Precipitation and characterization of two novel aluminum hydroxo phthalates formed in the presence of silicic acid

Horvath, Laszlo; Bilinski, Halka; Radics, Lajos; Ingri, Nils (2004) Precipitation and characterization of two novel aluminum hydroxo phthalates formed in the presence of silicic acid. Croatica Chemica Acta, 77 (3). pp. 469-476. ISSN 0011-1643

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Abstract

The present work, performed at constant ionic strength of 0.6 mol dm(-3) NaCl at 25 degreesC, is a continuation of long-term studies of the conditions necessary for initial clay formation in model systems containing organic acids, Al and Si. Solid phases and the precipitation boundary characterizing the system H+-Al3+-phthalic acid (H2L)-silicic acid were determined and compared with the previously found compound Al-2(OH)(4)L (-) 4H(2)O (A) of a monoclinic unit cell, which was formed in the absence of Si. Addition of Si induced precipitation of two novel compounds (B and C) of the orthorhombic unit cell. Compound B was formed at a low L/Al ratio (R less than or equal to 2) and was of variable composition: AlxSi1.450-0.725 (OH)(3.8+/-0.1x) L(.)6H(2)O. It was found by calculation that at R less than or equal to 2 the end member with x = 2, Al-2(OH)(4)L (.) 6H(2)O, determined the precipitation boundary. Compound C formed at R > 2 had the constant composition Al(OH)L (.) 3H(2)O. Formation constants beta(p,q,r) were determined for the general equation pH(+) + qAl(3+) + rL(2-) --> HpAlqLr. The obtained values for compounds B and C are: log beta(-4, 2, 1) = -7.40+/-0.10 and log beta (-1, 1, 1) = 1.55 +/- 0.05, respectively. In addition to chemical analysis, thermogravimetry (TG), X-ray diffraction (XRD), infrared spectroscopy (IR), solid state Al-27 MAS NMR, Si-29 MAS NMR and Na-23 MAS NMR techniques were used for better characterization of solids and to detect possible impurities in them. Aluminum was found to be hexa-coordinated in all compounds. The IR spectra suggest that the phthalate ion acted as a bidendate ligand, bridging two aluminum atoms in solids B and C.

Item Type:

Article

Uncontrolled Keywords:

aluminum hydroxo phthalates; formation constants; effect of silicic acid; model clay formations; solid state NMR; Al-27 MAS NMR; Si-29 MAS NMR; Na-23 MAS NMR; 0.6 m Na(Cl); initial clay formation; aqueous-solution; hydrolyzed aluminum(iii); Na+ system; equilibrium; silicon(iv); complexes; 25-degrees-C; spectra

Subjects:

NATURAL SCIENCES > Chemistry

Divisions:

Division of Physical Chemistry

Projects: