Hydrotalcite formation facilitates effective contaminant and radionuclide removal from acidic uranium mine barren lixiviant

Abstract

An assessment of hydrotalcite (HT) formation as a method to neutralise acidity and remove trace elements was undertaken using barren lixiviant from Heathgate Resources’ Beverley North in situ recovery (ISR) U mine in South Australia. This study demonstrated proof of concept in terms of the neutralisation of acidity and concomitant removal of a range of trace elements and U–Th series radionuclides from the barren lixiviant using MgCl2 as a supplementary Mg source to optimise Mg:Al mol ratios and NaOH as the neutralising agent. Hydrotalcite was the predominant mineral formed during neutralisation, hosting a range of elements including substantial U (∼0.2%) and rare earth elements (REE ∼0.1%). High U and REE recovery (∼99%) from barren lixiviant after HT precipitation indicates a potential to both remediate barren lixiviant and to offset remediation costs. Alternatively, HT precipitates formed during barren lixiviant neutralisation may be further stabilised via calcination, silicification or a combination thereof forming minerals potentially amenable for inclusion in a long-term waste repository at the cessation of ISR mining. Importantly, the composition of the neutralised barren lixiviant produced via HT precipitation is similar to that of existing groundwater allowing for the possibility of direct aquifer re-injection after remediation. A potential exists to apply this HT-based remediation technology to conventional or ISR U mines (or mines exploiting other commodities) and allows for the prospect of a fully integrated ISR mining, processing and lixiviant remediation strategy consistent with stringent environmental and mine closure standards.