The study of physicochemical and sorption characteristics of nickel and iron hexacyanoferrates with respect to cesium

Abstract

The decontamination of liquid media contaminated by anthropogenic radionuclides provides a serious technological challenge. Sorption methods are often used to perform this task. The paper studies the physico-chemical and sorption characteristics of pure samples of iron (samples 1 and 2) and nickel (samples 3 and 4) hexacyanoferrates with respect to caesium radionuclides. It is shown that iron hexacyanoferrates have better granulometric composition than nickel hexacyanoferrates due to a smaller quantity of fine fraction (0.5-10 µm), thus providing for easier sedimentation and filtration. The results of thermal gravimetric and differential thermal analysis have shown that the lower limit of thermal stability of all hexacyanoferrates was at least 200°С. This means that spent sorbents can be dried at 100–150°С. Nickel hexacyanoferrates demonstrated a slightly higher thermal stability as compared with iron hexacyanoferrates. The experiment performed with simulated solutions demonstrated that pH does not affect the sorption of caesium by hexacyanoferrates with the рН range of 0.5 to 11.5. The distribution coefficients of caesium varied from 3·104 to 3·105 cm3/g. The effect of sodium and potassium on the sorption of cesium by iron and nickel hexacyanoferrates was studied at the concentrations of Na+ and K+ of up to 5 mol/dm3. The study demonstrates that the sorption of caesium by iron hexacyanoferrates does not depend on sodium and potassium concentration; whereas in case of nickel hexacyanoferrates distribution coefficients of caesium slightly decrease with concentrations of sodium and potassium of 1 mol/dm3and higher. However, distribution coefficients of caesium remained at least 104 cm3/g under any of the conditions studied. Ammonium ions showed significantly stronger suppressing effect on caesium sorption at the concentration of 0.5 mol/dm3, which can be explained by similar ionic radii of hydrated Cs+ and NH4+. Thus, the iron and nickel hexacyanoferrates can be recommended for caesium separation from a wide spectrum of acidic, neutral, slightly alkaline and salty intermediate-level liquid radioactive wastes. © 2021 MEDICC Review. All rights reserved.