聚合氯化铁-腐殖酸(PFC-HA)絮体的粒度和分形维数的动态变化

通过采集PFC-HA絮体的单个样品和拍摄它们的二维图像,研究了在不同混凝条件下絮体的粒度和分形维数的变化.结果表明,原水pH的下降滞后了PFC-HA絮体的出现.原水pH≥7.0时,随着投药量的增加,PFC-HA絮体的分形维数D2(lgA-lgdL)和D3(lgV1-lgdL)随之降低,表明絮体的结构越来越疏松;而原水pH=5.0时,PFC-HA絮体的分形维数存在波动.在PFC的最佳投药量时,水力条件的优化可以提高HA的去除效果,但随着原水pH的下降,HA去除效果的提高程度也随之减小.在最佳水力条件下,PFC-HA絮体的粒度为数百微米,其分形维数值较大,表明絮体的结构较为密实.此外,PFC-HA絮体的粒度分布具有(类)分形特征,最佳水力条件下正的D.值表明絮体的粒度分布趋向平稳.在整个混凝搅拌过程中,PFC-HA絮体的分形维数的变化是与混凝的溶液化学条件、搅拌时间和分形维数类型有关,其D2具有先上升后下降的趋势,这一过程中絮体结构先趋向密实,然后趋向疏松.而且慢速搅拌过程中絮体的尺度也是先增加后下降.

Dynamic change of particle size and fractal dimensions of polyferric chloride-humic acid (PFC-HA) flocs

Single particles of PFC-HA (polyferric chloride-humic acid) flocs formed under different flocculation conditions were sampled and their images were taken with a charge coupled device (CCD) sensor. Through image analysis, the statistical data matrix of geometric parameters for the flocs indicated the dynamic changes of their particle size and fractal dimensions. At low initial pH values of the HA water, the appearance of PFC-HA flocs was postponed. After flocculating the HA water at an initial pH greater than 7.0 with PFC flocculant, the fractal dimensions of D2(lgA-lgdL) and D3(lgV1-lgdL) of the PFC-HA flocs decreased with the increase of PFC dosage, and the flocs showed a gradually looser structure. However, the fractal dimensions of PFC-HA flocs prepared from HA water at initial pH of 5.0 fluctuated with PFC addition. At the optimum PFC dosage, optimization of coagulation-flocculation agitation conditions could improve the HA removal rate, but at low initial pH, the enhancement effect was reduced. Compact PFC-HA flocs with high fractal dimension were formed at optimum agitation conditions, and their average diameter was hundreds of microns. Moreover, the particle size distribution (PSD) of these PFC-HA flocs was fractal, and the positive values of their fractal dimensions Dp show some steady states in their size distribution. In addition, during the coagulation-flocculation process, the fractal dimensions could be affected by the chemical conditions of the solution, agitation time and type of fractal dimension. In the low-speed agitation process, the PFC-HA flocs initially grew, and then their size began to reduce. The fractal dimensions D2 in 2D topological space increased at first, and then decreased at a certain agitation time, demonstrating that the PFC-HA flocs became more and more compact at first, but after some time their structure loosened.