Manganese (Mn) oxides have high Cd(II) sorption affinities and could effectively immobilize Cd(II) in soil and aquatic systems. However, coexisting Fe(II) can react with Mn oxides at oxic-suboxic interfaces, thereby affecting Cd(II) immobilization by Mn oxides. Mn(IV)-rich Mn oxides in the environment are readily to be reduced to Mn(III)-rich Mn oxides by natural organic matter. Herein, we determined the effects of Fe(II) on Cd(II) immobilization by Mn(III)-rich δ-MnO₂ (denoted as HE-MnO₂) at pH 5.5 and 7.5. Results show that Fe(II) decreased Cd(II) retention on HE-MnO₂ at pH 5.5 but had no effects at pH 7.5 due to the high Cd(II) adsorption affinity of HE-MnO₂ at high pH. Poorly crystalline Fe oxides, likely ferrihydrite, uniformly precipitated on HE-MnO₂ surfaces upon Fe(II) addition at both pHs. β-MnOOH formed at the high initial Fe(II) concentration at pH 7.5. Cd(II) was mainly adsorbed on HE-MnO₂ rather than the newly formed Fe oxides and β-MnOOH which had low Cd(II) adsorption capacities. The decrease of Cd(II) sorption in the presence of Fe(II) could be explained by the reduction of HE-MnO₂, the precipitation of Fe oxides on HE-MnO₂, and the competition of generated Mn(II) for the sorption sites. Cd(II) formed double-corner sharing (DCS) and double-edge sharing (DES) complexes with Mn(III) edge sites on HE-MnO₂. After the addition of Fe(II), Cd(II) formed only DCS complexes with Mn(III) edge sites. The alternation of the surface complexes caused by Fe(II) promoted Cd(II) desorption from HE-MnO₂. This work suggests that Fe(II) can decrease the removal efficiency of Cd(II) by Mn(III)-rich δ-MnO₂ at oxic-suboxic interfaces in the environment.

锰（Mn）氧化物具有高的Cd（II）吸附亲和力，可以有效地将Cd（II）固定在土壤和水生系统中。但是，共存的Fe（II）可以与Mn氧化物在氧-羧基界面反应，从而影响Mn氧化物对Cd（II）的固定。环境中富含Mn（IV）的Mn氧化物很容易被天然有机物还原为富含Mn（III）的Mn氧化物。在本文中，我们确定对Cd的Fe（II）的效果（II）固定化的Mn（III）的富δ-的MnO ₂（表示为HE-的MnO ₂在pH 5.5和7.5）。结果表明，Fe（II）在pH 5.5时降低了Cd（II）在HE-MnO ₂上的保留，但在pH 7.5时没有影响，因为HE-MnO ₂对Cd（II）的高吸附亲和力在高pH下。在两种pH下添加Fe（II）后，结晶度较弱的Fe氧化物（可能为亚铁酸盐）均会均匀沉淀在HE-MnO ₂表面上。在pH值为7.5的高初始Fe（II）浓度下会形成β-MnOOH。Cd（II）主要吸附在HE-MnO _2上，而不是Cd（II）吸附能力低的新形成的Fe氧化物和β-MnOOH。在Fe（II）存在下Cd（II）吸附的减少可以解释为HE-MnO ₂的还原，Fe氧化物在HE-MnO ₂上的沉淀以及生成的Mn（II）的竞争。吸附位点。Cd（II）与HE-MnO ₂上的Mn（III）边缘位点形成了双角共享（DCS）和双边缘共享（DES）络合物。添加Fe（II）后，Cd（II）仅形成具有Mn（III）边缘位点的DCS配合物。Fe（II）引起的表面配合物的交替促进了Cd（​​II）从HE-MnO _2中解吸。这项工作表明，铁（II）可以通过的Mn（III）的富δ-MnO的减少镉（II）的去除效率₂在环境好氧-低氧接口。