• Usher, Kayley
• Douglas, Grant B.
• Wendling, Laura
• Woods, Peter

Abstract

An assessment of hydrotalcite formation as a method to neutralise acidity and remove trace elements was undertaken using barren lixiviant from Heathgate Resources' Beverley In-Situ Recovery (ISR) uranium mine in South Australia. Batch-scale studies have demonstrated proof of concept in terms of the neutralisation of acidity and concomitant removal of a range of trace elements from the barren lixiviant using either MgO or MgO and sodium aluminate (NaAlO2). Hydrotalcite was the predominant mineral formed during the neutralisation of the barren lixiviant, hosting a wide range of contaminants including substantial uranium (∼1% U) and rare earth elements (∼2% REE). High U and REE recovery (∼99%) from barren lixiviant after hydrotalcite precipitation indicates a potential to both remediate barren lixiviant prior to aquifer re-injection and to offset remediation costs. Alternatively, hydrotalcite precipitates formed during barren lixiviant neutralisation may be further stabilised via calcination, silicification or a combination thereof. Both methods facilitate the formation of minerals potentially amenable for inclusion in a long-term waste repository at the cessation of ISR mining. Formation of a residual Na-SO4 brine during lixiviant neutralisation creates the option to use electrolysis to generate H2SO4 and NaOH, for use in mining activities and to also further offset lixiviant remediation costs. Importantly, the major and trace element composition of the neutralised barren lixiviant produced via hydrotalcite precipitation is similar to that of existing groundwater allowing for direct mine water disposal. In the Beverley context, the hydrotalcite-based remediation technique is considered a potential additional groundwater treatment, should it be required, for the future closure of its Beverley North operations. Whilst the ionic composition of Beverley's barren lixiviant would mean easier application of this technology there, there is potential to apply it to other uranium mines with suitable addition of reagents. Hence, this hydrotalcite-based remediation technology, after scale-up and performance validation, allows for the prospect of a fully integrated ISR mining, processing and lixiviant remediation strategy consistent with stringent environmental management and mine closure standards.

Topics

• impedance spectroscopy
• mineral
• inclusion
• Sodium
• precipitate
• precipitation
• trace element
• Uranium
• rare earth metal