School of Agriculture and Food Sciences/CRC CARE, The University of Queensland, St Lucia, QLD, 4072, Australia.
School of Medical Engineering, Foshan University, Foshan, Guangdong, China.
Environ Sci Pollut Res Int. 2018 Dec;25(34):34053-34062. doi: 10.1007/s11356-018-3301-7. Epub 2018 Oct 3.
When low-cost adsorbents are being used to remove contaminant ions (e.g. arsenate, vanadate, and molybdate) from wastewater, competitive adsorption/desorption are central processes determining their removal efficiency. Competitive adsorption of As, V, and Mo was investigated using equimolar oxyanion concentrations in single, binary, and tertiary combinations in adsorption isotherm and pH envelope studies while desorption of previously adsorbed oxyanions was examined in solutions containing single and binary oxyanion combinations. The low-cost adsorbent materials used were alum water treatment sludge (amorphous hydroxy-Al) and bauxite ore (crystalline Al oxides). Adsorption isotherm and pH envelope studies showed that Mo had only a small effect in decreasing adsorption of As and V but V and As had substantial and similar effects in reducing adsorption of the other. As had a greater effect than V in reducing adsorption of Mo and it was concluded that the affinity of oxyanions for the surfaces of water treatment sludge and bauxite followed the order As > V >> Mo. In 0.3 M NaCl electrolyte, desorption of previously adsorbed oxyanions amounted to 0.3-3.4% for V and As, and 11-20% for Mo. As had approximately four times greater effect than Mo in increasing desorption of V while V had about three times the effect of Mo in increasing desorption of As. Thus, the order of oxyanions in inducing desorption of the other oxyanions (i.e. As on V and As) was the same as that for adsorption selectivity: As > V >> Mo. Water treatment sludge was a more effective adsorbent than bauxite because it had a greater adsorption capacity for all three anions and, in addition, they were held more strongly so desorption in the background electrolyte was proportionately less. It was concluded that at similar molar concentrations, arsenate would tend to reduce adsorption of vanadate as well as displace vanadate already held on adsorbent surfaces while both anions will compete effectively with molybdate. The limiting factor for simultaneous removal of As, V, and Mo from multielement solutions by adsorption will therefore be the removal of Mo.
当使用低成本吸附剂从废水中去除污染物离子（如砷酸盐、钒酸盐和钼酸盐）时，竞争吸附/解吸是决定其去除效率的核心过程。在吸附等温线和 pH 包络研究中，使用等摩尔的含氧阴离子浓度研究了 As、V 和 Mo 的竞争吸附，同时在含有单一和二元含氧阴离子组合的溶液中研究了先前吸附的含氧阴离子的解吸。使用的低成本吸附材料是明矾水处理污泥（无定形羟基-Al）和铝土矿（结晶 Al 氧化物）。吸附等温线和 pH 包络研究表明，Mo 仅对降低 As 和 V 的吸附有很小的影响，但 V 和 As 对降低另一种吸附有很大的影响。As 对 Mo 的吸附影响大于 V，因此可以得出结论，含氧阴离子对水处理污泥和铝土矿表面的亲和力顺序为 As > V >> Mo。在 0.3 M NaCl 电解质中，先前吸附的含氧阴离子的解吸量为 V 和 As 的 0.3-3.4%，Mo 的 11-20%。As 对 V 的解吸影响约为 Mo 的四倍，而 V 对 As 的解吸影响约为 Mo 的三倍。因此，诱导其他含氧阴离子解吸的含氧阴离子的顺序（即 As 对 V 和 As）与吸附选择性相同：As > V >> Mo。水处理污泥是一种比铝土矿更有效的吸附剂，因为它对所有三种阴离子的吸附容量都更大，此外，它们的结合力更强，因此在背景电解质中的解吸比例相对较小。因此，在相似的摩尔浓度下，砷酸盐可能会降低钒酸盐的吸附，同时取代已吸附在吸附剂表面的钒酸盐，而这两种阴离子将有效地与钼酸盐竞争。因此，通过吸附从多元素溶液中同时去除 As、V 和 Mo 的限制因素将是 Mo 的去除。
