Reaction of OH-Al Polymers with Smectites and Vermiculites

Abstract--The effect of interlayering montmorillonite with different amounts ofhydroxy aluminum cation on the cation exchange capacity (CEC) and the point of zero charge (PZC) of the clay was studied. The CEC decreased as the A1 content of the clay increased. Both the CEC and the loss in the CEC were linearly dependent on the A1 content, thus indicating the predominance of a single polynuclear interlayered species. Its composition is [A16(OH)16.5] LS+. Acid base titration of the interlayered montmorillonites produced values for the PZC in the range 4.5-5.9, increasing with the A1 content of the materials. The values, however, did not represent real conditions of zero charge and some samples were still negatively charged at the determined PZC. The PZC values obtained by acid-base titration are thought to be adversely affected by secondary reactions involving the interlayered material with a concomitant release of soluble A1 in amounts dependent on the pH and ionic strength.

Section: The Cation Exchange Capacitymentioning

confidence: 71%

Cation Exchange Capacity and Condition of Zero Charge of Hydroxy-Al Montmorillonite

Helmy

Ferreiro

Bussetti

1994

“…Thus, it might be assumed that, for the HyA-Vt/Mt complexes formed at a higher OH/A1 ratio, larger sized HyA polymers were adsorbed on Vt. Aluminum polymers formed from hexameric ring structure [A16(OH)126+] might dominate over Al13 in the Vt and Mt interlayers, because the former has been reported to be preferentially adsorbed over the latter in the clay interlayers (Hsu 1992). Hsu (1992) suggested that some of the Al~3 polymers might be depolymerized to monomeric A1 in presence of clay.…”

Section: Resultsmentioning

confidence: 99%

“…Hsu (1992) suggested that some of the Al~3 polymers might be depolymerized to monomeric A1 in presence of clay. The monomeric A1, in turn, entered the clay interlayer and polymerized in situ.…”

Section: Resultsmentioning

confidence: 99%

Hydroxy-Interlayers in Expansible Layer Silicates and Their Relation to Potassium Fixation

Saha

Inoue

1998

Abstract--Hydroxyaluminosilicate (HAS) and hydroxyaluminum (HyA) ionic solutions having final A1 concentrations ranging from 3.74 to 4.00 mM; NaOH/AI molar ratios of 1.0, 2.0 and 2.5; and Si/A1 molar ratios of 0.00, 0.27-0.30, 0.51-0.56 and 0.95-1.01 were prepared through the interaction of AIC13, orthosilicic acid and NaOH solutions. When these solutions reacted with <2 p~m sized vermiculite (Vt) and montmorillonite (Mt), varying amounts of A1 and Si were fixed on Vt and Mt clays. Potassium fixation and exchange capacities of HyA/HAS (OH/A1 = 1.0, 2.0 and 2.5)-Vt and HyA/HAS (OH/AI = 2.0)-Mt complexes were compared with those of untreated Vt and Mt at added K levels ranging from 21 to 319 cmol c kg ~. The untreated Vt clay showed K fixation as high as 94 cmolc kg ~, in contrast to only 16 cmol~ kg ~ exchangeable K. The untreated Mt fixed a maximum of 9 cmol c K kg -1 out of a total K adsorption capacity of 67 creole kg-L In the HyA/HAS-Vt complexes, K fixation reduced drastically in comparison to untreated Vt, and ranged from 9 to 24 cmolc kg ~ out of their total K adsorption capacities of 61 to 81 cmol~ kg 1. In the HyA/HAS-Mt complexes, too, the amount of K fixed reduced to a great extent in comparison to Mt and ranged from 1.48 to 1.84 cmol c kg ~. Potassium became more exchangeable due to the presence of hydroxy-interlayers in the clays. The reduction in CEC and the well-known propping effects of hydroxy-cations' islands in the interlayers might have hindered K fixation by the complexes. The relationships of maximum K fixing capacities of the HyA/HAS-Vt complexes with the amounts of A1, Si and AI + Si fixed on Vt were all exponential and negative. However, the amount of AI + Si or only A1 fixed on Vt appeared to be the best indicator of K fixation capacities of hydroxyinterlayered Vt clay.

“…This behavior is typical of most montmorillonites. The sorption of various cations by hectorite and montmorillonite is different (Villemure 1990;Davison et al 1991), while some A1-OH polymers had similar preferential adsorption by both (Hsu 1992). Various species, such as metal-oxide pillars and organic or organometallic complexes, have recently been incorporated into the structure of synthetic hectorites to improve the catalytic properties of the products (Luca et al 1991;Barranlt et al 1992;Carrado 1992;Bergaya et al 1993).…”

Section: Introductionmentioning

confidence: 99%

Dissolution of Hectorite in Inorganic Acids

Komadel

1996

105

Abstract--The effect of acid type and concentration on the reaction rate and products of dissolution of hectorite in inorganic acids was investigated. The dissolution of hectorite in hydrochloric (HC1), nitric (HNO3) and sulphuric (H2SO4) acids was characterized using quantitative chemical analysis, infrared (IR) and multinuclear MAS NMR spectroscopies. The rate of dissolution increased with acid concentration and decreased in the order HC1 --> HNO 3 > H2SO 4 at the same molar concentration. No differences were found in the reaction products of hectorite treated with the three acids. The rate of Li dissolution was slightly greater than that of Mg at lesser acid concentrations (0.25 M), indicating that protons preferentially attack Li octahedra. The gradual changes in the Si-O IR bands reflects the extent of hectorite dissolution. The analysis of 298i MAS NMR spectra relative peak intensities with dissolution time and acid concentration provided direct dissolution rates for tetrahedral (Q3) Si. After acid dissolution, most Si was bound in a three dimensional framework site (Q4), but a substantial part also occurred in the Si(OSi)3OH (Q31 OH) and Si(OSi)2(OH)2 (Q22OH) environments. These three sites probably occur in a hydrous amorphous silica phase. Both Aliv and Alw rapidly disappeared from 27A1 MAS NMR spectra of the dissolution products with acid treatment. The changes in IR and MAS NMR spectra of hectorite due to acid dissolution are similar to those of montmorillonite.