Adsorption and separation behavior of palladium(II) from simulated high-level liquid waste using a novel silica-based adsorbents

Aiming at selective adsorption and separation of Pd(II) in nitric acid solution, a hybrid soft N and hard O donor adsorbent (TAMIA-EH+TOA)/SiO2-P (P = Polymer) was successfully synthesized. The adsorption performances of (TAMIA-EH+TOA)/SiO2-P adsorbent towards Pd(II) were systematically investigated as a function of contact time, effect of concentration of nitric acid, effect of temperature etc. Adsorption speed of Pd(II) was fairly fast and can reach equilibrium state within only 0.5 h. The distribution coefficient of Pd(II) was more than 103 when [HNO3] = 0.1. Though it decreased gradually with an increase in the concentration of HNO3, the adsorption selectivity of (TAMIA-EH+TOA)/SiO2-P adsorbent towards Pd(II) was still significant than other co-existing metal ions in the whole HNO3 range from 0.1 to 5 M. The adsorption isotherm of Pd(II) onto (TAMIA-EH+TOA)/SiO2-P adsorbent fitted well with Langmuir adsorption model but Freundlich isotherm model. The calculated results of adsorption thermodynamic parameters indicated that the adsorption process of Pd(II) was exothermic and happened in a natural way. Furthermore, the separation chromatography experiment by utilizing (TAMIA-EH+TOA)/SiO2-P adsorbent packed column was carried out. Based on the results of plotted elution curves, it was found that the successful recovery of Pd(II) (96.27%) was achieved by eluting with thiourea solution.