Recovery of Te, Bi and W from mine tailings and concentrates, using environmentally-benign Deep Eutectic Solvents at Björkdal Gold Mine, Sweden

The mining and minerals sector faces a dilemma: the transition away from hydrocarbons and race to net-zero requires enormous quantities of mineral resources for low-carbon technologies. However, mining and processing can be hugely energy-intensive and sometimes environmentally harmful, thus there is a need for novel solutions in extraction and processing. Gold ore processing in particular often features cyanide, which is highly toxic and has a large carbon footprint [1], and the often low Au concentrations can result in relatively large volumes of waste rock.

In addition, gold deposits are often also enriched in other metals, and the Björkdal mine produces gold concentrates and tailings that also contain Te, Bi and W. Initial data indicates a high degree of liberation for bismuth-tellurides which is promising for extraction. Currently, there is little incentive and few options by which to process and extract these additional metals for Mandalay Resources, the mine operator [2]. Developing a way in which these metals could be recovered rather than sent to tailings would be ideal for meeting some of the demand for these metals, without opening any new mines.

Deep Eutectic Solvents (DES), developed at the University of Leicester, are a promising advancement for both gold and by-product extraction [3][4]. DES are eutectic mixtures of an organic salt and a hydrogen-bond donor, which are powerful solvents and liquid at room temperature. The components are cheap, readily available and environmentally-benign compounds, such as choline chloride (Vitamin B4) and urea, and can be recycled and reused. Previous work on DES has demonstrated rapid leaching of Au, Ag, Sb, Te and other metals [1], including success with dissolution of tellurides and bismuth tellurides [5].

This project aims to understand the flows of Te, Bi and W through the Björkdal processing plant, and mineralogically characterise tailings and concentrates. This will be used to test the feasibility and impacts of inserting DES leaching stages, and/or altering the processing procedure or reprocessing tailings, in order to maximise by-product recovery in an environmentally-friendly and low energy process.

References:

[1] Norgate T and Haque N (2012) J Clean Prod 29-30:53-63

[2] Jenkin G et al. (2019) 15th SGA Biennial Meeting 4:1512-1515

[3] Abbott A et al. (2004) J Am Chem Soc 126 (29):9142-9147

[4] Smith E et al. (2014) Chem Rev 224 (21):11060-11082

[5] Jenkin G et al. (2016) Min Eng 87:18-24