高浓度悬浊液架桥絮凝分形体的形态学研究

Study on Morphologic Properties of Bridging Flocculated Fractal Aggregates for High Concentration Suspension

对85 kg/m3的黄河泥沙水进行了高浓度悬浊液架桥絮凝沉降试验,考察了架桥絮凝分形体的形态学特性,并用电镜观察了絮体构造。结果表明,絮体结构及其形成过程具有分形特征;参数“分维D”可用于定量表征分形絮凝体的形态学特性:①絮体生长机制以DLCA与RLCA模式为主,其生长模式从快速混合阶段的分枝状DLCA结构逐步向慢速絮凝阶段的密实RLCA构型演变;②粒径分布在3个区域,其曲线形状类似广义的正态分布,“分维”能定量确定絮体密实性与沉降特性达最佳时的粒径范围;③分形结构的不断演变引起絮体内部渗透性显著不同,分形絮体自由沉降规律不能用Stokes定律进行合理解释;④在一定粒径范围内,絮体有效质量密度与Stokes粒径存在双对数线性关系,絮体的孔隙率是影响其密实性的主要原因;⑤对相同含沙量的泥沙水絮凝时,A l2(SO4)3形成的无机混凝剂絮体结构与高分子架桥絮体分形结构相比,具有絮体粒径小、结构脆弱,能承受的剪切强度G值低等特点。

A high concentration suspension investigation was conducted on the Yellow River water with a silt concentration of 85 kg/m^3 , based on bridging flocculated settling experiments and SEM. The results indicate that the structure and formation process of the aggregates take on fractal characteristics, and fractal dimension D can be characterized into morphologic properties of fractal aggregates in quantity as follows ： ①The growth mechanism of fractal aggregates is mainly of the diffusion-limited cluster aggregation （DLCA） model and the reaction-limited cluster aggregation （RLCA） model. Their growth modes can change from an open-branching DLCA structure at the ：rapid mixing stage to a compact RLCA configuration at the slow flocculation stage; ② The data are distributed into three sized regions, the curve from the aggregates size distribution is similar to normal generalized distribution. The proper size distribution range resulted from the optimum compactness and settling characteristics can be obtained quantitatively by using the fractal dimension D ; ③ Continuous development and evolution of the fractal aggregate structures cause remarkably different permeate interior aggregates. The evolution irregularities of free sedimentation rates of fractal aggregates cannot be expressed by the Stokes Law; ④ Under a certain size limit, there is a linear correlation of the logarithm coordinates between effective mass density of aggregates and Stokes size. The porosity of a fractal aggregate is the main reason influencing the compactness of the aggregate ; ⑤ When the aggregate fractal structure formed by the addition of an inorganic coagulant and a high molecular flocculant reach the optimum states with the same raw silt content, the floc of the former has a more frangible fractal structure, which can endure a lower G value of sheafing strength.