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Modeling Competitive Adsorption of Arsenate with Phosphate and Molybdate on Oxide Minerals
Author(s) -
Manning Bruce A.,
Goldberg S.
Publication year - 1996
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1996.03615995006000010020x
Subject(s) - adsorption , arsenate , chemistry , goethite , inorganic chemistry , molybdate , denticity , phosphate , oxide , selenate , point of zero charge , surface charge , oxyanion , ion , arsenic , metal , catalysis , organic chemistry , selenium
The mobility of As in soils depends on several factors including redox potential, soil mineralogy, pH, and the presence of other oxyanions that compete with As for soil retention sites. We investigated the effects of pH and competing anions on the adsorption of arsenate [As(V)] on α‐FeOOH (goethite) and γ‐Al(OH) 3 (gibbsite). Batch equilibrium As(V) adsorption experiments were conducted with P and Mo as competing anions in order to produce single‐anion [As(V), P, and Mo] and binary‐anion [As(V)/P and As(V)/Mo] adsorption envelopes (adsorption vs. solution pH). Arsenate and P single‐anion adsorption envelopes were similar with substantial adsorption occurring across a wide pH range, including pH values above the points of zero charge of the oxides. Maximum Mo adsorption occurred across a narrower pH range (pH 4–6). On both oxides, equimolar P concentrations decreased As(V) adsorption within the pH range 2 to 11, whereas Mo decreased As(V) adsorption only below pH 6. The constant capacitance model was used to predict competitive surface complexation behavior between As(V)/P and As(V)/Mo using intrinsic equilibrium constants [ K anlon (int)] optimized from single‐anion data. In addition, the model was applied using one‐site (monodentate) and two‐site (monodentate + bidentate) conceptualizations of the oxide surface. The two approaches gave comparable fits to experimental adsorption data and were consistent with competitive adsorption observed in binary adsorption envelopes.