Crossflow filtration testing of INEEL radioactive and non-radioactive waste slurries

Development of waste treatment processes for the remediation of radioactive wastes is currently under way at the Idaho Nuclear Technology and Engineering Center (INTEC), located at the Idaho National Engineering and Environmental Laboratory (INEEL). INTEC, formerly known as the Idaho Chemical Processing Plant, previously reprocessed nuclear fuel to retrieve fissionable uranium. Liquid waste raffinates resulting from reprocessing were solidified into a calcine material. Waste treatment processes currently being considered include the dissolution of the solidified calcine material and separation of residual undissolved solids (UDS). UDS in solution must be removed prior to downstream processes such as solvent extraction and ion exchange. Filtration experiments were conducted at the INEEL using a crossflow filter apparatus on radioactive and non-radioactive waste slurries [N.R. Mann, T.A. Todd, Evaluation and Testing of the Cells Units Crossflow Filter on INEEL Dissolved Calcine Slurries, INEEL/EXT-98-00749, Idaho National Engineering and Environmental Laboratory, Idaho Falls, ID, 1998]. The purpose of this testing was to evaluate the removal and operational efficiency of crossflow filtration on slurries of various solids loadings. The solids loadings tested were 0.19, 2.44 and 7.94 wt.%, respectively. A matrix of test patterns was used to determine the effects of transmembrane pressure and axial velocity on filtrate flux. Filtrate flux rates for each solids loading displayed a high dependence on transmembrane pressure, indicating that pressure filtration resistance limits filtrate flux. Filtrate flux rates for all solids loading displayed a negative dependency on axial velocity. This would suggest axial velocities tested were efficient at removing filter cake. Prior to testing of actual waste slurries, baseline water runs were performed. Filtrate flowrates observed during baseline water runs exhibited substantial decreases despite numerous backpulses and rinses, suggesting particles that were deeply embedded within the filter membrane as the result of shear-induced deagglomeration