Soil- Co is generally concentrated in the horizons rich in organic material and clays within the
soil profile. Also, the calcium carbonate content in soil plays a significant role in Co retention. The
current work explores the possible mechanisms that might take place for Co retention in soil using pure
materials i.e. kaolinite and montmorillonite clay minerals, CaCO3 and humic acid. The retention data of Co was explored using different mathematical models i.e. the first degree equation, one site saturation model, the combined model (first degree equation + one site saturation) and the two site saturation model. The one site saturation model was the best fitting model to describe Co retention in the studied materials.
Fitting the sorption data to the Langmuir and Freuindlich isotherms was used to find out the possible
mechanisms that might control Co sorption by the examined materials and the Langmuir isotherm was
found to be the most suitable isotherm to describe Co retention by the studied materials. All the capacity constant parameter (a) values calculated from Langmuir isotherm were higher in the studied material suspensions at pH 7 than their values obtained at pH 6. Also, the values of the affinity constant parameter (b) of these adsorbents were higher at pH 7 than at pH 6.