A Liquid-Phase Precipitation Process for Selective Removal of Critical Inorganic Species from the Hanford Waste Streams

A liquid-phase precipitation (LPP) process was evaluated in a bench-scale setup for selective removal of radioactive species as well as key nonradioactive species from DOE aqueous waste streams. The DOE Hanford supernatant Tank stream (101-SY) in a simulated inactive form was employed for process evaluation. A developed solid–liquid equilibrium (SLE) thermodynamic framework with two predictive equations was used to model the experimental data. The preliminary data reveal that the LPP process is effective in separating: (1) alkaline cations (e.g., calcium, strontium, and likely barium) from their acidic and alkaline aqueous streams, (2) aluminum from acidic aqueous streams, and (3) phosphate and fluoride from both acidic and alkaline aqueous streams. The process is substantially less effective in separating alkali cations, including cesium, from aqueous streams. The sulfate concentration in the tested 101-SY stream was low (456 mg/L), which precludes drawing a conclusion regarding the effectiveness of the LPP process in removing sulfate. The technical feasibility and possible applicability of the LPP process across the DOE complex in treating different types of wastes (acidic-dissolved sludge, acidified supernatant, alkaline- dissolved sludge, and alkaline supernatant) were discussed.