Journal
ENVIRONMENTAL SCIENCE & TECHNOLOGY
Volume 42, Issue 6, Pages 2092-2098Publisher
AMER CHEMICAL SOC
DOI: 10.1021/es072059c
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In zerovalent iron treatment systems, the presence of multiple solution components may impose combined effects that differ from corresponding individual effects. The copresence of humic acid and hardness (Ca2+/Mg2+) was found to influence Cr(VI) reduction-by Fe-0 and iron dissolution in a way different from their respective presence in batch kinetics experiments with synthetic groundwater at initial pH 6 and 9.5. Cr(VI) reduction rate constants (k(obs),,) were slightly inhibited by humic acid adsorption on iron filings (decreases of 7-9% and 10-12% in the presence of humic acid alone and together with hardness, respectively). The total amount of dissolved Fe steadily increased to 25 mg L-1 in the presence of humic acid alone because the formation of soluble Fe-humate complexes appeared to suppress iron precipitation. Substantial amounts of soluble and colloidal Fe-humate complexes in groundwater may arouse aesthetic and safety concerns in groundwater use. In the coexistence of humic acid and Ca2+/Mg2+ contrast, significantly promoted aggregation of humic acid and metal hydrolyzed species, as indicated by XPS and TEM analyses, which remained nondissolved (> 0.45 mu m) in solution. These metal-humate aggregates may impose long-term impacts on PRBs in subsurface settings.
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