Adsorption of strontium on different sodium-enriched bentonites

Abstract

Bentonites from three different deposits (Wyoming, TX, USA and Bogovina, Serbia) with similar cation exchange capacities were sodium enriched and tested as adsorbents for Sr 2+ in aqueous solutions. X-Ray diffraction analysis confirmed successful Na-exchange. The textural properties of the bentonite samples were determined using low-temperature the nitrogen physisorption method. Significant differences in the textural properties between the different sodium enriched bentonites were found. Adsorption was investigated with respect to adsorbent dosage, pH, contact time and the initial concentration of Sr 2+. The adsorption capacity increased with pH. In the pH range from 4.0-8.5, the amount of adsorbed Sr 2+ was almost constant but 2-3 times smaller than at pH ≈11. Further experiments were performed at the unadjusted pH since extreme alkaline conditions are environmentally hostile and inapplicable in real systems. The adsorption capacity of all the investigated adsorbents toward Sr 2+ was similar under the investigated conditions, regardless of significant differences in the specific surface areas. It was shown and confirmed by the Dubinin-Radushkevich model that the cation exchange mechanism was the dominant mechanism of Sr 2+ adsorption. Their developed microporous structures contributed to the Sr 2+ adsorption process. The adsorption kinetics obeyed the pseudo-second-order model. The isotherm data were best fitted with the Langmuir isotherm model.

Discussion on the Comments of Slobodan K. Milonjic on the article entitled Adsorption of strontium on different sodiumenriched bentonites by Sanja R. Marinovic, Marija J. Ajdukovic, Natasa P. Jovic-Jovicic, Tihana M. Mudrinic, Bojana N. Nedic-Vasiljevic, Predrag T. Bankovic and Aleksandra D. Milutinovic-Nikolic, published in the Journal of the Serbian Chemical Society, vol. 82, issue 4, 2017, pp. 449-463

“…2 It is worth emphasizing that the original paper was already revised in the manner suggested by the Reviewers and the Editor of the Journal of the Serbian Chemical Society. Therefore, the authors will avoid potential further polemics with Dr Milonjić regarding the Marinović et al 1 paper that might become excessive. where c 0 and c t are the concentrations (mg dm -3 ) of Sr 2+ in a solution initially and after adsorption time t, respectively, V is the volume of solution (dm 3 ) and m ads is the adsorbent mass.…”

“…After the scientific paper entitled "Adsorption of strontium on different sodium-enriched bentonites", by Marinović et al 1 had been published, it was commented on by Milonjić. 2 The authors of the paper 1 have thoroughly considered all the comments.…”

“…Low values of the coefficient of determination (R 2 ) obtained for the Freundlich model suggested that the Freundlich model is not appropriate for the investigated system. Therefore, the Freundlich adsorption constant (n) was not taken into consideration in the paper by Marinović et al 1 for the determination of the nature of the investigated process. Hence, the conclusions drawn from the isotherm analysis were not in disagreement, as stated by the critic.…”