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United States Department of Agriculture

Agricultural Research Service

Arsenic and Selenium Adsorption Data
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The arsenic and selenium adsorption data and model fits presented in this data base are described in the research paper entitled Chemical Modeling of As(III, V) and Se(IV, VI) Adsorption by Soils Surrounding Ash Disposal Facilities by S. Goldberg, S. Hyun, and L.S. Lee published in Vadose Zone Journal 7:(in press) (2008). The objectives of this study were: i) to apply the constant capacitance model to describe As(III), As(V), Se(IV), and Se(VI) adsorption as a function of equilibrium solution As(III), As(V), Se(IV), and Se(VI) concentration by a set of soils obtained downgradient of three different fly ash disposal facilities; and ii) to test the model's ability describe the adsorption behavior of these ions on these soils. The adsorption behavior of these ions on these soils had been previously described using the Freundlich adsorption isotherm equation for As(III) and As(V) (Burns et al., 2006) and Se(IV) and Se(VI) (Hyun et al., 2006). Detailed experimental and modeling methods used to obtain the adsorption data and model fits are provided in the above publications. A summary will be provided below.
Arsenic and selenium adsorption was investigated on 18 surface soil samples from three utility sites within the United States (identified as Northeast, NE, Southeast, SE, and Midwest, MW) where ash landfills are presently in use or are planned. Soil properties previously determined by Burns et al. (2006) and Hyun et al. (2006), as well as, surface area are presented in Table 1.
Arsenic and selenium adsorption isotherms (amount adsorbed as a function of equilibrium solution ion concentration) for the soils were determined from 1 mM CaSO4 solution in batch systems. Initial ion concentrations ranged from 0 to 13 ?mol L-1 for Se(VI), 0 to 16 ?mol L-1 for As(III), 0 to 34 ?mol L-1 for Se(IV), and 0 to 66 ?mol L-1 for As(V). Solid suspension density was 20 g L-1 for As(V), 50 g L-1 for As(III) and Se(IV), and 100 g L-1 for Se(VI). Equilibration times were 16 hours for As(III) and Se(IV) and 48 hours for As(V) and Se(VI). After reaction, the samples were centrifuged, decanted, analyzed for pH, filtered, and analyzed for As and Se concentrations using graphite furnace atomic absorption spectrometry.
Explanation of the application of the constant capacitance model to describe As(III), As(V), Se(IV), and Se(VI) adsorption isotherms is provided in the above publication and references cited therein. The computer program FITEQL 3.2 (Herbelin and Westall, 1996) containing the constant capacitance model of adsorption was used to fit surface complexation constants to the experimental adsorption isotherm data. Initial input parameter values were capacitance: C = 1.06 F m-2 and surface site density: Ns = 2.31 sites nm-2 as in previous modeling studies of As(V) (Goldberg et al., 2005) and Se(IV) (Goldberg et al., 2007) adsorption by soils using the constant capacitance model.
The model was fit to the As(III), As(V), Se(IV), and Se(VI) experimental adsorption isotherms of all soil samples optimizing the following surface complexation constants: logK1As(III)(int) for arsenite, logK2As(V)(int) for arsenate, logK2Se(IV)(int) for selenite, and logK2Se(VI)(int) for selenate. Table 2 provides values of the optimized surface complexation constants. The ability of the constant capacitance model to describe As(III), As(V), Se(IV), and Se(VI) adsorption isotherms is indicated in the attached files. Goodness of model fit was evaluated using the overall variance, VY = SOS/DF, where SOS is the weighted sum of squares of the residuals and DF is the degrees of freedom (Herbelin and Westall, 1996).


  • Burns, P.E., S. Hyun, L.S. Lee, and I. Murarka. 2006. Characterizing As(III, V) adsorption by soils surrounding ash disposal facilities. Chemosphere 63:1879-1891.
  • Goldberg, S., S. Hyun, and L.S. Lee. 2008. Chemical modeling of As(III, V) and Se(IV, VI) adsorption by soils surrounding ash disposal facilities. Vadose Zone J. 7:(in press).
  • Goldberg, S., S.M. Lesch, and D.L. Suarez. 2007. Predicting selenite adsorption by soils using soil chemical parameters in the constant capacitance model. Geochim. Cosmochim. Acta 71:5750-5762.
  • Goldberg, S., S.M. Lesch, D.L. Suarez, and N.T. Basta. 2005. Predicting arsenate adsorption by soils using soil chemical parameters in the constant capacitance model. Soil Sci. Soc. Am. J. 69:1389-1398.
  • Herbelin, A.L., and J.C. Westall. 1996. FITEQL: A computer program for determination of chemical equilibrium constants from experimental data. Rep. 96-01, Version 3.2, Dep. of Chemistry, Oregon State Univ., Corvallis.
  • Hyun, S., P.E. Burns, I. Murarka, and L.S. Lee. 2006. Selenium(IV) and (VI) sorption by soils surrounding fly ash management facilities. Vadose Zone J. 5:1110-1118.
Table 1. Selected physical and chemical properties of soils used in this study
 ------------%------------m2g-1cmol kg-1----------------------g kg-1--------------------
NE1 25-3033170.521.815.55.920.270.320.240.27
NE1 35-4040250.527.
NE2 10-156017119.64.731.81.201.580.510.99
NE2 16-2159130.512.42.4511.40.631.090.360.53
NE3 50-549290.650.
NE4 46-5057150.918.25.818.31.301.590.501.04
SE1 48.56250.616.
SE1 605650.732.64.814.90.900.760.420.33
SE2 23.56630.313.64.18.400.180.410.310.06
SE3 5.56650.
SE3 38.56230.
MW1 179330.33.034.540.610.570.460.07
MW2 179510.
MW2 259710.
MW3 179510.
MW3 239510.521.81.42.960.
?Soil organic matter
Surface areas determined using ethylene glycol monoethyl ether adsorption as described by Cihacek and Bremner (1979).
?Dithionite-citrate-bicarbonate extractable iron and aluminum
?Oxalate (pH 3) extractable iron and aluminum
#Quickly (15 sec) dissolved iron in DCB solution
Table 2. Constant capacitance model surface complexation constants and goodness of fits
SoilLogK2As(V)(int)Vy?LogK1As(III)(int)Vy?LogK2Se(IV)(int)Vy?LogK2Se(VI)(int)Vy ?
NE1 25-305.5470.016.5381044.9890.0023.6240.05
NE1 35-406.8910.0053.6680.0096.5590.044.8490.01
NE2 10-157.3080.0058.2170.028.610.014.0970.02
NE2 16-216.9410.018.4060.47.1870.114.980.03
NE3 50-546.1480.0048.0870.567.9030.0065.1650.02
NE4 46-506.8590.0018.0560.0065.9570.0014.080.08
SE1 48.56.1240.057.5330.675.0770.013.9320.06
SE1 606.0520.0057.4180.544.9850.0063.7610.02
SE2 23.54.7930.027.2110.694.7290.0082.7190.04
SE3 38.54.7410.017.2340.444.7860.063.4170.02
MW1 175.2920.025.5760.0053.8690.0071.7540.02
MW2 174.7760.015.5160.013.7430.042.560.01
MW2 255.2810.015.7290.053.9370.032.6680.01
MW3 175.6410.0025.6760.053.5640.063.0380.02
MW3 235.5710.025.7520.063.3770.12.7680.007
? Goodness-of-fit equals the sum of squares (SOS) divided by the degrees of freedom (DF)



Last Modified: 8/13/2016
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