Fractional crystallization has been examined as a potential means of accelerating the remediation of mixed liquid waste at the Hanford Site. In the proposed process, a feed stream containing waste is partitioned by evaporating water and crystallizing a number of sodium salts. The salts are separated and ultimately treated in a bulk vitrification facility, while Cs and other radioactive species remain in solution and are sent to a waste treatment facility. The primary criterion by which performance was judged included the Cs content of the recovered crystals, the fraction of sodium recovered as crystals, and the fraction of feed sulfate that is diverted to the recovered crystals.

Previous work on fractional evaporative crystallization proved the feasibility of this method at the laboratory scale. Prior to pilot scale application, the robustness of the process was to be extended to include additional waste solutions that contained a number of organic compounds, including sodium glycolate (NaC₂H₃O₃), sodium acetate (NaC₂H₃O₂), tetrasodium EDTA dihydrate (Na₄C₁₀H₁₂N₂O₈•2H₂O), and trisodium HEDTA dihydrate (Na₃C₁₀H₁₅N₂O₇•2H₂O).

In the work to be discussed, the impact of organic compounds on the fractional evaporative crystallization process was explored. In particular, there were two major issues that were explored: (1) the effects of the organic compounds on the nucleation and growth kinetics of the inorganic sodium salts, and (2) whether or not the organic species remained in solution during the process. Either of these factors can alter the crystal size distribution and affect solid-liquid separation efficiency.

A methodology was developed in order to investigate potential interactions between organic species, along with the individual effects of each species on crystallization. Using this approach, it was determined that certain organics led to the crystallization of sodium sulfate instead of burkeite (Na₂CO₃∙2Na₂SO₄), which was the species crystallized in the absence of the organic compounds. In addition, organic species were responsible for process difficulties such as foaming during evaporation, film deposition on the crystallization equipment, and reduced solid-liquid separation efficiency.