Precise separation and efficient enrichment of palladium from wastewater by amino-functionalized silica adsorbent

An amine-based functionalized mesoporous silica (SBA-15-TEPA) adsorbent constructed from mesoporous silica was produced to realize efficient and highly selective recovery of palladium from wastewater. SEM-EDS, TEM, TG-DSC, and N2 adsorption-desorption isotherm were used to evaluate the as-prepared SBA-15-TEPA, and the results demonstrate that the material has a good open pore structure, a high loading rate, and a sizable specific surface area. The performance analysis demonstrates that SBA-15-TEPA exhibits excellent selectivity (Separation factor of palladium for impurity ions >5565) in a broad range of acidity and good repeatability (≥5) toward palladium, good repeatability is important for clean adsorption, with a maximal capacity of 94.92 mg Pd/g at pH = 1.5 at 315 K. 0.1 M thiourea - 0.1 M HNO3 was capable of desorbing the adsorbed Pd(II) almost entirely. The mechanism of adsorption and desorption was investigated by FT-IR, XPS and DFT calculation, which proves that the coordination structure occurs mainly between N in the adsorbent and Pd(II) with NO3− participation for change balance, i.e., the strong chemical complexation between the electron pair acceptor Pd(II) and the electron pair donor N. The dynamic separation of Pd(II) by SBA-15-TEPA from simulated electroplating wastes was evaluated by column experiment, and nearly 100% recovery of Pd(II) was obtained with demonstrating outstanding enrichment coefficients (>104). SBA-15-TEPA met the requirements of dynamic adsorption experiments and successfully achieved the complete separation and high enrichment of palladium from waste liquids in high throughput. This result fills the gap where functionalized silicon-based materials could not be separated and enriched for palladium in column experiments and will also provide new ways to address palladium scarcity, environmental protection and ensure cleaner production.