In Situ Chemical Reduction of Cr(VI) in Groundwater Using a Combination of Ferrous Sulfate and Sodium Dithionite:  A Field Investigation

Abstract

A field study was conducted to evaluate the performance of a ferrous iron based in situ redox zone for the treatment of a dissolved phase Cr(VI) plume at a former industrial site. The ferrous iron based in situ redox zone was created by injecting a blend of 0.2 M ferrous sulfate and 0.2 M sodium dithionite into the path of a dissolved Cr(VI) plume within a shallow medium to fine sand unconfined aquifer formation. Monitoring data collected over a period of 1020 days after more than 100 m of linear groundwater flow through the treatment zone indicated sustained treatment of dissolved phase Cr(VI) from initial concentrations between 4 and 8 mg/L to less than 0.015 mg/L. Sustained treatment is assumed to be primarily due to the reduction of Cr(VI) to Cr(III) by ferrous iron adsorbed to, precipitated on, and/or incorporated into aquifer iron (hydr)oxide solid surfaces within the treatment zone. Precipitated phases likely include FeCO3 and FeS based on saturation index considerations and SEM/EDS analysis. The detection of solid phase sulfites and thiosulfates in aquifer sediments collected from the treatment zone more than 2 years following injection suggests dithionite decomposition products may also play a significant role in the long-term treatment of the dissolved phase Cr(VI).

Dechlorinating transformation of propachlor through nucleophilic substitution by dithionite on the surface of alumina

“…Dithionite is a relatively inexpensive sulfur compound which has long been used extensively in industrial applications (de Carvalho and Schwedt 2002). As to environmental cleaning purposes, in recent years, dithionite has been used to treat soils and sediments to enhance pollutant decomposition in soils and groundwater, and dithionite itself was decomposed into environmentally benign compounds (Boparai et al 2006;Ludwig et al 2007). However, the reaction pathways of dithionite in soils may be very complex due to the existence of various active components in the subsurface environment.…”

Potential aquifer vulnerability in regions down-gradient from uranium in situ recovery (ISR) sites

“…Next, reverse osmosis restoration involves continued groundwater extraction, treatment, and reinjection of the treated water into the subsurface. In-situ chemical reduction and bioremediation technologies make use of chemical amendments to drive immobilization of redox-sensitive elements; such remediation processes have been demonstrated in the field for metal(loid)-contaminated groundwater (including uranium) using iron-reducing bacteria (e.g., Anderson et al, 2003), sulfate-reducing bacteria (e.g., Saunders et al, 2005Saunders et al, , 2008Wu et al, 2006;Watson et al, 2013), and injections of reductants such as dithionite, ferrous iron, or sulfide (e.g., Ludwig et al, 2007). The U.S. EPA has developed a series of technical framework documents that should be consulted for the application of MNA as a tool to restore aquifers following ISR operations (US EPA, 2007a,b;.…”

Nitrate removal from water using UV-M/S2O4 2− advanced reduction process

“…In addition to its industrial uses, dithionite is widely used by soil scientists to reductively extract iron from soils (Gan et al 1992). The ability to reduce iron has also been applied to developing in situ aquifer remediation technology where iron in aquifer solids is reduced by dithionite and the reduced iron subsequently reduces oxidized contaminants (Szecsody et al 2004;Ludwig et al 2007).…”