The mill tailings from uranium mines constitute very low-level, long-lived, radioactive process waste. Their long-term management therefore requires a good understanding of the geochemical mechanisms regulating the mobility of residual uranium and radium-226. This article presents the results of the detailed characterization of the tailings resulting from the dynamic leaching processes used on the ore of the La Crouzille mining division and stored at the Bellezane site (Haute-Vienne, France) for over 25 years. A multi-scalar and multidisciplinary approach was developed based on a study of the site's history, on the chemical, radiological and mineralogical characterizations of the solid fraction of the tailings, and on porewater analyses. These were complemented by thermodynamic equilibrium models to predict the long-term mobility of U and 226Ra. Weakly acidic (pH = 6.35) and oxidizing (Eh = 138 mV/SHE) porewaters had a sulfated-magnesian facies ([SO4]tot = 43 mmol/L; [Mg]tot = 33 mmol/L) with an accessory calcium bicarbonate component (TIC = 25 mmol/L; [Ca]tot = 13 mmol/L) and dissolved concentrations of uranium and 226Ra of 12 × 10-6 mol/L and 0.58 Bq/L respectively. Ultra-filtration at 10 kDa indicated the absence of colloidal phases. The characterization of the tailings confirmed their homogeneity from a radiological, chemical and mineralogical point of view. The residual U and 226Ra concentrations measured in the solid were 160 ppm and 25 Bq/g respectively, in accordance with the initial ore grades and mill yields, or more than 99% of the total stock. In terms of chemical and mineralogical composition, the tailings were mainly composed of minerals from the granitic ore (quartz, potassium feldspar, plagioclases and micas) in association with their weathering products (smectite and ferric oxyhydroxides) and with neo-formed minerals following rapid diagenesis after neutralization of the tailings before their emplacement (gypsum and barite). All these minerals are effective traps for the retention of U and 226Ra. The uranium is distributed partly in micrometer scale uraninite and coffinite refractory phases embedded in grains of quartz, and partly sorbed to smectite and ferric oxyhydroxides. The 226Ra on the other hand is trapped mainly within the barite. The aqueous concentrations of U and 226Ra could be described using a thermodynamic approach so that their long-term mobility can subsequently be assessed by modeling. The paragenesis of the tailings could be seen to be stable over time with the exception of neo-formed gypsum and calcite, which will gradually dissolve. The presence of retention traps offering surplus capacity, i.e. smectite, ferric oxyhydroxides and barite, will maintain the U and the 226Ra at very low aqueous concentrations, even under oxidizing conditions. Moreover, the low permeability of the mill tailings leads, in the case of 226Ra, to behavior dictated only by the radioactive decay.

中文翻译：

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来自Bellezane矿场（法国）的铀厂尾矿的长期反应性的多尺度研究。

铀矿的工厂尾矿构成低水平，长寿命的放射性过程废物。因此，他们的长期管理需要对调节残留铀和镭226的迁移性的地球化学机制有很好的了解。本文介绍了尾矿的详细表征结果，这些尾矿是通过在La Crouzille采矿部门的矿石上使用并在Bellezane工地（法国上维埃纳）存储了25年以上的动态浸出工艺产生的。基于对该矿场历史的研究，尾矿固形物的化学，放射学和矿物学特征以及孔隙水分析，开发了一种多尺度和多学科的方法。通过热力学平衡模型对这些元素进行补充，以预测U和226Ra的长期迁移率。弱酸性（pH = 6.35）和氧化性（Eh = 138 mV / SHE）孔隙水具有硫酸镁相（[SO4] tot = 43 mmol / L； [Mg] tot = 33 mmol / L），并带有碳酸氢钙组分（TIC = 25 mmol / L； [Ca] tot = 13 mmol / L），铀和226 Ra的溶解浓度分别为12×10-6 mol / L和0.58 Bq / L。10 kDa的超滤表明没有胶体相。从放射学，化学和矿物学的观点来看，尾矿的特征证实了它们的同质性。根据初始矿石品位和轧机产量，固体中残留的U和226Ra浓度分别为160 ppm和25 Bq / g，或占总库存的99％以上。就化学和矿物学组成而言，尾矿主要由花岗岩矿石中的矿物（石英，长石钾，斜长石和云母）以及其风化产物（绿土和羟基氧化铁）以及快速成岩后的新形成矿物组成。在中和尾矿之前将其中和（石膏和重晶石）。所有这些矿物都是保留U和226Ra的有效陷阱。铀的一部分分布在微米级的铀矿中，并嵌入石英晶粒中的有限难熔相，一部分吸附在蒙脱石和羟基氧化铁中。另一方面，226Ra主要被困在重晶石中。可以使用热力学方法描述U和226Ra的水溶液浓度，以便随后可以通过建模评估其长期迁移率。可以看到，随着新形成的石膏和方解石逐渐消失，尾矿的共生随着时间的推移是稳定的。提供富余容量的保留阱（即蒙脱石，羟基氧化铁和重晶石）的存在，即使在氧化条件下，也会将U和226Ra维持在非常低的水溶液浓度下。此外，在226Ra的情况下，磨矿尾矿的低渗透性导致仅由放射性衰变决定的行为。提供富余容量的保留阱（即蒙脱石，羟基氧化铁和重晶石）的存在，即使在氧化条件下，也会将U和226Ra维持在非常低的水溶液浓度下。此外，在226Ra的情况下，磨矿尾矿的低渗透性导致仅由放射性衰变决定的行为。提供富余容量的保留阱（即蒙脱石，羟基氧化铁和重晶石）的存在，即使在氧化条件下，也会将U和226Ra维持在非常低的水溶液浓度下。此外，在226Ra的情况下，磨矿尾矿的低渗透性导致仅由放射性衰变决定的行为。