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+/Mg 2+) was found to influence Cr(VI) reduction by Fe0 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 (kobs) 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 contrast, the coexistence of humic acid and Ca 2+/Mg2+ significantly promoted aggregation of humic acid and metal hydrolyzed species, as indicated by XPS and TEM analyses, which remained nondissolved (>0.45 μm) in solution. These metal-humate aggregates may impose long-term impacts on PRBs in subsurface settings.
|Number of pages||7|
|Journal||Environmental Science and Technology|
|Publication status||Published - 15 Mar 2008|
ASJC Scopus subject areas
- Environmental Engineering
- Environmental Science(all)
- Environmental Chemistry