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Abstract
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Bentonite is a traditional low-cost efficient adsorbent, which has high potential for heavy metal removal from wastewaters due to its abundance, chemical and mechanical stability, high exchange capacity, and unique structural properties. In the present work, bentonite and bentonite/bio-coal composite were synthesized and utilized as a natural, low-cost, and eco-friendly adsorbents for adsorption of chromium (VI) ions from aqueous solutions. Bentonite (Bent) and apricot leaves were used to produce bentonite/bio-coal (Bent/BC) composite. FT-IR, XRD, SEM/EDX map, XRF, TGA and SMB (special surface) analysis were carried out to study the characteristics of these materials. The results showed that Bent and Bent/BC have an appropriate surface and characteristics for adsorption process. The isotherm behavior of adsorption process was investigated using Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherm models. Regarding the correlation coefficient (R2) obtained from isotherm models, it was concluded that the equilibrium behavior of the process is more describable with Langmuir isotherm model than other ones. The maximum adsorption capacity (qe, mg/g) determined by Langmuir isotherm model for Bent and Bent/BC was 59.523 and 64.102 mg g−1 respectively. Based on regression coefficient values, the pseudo-second order was found suitable than first-order kinetic model. Also it has regular behavior of qe.exp with qe.cal. The amount of enthalpy (ΔH°) for the chromium(VI) ions adsorption process using Bent and Bent/BC was determined to be −23.916 and −28.273 kJ mol−1 respectively, which indicates that the adsorption process is exothermic. According to the parameters ΔH°, RL, n and E, it was determined that the chromium (VI) adsorption process using Bent and Bent/BC adsorbents is physical and desirable.
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