(477c) The Nature and Quantity of Solids Suspended in Hanford Nuclear Waste Supernatants

The Hanford Site contractors are currently designing and constructing a waste treatment process to treat highly concentrated sodium-bearing supernatants. The treatment process is expected to require suspended solids removal. In order to design the solids removal process, basic properties of suspended solids (size, density, chemical composition, shape, abrasively, quantity, etc.) are required. In order to provide insight in the solids characterization, a three pronged approach was taken: 1) Evaluate historic records on the solids concentration in supernatant grab samples; 2) characterize two samples that contained a floating solids layer at the surface; and 3) perform filtration studies of waste supernatants to characterize those solids that are not visible. The historic records indicated that the overwhelming majority of grab samples had no visible solids, however, 5 out of 163 had between 0.1 and 0.5 volume % solids. The characterization of floating solids indicated that they could be large and be smooth-surfaced aggregates. Particulates made of the aggregates could be up to 200 microns in diameter. Such solids were suspended by complex reactions of saponification, adsorption of organics, and available surface area for the adsorption of organics. The filtration studies determined that other suspended solids were simply very small particles, usually less than 2 microns in diameter, that were extremely slow to settle. These include both organic and metalloid particles.