Adsorption of Phosphate and Tartrate on Hydroxy‐Aluminum–Oxalate Precipitates

Abstract

Sorption of phosphate in the presence of low molecular mass organic ligands on hydroxy‐Al–organics coprecipitates may be the rule and not the exception in rhizospheric soils. We studied the competitive sorption of phosphate and tartrate on hydroxy‐Al–oxalate precipitates obtained by coprecipitating Al and oxalate at pH 7.0 and initial oxalate/Al molar ratios of 0, 0.1, 0.2, and 0.5. The noncrystalline precipitates showed different chemical and physicochemical properties. Oxalate was not homogeneously distributed throughout the solids, and the greater its content in the samples, the higher the surface area, reactivity, and solubility of the solids. Oxalate was released from each complex mainly at pH <5.0 and >7.0 and more in the presence than in the absence of phosphate or tartrate. More phosphate than tartrate was sorbed on the samples, but tartrate appeared to be more specific than phosphate in replacing oxalate. The quantity of phosphate and tartrate sorbed on the organomineral complexes, containing greater amounts of oxalate, was little affected by pH (4.0–9.0), probably due to the release of oxalate from the surfaces of the complexes by increasing the pH. When mixtures of equimolar amounts of the two ligands were added at pH 4.0 to 9.0, more phosphate than tartrate was sorbed on the organomineral solids. The sorbed tartrate/sorbed phosphate molar ratio was always <1.0, but usually increased by decreasing pH and increasing the content of oxalate in the precipitates. At pH ≤5.0 the presence of high tartrate concentrations reduced the phosphate sorption, releasing Al and Al‐bounded oxalate. Only at pH >5.0 could the decrease in sorption of phosphate be attributed mainly to competition in sorption between the organic and inorganic ligands for different sorption sites.

Chemical and spectroscopic characterization of insoluble and soluble humic acid fractions at different pH values

“…Therefore, the lack of such bands in our samples does not mean that they do not contain aluminum hydroxides. The other typical Al hydroxide bands are at 1,025, 970, and 531 cm −1 [43]. The first two bands are overlapped by Si-O absorption at 1,030 cm −1 , but a strong band at 530 cm −1 cannot be attributed to silicates and could indicate the presence of aluminum hydroxides.…”

Synthesis and characterization of Al13-oxalate gel with Keggin structure

“…The diffraction pattern of the gel is obviously different from that of Al 13 -sulfate crystal in which the latter has sharp peaks, but in the diffraction pattern of the gel, there are still four obvious wide peaks occurring at 2θ 19.6° (d=0.453), 28.5° (d=0.312), 38.99° (d=0.231) and 60.5° (d=0.153), respectively. The diffraction pattern of the gel is not only different from that of fresh aluminum gels synthesized by Liu Jing and Zhao Fenghua (2009), which only has two shoulders occurring at 2θ of 18° and 28°, but also significantly distinguishable from that of Al-oxalate gels with different molar ratios of oxalate/Al, which were synthesized by Cristofaro et al (2000) (on the top right corner of Fig. 1), and almost no peaks appeared.…”

“…So, although it has no well-known tetrahedron-shaped structure of Al 13 -sulfate crystal, the crystallinity of the gel sample has developed relatively. (Cristofaro et al, 2000). d. Spacing in nanometer.…”

Effects of Oxalate and Humic Acid on Arsenate Sorption by and Desorption from a Chinese Red Soil

“…However, research on the effects of organic ligands on As(V) sorption and desorption in soil is very limited (Liu et al, 2001). Soil, especially the rhizosphere soil, has a relatively high content of low molecular weight organic anions, such as oxalate (Jones, 1998;De Cristofaro et al, 2000). Humic acid accounts for a large part of soil organic carbon.…”

“…Humic acid accounts for a large part of soil organic carbon. Both of them are highly reactive toward metal oxides and clay minerals (Sibanda and Young, 1986;Bhatti et al, 1998a, b;De Cristofaro et al, 2000) and therefore may have a profound effect on As(V) sorption onto and desorption from soil. The only literature available for the effect of oxalate is a description of the phenomenon of competitive sorption of As(V) and oxalate on goethite (Liu et al, 2001) and the relevant mechanism is poorly understood.…”