Stability of ion exchange resin under freeze-thaw or dry-wet environment

Ion exchange resins have widely been used in mineralization studies of organic materials. However, the stability of resin (anionic and cationic) under changing physical environmental conditions is not well known. Our objective was to evaluate N and P adsorption or desorption characteristics of resins exposed to freeze-thaw or dry-wet cycles. Mixed bed resins (1:1 oven-dry mass strong base anion A464-D and strong acid cation C-249) were subjected to 0,1, and 30 freeze-thaw or dry-wet cycles. To accomplish the dry-wet cycles, fresh resin was kept in a forced-air oven at 25 (±2)°C for 28 h and rewetted to initial moisture condition for 20 h. To accomplish the freeze-thaw cycle, fresh resin was frozen for 16 h and thawed to room temperature for 8 h daily. At the end of the freeze-thaw or dry-wet cycles, resin was equilibrated with 3.2 mM L^-1 NH₄-N, 3.2 mM L^-1 NO₃-N, or 0. 97 mM L^-1 PO₄-P for a period of 1 h. Dry-wet cycles induced desorption of N and P associated with shrinkage of resins and expulsion of interstitial liquid. At the highest dry-wet cycle, 3.3, 0.35, and 0.15% of the total adsorbed PO₄-P, NH₄-N, and NO₃-N was desorbed, respectively. Scanning electron microscopy (SEM) revealed that the dry-wet or freeze-thaw cycles did not alter the physical integrity of these resins. Freeze-thaw cycles had no effects on N and P adsorption or desorption characteristics of resins of the specific resins used in this study. Ion exchange resins used for in situ nutrient monitoring should be screened using similar techniques to assess its adsorption and desorption stability and physical integrity to fluctuating environmental conditions. Resin types and stability should be mentioned when comparisons are made to other studies.