Organic and inorganic phosphate interactions with soil hydroxy-interlayered minerals

Abstract

Background Even though extensive work has been done on P interactions with free Al-and Fe-hydroxide minerals, limited or no information exists on sorption/desorption processes of organic and inorganic phosphate forms with soil hydroxy-interlayered minerals.Purpose The purpose of this study was to assess the potential of soil clays rich in hydroxy-interlayered vermiculite (HIV) and smectite (HIS) minerals to adsorb and release inorganic and organic P forms as compared to geological reference gibbsite and goethite minerals. Methods Seven-day P adsorption/desorption experiments were conducted involving six soil clays containing >40% HIV, two soil clays containing >55% HIS, and two reference goethite and gibbsite clays equilibrated with P pools consisting of 10 mg P g -1 clay from KH 2 PO 4 or inositol hexakisphosphate. Results The results indicated a strong tendency for HIV and HIS minerals to sorb P at amounts equivalent to or even higher than those sorbed by gibbsite or goethite minerals. Organic P was sorbed at higher quantities and was retained with greater energy than inorganic P forms. Ammonium oxalate-treated samples produced a clearer picture of the net contribution of hydroxy-interlayered minerals to P sorption capacity compared to free Al/Fe hydroxide components, but the degree of Al-hydroxy-interlayering somewhat obscured P-sorption mineral quantity correlations. Increasing Psorption equilibration times generally increased total inorganic and organic-sorbed P loads only of the ammonium oxalate treated samples, suggesting increased P interaction with less accessible interlayer reactive sites. Reaction times had no significant effect on P desorption characteristics, although some samples released less P at longer equilibration times probably due to readsorption processes. Conclusions The findings suggest that soils containing high amounts of hydroxy-interlayered minerals may act as good P sinks and tolerate higher organic P loads than free Al or Fe hydroxides without increasing risks of P contamination.

Capacidade máxima de adsorção de fósforo relacionada a formas de ferro e alumínio em solos subtropicais

“…O efeito de cimentação e de recobrimento que os óxidos de Fe e a matéria orgânica exercem sobre os demais componentes da fração argila dos solos pode impedir que eles manifestem sua atividade de superfície (Souza Junior et al, 2007) e do Al presente nas entrecamadas dos minerais de argila do tipo 2:1, que podem adsorver grande quantidade de P (Karathanasis & Shumaker, 2009). Ao retirarem esses componentes do solo, os minerais residuais expõem suas superfícies, que, de modo geral, também apresentam grande quantidade de hidrolixas.…”

“…Entretanto, para as amostras que apresentaram CMAP < CMAP d evidencia-se o acúmulo de minerais, como a gibbsita, os minerais de argila 1:1 (Ct) e 2:1 com Al na entrecamada (vermiculita e, ou, esmectita), com grande afinidade pelos íons fosfato após a remoção dos óxidos de Fe. Esses minerais presentes na argila d apresentam superfícies hidroxiladas associadas aos grupos funcionais superficiais aluminol ([]Al-OH) e silanol ([]Si-OH), os quais podem ter grande participação na adsorção de P (Novais & Smyth, 1999;Penn et al, 2005;Karathanasis & Shumaker, 2009). Esta interpretação é comprovada quando se analisam os difratogramas da fração argila concentrada em óxidos de Fe e da argila d para as amostras de Horizonte (CMAP d < CMAP), Serra do Aleixo (CMAP d ~ CMAP) e Vila Branca (CMAP d > CMAP) (Figura 3).…”

“…Outros autores já encontraram elevada adsorção de P para óxidos de Fe mais cristalinos (Peña & Torrent, 1984;Torrent, 1987), gibbsita (Leal & Velloso, 1973;Lopes & Cox, 1979;Eberhardt et al, 2008;Barbieri et al, 2009;Pozza et al, 2009), caulinita (Goldberg & Sposito, 1985) e minerais de argila 2:1 com hidroxi-Al nas entrecamadas (Penn et al, 2005;Karathanasis & Shumaker, 2009 O P-rem na fração argila variou entre 1,29 e 31,60 mg L -1 e apresentou elevada e significativa e correlação negativa (r = -0,86, R 2 = 0,74, p < 0,01) com a CMAP (Figura 4a). Para cada aumento de 1 mg L -1 de P-rem, observa-se decréscimo de 54,11 mg kg -1 na CMAP.…”

Identification of inositol hexakisphosphate binding sites in soils by selective extraction and solution 31P NMR spectroscopy

“…This can occur by adsorption to aluminum (Al) and iron (Fe) hydroxides/oxides, clays, or calcite, association with organic matter, or precipitation with cations as phytate (salts of myo-IP 6 ) (Celi and Barberis, 2007;Karathanasis and Shumaker, 2009). Adsorption may occur through a ligand exchange mechanism between the phosphate groups and surface reactive OH − or H 2 O groups on the adsorbents (Celi and Barberis, 2007;Ognalaga et al, 1994), although a recent study indicates that the adsorption to goethite occurs as an outer sphere complexation in which hydrogen bonds between the surface of goethite and IP 6 are formed (Johnson et al, 2012).…”

Effect of pH on the release of soil colloidal phosphorus

“…Moreover, a high pH increased the negative charge on the colloids and grain surfaces and enhanced electrostatic repulsion to facilitate colloid release (Hu et al 2008). In addition, P distribution on the colloids, which is dependent on surface property and chemical composition of colloids (Karathanasis and Shumaker 2009), determines the transformation of P species (Sato et al 2009) and transportation of P (Filella et al 2006). The pH, oxalateextractable Fe and Al, and organic carbon were shown to be the main factors influencing the P sorption index in soils (Martinez et al 1996;Xi et al 2007).…”