Remediation of a Marine Shore Tailings Deposit and the Importance of Water鈥揜ock Interaction on Element Cycling in the Coastal Aquifer

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• 作者：Bernhard Dold ; Nouhou Diaby ; Jorge E. Spangenberg
• 刊名：Environmental Science & Technology
• 出版年：2011
• 出版时间：June 1, 2011
• 年：2011
• 卷：45
• 期：11
• 页码：4876-4883
• 全文大小：1125K
• 年卷期：v.45,no.11(June 1, 2011)
• ISSN：1520-5851

文摘

We present the study of the geochemical processes associated with the first successful remediation of a marine shore tailings deposit in a coastal desert environment (Bah铆a de Ite, in the Atacama Desert of Peru). The remediation approach implemented a wetland on top of the oxidized tailings. The site is characterized by a high hydraulic gradient produced by agricultural irrigation on upstream gravel terraces that pushed river water (500 mg/L SO₄) toward the sea and through the tailings deposit. The geochemical and isotopic (未²H_water and 未¹⁸O_water, 未³⁴S_sulfate, 未¹⁸O_sulfate) approach applied here revealed that evaporite horizons (anhydrite and halite) in the gravel terraces are the source of increased concentrations of SO₄, Cl, and Na up to 1500 mg/L in the springs at the base of the gravel terraces. Deeper groundwater interacting with underlying marine sequences increased the concentrations of SO₄, Cl, and Na up to 6000 mg/L and increased the alkalinity up to 923 mg/L CaCO₃ eq. in the coastal aquifer. These waters infiltrated into the tailings deposit at the shelf-tailings interface. Nonremediated tailings had a low-pH oxidation zone (pH 1鈥?) with significant accumulations of efflorescent salts (10鈥?0 cm thick) at the surface because of upward capillary transport of metal cations in the arid climate. Remediated tailings were characterized by neutral pH and reducing conditions (pH 7, Eh 100 mV). As a result, most bivalent metals such as Cu, Zn, and Ni had very low concentrations (around 0.01 mg/L or below detection limit) because of reduction and sorption processes. In contrast, these reducing conditions increased the mobility of iron from two sources in this system: (1) The originally Fe(III)-rich oxidation zone, where Fe(III) was reduced during the remediation process and formed an Fe(II) plume, and (2) reductive dissolution of Fe(III) oxides present in the original shelf lithology formed an Fe鈥揗n plume at 10-m depth. These two Fe-rich plumes were pushed toward the shoreline where more oxidizing and higher pH conditions triggered the precipitation of Fe(III)hydroxide coatings on silicates. These coatings acted as a filter for the arsenic, which naturally infiltrated with the river water (500 渭g/L As natural background) into the tailings deposit.