Document Detail

Influences of humic acid, bicarbonate and calcium on Cr(VI) reductive removal by zero-valent iron.
MedLine Citation:
PMID:  19232679     Owner:  NLM     Status:  MEDLINE    
The influences of various geochemical constituents, such as humic acid, HCO(3)(-), and Ca(2+), on Cr(VI) removal by zero-valent iron (Fe(0)) were investigated in a batch setting. The collective impacts of humic acid, HCO(3)(-), and Ca(2+) on the Cr(VI) reduction process by Fe(0) appeared to significantly differ from their individual impacts. Humic acid introduced a marginal influence on Fe(0) reactivity toward Cr(VI) reduction, whereas HCO(3)(-) greatly enhanced Cr(VI) removal by maintaining the solution pH near neutral. The Cr(VI) reduction rate constants (k(obs)) were increased by 37.8% and 78.3%, respectively, with 2 mM and 6 mM HCO(3)(-) in solutions where humic acid and Ca(2+) were absent. Singly present Ca(2+) did not show a significant impact to Cr(VI) reduction. However, probably due to the formation of passivating CaCO(3), further addition of Ca(2+) to HCO(3)(-) containing solutions resulted in a decrease of k(obs) compared to solutions containing HCO(3)(-) alone. Ca(2+) enhanced humic acid adsorption led to a minor decrease of Cr(VI) reduction rates. In Ca(2+)-free solutions, humic acid increased the amount of total dissolved iron to 25 mg/l due to the formation of soluble Fe-humate complexes and stably dispersed fine Fe (oxy)hydroxide colloids, which appeared to suppress iron precipitation. In contrast, the coexistence of humic acid and Ca(2+) significantly promoted the aggregation of Fe (oxy)hydroxides, with which humic acid co-aggregated and co-precipitated. These aggregates would progressively be deposited on Fe(0) surfaces and impose long-term impacts on the permeability of PRBs.
Tongzhou Liu; Pinhua Rao; Irene M C Lo
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't     Date:  2009-02-20
Journal Detail:
Title:  The Science of the total environment     Volume:  407     ISSN:  0048-9697     ISO Abbreviation:  Sci. Total Environ.     Publication Date:  2009 May 
Date Detail:
Created Date:  2009-03-30     Completed Date:  2009-06-04     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  0330500     Medline TA:  Sci Total Environ     Country:  Netherlands    
Other Details:
Languages:  eng     Pagination:  3407-14     Citation Subset:  IM    
Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Hong Kong.
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MeSH Terms
Bicarbonates / chemistry*
Calcium Carbonate / chemistry*
Chromium / chemistry*
Humic Substances*
Iron / chemistry*
Surface Properties
Water Pollutants, Chemical / chemistry*
Water Purification / methods
Reg. No./Substance:
0/Bicarbonates; 0/Humic Substances; 0/Water Pollutants, Chemical; 471-34-1/Calcium Carbonate; 7439-89-6/Iron; 7440-47-3/Chromium

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