某铀矿区水稻土—地表水铀含量对稻米铀含量的影响

以水稻土—地表水铀含量为视角,从水稻土剖面铀含量分布规律、水稻土与下伏岩体稀土元素特征、不同河流不同河段水稻土—地表水—稻米铀含量特征、水稻土与稻米铀含量关系4个方面研究721铀矿区稻米铀含量成因。结果表明,水稻土剖面铀含量从表层至半风化花岗质基岩层呈明显降低的特征,说明水稻土铀含量高的原因不是土壤母质铀含量高;岩石与水稻土稀土元素标准化模式均表现为向右倾斜型,均属轻稀土富集型,轻稀土分馏明显,表明水稻土为还原环境,吸附作用较强;不同河流不同河段水稻土—地表水—稻米铀含量平均值的特性均为上游最低、中游最高、下游次之。铀矿区地表水环境符合铀元素在水稻土中被平衡吸附的动力学条件,有利于铀元素在矿区内河流中游地区的水稻土中沉淀富集;正在采矿区水稻土与稻米铀含量具有高度的空间耦合性,呈指数正相关关系,相关系数0.749。矿区内河流沿岸稻米铀含量的分布特征是由铀元素的迁移途径决定的"采矿活动(铀尾矿露天堆放)→地表水→水稻土"。

Effect of Uranium Contents of Paddy Soil and Surface Water on Uranium Contents of Rice in a Uranium Mining Area

In order to explore contributing factors for uranium contents in rice of a uranium mining area, distribution of uranium contents in paddy soil profiles, REE characteristics in paddy soils and underlying bedrock, characteristics of uranium contents of paddy soil, surface water, and rice in different reaches of two rivers, and relationship between uranium contents of paddy soils and rice were investigated from perspective of uranium content characteristics in paddy soil and surface water. The results show that uranium contents of paddy soil profiles significantly drop from surface of paddy soil to semi-weathering of granitic bedrock, which means high uranium content in paddy soil is not due to high content of uranium in the soil parent material. The normalized patterns of REE in rocks and paddy soils are basically the same, and are characterized by enrichment of LREE and depletion of HREE, indicating reductive environment of paddy soil with strong adsorption. The average value of uranium contents in surface water, paddy soil and rice from different reaches shows the highest in the midstream, the lower in the downstream, and the lowest in the upstream. The environment of surface water in uranium mining area is in accordance with dynamic conditions of a large amount of equilibrium adsorption of uranium elements in paddy soil, which is beneficial to precipitation and enrichment of uranium in paddy soil in the midstream exploiting mine area. There is a high spatial coupling of uranium content in rice and paddy soil, and a exponential function regression equation with correlation coefficient of 0.749 can be established. All researches confirm the migration path of uranium of first in uranium tailings, then in surface water; the third in paddy soil and at last in rice, which contributes to the characteristics of uranium contents in rice. Thus, uranium content of rice in middlestream area is the highest, followed by downstream area, and the lowest is in upstream area.