CSIRO Land and Water, PMB 2, Glen Osmond, Australia.
J Environ Qual. 2011 May-Jun;40(3):679-95. doi: 10.2134/jeq2010.0139.
The speciation and distribution of Co in soils is poorly understood. This study was conducted using x-ray absorption spectroscopy (XAS) techniques to examine the influence of soluble cobalt in the +2 oxidation state (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, Co was found to be associated with Mn oxide fraction (23 to 100% of total Co) and Fe oxide fractions (0 to 77% of total Co) of the soils as either Co(II) species or a mixed Co(II), and Co in the +3 oxidation state (Co[III]) species. The surface speciation of Co in the Mn oxide fraction suggests an innersphere complex was present and the speciation of Co in the Fe oxide fraction was an innersphere 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 amount (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.
土壤中钴的形态和分布仍不清楚。本研究采用 X 射线吸收光谱（XAS）技术，考察了溶解态钴（Co[II]）老化、浸水-干燥循环以及活体水稻根系对添加的 Co(II)在土壤中形态和分布的影响。在老化和浸水-干燥循环研究中，发现 Co 与土壤的 Mn 氧化物（23%至 100%的总 Co）和 Fe 氧化物（0%至 77%的总 Co）有关，其存在形式为 Co(II)物种或 Co(II)和 Co(III)混合物种。Mn 氧化物中 Co 的表面形态表明存在内球络合物，Fe 氧化物中 Co 的形态为内球表面络合物。活体根系箱实验表明，Mn 氧化物中的 Co 形态与老化和浸水-干燥循环研究相似（13%至 76%的总 Co）。然而，Fe 氧化物对 Co 的保持不重要。根系箱处理中相当一部分 Co（24%至 87%的总 Co）被鉴定为 Co 沉淀。这一发现的重要性在于，在水稻根系存在的情况下，Co 重新分配到 Co 沉淀中。本工作证实了先前的宏观研究结果，即 Mn 氧化物在土壤中 Co 的固定中很重要，在研究 Co 的形态时需要考虑根系的影响。本研究获得的信息将用于改进模型，以预测 Co 在陆地环境中的生物可利用性和变异性。
