Adsorption of tungstate (WO4) on birnessite, ferrihydrite, gibbsite, goethite and montmorillonite as affected by pH and competitive phosphate (PO4) and molybdate (MoO4) oxyanions
Adsorption of tungstate (WO4) on birnessite, ferrihydrite, gibbsite, goethite and montmorillonite as affected by pH and competitive phosphate (PO4) and molybdate (MoO4) oxyanions
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DOI：
10.1016/j.clay.2017.04.009
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发表时间：
2017-07-01
影响因子：
5.6
通讯作者：
Hashimoto, Yohey
中科院分区：
文献类型：
--
作者：
Iwai, Tomoe;Hashimoto, Yohey
了解钨酸盐在土壤矿物组分上的吸附特性，对于阐明钨酸盐在土壤和水体中的迁移性具有重要意义。本研究的目的是表征选定土壤粘土矿物对WO 4的吸附（三水铝石、水铁矿、针铁矿、水钠锰矿和蒙脱石），并研究了pH对WO 4与PO 4和MoO 4在这些粘土矿物上竞争吸附的影响。在酸性至碱性范围内，三水铝石对WO_4的吸附能力顺序为：羟基氧化铁>水钠锰矿>蒙脱石。除水铁矿的吸附特性与溶液pH无关外，所有矿物在酸性条件下对WO 4的最大吸附量都较大。我们发现，在酸性条件下WO 4对粘土矿物的亲合力高于PO 4，在碱性条件下WO 4对粘土矿物的亲合力高于MoO 4。在酸性和碱性条件下，WO 4吸附量大于PO 4和MoO 4。在三水铝石的情况下，例如，吸附的WO 4/吸附的PO 4摩尔比在pH 4时为1.10，在pH 8时为0.49，而吸附的WO 4/吸附的MoO 4摩尔比在pH 4时为1.16，在pH 8时为8.19。与其他粘土矿物不同，水钠锰矿和蒙脱石表现出独特的吸附行为，溶液中PO 4和MoO 4的存在沿着pH值的增加而增强了WO 4的吸附。
The knowledge about adsorption characteristics of tungstate (WO4) on soil mineral components is critical to elucidate WO4 mobility in the soil and aqueous systems. The objectives of this study were to characterize WO4 adsorption on selected soil clay minerals (gibbsite, ferrihydrite, goethite, birnessite and montmorillonite), and to investigate the competition in adsorption of WO4 with PO4 and MoO4 on these clay minerals as affected by pH. Based on an adsorption isotherm study, adsorption affinity for WO4 follows the order of gibbsite = Fe (oxyhydr) oxides > birnessite > montmorillonite in acid to alkaline pH ranges. The adsorption maximum of WO4 was greater in the acid pH for all minerals with an exception of ferrihydrite whose adsorption characteristics were independent on solution pH. We found that WO4 has higher affinity for clay minerals than PO4 under acid pH, and than MoO4 under alkaline pH. This is evidenced by the result that, by adding WO4 and oxyanions with the same molar ratio, more WO4 than PO4 and MoO4 was usually adsorbed on soil minerals in acid and alkaline pH, respectively. In a case of gibbsite, for example, the adsorbed WO4/adsorbed PO4 molar ratio was 1.10 at pH 4, and 0.49 at pH 8, whereas the adsorbed WO4/adsorbed MoO4 molar ratio was 1.16 at pH 4, and 8.19 at pH 8. Unlike other clay minerals, birnessite and montmorillonite showed a unique adsorption behavior that the presence of PO4 and MoO4 in solution enhanced the WO4 adsorption along with the increase of pH. The information reported herein provides for better understanding of WO4 adsorption on major soil clay minerals in relation to the solution pH and competitive oxyanions.