强场预磁化对高浊度黏土污水混凝沉降的影响

Effect of high magnetic field pre-magnetization on the floc-culation sedimentation of high turbidity clay sewage

高浊度矿物污水难以高效澄清处理的主要原因之一是黏土矿物颗粒表面荷电且包覆有一层“水化膜”,使得矿物颗粒凝聚、絮凝困难。为了提升高浊度污水的混凝澄清效果,降低化学药剂用量,将强场预磁化处理引入混凝沉降过程,采用预磁化-混凝沉降工艺处理高浊度黏土污水。通过单因素变化试验及多因素正交试验,研究了磁场强度、磁化时间等预磁化工艺参数及药剂制度对黏土污水澄清效果的影响。研究结果表明,强磁场作用对高浊度黏土污水的性质具有显著影响,从而使得污水的混凝澄清效果显著提升。黏土絮团的平均沉降速度增大1.92倍,沉降20min时的尾泥体积减少38.9%,上清液透光率提高54.1%。预磁化最佳的磁场强度范围为178~241mT。磁场强度减小,磁化效果迅速减弱;磁化强度增加,磁化效果无明显增强。预磁化最佳的磁化时长为90s左右。在获得同等澄清效果的情况下,预磁化-混凝沉降比常规混凝沉降的絮凝剂用量减少了50%,CaCl2用量减少了75%。同时,最终尾泥体积反而减小了14.65%。机理分析表明,强场预磁化对矿粒表面的双电层结构及水分子排列构型具有较大影响,从而显著减小了zeta电位减小、减薄了矿粒表面的水化膜。矿粒表面性质的改善可以显著提升黏土矿粒的凝聚效率、促进矿粒与絮凝剂分子的结合,从而提升了高浊度黏土污水的混凝效果。本工作为高泥化矿物污水的澄清处理提供了一种绿色高效的新方法。

One of the major problems that hinders the effective flocculating setting of high turbidity sewage (HTS) is that the clay particle surface is covered by a “hydration layer” and is electrical charged.This complex surface property of clay particle impedes coagulation and flocculation.In order to improve the sedimentation of HTS and reduce the addition of chemical reagents,high magnetic field was employed to pre-magnetize the HTS before the traditional flocculation process.Factors influencing the pre-magnetization and flocculation (PMF),such as magnetic field intensity,magnetizing time,coagulant and flocculant dosage,were carefully studied by both single factor experiments and orthogonal tests,using a home-made clay HTS.It was observed that the properties of HTS were significantly affected by high-field magnetizing,thus improving clay particle coagulation and flocculation.Compared with the conventional flocculation,the PMF technique had a much better sedimentation effect (after20 minutes flocculation).The settlement rate of the clay floccules increased by1.92 times,the tailing slurry volume decreased by 38.9%,and supernatant transmittance increased by 54.1%,respectively.The optimum magnetic field intensity and magnetizing time were proved as178-241 mT and 90 s,respectively.Further decrease of the magnetic field intensity would lead to a sharp decrease of flocculation.The flocculation would not increase with a further increase of magnetic field intensity.To achieve a similar settlement effect,the PMF technique consumes less chemical reagents,compared with the traditional flocculation technique.The coagulant and flocculant dosage was reduced by 75% and 50%,respectively.In addition,the tailing slurry volume was reduced by14.65%,which is helpful for the subsequent sludge treatment.Careful characterization shows that the zeta potential of clay particles was re-markably reduced by the 90 s pre-magnetization under a178-242 mT magnetic field.It was found that the high field pre-magnetizing had a remarkable influence on the molecule structure of the hydration shell and the electric double layer on the particle surface.The decrease of the zeta po- tential and the thickness of hydration layer on the particle surface reduced the electrostatic repulsion both between the clay particles and between the clay particles and the flocculant molecule.The reformative surface properties improved the particle coagulation and the flocculation.As a result,the sedimentation of HTS was improved.This work provides a promising green and efficient method for mineral HTS treatment.