High acidity- and radiation-resistant triazine-based POPs for recovery of Pd(II) from nuclear fission products

The recovery of platinum group metals (PGMS) from high-level radioactive liquid waste (HLLW) not only has a complementary role in alleviating the shortage of rare precious metals but also is helpful for the final disposal of radioactive waste. In this work, a new cationic covalent triazine framework (CTF) named as cationic pyridyl triazine polymeric network (CPTPN) is designed and synthesized by ZnCl2-catalyzed ionothermal method for recovering of Pd(II) from HLLW. The excremental results shows that palladium can be efficiently adsorbed by CPTPN from 3 M HNO3 solution via anion exchange with fast adsorption kinetics with adsorption equilibrium reached in 10 min. The adsorption isotherm for Pd(II) follows the Langmuir model, which reveals the maximum adsorption capacity (qm) of 339.8 mg g−1 and 389.7 mg g−1 at 3 M HNO3 for CPTPN-Cl and CPTPN-NO3 , respectively. Further studies show that the qm of CPTPN-NO3 in 6 M HNO3 can reach a higher level at 428.6 mg g−1, which is the highest record for Pd(II) recovery in 6 M HNO3. In addition to high thermal stability, CPTPN exhibits a good irradiation stability with excellent adsorption performance maintained after 1000 kGy of γ-irradiation. Furthermore, CPTPN has an excellent adsorption selectivity for Pd(II) in simulated HLLW. Although the selectivity of CPTPN-Cl for Pd(II) is found to be unsatisfactory due to the significant co-adsorption of Ag(I), this problem can be well solved by changing Cl− ions in CPTPN-Cl to NO3−. Both CPTPN-Cl and CPTPN-NO3 show excellent reusability in 5 adsorption–desorption cycles. Thus, CPTPN can be considered as a candidate adsorbent that can tolerate high irradiation and high acidity for selective recovery of Pd(II) from HLLW.