Adsorption studies of molybdate(VI)-⁹⁹Mo onto nano zirconium hydroxide gel

Zr(OH)₄ gels have been prepared by sol-gel method using isoamyl alcohol/ammonia mixture of different concentrations. The nano Zr(OH)₄ gel obtained using 80% isoamyl alcohol and diluted ammonia (6%) gave the highest ⁹⁹Mo distribution coefficient. SEM images indicated a jelly-like appearance of the optimum Zr(OH)₄ gel. XRD analysis proved that Zr(OH)₄ gel is an amorphous material. HRTEM analysis indicated a particle size of ≤100 nm with the existence of particle aggregates. According to DLS studies, the hydrodynamic diameter was found to be 78.82 nm (with a mean number percentage of 21.1%), while zeta potential was found to be 29.2 mV N₂ adsorption/desorption chromatographic analysis calculations stated a BET surface area of 151 m²/g and an average pore diameter of 1.93 nm. Molybdate(VI)-⁹⁹Mo adsorption process onto the optimum Zr(OH)₄ gel was found to follow pseudo 2nd order and (to some extent) film diffusion mass transfer kinetic models. The adsorption isotherm was found to follow Langmuir model. From kinetic and adsorption isotherm studies it could be determined that the optimum Zr(OH)₄ gel has E_a, ΔH° and ΔS° values of 31.29, 50 and 0.185 kJ/mol, respectively, in addition to ΔG° values of -5.09, -7.86 and -11.56 kJ/mol at 25, 40 and 60 °C, respectively. Static molybdate(VI)-⁹⁹Mo capacity (determined from Langmuir adsorption model) was found to be 292.4, 333.3 and 357.1 mg/g at 25, 40 and 60 °C, respectively, while dynamic capacity was found to be 134.3 mg/g at 25 °C.