Adsorption of arsenic by natural aquifer material in the San Antonio-El Triunfo mining area, Baja California, Mexico |
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Authors: | A Carrillo J I Drever |
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Institution: | (1) Dept. of Geology and Geophysics, University of Wyoming, Laramie, Wyoming 87201-3006, USA, US |
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Abstract: | Several experiments of arsenic (As) adsorption by aquifer material of the San Antonio-El Triunfo (SA-ET) mining area were
conducted to test the feasibility of this material acting as a natural control for As concentrations in groundwater. This
aquifer material is mineralogically complex, composed of quartz, feldspar, calcite, chlorite, illite, and magnetite/hematite.
The total iron content (Fe2O3) in the fine fraction is ∼12%, whereas Fe2O3 in the coarse fraction is <10 wt%. The experimental percent total As adsorbed vs. pH curves obtained match the topology of
total As adsorbed onto iron oxi-hydroxides surface (arsenate + arsenite; high adsorption at low pH, low adsorption at high
pH). A maximum of about 80% adsorbed in the experiments suggests the presence of arsenite in the experimental solutions. The
experimental adsorption isotherm at pH 7 indicates saturation of surface sites at high solute concentrations. Surface titration
of the aquifer material indicates a point of zero charge (PZC) for the adsorbent of about 8 to 8.5 (PZC for iron oxyhydroxides
=7.9–8.2). Comparison between experimental and modeled results (using the MICROQL and MINTEQA2 geochemical modeling and speciation
computer programs) suggests that As is being adsorbed mostly by oxyhydroxides surfaces in the natural environment. Based on
an estimated retardation factor (R), the travel time of the As plume from the SA-ET area to La Paz and Los Planes is about 700 to 5000 years.
Received: 17 March 1997 · Accepted: 8 September 1997 |
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Keywords: | Arsenic adsorption Arsenic contamination Oxyhydroxides surfaces |
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