Distribution and Forms of Cobalt and Its Relationship to Mineralogical Composition in Soils of the 10th of Ramadan City,Egypt

T
he current study aims at comprehending the distribution of the different forms of cobalt and its relationship to the mineralogical composition of soils of the 10th of Ramadan city. Eight representative soil profiles were selected from the study area. Results showed that soil texture ranged from sand to sandy loam. Soil pH ranged from 6.98 to 8.68. EC values ranged from 8 to 8. 12 dSm-1 at 25°C whereas the predominant cations followed the descending order: Ca2+>Mg2+>Na+>K+, while the anions followed the sequence: SO42- >Cl- >HCO3-. The predominant clay minerals were kaolinite, montmorillonite and illite, accompanied with accessory minerals in the descending order; quartz >gypsum >dolomite >calcite >aragonite >hematite >muscovite > potassium feldspar. The total cobalt (Co) content ranged from 1.42 to 6.51 mgkg-1 and the DTPA-extractable Co content ranged from 0.65 to 1.75 mgkg-1. The successive extraction (fractionation of Co) exhibited that the residual form was the most dominant one where its percentage ranged from 34.01 to 82.90 %. The soluble, exchangeable, carbonate bound, Fe-Mn bound and organic bound forms ranged from: 1.38 to 4.23 %, 5.26 to 45.58 %, 1.79 to 7.34 %, 2.63 to 7.75 %, and 2.29 to 9.52 %, respectively. Thus, it can be said that the following sequence characterized the distribution of Co forms among the different fractions: Residual >>exchangeable >organic-bound >Fe-Mn-bound > carbonate-bound >soluble. Accordinly, the obtained results evidently showed that there were relation between cobalt forms and mineralogical composition of soils.