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Aluminium solubility related to secondary solid phases in upper B horizons with spodic characteristics
Author(s) -
Simonsson,
Berggren
Publication year - 1998
Publication title -
european journal of soil science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.244
H-Index - 111
eISSN - 1365-2389
pISSN - 1351-0754
DOI - 10.1046/j.1365-2389.1998.00153.x
Subject(s) - solubility , imogolite , chemistry , gibbsite , dissolution , oxalate , solubility equilibrium , pyrophosphate , podzol , aluminium , inorganic chemistry , soil water , allophane , mineralogy , nuclear chemistry , clay minerals , geology , organic chemistry , enzyme , soil science
We examined the aluminium solubility in the upper B horizon of podzols and its relation to the solid phase of the soil in 60 samples covering a pH range from 3.8 to 5.1. Solid phases were characterized by extractions with acid oxalate and pyrophosphate (pH 10). The solubility of Al was studied in a batch experiment in which samples were equilibrated with 1 m m NaCl at 8°C for 5 days. We also monitored the dissolution kinetics of Al and Si, in some samples. The oxalate and pyrophosphate extractions suggested that secondary Al was mainly organically bound in most soils, and imogolite‐type materials seemed to constitute much of inorganic secondary Al. No single gibbsite or imogolite equilibrium could explain Al 3+ activities. In all samples Al solubility, defined as log{Al 3+ } + 1.65pH, was closely related to the molar ratio of aluminium to carbon in the pyrophosphate extracts (Al p /C p ). Solubility increased with the Al p /C p ratio until the latter reached ≈ 0.1. This indicated that solubility was controlled by organic complexation, at least when Al p /C p was small. Silica dissolved slowly in most soils used in the kinetic experiments. We conclude that imogolite‐type materials in the upper B horizon dissolved slowly because of coating with humic substances or ageing or both.