Investigation on effects of ion exchangers structure and functional groups on the Re(VII) ions adsorption behavior from aqueous solution
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©, © The Korean Society of Mineral and Energy Resources Engineers (KSMER). Alteration adsorption properties of Re(VII) on two resins with different functional groups and structure, weak base/macroporous and strong base/gel type, Purolite A170 (A170) and Dowex 21K (21K) respectively, were investigated experimentally and interpreted by isotherm, kinetic and thermodynamic modeling. Following the comparison of coefficient of determination values, the Freundlich and D-R isotherm models were found to be more suitable for description of investigated systems (R2 > 0.99). The Langmuir isotherm capacities (qm) were indicated that the perrhenate ions (ReO4-) adsorption is higher for weak base/macroporous type resin rather than the other at pH 3 in the presence of 50–250 mg L-1Re (166.67 and 142.86 mg g-1, respectively). Also, the results from EDX studies corroborated this phenomenon. The adsorption reaction on both adsorbents was found to be chemically with mean free energy, E, as 12.18 and 13.62 kJ mol-1for A170 and 21K, respectively. Kinetics of adsorption was studied by fitting the data into different mechanisms, among which the pseudo-second order mechanism was found successful for both used resins, but in case of 21K, the rate of perrhenate ions uptake was more rapid than A170. That is possibly attributed to the presence of strong base (quaternary amine) in functional groups. ?G values obtained were all negative for both resins indicating a spontaneous adsorption process. The positive values of both ?H (3.34 kJ mol-1) and ?S (27.31 J mol-1 K-1) obtained suggest an endothermic reaction and in increase in randomness at the solid–liquid interface during the adsorption onto the A170 resin while for 21K, the negative changes in enthalpy and entropy provide an indication that the process is endothermic as well as it follows associative mechanism.
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