prevent clogging of pumps and pipelines. For in-tank pro-Bimodal suspensions of nanometer-sized boehmite particles and cessing steps such as sludge washing and leaching, sludges micron-sized gibbsite particles in 0.10 M NaNO 3 are used as modmust exhibit rapid sedimentation, yielding sedimented els to gain insight into the physical properties of agglomerating sludges with the highest possible packing densities to colloidal suspensions containing bimodal distributions of primary achieve efficient solid/liquid separations.
particles. Results on the gibbsite-boehmite mixtures show that the
Unfortunately, a bewildering array of sludge types exist, presences of small particles in a suspension can have a dramatic containing a wide range of particle sizes, shapes, and compoimpact on the rheological, sedimentation, and filtration charactersition. The range in sludge types is reflected in a wide range istics of suspensions of larger particles. Transmission electron miof observed slurry properties. Viscosities measured for slurcrographs show that boehmite forms a coating on the larger gibbsite particles. The coating provides steric repulsion and reduces ries containing colloidal oxides representative of sludges can the attractive interactions between the larger particles, leading to range from less than 10 cP to more than 25,000 cP at solids viscosity decreases and greater densification of sediments and filter loading of only a few volume percent. Some sludges exhibit cakes. A model has been developed to rationalize observed proprapid sedimentation and yield sediment cakes with solids erty changes based on the range of agglomerate structures that loading in excess of 5 vol%. Other sludges exhibit negligible can form in mixtures of large and small particles. Results are sedimentation at solids loadings as low as 1 vol% (3). Difdiscussed in the content of the processing of nuclear waste sludges, ferences in sludge behavior are associated with the formation but are applicable to a wide range of bimodal suspensions. ᭧ 1997