Removal of boron from aqueous solutions by adsorption using natural adsorbents
Yüksel, Seren (2008) Removal of boron from aqueous solutions by adsorption using natural adsorbents. [Thesis]
Official URL: http://192.168.1.20/record=b1226364 (Table of Contents)
Removal of boron ions from boron containing aqueous solutions using lignite, natural zeolite (clinoptilolite) and fly ash adsorbents was studied. This study demonstrated that boron removal was controlled by the material type and operational conditions (pH, amount of the adsorbent, adsorption time, temperature). The experiments show that a considerable amount of boron (>90 %) can be removed from water with fly ash under suitable conditions of pH 10, adsorbent amount of 100 g/L, for an adsorption time of 24 hours at 25 °C. Percentage of boron removed by zeolite and demineralized coal remained at less than 20 under the same conditions. Freundlich, Langmuir and Dubinin-Radushkevich isotherms for the adsorbents were obtained. The adsorption of boron on demineralized lignite fitted to Langmuir isotherm, whereas adsorption on zeolite was explained by Freundlich isotherm. The adsorption on fly ash was considered to fit both Langmuir and Freundlich isotherms. Dubinin-Radushkevich model was used to calculate adsorption energies (E) and for thermodynamic and kinetic analysis. Since E values are less than 8 kJ/mol, the type of adsorption resembles physical adsorption due to weak van der Waals forces. (change in Gibbs free energy)° of adsorption of boron on fly ash was found between 3 and 4.5 kJ/mol for different temperatures. The (change in entropy)° and (change in enthalpy)° values of the adsorption were 0,03 kJ/molK and 13,61 kJ/mol, respectively. To analyze the adsorption kinetically, three models were considered. The pseudo-second-order model was determined to be the most suitable for adsorption on fly ash, whereas the affect of intraparticle diffusion is also considered as significant.
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