The catalytic behavior of Sr2+, Cs+, and NO3− in the molten salt oxidation of waste mixed resin

• The CH 2 N(CH) 3 and SO 3 H in the mixed resin convert into nitrate and sulfate in melt successively. • The nitrate can catalyze the oxidation of the resin and promote production of sulfate. • After functional groups destruction, Sr 2+ and Cs + promote the oxidation of resin in the melt. Waste mixed resin (MR) doped with Sr 2+ and Cs + is harmful to the environment. MR can be safely decomposed via molten salt oxidation (MSO) in Li 2 CO 3 -Na 2 CO 3 -K 2 CO 3 melt. During the MSO process of MR, the quaternary ammonium groups and sulfonic acid groups decompose to form nitrate and sulfur compounds in the temperature ranges of 473–523 K and 573–623 K, with average activation energies of 252.08 kJ/mol and 391.77 kJ/mol, respectively. Compared with binary carbonates, ternary carbonates, with a lower melting point of 393℃, is conducive to the formation of nitrates,which can increase the destruction and removal efficiency (DRE) values of MR to 65.12 %. The sulfate level in waste salt obtained after subjecting MR to MSO reached 25.4 % at 773 K, which is higher than that of the cation-exchange resin (823 K, 20.2 %). Moreover, the presence of NO 3 − encouraged the production of O 2− in the molten salt. Changes in the E O2 values of the reactions for O 2− generation in carbonate and nitrate salts were calculated by HSC Chemistry 6.0. When the metals are Na and K, the E O2 of nitrate is more negative than that of carbonate. Linear sweep voltammetry shows that E O2 shifts from 0.67 V, 0.52 V, 0.75 V, and 0.61 V to 0.22 V, 0.27 V, 0.71 V, and 0.56 V, respectively. This is because nitrate, Li + , Sr 2+ , and Cs + can increase the concentration of O 2− and promote the MSO of waste MR doped with Sr 2+ and Cs + . Thus, this work firstly proves the catalytic behavior of Sr 2+ , Cs + , and NO 3 − in MSO of MR, and confirms the fact that MSO can safely process waste MR.