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چکیده
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Little research has been done to study the role of soil parameters in cobalt (Co) retention, release and theprocesses involved in calcareous soils of arid and semi-arid regions. We studied the Co sorption and des-orption capacity of various calcareous soils using batch technique. The sorption and desorption behaviorof Co varied greatly among the studied soils. The sorbed fraction ranged from 92.3% to 97.2% and from51.0% to 71.8%, when 5 and 200 mg Co l−1, was added to the soil samples, respectively. Cobalt sorptioncurves were well fitted with Langmuir, Freundlich, and linear equations. The values of the distributioncoefficients obtained from linear equation ranged from 9.5 l kg−1to 23.4 l kg−1. Desorption experimentsresulted in a Co recovery ranged from 3.6% to 11.4%, indicating a low desorption of Co from soils. Theresults of the geochemical modeling indicated that under low Co addition, the solutions were under-saturated with respect to Co(OH)2(am), Co(OH)2(c), Co3(PO4)2(s), CoCl2(s), CoHPO4(s), CoCl2·6H2O(s), andCoO(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 hys-teresis indices indicated that desorption of freshly sorbed Co with 0.01 M CaCl2was hysteretic in all soilsand 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 thepresence of CaCO3in soils. These findings suggested that calcareous soils are able to retain strongly Coin which the movement of Co in the soil profile would be negligible. Thus, little risk of groundwatercontamination can be expected with Co in these calcareous soils.
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