Assessing resource recovery potentials of industrial metal-bearing by-products using bioleaching.

The global transition to a circular economy calls for research and development on technologies facilitating sustainable resource recovery from wastes and by- products as some possessing comparable or superior quality to natural ores. Traditional methods e.g., pyrometallurgy and hydrometallurgy are considered as inefficient for processing secondary resources as they often cause harmful emissions and loss of metals, require high capital cost. Bioleaching, which emerges as an eco-friendly and cost-effective alternative to conventional methods, is well established for metal extraction from low-grade sulfidic ores, tailings, and metallurgical side streams, yet the method is at the research stage for other secondary resources such as metallurgical slag and dust, fly ash, e- waste. The aim of this PhD study was assessing the resource recovery potentials of industrial metal-bearing by-products using biomining. Firstly, this study critically reviewed the microbial diversity and specific mechanisms of bioleaching as well as the current operations and approaches of bioleaching at various scales and summarised the influence of a broad range of operational parameters. Then, suggested an optimisation route for bioleaching of metal-bearing materials for laboratory scale bioleaching operations to further inform pilot/commercial scale operations. Further to this, feasibility of extracting metals from two industrial metal-bearing by-products which were basic oxygen steelmaking dust (BOS-D) and goethite were investigated using Acidithiobacillus ferrooxidans. Taguchi orthogonal array design was used to evaluate the effect of four parameters which were pulp density, energy source concentration, inoculum concentration, and pH at three different levels. Then methods were explored for enhancing and scaling up the extraction of metals from BOS-D. Finally, techno-economic assessment conducted for two potential industrial scale bioleaching technologies including an aerated bioreactor and an aerated and stirred bioreactor, for different metal recovery scenarios from the industrial metal-bearing by-products.