湖南某铀尾矿库周边土壤外源铀输入机制的研究

选择湖南某铀尾矿库周边的3条土壤剖面S1、S2、S3作为研究对象,通过与区域上背景剖面以及尾矿库中铀尾砂样品的地球化学特征对比,并结合逐级化学提取技术,讨论了土壤中外源铀的输入机制。研究表明:(1)铀尾矿库对周边土壤已产生了铀污染,其中,近源土壤剖面S1、S2遭受了重度铀污染,以单因子指数法表征的污染指数Pi分别为18.98和14.76,随着远离污染源,土壤的铀污染程度呈降低趋势(如远源的剖面S3的Pi=1.35)。(2)作为农业土壤,由于受耕作过程中的人为扰动,外源铀的输入已贯穿了整个剖面。(3)土壤中外源铀的输入,特别是对于遭受了重度铀污染的近源土壤剖面,主要包括两种机制,一是随铀尾砂的机械混入,二是随渗滤液的离子输入,以前者为主。然而,对于土壤中占绝对优势的专性吸附态(Ⅱ)外源铀,主要来自于后者的贡献。随铀尾砂机械混入的铀,其赋存形态在土壤中得到了继承;随渗滤液的离子输入的铀,主要专性吸附在土壤基质上。本研究为有效开展铀尾矿库的治理提供了重要参考依据。

Input Mechanisms of Exotic Uranium in Soils around a Uranium Mill Tailings Pond in Hunan Province, China

In this paper we took three soil profiles (i.e., S1, S2 and S3),around a uranium mill tailings pond in Hunan Province, China as the research objective, and discussed input mechanisms of exotic uranium in the soils by contrasting their geochemical characteristics with those of the background profiles and uranium mill tailings sands in the study area by using sequential chemical extraction technique. Results show as follows. (1) The uranium mill tailings pond has given rise to the uranium contamination to ambient soils, and the uranium contamination degree in the soils displays a decreasing trend with increasing distance from the contamination source. For example, the profiles S1 and S2 near the source received heavy uranium contamination and their uranium pollution index (Pi) characterized by the single factor index method are 18.98 and 14.76, respectively, and the profile S3 far away from the source is subjected to slight uranium contamination (i.e., Pi=1.35). (2) As the agricultural soils, the input of exotic uranium into them has been through the whole profiles due to the anthropogenic disturbance in the process of cultivation. (3) The input of exotic uranium of soils, especially for that in the heavily uranium-polluted soils near the source, mainly includes two mechanisms, namely, the one is physical interfusion of uranium carried by tailings sands, and the other is the entrance of water-soluble uranium ion carried by seepage fluid from the pond, and the former is the dominant. However, for the exotic uranium of specific adsorption state, which possessed absolute superiority in the amount among various speciations of exotic uranium in the soils, it is mainly contributed from the latter. For uranium carried by tailings sands, its speciations are inherited in the soils, and for uranium carried by seepage fluid, it is mainly specifically adsorbed onto the soil matrices. This study provides a useful scientific reference for effective governance of the uranium mill tailings pond.