Effects of Ni incorporation on the reactivity and stability of hausmannite (Mn3O4): Environmental implications for Mn, Ni, and As solubility and cycling
Effects of Ni incorporation on the reactivity and stability of hausmannite (Mn3O4): Environmental implications for Mn, Ni, and As solubility and cycling
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DOI：
10.1016/j.chemgeo.2020.119862
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发表时间：
2020-12
期刊：
影响因子：
3.9
通讯作者：
Boyoung Song;Elizabeth B. Cerkez;E. Elzinga;Bojeong Kim
中科院分区：
文献类型：
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作者：
Boyoung Song;Elizabeth B. Cerkez;E. Elzinga;Bojeong Kim
痕量金属结构杂质在 Mn (II/III) 氧化物中很常见，但它们对氧化物反应性和稳定性的影响尚未经过实验评估。本研究首次通过测量原始和 Ni 取代的黑锰矿 (MnIIMnIII2O4)（Ni 含量为 1 和 2wt%）在 pH5 下在有/无亚砷酸盐 (As(III)) 的情况下进行 8 小时间歇反应的矿物溶解程度来量化这种影响。 Ni 取代发生在 Mn(III) 八面体位点，导致晶格参数发生显着的结构改变，同时 Jahn-Teller 畸变降低，特别是在 2wt% 时。在酸性和还原溶解（使用 As(III)）中，相对于原始矿物，Ni 取代的黑锰矿表现出增强的 Mn 释放，同时结构 Ni 的释放随着取代百分比的增加而增加。当 As(V) 释放按表面积归一化时，Ni 取代的黑锰矿表现出比原始相更高的 As(III) 氧化百分比。此外，在 Ni 取代的黑锰矿中观察到较高的 Mn(II):As(V) 比例。 AsK边X射线吸收光谱和衰减全反射傅里叶变换红外光谱分析表明，As(III)氧化导致双核二齿As(V)表面配合物的形成。 Ni取代黑锰矿的反应活性增强可能是由于矿物稳定性降低，从而促进矿物溶解加速和结构锰释放增加，导致高反应位点的形成/暴露。因此，结构杂质决定了Mn(II/III)氧化物的性质、反应性和稳定性，影响溶解水平和氧化还原反应的程度，这些共同影响表面环境中过渡金属和准金属的命运和循环。
Trace metal structural impurities are common in Mn (II/III) oxides, yet their effects on the oxides' reactivity and stability have not been experimentally assessed. The present investigation quantifies such effects for the first time by measuring the extent of mineral dissolution of pristine and Ni-substituted hausmannite (MnIIMnIII2O4) (at 1 and 2 wt% Ni) in 8-h batch reactions at pH 5 with/without arsenite (As(III)). Ni substitution occurred at Mn(III) octahedral sites, causing noticeable structural modification in lattice parameters with a decrease in Jahn-Teller distortion, particularly at 2 wt%. In both acidic and reductive dissolution (with As(III)), the Ni-substituted hausmannite exhibited enhanced Mn release relative to the pristine mineral, with concurrent release of structural Ni increasing with substitution percentage. When As(V) release was normalized by surface area, Ni-substituted hausmannite showed a higher As(III) oxidation percentage than the pristine phase. Further, higher ratios of Mn(II):As(V) were observed in Ni-substituted hausmannite. AsK-edge X-ray absorption spectroscopy and attenuated total reflectance-Fourier transform infrared spectroscopy analyses indicated that As(III) oxidation lead to the formation of binuclear bidentate As(V) surface complexes. Enhanced reactivity of Ni-substituted hausmannite may be attributed to lowered mineral stability, which promotes accelerated mineral dissolution and increased structural Mn release, resulting in formation/exposure of highly reactive sites. Thus, structural impurities dictate the properties, reactivity, and stability of the Mn(II/III) oxides, affecting the level of dissolution and the extent of redox reactions, which together impact the fate and cycling of transition metals and metalloids in surface environments.