Sorption and mobility of Co(II) in relation to soil properties

- Soil pH governs Co(II) sorption capacity, as well as the mobility.
- Sorbed Co(II) is distributed in Fe,Mn-oxide, carbonate and exchangeable fractions.
- Mobility of Co(II) increases with contamination level regardless of soil type.
- Stabilization induced by aging is more pronounced in soil with higher pH.
- Extraction of Co(II) can be achieved by EDTA, HCl or CaCl2, depending on soil type.

The kinetic and equilibrium sorption data of Co(II) ions were obtained from batch sorption experiments, using soils samples with a wide range of texture, carbonate and organic content. Sequential extraction protocol was applied to evaluate Co(II) interactions with soil fractions. The parameters, obtained from kinetic and isotherm data modeling, as well as the results of Co(II) distribution and desorption studies, were correlated with soil properties. Kinetics of Co(II) sorption was fast and obeyed the pseudo-second order kinetic model at the contact time ranged from 30 min to 30 days, using Co(II) concentration of 1.5 × 10− 3 mol L− 1. Maximum sorption capacities were highly correlated with soil pH. The sorbed Co(II) was associated with Fe,Mn-oxide and carbonate phase of calcareous soil, whereas in other soil types ion-exchangeable fraction was dominant. The effect of aging on Co(II) stabilization in soil was more pronounced for lower contamination levels and soils with higher pH. For non-calcareous soils, the desorption of Co(II) could be achieved by EDTA and HCl solutions.