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电镀工业是我国经济发达地区的重要加工行业,由于其在工业中适用性高,广泛分布于各个工业部门,电镀生产在耗费大量工艺用水的同时,也产生大量的电镀废水[1]。电镀废水具有重金属含量高、毒性大、污染物杂、环境危害严重等特点[2-4],属于难处理的工业废水。目前电镀废水的处理工艺主要采用物化预处理+生化处理+深度处理的组合工艺,涉及中水回用的主要采用膜分离技术[5],淡水回用于生产漂洗工段.常规的废水深度处理工艺不能彻底将其从水中去除,出水无法稳定达到电镀污染物排放标准(GB 21900-2008)的排放标准,开发高效的深度处理工艺已成为水处理领域的关注点。
臭氧氧化作为一种绿色处理工艺具有易操作、污染物去除效率高、无二次污染等优点已被广泛运用于饮用水和废水深度处理领域[6-9] 。由于臭氧氧化具有一定的选择性[10-11],研究人员开发了多相催化臭氧化技术克服了上述缺点,通过在臭氧氧化过程中加入非均相催化剂,使水中溶解性臭氧在催化剂表面发生链式反应产生羟基自由基(·OH)[12-13],从而提高水中有机物的去除率。
常见的非均相臭氧催化剂有金属氧化物(MnO2、FeOOH、TiO2等)[14-16]、多金属负载催化剂(RuO2/Al2O3、MnO2/Al2O3、TiO2/Al2O3等)[17-19]、矿物(Cu/堇青石、Mn/蜂窝陶瓷[20]等)和活性炭(MnOx/GAC[21]、多壁碳纳米管等)。目前工程项目中应用较广的催化剂多以球形陶瓷颗粒为载体负载多金属氧化物,常装填于固定床形式的反应器[22]内进行进行臭氧催化反应,但其传质效率低,水流易产生局部短流,影响臭氧催化氧化对水中有机物的去除效率。为了开发更为高效、稳定和经济的臭氧催化剂,研究人员除了在催化剂表面负载的活性组进行改进外,对催化剂的结构也进行了研究及优化。
基于陶瓷膜具有优异的化学性能,研究人员就臭氧预氧化+陶瓷膜工艺去除有机物和陶瓷膜改性催化臭氧氧化等开展了相关研究。2003年SCHLICHTER等[23]首次将臭氧氧化和陶瓷膜过滤相结合处理地表水和微污染原水,之后臭氧与陶瓷膜结合的相关研究开始逐渐增多。BYUN等[24]对陶瓷膜进行了改性,将氧化锰或氧化铁负载于陶瓷膜制备成催化膜,发现有机物的去除取决于陶瓷膜被金属氧化物纳米粒子包覆的类型,而且氧化锰膜的性能优于其他测试膜。我国对臭氧/陶瓷膜工艺的研究起步较晚,2011年清华大学的张锡辉课题组首先在国内使用臭氧预氧化/陶瓷膜组合工艺处理水中甲硫醚[25],此后该课题组使用该技术在饮用水处理、微污染水净化等领域的研究。
本研究以陶瓷膜为载体,采用浸渍-焙烧工艺制备了多组分臭氧催化过滤膜,实现了膜分离技术与催化臭氧氧化技术的同步耦合,利用陶瓷过滤膜的微米级孔道过滤废水,可实现污染物的定向移动,有效地促进了扩散传质,同时微米级孔道内部负载的催化剂,增大了催化模块的有效催化比表面积。利用XRD、SEM、DEX等技术对催化过滤膜进行了表征,并以电镀园区物化预处理后的混合废水为研究对象,考察催化过滤膜在常温下臭氧氧化过程中的催化活性。
陶瓷负载型MnO2-CeO2-La2O3臭氧催化过滤膜的制备及表征
Preparation and characterization of MnO2-CeO2-La2O3 ozone catalytic ceramic filtration membranes
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摘要: 以陶瓷膜为载体,采用浸渍-焙烧法制备了MnO2-CeO2-La2O3臭氧催化过滤膜,使用SEM、EDS和XRD等分析方法对其形貌和结构进行了表征分析。以电镀园区预处理混合废水为处理对象,考察了所制备的催化过滤膜在同步臭氧催化氧化和膜过滤作用下的催化活性。结果表明,在浸渍液中Ce3+、La3+、Mn2+的质量比为2:2:1、焙烧时间为3 h和焙烧温度为800 ℃下制备出的催化过滤膜对电镀园区废水有较好的催化性能。在臭氧投加量为5 mg·L−1,跨膜压差为0.15 MPa,回流比为90%的条件下,废水COD的去除率可达到51.2%,与未负载催化剂的陶瓷膜相比,COD去除率提高了23.8%,稳定性实验测试结果表明,以上制备的催化过滤膜具有良好的稳定性能。以上研究结果可实现膜分离技术与催化臭氧氧化技术的耦合,提高出水水质,增强催化过滤膜的抗污染能力。Abstract: MnO2-CeO2-La2O3 ozone catalytic ceramic filtration membranes were prepared by impregnation-calcination method using ceramic membranes as carriers, and the morphology and structure were characterized by SEM, EDS and XRD. The catalytic activity of the membranes prepared in this work was explored under the synchronous processes of catalytic ozonation and membrane filtration when the pretreatment mixed wastewater from an electroplating park was taken as the treating object. The results indicated that the catalytic filter membranes prepared at the mass ratio of 2:2:1 for Ce3+, La3+ and Mn2+ in the impregnation solution, calcination time of 3 h and 800 °C had a good catalytic performance. At the ozone dosage of 5 mg·L−1, transmembrane pressure of 0.15 MPa, and reflux ratio of 90%, the COD removal rate of wastewater could reach 51.2%, it increased by 23.8% compared with the ceramic membranes without loading catalysts. In addition, the stability tests demonstrated that the ozone catalytic ceramic filtration membranes had a good stability. Above all, the coupling of the membrane separation technology and catalytic ozonation was realized, and the effluent water quality was improved, and the anti-pollution ability of the catalytic filtration membranes were enhanced.
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表 1 催化过滤膜各活性组分元素含量
Table 1. Element content of active components of the catalytic ceramic filtration membranes
元素 质量分数/% 原子分数/% O 48.07 65.11 Al 40.08 32.17 Mn 3.65 1.44 La 4.21 0.66 Ce 3.99 0.62 表 2 催化过滤膜的性能参数
Table 2. Parameters of the catalytic ceramic filtration membranes
陶瓷膜种类 孔隙率/
%孔径
/
nm纯水通量
/
(L·(m2·h·Mpa)−1)盐酸可溶率/
%陶瓷膜基体 33 50 2 000 — 负载后的陶瓷膜 26 30 1 260 0.6 -
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