Dissolution of Magnetite by Etidronic Acid: Dependence on Diprotic and Monoprotic Conjugates
Dissolution of Magnetite by Etidronic Acid: Dependence on Diprotic and Monoprotic Conjugates
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DOI：
10.1016/j.ica.2023.121561
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发表时间：
2023-05
影响因子：
2.8
通讯作者：
J. King;Demi Brown-;Sarah Hill;J. Tope;Peter Krenzke;Luke J. Venstrom;Paul F. Smith
中科院分区：
文献类型：
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作者：
J. King;Demi Brown-;Sarah Hill;J. Tope;Peter Krenzke;Luke J. Venstrom;Paul F. Smith
对40年前提出的四元羟乙膦酸（HEDP）溶解Fe_3O_4的机理进行了修正。我们再现了先前观察到的活化能和反应顺序的膦酸酯与选择性的子集的实验条件，表明，双质子HEDP-而不是以前报道的三元HEDP-是最终限制该机制的物种通过质子化磁铁矿oxos和解吸Fe 3+。这一建议的步骤是一致的形态图显示一元HEDP作为自发螯合剂的三价铁低于pH 3，在部分可溶的沉淀物的形式。因此，虽然使用三元酸或四价酸增加了磁铁矿溶解速率，但较低的pH促进了三价铁的再沉淀。这可能导致之前报告的HEDP（0.6Fe：1HEDP）中磁铁矿溶解度的至少一个上限-以及在观察到的最快溶解动力学条件下报告的任何其他上限-被低估。通过在pH 5下溶解Fe 3 O 4，以速率为代价避免了对产率的这种限制。
A mechanism of Fe3O4dissolution by the tetraprotic etidronic acid (HEDP) proposed 40 years ago is revised here. We reproduce the previously observed activation energy and reaction order of phosphonate with a selective subset of experimental conditions, showing that diprotic HEDP- and not the previously reported triprotic HEDP- is the species ultimately limiting the mechanism by protonating magnetite oxos and desorbing Fe3+. This proposed step is consistent with a speciation diagram showing monoprotic HEDP as the spontaneous chelator of ferric iron below pH 3, in the form of a partially soluble precipitate. Hence, while the magnetite dissolution rate is increased using the tri or tetraprotic acids, lower pH promotes reprecipitation of ferric iron. This has likely resulted in at least one previously reported upper bound for magnetite solubility in HEDP (0.6Fe:1HEDP)- and any others reported under conditions of the fastest observed dissolution kinetics- to be underestimated. This restriction on yield is avoided at the cost of rate by dissolving Fe3O4at pH 5.