GEL Adsorption Processing for Waste Solidification in 'NZP' Ceramics

Abstract

ABSTRACTSimulated PW-4b waste solution along with Na additive was mixed with Zr-P-O gel, dried and then fired to form the desired sodium zirconium phosphate, NaZr2 (PO4) 3 [NZP] ceramic. NZP and monazite were the only phases produced upon firing at 900°C with 10 to 40% of PW-4b mixed with the gel. CsZr2(PO4) 3 which is isostructural with NZP was also identified when fired under reducing conditions. The -200 mesh powders of these waste forms prepared under reducing conditions showed excellent leach resistance under hydrothermal conditions.Alternatively, PW-4b and Three Mile Island (TMI) wastes were adsorbed on Zr-P-O gel in a column. The gel was dried, pelletized and fired to form the desired [NZP] ceramic. Cesium was found to be selective on the Zr-P-O gel because no breakthrough of Cs was detected up to 38 column volumes of TMI waste. Thus, it is possible to use a tailored gel to sorb Cs and/or Sr from accident waste water and then fired the bed to form the [NZP] ceramic below 1000°C. The main advantages of the gel adsorption process are its simplicity and its enormous compositional flexibility.