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首页> 外文期刊>Environmental Science & Technology >Formation and dissolution of single and mixed Zn and Ni precipitates in soil: Evidence from column experiments and extended X-ray absorption fine structure spectroscopy
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Formation and dissolution of single and mixed Zn and Ni precipitates in soil: Evidence from column experiments and extended X-ray absorption fine structure spectroscopy

机译：土壤中单一和混合的Zn和Ni沉淀物的形成和溶解：来自柱实验和扩展X射线吸收精细结构光谱的证据

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The stability and the formation and dissolution kinetics of mixed trace metal precipitates in soils are currently unknown. The objective of this study was to investigate slow sorption and release processes of Zn and Ni in a loamy soil using a combination of soil column experiments and extended X-ray absorption fine structure (EXAFS) spectroscopy. To investigate slow sorption processes, the soil material was packed into columns and leached with 5400 pore volumes of 10(-2) M CaCl2 solutions containing either ZnCl2 (5.2 x 10(-5) M) or NiCl2 (5.2 x 10(-5) M) or both ZnCl2 and NiCl2 (5.2 x 10(-5) M each). The Zn and Ni concentrations in the column effluents were monitored. The metal breakthrough curves showed that slow sorption processes lead to metal retention, whereby Zn was more strongly retained than Ni. In the experiment with both Zn and Ni present, amounts of Zn and Ni similar to those in the experiments with either Zn or Ni alone were retained. Analysis of soil samples by EXAFS spectroscopy showed that layered double hydroxide (LDH)-type precipitates had formed in all columns and that a mixed ZnNi-LDH had formed in the presence of both Zn and Ni. The dissolution of those precipitates under acidic conditions was assessed by subsequent leaching of the columns with a 10(-2) M CaCl2 solution at pH 3.0 (similar to 3000 pore volumes). When only Zn was present, 95% of the retained Zn was leached at pH 3. In contrast, only 23% of the retained Ni was leached in experiments with Ni alone. When Zn and Ni were present, 90% of the retained Zn and 87% of the retained Ni were released upon acidification. EXAFS analysis revealed that the LDH phases in the Zn experiment and the Zn-Ni experiment had been completely dissolved, while the LDH phase formed in the Ni experiment was still present. The higher resistance of Ni-LDH against dissolution at low pH could also be shown in dissolution studies with synthetic Zn-LDH, Ni-LDH, and ZnNi-LDH. Our results suggest that the individual rates at which Zn and Ni cations enter into the LDH structure determine the composition of the mixed ZnNi-LDH precipitate, and that the LDH composition determines the rate at which the LDH phase dissolves under acidic conditions.
机译：目前尚不清楚土壤中混合的痕量金属沉淀物的稳定性以及形成和溶解动力学。这项研究的目的是结合土壤柱实验和扩展X射线吸收精细结构（EXAFS）光谱技术研究壤土中Zn和Ni的缓慢吸附和释放过程。为了研究缓慢的吸附过程，将土壤材料装填到柱子中，并用5400孔体积的10（-2）M CaCl2溶液浸出，其中包含ZnCl2（5.2 x 10（-5）M）或NiCl2（5.2 x 10（-5） ）M）或ZnCl2和NiCl2（两者分别为5.2 x 10（-5）M）。监测柱流出物中的Zn和Ni浓度。金属穿透曲线表明，缓慢的吸附过程导致金属保留，其中Zn比Ni保留更牢固。在同时存在Zn和Ni的实验中，保留了与单独使用Zn或Ni的实验中相似的Zn和Ni的量。通过EXAFS光谱分析土壤样品表明，在所有色谱柱中均形成了层状双氢氧化物（LDH）型沉淀物，并且在同时存在Zn和Ni的情况下形成了混合ZnNi-LDH。这些沉淀物在酸性条件下的溶解度通过随后用pH为3.0（约3000孔体积）的10（-2）M CaCl2溶液浸提柱进行评估。当仅存在Zn时，在pH 3下浸出95％的保留Zn。相反，在单独使用Ni的实验中，仅浸出23％的保留Ni。当存在Zn和Ni时，酸化时释放出90％的保留的Zn和87％的保留的Ni。 EXAFS分析表明，Zn实验和Zn-Ni实验中的LDH相已经完全溶解，而Ni实验中形成的LDH相仍然存在。在合成Zn-LDH，Ni-LDH和ZnNi-LDH的溶出度研究中，Ni-LDH在较低pH值下对溶出度的抵抗力也更高。我们的结果表明，Zn和Ni阳离子进入LDH结构的速率决定了混合的ZnNi-LDH沉淀的组成，而LDH组成决定了LDH相在酸性条件下的溶解速率。

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