Equilibrium modeling in adsorption of Re and Mo ions from single and binary aqueous solutions on Dowex 21K resin

The present study deals with the competitive adsorption of rhenium (Re) and molybdenum (Mo) ions onto Dowex 21K from single component and binary systems. The equilibrium adsorption data were obtained at different initial concentrations (50–250 mg/l), 12 h contact time, 290 K temperature, and resin dosage of 0.05 g at pH around 0.5. The single system equilibrium adsorption data were fitted via non-linear regression techniques to Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich (D–R) isotherm models. Both Freundlich and D–R isotherms for Re and Langmuir and D–R isotherms for Mo suitably described the adsorption equilibrium data. Equilibrium isotherms for the binary adsorption of Re and Mo ions onto Dowex 21K have been analyzed using Extended Langmuir, Modified Langmuir, Extended Freundlich and Langmuir–Freundlich models. The competitive Extended Freundlich model fitted the binary adsorption equilibrium data satisfactorily and adequately. Results of investigation on the mutual interference effects of Mo ions on Re adsorption capacity indicated that although Dowex 21K has generally higher affinity toward Re ions, the adsorption of perrhenate ions () is suppressed by a factor of about 49% in the presence of molybdenum ions. The adsorption of perrhenate ion is affected by competitive inhibition and shield preventing effects

Investigation on effects of ion exchangers structure and functional groups on the Re(VII) ions adsorption behavior from aqueous solution

©, © 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

Mechanism and equilibrium modeling of Re and Mo adsorption on a gel type strong base anion resin

© 2017, Pleiades Publishing, Ltd. A static-batch technique was used to demonstrate the adsorption behavior of Re (VII) and Mo ions onto Dowex 21K at equilibrium in single and binary component systems. The single equilibrium adsorption data were modeled through a linear form of four widely used equilibrium isotherm equations. The results indicated that Freundlich and D-R models for Re, and Temkin and D–R isotherms for Mo fitted the obtained data satisfactorily. Binary adsorptions of Re and Mo ions onto Dowex 21K were also analyzed using Extended Langmuir, Modified Langmuir, Extended Freundlich and Langmuir–Freundlich models. The competitive Extended Freundlich model fitted the binary adsorption equilibrium data adequately. Studies on mutual interference effects of Mo ions on Re adsorption capacity indicated that the adsorption of perrhenate ions is always suppressed. In this perspective, the results from EDX studies confirmed the rhenium atom decrease in the simulated Re–Mo adsorption. However, under the studied conditions the affinity of the Dowex 21K for rhenium ions is marginally greater than that of molybdenum ions