Cobalt sorption–desorption behavior of calcareous soils from some Iranian soils

Abstract

Little research has been done to study the role of soil parameters in cobalt (Co) retention, release and the processes involved in calcareous soils of arid and semi-arid regions. We studied the Co sorption and desorption capacity of various calcareous soils using batch technique. The sorption and desorption behavior of Co varied greatly among the studied soils. The sorbed fraction ranged from 92.3% to 97.2% and from 51.0% to 71.8%, when 5 and 200mg Col−1, was added to the soil samples, respectively. Cobalt sorption curves were well fitted with Langmuir, Freundlich, and linear equations. The values of the distribution coefficients obtained from linear equation ranged from 9.5lkg−1 to 23.4lkg−1. Desorption experiments resulted in a Co recovery ranged from 3.6% to 11.4%, indicating a low desorption of Co from soils. The results of the geochemical modeling indicated that under low Co addition, the solutions were undersaturated with respect to Co(OH)2(am), Co(OH)2(c), Co3(PO4)2(s), CoCl2(s), CoHPO4(s), CoCl2·6H2O(s), and CoO(s), whereas under higher Co addition, the solutions were undersaturated with respect to Co(OH)2(am), CoCl2(s), CoCl2·6H2O(s), CoO(s), CoHPO4(s), and saturated with respect to Co3(PO4)2(s), and CoCO3(s). The hysteresis indices indicated that desorption of freshly sorbed Co with 0.01M CaCl2 was hysteretic in all soils and low mobility and leaching potential of freshly sorbed Co can be expected from these calcareous soils. Statistical correlations revealed that Co sorption and desorption onto the soils were influenced by the presence of CaCO3 in soils. These findings suggested that calcareous soils are able to retain strongly Co in which the movement of Co in the soil profile would be negligible. Thus, little risk of groundwater contamination can be expected with Co in these calcareous soils.