Immobilization of perrhenate using synthetic pyrite particles: Effectiveness and remobilization potential

• Published in: The Science of the total environment 2020-07, Vol.725, p.138423-138423, Article 138423
• Main Authors: Wang, Ting, Qian, Tianwei, Zhao, Dongye, Liu, Xiaona, Ding, Qingwei
• Format: Article
• Language: English
• Subjects: Perrhenate; Pertechnetate; Pyrite; Radionuclide; Reductive immobilization; Soil remediation
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2020.138423

Radioactive pertechnetate (TcO4−) has been detected in nuclear waste affected soil and groundwater, posing significant effect on human health and the environment. Yet, cost-effective remediation of Tc-contaminated soil and groundwater remains challenging. To address this critical technology need, we prepared a class of pyrite (FeS2) particles for effective immobilization of pertechnetate. Using perrhenate (ReO4−) as a non-radioactive surrogate of TcO4−, we tested the immobilization effectiveness of the material through batch kinetic experiments, and evaluated the remobilization potential of immobilized Re under anoxic (sealed from air) and oxic (exposed to air) conditions and in the presence of humic acid (HA), EDTA, nitrate, and a Chinese loess soil. The results showed that more acidic pH gave faster Re(VII) removal due to more abundant electron sources (Fe2+ and S22−). X-ray diffraction (XRD) and/or X-ray photoelectron spectroscopy (XPS) analyses confirmed formation of ReO2/ReS2 as the major reduction products. The immobilized Re remained highly stable when aged for 360 days under anoxic conditions at different influence factors. Yet, the immobilized Re was vulnerable to oxygen oxidation, and about 78% of Re was remobilized after 40 days of exposure to air regardless of the initial pH (3.5–9.0) due to excessive pyrite oxidation and the associated pH drop (~2). HA at 120 mg/L inhibited Re remobilization under oxic conditions, which lowered the Re remobilization by ~21% after 40 days of oxic aging. The presence of EDTA facilitated dissolution of Fe but inhibited the dissolution of Re under oxic conditions. Nitrate showed negligible effect on Re remobilization. The presence of a Chinese loess soil effectively inhibited Re remobilization under both oxic and anoxic conditions, lowering the leachable Re by ~32% under oxic conditions. The findings may guide engineered application of pyrite particles as a long-lasting reducing material for immobilization pertechnetate or similar redox-active contaminants in soil and water. [Display omitted] •Synthetic FeS2 particles can effectively reduce soluble Re(VII) into insoluble Re(IV).•Both Fe2+ ions and disulfide (S22−) ions were involved in reduction of Re(VII).•More acidic pH progressively accelerated the total Re removal.•Immobilized Re remained stable after 360 days of aging under anoxic conditions.•Humic acid, EDTA and soil inhibited Re remobilization under oxic conditions.