Arsenic Attenuation By Oxidized Aquifer Sediments in Bangladesh

Journal Article · Fri Jul 13 04:00:00 EDT 2007 · Sci.Total Environ.379:133-150,2007

DOI:https://doi.org/10.1016/j.scitotenv.2006.11.029· OSTI ID:909732

Stollenwerk, K G; Breit, G N; Welch, A H; Yount, J C; Whitney, J W; Foster, A L; Uddin, M N; Majumder, R K; Ahmed, N

Recognition of arsenic (As) contamination of shallow fluvio-deltaic aquifers in the Bengal Basin has resulted in increasing exploitation of groundwater from deeper aquifers that generally contain low concentrations of dissolved As. Pumping-induced infiltration of high-As groundwater could eventually cause As concentrations in these aquifers to increase. This study investigates the adsorption capacity for As of sediment from a low-As aquifer near Dhaka, Bangladesh. A shallow, chemically-reducing aquifer at this site extends to a depth of 50 m and has maximum As concentrations in groundwater of 900 {micro}g/L. At depths greater than 50 m, geochemical conditions are more oxidizing and groundwater has < 5 {micro}g/L As. There is no thick layer of clay at this site to inhibit vertical transport of groundwater. Arsenite [As(III)] is the dominant oxidation state in contaminated groundwater; however, data from laboratory batch experiments show that As(III) is oxidized to arsenate [As(V)] by manganese (Mn) minerals that are present in the oxidized sediment. Thus, the long-term viability of the deeper aquifers as a source of water supply is likely to depend on As(V) adsorption. The adsorption capacity of these sediments is a function of the oxidation state of As and the concentration of other solutes that compete for adsorption sites. Arsenite that was not oxidized did adsorb, but to a much lesser extent than As(V). Phosphate (P) caused a substantial decrease in As(V) adsorption. Increasing pH and concentrations of silica (Si) had lesser effects on As(V) adsorption. The effect of bicarbonate (HCO{sub 3}) on As(V) adsorption was negligible. Equilibrium constants for adsorption of As(V), As(III), P, Si, HCO3, and H were determined from the experimental data and a quantitative model developed. Oxidation of As(III) was modeled with a first-order rate constant. This model was used to successfully simulate As(V) adsorption in the presence of multiple competing solutes. Results from these experiments show that oxidized sediments have a substantial but limited capacity for removal of As from groundwater.

• Research Organization: Stanford Linear Accelerator Center (SLAC)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC02-76SF00515
• OSTI ID: 909732
• Report Number(s): SLAC-REPRINT-2007-159
• Journal Information: Sci.Total Environ.379:133-150,2007, Journal Name: Sci.Total Environ.379:133-150,2007 Vol. 379; ISSN STENDL; ISSN 0048-9697
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
ACID CARBONATES
ADSORPTION
AQUIFERS
ARSENIC
ATTENUATION
BANGLADESH
CAPACITY
OXIDATION
Other
OTHER
SEDIMENTS
WATER SUPPLY