Corrosion Properties of Organic Compounds in Double-Shell Tanks at the Hanford Site

A range of organic compounds is present in Hanford double‑shell tank (DST) wastes, some of which have demonstrated the ability to inhibit corrosion of carbon steel tank liners. Despite this observed benefit, the underlying mechanisms remain insufficiently understood, and discrepancies exist between potential corrosion‑inhibiting species and those identified in the DST chemistry control data quality objectives (DQOs). This study investigates the electrochemical behavior of Fe³⁺/Fe²⁺ complexes with selected complexing and non‑complexing organic ligands to clarify their roles in corrosion processes relevant to DST environments.Electrochemical testing showed that EDTA, HEDTA, and NTA form Fe³⁺/Fe²⁺ complexes that remain electrochemically active in alkaline solutions, producing distinct low‑potential redox features attributed to differential complexation of ferrous and ferric ions. Raman spectroscopy confirmed the formation of new metal‑chelate coordination structures for these ligands. In contrast, gluconate, IDA, citrate, adipate, succinate, glycine, and palmitic acid exhibited no additional redox activity and no Raman‑detectable structural changes beyond the baseline solution. Corrosion testing of A537 carbon steel in alkaline nitrate/nitrite simulants further demonstrated that EDTA, HEDTA, and NTA decreased the corrosion potential, whereas non‑complexing organics showed negligible effect. These findings indicate that only a subset of organic ligands—specifically EDTA, HEDTA, and NTA—can form electrochemically active Fe‑complexes capable of lowering corrosion potential under alkaline tank conditions.