Aquifer restoration at uranium in situ leach sites

Industrial Deployment of Reactive Transport Simulation: An Application to Uranium In situ Recovery

“…Additional steps or sequences can be adapted with the injection of a reducing agent to prevent the oxidation of sensitive redox elements, and/or a mixing step with fresh waters (IAEA 2001(IAEA , 2005. Return of experience and associated reactive transport simulations both highlight the limited efficiency of pump and treat based solutions (Anastasi and Williams 1984;Hall 2009). Indeed, these solutions focus only on the aqueous fraction of the chemicals of concern, which may be in specific case a minor part of the targeted elements (see Fig.…”

Potential aquifer vulnerability in regions down-gradient from uranium in situ recovery (ISR) sites

“…Up until about 1981, virtually all of these sites utilized alkaline reagents such as ammonia-or sodium-carbonate/ bicarbonate. The difficulty of restoring ammonia-based sites led to a quick shift in emphasis to sodium bicarbonate-or carbon dioxide-based leaching chemistry by the early 1980s (Anastasi and Williams, 1984;Mudd, 2001). State-of-the-practice today in the US involves using O 2 and CO 2 gas in the initial injection solution (Campbell et al, 2007;NRC, 2009a,b;Johnson et al, 2010), which also accomplishes the oxidation and aqueous-complexing requirements to enhance uranium dissolution.…”

“…Increasing pH>~8 can liberate Se and As oxyanions sorbed onto iron-oxyhydroxides (Smedley and Kinniburgh, 2002;Goldberg, 2014), and this can be a trigger to mobilize these anions and impact down-gradient water resources in situations where natural attenuation processes are insufficient to sequester these arsenic and selenium anions. Table 2 provides groundwater quality data for selected metals prior to ISR and after aquifer restoration at several sites in Wyoming and Nebraska (Anastasi and Williams, 1984;Davis and Curtis, 2007;Borch et al, 2012). The water quality data indicate that several trace metals and anions including As, Se, Mo, V, Mn, Fe, U, Ra, and sulfate are likely to be liberated during ISR and may remain in groundwater even after post-ISR restoration efforts are completed.…”