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Shale weathering: a lysimeter and modelling study for flow, transport, gas diffusion and reactivity assessment in the critical zone
Journal of Hydrology ( IF 5.9 ) Pub Date : 2020-08-01 , DOI: 10.1016/j.jhydrol.2020.124925
Joachim Tremosa , Mathieu Debure , Sathya Narayanasamy , Paul-Olivier Redon , Diederik Jacques , Francis Claret , Jean-Charles Robinet

Abstract Shale weathering was characterized and quantified in a lysimeter and modelling study that jointly considered the flow, transport, gas diffusion and reactivity processes induced by exposure to the atmosphere of a recently excavated shale. In this mechanically disaggregated shale presenting preferential pathways for water and a hydraulic conductivity at saturation of 100 cm/day, the water content and the seasonal saturation and desaturation cycles were identified as the main driving mechanisms of shale alteration. The water content determined the diffusion of gaseous oxygen in the shale’s unsaturated porosity, which gave rise to a zonation of the oxidation of pyrite, contained at 1 wt% in the shale. The acidification associated with this oxidation of pyrite was efficiently buffered by calcite but a release of sulphates, cations, iron and trace metals (Pb, Ni, Zn, Co, Cu and As, mainly) was observed. Besides pyrite and calcite dissolution, iron (oxy-)hydroxide formed and proved to be a good phase for sorbing trace metals, whose content remained at low concentrations in the drainage water. Seasonal precipitation of gypsum was also identified, in connection with the summer desaturation of the shale’s shallow layers. The hydraulic, chemical and mineralogical observations made in the lysimeters were reproduced using HP1, a reactive transport code, under unsaturated conditions. It was possible to account for the gas diffusion where O2 availability controlled the reactivity with the shale, depending on the meteorological conditions and the drainage at the base of the lysimeter.

中文翻译:

页岩风化:用于临界区流动、输运、气体扩散和反应性评估的蒸渗仪和模型研究

摘要 在蒸渗仪和建模研究中对页岩风化进行了表征和量化,该研究联合考虑了最近挖掘出的页岩暴露在大气中引起的流动、输送、气体扩散和反应过程。在这种机械分解的页岩中,在 100 厘米/天的饱和度下呈现出优先的水通道和水力传导率,含水量和季节性饱和度和去饱和度循环被确定为页岩蚀变的主要驱动机制。水含量决定了气态氧在页岩不饱和孔隙中的扩散,这导致了页岩中 1 wt% 的黄铁矿氧化带。与黄铁矿氧化相关的酸化被方解石有效缓冲,但硫酸盐、阳离子、观察到铁和痕量金属(主要是 Pb、Ni、Zn、Co、Cu 和 As)。除了黄铁矿和方解石溶解外,氢氧化铁形成并被证明是吸附痕量金属的良好相,其含量在排水中保持低浓度。还确定了石膏的季节性降水,与页岩浅层夏季去饱和有关。在蒸渗仪中进行的水力、化学和矿物学观察是在不饱和条件下使用 HP1(一种反应传输代码)再现的。根据气象条件和蒸渗仪底部的排水情况,可以解释气体扩散,其中 O2 可用性控制与页岩的反应性。氢氧化铁形成并被证明是吸附痕量金属的良好相,其含量在排水中保持低浓度。还确定了石膏的季节性降水,与页岩浅层夏季去饱和有关。在蒸渗仪中进行的水力、化学和矿物学观察是在不饱和条件下使用 HP1(一种反应传输代码)再现的。根据气象条件和蒸渗仪底部的排水情况,可以解释气体扩散,其中 O2 可用性控制与页岩的反应性。氢氧化铁形成并被证明是吸附痕量金属的良好相,其含量在排水中保持低浓度。还确定了石膏的季节性降水,与页岩浅层夏季去饱和有关。在蒸渗仪中进行的水力、化学和矿物学观察是在不饱和条件下使用 HP1(一种反应传输代码)再现的。根据气象条件和蒸渗仪底部的排水情况,可以解释气体扩散,其中 O2 可用性控制与页岩的反应性。与页岩浅层夏季去饱和有关。在蒸渗仪中进行的水力、化学和矿物学观察是在不饱和条件下使用 HP1(一种反应传输代码)再现的。根据气象条件和蒸渗仪底部的排水情况,可以解释气体扩散,其中 O2 可用性控制与页岩的反应性。与页岩浅层夏季去饱和有关。在蒸渗仪中进行的水力、化学和矿物学观察是在不饱和条件下使用 HP1(一种反应传输代码)再现的。根据气象条件和蒸渗仪底部的排水情况,可以解释气体扩散,其中 O2 可用性控制与页岩的反应性。
更新日期:2020-08-01
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