction, since metallic phosphorous gases react with the reduced iron and form Fe-P alloy.