Society must actively move towards more circular economies. Alkaline minerals consitute some of the largest waste streams, yet many are difficult to recycle. This project investigates the UK’s rich history of steel production; the remnants of such industrial activity poses both challenges and opportunities. For example, residual ‘slag’ heaps are a clear point source for release of potentially harmful elements, but also might be re-worked to recover the trace metals of increasing value. Slag heaps might also be an effective location for carbon sequestration to help counterbalance increasing CO2 emissions. To evaluate both the positive and negative impacts of such deposits, it is critical to understand how slag is chemically weathered.
This project focusses on the behaviour, speciation and stable isotope systematics of two trace metals that exist in high concentrations in slag heaps: vanadium (V) and rhenium (Re). Vanadium is used in both existing and new technologies. However, it can have a toxicity similar to arsenic when it exists as vanadate; leading to its increasing recognition as a serious environmental hazard . Rhenium (atomic weight 186) is strongly enriched in coal and mine tailings and highly mobile in oxic environnements, making it an ideal tracer of weathering of anthropogenic deposits such a slag heaps. These novel methods of monitoring legacy deposits will be essential in helping steel makers manage current and future production of slag.
Consett Steelworks in County Durham was operational from the 1840s to 1980 (Figure 1). The site is underlain by Carboniferous Lower Peninne coal measures. The residual slag heaps are completely buried, but have been drilled to examine the potential of the site for carbon sequestration . As the slag heaps are weathered, they release alkaline, metal-rich leachates into soils and streams which eventually drain into the River Derwent. The pH of the system is elevated (>10.5). Spectacular carbonate “tuffa” precipitate as a result of these unusual river water chemistries (Figure 2). The hydrology, mineralogy and river water trace metal concentrations have been studied [e.g., 2, 3] thus providing necessary context for examining isotopic compositions.
This project will aim to:
• Determine the retention and release pathways for V and Re from slag heaps
• Determine the speciation of V and Re in proximal soils and river water
• Provide the first combined Re-V isotopic dataset and evaluate the relationship between speciation and isotopic fractionation
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Figure 1: Consett Steelworks circa 1950
Figure 2: A “Tuffa” made of calcium carbonate in the river Derwent circa 2017