Mechanisms of anti-agglomeration and anti-clogging by using zero-valent iron entrapmented in calcium alginate beads

doi:10.11949/0438-1157.20191366

Abstract

Abstract:

Zero-valent iron micron-particles have been successfully entrapped in calcium alginate beads (CAZ) by using sodium alginate (SA), calcium chloride, micro zero-valent iron (MZVI). Through static beaker experiment and dynamic PRB model experiment, the performance of CA in Cr(Ⅵ) removal was discussed, and the mechanisms of CA avoiding agglomeration and blocking were analyzed by scanning electron microscopy. The results show that the application of CA gel particles can significantly improve the Cr (Ⅵ) removal performance of MZVI. Compared with MZVI, the removal rate and reaction rate of Cr(Ⅵ) by CAZ are 7.1 times and 23.0 times, respectively. The increased treatment capacity of Cr(Ⅵ) contaminated groundwater was mainly attributed to higher utilization rate caused by CAZ reactor more than by MZVI, and the increased MZVI reaction rate was the main reason for lower Cr(Ⅵ) effluent concentration in CAZ reactor than that in MZVI reactor. Analysis results by scanning electron microscopy showed that rich skeleton framework and pore structures were formed by crosslinking reaction of SA and calcium chloride. For this pore structure which played a skeleton supporting role, the defects of agglomeration and reduced specific surface in Fe⁰ caused by gravity were overcame. In prior period, significantly decreased effluent volume in dynamic PRB test could be attributed to the release of MZVI particles which were fixed on CA surface, together with precipitates which broke through CA surface. In later period, most MZVI particles were fixed in CA while the complex-precipitation of (Fe_xCr_1-_x)(OH)₃ was trapped inside the pore structure, which could efficiently alleviate the blocking problems caused by long and continuous operation of Fe⁰-PRB system.

Key words: calcium alginate(CA), hexavalent chromium, groundwater remediation, permeable reactive barrier(PRB), zero-valent iron(ZVI)

摘要：

以海藻酸钠（SA）、氯化钙、微米零价铁（MZVI）为原料，制备了海藻酸钙（CA）固定化MZVI填料（CAZ），通过静态烧杯实验和动态PRB模型实验，探讨了CA运用对Cr(Ⅵ)的去除性能的影响，并通过电镜扫描分析了CA避免团聚、堵塞机制。实验结果表明，CA凝胶颗粒的运用能显著提升MZVI的除Cr(Ⅵ)性能，CAZ相比MZVI对Cr(Ⅵ)的去除率和反应速率分别提升7.1倍、23.0倍；MZVI利用率的提高是CAZ反应器处理Cr(Ⅵ)水量显著大于MZVI反应器的主要原因，MZVI反应速率的提高是CAZ反应器出水Cr(Ⅵ)浓度显著低于MZVI反应器的主要原因。电镜扫描结果表明，SA与氯化钙交联形成的CA具有丰富的骨架孔道结构，具有骨架支撑作用，能有效克服MZVI颗粒因重力作用导致团聚、降低比表面积的缺陷。CA表层固定的MZVI颗粒与Cr(Ⅵ)反应生成的(Fe_xCr_1-_x)(OH)₃ 络合沉淀会冲破CA表层外壳，释放到零价铁-渗透反应墙（Fe⁰-PRB）系统中，导致PRB反应初期出现堵塞现象；大部分MZVI颗粒被固定在CA内部，CA内部有较多孔隙结构，这些孔隙结构会控制(Fe_xCr_1-_x)(OH)₃ 络合沉淀释放，从而缓解了Fe⁰-PRB后期长期运行持续堵塞的问题。

关键词: 海藻酸钙, Cr(Ⅵ), 地下水修复, 渗透反应墙, 零价铁

CLC Number:

X 705

Wenhui ZHU, Xiahui WANG, Xintong YANG, Xingrun WANG, Jun HE, Guoxin HUANG, Guohua JI. Mechanisms of anti-agglomeration and anti-clogging by using zero-valent iron entrapmented in calcium alginate beads[J]. CIESC Journal, 2020, 71(5): 2344-2351.

朱文会, 王夏晖, 杨欣桐, 王兴润, 何俊, 黄国鑫, 季国华. 海藻酸钙固定化零价铁抗团聚及堵塞的作用机制[J]. 化工学报, 2020, 71(5): 2344-2351.

Figures/Tables 10

Fig.1 Photos of MZVI prepared

Fig.2 Photos of CAZ prepared

Fig.3 Schematic diagram of PRB test device

Fig.4 Variation of removal rate as a function of time with two fillers

Fig.5 ln(c0/c)-t fitting curve at different media

Fig.6 Adsorption of Cr(Ⅵ) as a function of time with different CA mass concentration

Fig.7 Effluent Cr(Ⅵ) concentration change of reactor

Fig.8 Variation of daily treatment capacity of reactor

Fig.9 Scanning electron microscopy images of CA[(a) and (b) were prepared after freeze-drying; (c) Fe0 on the surface of CA without freeze-drying; (d) Fe0 on the internal of CA without freeze-drying]

Fig.10 Scanning electron microscopy images of CAZ[(a) Fe0 on the surface of CA for 3 h reaction in Cr(Ⅵ) solution; (b) Fe0 on the surface of CA for 24 h reaction in Cr(Ⅵ) solution; (c) and (d) internal space of CAZ]

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