Potassium nickel hexacyanoferrate–polyacrylonitrile composite for removing cobalt, strontium, and cesium from radioactive laundry wastewater

The applicability of potassium nickel hexacyanoferrate–polyacrylonitrile (KNiFC–PAN) for the sorption of Co²⁺, Sr²⁺, and Cs⁺ from radioactive laundry wastewater generated in nuclear power plants was investigated. Competitive sorption of Co²⁺, Sr²⁺, and Cs⁺ onto KNiFC–PAN was studied for single, binary, and ternary solutions. The Langmuir, Freundlich, Kargi–Ozmıhci, Koble–Corrigan, and Langmuir–Freundlich models predicted the single-sorption data (R² ≥ 0.942, sum of squared error ≤ 0.105). The sorption isotherms were nonlinearly favorable (Freundlich coefficient, N_F = 0.288–0.842). According to the Langmuir, Freundlich, Kargi–Ozmıhci, Koble–Corrigan, and Langmuir–Freundlich models, at pH 5 (C₀ = 20 mM), KNiFC−PAN exhibited the highest maximum sorption capacity (q_mL) for Cs⁺ among the investigated cations, wherein the primary mechanism was physical sorption. The competition between the metal ions in the binary and ternary systems reduced the respective sorption capacities. Binary and ternary sorption models, such as the ideal adsorbed solution theory (IAST) model coupled with Freundlich (IAST–Freundlich), IAST–Langmuir, and IAST–Langmuir–Freundlich models, were fitted to the experimental data; among these, the IAST–Freundlich model was the most accurate for the binary and ternary systems. The presence of sodium 4-n-octylbenzenesulfonate and dodecylbenzene–sulfonic acid sodium salt as anionic surfactants strongly affected the sorption capacity on KNiFC–PAN owing to increased distribution coefficients (K_d) of Cs⁺, Sr²⁺, and Co²⁺. Thus, KNiFC–PAN is promising for removing Cs⁺, Sr²⁺, and Co²⁺ from radioactive laundry wastewater.