75Se radioisotope adsorption using Turkeyʹs Reşadiye modified bentonites

The preparation of modified bentonites was studied to investigate their selenium adsorption properties in aqueous media. Turkeyʹs Reşadiye sodium bentonite was modified with hexadecylpyridinium and aluminium polyoxy cations and characterised using different techniques. The results showed that the organic- and organic–inorganic-bentonites were produced successfully with a homogenous structure, the surface charge changed from negative to positive, and the modified bentonites were thermally stable up to 200 °C. Basal spacing of bentonite varied from 1.11 nm to 1.86 nm and from 1.11 nm to 2.02 nm in the organic- and organic–inorganic-bentonites, respectively. The specific surface areas decreased from 43.66 m2/g to 3.01 and 1.93 m2/g, in bentonite, organic- and organic-inorganic-bentonites, respectively. Selenium adsorption properties were investigated with the batch technique using the prepared modified bentonites and 75Se radioactive solutions. The effects of the solid/liquid ratio, pH, reaction time, and solution concentration (SeIV) on the adsorption properties were studied. Then, second, pseudo-first and pseudo-second order kinetic models were tested to predict the adsorption constants. The pseudo-second order kinetic model fitted the results very well, revealing that the rate-limiting step is the chemical adsorption between the SeIV anions and the adsorbents. The applied Langmuir and Freundlich isotherms showed that the adsorption equilibrium followed Langmuirʹs isotherm. The results confirmed that the Se adsorption efficiency of the Reşadiye sodium bentonite can be increased from 7% up to 100%, depending on the experimental conditions and the chosen modified bentonites. Therefore, barriers containing organic- and inorganic-modified sodium bentonites were assumed to have an effective role in remediation of radioactive or nonradioactive selenium pollution in aqueous media contaminated by mining activities, fossil fuel processing and combustion, and industrial, agricultural and metallurgical processes.