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In Situ Redox Manipulation by Dithionite Injection: Intermediate‐Scale Laboratory Experiments
Author(s) -
Istok J.D.,
Amonette J.E.,
Cole C.R.,
Fruchter J.S.,
Humphrey M.D.,
Szecsody J.E.,
Teel S.S.,
Vermeul V.R.,
Williams M.D.,
Yabusaki S.B.
Publication year - 1999
Publication title -
groundwater
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.84
H-Index - 94
eISSN - 1745-6584
pISSN - 0017-467X
DOI - 10.1111/j.1745-6584.1999.tb01187.x
Subject(s) - in situ , redox , dithionite , scale (ratio) , chemistry , computer science , environmental science , inorganic chemistry , biochemistry , cartography , geography , organic chemistry , enzyme
The goal of in situ redox manipulation (ISRM) is to create a permeable treatment zone capable of removing redox‐sensitive contaminants from ground water. The objective of this study was to evaluate the effectiveness of one promising ISRM technology: chemical reduction of aquifer sediments by sodium dithionite (Na 2 S 2 O 4 ) injection. The technology was evaluated in intermediate‐scale laboratory experiments designed to investigate the kinetics of Fe(III)‐reduction and dithionite‐disproportionation reactions in a radial flow field over similar transport distances (∼ 7 m) and time scales (∼ 72 hours) as those used in a field trial for remediation of chromate contaminated ground water at the Department of Energy Hanford site in Washington state. Four hundred liters (∼ 1 pore volume) of 0.1 M Na 2 S 2 O 4 in a 0.4 M K 2 CO 3 /0.04 M KHCO 3 buffer were injected at a rate scaled to field values. Dithionite breakthrough curves at sampling ports were approximately described by the advection‐dispersion equation with a two‐part reaction model containing first‐order rate coefficients for dithionite reaction with sediment Fe(III) (k 1 = 0.13 hr −1 ) and dithionite disproportionation (k 2 = 0.05 hr −1 ). Analyses on sediment cores collected from the physical model indicated that substantial Fe(III) was reduced to Fe(II) and that the dithionite‐treated sediment was capable of removing 2 mg/L chromate from ∼ 100 column pore volumes of synthetic ground water. These results indicate that the ISRM technology is a potentially feasible method for removing chromate from Hanford ground water.