TITLE:
Sorption Kinetics of 152Eu to Different Granitic Materials in Carbonate Systems
AUTHORS:
Fidelis Sameh Ebong, Gillian Nkeudem Asoba, Nick Evans
KEYWORDS:
Sorption Kinetics, First Order, Second Order, Intraparticle Diffusion
JOURNAL NAME:
Journal of Geoscience and Environment Protection,
Vol.14 No.9,
September
29,
2026
ABSTRACT: Granitic rocks are being considered as burial sites for high- and medium-level radioactive wastes by many countries. These rocks have predominantly three mineral phases, which include mica, quartz and feldspars. The rate of inorganic ion sorption on mineral surfaces is not well understood, partly because of the complex processes occurring at mineral-water interfaces. Estimation of the kinetic functions and appropriate sorption constants from batch experiments can provide an insight into the sorption processes. This work aims at determining rate constants and reaction orders. Sorption kinetic experiments were conducted using granitic rock and component minerals to understand how different carbonated systems will affect the rate constants and to determine the rate constant and see which sorption mechanisms are dominant. The granitic rocks and minerals were first reduced in size. Samples were crushed and pulverised using a ball mill and sieved to obtain a particle size range of 46 to 250 μm. 0.2 g of the pulverised samples were mixed with 40 cm3 of non-active research-grade EuCl3 solution, giving a solid-liquid ratio of 1:200. Experiments with 152Eu were analysed using the Cobra(II) Auto Gamma counting between 100 to 1500 keV at 2 sigma. 1 × 10−5 mol∙dm−3 solutions of EuCl3 were prepared. Different amounts of carbonate were added into the solution to give carbonate concentrations of 1 × 10−2 and 1 × 10−6 mol∙dm−3 for high carbonate (HC) and low carbonate (LC) systems, respectively. The results for BG showed that data fitted best to the Langmuir model with saturation of sorption sites. This is evident from the Langmuir linearised isotherm. R2 values for CF, LC and HC systems were close to one. Calculated Rd values showed the effect of carbonate for sorption in the three systems. Mean Rd values were calculated as 97 cm3∙g−1 for CF, 81 cm3∙g−1 for LC and 21 cm3∙g−1 for HC systems. Thus, the Rd decreased as the concentration of carbonate increased in solution. Using the linearised Langmuir isotherms, the maximum concentrations of Eu bound after 520 hours were calculated as 7.8 × 10−6, 7.7 × 10−6, and 6.9 × 10−6 mol∙dm−3 for CF, LC and HC systems, respectively. Sorption was fast initially, and reached saturation at longer equilibration times (desorption observed for Eu sorption to MM in CF system above 42 h equilibration). The presence of carbonate in solution altered the overall speciation of the metal in solution, which can affect sorption rates. Results showed that sorption to mica was not strongly dependent on intraparticle diffusion. Pseudo-second order rate constants were calculated for samples and for mica, the constants for CF, LC and HC systems were −980, −7.3 and −3.7 (mol∙g−1∙h−1), respectively. Overall, the study was able to determine first- and second-order rate constants, which can be used in geochemical models to understand sorption mechanisms for granitic rocks and minerals.