Physico-Chemical and Thermodynamic Adsorption Studies of A Few Soils from Delta and Oyo State, Nigeria

Comprehensive study of the physico-chemical properties and interactions of cations with soils is a crucial research need for the development of more sustainable agricultural systems. The analysis of physico-chemical and thermodynamic adsorption studies of various soils from Delta and Oyo State, Nigeria, is the main emphasis of this paper. Two surface soils from the Cocoa Research Institutes of Nigeria (CRIN) and the Isoko North Local Government of Delta State were compared for their physico-chemical properties and heavy metal speciation. The effects of adsorption duration, pH, initial sorbate concentration, and ionic strength were also studied in relation to the adsorption of Cd2+, Pb2+, Cu2+, and Zn2+ ions. On the equilibrium and thermodynamics of the adsorption process, more investigation was conducted. The physico-chemical studies revealed that soil from CRIN had a pH of 6.1 in water and 5.4 in KCl, whereas soil from Isoko North had a pH of 4.3 in water and 3.0 in KCl. The largest percentages of organic matter are found in the soil from Isoko North (3.07%) and CRIN (3.82%). For both soils, the order of exchangeable bases was Ca > K > Mg > Na. The heavy metal concentrations in both soils were in the following order: Zn > Cu > Ni > Pb > Cd = Al; CRIN: 3.82meq/100g for CEC; Isoko North: 2.85meq/100g for CEC. In contrast to CRIN soil, Isoko North soil showed a larger bulk density and a superior hydraulic conductivity. Extractable elements were present in both soils in the following order: Mn > Fe > Zn > Cu. The base saturation in the CRIN soil was higher than the base saturation in the Isoko North soil, which was lower at 60.73%. Zn, Pb, and Cd were the outcomes of the heavy metal speciation for both soils. The equilibrium adsorption data, which were closely related to the Langmuir isotherm model, showed that the maximum capacity of lead for soil from Isoko North was 5.8140 mmol/g and for soil from CRIN was 7.6335 mmol/g. Thermodynamic investigations showed that the adsorption process was spontaneous for simply Cu2+ (for soil from CRIN) and non-spontaneous for other metal ions from both soils. Metal ions from both soils displayed exothermic and endothermic adsorption, respectively, for Cd2+ and Cu2+ (for soil from CRIN).