Multi-criteria optimization of uranium exploitation by In Situ Recovery 

Abstract

Worldwide, In situ recovery (ISR) is the most widely used uranium mining technique. As of 2022, it accounted for 55% of global uranium production. Uranium ISR consists in dissolving the ore minerals using an acidic leaching solution directly within the deposit through a series of injection and extraction wells. The U-enriched solution is then pumped to the surface in order to separate the dissolved uranium from the acid solution. Reagents are then recycled before being reinjected into the deposit. The key advantage of ISR over conventional underground and open-pit mining lies in its significantly reduced costs and environmental footprint since it generates no tailings or solid waste and does not require excavation of the rock. It is by far the most cost effective extraction technique. However, an ISR exploitation impacts the groundwater quality by increasing the concentration of dissolved elements (SO4, ...) and decreasing the pH. Subsequently, groundwater impacted by acid ISR mining is typically remediated using various rehabilitation strategies.   This study aims to forecast uranium production and predict the long-term environmental footprint of such exploitation using a reactive transport modeling approach. To do so, we will use HYTEC,  an  investigative tool to assess both production and the environmental footprint of an ISR mining site. HYTEC includes the three-dimensional hydrogeochemical simulation of the relevant chemical reactions which govern uranium production and the long-term evolution of the aquifer. The model is applied to an uranium deposit of the KATCO mine in Kazakhstan that has not been exploited yet. This model can simulate the 3D evolution of the aquifer geochemistry during and after the production phase.   We will study how operating parameters (well design, injection-production rates, acidity and oxidation levels, …) impact both the uranium production and the environmental footprint of the ISR exploitation. The environmental footprint can be described in terms of distance and time. The distance is generally controlled by the migration of sulfate ions resulting from the injection of sulfuric acid, which have low reactivity and hence an important mobility. Acidity or pH is the parameter which influences the duration of the impact, as H+ has a very important reactivity and can also be stored locally by adsorption on clay mineral surfaces. The geochemical model, previously developed in a separate study, suggests that cationic sorption on clay surfaces and the precipitation of secondary minerals like gypsum regulate the behavior of contaminants (SO4, pH) over extended durations and distances.