高分子絮凝剂对泥沙絮体分形结构的影响

黄河泥沙架桥絮凝沉降实验与电镜实验研究表明,絮体结构具有分形特性。文章讨论了高分子絮凝剂的架桥絮凝机理以及高分子所带电荷种类、高分子的分子量、投加剂量与浓度对絮体分形结构的影响,并用表征絮体结构分形特性的参数“分维D”定量分析了这种影响规律。同时,对比了相同含沙量下无机混凝剂絮体与高分子架桥絮体结构达最佳时的分形特征及所需的混凝控制指标Gt值。     

絮体性能及其工艺调控的研究与进展

絮体结构和强度特征是絮凝过程的重要参数。在简要回顾絮体分形结构研究的基础上，对絮体结构与强度的测定方法、絮体结构形成的影响因素及其工艺调控的研究进展进行了概括性介绍。结合部分实验研究，着重讨论了水力条件对于絮体性能的影响和絮体重组、历史的演化机理，结果表明，     

絮体性能及其工艺调控的研究与进展

絮体结构和强度特征是絮凝过程的重要参数。在简要回顾絮体分形结构研究的基础上,对絮体结构与强度的测定方法、絮体结构形成的影响因素及其工艺调控的研究进展进行了概括性介绍。结合部分实验研究,着重讨论了水力条件对于絮体性能的影响和絮体重组、历史的演化机理,结果表明,逐步增强的水力剪切条件有助于改善絮体的结构和强度：     

壳聚糖絮凝动力学研究

通过不同情况下 ,壳聚糖絮凝皂土颗粒 ,絮体大小随时间的变化过程来研究絮凝动力学。研究认为水力梯度 G值是影响稳态絮体尺寸的关键因素 ;初始浊度和壳聚糖相对分子质量对稳态絮体尺寸和形成稳态絮体的时间亦有影响     

纳米SiO2与聚合铝PAC对含有机微污染物低浊水的絮凝形态学特性

在含有水溶性有机微污染物.十二烷基硫酸钠(SDS)的6NTU高岭土悬浊液中,投加纳米SiO2稳定分散液与聚合铝PAC进行动态混凝试验与静沉试验,借助图像分析技术与分形理论,探讨了纳米SiO2与PAC对含水溶性污染物低浊水的絮凝形态学特性.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与分形结构的动态演变规律;絮凝体生长模式从开放的分枝状DLCA结构逐步向密实的RLCA构型演变.分形结构的不断演变引起絮体内部渗透性变化,絮体沉降性能逐步改善,分维值升高;SDS的存在对絮凝初PAC的混凝起阻碍作用,纳米SiO2能使颗粒生长的速度加快.纳米SiO2有助于有机物的去除,但对无机杂质的去除效果不如PAC;以纳米SiO2为助凝剂,能促使PAC絮体有效质量密度增加,使PAC对SDS的去除率提高,分维值增加.     

含沙高浊水最佳絮凝条件的确定

在含沙量为85kg／m^2的悬浊液中投加阳离子高分子聚合物,研究不同絮凝条件下絮体的自由沉速、结构密实程度、浑液面沉速与上清液余浊等的变化规律。利用“分维”作为定量控制参数研究含沙高浊水絮凝效果迭最佳时的絮凝条件（如搅拌速率、搅拌时间、高分子浓度等）,探讨了最佳絮凝条件下不同原始泥沙浓度对絮体分形结构的影响规律。实验得出85kg／m^2泥沙絮体结构密实性达最佳时的水力剪切强度Ct值存在两个临界值：快速絮凝阶段C1t1=2350,慢速絮凝阶段G2t2=12420。     

无机悬浮颗粒的混凝特性和絮凝体形态学研究

研究了絮凝体的形成过程及其形态学特性.结果表明，无机悬浮颗粒体系的最佳混凝pH值在7～8之间，在低投药量时，压缩双电层和吸附电中和是主要的混凝机理，在高投药量条件下，则是卷扫絮凝起主导作用.絮凝体平均粒径和分形维数都随搅拌时间的延长而增大，并最终趋于稳定.在pH=7和以硫酸铝作为混凝剂的条件下，形成的絮凝体最大粒径为0.3mm，对应的分形维数在1.78左右.随着投药量的增大，絮凝体分形维数的变化较小，但絮凝体平均粒径显著增加;当投药量过高时，网扫絮凝作用下的絮体结构松散，抗剪切能力差，具有较小的平均粒径和分形维数.     

絮凝-超滤去除城市污水中有机物的实验研究

分别以聚合氯化铝(PAC)、三氯化铁(FeCl_3)为絮凝剂,采用絮凝-超滤工艺处理城市污水厂二级出水,考察了絮凝-超滤联合工艺对污水中有机物的去除效果,分析了有机物的三维荧光特征,并探讨了絮体的分形维数及对超滤膜通量的影响。实验结果表明,絮凝预处理强化了超滤对污水中有机物的去除率,FeCl_3+UF对UV_(254)和DOC的去除率分别可达62.1%、79.6%,PAC+UF对UV_(254)和DOC的去除率分别可达68.6%、85.4%。PAC形成的絮体分形维数比FeCl_3要小,形成的絮体更加疏松,更有利于延缓膜通量的下降速度。     

有机絮凝剂对铁矿相沉降性能影响及其吸附机理

通过模拟拜耳法赤泥沉降过程研究了聚丙烯酸铵(PAAA)、阴离子聚丙烯酰胺(APAM)和氧肟酸絮凝剂(HPAM/HCPAM)对赤铁矿和针铁矿沉降性能的影响规律和絮凝后絮体的粒径分布及分形维数,并利用傅里叶变换红外光谱探讨了絮凝剂与铁矿相的吸附机理。在不同类型絮凝剂中,添加氧肟酸絮凝剂铁矿相沉降速度最快,且氧肟酸含量越高,沉降性能越好;聚丙烯酸铵和阴离子聚丙烯酰胺絮凝剂对铁矿相沉降性能影响较小;同等条件下赤铁矿沉降速度要远高于针铁矿,增加絮凝剂添加量有助于提高针铁矿沉降速度。在赤铁矿絮体中,添加PAAA絮体粒径最大,HPAM絮体分形维数最大、致密性最好;在针铁矿絮体中,添加APAM絮体粒径最大,HCPAM絮体分形维数最大、致密性最好。氧肟酸絮凝剂与铁矿相形成结构稳定、吸附能力强的五元环状螯合物,增强了赤铁矿和针铁矿的絮凝效果;PAAA通过双齿桥接配位与赤铁矿表面发生吸附,通过单齿配位与针铁矿表面发生吸附,其吸附能力弱于五元环;APAM与赤铁矿和针铁矿表面发生化学吸附,沉降性能差。     

有机絮凝剂对铁矿相沉降性能影响及其吸附机理

通过模拟拜耳法赤泥沉降过程研究了聚丙烯酸铵(PAAA)、阴离子聚丙烯酰胺(APAM)和氧肟酸絮凝剂(HPAM/HCPAM)对赤铁矿和针铁矿沉降性能的影响规律和絮凝后絮体的粒径分布及分形维数,并利用傅里叶变换红外光谱探讨了絮凝剂与铁矿相的吸附机理。在不同类型絮凝剂中,添加氧肟酸絮凝剂铁矿相沉降速度最快,且氧肟酸含量越高,沉降性能越好;聚丙烯酸铵和阴离子聚丙烯酰胺絮凝剂对铁矿相沉降性能影响较小;同等条件下赤铁矿沉降速度要远高于针铁矿,增加絮凝剂添加量有助于提高针铁矿沉降速度。在赤铁矿絮体中,添加PAAA絮体粒径最大,HPAM絮体分形维数最大、致密性最好;在针铁矿絮体中,添加APAM絮体粒径最大,HCPAM絮体分形维数最大、致密性最好。氧肟酸絮凝剂与铁矿相形成结构稳定、吸附能力强的五元环状螯合物,增强了赤铁矿和针铁矿的絮凝效果;PAAA通过双齿桥接配位与赤铁矿表面发生吸附,通过单齿配位与针铁矿表面发生吸附,其吸附能力弱于五元环;APAM与赤铁矿和针铁矿表面发生化学吸附,沉降性能差。     

A population balance model for flocculation of colloidal suspensions by polymer bridging

A detailed population balance model for flocculation of colloidal suspensions by polymer bridging under quiescent flow conditions is presented. The collision efficiency factor is estimated as a function of interaction forces between polymer coated particles. The total interaction energy is computed as a sum of van der Waals attraction, electrical double layer repulsion and bridging attraction or steric repulsion due to adsorbed polymer. The scaling theory is used to compute the forces due to adsorbed polymer and the van der Waals attraction is modified to account for presence of polymer layer around a particle. The irregular structure of flocs is taken into account by incorporating the mass fractal dimension of flocs. When tested with experimental floc size distribution data published in the literature, the model predicts the experimental behavior adequately. This is the first attempt towards incorporating theories of polymer-induced surface forces into a flocculation model, and as such the model presented here is more general than those proposed previously.     

计算机视觉检测系统在絮凝处理中的应用

絮凝法是废水处理过程中应用最广泛的一种方法。絮凝剂的性质直接影响絮凝效果。作者对计算机视觉检测系统在废水絮凝处理过程中的应用进行了研究。首先介绍了计算机絮凝检测系统的构成及设计原理和方法．然后通过对两种絮凝剂在模拟废水中的絮凝沉淀实验,用计算机视觉检测系统的图像获取功能对絮凝的全过程进行跟踪拍摄,并利用计算机图像处理技术对絮体图像进行分析,找出与絮体沉降特性有关的图形参数．得到絮体图像灰度值与溶液浊度之间的关系曲线,并提出利用絮体图像灰度直方图来判定絮凝沉淀的终点的方法,为絮凝过程的自动化控制提供依据。     

The structure and strength of depletion force induced particle aggregates

Aggregating fine particulate matter is common practice in many industrial solid-liquid separation processes. Data obtained in this work on dilute aqueous dispersions of model colloidal polystyrene latex spheres indicate that depletion flocculation, which uses non-adsorbing polymer, can yield very compact aggregates. Flocculation of the negatively charged latex particles was induced by the addition of a poly(acrylic acid) at pH 10. The structural compactness of the latex flocs formed in the dilute dispersions was characterised using small-angle static light scattering in terms of mass fractal dimensions. Rheological measurements on the concentrated latex dispersions in the presence of the non-adsorbing polyacid showed Bingham yield stress behaviour. Both the compactness and strength of the latex flocs were found to be significantly dependent upon the level of the polyacid, as well as the concentration of the initial particles. In particular, as the level of the polyacid was raised the floc compactness decreased, whereas its strength increased. They were both seen to level off at high polymer concentrations. Atomic force microscopy measurements were made at varying concentrations of the polyacid to provide a qualitative explanation of the observed floc structural behaviour of the dilute dispersions. By combining the fractal dimension and the Bingham yield stress we were also able to estimate the energy required to separate the flocs into single units in the concentrated dispersions. It was concluded that the interparticle interaction energy is the key to understanding the dependence of both the floc structure and strength on the polymer concentration.     

Destabilization of model silica dispersions by polyelectrolyte complex particles with different charge excess,hydrophobicity, and particle size

Nonstoichiometric polyelectrolyte complex dispersions (PECs) with different charge excess and hydrophobicity as well as different average hydrodynamic particle size were used to induce flocculation of oppositely charged silica dispersions. PECs were formed with poly(diallyldimethylammonium chloride) (PD) as polycation and poly(styrene‐p‐sodium sulfonate) (NaPSS) and poly(acrylamide‐co‐sodium acrylate) (PR2540) as polyanions. PD was used as single polymer flocculant too. Flocculation process was characterized by optical densities of supernatants OD₅₀₀, by UV/VIS spectrometry, and determination of average floc sizes D(v; 0.5) as well as volume distribution of floc sizes by laser diffraction and determination of sedimentation velocity s by means of LUMiFuge? 114. It was found that the reaction process between silica and the used flocculants could be divided into three intervals (destabilization, flocculation optimum, and restabilization) as it is known for all other polymer flocculants. For an effective flocculation of a charged substrate, both electrostatic as well as hydrophobic interactions play an important role. The interval up to the beginning of the flocculation optimum is mainly ascertained by electrostatic interactions (the charge density of the flocculant) but the broadness of flocculation optimum depends largely on hydrophobic interactions. Hydrophobic interactions also play an important role for shear stability of the formed flocs. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3776–3784, 2007     

强化混凝用于微污染水的处理研究

采用一种新型的机械-水平隔板絮凝池来强化微污染水的混凝工艺.通过小试确定了最佳连续流工况,絮凝剂PAS在连续流工况下混凝处理长江水的最佳条件是:Gt=28 200,最佳投加量为10mg·L-1(以An+计),pH=～8,可不调.通过观察絮体形貌,发现机械.水平隔板絮凝反应池有较好的同向絮凝效果,不但通过逐渐降低的速度梯度G,使絮体一步步成长为体积较大且密实的颗粒,同时又很好地避免了已经长大的絮凝体的再破碎,能为絮凝剂的混合和反应提供所需的条件,强化了混凝,提高了出水质量.     

Comparison of two cationic polymeric flocculant architectures on the destabilization of negatively charged latex suspensions

Flocculation studies between cationic polymers and oppositely charged colloidal particles are reported in which both flocculation kinetics and floc structures are systematically investigated. The flocculation rate constant, stability ratio and kinetics laws are experimentally determined using particle counting for two polymer architectures; a cationic linear polymer and a two-branched polymer. Comparisons are also made using NaCl at different ionic concentrations for the destabilization of the colloidal particles. Detailed measurements of electrophoretic mobility and kinetics rate constants on varying the polymer dosage are reported. Results suggest that the polymer architecture plays important roles on the polymer dosage for the rapid destabilization of the colloidal suspension. The branched polymer at optimal dosage exhibits the highest flocculation rate constant, whereas on the other hand, the linear polymer concentration range of flocculation is larger. In both cases, polymer flocculation is more efficient by a factor of 5-6 than charge screening effects due to the presence of salt. Analysis of the stability ratio indicates that tele-bridging flocculation and electrostatic forces dictate the stability of the charged latex particle suspension. It is shown that the fractal concepts which are valid for aggregation processes are also applicable here and branched polymers as well as linear polymers yield to the formation of compact flocs in comparison to those obtained with salt.     

Aggregate structures formed via a bridging flocculation mechanism

A high molecular weight cationic polyelectrolyte has been used to flocculate a colloidal dispersion of anionic polystyrene latex particles. The polymer used had a high charge density and the flocculation occurred at a solution pH where both the polymer and the particles were fully charged. Under these conditions, flocculation is expected to occur through a bridging flocculation mechanism. Low angle laser light scattering has been used to follow the flocculation process as a function of time; parameters of interest were the aggregate sizes, size distributions, and aggregate mass fractal dimensions. The light scattering measurements showed that the flocs formed had a mass fractal character. All the systems examined here were overdosed with respect to the optimum flocculation concentration of polymer. Under these conditions, decreasing the polymer concentration was seen to result in an increased flocculation efficiency. A secondary growth process was also observed whereby initially formed fractal aggregates can subsequently aggregate again. These larger aggregates are also expected to be mass fractals although this cannot be determined from the light scattering measurements due to the superposition of Fraunhofer diffraction effects. This type of fractal-in-fractal character is unusual.     

Characterization of floc size, strength and structure under various coagulation mechanisms

Flocs generated by various coagulation mechanisms exhibit different size, strength and structure. The properties and fractal dimensions of flocs formed under three common coagulation mechanisms, i.e. charge neutralization, sweep and bridging, were investigated at various hydraulic conditions. The results showed that the floc size decreased with the increasing average velocity gradient G and the stable floc size exponent γ was of the following hierarchy: charge neutralization (0.6107) > sweep (0.5618) > bridging (0.3674). Furthermore, fractal dimensions of flocs were the highest when formed by sweep and the lowest when generated by bridging flocculation. The mass fractal dimensions measured by light scattering were between 2.0 and 3.0 and the floc strength was between 0.01 and 0.58 N m^− 2. An intrinsic unity of the relationship among floc size, fractal dimensions, floc strength under the three coagulation mechanisms was demonstrated.