助留体系对PCC悬浮液形成絮体分形特征的影响

研究了造纸湿部常用助留体系对沉淀碳酸钙(PCC)悬浮液的絮凝作用,应用图像分析法计算絮体的分维.助留体系能使PCC悬浮液中形成形状复杂的絮体,具有自相似性的分形特征.絮体的分维和沉淀后水浊度之间表现出良好的相关性.研究中采用CPAM时,形成絮体的分维最大值为1.6468.由PAC/APMP舣元体系形成的絮体,其最大分维值为1.7189,电荷中和和架桥作用絮凝机理的联合,以及相反电荷聚合物之间的较强的静电相互作用,使得絮体更加密实,分维更高.微粒体系形成絮体的分维比CPAM单元体系和双元聚合物体系更大,而且微粒用量越大,分维值越大,这表明微粒体系形成的絮体更致密,且微粒用量对絮体结构有影响.     

CPAM对PCC悬浮液絮凝作用的分形研究

絮体具有分形结构特征,研究了造纸湿部常用助留剂--阳离子聚丙烯酰胺(CPAM)对沉淀碳酸钙(PCC)悬浮液的絮凝作用,应用图像分析法计算絮体的分维.CPAM能使PCC悬浮液中形成形状复杂的絮体,具有自相似性的分形特征.絮体的分维和沉淀后的上清液浊度之间表现出良好的相关性.CPAM形成絮体的分维在1.3062～1.6468范围内,且其与CPAM的用量、电荷密度及分子质量有关.对于研究中采用的3种CPAM,电荷密度较高的CPAM,形成絮体的分维较高;分子质量较大的CPAM形成的絮体分维相对较低.     

分形分析GCC絮体结构特征及其对手抄片性能的影响

重质碳酸钙加入浆中前对其进行絮凝,在提高其添加量的同时尽可能使纸张强度降低最小。填料絮体特性,如絮体粒径、结构对絮凝效果有较强的影响。本文使用质量分形分析方法来确定絮体结构对絮凝系统的影响,利用光衍射光谱得到三种不同絮凝剂体系在高剪切条件下絮凝的絮体质量分析维数。该三种絮凝剂体系分别为单聚合物C-PAM、双阳离子聚合物p-DADMAC/C-PAM、大聚合物组合C-PAM/大聚合物,采用这三种絮凝剂体系对填料进行絮凝,絮凝后加到浆中抄成手抄片,然后研究其对手抄片性能的影响。研究发现,经C-PAM/大聚合物絮凝的GCC加填后的手抄片抗张指数得到了最大的改善。从质量分形分析结果可知,这是由于该絮凝剂体系使填料在絮凝过程中形成絮体更紧密,更接近于球形。手抄片截面分析也表明,采用C-PAM/大聚合物絮凝剂体系絮凝GCC絮体具有更均一的粒径。综上所述,分形分析能使我们更好地理解絮凝填料的特性和它们对纸张性能的影响：加填填料絮体越致密,越接近于球形,越有利于改善抄造纸张的抗张指数。     

钛酸钠纳米管/CPAM对高岭土的絮聚作用

利用水热法合成了钛酸钠纳米管,并用TEM、Zeta电位对其进行表征,联合使用颗粒分散度分析仪与动态滤水仪研究了钛酸钠纳米管单独及与阳离子聚丙烯酰胺(CPAM)联合使用时对高岭土的絮聚作用。结果表明,钛酸钠纳米管自身对高岭土悬浮液仅有微弱的絮凝作用,但与CPAM联合使用时,可引起高岭土的显著絮聚。絮聚具有普通阴离子微粒助留体系的特征。与球状纳米二氧化钛相比,钛酸钠纳米管的微粒桥联作用使其在较低的用量下获得对高岭土的最大絮聚作用。另外,钛酸钠纳米管/CPAM所引发的高岭土絮聚具有抗剪切作用。     

脱墨浆中胶黏物的絮聚行为研究

利用聚集光束反射测量仪(FBRM)对脱墨浆中胶黏物粒子在阴离子垃圾捕捉剂(PDAD-MAC)作用下的絮聚行为进行了研究,并结合激光粒度仪、浊度仪、Zeta电位仪等对其结果进行了验证.实验结果表明,PDADMAC用量为20 mg/L时,对胶黏物的絮聚效果最佳,此时接近理论电荷等电点,继续增加PDADMAC用量,体系超过等电点,电荷发生逆转,胶黏物粒子重新分散.由FBRM得出的胶黏物絮聚动力学可知,其絮聚过程分为溶解性物质凝聚和胶体性物质絮凝两个阶段.为了得到较好的胶黏物控制效果,提高PDADMAC的使用效率,应避免在过高的碱性条件下进行使用.     

微粒助留系统絮凝行为的研究

采用影像分析和激光散射来研究微粒助留系统在不同浆料中的絮凝行为,发现无论使用哪种微粒系统,阳离子聚合物的用量都对絮体尺寸有很大的影响,而微粒组分的用量仅在阳离子聚丙烯酰胺(CPAM)-膨润土系统中对絮体尺寸有影响。用光散射测定的絮凝指数受到聚合物用量和微粒组分用量的共同影响。在手抄片成型过程中絮凝指数与填料的留着有很好的相关性。     

市政污泥与造纸污泥的脱水性能差异及其调质机理

为比较不同来源、性质的污泥脱水性能差异和调质机理,以CST为脱水性能评价指标,选用不同类型的PAM对两种污泥分别调质,进一步考察了调质过程中CST、上清液浊度、中位粒径及表面形貌的变化趋势,系统研究不同污泥脱水性能差异的原因。结果表明:与市政污泥相比,造纸污泥沉降性能和脱水性能更好,这主要归因于其较大的污泥絮体粒径和较低的Zeta电势;相对分子质量为1000万-1200万的CPAM对两种污泥均具有较好的调质效果;造纸污泥调质初期污泥上清液浊度迅速下降,当CPAM用量为0.5mg/g DS时,浊度即比原污泥下降75.0%;调质过程中造纸污泥絮体粒径增长速度明显更快;结合SEM分析发现未调质污泥以片状结构排列,以最佳CPAM投加量调质后的污泥呈多孔三维结构,此时絮体强度较高,过调质后污泥絮体结构则发生一定的坍塌。造纸污泥由于有不溶性纤维长链作为骨架材料,调质后三维结构更明显。     

微粒助留剂系统的絮凝机理

微粒助留系统（CPAM和阴离子高岭土）被用于纤维絮凝的研究。和单组分系统（CPAM）相比，双组分系统的效率随着微粒表面吸附的聚合物的增加而增加。这一结论是由高岭土和添加了不同用量的CPAM的纤维之间的结合实验得出的。另一系列实验表明，在加入微粒助留剂之前，添加一种低分子量聚合物可以增强微粒系统的效率。这种低分子量聚合物可以起到区域阻塞的作用，从而增加了助留剂聚合物分子链的延伸。     

原子力显微镜观测絮凝剂与高岭土悬浮液的微观吸附形貌

分离到一种具有强絮凝特性的芽孢杆菌Bacillus sp.F2,并构建了絮凝基因组文库,从中筛选而获得表达絮凝活性的大肠杆菌阳性克隆子FC2,絮凝实验测定FC2的絮凝率为90%。采用云母片吸附的方式,较好地捕捉到了克隆菌FC2产生的絮凝体的微观结构,并采用轻敲模式下的原子力显微成像技术,对其吸附高岭土悬浮液形成的絮凝体的微观形貌进行了观测。与末加絮凝剂的高岭土悬浮液相比,加入FC2絮凝剂的高岭土悬浮液形成的絮凝体出现较大、紧密的球形颗粒结构,且表面粗糙,凹凸程度大,具有大的比表面积和吸附液体悬浮颗粒的能力。当向高岭土悬浮液中加入FC2絮凝剂后,絮凝颗粒由不定形且松散的结构转变为密集分布、水平尺寸均匀的球形结构,表明FC2絮凝剂中的凝集素容易使高岭土悬浮颗粒以絮凝体为吸附中心包裹在其表面,从更直观上进一步证实了FC2絮凝剂的除污效能,为研究生物絮凝剂的絮凝机理提供了有力的依据。     

CPAM用量对填料絮聚体稳定性和成纸性能的影响

填料经预絮聚后以絮聚体的形式加填纸张中,絮聚体在湿部的尺寸及稳定性对纸张性能有着重要影响。采用不同用量的阳离子聚丙烯酰胺(CPAM)对沉淀碳酸钙(PCC)进行预絮聚,通过絮聚体粒径的变化,研究了不同剪切条件下PCC絮聚体抗剪切与再絮聚效果,并考查了所得絮聚体对成纸性能的影响。结果表明,随着CPAM用量从1%增加至7%,絮聚体粒径由23.37μm增大至31.92μm。与常规PCC加填方法相比,当CPAM用量为3%~7%且加填量55%时,预絮聚加填纸张留着率均可提高约3个百分点左右。当CPAM用量为3%,填料含量为30%时,预絮聚加填比常规加填纸张抗张指数提升了约16%,而CPAM用量高于3%时所得的大粒径絮聚体对成纸抗张指数反而不利,且纸张白度有所降低。     

CNF/CPAM共絮聚增强PCC絮聚体稳定性研究

添加纤维素纳米纤维(CNF)协同阳离子聚丙烯酰胺(CPAM)对沉淀碳酸钙(PCC)进行预絮聚,对不同CNF用量下絮聚体尺寸进行了测定。通过强度因子和再絮聚因子分别对絮聚体强度性能和再絮聚性能进行表征,结果表明当CNF添加量为5%左右时,絮聚体的强度性能和再絮聚性能较佳。对CNF絮聚PCC的机理进行了分析,CNF大的比表面积和高长径比增强了PCC与CPAM的桥连絮聚,使得絮聚体更为密实,强度提升。     

Breakage, regrowth, and fractal nature of natural organic matter flocs

The growth, breakage, regrowth, and fractal nature of flocs was investigated by use of a laser diffraction particle sizing device. A range of coagulants were investigated for the coagulation of natural organic matter (NOM) and compared to other coagulated systems. The results showed NOM floc structural characteristics varied in steady-state size depending upon which coagulant was used. When compared to other systems, the order of floc size was Fe precipitate > Fe-NOM > latex (in NaCl solution). Floc regrowth after exposure to high shear was limited for all of the flocs under investigation other than for latex in an inert electrolyte. This highlighted differences in the internal bonding structure of flocs, with the results suggesting that physical bonds have a capacity to re-form after breakage. Fractal dimension analysis by small-angle laser light scattering (SALLS) had limited applicability to large flocs that dominated all of the systems under investigation, but the degree of compaction increased as flocs were broken in high shear. This provided a possible mechanistic reason for the irreversible breakage seen.     

The impact of zeta potential on the physical properties of ferric--NOM flocs

The physical properties of natural organic matter (NOM) flocs, such as size, growth rate, and strength, were investigated using a laser diffraction particle sizing device. Conditions were set such that varying carbon coagulant ratio and zeta potential could both be investigated. Results demonstrated a link between zeta potential and coagulation and flocculation performance, with the production of strong flocs and low residual concentrations when the zeta potential was minimized. The overall strength of the connection points within the floc were determined by a combination of steric interactions, polymer bridging, van der Waals forces, and electrostatic forces. Hence, both dose ratio and zeta potential are important in understanding floc properties. Floc growth was dominated by dose ratio, whereas the response to elevated shear was strongly related to zeta potential. The steady-state floc size was a combination of both factors. This allowed the continued development of a qualitative model in order to engineer optimal floc properties when coagulating NOM.     

甘蔗汁中絮凝物产生的影响因素

为了解决甘蔗汁絮凝物沉淀引起的饮料浑浊问题,以甘蔗汁为原料,对膜滤后的甘蔗清汁中影响絮凝物生成的因素进行了研究。通过控制温度、pH来研究二者对絮凝物产生的影响,并对絮凝物中蛋白质、总糖、灰分等成分进行分析,利用傅里叶红外光谱和扫描电镜能谱仪观测絮凝物官能团结构和组成元素。研究发现,温度对生成絮凝物的影响较小。絮凝物的产量随pH的升高而增加,推断氢氧根会促进甘蔗汁中絮凝物的产生。傅里叶红外光谱结果表明,絮凝物主要由多糖、蛋白质以及灰分等物质构成。通过能谱分析电子扫描和红外扫描可以看出,絮凝物中含有铁、钙、磷、硅、锰等无机离子。说明在碱性条件下,糖类与蛋白质分子相互作用产生絮凝结构,铁、钙等金属离子生成的氢氧化铁、氢氧化钙与蛋白质和多糖产生的絮凝结构网络在一起,形成饮料中的絮凝沉淀物。     

凹凸棒黏土助留助滤效果研究

探讨了凹凸棒黏土与阳离子聚丙烯酰胺(CPAM)组成的微粒助留助滤体系的助留助滤效果及相关机理,并与CPAM-膨润土助留助滤体系进行了比较。结果表明,高剪切处理后的凹凸棒黏土微粒解聚分丝、具有更好的分散性能,提高了助留助滤效果。当凹凸棒黏土微粒用量为0.4%、CPAM用量为0.05%时,处理后的凹凸棒黏土助留助滤效果与商品膨润土相当,抄造纸张的强度性能略好。用聚焦光束反射原理测定絮体弦长及其分布发现,处理后凹凸棒黏土的絮体弦长大于未处理凹凸棒黏土的絮体弦长,但小于商品膨润土的絮体弦长。     

Permeability of collapsed cakes formed by deposition of fractal aggregates upon membrane filtration

We have investigated, theoretically, the physical properties of cake layers formed from aggregates to obtain a better understanding of membrane systems used in conjunction with coagulation/flocculation pretreatment. We developed a model based on fractal theory and incorporated a cake collapse effect to predict the porosity and permeability of the cake layers. The floc size, fractal dimension, and transmembrane pressure were main parameters that we used in these model calculations. We performed experiments using a batch cell device and a confocal laser-scanning microscope to verify the predicted specific cake resistances and porosities under various conditions. Based on the results of the model, the reduction in inter-aggregate porosity is more important than that in intra-aggregate porosity during the cake collapsing process. The specific cake resistance decreases upon increasing the aggregate size and decreasing the fractal dimensions. The modeled porosities and specific cake resistances of the collapsed cake layer agreed reasonably well with those obtained experimentally.     

How the natural organic matter to coagulant ratio impacts on floc structural properties

Periods of elevated natural organic matter (NOM) loadings at water treatment works (WTW) can lead to operational problems as a result of deterioration in floc structural quality. This study used a range of diagnostic tools to evaluate floc structure with increasing organic fraction in the floc. It was observed that when the organic fraction in the floc went significantly over a mass ratio of 1 mg of DOC to 1 mg of Fe (coagulant), the floc size, settling velocity, fractal dimension, and strength were seen to decrease even when the NOM removed during coagulation remained high. A model was proposed to explain these changes that was dependent upon the adsorption of NOM on primary particle surfaces. The operational significance of these results suggests that for the coagulant under investigation the correct coagulant dose must be applied to give good floc structure.