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.