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Pyrolysis of spent ion exchange resins is used to reduce radioactive waste volume and to make the final waste form more stable. The weight loss of cation exchange resin after pyrolysis is only 50%, while that of anion exchange resin is 90%. Fundamental experiments were performed to investigate the reason for the small weight loss of the former. The cation resin consists of base polymer and functional sulfonic acid groups. Chemical analyses •of the pyrolysis products showed that 65% of the functional groups decomposed at about 300°C and generated S0 2 gas. However, only a small amount of the base polymer was pyrolyzed even at 600°C and the weight loss was only 50%. TheIR and XPS studies on the residue showed that 35% of the functional sulfonic acid groups was converted to sulfonyl and sulfur bridges between the base polymers during pyrolysis. These bridges made the base polymers thermally stable. Therefore, the small weight loss of the cation resin was attributed to formation of bridges, which originated from the functional groups.

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