Sorption of Inorganic Phosphate by Iron‐ and Aluminium‐ Containing Components

Abstract

The amounts of inorganic P sorbed by a range of Fe-and Al-containing components varied appreciably and decreased in the order allophane > fresh A1 gel > Fe gel pseudoboehmite > aged AI gel > dried Fe gel > Fe-coated kaolinite > hacmatite > goethite > akaganeite > gibbsite = ground kaolinite > dispersed kaolinite. A1 gel sorbed 30 to 70 times more P than gibbsite. and Fe gel sorbed approximately 1 0 times more P than its crystalline analogues (haematite. goethite. and akaganeite). Despite large differences in the extent of P sorption. the form o f the isotherm was essentially the same for each sorbent. The ability of freshly-prepared A1 gel suspensions to sorb P decreased with ageing, a property not shown by Fe gel. Drying of Fe gel at 80 "C. however, caused an approximately 4-fold decrease in P sorption. Precipitation of Fe gel (2% Fe) on the surface of kaolinite increased P sorption by a factor of 10. The occurrence of Fe gel as a coating apparently presents more sorption sites to solution per unit weight of Fe gel than Fe gel alone. A linear relationship ( r = 0.98) was obtained between the amount O H -sorbed per unit increase in pH value ('hydroxyl buffering') and the overall P sorption maximum for each sorbent. Hydroxyl buffering provided a better index of P sorption potential than specific surface area. Except for the crystalline Fe sorbents, isotherms obtained by plotting fractional sorption saturation against final solution P concentration for the sorbents were essentially coincident with those for several contrasting soils. For crystalline Fe components a lower relative amount of weaker sorption, as opposed to chemisorption, of the overall sorption maximum was obtained. Differences in the extent of P sorption. however. appear t o be primarily related to the number of functional M-OH groups presented at the solid-solution interface. IntroductionTHE RESULTS of several studies (Williams et af., 1958; Broomfield, 1965; Saunders, 1965;Syers et al., 1971) indicate that the sorption of inorganic phosphate (P) by soils of pH less than 7 is closely related to the amounts of reactive Fe and Al components. It is well established in the literature, however, that the Fe and Al components which occur in soils vary appreciably in their ability to sorb P. In general, short-range order (amorphous) hydrous metal oxides of Fe and Al sorb considerably greater amounts of P than do their crystalline counterparts (Gastuche et al.. 1963; Bache, 1964) and hydrous metal oxides usually sorb more P than layer silicates (Muljadi et al., 1966). Allophanic materials also sorb appreciable amounts of P (Cloos et al.. 1968).

Sampling, sample treatment and quality assurance issues for the determination of phosphorus species in natural waters and soils

“…This increases organic matter solubility and exposes formerly protected mineral surfaces, and has been attributed to increases in oxalate-extractable silica of up to 200% following drying of Swedish spodic B horizons [68]. Soil drying also increases the crystallinity of pure iron and aluminium oxides, which reduces the specific surface area and phosphorus sorption capacity of these minerals [69]. However, this is inconsistent with reports of increased sorption capacity of dried soils for phosphate and sulphate [70,71].…”

Adsorção de fósforo em frações argila na presença de ácido fúlvico

“…Hingston et al (1978) postularam que o mecanismo de ligação para adsorção específica de diversos ânions inorgânicos sobre goethita ocorreu pelo deslocamento de OH ligadas com Fe e Al por coordenação simples. Mclaughlin et al (1981) observaram, entre sistemas mineralógicos sintéticos formados por goethita, hematita, caulinita e caulinita contendo Fe precipitado em superfície, que a goethita foi o material que mais adsorveu P. Para esse acontecimento caberia a explicação de Fontes & Weed (1996), os quais relatam que a goethita, por ter maior densidade de OH em coordenação simples em uma de suas faces cristalográficas (100), proporcionou maior afinidade de ligação com íons de fosfato (Atkinson et al, 1974;Parfitt et al, 1976), sendo isso também observado para hematita em menor intensidade.…”

Forms and Availability of Soil Phosphorus in Temperate Forests in Southern Chile and Flanders

“…Andosols are characterized by a high phosphate retention capacity due to the presence of allophanes, imogolite, Al and Fe (oxy)hydroxides and Al and Fe humus complexes (Driessen & Dudal 1991). P sorption on inorganic surfaces includes: (i) ligand exchange of aluminium oxides and -hydroxides (McLaughlin et al 1981), as well as of surface-bound silicate and bisulphate (Rajan & Fox 1975) and (ii) precipitation of Al phosphates. Andosols contain relatively large fractions of organic matter, which play an ambiguous role for P sorption: (i) organic matter counteracts P sorption by blocking P sorption sites and by competition between P and organic anions for sorption sites (Mora & Canales 1995), (ii) organic matter stimulates P sorption by stabilizing Al/Fe surfaces and organic matter promotes formation of new anion sorption sites (Kwong & Huang 1979).…”