High-gradient magnetic separation for the treatment of high-level radioactive wastes

Argonne National Laboratory is developing an open-gradient magnetic separat ion (OGMS) system to fractionate and remove nonglass-forming species from h igh-level radioactive wastes (HLW); however, to avoid clogging, OGMS may re quire high-gradient magnetic separation (HGMS) as a pretreatment to remove the most magnetic species from the HLW. In this study, the feasibility of u sing HGMS in the pretreatment of HLW was demonstrated. A HLW simulant of Ha nford's C-103 tank waste, which contained precipitated hydroxides and oxide s of Fe, Al, Si, and Ca, was used. Preliminary fractionation results from a 0.3-T bench-scale HGMS unit showed that a significant amount of Fe could b e removed from the HLW simulant. Between 1 and 2% of the total Fe in the sl udge was removed during each stage, with over 18.5% removed in the 13 stage s that were carried out. Also, in each stage, the magnetically retained fra ction contained about 20% more Fe than the untreated HLW; however, it also contained a significant amount of SiO2 in relatively large particles. This indicated that SiO2 was acting possibly as a nucleation agent for Fe (i.e, an Fe adsorbent) and that the fractionation was based more on size than on magnetic susceptibility.