Extractable Concentrations of Cobalt from Serpentine Soils with Several Single-Extraction Procedures

In this study, we selected three soil pedons on the shoulder, backslope, and footslope along a serpentine toposequence to measure cobalt (Co) extractability using six single-extraction procedures. These extraction procedures are distilled water, 0.11 M acetic acid in the first step of the BCR sequential extraction (BCR1), 1 M ammonium acetate (NH4OAc; pH 7.0), 0.01 M calcium chloride (CaCl2), diethylenetriamine pentaacetic acid (DTPA), and 0.1 M hydrochloric acid (HCl). Although the Co concentrations in the water extracts of the study soils ranged from 0.15 to 0.93 mg kg(-1), those with HCl extraction can be up to 22.1 mg kg(-1). The extractable Co concentrations in the study soils demonstrate that the extraction capacity is in the order HCl > DTPA > CaCl2 >= NH4OAc > BCR1 > H2O. The percentages of extractable Co after applying the six single-extraction procedures reveal that Co mobility is greatest in the soils on the backslope, moderate on the footslope, and least mobile on the shoulder.