Overview

Project Highlights:

  • Conventional mineral extraction from mined ores is often performed using hazardous solvents (e.g. cyanidation). Deep eutectic solvents provide a “greener” alternative
  • This project will investigate the (hitherto unexplored) potential environmental impacts of minerals processing using these solvents including river, soil and groundwater pollution
  • Project will use a combination of field measurements, laboratory and mesocosm experiments and numerical modelling

Overview:

Conventional mineral extraction from mined ores (e.g. for metals) is often an energy-intensive process, requiring either smelting or leaching at elevated temperature, or the use of large quantities of strong acids or bases that are energy intensive to produce. Furthermore, some treatments, most notably cyanidation hydrometallurgy, have poor public perception (e.g. residual cyanide trapped in mine tailings as well as being a poison to wildlife can also facilitate the release of toxic metals, such as mercury). Deep eutectic solvents (DES), such as Ethaline (choline chloride + ethylene glycol; Jenkin et al., 2016), provide a “greener” alternative for the extraction of metals from ores with less energy, lower costs and (in principle) fewer environmental impacts. They can also help with the co-extraction of rare e-tech elements such as tellurium (used in solar photovoltaic cells). However, the actual environmental risks associated with waste products from mineral processing using DES have not yet been quantified. In this project, the impacts of DES-processed ore waste (tailings) on soil function and on the leaching of potentially toxic components to ground and surface waters will be assessed using a combination of manipulative field and lab experiments and numerical modelling. The project will examine the degredation of the organic solvent in the tailings, the mobility of residual metals, the toxicity of residual solvent, its breakdown products, and dissolved metal load to soil function and the potential for ground and surface water pollution. Given the potential surge in DES applications in the minerals processing industry in the near future, the project is likely to have significant and immediate impact and could be used to define industrial best practice.

Figure 1: Left: Protesting against the use of cyanide in conventional ore processing (NurPhoto via Getty Images).  Right: Mine tailings dam failure in  British Columbia (Picture from The Northern Miner). Ore-processing using DES could reduce the environmental burden of such operations but their environmental profile has yet to be properly quantified.

Methodology

Laboratory experiments will be conducted to determine the effects of fine-grained particulate tailings composed of waste metalliferous minerals containing residual organic solvent and its breakdown products, the oxidising agent (e.g. iodine) and dissolved metals, on key soil functions (e.g. nitrification, respiration). The leaching potential of hazardous components will be determined using mesocosm and leaching column experiments, supported by numerical modelling. Scenarios such as oxygen-limited tailings ponds, oxygenated stacked tailings, and a catastrophic spillage will be simulated. The dynamics of solute transport and transformation in soils, groundwater and rivers will also be explored using state-of-the-art solute transport and reaction models.

Training and Skills

You will become proficient in the design and execution of manipulative experiments looking at solute – soil interactions. You will master techniques for the measurement of tailings mineralogy and chemistry, soil properties and function, fluid flow in soils, sampling pore water for solute analysis and the monitoring of leachate in soil columns. You will also become an expert in the application of state of the art modelling of flow, solute transport and reaction in soil.

You will join a thriving community of environmental scientists studying aspects of environmental pollution and have access to a range of cutting-edge analytical and field equipment.

Timeline

Year 1: Assess from the literature and from preliminary experiments with DES, the potential contaminant burden which could be associated with waste from ore processing using DES. Characterise the likely behaviours of the component contaminants and breakdown products and perform screening assessment of associated risks. Design preliminary experiments to measure impacts of key contaminants on receiving soil and aquatic systems. Familiarisation with modelling tools and perform initial simulations for solute transport and reaction.

Year 2: Plan and conduct manipulative experiments on contaminant effects in soil and aquatic systems (e.g. effects on key functions such as nitrification). Plan and conduct leaching column experiments to quantify contaminant mobility and validate models. Perform model simulations for advection, diffusion and reaction of contaminants of interest in receiving soils, tailing ponds and downstream environments. Presentations at national meetings.

Year 3: Apply understanding gained from lab and field experiments and from modelling to real environmental scenarios (in which DES are being used to process ores or where they are planned to substitute conventional ore processing techniques: sites to be confirmed). Assess the behaviour of contaminants and associated risks. Make management recommendations for best practice to minimise these risks. Publication of papers and conference presentations, with a target of presenting at international meetings. Complete analysis and write thesis.

Partners and collaboration (including CASE)

Professor Gawen Jenkin, Dr Mick Whelan and Dr Dan Smith will supervise this project. The group have interests in ore mineralogy and extraction and in understanding the fate and transport of environmental contaminants in terrestrial and aquatic systems. The Leicester team have excellent links with industry and have a large well-funded group including NERC projects TeaSe (Tellurium and Selenium Cycling and Supply) and FAMOS (From Arc Magmas to Ores).

Further Details

Contact details: Professor Gawen Jenkin (grtj1@le.ac.uk) and Dr Mick Whelan (mjw72@le.ac.uk), in the School of Geography, Geology & the Environment, University of Leicester (https://www2.le.ac.uk/departments/geoggeolenv