Magnetic ternary nanocomposite from ultra-purified metakaolin for radioactive decontamination: sorption mechanisms...

Magnetic geopolymer nanocomposites are novel materials at the forefront of material science, with the potential to revolutionize innovative applications. Ultra-purified metakaolin (U-PMK) was used to synthesize a plain MK-based geopolymer (UPMK100), along with eight binary and ternary nanocomposites incorporating nano-sized U-P kaolin and γ-Fe₂O. This broad spectrum yielded six magnetic nanocomposites. Preliminary sorption experiments of ¹³⁴Cs onto the nine sorbents were designed and assessed using the response surface methodology. Both U-PMK100 and its magnetic ternary (MU-PMK80) nanocomposite were the best choices. Microstructures of both sorbents along with their raw materials were characterized using different techniques. The saturation magnetization of MU-PMK80 recorded the highest value in literature (5.85 emu/g). Batches for the removal of ¹³⁴Cs, ⁶⁰Co, and ^152+154Eu onto U-PMK100 and MU-PMK80 were designed, and the highest experimental percentage removal was given to MU-PMK80 (¹³⁴Cs > ⁶⁰Co > ^152+154Eu; 47.53, 35.00, and 21.00 mg/g at 333 K, respectively). Data were analyzed using Langmuir, Freundlich, and D-R isotherm models. All radionuclides were heterogeneously chemisorbed onto U-PMK100, while only ^152+154Eu was monolayered sorbed onto MU-PMK80. Values of the mean free energy revealed that sorption of ¹³⁴Cs was controlled by a chemical sorption mechanism, while ⁶⁰Co and ^152+154Eu belong to the particle diffusion one, for both sorbents. The thermodynamic parameters indicated that ¹³⁴Cs and ⁶⁰Co radionuclides were spontaneously sorbed, while ^152+154Eu sorption became spontaneous only at 333 K.