Unrefined Humic Substances as a Potential Low-cost Remediation Method for Groundwater Contaminated with Uranium in Acidic Conditions
Doctor of Philosophy (PhD)
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Uranium, Acidic plume, Humic substances, Sorption
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Anthropogenic activities such as uranium mining and milling, nuclear weapons production, and nuclear reprocessing have left a legacy of groundwater and soil contaminated with uranium that needs to be addressed. Therefore, developing new remediation technologies to sequester uranium in situ is crucial. The objective of the study was to determine if low-cost commercially available unrefined humic substances, such as Huma-K, can be used to facilitate uranium sorption to minerals in soil and sediment. Sediments from the saturated zone beneath the F-Area seepage basins at the Savannah River Site (SRS) in South Carolina were used for the present study. The SRS site is analogous to many contaminated locations where groundwater acidity enhances uranium and other contaminants mobility.
First, a variety of techniques were applied to characterize Huma-K and SRS sediment. Characterization studies showed that Huma-K possesses functional groups that have an acidic nature such as carboxyl and phenol groups. For SRS sediment, a mineral composition of mainly quartz (93.2%), kaolinite (5.1%), and goethite (1.1%) was identified.
Second, the interactions between Huma-K and SRS sediment were investigated through batch experiments. Sorption, homogeneous precipitation, and surfaced-induced precipitation were observed to be enhanced at pH 4. However, Huma-K removal from solution decreased with an increase of pH. The sorption behavior was not able to be described by any of the models employed (pseudo-first, pseudo-second, Langmuir, and Freundlich).
Third, the interactions between uranium and SRS sediment with and without Huma-K amendment were investigated. In acidic conditions (pH 3-5), the sorption capacity of SRS sediment amended with Huma-K was significantly increased compared to plain sediment. At circumneutral conditions, uranium removal from solution decreased for SRS sediment amended with Huma-K, compared with plain sediments, likely as a result of the formation of aqueous uranium-humic complexes. In summary, the results from the present study suggest that Huma-K, and likely other unrefined humate products, has the characteristics and effects necessary to be suitable for subsurface injection to remediate uranium in acidic groundwater conditions. The treatment zone will persist as long as the pH does not increase sufficiently to cause soil-bound Huma-K to be released, remobilizing uranium.
Gonzalez Raymat, Hansell, "Unrefined Humic Substances as a Potential Low-cost Remediation Method for Groundwater Contaminated with Uranium in Acidic Conditions" (2018). FIU Electronic Theses and Dissertations. 3864.
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