ABSTRACT

Magnesium hydroxide is commonly used as a coagulant for treating reactive dyes wastewater. However, the flocs are relatively small and coagulation process needs longer sedimentation time. Large flocs and short operation time are important for good coagulation performance. Coagulation floc formation and growth processes using magnesium hydroxide and polyacrylamide (PAM) dual-coagulant were investigated with controlled experiments through flocculation index (FI), floc size distribution, zeta potential, scanning electron microscopy and Fourier transform infrared spectroscopy. The final average floc size reached 58.5 and 4.96 μm with and absence of PAM addition during slow mixing periods. PAM feeding time and magnesium hydroxide formation time can affect the floc formation and growth processes. The results showed that floc formed rapidly during magnesium hydroxide generation within 90 s and flocs aggregated together by PAM bridging function. Reactive orange removal efficiency reached 99.3% with rapid mixing 250 rpm at 90 s during 100 mg/L magnesium ion addition, then adding 6 mg/L PAM at the beginning of slow mixing period in dual-coagulant system.

摘要

氢氧化镁通常用作处理活性染料废水的混凝剂。但絮凝物相对较小，混凝过程需要较长的沉降时间。大的絮凝物和短的操作时间对于良好的混凝性能很重要。通过絮凝指数 (FI)、絮体尺寸分布、zeta 电位、扫描电子显微镜和傅里叶变换红外光谱等受控实验研究了使用氢氧化镁和聚丙烯酰胺 (PAM) 双混凝剂的混凝絮体的形成和生长过程。在缓慢混合期间添加和不添加 PAM 的最终平均絮状物尺寸达到 58.5 和 4.96 μm。PAM进料时间和氢氧化镁形成时间会影响絮状物的形成和生长过程。结果表明，在氢氧化镁生成过程中，絮体在90 s内迅速形成，絮体通过PAM桥接作用聚集在一起。在加入100 mg/L镁离子的过程中，以250 rpm的速度在90 s快速混合，然后在双混凝系统的缓慢混合阶段开始时加入6 mg/L PAM，活性橙去除率达到99.3%。