Hydroxyaluminosilicate Ions Research Articles

SPECIATION OF ALUMINUM IN HYDROXYALUMINUM AND HYDROXYALUMINOSILICATE IONS FIXED BY MONTMORILLONITE, USING 27Al-NMR AND ICP-AES

We tried to elucidate the chemical species of hydroxyaluminum (HyA) and hydroxyaluminosilicate (HAS) ions intercalated into the Mt focusing on the Al by means of 27 Al-NMR, inductively coupled plasma atomic emission spectroscopy (ICP-AES), differential thermal analysis (DTA), x-ray diffraction (XRD), and fourier-transform infrared (FTIR). Using 27 Al-NMR and ICP-AES, the Al in a Al-OH-Si(OH) 4 mixture was separated into three fractions; Al 13 , Al SYM , and Al NON . The Al 13 and Al SYM were quantitatively determined by 27 Al-NMR at 62.5 and 0 ppm, respectively. The Al NON was defined as the Al which can be determined by ICP-AES but not by 27 Al-NMR. The Al SYM was attributed to electrically-symmetric octahedral Al including monomer (and dimer) HyA ions, and the Al NON was attributed to electrically-asymmetric Al including HAS and/or polymer HyA ions. Among the HAS and HyA solutions prepared, the proportion of Al 13 ion was higher in the smaller Si/Al ratio. The HAS solutions with the Si/Al ratio greater than 0.24 contained no Al 13 ion. As result of adsorption kinetics of Al 13 , Al SYM , Al NON , and orthosilicic acid in three solutions on the montmorillonite (Mt), most of the adsorption reaction occurred within I min., and Al 13 and HAS ions were selectively adsorbed by Mt compared with the Al SYM . The HyA-Mt complex showed a great expansion in the d-spacing compared with Mt, and the d-spacing of the HyA-Mt was 1.64 nm and its peak was broad. On the other hand, the strongest peak of the HAS-Mt was mostly at around 1.80 nm, irrespective of the Si/Al ratios of the HAS ions used. Intercalation of HAS ions may occur completely since the enlargement of the d-spacing was clearly seen by XRD and no specific absorption bands were not seen by FTIR. Most of the thermal characteristics of the Mt would be modified by the intercalated HAS ions with a higher Si/Al ratio greater than 0.05. These results indicate that, upon the intercalation of Mt, the outer surface properties detectable by the FTIR were not modified greatly, while the internal surface structure of the complex detected by XRD and DTA analyses was modified greatly. Al 1 3 ions could not be fixed in the interlayer space of the Mt, and most of the changes was brought by the fixation of HAS ions in the internal space of Mt.

Kinetics of citrate-induced selenite desorption from montmorillonite as affected by complexation with hydroxyaluminum and hydroxyaluminosilicate ions

AbstractThe citrate-induced desorption kinetics of pre-adsorbed Se from montmorillonite (Mt) and its complexes with hydroxyaluminum (HyA-Mt) and hydroxyaluminosilicate (HAS-Mt) were studied. The mole fraction of pre-adsorbed Se released in 24 h from different clays followed the trends of Mt>> HAS-Mt> HyA-Mt with a significant increase with elevated citrate concentration in the desorbing solution. In contrast, the amount of Se adsorbed per unit mass of different clays followed a clear-cut opposite trend of HyA-Mt>HAS-Mt>>Mt. The Se desorption kinetics in different systems indicated multiple rate characteristics; where an initial fast reaction (0.25–2 h) was followed by a slow reaction (2–16 h). Of the six different kinetic models tested (zero-, first-, and second-order; power function, Elovich, and parabolic diffusion), the second-order rate equation showed the overall best fit to the fast and slow desorption kinetic data from the clays. Based on second-order rate constants, the rates of the mole fraction of Se desorption by citrate from different clay systems at 298 K followed the order Mt > HAS-Mt >> HyA-Mt. For both fast and slow reaction, the rates of desorption increased proportionally with the level of citrate. Replicate experiments conducted across a range of temperature (288–318 K) yielded Arrhenius parameters that followed the order HyA-Mt > HAS-Mt >> Mt. Considering that a lower mole fraction of Se desorption after a particular reaction period, slower desorption kinetics, and a greater activation energy of desorption are the indices of increased adsorption bond strength, the results clearly indicate that HyA- and HAS-interlayering and coatings on Mt not only augmented its Se adsorption affinity and capacity, but also increased the adsorption bond strength. Silication in HyA not only reduced the Se adsorption capacity, but also weakened the adsorption bond strength. This establishes a significant role of HyA/HAS-interlayering and coating on Mt in influencing the rate of citrate-induced release of Se. Reduction in surface-positive potential following citrate adsorption on the clay surface, a direct ligand exchange between Se and citrate, and structural dissolution are possible mechanisms responsible for citrate-induced Se desorption in the present study.

Role of hydroxy-aluminosilicate ions (proto-imogolite sol) in the formation of humic substances

Little is known of the role of solution species of soil aluminosilicates in the formation of humic substances. Catalysis by hydroxy-aluminosilicate (HAS) ions, one of the major forms of soluble aluminum and silicon and the precursor of noncrystalline aluminosilicates in acidic natural environments, in catechol humification was investigated in this study by using UV-visible, FTIR, and solid state 13C CP–MAS NMR spectroscopies, X-ray diffractometry, atomic force microscopy, and elemental analysis. Hydroxy-aluminosilicate ions substantially promoted the oxidative polymerization and ring cleavage of catechol, resulting in the formation of black precipitates of humic macromolecules. This abiotic catalysis by HAS ions merits close attention in understanding the formation and related geochemistry of humic substances especially in acidic environments in temperate and subtropical regions.

Phosphate Adsorption Behavior of Hydroxyaluminum- and Hydroxyaluminosilicate-Vermiculite Complexes.

Phosphate adsorption behavior of vermiculite (Vt) complexed with hydroxyaluminum (HyA) and hydroxyaluminosilicate (HAS) ions were studied at equilibrating solution pH ∼ 5.0. The HAS ions were prepared from solutions containing HyA ions and orthosilicic acids at an Al concentration of ∼4 mM; Si/Al atomic ratios of 0, 0.25, 0.50, and 1.0; NaOH/Al molar ratios of 1.0, 2.0, and 2.5. At initial P concentration of 0.25 to 50 mM, the adsorption of phosphate by these complexes decreased with increase in the NaOH/Al and Si/Al ratios of hydroxy materials fixed on Vt. When adsorption data were evaluated using the Scatchard plots of Langmuir equation, multiple linear relationships were observed which suggested the presence of multiple population of adsorption sites that have a differing affinity for phosphate ions. Both adsorption maxima and binding energy for the adsorption sites in the higher (region I) and lower (region II) affinity regions of different complexes were in decreasing trends with increasing NaOH/Al and Si/Al ratios of the fixed ions. The total phosphate adsorption maxima of different complexes ranged from 0.40 to 0.96 mmole g -1 in comparison to only 0.17 mmole g -1 as found for untreated Vt. Ligand exchange reactions in which phosphate ions displaced OH or OH 2 groups from coordination shells of structural Al on the edges of Vt and HyA or HAS polymers fixed on external planar surfaces and/or interlamellar spaces of Vt may be involved in the phosphate adsorption processes in region I. In region II, phosphate adsorption may be occurred through ligand exchange predominantly with OH groups linking Al atoms inside the polymeric structure of the fixed HyA or HAS ions. In the HAS-Vt complexes, upon phosphate adsorption, the resultant HAS-phosphate complexes were substantially to almost entirely expelled from the interlamellar spaces of Vt. While, only a partial expulsion of the interlayer HyA-phosphate complexes was noticed following phosphate adsorption by the HyA-Vt complexes. Very high phosphate adsorption capacities of the complexes as evaluated in the present study merit attention in P-fertility management in acidic and nonallophanic Andisols and related soils.

A comparison of some commonly used adsorption isotherms in describing phosphate adsorption by hydroxy-interlayered expansible clays

Several commonly used adsorption isotherms were applied to phosphate adsorption data for 24 different complexes of hydroxyaluminum (HyA) or hydroxyaluminosilicate (HAS) ions with montmorillonite (Mt) or vermiculite (Vt) clays. The applied isotherms were evaluated with regards to their goodness of fit utilizing different criteria adopted by several earlier workers for this purpose. Relative merits and limitations of those criteria were discussed on statistical ground. The isotherm equations were found to describe the phosphate adsorption data with different levels of success. The two surface Langmuir equation was found to be the best in describing the adsorption data suggesting the existence of two different populations of adsorption sites on the HyA/HAS-Mt/Vt complexes that have varying affinities for phosphate ions. The OH or OH 2 groups coordinated with Al atoms at the broken edges of HyA or HAS polymers fixed on the external planner surfaces, and/or in the interlayer spaces of Mt/Vt were assumed to be predominantly involved in the ligand exchange reaction of phosphate adsorption in Region I. Ligand exchange predominantly with OH groups linking Al atoms inside the polymeric structure of the fixed HyA or HAS ions was assumed to be the principal adsorption process in Region II. The Temkin equation, however, was almost equally successful which was followed by the Freundlich equation in terms of their goodness of fit. The estimated adsorption parameters of different equations fitted were although numerically different but were positively and significantly correlated with each other at 1% level of significance suggesting that these parameters are relevant to describe phosphate adsorption behavior of the complexes as well as possess wide confidence limits.

Interlayer Adsorption of Polymeric Hydroxy‐Aluminosilicate Ions by Montmorillonite

AbstractAdsorption of polymeric hydroxy‐aluminosilicate (HAS) ions by montmorillonite and the formation of siliceous Al interlayers were studied. The interaction of HAS ions with Ca‐montmorillonite exhibited a linear C‐type adsorption isotherm within the range of solution Al and Si levels commonly found in acidic soils (10−5 to 10−4 M), suggesting a high capacity of Ca‐montmorillonite to adsorb HAS ions from solution. A soluble Si concentration of >6.6 × 10−5 M was required for the formation of HAS species and their adsorption by montmorillonite. The interlayer spacing (12.2–16.8 Å at 25°C and air dried) and the intensity of the major infrared bands of the adsorbed HAS ions (940 and 3500 cm−1) in the HAS‐montmorillonite complexes were found to increase with the increasing amount of HAS ions adsorbed, which further substantiated the interlayer adsorption mechanism for HAS‐smectite interactions. The partial interlayering of HAS ions in Ca‐montmorillonite resulted in the formation of HAS‐clay complexes with basal spacings of ≈12Å (at 25°C, air dried). The data suggest that the partial hydroxy‐interlayers of natural clays in acidic environments in temperate and subtropical regions may be siliceous in nature, depending on the Si level in soil solutions and other natural waters.

Ionic Factors Affecting the Formation of Short‐Range Ordered Aluminosilicates

AbstractThe formation of short‐range ordered aluminosilicates is substantially influenced by organic and inorganic ligands, metallic cations, and montmorillonite. Chemical composition, size, number, and nature of the functional groups, and concentrations of non‐humified organic acids play a vital role in perturbing the formation of allophanes and imogolite. Humic substances also substantially perturb the interactions of hydroxy‐Al ions with orthosilicic acid and thus inhibit the formation of these aluminosilicates. Inorganic ligands such as phosphates and sulfates vary in their ability to impede the formation of these aluminosilicates. Iron has a stronger inhibiting effect than Mn on imogolite formation, resulting in the formation of poorly ordered mineral colloids. Adsorption of hydroxy‐aluminosilicate (HAS) in the interlayers of montmorillonite results in an expanded structure. The transformation of HAS ions to noncrystalline aluminosilicates can, therefore, be affected by naturally occurring expansible layer silicates such as montmorillonite. These ionic factors perturb the genesis of allophane and imogolite to various extents, resulting in the formation of ill‐defined aluminosilicate complexes, HAS‐interlayered expansible layer silicates, and/or precipitated hydroxy‐Al‐organic or ‐inorganic complexes. Organic and inorganic ligands with a strong affinity for Al significantly modify the nature of the soluble products, which range from proto‐imogolite sol complexed with organic or inorganic ligands to hydroxy‐Al‐organic or‐inorganic complexes.

Composition and behavior of aluminum ions and colloidal aluminosilicates in acidified terrestrial waters

Abstract The composition of aluminum in seven acidified lake and river waters in the Tohoku district was studied, and Al3+ and hydroxy-Al (HA) ions were identified in the acidified waters. These acidified terrestrial waters contained a small but significant amount of hydroxyaluminosilicate (HAS) ions. Colloidal alumino- silicates (>0.2 μm) identified in the waters were characterized by the predomi- nance of proto-imogolite allophane and/or allophane. The white precipitates and gelatinous materials formed in the acidified terrestrial waters were com- posed of precipitated allophane. The acidic substances of the terrestrial waters were mainly composed of Al3+, HA, and HAS ions. HAS ions and HAS colloids were first identified in the lake and river waters. The presence of HAS ions and HAS colloids in the waters provides valuable information on the formation mechanism of precipitated allophane in the acidified terrestrial waters. The reaction giving a peculiar bluish-white color in some lakes could arise from ...

Adsorption of Humic Substances by Hydroxyaluminum‐ and Hydroxyaluminosilicate‐Montmorillonite Complexes

AbstractThe interaction between humic substances purified from an Andisol and montmorillonite (Mt) complexed with hydroxyaluminosilicate (HAS) or hydroxyaluminum (HyA) ions was studied. The HAS ions were formed from solutions containing HyA ions and orthosilicic acid at an Al concentration of 4 mM; Si/Al atomic ratios of 0, 0.25, 0.5, 0.75, and 1.0; and a NaOH/Al molar ratio of 2.0. The adsorption of humic substances by HAS‐Mt and HyA‐Mt complexes increased as pH decreased in the adsorption systems. At concentrations of 10 to 1000 mg humic substance L−1 and pH 5.5, the adsorption of humic acid by these complexes decreased with an increase in the Si/Al atomic ratio of hydroxy materials fixed in interlamellar spaces of Mt, whereas the adsorption of fulvic acid followed almost the opposite trend. When the adsorption data of humic substances by these complexes were evaluated using the Eadie‐Hofstee plot of the Langmuir adsorption equation, multiple linear relationships were obtained, indicating the presence of multiple populations of sites that have a differing affinity for humic substances. A ligand exchange reaction, in which humic substances displaced OH or OH2 groups from the coordination shells of structural Al on the edges and HAS or HyA polymers fixed on the edges, external planar surfaces, and/or the interlamellar spaces of Mt, may be involved in the adsorption processes. The results indicate that besides HyA ions, the reactivity of HAS ions in humus accumulation and the pedogenic implication in soil environments merit attention.

Hydroxy-aluminosilicate interlayers in montmorillonite: implications for acidic environments

Hydroxy-aluminosilicate (HAS) ions are one of the major forms of soluble aluminium and the precursor of non-crystalline aluminosilicates in acidic (pH<5.5) environments1–6. Acidification in acid-vulnerable areas7,8 would thus promote HAS formation. Over four decades the study of interactions of soluble aluminium species with clay minerals has been focused on the deposition of hydroxy-aluminium in interlayer spaces of expandable layer silicates9–12. Although the synthesis of 'hydroxy-silicoaluminium pillared smectites' as cracking catalysts has been recently attempted13, the nature of the dominant species adsorbed by smectites from the mixture of HAS, hydroxy-aluminium ions and silicic acid remains obscure. Here we provide evidence that HAS ions can be adsorbed in the interlayer spaces of montmorillonite, resulting in an expanded structure, and so the natural occurrence of HAS-interlayered layer silicates merits attention. Furthermore, the transport of HAS ions, their transformation to non-crystalline aluminosilicates and the levels of toxic solution aluminium species in acidic terrestrial and aquatic environments can thus be affected by naturally occurring expandable layer silicates such as montmorillonite.

Fixation of hydroxy aluminosilicate ions (proto-imogolite) on smectite

Abstract Hydroxy aluminosilicate (HAS) ions, which were derived from solutions containing hydroxy Al (HA) ions and orthosilicic acid for various Si/Al atomic and NaOH/Al molar ratios and at the initial Al concentrations of 3.8 and 15.2 mM, were strongly fixed in the interlayer spaces of smectite. After treatment of the HAS-smectite complexes with 1/3 M AlCl3, the amount of KC1 exchangeable Al3+ adsorbed on the complexes (“strong” acid exchange sites) was approximately 77 to 39% of that on smectite, whereas the amount of exchangeable H+ adsorbed on the complexes (“weak” acid exchange sites) was approximately 4.4 to 2.7 times as large as that on smectite. The complexation of HAS ions with smectite decreased the CEC from 0.65 to 0.27–0.48 meq/g, depending on the Si/Al atomic and NaOH/Al molar ratios and the Al concentration. The HAS-fixation on smectite was also confirmed by X-ray diffraction analysis. The phosphate retention by the HAS-smectite complexes was approximately 40 to 70 times as high as that by smectite. The HAS-fixation in the interlayer spaces of smectite caused a marked decrease of the swelling ability. The present results indicate that the fixation of HAS ions on smectite markedly alters its physical and chemical characteristics, such as swelling and shrinkage, CEC, anion retention, and probably K+ and NH4 + fixation.