Sum of base cations vary between 0.84 and 3.16 cmol (+)/kg, and base saturation percentage is very low, leading to the classification of these soils in the group of desaturated Andosols. CEC is high, up to 36 cmol (+)/kg in the humiferous horizons. They present the same A(B)C horizonation, low bulk density (0.64 to 0.92 g/cm3) and very high porosity (58 to 71%). The raw andosol adsorbs much more phosphate ions than its fine fraction (0-2 m) because of the destruction of the allophane – humus complex during various extraction operations (crushing and dispersing).Īndosols of the upper zone of the eastern slope Bambouto Mountains are developed mainly on basaltic and trachytic rocks.
Minerals with hy-droxyl groups like allophane, gibbsite and goethite are responsible for the phosphate ions adsorption but these hydroxyl groups are destroyed in acidic medium. The removal of organic matter using hydrogen peroxide aqueous solutions enables to increase the quantity of the adsorbed phosphate ions at pH 6.6 from 4.15 mg/g to 6.10 mg/g. The adsorption ki-netics of the phosphate ions is of second order. Some surface properties like zero point charge (4.4), cationic exchange capacity (32.2 meq/100g), surface area (50.12 m2/g) of the material were measured. The particle size distribution analysis has revealed a low clay content (9 %) meanwhile the silt content is high (70 %).
The present work is focussed on the characterisation and the study of the surface properties of the Mount Bam-bouto andosols in view of their use in the adsorption of phosphate ions.
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