Abstract

The present review is devoted to the sorption properties of magnetite towards hexavalent chromium ions and the possibility of its use as a sorbent for removing these toxic ions from contaminated aqueous solutions. The behavior of magnetite nanoparticles in aqueous solutions has been also investigated. It has been shown that two processes occur simultaneously during the sorption of chromium(VI) ions by magnetite: ordinary adsorption and chemisorption (redox reaction between hexavalent chromium ions and magnetite). The latter is accompanied by the oxidation of iron(II) in magnetite to iron(III) and the reduction of chromium(VI) ions to chromium(III) with the formation of maghemite and a number of other compounds, including mixed chromium(III) compounds with iron, in the surface layer of magnetite (or onto its surface). It has been demonstrated that the kinetics of the redox process between chromium(VI) and magnetite is described by the first-order reaction equation with respect to the concentration of chromium(VI) ions in a solution. As a result of chemisorption, unlike the case of traditional sorbents, chromium(VI) is irreversibly bound by magnetite, which eliminates the reentry of its ions into the environment. Here, the sorption capacity of magnetite irreversibly decreases in the course of its saturation with chromium. In addition, the sorption capacity of magnetite towards chromium(VI) ions also decreases along with increasing pH of the purified solution, and at pH > 11 it becomes almost zero.

中文翻译：

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磁铁矿对铬（VI）离子的吸附规律（综述）

摘要

本综述致力于磁铁矿对六价铬离子的吸附特性以及其用作从污染水溶液中去除这些有毒离子的吸附剂的可能性。还研究了磁铁矿纳米粒子在水溶液中的行为。已经表明在磁铁矿吸附铬（VI）的过程中同时发生两个过程：普通吸附和化学吸附（六价铬离子与磁铁矿之间的氧化还原反应）。后者伴随着磁铁矿中的铁（II）氧化为铁（III），铬（VI）离子还原为铬（III），形成了磁赤铁矿和许多其他化合物，包括混合铬（III） ）在磁铁矿的表层（或其表面）中与铁形成化合物。已经证明，关于溶液中铬（VI）离子的浓度，通过一阶反应方程式描述了铬（VI）和磁铁矿之间氧化还原过程的动力学。化学吸附的结果是，与传统吸附剂不同，铬（VI）被磁铁矿不可逆地结合，从而消除了其离子重新进入环境的过程。在此，磁铁矿的吸附能力在其被铬饱和的过程中不可逆地降低。另外，磁铁矿对铬（VI）离子的吸附能力也随着纯化溶液pH值的增加而降低，并且在pH> 11时几乎变为零。