Date of Award


Degree Type


Degree Name

Doctor of Philosophy


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 Fe{dollar}\sb2{dollar}O{dollar}\sb3{dollar}-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 160{dollar}\sp\circ{dollar}C to 300{dollar}\sp\circ{dollar}C 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{dollar}\sp{lcub}-1{rcub}{dollar} (12.6 kcal mol{dollar}\sp{lcub}-1{rcub}{dollar}). Extrapolation to a typical tropical soil temperature would indicate a conversion time of one year at 100{dollar}\sp\circ{dollar}C and about 54 years at 25{dollar}\sp\circ{dollar}C.;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.



To view the content in your browser, please download Adobe Reader or, alternately,
you may Download the file to your hard drive.

NOTE: The latest versions of Adobe Reader do not support viewing PDF files within Firefox on Mac OS and if you are using a modern (Intel) Mac, there is no official plugin for viewing PDF files within the browser window.