电化学驱动水钠锰矿高效吸附去除混合重金属离子

High-efficiency adsorption removal for multiple heavy metal ions using birnessite under electrochemical drive

锰氧化物被广泛用作重金属离子吸附剂,电化学调控其氧化还原反应程度可提高重金属吸附容量.然而,多种重金属离子共存时的电化学吸附过程及相互影响机理尚不清楚.本工作采用多周恒流充放电方式研究了水钠锰矿对Cd^(2+)、Zn^(2+)、Pb^(2+)与Ni^(2+)单独及共存时的电化学吸附性能及机理,同时考察了氧化还原程度对吸附性能的影响.结果表明,重金属离子的电化学吸附容量明显高于断路条件下的物理化学吸附容量.在0.5 mmol·L^(-1)单一及多种重金属离子混合溶液中,水钠锰矿电化学吸附容量大小顺序均为Pb^(2+)>Cd^(2+)>Zn^(2+)>Ni^(2+).在单一重金属离子溶液中,Cd^(2+)、Zn^(2+)、Pb^(2+)和Ni^(2+)的去除率分别为41.8%、37.2%、85.6%与31.3%.多重金属离子共存时,Pb^(2+)的去除率受其他重金属离子影响较小.Pb^(2+)优先占据水钠锰矿上吸附位点阻碍了Cd^(2+)、Zn^(2+)与Ni^(2+)的吸附,导致相应去除率分别降至19.9%、11.6%和5.4%.共吸附过程中,Cd^(2+)对Zn^(2+)与Ni^(2+)有抑制作用,Zn^(2+)与Ni^(2+)互相抑制且Zn^(2+)对Ni^(2+)抑制作用较强.随着水钠锰矿氧化还原程度加剧,Pb^(2+)去除率明显增加,Cd^(2+)、Zn^(2+)和Ni^(2+)的去除率变化不大.该研究可为锰氧化物用于电化学吸附处理重金属污染废水提供基础数据和参考.

Manganese oxides are widely used as adsorbents for heavy metal ions,and their adsorption performance can be enhanced by the electrochemical control of the redox degree.However,the electrochemical adsorption process and interaction mechanism are still enigmatic at the co-existence of multiple heavy metal ions.In this work,the individual and competitive electrochemical adsorption performance and mechanism of birnessite for Cd^(2+),Zn^(2+),Pb^(2+) and Ni^(2+) were investigated by multi-cycle galvanostatic charge-discharge,and the effect of redox degree on the electrochemical adsorption performance was also studied.The results indicated that the electrochemical adsorption capacity was much higher than the physicochemical adsorption capacity of birnessite for these heavy metal ions.In the solutions containing 0.5 mmol·L^(-1) individual or mixed heavy metal ions,the electrochemical adsorption capacity follows the order of Pb^(2+)>Cd^(2+)>Zn^(2+)>Ni^(2+).The individual electrochemical removal efficiency was 41.8%,37.2%,85.6%and 31.3%for Cd^(2+),Zn^(2+),Pb^(2+) and Ni^(2+),respectively.In the solutions containing mixed heavy metal ions,the electrochemical removal efficiency of Pb^(2+) seemed not to be remarkably affected by the presence of other heavy mental ions.The preferential occupation of adsorption sites by Pb^(2+) obviously impended the electrochemical adsorption of Cd^(2+),Zn^(2+) and Ni^(2+) on birnessite,leading to decreases of their removal efficiency to 19.9%,11.6%and 5.4%,respectively.The presence of Cd^(2+) inhibited the adsorption of Zn^(2+) and Ni^(2+),and the adsorption of Zn^(2+) and Ni^(2+) inhibited each other,with Zn^(2+) exhibiting a stronger inhibitory effect on Ni^(2+).With increasing redox degree of birnessite,the removal efficiency of Pb^(2+) significantly increased,while that of Cd^(2+),Zn^(2+) and Ni^(2+) showed little change.This study provides basic data and reference for the application of manganese oxides in electrochemical adsorption of heavy metal contaminated wastewaters.