海藻酸钙固定化零价铁抗团聚及堵塞的作用机制

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

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(FexCr1-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(FexCr1-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。

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(FexCr1-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.