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Cobalt Distribution and Speciation: Effect of Aging, Intermittent Submergence, In situ Rice Roots
Citation:
BEAK, D. G., J. K. Kirby, M. J. McLaughlin, G. M. HETTIARACHCHI, AND R. Khatiwada. Cobalt Distribution and Speciation: Effect of Aging, Intermittent Submergence, In situ Rice Roots. JOURNAL OF ENVIRONMENTAL QUALITY. American Society of Agronomy, MADISON, WI, 40(3):679-695, (2011).
Impact/Purpose:
The information gained from this study will be used to improve models to predict the lability and hence the availability of Co in terrestrial environments.
Description:
The speciation and distribution of cobalt (Co) in soils is poorly understood. This study was conducted using X-ray absorption spectroscopy (XAS) techniques to examine the influence of soluble Co(II) aging, submergence-dried cycling, and the presence of in vivo rice roots on the speciation and distribution of added Co(II) in soils. In the aging and submerged-dried cycling studies, the Co was found to be associated with manganese (Mn) oxide fraction (23% to 100% of total Co) and iron (Fe) oxide fractions (0 to 77% of total Co) of the soils as either Co(II) species or a mixed Co(II) and Co(III) species. The surface speciation of Co suggests in the Mn oxide fraction suggested an inner-sphere complex was present, and the speciation of Co in the Fe oxide fraction was an inner-sphere surface complex. The in vivo root box experiments showed similar Co speciation in the Mn oxide fraction (13% to 76% of total Co) as the aging and submerged-dried cycling studies; however, the Fe oxide fraction of the soil was unimportant in Co retention. A significant percentage (24 % to 87% of total Co) of the Co in root box treatments was identified as a Co precipitate. The importance of this finding is that in the presence of rice roots the Co is redistributed to a Co precipitate. This work confirmed earlier macroscopic work that Mn oxides are important in the sequestration of Co in soils and the influence of roots needs to be taken into account when addressing Co speciation. The information gained from this study will be used to improve models to predict the lability and hence the availability of Co in terrestrial environments.
