On 30/1/2022 , Khawla Qamhieh published a new study in Colloids and surfaces A: Physiochemical and engineering aspects titled The retention of multivalent pollutants in mineral layers. The article aimed to investigate the sorbent of radioactive pollutants on montmorillonite Clay in order to remove radioactive pollutants in aqueous solution, as clay has great potential for ion exchange technique. The results of this study demonstrated that the high retention capacity of clay minerals allows them to be used as ion exchangers providing an effective barrier against radioactive migration. In our study we applied the grand canonical Monte Carlo (MC) simulations to describe the ion exchange or competition between the counterions of different valences. Our study shows that the surface charge density is an important parameter affecting the competition between different cationic species, and the multivalent species will be more abundant in the double layer for high values of |σ|, where the surface charge densities used here, 0.7–3 e/nm2, are such that in the presence of di- or multivalent cations ion-ion correlations will play a spectacular role. These results are in good agreement with what Voukadinova et al. describe in their study for the energetics of counterion adsorption in the electrical double layer [42]. The retention capacity of the pollutants quantified by the proposed equation for retention coefficient γ _is dependent on the valence of the pollutants, the surface charge density, and on the bulk concentrations of the pollutants and of other cations, monovalent, or divalent ones. It is found that the retention is increased by increasing the valence of the pollutants, and the surface charge density. While it is decreased by increasing the bulk concentration of the pollutants and of other cations in agreement with the results previously reported for sorption of various ions on a variety of sorbent [25]. The retention coefficient calculated with Poisson-Boltzmann (PB) theory is underestimated by one or two orders relative to the one calculated with Monte Carlo (MC) simulations because of the neglect of ion-ion correlations in the mean-field PB theory. Our results prove that the primitive grand canonical Monte Carlo (MC) simulations is an excellent and safe method to analyze the sorption of multivalent radioactive pollutants by montmorillonite clay modeled as DL. Also, prove that the proposed equation for retention coefficient γ _is a good tool to quantify the ion exchange between the counterions of different valences in montmorillonite clay. Furthermore, the agreement of our results with the previous studies emphasizes the strength and the credibility of our approach. This approach and γ _equation for retention coefficient may be of great help in analyzing ion exchange method for extracting and recovering radioactive pollutants from aqueous solutions to assure clean and healthy ground water.
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