Mechanisms of Sorption of Cesium and Strontium by Ferrocyanide-Modified Clinoptilolite at Their High Concentration in Solutions

The kinetics of cesium and strontium sorption by natural clinoptilolite and its ferrocyanide-modified analogs, NPF-Cl and NPF-Cl (Ca-form), from solutions of various compositions containing 100 mg L–1 sorbate was studied, and the texture and porosity of the sorbent samples before and after the sorption of cesium and strontium were determined. The sorption process occurs in three-stages and is limited by a heterogeneous ion exchange reaction (HIOR) on the ferrocyanide phase located on the outer surface of clinoptilolite and in its macropores, internal diffusion of cesium and strontium into sorbent granule, and precipitation of ferrocyanide phases of complex composition in small mesopores and micropores of sorbents. The HIOR and precipitation occur with involvement of solution components (sodium, calcium, and iron). Sorption of cesium and strontium is accompanied by a significant change in the texture and porosity of the sorbents.