Institute for Sanitary Engineering, Water Quality and Solid Waste Management (ISWA), University of Stuttgart, Bandtäle 2, 70569 Stuttgart, Germany.
Molecules. 2020 Nov 9;25(21):5202. doi: 10.3390/molecules25215202.
Phosphonates are widely used as antiscalants for softening processes in drinking water treatment. To prevent eutrophication and accumulation in the sediment, it is desirable to remove them from the membrane concentrate before they are discharged into receiving water bodies. This study describes batch experiments with synthetic solutions and real membrane concentrate, both in the presence of and absence of granular ferric hydroxide (GFH), to better understand the influence of ions on phosphonate and phosphate adsorption. To this end, experiments were conducted with six different phosphonates, using different molar Ca:phosphonate ratios. The calcium already contained in the GFH plays an essential role in the elimination process, as it can be re-dissolved, and, therefore, increase the molar Ca:phosphonate ratio. (Hydrogen-)carbonate ions had a competitive effect on the adsorption of phosphonates and phosphate, whereas the influence of sulfate and nitrate ions was negligible. Up to pH 8, the presence of Ca had a positive effect on adsorption, probably due to the formation of ternary complexes. At pH > 8, increased removal was observed, with either direct precipitation of Ca:phosphonate complexes or the presence of inorganic precipitates of calcium, magnesium, and phosphate serving as adsorbents for the phosphorus compounds. In addition, the presence of (hydrogen-)carbonate ions resulted in precipitation of CaCO and/or dolomite, which also acted as adsorbents for the phosphorus compounds.
膦酸盐被广泛用作饮用水处理软化过程中的阻垢剂。为了防止富营养化和在沉积物中的积累，在将它们排放到接收水体之前，希望从膜浓缩物中去除它们。本研究描述了在存在和不存在颗粒状氢氧化铁（GFH）的情况下，用合成溶液和实际膜浓缩物进行的批量实验，以更好地了解离子对膦酸盐和磷酸盐吸附的影响。为此，使用不同的 Ca:膦酸盐摩尔比，用六种不同的膦酸盐进行了实验。GFH 中已有的钙在消除过程中起着重要作用，因为它可以重新溶解，并因此增加 Ca:膦酸盐摩尔比。（氢）碳酸盐离子对膦酸盐和磷酸盐的吸附具有竞争作用，而硫酸盐和硝酸盐离子的影响可以忽略不计。在 pH 值为 8 以下时，Ca 的存在对吸附有积极影响，这可能是由于形成了三元配合物。在 pH 值>8 时，观察到去除率增加，这可能是由于 Ca:膦酸盐配合物的直接沉淀或钙、镁和磷酸盐的无机沉淀物的存在作为磷化合物的吸附剂。此外，（氢）碳酸盐离子的存在导致 CaCO 和/或白云石的沉淀，这也作为磷化合物的吸附剂。
