Mine-derived ochre precipitates: a potential selenium trap

Bullock, L. A., Parnell, J., Armstrong, J. G.T. and Perez, M. (2019) Mine-derived ochre precipitates: a potential selenium trap. Applied Earth Science: Transactions of the Institute of Mining and Metallurgy, 128 (2), 41-42. (doi:10.1080/25726838.2019.1601352).

Abstract

The UK coal and base metal mining legacy has led to extensive areas of excavation, pits and spoil left behind from centuries of extraction. Many of these commodities involved extraction from pyrite-rich host rocks and sources. Prolonged exposure of pyritic spoil heaps has led to the development of voluminous alteration products formed by oxidative water flow through the rocks. Alteration causes decomposition of the pyrite to iron oxyhydroxide, which is carried in colloidal form (ochre) by springs and acid mine drainage (AMD) from mine sites. Weathered host rocks and resultant ochreous precipitates may be rich in trace elements, such as arsenic, lead, cadmium, thallium and potentially selenium, an ‘E tech’ element, used in alloys, photovoltaic products and nanotechnologies. While AMD and release of trace elements may pose an environmental threat through water and ground contamination, ochre precipitates may act as a remediation material, trapping elements such as selenium, resulting in hyper-enriched ochres. The widespread occurrence of ochres in UK coal and base metal mining regions may therefore present a unique ‘E tech’ trace element source, and prevent a toxicity problem that they were once thought to be responsible for.

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