Arsenate and Phosphate Adsorption in Relation to Oxides Composition in Soils: LCD Modeling

Abstract

The pH dependent solid-solution distribution of arsenate and phosphate in five Dutch agricultural soil samples was measured in the pH range 4-8, and the results were interpreted using the LCD (ligand and charge distribution) adsorption modeling. The pH dependency is similar for both oxyanions, with a minimum soluble concentration observed around pH 6-8. This pH dependency can be successfully described with the LCD model and it is attributed mainly to the synergistic effects from Ca adsorption. The solubility of phosphate is much lower than that of arsenate. This big difference cannot be sufficiently explained by the reduction of small amount of As(V) into As(III), neither by slow desorption/adsorption. The difference between phosphate and arsenate in their solid-solution distribution becomes larger with the increase of aluminum (hydr)oxides (Al-oxides) contribution to the total amount of metal (Al and Fe) (hydr)oxides. The influence of Al-oxides is much larger than its relative amount extracted from the soils. When Al-oxides account for >40% of the soil oxides, the whole adsorbents behave apparently similarly to that of pure Al-oxides. These results indicated that surface coating and substitution may have modified significantly oxyanion adsorption to Fe-oxides in soils, and how to account for this complexity is a challenge for geochemical modeling.

Arsenic Adsorption onto Minerals: Connecting Experimental Observations with Density Functional Theory Calculations

“…Surface complexation modeling (SCM) techniques such as the charge distribution multi-site complexation (CD-MUSIC) [76,95,[98][99][100][101][102][103][104][105][106], the extended triple-layer model [107], isotherm modeling [108,109], and the ligand and charge distribution model (LCD) [110,111] have been used to model As species in solution and adsorbed to mineral surfaces. In general, SCM models use experimental data or quantum mechanics results such as equilibrium constants, bond lengths, and surface charges to calculate the adsorption isotherms of As on Fe mineral surfaces.…”

“…In general, SCM models use experimental data or quantum mechanics results such as equilibrium constants, bond lengths, and surface charges to calculate the adsorption isotherms of As on Fe mineral surfaces. When integrated, the CD-MUSIC and LCD SCMs are able to model humic substances interacting with Fe surfaces and the effect they have on As adsorption [111,112]. SCM can be used to interpret interactions among As, mineral surfaces, and organic and inorganic ligands, as well as charge and protonation effects.…”

Phosphate alteration of chloride behavior at the boehmite–water interface: New insights from ion-probe flow adsorption microcalorimetry

“…surface area, particle size, isoelectric point and crystallinity) which are governed largely by the identity and structure of the lattice metal or by molar ratios of individual metal centers in double-hydroxides and mixed-metal oxides. For example, because of their high reactivity at environmental pH values, aluminum (Al) and iron (Fe)-(hydr)oxides can interact strongly with a variety of solutes, including inorganics [1][2][3][4][5], metals [6][7][8], and organic ions [9][10][11][12][13]. The second interpretation considers physicochemical and catalytic properties (chemical surface heterogeneity) based on morphology of the (hydr)oxide surface, particularly the Lewis (or Brønsted) acidity and basicity of hydroxyl groups.…”

Phosphorus Leaching from an Organic and a Mineral Arable Soil in a Rainfall Simulation Study

“…The mobilization and transport mechanism of P in soils results from the physicochemical processes of sorption–desorption and precipitation–dissolution (Bünemann et al, 2012). The presence or absence of Al, Fe (hydr)oxides, Ca, clay minerals, and organic matter (Cui and Weng, 2013; Fink et al, 2016; Gérard, 2016; Bulmer et al, 2018) are all important when evaluating potential P losses in soil. Organic matter is known to compete with P for sorption sites; however, previous studies have found it unlikely to bind directly with P (McDowell and Condron, 2001).…”