a phenolic , cesium - specific , cation exchange resin is prepared by neutralizing resorcinol with potassium hydroxide , condensing / polymerizing the resulting intermediate with formaldehyde , heat - curing the resulting polymer to effect cross - linking and grinding it to desired particle size for use . this resin will selectively and efficiently adsorb cesium ions in the presence of a high concentration of sodium ions with a low carbon to cesium ratio .