MAGNETIC-SEEDING FILTRATION

ABSTRACT

Magnetic-seeding filtration consists of two steps: heterogeneous particle flocculation of magnetic and nonmagnetic particles in a stirred tank and high-gradient magnetic filtration (HGMF). The effects of various parameters affecting magnetic-seeding filtration are theoretically and experimentally investigated. A trajectory model that includes hydrodynamic resistance, van der Waals, and electrostatic forces is developed to calculate the flocculation frequency in a turbulent-shear regime. Fractal dimension is introduced to simulate the open structure of aggregates. A magnetic-filtration model that consists of trajectory analysis, a particle build-up model, a breakthrough model, and a bivariate population-balance model is developed to predict the breakthrough curve of magnetic-seeding filtration. A good agreement between modeling results and experimental data is obtained. The results show that the model developed in this study can be used to predict the performance of magnetic-seeding filtration without using empirical coefficients or fitting parameters.

     

磁性液体在外施磁场下的方向性弱絮凝行为

磁性液体是一种高分子稳定胶体,实验观察发现磁性液体在外施磁场作用下,磁性颗粒沿着外磁场方向形成一定有序排列的球链簇,却又不是絮凝使胶体系统失稳,显示出与其它胶体系统的不同之处。在一般胶体系统中弱絮凝行为表现不明显,不引起重视,通过计算分析发现磁性液体在外加磁场下弱絮凝行为表现却异常明显,而且弱絮凝行为存在着方向性,又不使胶体系统失稳,与实验和实际应用相符。从而揭示了磁性液体在外施磁场作用下各向异性的机理,并且很好地解释了光波在在外施磁场作用下的磁性液体中会产生光的双折射效应等现象。     

Floc Formation,Size Distribution,and its Transformation Detected by Online Laser Particle Counter

Abstract

Coagulation and flocculation are widely applied in water and wastewater treatment. Removal of suspended particles is essential in water treatment and greatly depends upon the performance of the coagulant and the production of flocs with suitable properties. For monitoring floc size, formation, and size transformation, no particle size method now can be considered ideal. In this work an on‐line laser particle counter was used to follow coagulation with aluminum sulfate. The experiments showed that the floc formation and floc size distribution could be well monitored. The results showed that it is feasible to use particle counting for dosage control and for monitoring changes in floc formation, transformation and size distribution.     

磷矿酸解渣与聚丙烯酰胺絮凝动力学

通过激光粒度仪在线监测搅拌槽内聚丙烯酰胺与磷矿酸解料浆的絮凝过程 ,研究了絮凝剂加入量、絮凝温度、搅拌速度和酸解渣原始平均粒径对絮凝动力学的影响 .用电泳试验测定酸解渣的表面电性 ,合成不同荷电类型的絮凝剂及通过絮凝剂加入量对絮凝过程的影响实验可以判定磷矿酸解渣与聚丙烯酰胺的絮凝过程符合架桥机理     

基于介观尺度模拟的污泥絮凝形态及机理

用介观动力学的方法对胶体颗粒与高分子链的絮凝过程进行了模型研究,并根据模型结果对污泥和阳离子聚丙烯酰胺的絮凝过程和污泥脱水机理进行有针对性的探讨。通过建立粗粒化模型和经验势函数力场有效模拟了负电性的胶体颗粒与阳离子型高分子链的絮凝过程;模拟得出了絮凝的外观形态,证明了高分子链对胶体颗粒的桥接作用以及表面电荷的中和作用对絮凝的影响;并对絮凝反应过程的体系势能变化进行了研究。对实际污泥胶体颗粒和阳离子聚丙烯酰胺溶液拍摄了电镜图片并观察了其吸附过程;最后研究了高分子链离子度对溶液体系絮凝的影响,验证了离子度的增加有利于絮凝体的形成,但同时也由于絮凝体结构的复杂而对污泥脱水造成了一定的不利影响。     

磁加载絮凝处理含铜废水

目前磁加载絮凝技术已被研究用于处理多种类型的废水,然而关于此技术中磁粉作用机理方向少有报道。为了解决这一问题,本文采用磁加载絮凝法处理模拟微蚀铜废水,研究了磁粉的加入对Cu²⁺和浊度去除率、絮体沉降速率以及絮体粒径的影响,深入分析了磁粉的作用规律和机理,为磁加载絮凝法应用到实际工程中提供了理论依据和技术参数。结果表明,当磁粉投加量和粒径分别取2.0g/L和300～400目时,磁加载絮凝效果最好。此时,Cu²⁺和浊度去除率均达到最高值98.53%和94.72%,比传统絮凝法高出4.11%和0.61%;絮体沉降速率最快,达5cm/min,是传统絮凝沉降速率的3.64倍;絮体粒径D₅₀也达到最大值41.94μm,较传统絮体粒径大20μm。磁粉投加量过多或过少、粒径过大或过小都会相应地减慢磁絮体的生长速率。     

Separation of Phosphorus and Magnetic Mineral Fines from Siderite Reductive Ore by Applying Magnetic Flocculation

The characteristics of siderite reductive ore and the ultrafine grinding-magnetic flocculation separation (MFS) of this ore were investigated in the present work. The results indicated that the iron phase in the raw ore was predominantly metallic iron with an iron particle size below 30 μm, and the phosphorus compound was apatite. By applying MFS to siderite reductive ore containing 37.14% Fe and 0.52 P, a concentrate assaying 66.37% Fe and 0.19 P with 74.32% recovery was produced. The iron recovery increased by 5.77% compared with the results of the conventional magnetic separation. The high efficiency in phosphorus removal and iron recovery achieved by the MFS process may be attributed to the adequate liberation of iron particles and the increase in magnetic force on the iron mineral fines in the form of flocs in a magnetic field.     

The Effect of Ozonation on Particle Size Distribution for Recirculating Aquacultural Seawater: Analysis of Particle Flocculation and Breakup

ABSTRACT

Solids removal is very important for water quality maintenance in recirculating aquaculture systems (RAS). Ozonation is a practical water treatment which can promote the solids removal. However, the characteristics of ozonation effects on particles are still unclear. In this study, the effect of ozonation on particle size distribution (PSD) was investigated for seawater from a RAS of Pacific white shrimp (Litopenaeus Vannamei). Both flocculation and breakup of particles were demonstrated during ozonation treatment, which resulted in changes of PSD. By using a fractal characteristic value (D_f), the flocculation process could be divided into three stages of preparation, growth and steady. Besides, the flocculation efficiency varied parabolically with contact time. A higher ozone dosage resulted in a shorter preparation stage, along with a longer growth stage (namely lasting a longer flocculation effect) and thus a relatively higher limit of parabolic flocculation efficiency. However, the limit would reach a peak and probably be accompanied with a more breakup of particles. The best flocculation efficiency was 43% at ozone dosage of 3.5 mg/L with 5 min contact time. Furthermore, a higher ozone dosage could produce more ammonia.     

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.     

Classification mechanism of the chute, a liquid-phase remover of fines in the micrometre range from a batch of porous particles

A simple and effective classification method, the ‘chute’, has been developed for the liquid-phase removal of fines from a batch of porous (catalyst) particles in the micrometre range. The chute is a continuous sedimentation fractionator, working in the gravitational field. Equations based on the sedimentation of particles were derived for the particle size distribution density function at a given position on the chute as a function of the initial size distribution density function. The particle size distribution on the chute appears to be only a function of the physical constants of the fluid, the particles and the dimensions of the chute. To verify the model equations, experiments with the chute were carried out at different suspension flows and chute angles. It was found that the experimental particle size distribution density functions at various positions on the chute were predicted reasonably well. Due to local disturbances near the bottom of the chute, the experimental curves exhibit a less sharp cut-off in the particle size distribution density function than was predicted by the model equations.     

磁絮凝技术深度处理焦化废水的试验研究

采用磁絮凝技术对焦化废水生化出水进行试验研究,以CODCr、氨氮、浊度去除率为考察指标,讨论了聚合硫酸铁(PFS)投加量、聚丙烯酰胺(PAM)投加量、磁粉投加量、沉降时间、投加方式等因素对处理效果的影响。结果表明:先投加磁粉,再投加PFS,最后加絮凝剂PAM的投加方式最好,磁粉最佳投加量为400 mg/L,PFS最佳投加量为800 mg/L,PAM最佳投加量为8 mg/L,最佳沉降时间为20 min。CODCr、氨氮、浊度去除率分别达到62.5%、22.3%和92.2%。采用该技术既可提高絮凝效果,又缩短了沉降时间,有很好的现实意义。     

Particle Flocculation and Filtration by High-Gradient Magnetic Fields

Abstract

Flocculation and filtration of micrometer-sized particles in a high-gradient magnetic field (HGMF) were investigated. Experiments were conducted using a cryogenic magnet of 6 Tesla maximum strength. Hematite particles were used for flocculation and filtration experiments. A new approach of using magnetic fields to enhance separation of weakly magnetic particles was also investigated. This approach is based on magnetic seeding which involves flocculation of existing nonmagnetic particles with injected paramagnetic particles. A particle-flocculation model was developed based on trajectory analysis. External forces due to gravity and magnetism, and interparticle forces such as electrostatic, hydrodynamic, magnetic dipole, and van der Waals forces, were taken into consideration in these models.

     

Para- and Dia-Magnetic Particle Flocculation in a Magnetic Field

Abstract

An experimental apparatus has been assembled for the study of high-gradient magnetic separations of para- and dia-magnetic particles suspended in a liquid. The components of this system include a cryogenic magnet, equipment for light-intensity measurements, and a dynamic light-scattering technique for transient particle-size measurements. The flocculation of paramagnetic hematite particles of approximately 200-nm diameter under the influence of a uniform magnetic field is experimentally investigated. The effect of solution pH on particle growth as a result of flocculation is examined with and without the presence of the magnetic field. Results show that the flocculation rate of hematite particles increases with the intensity of the magnetic field.     

Effect of charge density,molecular weight,and hydrophobicity on polycations adsorption and flocculation of polystyrene latices and silica

Adsorption and flocculation behavior of two series of synthetic polycations was investigated in dispersions of silica and polystyrene latices with various particle size and surface charge densities. Polycations of the first series (polydiallyldimethyl ammonium chloride‐PDADMAC) varied in molecular weight only, while polycations of the second series (derivatives of polymethacrylic acid) varied in both molecular weight and hydrophobicity. We have found that maximum adsorbed amount of high molecular weight PDADMAC on latex particles was nearly independent of the surface charge density when the particle size was comparable to the polymer coil dimensions in solution. Both low and high molecular weight PDADMACs were efficient flocculants, although significantly lower amounts of high molecular weight polyelectrolyte were required for the phase separation in the dispersions due to particles aggregation through “charge patch” mechanism. The increase of polymer hydrophobicity leads to higher adsorbed amounts and broadening of flocculation window by polycations of the second series on both substrates. However, no strong enhancement of segment–surface interactions on hydrophobic substrates was observed. Since formation of multilayers upon adsorption was also excluded, the difference in adsorption and flocculation behavior was related to the more compact conformation of hydrophobically associating derivatives in solution and at the interface. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3422–3429, 2006     

Acrylic latices stabilized by polymerizable non-ionic surfactant

The final latex particle size is controlled by the concentration of polymerizable non-ionic surfactant NE-40 in the emulsion copolymerization of methyl methacrylate (MMA) and butyl acrylate (BA). The particle size decreases with increasing NE-40 concentration and increases with increasing persulphate initiator concentration. The dependence of particle size on the initiator concentration does not follow conventional Smith–Ewart theory, which is attributed to the bridging flocculation process during the particle nucleation period. The differences in the particle nucleation and growth stages and colloidal stability observed in the NE-40 and nonyl phenol-40 mol ethylene oxide adduct (NP-40) stabilized systems can be attributed to the different distribution patterns of surfactant molecules in the particles. Experimental data also indicate that the particle size decreases with increasing electrolyte concentration, or agitation speed. The total scrap, presumably caused by the bridging flocculation process, increases rapidly with increase in the NaCl concentration The amount of large flocs formed during polymerization is generally greater for the run operated at higher agitation speed. As expected, the latex products stabilized by non-ionic surfactants show excellent stability toward added sodium salt.     

Dual-polymer flocculation with unmodified and ultrasonically conditioned flocculant

Dual-polymer flocculation with unmodified and ultrasonically conditioned flocculant is presented in this paper. In the experiments two types of suspensions, i.e. chalk dust and kaolin clay in RO water were investigated. In the former case the bridging mechanism was expected whereas in the latter case charge neutralization and charge patching mechanisms should be dominant. The measurements were carried out in a laboratory setup for on-line particle size distribution (PSD) analysis consisting of stirred vessel with turbine mixer, laser particle size analyzer Fritsch Analysette 22 and peristaltic pump. The flocculation kinetics is described in terms of PSD and mean particle diameter change in time. Authors proved that ultrasonic conditioning may be an effective alternative for a dual-polymer flocculation where two different flocculants are used. In some cases the mechanical strength of flocs, created by combination of unmodified and conditioned polymers, was improved which resulted in reduction of time needed to achieve the steady state of the system.     

磁絮凝法处理泵站溢流污水试验研究

针对合流制泵站溢流污水的特点,通过与传统工艺处理效果对比,采用磁絮凝法进行处理,即在投加絮凝剂的同时投加磁种,并引入磁场来促进絮凝过程.从磁种投加量、磁种-絮凝剂投配比、磁感应强度、pH和沉降时间等方面研究磁絮凝法处理泵站溢流污水的优越性.结果表明,当磁种投加量为250mg·L-1、絮凝剂投加量为2.5mL·L-1、磁感应强度为50mT、pH为6时处理效果最好.采用磁絮凝法处理泵站溢流污水降低了絮凝过程中的沉降时间,节约了成本.     

Aggregation Experiments on Fine Fly Ash Particles in a Gradient Magnetic Field

Aggregation experiments were conducted on two kinds of fly ash particles in the size range of 0.023–9.314 μm in a gradient magnetic field produced by permanent magnetic rings. The two types of fly ash particles were obtained from Dongsheng and Datong coal combustion. The effect of particle size, total particle mass concentration, particle residence time in the magnetic field and gas velocity were examined. Experimental results showed that the removal efficiencies in a gradient magnetic field are much higher than those in a uniform magnetic field. The total and single‐sized particle removal efficiencies can be improved by increasing the total particle mass concentrations and the particle residence time in the magnetic field or reducing the gas velocity. Mid‐sized particle removal efficiencies are higher than those of the larger and smaller ones. With the increase in total particle removal efficiencies, the particle size corresponding to the maximum values of single‐sized particle removal efficiencies and the particle number median diameters both decrease. Both the single‐sized and total removal efficiencies for the particles from the Dongsheng coal combustion are higher than those from the Datong coal combustion.     

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.     

磁性能优化纳米Fe3O4合成工艺

通过化学共沉淀法制备了纳米Fe3O4粉体,研究了反应物配比和反应温度对磁性粒子的物相以及磁性能的影响,优化了合成工艺。通过对二元参数的选择和严格控制,可以制备出磁化率高、粒径分布相对较好的球形磁性颗粒,干燥后获得纳米磁性粉体。