Physicochemical and Thermodynamic Adsorption Studies of a Ferric Luvisol Soil in Western Nigeria

• Published in: Soil & sediment contamination 2010-01, Vol.19 (1), p.119-131
• Main Authors: Olu-Owolabi, B. I., Adebowale, K. O., Oseni, O. T.
• Format: Article
• Language: English
• Subjects: Adsorption; Calcium; cation exchange; Cation exchanging; Cations; Chemical equilibrium; Exchange; exchange capacity; Ion exchange; Ions; langmuir; Organic matter; Physicochemical properties; Potassium; Reluctance; Sediment pollution; Selectivity; Soil; Soil (material); Soils; Thermodynamics
• ISSN: 1532-0383; 1549-7887
• DOI: 10.1080/15320380903390570

An adequate knowledge of the physico-chemical properties and interaction of cations with soils is a critical research need for developing improved understanding of sustainable agricultural practices. This work therefore focuses on the study of the physico-chemical properties and equilibrium thermodynamics of adsorption of cations on Ferric Luvisols from Western Nigeria. All soil samples showed moderately similar characteristics in terms of the physico-chemical parameters investigated. The pH of the various soil samples in water varied from 6.70-7.40, typical of soils found in humid regions. The organic matter contents were low, in the range of 0.93-3.23%. The exchangeable bases and cation exchange capacity were also moderately low, with the latter having a range of 1.42-1.99 cmol c /kg. This may be attributed to their low clay content (range 8.32-18.32%). The exchange reactions of calcium (Ca) and potassium (K) at 30°C and 60°C were studied. Thermodynamic parameters derived from experimental results were determined for K-Ca and Ca-K exchange reactions on the soil samples. The selectivity coefficients (K c ) of the Ca-K and K-Ca exchange were found to decrease with increase in K and Ca-loading. The decrease was more pronounced for K-Ca exchange. The low selectivity coefficients with an increase in K loading indicated a greater affinity of the soils for Ca than K. The high equilibrium constants and the negative values of the standard free energy (ΔGdeg;) for the exchange of K for Ca revealed a preference of all the soils for Ca relative to K ions. Also ΔGdeg; values for the reaction Ca-soil to K-soil were positive, which indicated the reluctance of Ca-soil to be converted to K-soil.