Competitive Sorption of Arsenate and Phosphate on Different Clay Minerals and Soils

Abstract

Sorption and desorption of AsO4 on or from different soil components may have a dominant role in regulating As mobility in soils. The objectives of this work were to provide information on the factors that influence the competitive sorption of AsO4 and PO4 in soil. We studied the competitive sorption of PO4 and AsO4 on selected phyllosilicates, metal oxides, synthetic organo‐mineral complexes, and soil samples as affected by pH (4.0–8.0), ligands concentration, surface coverage of the oxyanions on the samples and the residence time. We found that Mn, Fe, and Ti oxides and phyllosilicates particularly rich in Fe (nontronite, ferruginous smectites) were more effective in sorbing AsO4 than PO4 In fact, by adding AsO4 and PO4 as a mixture (AsO4/PO4 molar ratio of 1) more AsO4 than PO4 was usually sorbed on birnessite, pyrolusite, goethite, nontronite, and ferruginous smectite, but more PO4 than AsO4 was sorbed on noncrystalline Al precipitation products, gibbsite, boehmite, allophane, and kaolinite. For example, at pH 5.0 the sorbed AsO4/sorbed PO4 molar ratio (rf) was 1.81 for birnessite, 1.05 for nontronite, but was only 0.45 for kaolinite and 0.14 for allophane. For montmorillonite, illite, and vermiculite the rf values were slightly <1. For soil samples, particularly rich in kaolinite, halloysite, allophane, and containing relatively large amounts of organic C, the rf values were usually much <1. For all the samples, the rf values increased by decreasing the pH and with the residence time of the oxyanions. The sorption of AsO4 (or PO4) on goethite and gibbsite decreased by increasing the initial PO4/AsO4 (or AsO4/PO4 molar ratio) up to 2.0. However, PO4 inhibited AsO4 sorption more on gibbsite than on goethite, whereas AsO4 prevented PO4 sorption more on goethite than on gibbsite. The data reported in this paper suggest that the mobility, the bioavailability, and the toxicity of As in soil environments may be greatly affected by the nature of soil components, pH, presence of anions (PO4), and residence time.

Removal of arsenate from water by using an Fe–Ce oxide adsorbent: Effects of coexistent fluoride and phosphate

“…The ability of phosphate to compete with arsenate in binding at the surface sites of goethite as well as soil has well been documented [9][10][11][12][13]. In view of the fact that similar amounts of phosphate and arsenate were adsorbed on goethite samples at pH 3.0-8.5, Liu et al [12] speculated that these anions compete primarily for a similar set of surface sites on this mineral, while there are some sites that are specific for arsenate and phosphate adsorption, respectively.…”

A Gel Probe Equilibrium Sampler for Measuring Arsenic Porewater Profiles and Sorption Gradients in Sediments: II. Field Application to Haiwee Reservoir Sediment

“…Phosphate competes directly with both As(III) and As(V) for surface sites on Fe oxides (2,3,(5)(6)(7)(8)(9)(10), but has a stronger inhibitory effect on As(V) (see Part I,11). Inorganic carbon may also suppress As adsorption when concentrations are elevated in groundwater because of microbial respiration of organic carbon and/or carbonate mineral dissolution (12)(13)(14)(15).…”

Adsorption of arsenate on soils. Part 2: Modeling the relationship between adsorption capacity and soil physiochemical properties using 16 Chinese soils

“…Manning and Goldberg (1997) found that Fe oxide was the most important mineral influencing adsorption of arsenate. In addition, organic matter, dissolved organic carbon and phosphate in soils have all been demonstrated to suppress arsenate adsorption by displacing adsorbed arsenate from soils (Grafe et al, 2001;Liu et al, 2001;Violante and Pigna, 2002). Some studies have also examined the influence of pH on arsenic adsorption by soils.…”