TITLE:
Application of Surface Complexation Model to 63Ni Sorption to Selected Granitic Rocks and Minerals: Sorption at Varying pH
AUTHORS:
Fidelis Sameh Ebong, Gillian Nkeudem Asoba, Frederick Ngolemasango Ediage, Nick Evans
KEYWORDS:
Surface Complexation, Sorption, Granitic Materials
JOURNAL NAME:
Journal of Geoscience and Environment Protection,
Vol.13 No.4,
April
18,
2025
ABSTRACT: The immobilisation of radionuclides in groundwater environments cannot be explained solely by the empirical models. These empirical models are not sensitive to the varying conditions that are found in nature. Sorption has been shown to be very sensitive to pH, Eh and ionic strength of the solution in which the radionuclides are found. Batch sorption experiments at different ionic strengths were conducted and LogK constants for the sorption processes were determined. JChess Geochemical code was used to compare experimentally and predicted Log K constants obtained from surface complexation reactions with different granitic rock samples. For pH dependent sorption, 1 × 10−5 mol·dm−3 solutions of NiCl2 were prepared, and the pH was adjusted from 4 to 11, with intervals of 0.6 to 0.8 on the pH scale using NaOH (aq) and HCl (aq). Different concentrations of pH adjusting solutions were made from very weak to very strong acid or base. Sample separation was performed and counting was performed for Ni using the scintillation counter. Packard TRI-CARB 2750 TR/LL Liquid Scintillation Counter: Used for Ni sorption studies, counting from 0 to 67 keV to 2σ. Results showed varying sorption properties from one granitic mineral to the other. There was no effect of ionic strength on the sorption of Ni to Muscovite Mica (MM). Varying pH sorption isotherms for Ni sorption to Orthoclase Feldspar, showed experimental data and modelled matched for monodentate and bi dentate sorption using the same experimental conditions, modelling done assuming mono and bidentate complex formation. The following conclusions can be made after studying varying pH sorption profiles of selected granitic rocks and mineral in different NaCl concentrations, using different models. Ni sorption is suppressed in the presence of NaCl, due to competition for the sorption sites.