海藻酸钠包覆型Fe-Cu双金属PRB填料的除Cr(Ⅵ)特性

Fe⁰与Cr(Ⅵ)发生表层反应使Fe⁰-渗透反应墙(PRB)利用率很低。针对Fe⁰利用率低问题,研究了海藻酸钠(SA)包覆型铁粉填料(SAC)和SA包覆型Fe-Cu双金属填料(SAB)对受污染地下水中Cr(Ⅵ)的去除影响;实验结果表明,SAB效果最好。SAB中双金属的化学吸附占主导作用,SA自身对Cr(Ⅵ)的吸附容量很小。SAB₂(镀铜1%)的FEI电镜扫描及XPS能谱分析结果表明,SA与2价金属阳离子Ca²⁺交联形成孔隙结构,不仅为双金属的附着提供了大量的吸附点位,还可使Cr(Ⅵ)进入到内部与双金属反应;Cu在Fe⁰与Cr(Ⅵ)反应中起催化剂作用,通过自身化合态变化传递Fe⁰失去的电子。在中性条件下,对SAB进行动力学拟合,符合准一级化学反应动力学。且随着镀铜量的增加,SAB反应速率常数k逐渐增大;随着初始Cr(Ⅵ)浓度的增大,SAB₂反应速率常数k逐渐下降;随着双金属投加量的增大,SAB₂反应速率常数k线性递增。相比SAC和纯铁粉,SAB具有较大的去除能力和较高的反应速率,采用SAB治理Cr(Ⅵ)污染地下水是可行的。

Characteristics of removing Cr(Ⅵ) of Fe-Cu bimetal PRB coated by sodium alginate

The surface reaction between zero-valent iron and Cr(Ⅵ)makes the utilization rate of Fe⁰-permeable reactive barrier(PRB)very low.In order to resolve this problem,sodium alginate(SA)was used to coat cast iron(SAC)and copper-iron bimetallic particles(SAB),and they were tested in treating chromium-polluted groundwater.The results show that SAB is the best.Adsorption capacity of SA to Cr(Ⅵ)is small,chemisorptions of copper-iron bimetallic particles in SAB plays main role.As indicated by FEI and XPS,pore structures were created by cross-linking of SA with Ca²⁺,which not only provided a lot of attaching points for bimetallic particles,but also diffusion path for Cr(Ⅵ)to enter interior of copper-iron bimetallic particles.The results of XPS also indicate that variation of copper valence was used for transfer of electrons from reaction of Cr(Ⅵ)by Fe⁰ and the role of copper is as if a catalyst.Under neutral condition,the removal process of Cr(Ⅵ)by SAB follows the pseudo first-order kinetics.The rate constant k increase with increasing copper loading(for SAB)and copper-iron bimetal amount(for SAB₂), and decrease with Cr(Ⅵ)concentration(for SAB₂).The rate constant is higher and removal capacity greater for SAB than for cast iron powder.Using SAB as the PRB is feasible for remediation of chromium contaminated groundwater.