Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtse River) Ministry of Agriculture, College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, China; Department of Civil & Environmental Engineering, University of Wisconsin-Madison, Madison, WI 53706, USA.
Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtse River) Ministry of Agriculture, College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, China.
Environ Pollut. 2020 Jan;256:113462. doi: 10.1016/j.envpol.2019.113462. Epub 2019 Oct 24.
Natural birnessite-like minerals are commonly enriched in various transitional metals (TMs), which greatly modify the mineral structure and properties. However few studies are yet conducted systematically on the effects of TM doping on birnessite reactivity towards Cr(III) oxidation. In the present study, the transformation behaviors of Cr(III) on Co-, Ni-, V-containing birnessites were investigated. Co and Ni doping generally decrease the mineral crystalline sizes and hydrodynamic sizes (D) while V-doping greatly decreases the crystalline sizes but not the D, owing to particle aggregation. Co and Ni firstly decrease and then increase the mineral zeta potentials (ζ) at pH4 while V decreases ζ. Electrochemical specific capacitances for Co-containing birnessites are gradually reduced, while those for Ni-doped birnessites are slightly reduced and for V-doped birnessites increased, which have a positively linear relationship with the amounts of Cr(III) oxidized by these samples. Cr(III) removal efficiencies from solution by these Co-, Ni- and V-containing birnessites are 26-51%, ∼62-72% and ∼96-100%, respectively, compared to ∼92% by pure birnessite. Cr(III) oxidation kinetics analysis demonstrates the gradual decrease of Mn(IV) and concurrent increase of Mn(III) and the adsorption of mainly Cr(III) on mineral surfaces. A negatively linear relationship exists between birnessite lateral sizes and the proportions of Mn(IV/III) consumed to oxidize Cr(III). Apparent initial Cr(III) oxidation rate (k) for Co-containing birnessites are greatly reduced, while those for Ni-doped samples moderately decreased and for V-doped samples first increased and then decreased. A positively or negatively linear relationship exists between k or the amount of Mn(II) released and the mineral Mn(IV) content respectively. Cr(III) oxidation probably initiates from layer edge sites of Ni-doped birnessites but the vacancies of Co- and V-containing birnessites. These results provide insights into the reaction mechanisms of Cr(III) with natural birnessite-like minerals.
天然水钠锰矿通常富含各种过渡金属（TMs），这极大地改变了矿物的结构和性质。然而，目前对于 TM 掺杂对水钠锰矿对 Cr(III)氧化反应性的影响还缺乏系统的研究。本研究考察了 Co、Ni、V 掺杂水钠锰矿中 Cr(III)的转化行为。Co 和 Ni 掺杂一般会降低矿物的结晶度和水动力粒径（D），而 V 掺杂则会大大降低结晶度但不会降低 D，这是由于颗粒聚集。Co 和 Ni 首先降低然后增加 pH4 时矿物的zeta 电位（ζ），而 V 则降低 ζ。Co 掺杂水钠锰矿的电化学比电容逐渐降低，而 Ni 掺杂水钠锰矿的比电容略有降低，V 掺杂水钠锰矿的比电容增加，与这些样品氧化的 Cr(III)量呈正线性关系。与纯水钠锰矿相比，这些 Co、Ni 和 V 掺杂水钠锰矿从溶液中去除 Cr(III)的效率分别为 26-51%、62-72%和 96-100%。Cr(III)氧化动力学分析表明 Mn(IV)逐渐减少，Mn(III)同时增加，主要是 Cr(III)吸附在矿物表面。水钠锰矿横向尺寸与用于氧化 Cr(III)的 Mn(IV/III)消耗比例之间存在负线性关系。Co 掺杂水钠锰矿的表观初始 Cr(III)氧化速率（k）大大降低，而 Ni 掺杂样品的 k 值适度降低，V 掺杂样品的 k 值先增加后降低。k 或释放的 Mn(II)量与矿物 Mn(IV)含量之间存在正或负线性关系。Cr(III)氧化可能从 Ni 掺杂水钠锰矿的层边位点开始，但 Co 和 V 掺杂水钠锰矿的空位也参与了反应。这些结果为了解天然水钠锰矿类矿物与 Cr(III)的反应机制提供了依据。
