FRACTIONAL CRYSTALLIZATION LABORATORY TESTING FOR INCLUSION & COPRECIPITATION WITH ACTUAL TANK WASTE

Abstract

Fractional crystallization is being considered as a pretreatment method to support supplemental treatment of retrieved single-shell tank (SST) saltcake waste at the Hanford Site. The goal of the fractional crystallization process is to optimize the separation of the radioactivity (radionuclides) from the saltcake waste and send it to the Waste Treatment and Immobilization Plant and send the bulk of the saltcake to the supplemental treatment plant (bulk vitrification). The primary factors that influence the separation efficiency are (1) solid/liquid separation efficiency, (2) contaminant inclusions, and (3) co-precipitation. This is a report of testing for factors (2) and (3) with actual tank waste samples. For the purposes of this report, contaminant inclusions are defined as the inclusion of supernatant, containing contaminating radionuclides, in a pocket within the precipitating saltcake crystals. Co-precipitation is defined as the simultaneous precipitation of a saltcake crystal with a contaminating radionuclide. These two factors were tested for various potential fractional crystallization product salts by spiking the composite tank waste samples (SST Early or SST Late, external letter CH2M-0600248, ''Preparation of Composite Tank Waste Samples for ME-21 Project'') with the desired target salt and then evaporating to precipitate that salt. SST Early represents the typical composition of dissolved more » saltcake early in the retrieval process, and SST Late represents the typical composition during the later stages of retrieval. « less