Treating Nuclear Waste With Sulfides

Metal sulfides may make it easier to remove radioactive strontium-90 from nuclear waste (Proc. Natl. Acad. Sci. USA, DOI: 10.1073/pnas.0711528105). To minimize the need for waste storage space, handlers would like to be able to remove ⁹⁰Sr from bulk waste so they can immobilize and store just the radioactive component. Common adsorbents, however, may decompose in the extremely alkaline environment of many waste streams. These streams also have high salt concentrations that challenge selective uptake of Sr²⁺. Now, a research group led by Mercouri G. Kanatzidis of both Northwestern University and Argonne National Laboratory has found that layered metal sulfides may circumvent those problems. The material, K₂xMnxSn_3-xS₆ (x = 0.5-0.95, shown), is composed of MnS₆ and SnS₆ octahedra connected through the sulfur ligands with exchangeable K⁺ ions located between the layers. The researchers found that the layered sulfide removed more than 92% of Sr²⁺ from solutions ranging from pH 3.2 to pH 14.0. The material was also selective for Sr²⁺ in strongly alkaline environments incorporating cations from Groups 1 and 2.