CO2对层状双金属氢氧化物所吸附六价铬的脱附浓缩及其作用机制研究

Chromium pollution control and chromium reuse are important issues of today's environmental protection and comprehensive utilization of resources. Hexavalent chromium of high toxicity and mobility, is the main existing form of chromium pollutants in wastewater and the effective treatment of hexavalent chromium is very difficult. Layered double hydroxides (LDHs) can remove hexavalent chromium in wastewater effectively by adsorption. So far, there is no economic and efficient method for hexavalent chromium concentration and LDHs regeneration, which greatly limits the applications of LDHs in treating industrial wastewater containing hexavalent chromium by adsorption and desorption. Our previous research found the adopted multiple CO2 desorption method can efficiently and simultaneously achieve the goals of hexavalent chromium desorption and concentration as well as LDHs regeneration. However, this desorption method has such disadvantages as complex operation and higher cost. In view of the existing shortcomings of this desorption method, in this proposal, we will systematically study the effect of metal type of LDHs, the existing form of CO2 and the external conditions on the desorption and concentration of hexavalent chromium. The interaction rules among CO2, LDHs and hexavalent chromium will be further revealed in order to clarify the mechanism of desorption and concentration of hexavalent chromium by CO2. The goal is to further increase the one-time desorption rate of hexavalent chromium so as to improve the efficiency and reduce the cost. The results will provide theoretical basis for the practical applications of LDHs in the treatment of wastewater containing hexavalent chromium. It can also offer a useful reference for solving chromium environmental pollution and the reuse of chromium resource.

铬污染治理及铬的回收利用是当今环境保护和资源综合利用的重要课题。高毒性和高迁移性的六价铬是废水中铬污染物的主要存在形式，其有效治理困难。层状双金属氢氧化物(LDHs)可以有效吸附去除废水中的六价铬，但是目前尚无经济、高效的脱附浓缩六价铬同时循环再生LDHs的方法，这极大地限制了LDHs在吸/脱附处理含铬废水中的应用。申请人前期研究发现气态CO2多次连续脱附法可同时有效实现LDHs中六价铬的脱附浓缩和LDHs的再生，但该脱附方法存在操作复杂且成本较高等问题。针对该方法目前存在的不足，本项目拟系统研究LDHs的金属种类、CO2的赋存形式及外界条件等对六价铬脱附浓缩的影响，揭示CO2、LDHs和六价铬的相互作用规律，阐明CO2脱附六价铬的作用机制，目标是大幅提高六价铬的一次性脱附率从而提高效率和降低成本。本项目将为LDHs处理含铬废水的实际应用提供理论依据，也为铬污染的解决和铬资源回用提供参考。

六价铬污染的治理及铬资源的回收利用是当今环境保护和资源综合利用的重要课题。层状双金属氢氧化物(LDHs)可以有效吸附去除废水中的六价铬，采用气态CO2辅助Cr(VI)脱附法可同时实现LDHs中六价铬的有效脱附和LDHs的再生。本项目合成了约30种含不同金属种类和不同金属比例LDHs吸附材料，系统研究了不同金属种类和比例的LDHs对六价铬的吸/脱附能力，分析了吸脱附前后LDHs的结构和形貌变化规律，并深入探究了气态CO2法脱附六价铬的最佳外界条件。结果表明，Zn:Al=3:1、Ni:Fe=4:1和Ni:Al=3:1的LDHs对六价铬的吸附率较高，分别约为46.52%，40.62%和74.82%；在压力5MPa、4h、温度为30℃的最优条件下，三种LDHs的一次脱附率分别为44.81%、16.11%和16.70%。基于以上结果，得到ZnAl(3:1)-LDHs对六价铬的吸/脱附效果最好，并进一步进行了CO2连续脱附实验。经4次连续脱附，最终的脱附效率可以提高到87.72%。XRD, SEM 和 TEM表明吸脱附前后LDHs的结构和形貌无明显变化，IR结果表明在高压密闭体系中部分CO2形成了 HCO3-和CO32-。此外，本项目设计了一种利用高压CO2对吸附重金属残渣进行连续脱附的实验装置并提出了一种通过一步机械球磨制备层状双金属氢氧化物的新方法。这些成果对提高六价铬的一次性脱附率和总脱附率提供了一定的理论依据，同时为LDHs处理含铬废水的实际应用提供理论支持，对铬污染的解决和铬资源回收利用提供一种新思路。研究成果部分已发表在ACS Catalysis、Catalysis Science & Technology 、New Journal of Chemistry、Inorganic Chemistry Communications等期刊杂志上7篇，申请专利5项。.