Abstract In-situ recovery is a common method of mining U ore. This technique involves injecting an oxidant to oxidize U deposited as insoluble U(IV) to soluble U(VI) and a complexing agent to form mobile U(VI) compounds, which are extracted from mining waters. Unfortunately, U concentrations often remain elevated in groundwater following this mining process. One promising technique to decrease U concentrations to acceptable levels is in-situ remediation where a reductant is injected into the mined area to reduce U(VI) back to insoluble U(IV). Here we assess the efficacy of the chemical reductant dithionite to reduce U(VI) concentrations. While dithionite can reduce environmental Cr(VI), dithionite has previously never been tested for reducing U(VI) in the environment. We determine how effectively dithionite remediates U(VI) contamination using aqueous U concentration and δ238U data. U concentrations and δ238U decrease during the dithionite experiment, demonstrating that dithionite induces U(VI) reduction. As dithionite is removed by pumping, U concentrations and δ238U increase towards background levels, but U(VI) reduction continues for an extended period. Measurements demonstrate that re-oxidation and remobilization does not appear to occur due to the reducing condition of groundwater.

中文翻译：

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在原位回收矿中通过连二亚硫酸盐还原和潜在修复 U(VI)：δ238U 获得的见解

摘要 原位回收是开采铀矿的常用方法。该技术包括注入氧化剂将作为不溶性 U(IV) 沉积的 U 氧化为可溶性 U(VI)，并注入络合剂以形成可移动的 U(VI) 化合物，这些化合物是从采矿水中提取的。不幸的是，在这个采矿过程之后，地下水中的 U 浓度通常仍然很高。将 U 浓度降低到可接受水平的一种有前景的技术是原位修复，其中将还原剂注入矿区以将 U(VI) 还原为不溶性 U(IV)。在这里，我们评估了化学还原剂连二亚硫酸盐降低 U(VI) 浓度的功效。虽然连二亚硫酸盐可以减少环境中的 Cr(VI)，但以前从未测试过连二亚硫酸盐可以减少环境中的 U(VI)。我们使用水相 U 浓度和 δ238U 数据确定连二亚硫酸盐如何有效地修复 U(VI) 污染。在连二亚硫酸盐实验期间 U 浓度和 δ238U 降低，表明连二亚硫酸盐诱导 U(VI) 还原。随着抽吸去除连二亚硫酸盐，U 浓度和 δ238U 向背景水平增加，但 U(VI) 减少持续了很长一段时间。测量表明，由于地下水的还原条件，似乎不会发生再氧化和再动员。