Kaolin-smectite transformations and soils of midwestern Nigeria

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" Kaolin-smectite transformations and soils of midwestern Nigeria "
O. I. S. Imasuen W. S. Fyfe

Document Type	:	Latin Dissertation
Language of Document	:	English
Record Number	:	1112547
Doc. No	:	TLpq303638704
Main Entry	:	O. I. S. Imasuen
	:	W. S. Fyfe
Title & Author	:	Kaolin-smectite transformations and soils of midwestern Nigeria\ O. I. S. ImasuenW. S. Fyfe
College	:	The University of Western Ontario (Canada)
Date	:	1988
student score	:	1988
Degree	:	Ph.D.
Page No	:	1
Abstract	:	One of the most important components of the soil which influences its capacity for sustained plant production is the nature and quality of the clay minerals. Most fertile soils are dominated by the smectite clays which have a high capacity for ion-exchange and water retention. Under conditions of sustained leaching by rainwater older soils become dominated by kaolinite-gibbsite Fe2O3-quartz minerals as in most tropics. Such soils have limited capacity for high levels of production. Such soils covering the midwestern part of Nigeria contain predominantly kaolinite, quartz and crystalline Fe and Al oxides which under acid conditions have low cation retention and buffering capacity. The objective of this study is to explore (i) experiments which might produce kaolinite-smectite transformation in reasonable times and (ii) the significance for soil productivity in midwestern Nigeria. The kaolinite-smectite conversion experiments were performed at temperatures ranging from 160C to 300C under varying water vapour pressure. The starting materials included kaolinite, magnesium hydroxide, calcium oxide, sodium silicate and silicic acid mixed in the ratio of 5:4:1:1:2 respectively. After a given reaction time at each temperature, the products were examined by x-ray powder diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) equipped with energy-dispersive analyzer (EDX). The results of the transformation experiments show that the products contain smectite, serpentine, garronite and wairakite. The rate of reaction appears to obey a simple Arrhenius equation with an activation energy of 52.72 kJ mol (12.6 kcal mol). Extrapolation to a typical tropical soil temperature would indicate a conversion time of one year at 100C and about 54 years at 25C. Mineralogical and geochemical data obtained for 38 samples from different locations across midwest Nigeria indicate the soils contain mainly kaolinite and quartz. A Chemical Productivity Index (CPI) defined for these soils produces values that are comparable to those obtainable for infertile soils of the Amazon and Niger Delta. It is therefore recommended that the transformation of these predominantly kaolinitic soils to smectite could well be a progressive step which would increase the soil quality.
Subject	:	Earth sciences
	:	Geology