Fe-Mn nodules are widely distributed and regarded as excellent adsorbents for heavy metals. Their adsorption-desorption reactions with heavy metal ions are usually accompanied by redox processes. Herein, Fe-Mn nodules were used as adsorbents for Cd(II) and As(III,V) at a constant cell voltage under electrochemically controlled reduction and oxidation, respectively. The results showed that the adsorption performance for Cd(II) and As(III,V) was enhanced respectively due to the decrease and increase of Mn average oxidation state (Mn AOS) in Fe-Mn nodules. High birnessite content and Mn average oxidation state (Mn AOS) improved the adsorption of Cd(II) and As(III,V). The adsorption capacity for Cd(II) and total As increased with increasing voltage. With increasing pH, the adsorption capacity for Cd(II) increased first and then reached equilibrium, and that of total As decreased and then increased. The Cd(II) electrochemical adsorption capacity (129.9 mg g-1) and the removal efficiency for total As at 1.2 V (83.6 %) in As-containing wastewater at an initial concentration of 4.068 mg L-1 were remarkably higher than the corresponding inorganic adsorption performance (9.46 mg g-1 and 70.5 %, respectively). This work may further promote the application of natural Fe-Mn nodules in the adsorption of heavy metals from wastewaters.

中文翻译：

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天然铁锰结核对镉和砷的电化学吸附。

铁锰结核分布广泛，被认为是重金属的优良吸附剂。它们与重金属离子的吸附-解吸反应通常伴随氧化还原过程。在此，在电化学控制的还原和氧化下，在恒定的电池电压下，Fe-Mn结核分别用作Cd（II）和As（III，V）的吸附剂。结果表明，由于Fe-Mn结核中Mn平均氧化态（Mn AOS）的减少和增加，分别提高了Cd（II）和As（III，V）的吸附性能。高水钠锰矿含量和Mn平均氧化态（Mn AOS）改善了Cd（II）和As（III，V）的吸附。Cd（II）和总As的吸附容量随电压的升高而增加。随着pH值的增加，Cd（II）的吸附容量先增加然后达到平衡，总砷的含量先降低后升高。初始浓度为4.068 mg L-1的含砷废水中Cd（II）的电化学吸附容量（129.9 mg g-1）和对总砷的去除效率为1.2 V（83.6％）无机吸附性能（分别为9.46 mg g-1和70.5％）。这项工作可以进一步促进天然铁锰结核在废水中重金属吸附中的应用。