Efficient separation of palladium from nitric acid solution by a novel silica-based ion exchanger with ultrahigh adsorption selectivity

Palladium (Pd) in high level liquid waste (HLLW) is a valuable alternative resource besides its natural reserves. On the other hand, the presence of Pd has extremely negative impacts on the vitrification process of HLLW. To separate Pd from HLLW, a novel silica-based adsorbent named HEMAP/SiO2-P was designed and prepared by using 2-hydroxyethyl-2-methyl-2-propenoate phosphate as the functional group donor, dichloromethane as the diluent and styrene-divinylbenzene modified silica particle as the carrier. The experimental results reveal that HEMAP/SiO2-P possesses excellent adsorption selectivity (SFPd/other metals > 183.2) and large adsorption capacity (393.4 mg/g) towards Pd in 1 M HNO3 solution. Moreover, column experiments show that the adsorbent can effectively separate Pd from other coexisting metal ions in simulated HLLW with the recovery yield of 99.4%. The experimental and characterization analyses as well as DFT calculations confirm that the adsorption mechanism involves ion exchange between Pd(II) and H+ (in P-OH) accompanied by the transfer of charge.