SILICA FOULING OF ANION-EXCHANGE RESINS IN URANIUM IN-SITU RECOVERY: CURRENT UNDERSTANDING AND REGENERATION APPROACHES

Abstract

The growing share of in-situ leaching (ISL) in global uranium mining is increasing the demands on the efficiency of ion-exchange processing of pregnant solutions. Strongly basic anion exchange resins that sorb uranyl sulfate or uranyl carbonate complexes are typically used for uranium extraction. Over long periods of operation, their properties deteriorate due to the accumulation of silicon compounds released into the solution during the leaching of silicate rocks. This review examines the mechanisms of silicon fouling of anion exchange resins used in ISL, as well as existing methods for desilication and regeneration. An analysis of scientific publications and technical materials shows that fouling is primarily due to the penetration of silicic acid into the resin pores and its subsequent polymerization. With localized increases in pH, silicate anions can also interact with exchange sites. The formation of oligomeric and polymeric siloxane structures hinders mass transfer, blocks active sites, and reduces the uranium sorption capacity. Alkaline treatment with NaOH and fluoride-containing reagents are used for regeneration. Alkaline solutions are technologically simpler, but less effective against highly polymerized silica phases and, under harsh conditions, can damage the resin. Fluoride systems provide deeper silicon removal but place increased demands on the corrosion resistance of equipment and wastewater treatment. Therefore, the regeneration process must ensure silicon removal without significantly reducing the mechanical strength and sorption properties of the resin.