A critical evaluation of 1 m kci-extraction method for determining exchangeable al ions in variable charge soils

Shin-Ichiro Wada

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To explain why soils rich in variable charge materials often lack 1 M KCI-extractable Al ions, I proposed a mechanism, an “induced hydrolysis” of exchangeable Al ions in the presence of variable charge materials at high salt concentrations. I extracted exchangeable Al from mixtures of a montmorillonite saturated with Al and a synthetic goethite using a 1 M KCI solution. The amount of the extractable Al (per unit weight of the montmorillonite) decreased with increasing proportion of the goethite in the mixtures. I interpreted this experimental result as supporting the proposed mechanism, i.e., H+released in the hydrolysis of Al is adsorbed on the goethite in a concentrated KCI solution and this removal of H+induces further hydrolysis, resulting in the polymerization or precipitation of Al as hydroxides. I calculated the amount of monomeric, therefore extractable, Al as a function of the goethite content in the 1 M KCI-montmorillonite-goethite mixtures. The calculated amounts agreed well with the experimentally determined ones in the whole range of goethite content examined.

Original languageEnglish
Pages (from-to)153-160
Number of pages8
JournalSoil Science and Plant Nutrition
Issue number2
Publication statusPublished - Jan 1 1987


All Science Journal Classification (ASJC) codes

  • Soil Science
  • Plant Science

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