Abstract:

With lithium (Li) mining increasing, understanding the environmental fate of waste materials has become key in minimising impact of extraction. Quebec has been mining Li since the 1960s, with the LCT-pegmatites hosting large spodumene deposits. The UK is developing a Li supply chain through mining and processing of Li-bearing granites in Cornwall. By considering historic, current, and prospective mine sites the release of elements of interest (EOI) in Li mine environments can be quantified.

Geochemistry and mineralogy show the metal bearing phases in the materials. This can be correlated with phases identified through sequential extractions and 24-hour solubility tests to quantify metal release. Bacterial presence is identified through DNA extraction and 16S sequencing to identify microbial contributors to weathering.

Elevated concentrations of Li, Sr, Cs, Rb, Ni and Cr were identified for the Quebec and Cornish Li mine wastes. Ta and Nb concentrations were high in Quebec samples (over 100ppm). Cr, Mn, and Zn exceeded governmental soil guidelines (250ppm, 1000ppm, and 500ppm) for Quebec in most samples. Some UK samples exceeded UK CLEA soil guideline Ni concentrations. 0.005 wt. % S concentrations allude to neutral/saline mine drainage risk. The EOIs were exhibited in accessory phases such as spodumene, chromite, and columbite-tantalite showing EOIs are tightly bound. Sequential extractions identified the EOIs in the residual phases and freshwater solubility tests demonstrated the influence of pH on major and trace element release. Further studies to investigate influencing bacterial contributors to metal release are ongoing, with studies proving little EOI leaching in all cases.

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Prof. Karen Hudson-Edwards