Long-Term Stability of Organic Carbon-Stimulated Chromate Reduction in Contaminated Soils and Its Relation to Manganese Redox Status

Abstract

In-situ reduction of toxic Cr(V1) to less hazardous Cr(II1) is becoming a popular strategy for remediating contaminated soils. However, the long term stability of reduced Cr remains to be understood, especially given the common presence of MnfIIIJV) oxides that reoxidize Cr(II1). This 4.6 year laboratory study tracked Cr and Mn redox transformations in soils contaminated with Cr(V1) which were then treated with different amounts of organic carbon (OC). Changes in Cr and Mn oxidation states within soils were directly and nondestructively measured using micro X-ray absorption near edge structure spectroscopy. Chromate reduction was roughly lst-order, and the extent of reduction was enhanced with higher OC additions. However, significant Cr(II1) reoxidation occurred in soils exposed to the highest Cr(V1) concentrations (2,560 mg kg"'). Transient Cr(II1) reoxidation up to 420 mg kg1 was measured at 1.1 years after OC treatment, followed by further reduction. Chromate concentrations increased by 220 mg kgm1 at the end of the study (4.6 years) in one soil. The causal role that Mn oxidation state had in reoxidizing Cr was supported by trends in Mn K-edge energies. These results provide strong evidence for longterm dependence of soil Cr oxidation states on balances between OC availability and Mn redox status.

Effectiveness and longevity of a green/food waste derived compost packed column to reduce Cr(VI) contamination in groundwater

“…We have found in other column experiments that reduction by compost organic matter alone is comparatively short-lived (Aspray, unpublished). In terms of microbial reduction mechanisms, it is likely that Cr(VI) was reduced indirectly in the column by metabolic endproducts including Fe(II) and H 2 S [22,23]. Certainly the analysis of H 2 S in water samples (data not shown) during phase II sampling, suggests the presence of sulphate reducing bacteria and the possibility for indirect Cr(VI) reduction by this metabolic end-product.…”

Synchrotron-based techniques for plant and soil science: opportunities, challenges and future perspectives

“…More recently, μ-XAS was used by McNear et al (2007) to identify Ni and Al layered double hydroxide phases in a soil contaminated by a Ni refinery and treated with lime. Tokunaga et al (2007) used Mn and Cr K-edge XAS to investigate the role of organic matter and soil Mn in the reduction and stability of Cr in contaminated soils. This study evidenced the importance of organic C availability and Mn redox status for the long-term stability of Cr reduction strategies for soil remediation.…”

The Adsorption of Cd(II) on Manganese Oxide Investigated by Batch and Modeling Techniques

“…Owing to the high surface charge density, various Mn oxides (e.g., including pyrolusite (β-MnO 2 ) and birnessite (δ-MnO 2 )) have been extensively as high efficient adsorbents to remove arsenic [ 14 , 15 , 16 , 17 ], nickel [ 18 , 19 ], lead [ 20 , 21 , 22 ], mercury [ 23 , 24 ], and chromium [ 25 , 26 , 27 ]. It is demonstrated that birnessite has hexagonal layer symmetry and may possess a variable number of octahedral cationic vacancies within their layer, which provides the abundant strong adsorption sites for heavy metals [ 28 , 29 ].…”