Removal of Boron from aqueous solutions by adsorption using fly ash, zeolite and demineralized lignite

In the present study for the purpose of removal of boron from water by adsorption using adsorbents like fly ash, natural zeolite and demineralized lignite was investigated. Boron in water was removed with fly ash, zeolite and demineralized lignite with different capacities. 94% boron was removed using fly ash. Batch experiments were conducted to test removal capacity, to obtain adsorption isotherms, thermodynamic and kinetic parameters. Boron removal by all adsorbents was affected by pH of solution; maximum adsorption was achieved at pH 10. Adsorption of boron on fly ash was investigated by Langmuir, Freundlich, Dubinin-Radushkevich models. Standard entropy and enthalpy changes of adsorption of boron on fly ash were, =S0 = -0.69 kJ/mol K and =H0 = -215.34 kJ/mol, respectively. The negative value of S0 indicated decreased randomness at the solid/solution interface during the adsorption boron on the fly ash sample. Negative values of H0 showed the exothermic nature of the process. The negative values of G0 implied that the adsorption of boron on fly ash samples was spontaneous. Adsorption of boron on fly ash occurred with a pseudo-second order kinetic model, intraparticle diffusion of boron species had also some effect in adsorption kinetics

Removal of boron from aqueous solutions by adsorption using natural adsorbents

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