Characteristics of Fe oxide minerals and their roles in arsenic hydrogeochemistry in high arsenic aquifer sediments
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摘要: 含水层沉积物中含铁矿物的特征与活性会影响砷的迁移转化行为。通过内蒙古含水层沉积物含铁矿物的溶解、还原动力学实验，研究了沉积物含铁矿物特征和活性及其与砷运移的关系。结果表明，沉积物中具还原活性的铁氧化物总量(m0)与岩性有关，细砂为52 μmol/g，黏土为45 μmol/g。初始还原速率k′均在10-5 s-1的数量级。表征活性均匀度的参数γ值介于合成铁氧化物矿物和表层沉积物之间。沉积物中Fe(Ⅲ)氧化物的还原活性主要介于人造纤铁矿与针铁矿的活性水平范围内。沉积物中可能存在两类活性水平不同的Fe(Ⅲ)氧化物。As更倾向于吸附在活性较强的Fe(Ⅲ)氧化物上。还原环境中，活性较强的Fe(Ⅲ)氧化物的还原性溶解，促进了沉积物中砷的释放。Abstract: Characteristics and reactivity of iron-bearing minerals control arsenic transfer and transformation in aquifer systems. In this study, aquifer sediments obtained from Inner Mongolia were investigated by kinetic experiments to study the connection between characteristics and reactivity of Fe-bearing minerals in aquifer sediments and As reactivity. Results showed that lithology controls the amount of total reactive Fe(Ⅲ) oxides (m0) in sediments. The value of m0 was 5.2 μmol/g in fine sand and 45 μmol/g in silty clay. The initial rate k′ values for both silty clay and fine sand were within the order of magnitude of 10-5 s-1. The value of parameter γ that characterizes heterogeneity of reactivity lay between synthetic Fe(Ⅲ) oxide minerals and shallow sediments. There may be two different Fe(Ⅲ) oxides in terms of reactivity in sediments: highly reactive Fe(Ⅲ) oxides and lowly reactive Fe(Ⅲ) oxides. Arsenic prefers to be adsorbed on the Fe(Ⅲ) oxides with high reactivity. In anoxic conditions, the reductive dissolution of Fe(Ⅲ) oxides with high reactivity in sediments led to arsenic release into groundwater.
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Key words:
- Inner Mongolia /
- kinetic /
- iron oxides /
- groundwater /
- waterrock interaction
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