粤北某铀矿区土壤中铀同位素组成特性及环境示踪

The sources of uranium (U) pollution in the area of uranium mining/milling site not only come from anthropogenic activities like mining and milling process, but might also originate from the natural weathering process of the uranium ores. It is an interesting and significative scientific issue to distinguish the source of uranium pollution. Anthropogenic activities like mining and milling process make uranium exposed from underground to the earth surface. The extreme condition of strong acid with severe oxidation-reduction in the hydrometallurgical process isolates the uranium from the ores, and changes its geo-chemical speciation and oxidation states. Consequently, considerable amount of mobile uranium may migrate into surface environment through waste cycle like tailings. The ratio of the uranium isotopes might notably change compared to natural weathering process. The main purpose of this project is to identify the different characteristics of isotopic compositions (238U, 235U and 234U) of uranium induced by natural weathering (original uranium ore) and human activities (tailings and U-bearing wastewater), and to establish a source identification system of uranium pollution in typical soils from different areas of the uranium mine site. The study of identifying the differences between the characteristics of uranium pollution by natural weathering and human activities could provide a quantification method for pinpointing the contribution of different uranium pollution sources. It would enrich the study on uranium environmental contamination in an innovative way with considerable scientific merits, which would provide guidance on the prevention and control of uranium pollution.

环境铀污染不仅可来源于含铀矿产资源的开发利用等人为活动，也可能来源于这些矿产的自然风化过程。如何识别铀的污染来源是十分值得研究的科学问题。工业活动(如铀矿开采、水冶等)将原来封存于地下的铀带入地表环境，在强酸强氧化等条件下将铀从铀矿中分离出来，改变了铀原有价态和赋存形态，有相当部分进入生态环境。这一过程所导致的铀同位素组成的变化比起自然风化作用所引起的应更加明显。本项目拟通过对比研究典型铀矿区原生铀矿及其水冶过程的废水和铀尾矿中铀同位素组成(238U，235U和234U)特性，建立自然生态过程和人为活动过程中铀同位素组成的端元，并分析矿区不同土壤的铀同位素组成与各端元之间的响应关系，从而建立定量解析人类活动带来的铀环境污染的同位素源识别体系，为定量示踪和判别环境铀污染的来源提供可靠的科学依据，有较高的科学理论研究价值和对铀污染防治的实践指导意义。

研究结果发现：粤北某铀矿区沥青铀矿的234U/238U活度比1.0059±0.0018，铀尾矿1.1579±0.0018，说明在铀矿用强酸堆浸后，234U/238U将显著提高；234U/238U与铀含量存在较好的相关性，反映样品铀含量与234U/238U有较好的同源性。对铀矿区多个土壤剖面样品中238U/235U测试表明，δ238/235U组成随土壤剖面深度增加而增大，表明土壤浅层更富集轻铀同位素235U，而土壤深层更富集重铀同位素238U。此外，水库柱状沉积物系列样品、上游溪流沉积物样品、背景区沉积物以及铀矿等样品的206Pb/207Pb与208Pb/206Pb之间有非常好的相关性。研究所获得的阶段性数据为深入开展铀矿区放射性元素及重金属污染的多同位素示踪奠定重要基础。