The form, distribution and mobility of arsenic in soilscontaminated by arsenic trioxide, at sites in southeast USA
Soils from many industrial sites in southeastern USA arecontaminated with As because of the application of herbicide containingAs2O3. Among those contaminated sites, two industrial sites, FW and BH,which are currently active and of most serious environmental concerns,were selected to characterize the occurrence of As in the contaminatedsoils and to evaluate its environmental leachability. The soils are bothsandy loams with varying mineralogical and organic matter contents.Microwave-assisted acid digestion (EPA method 3051) of the contaminatedsoils indicated As levels of up to 325 mg/kg and 900 mg/kg (dry weightbasis) for FW and BH soils, respectively. However, bulk X-ray powderdiffraction (XRD) analysis failed to find any detectable As-bearingphases in either of the studied soil samples. Most of the soil As wasobserved by scanning electron microscopy, coupled with energy dispersiveX-ray spectroscopy (SEM/EDX), to be disseminated on the surfaces offine-grained soil particles in close association with Al and Fe. A fewAs-bearing particles were detected in BH soil using electron microprobeanalysis (EMPA). Synchrotron micro-XRD and X-ray absorption near-edgestructure (XANES) analyses indicated that these As-rich particles werepossibly phaunouxite, a mineral similar to calcium arsenate, which couldhave been formed by natural weathering after the application of As2O3.However, the scarcity of those particles eliminated them from playing anyimportant role in Assequestration.Synthetic acid rain sequential batchleaching experiments showed distinct As leaching behaviors of the twostudied soil samples: BH soil, which has the higher As content, showed aslow, steady release of As, while FW soil, with a lower As content,showed a much quicker release and lower overall retention of As uponleaching. Sequential chemical extraction experiments were carried outusing a simplified 4-step sequential chemical extraction procedure (SCEP)previously developed to characterize the fractionation of As and betterunderstand the different leaching behaviors of the two studied soils. Itwas shown that only about 50 percent of the total extractable As wasremoved by the first two extraction steps, which represented the mostweakly bonded and readily available As forenvironmental leaching.Compared with the sequential leaching experiments, it was furtherindicated that only half of the As associated with phases extracted bythe second SCEP step was mobilized by SPLP leaching. Althoughmicrowave-assisted acid digestion results showed similar Al and Fecontents in both soils, the sequential chemical extraction experimentsindicated that BH soil has a much higher content of amorphous Al and Fephases and that a comparably higher portion of soil As was associatedwith those materials. The experimental results suggest that remediationefforts for the contaminated sites can be directed towards enhancing theformation of more stable As-bearing compounds in the soils to reduce theenvironmental leachability of As.
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- Sponsoring Organization:
- USDOE Director. Office of Science. Basic EnergySciences
- DOE Contract Number:
- DE-AC02-05CH11231
- OSTI ID:
- 918681
- Report Number(s):
- LBNL-63380; APPGEY; R&D Project: 468212; BnR: KC0303020; TRN: US200819%%402
- Journal Information:
- Applied Geochemistry, Vol. 22; Related Information: Journal Publication Date: 2007; ISSN 0883-2927
- Country of Publication:
- United States
- Language:
- English
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