School of Agriculture and Food Sciences, The University of Queensland, St Lucia, QLD 4072, Australia.
School of Medical Engineering, Foshan University, Foshan, Guangdong, China.
J Environ Manage. 2018 Jul 15;218:190-199. doi: 10.1016/j.jenvman.2018.04.038. Epub 2018 Apr 19.
The potential to use water treatment sludge and bauxite as active filter media in constructed wetlands to remove As, V and Mo from alkaline drainage originating from seawater-neutralized bauxite processing residue was evaluated in laboratory batch and column studies. Batch adsorption studies showed that increasing the electrolyte concentration from 0.01 to 0.30 M NaCl (the typical electrolyte strength of the drainage) increased adsorption of all three oxyanions onto both media while increasing initial pH from 6.7 to 8.3 (the typical pH of drainage) and using granules (1-2 mm dia.) rather than ground material (<0.2 mm) both decreased adsorption. Kinetic studies showed that while ionic strength had little effect on the contact time required to reach maximum adsorption, increased initial pH increased the time to reach maximum adsorption for Mo on both media and increased particle size increased the time required for maximum adsorption of all three oxyanions onto both media. In batch experiments, at initial elemental concentrations of 1 and 50 mg L, adsorption from multi-element solutions (compared with single element ones) was reduced in the order: Mo » As > V. In continuous flow column studies from single element solutions (1 mg L), breakthrough curves for Mo occurred first and greater than three times more eluent passed through the columns before breakthrough of V and then As occurred. When multi-element solutions were used, less volume of eluent was required for breakthrough of all three anions and the volume required before breakthrough of As was greatly reduced compared to that for V. The possibility that the strong ability of V to compete with As and particularly Mo could cause desorption of previously adsorbed Mo and As and their movement through a wetland filter needs to be further investigated. It was concluded that molybdate is the least strongly held oxyanion and that a decrease in solution pH within the wetland would greatly improve Mo removal efficiency.
实验室批处理和柱研究评估了将水处理污泥和铝土矿用作从海水中和的铝土矿加工残渣产生的碱性排水中去除 As、V 和 Mo 的人工湿地中活性滤料的潜力。批处理吸附研究表明，将电解质浓度从 0.01 增加到 0.30 M NaCl（排水的典型电解质强度）增加了所有三种含氧阴离子在两种介质上的吸附，而将初始 pH 值从 6.7 增加到 8.3（排水的典型 pH 值）以及使用颗粒（1-2 毫米直径）而不是研磨材料（<0.2 毫米）都降低了吸附。动力学研究表明，虽然离子强度对达到最大吸附所需的接触时间几乎没有影响，但增加初始 pH 值会增加 Mo 在两种介质上达到最大吸附的时间，并增加粒径会增加三种含氧阴离子在两种介质上达到最大吸附所需的时间。在批处理实验中，在初始元素浓度为 1 和 50 mg/L 时，与单一元素溶液相比，多元素溶液（Mo>As>V）的吸附减少。在单一元素溶液（1 mg/L）的连续流动柱研究中，Mo 的穿透曲线首先出现，并且通过柱子的洗脱液体积超过 V 然后 As 穿透的三倍以上。当使用多元素溶液时，所有三种阴离子的穿透所需的洗脱液体积更少，并且与 V 相比，As 穿透之前所需的洗脱液体积大大减少。需要进一步研究 V 与 As 和特别是 Mo 竞争的强烈能力是否会导致先前吸附的 Mo 和 As 的解吸及其通过湿地过滤器的移动。结论是钼酸盐是结合最弱的含氧阴离子，湿地内溶液 pH 值的降低将大大提高 Mo 的去除效率。
