Adsorption, desorption and oxidation of arsenic affected by clay minerals and aging process |
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| Authors: | Z Lin R W Puls |
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| Institution: | (1) U.S. EPA, National Risk Management and Research Laboratory, Subsurface Protection and Remediation Division, P.O. Box 1198 Ada, OK 74820-1198, USA e-mail: lin.zhixun@epamail.epa.gov, Tel: +580-436-8604, Fax: +580-436-8703, US |
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| Abstract: | Adsorption/desorption and oxidation/reduction of arsenic at clay surfaces are very important to the natural attenuation of
arsenic in the subsurface environment. Although numerous studies have concluded that iron oxides have high affinities for
the adsorption of As(V), very little experimental work has addressed the arsenic attenuation capacities of different clay
minerals and aging process affecting the transformation of arsenic. The abundance of clay minerals in a variety of geochemical
environments and their influence on adsorption of contaminants suggests a need for more experimental work to characterize
the adsorption desorption, and oxidation of arsenic on clay minerals. In this investigation three types of clay mineral were
studied: the 1 : 1 layer clays halloysite (IN), sedimentary M-kaolinite, and weathered EPK-kaolinite]; the 2 : 1 layer clays
illite (MT) and illite/montmorillonite (MT)]; the 2 :>: 1 layer clay chlorite (CA)]. The halloysite and the chlorite had
much greater As(V) adsorption (25–35 folds) than the other clay minerals. The clay minerals had lower As(III) adsorption than
As(V) adsorption, and the adsorption was affected by pH. Desorption of arsenic from the clay minerals was significantly influenced
by the aging process. The quantities of extractable As(III) and As(V) decreased with increasing aging time. The results demonstrated
that oxidation of As(III) to As(V) occurred on the clay surfaces, whereas reduction of As(V) to As(III) was not found in any
of the clay minerals studied. The oxidation of As(III) was affected by the types of clay and aging time.
Received: 22 March 1999 · Accepted: 15 April 1999 |
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| Keywords: | Arsenic Natural attenuation Remediation |
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