Highly Selective Adsorption and Recovery of Palladium from Spent Catalyst Wastewater by 1,4,7,10-Tetraazacyclododecane-Modified Mesoporous Silica

A new silicon-based adsorbent with good adsorption performance on Pd(II) was synthesized from mesoporous silica as a carrier and 1,4,7,10-tetraazacyclododecane as a functional ligand. The batch method was used to investigate and evaluate the adsorption performance of the adsorbent on Pd(II) in HCl-HNO3 solution. Influencing factors such as the contact time, pH, temperature, initial Pd(II) concentration, and elution conditions on adsorption and elution were systematically investigated and optimized. Simultaneously, adsorption kinetics, thermodynamics, and adsorption isotherms were investigated. The results revealed that under optimal adsorption conditions, the recovery rate of the adsorbent to Pd(II) could reach 98.30–99.75% in a mixed solution, which was mostly unaffected by other impurity ions. After five adsorption–desorption cycles, the recovery rate of the adsorbent to Pd(II) remained more than 93%. Pd(II) adsorption by the adsorbent was rapid within 30 min, and the recovery rate could reach 85%. In combination with density functional theory calculations, an adequate recovery mechanism was proposed to describe the selective adsorption and desorption process of Pd(II), in which the chemical adsorption dominated. As a result, this material can adsorb and recover Pd(II) with high selectivity, a rapid adsorption rate, good stability, and reusability, making it ideal for recovering waste palladium resources under acidic conditions.