Abstract High‐phosphate and high‐fluoride sludges represent some of the most challenging waste streams within the Hanford High‐Level Waste (HLW) inventory due to solubility constraints, impacts on glass loading, and corrosion risks during vitrification. This study presents a systematic, experimentally constrained evaluation of phosphate and fluoride dissolution from simulated Hanford HLW sludge under conditions relevant to potential direct‐feed vitrification flowsheets. Multi‐stage washing experiments were performed using process water, 1 M NaOH, and a high‐sodium (3.8 M Na) simulant to quantify equilibrium‐controlled dissolution behavior and solubility limits as a function of solids loading and solution recycle. Results demonstrate a strong sodium common‐ion suppression effect on natrophosphate solubility and reveal practical limits on phosphate and fluoride removal when wash solutions are reused. Although no kinetic rate measurements were performed, the data establish conservative solubility bounds that directly inform HLW feed preparation strategies, wash water management, and secondary waste generation. These findings support applied flowsheet design and risk reduction efforts for direct‐feed HLW vitrification rather than the discovery of new chemical mechanisms.
Westesen et al. (2026) studied this question.