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

Wagland, Stuart - Associate SupervisorThe 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.PhD in Wate

Techno-economic assessment of bioleaching for metallurgical by-products

This study focused on the economic feasibility of two potential industrial-scale bioleaching technologies for metal recovery from specific metallurgical by-products, mainly basic oxygen steelmaking dust (BOS-D) and goethite. The investigation compared two bioleaching scaling technology configurations, including an aerated bioreactor and an aerated and stirred bioreactor across different scenarios. Results indicated that bioleaching using Acidithiobacillus ferrooxidans proved financially viable for copper extraction from goethite, particularly when 5% and 10% pulp densities were used in the aerated bioreactor, and when 10% pulp density was used in the aerated and stirred bioreactor. Notably, a net present value (NPV) of $1,275,499k and an internal rate of return (IRR) of 65$119,816,550 and an operational expenditure (OPEX) of $5,896,580/year. It is expected that plant will start to make profit after one year of operation. Aerated and stirred bioreactor plant appeared more reliable alternative compared to the aerated bioreactor plant as the plant consists of 12 reactors which can allow better management and operation in small volume with multiple reactors. Despite the limitations, this techno-economic assessment emphasized the significance of selective metal recovery and plant design, and underscored the major expenses associated with the process.This research was funded by the European Regional Development Fund as part of the Interreg Northwest Europe project “Regeneration of past metallurgical sites and deposits through innovative circularity for raw materials” (REGENERATIS) (NWE918)

Bioleaching metal-bearing wastes and by-products for resource recovery: a review

The global transition to a circular economy calls for research and development on technologies facilitating sustainable resource recovery from wastes and by-products. Metal-bearing materials, including electronic wastes, tailings, and metallurgical by-products, are increasingly viewed as valuable resources, with some possessing comparable or superior quality to natural ores. Bioleaching, an eco-friendly and cost-effective alternative to conventional hydrometallurgical and pyrometallurgical methods, uses microorganisms and their metabolites to extract metals from unwanted metal-bearing materials. The performance of bioleaching is influenced by pH, solid concentration, energy source, agitation rate, irrigation rate, aeration rate, and inoculum concentration. Optimizing these parameters improves yields and encourages the wider application of bioleaching. Here, we review the microbial diversity and specific mechanisms of bioleaching for metal recovery. We describe the current operations and approaches of bioleaching at various scales and summarise the influence of a broad range of operational parameters. Finally, we address the primary challenges in scaling up bioleaching applications and propose an optimisation strategy for future bioleaching research.European Union funding: REGENERATIS, (European Regional Development Fund)

Unlocking the hidden value of industrial by-products: Optimisation of bioleaching to extract metals from basic oxygen steelmaking dust and goethite

In this study, the potential of bioleaching to extract valuable metals from industrial by-products, specifically basic oxygen steelmaking dust (BOS-D) and goethite was investigated. These materials are typically discarded due to their high zinc content and lack of efficient regeneration processes. By using Acidithiobacillus ferrooxidans, successful bioleaching of various metals, including heavy metals, critical metals, and rare earth elements was achieved. The Taguchi orthogonal array design was used to optimise the bioleaching process, considering four variables at three different levels. After 14 days, the highest metal extraction for the BOS-D (11.2 mg Zn/g, 3.2 mg Mn/g, 1.6 mg Al/g, 0.0013 mg Y/g, and 0.0026 mg Ce/g) was achieved at 1% solid concentration, 1% energy source concentration, 1% inoculum concentration, and pH 1.5. For goethite, the optimal conditions were 1% solid concentration, 4% energy source concentration, 10% inoculum concentration, and pH 2 resulting in a extraction of 26.6 mg Zn/g, 2.1 mg/g Mn, 1.8 mg Al/g, 0.01 mg Co/g, 0.0022 mg Y/g. These findings are significant, as they demonstrate the potential to extract valuable metals from previously discarded industrial by-products. The extraction of such metals can have substantial economic and environmental implications, while simultaneously reducing waste in the metallurgical industry. Furthermore, the preservation of initial concentration of iron in both BOS-D and goethite residues represents a significant step towards implementing more sustainable industrial practices.European Union funding: NWE91

Assessing metal recovery opportunities through bioleaching from past metallurgical sites and waste deposits: UK case study

Recovery of metals from former industrial areas (also called brownfields) and closed landfill sites, are critical for future sustainable development and reducing the environmental risks they posed. In this study, the feasibility of using bioleaching for resource recovery of raw and secondary raw materials from a former metallurgical site and deposit (PMSD) located in the UK was investigated. Determination of the physicochemical parameters (conductivity, pH, moisture and ash content) that can affect bioleaching performance along with metal content analysis were carried out. Field measurement were also carried out using a portable X-ray fluorescence (pXRF) spectrometer as a rapid measurement tool and compared with the induced coupled mass spectrometry (ICP-MS) results. Fe (469,700 mg/kg), Ca (25,900 mg/kg) and Zn (14,600 mg/kg) were the most dominant elements present in the samples followed by Mn (8,600 mg/kg), Si (3,000 mg/kg) and Pb (2,400 mg/kg). The pXRF results demonstrated minimal variance (<10%) from the ICP-MS results. The preliminary assessment of bioleaching using Acidithiobacillus ferrooxidans at 5% pulp density with 22 g/L energy source and 10% (v/v) inoculum at pH 1.5 showed that 100% of Ti and Cu, 32% of Zn and 24% of Mn was recovered from the sample material, highlighting opportunities for the recovery of such metals through bioleaching processes

Extracting metal ions from basic oxygen steelmaking dust by using bio-hydrometallurgy

This study aimed to optimise metal extraction from secondary hazardous sources, such as basic oxygen steelmaking dust (BOS-D). Initially, three batch systems approaches, including bioleaching using Acidithiobacillus ferrooxidans, chemical leaching using choline chloride-ethylene glycol (ChCl-EG) and a combined approach were compared. Then, scaling up was evaluated through a semi-continuous bioleaching column system with varied leachate recirculation over 21 days, focusing on Y, Ce, Nd, Li, Co, Cu, Zn, Mn, and Al. Bioleaching outperformed the control experiments within 3 days in the batch, demonstrating the key role of A. ferrooxidans. Chemical leaching conducted with a solid concentration of 12.5 % (w/v) successfully dissolved over 50 % of all metals within 2 h. For rare earth elements (REE), both bioleaching and hybrid leaching outperformed chemical leaching. However, considering factors such as process duration, overall efficiency, and ease of extraction, chemical leaching was the most effective method. Leachate recirculation reached a plateau after 11 days, resulting in extraction efficiency of 39 % when semi-continuous column set-up was used. Interestingly, variations in recirculation rates did not influence the extraction efficiency. Overall, this study emphasizes the considerable potential of bioleaching for metal recovery, but also highlights the need for further studies for enhancing permeability for percolation methods and optimisation, particularly in parameters such as aeration rate, when transitioning to larger scale systems.This research was funded by the European Regional Development Fund as part of the Interreg Northwest Europe project “Regeneration of past metallurgical sites and deposits through innovative circularity for raw materials” (REGENERATIS) (NWE918)