Specific surface area and surface charge characteristics of some Alfisols and Ultisols from Nigeria were studied. Specific surface are measured by ethylene glycole retention was generally 2 to 3 times greater than the specific surface area measured by N2 adsorption for both surface and subsoil samples. Soils derived from basalt had the greatest surface area per gram of clay as measured by both methods.The surface charge‐pH curves of the soils bear the characteristic features of metallic oxides, indicating that surface charge behaviour of the soils studied follows the constant potential model. Values of PZC for Alfisol and Ultisol samples ranged from pH 3.0 to 3.9. Subsoils generally have higher PZC than corresponding surface horizons. Specific adsorption of sulfate resulted in a shift of the PZC to a higher value and an increase in the magnitude of positive charge.Cation and anion retention measurements showed that soils derived from basement complex rocks and sandstones contain negligible amount of positive charge while soils from basalts bear moderate amount of positive charge at their natural pH condition. Evidence also indicated that the Alfisols and Ultisols bear a small amount of permanent negative charge ranging from 1 to 4 meq/100 g.The limitation of using CEC value determined by conventional procedures as a criteria for soil taxonomy is discussed.
Clay minerals in eight soil profiles from southern Nigeria were investigated by means of X‐ray diffraction, infrared spectroscopy, differential thermal analysis, and electron microscopy. These soils are derived from basement complex rocks, arenaceous sedimentary rocks and basalts.Kaolinite is the most predominant clay mineral for all the soils studied. A pronounced variation in clay mineralogy was found in the soils derived from basement complex rocks sampled at various locations along a toposequence. Halloysite occurs in freshly weathered materials, while smectite is found in poorly drained, lower members of the toposequence.Gibbsite occurs in soil derived from cretaceous arenaceous rocks in the high rainfall area. Among all soils studied, the highest amounts of amorphous Al silicate and extractable Fe and Al oxides were found in those derived from basalts. In all cases, Fe oxides exist predominantly in crystalline forms.
Silica sorption by some Alfisols and Ultisols from southern Nigeria was studied. The percentage of silica lost from a solution brought into contact with a soil is called the index of silica reactivity (ISR).For reference samples, the scale of ISR follows the order kaolinite < < goethite < gibbsite. For soils where Iron oxides are the only sorbing phases, ISR is ruled by the part of the total specific surface area due to these oxides. More generally, however, ISR is sensitive to both the nature and the magnitude of the surface area so that soils rich in gibbsite exhibit higher ISR than the soils devoid of this mineral. To become useful as a comparative index, ISR should be amended so as to also take into account the specific reactivity of the different minerals with respect to soluble silica.
gungen konnen daher Anilinriickstande nur in geringsten Mengen im Bodenwasser auftreten. ln alien Fallen wird die Adsorption von einem Hysteresis-EITekt begleitel. Allerdings /eigle sich deutlich, dass Salzl6sunge[i(CaCl2t eine hohere Freiselzungskraft aufweisen. Einfluss des Httmus-tind Bodcnwassergchaltes au/ die Adsorption des Anilins Die Adsorplion des Anilins im Boden hSngl vom Humusgehait ab. Dabei scheint der Frakiion der Huminsauren eine entscheidende Bedeutung zuzukommen. Der konkurreierende Efl'ekt des Bodenwassers auf die Adsorption des Anilins wurde aufge^eigt. Die Konzentration der kollodialen Bodensuspension beeinflusst die Adsorption stark. Unter naturlichcn Bedin-,r .• 350 A. Moreale, A. Gallez et R, Van. Bladel'
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