Presence and impact of silica and organics in uranium in-situ leaching solutions

All uranium deposits of Uzbekistan mined by in-situ leaching (ISL) method belong to the so-called sandstone type and are formed on the redox barrier, with the Loyliken deposit, belonging to the so-called basal type, formed on the gley barrier, and all the rest, belonging to the roll type - on the complex gley-sulfur-hydrogen barrier. In all cases, the initial reducing agent is carbonized plant detritus (CPD), which is charred plant flakes scattered in sandstone, usually not exceeding 1 mm in cross-section - with the difference that at the gley barrier it is the direct uranium reducing agent, and at the gley-sulfur barrier a significant part of uranium is reduced by hydrogen sulfide, which is a product of biochemical reduction of sulfate ions contained in formation water by the same CPD (the so-called sulfate- reduction reaction). Among other conditions necessary for the formation of conditioned uranium mineralization, it is required that the CPD content in the formation is not less than 0.05% per organic carbon (Сorg). At the same time, uranium concentration in almost all sandstone deposits of Uzbekistan is comparable to Сorg concentration.