Stress-Controlled Filtration with Compressible Particles

This paper documents a novel filtration technology that incorporates low-stiffness filter matrix particles. The application of isotropic stresses leads to the compression of particles and ensuing pore throat size reductions in the filter matrix. The filtration capacity of the matrix is improved with increasing confinement because the retention of filtrate particles increases due to particulate plugging and bridging on the reduced pore throats. Conversely, relaxing the applied stresses renders system expansion, increased pore throat sizes, and enhanced flushing of entrapped particles from the filter. Experimental results indicate that this technology is most efficient in cases where particle retention occurs due to geometrical constraints (i.e., bridging); however, the system can also render filtration by surface deposition due to the net electrical attraction between the filtrate and filter. Experimental results are analyzed by considering particle-scale filtration mechanisms.     

Removal of Inclusions from Aluminum Through Filtration

Filtration experiments were carried out using both an AlF₃ slurry-coated and an uncoated Al₂O₃ ceramic foam filter to study the removal of nonmetallic inclusions and impurity elements. The results showed that the 30-ppi ceramic foam filter removed up to 85 pct inclusions from aluminum. Several pictures of two- and three-dimensional morphologies of both nonmetallic and intermetallics inclusions also have been presented. The following contributing mechanisms for the removal of nonmetallic inclusions in the deep-bed filtration mode are proposed: (1) collision with walls and interception effect and (2) the formation of both intermetallic and nonmetallic inclusion bridges during filtration. Fluid dynamics modeling of inclusion attachment to the filter walls showed that most inclusions, especially those with larger sizes, are entrapped at the upper part of the filter, whereas smaller inclusions are dispersed well throughout the filter. The calculated inclusions removal fractions for the 30-ppi filter showed that almost all inclusions >125 μm are removed, and inclusions ~5 μm in size are removed up to 85 pct. The interfacial energy between two collided same-size inclusions was calculated, indicating that a strong clustering of inclusions may result within the filter window. Magnesium impurities were removed up to 86 pct by the AlF₃ slurry-coated filter. The filter acted in active filtration mode in addition to the contribution of the air oxidation of dissolved [Mg], which was calculated to be 13 pct. The total mass transfer coefficient of dissolved [Mg] to the reaction interface was calculated to be 1.15 × 10⁻⁶ m/s.     

Assessment of Subballast Filtration under Cyclic Loading

This paper presents an investigation into the seepage hydraulics of a layer of subballast filter subjected to cyclic loading in a fully saturated environment. A multilayer mathematical approach was used to predict the time-dependent permeability of this filter, with a reduction in porosity as a function of compression under cyclic loading, and the amount of base soil (<150?μm) trapped within the filter voids being the two main aspects of this proposed model. Laboratory test results conducted on a novel cyclic loading permeameter apparatus were used to validate the proposed model. The family of equations that are an integral part of the proposed model are then presented in the form of compact visual guidelines anticipated to provide a more practical tool for railway design practitioners.     

Further Advancement in Filtration Criteria through Constriction-Based Techniques

In this technical note, the concept of constriction size in design is highlighted while elucidating some of the limitations of current professional guidelines that are only based on particle size ratios. The implications of the controlling constriction size, Dc35, and the self-filtering constriction size, Dc95, are elaborated on; Dc35=constriction size whereby 35% of the filter constrictions are finer than this, and Dc95=constriction size whereby 95% of the filter constrictions are finer than this. Combining the salient findings of two recent papers by Indraratna et al. in 2007 and Indraratna and Raut in 2006, a further refinement for filter design, i.e., Dc35/d85* ? 1, is introduced here based on the self-filtering base fraction and controlling constriction size of the filter, where the specific parameter d85*=value of d85 of the base soil grading curve modified by the self-filtering constriction size, Dc95. The proposed criterion is verified using several large-scale tests carried out at the University of Wollongong and numerous test data available in the literature.     

Aqueous Ions in Process Water and Cake Moisture During Iron Ore Filtration

In mineral beneficiation plants, aqueous ions from the process water concentrate within the filter cake moisture. These high concentrations of ions can lead to operational issues during downstream processes. This paper examines the ionic content of iron ore slurry before it was filtered at an operating hematite beneficiation plant and compared it with the ionic content of the moisture in the resultant filter cake. Water analyses were conducted to determine the sodium, potassium, calcium, magnesium, fluoride, chloride, nitrate, nitrite, carbonate, sulfate, and phosphate concentrations in both filter feed slurry and filter cake moisture. Results have shown that all tested ions within the process are more concentrated within the filter cake moisture than in the filter feed slurry. This has been attributed to the physical and chemical interactions of these ions with the iron ore particle surfaces. Of these ions, phosphorus concentrates most with the filter cake moisture content having a phosphorus content that is 24.67 times that of the filter feed slurry.     

一种尾矿物料的压滤脱水试验研究

针对堆积型铝土矿开发应用过程中洗矿尾矿固液分离难题,在应用压滤脱水技术处理铝土矿微细尾矿的试验研究基础上,开展铝土矿尾矿泥的压滤脱水半工业―工业试验研究,探讨压滤机滤室腔型、滤布、入料浓度和助滤介质等因素对矿泥压滤效率的影响。研究发现压滤机滤腔结构、滤室厚度等制造参数对尾矿泥压滤脱水效率有显著影响,滤布的透气、滤水性能对压滤生产影响较大,入料浓度与压滤效率呈显著的正相关关系,添加改性助滤剂有利于提高压滤效率和降低滤饼含水率。该研究可为完善压滤生产技术,寻求经济合理的配套生产工艺、设备,实施大规模工业化的压滤生产提供科学依据。这种提升压滤效率和降低处理成本的方法途径探索,对矿山尾矿及其他难处理物料的固液分离具有较好的借鉴价值。     

Volumetric Clarifying Filtration of Urban Source Area Rainfall Runoff

Volumetric clarification is a common storm-water unit operation for hydrologic attenuation that couples particulate matter (PM) separation. Recent volumetric clarification can also include integrated filtration. This study examines the unsteady hydraulic and head loss response of a volumetric clarifying filter (VCF) system to urban source area hydrologic loadings in Baton Rouge, La for 19 fully captured events. The rainfall-runoff response of the 1,088?m2 paved watershed is examined as a direct VCF loading. Watershed responses yielded two classes of behavior; high volume events with an equilibrium volumetric runoff coefficient from 0.6–0.8 while low volume events were 0.4–0.6. Runoff PM as suspended sediment concentration (SSC) yielded coarse heterodisperse influent particle-size distributions (PSDs); transformed to finer and more monodisperse PSDs after treatment. While event-mean head loss is less than 25 mm, instantaneous values up to 200 mm were dependent on instantaneous flow to the filters. Without backwashing, filter ripening head loss is small due to the coarse uniform filter media and radial filter configuration, with a loss of 2% porosity across the series of 19 events. Despite filter ripening an Ergun model was capable of predicting head loss across the entire flow rate range. Head loss and flow frequency distributions were exponential. Results indicate that a volumetric clarifier, filter geometry, and engineered media combination are capable of reducing effluent SSC to <30?mg/L through serial mechanisms of sedimentation followed by filtration.     

Deterministic-Based Model of Slow Sand Filtration. II: Model Application

This paper describes the use of a deterministic slow sand filter process model to investigate and assess some of the fundamental aspects and mechanisms operating during slow sand filtration (SSF). These include the role of the schmutzdecke, biomass development, and the initial condition of the filter, to the overall process performance. The SSF process model has been developed recently and is described in a companion paper by Campos et al., in 2006. It attempts to provide a simulation of the physicochemical and biological processes responsible for the filtration mechanisms operating in SSF. The simulation of filter runs has been carried out with the help of extensive pilot plant data provided by Thames Water Utilities Ltd., involving both uncovered and covered filter beds. The results demonstrate that the presence and nature of a schmutzdecke layer profoundly influence the spatial and temporal development of interstitial biomass within the sand and, consequently, the headloss profile. Microbial interactions in the filter bed play a fundamental role in the process and are involved in setting the pattern and magnitude of headloss development. The model also demonstrates the significance of residual deposits within the filter after surface cleaning, on the subsequent filter behavior.     

Does Filtration Efficiency Affect Measurements of Particle Chemical Composition?

A direct method to measure filtration efficiency was developed and used for the determination of the efficiency of a Nuclepore filter. This needs two equivalent filtration systems operated in sequence. The amount of particulate matter collected on each system is measured and introduced in a simple formula. The particulate masses deposited on the filters in each system were measured as total mass, by balance gravimetry, and as individual elemental masses, by PIXE (particle induced X-ray emission). With this very general method it was possible to determine the efficiencies of a 0.4 μm Nuclepore filter operated with a stacked filter unit for particles less than 2.5 μm in total mass and elemental masses. The experiment showed that the efficiency of this filter is very poor for some specific elements, like sulfur, that are concentrated in very small particles.     

立盘过滤机过滤铝土矿正浮选精矿的试验研究

介绍采用小型立盘过滤机对铝土矿正浮选精矿的过滤试验,利用Minitab软件对过滤的运行时间、进料浓度、真空度及过滤机产能试验数据进行多元回归分析,试验取得较好效果。与生产中使用的新型陶瓷圆盘真空过滤机相比,其滤饼含水量和滤液浮游物含量两项过滤指标相当,产能提高,采用无纺布过滤精度较高,在相同过滤面积条件下,设备价格低于陶瓷圆盘真空过滤机20％以上。     

Assessment of Fate of Manganese in Oxide-Coated Filtration Systems

This study employed pilot-scale filters to examine the fate of Mn in MnOx(s)-coated filter media as a function of filter-applied pH and backwash conditions. A key operational issue for continuous efficient Mn(II) removal was maintenance of appropriate levels of free chlorine to ensure coated media regeneration. Neutral or slightly acidic pH promoted Mn(II) sorption and subsequent oxidation on MnOx(s)-coated media. Alkaline influent pH (pH > 7) allowed some soluble Mn(II) oxidation by free chlorine prior to filtration, resulting in significant Mn removal by MnOx(s) particle filtration. Increased backwash rates removed greater amounts of MnOx(s) from the filter media. The combination of MnOx(s) accumulation on filter media during filtration and its partial removal during backwash maintained a net amount of MnOx(s) coating sufficient for catalyzing further soluble Mn(II) removal, yet it did not significantly alter the size of the media.     

铜电解液过滤系统的技术改造与运用

分析了某铜业公司电解厂过滤系统中存在的主要问题,并相应采取了对压滤机和净化过滤机进行技术升级改造的解决措施。改造后,阳极泥含铜率从22.3%下降至15.8%,阳极泥含水率由35.2%下降至21.5%,阴极铜优品率得到显著提升。     

氢氧化铝过滤方法的改进及实践

本文结合中州铝厂的生产实际,对影响平盘过滤机产能因素进行了分析,提出了提高平盘过滤机产能的方法.     

Effect of Media Grain Shape on Particle Straining during Filtration

This paper investigates how straining mechanisms of angular media (crushed limestone) provide improved filtration performance compared to rounded media (river stone). Columns of granular media were set in resin, sectioned, photographed, and digitized to produce a three-dimensional model of pore space geometry. This process was repeated for four filter media, each representing different grain shapes or packing densities. From measured pore throat distributions, a stepwise particle movement model was used to estimate the maximum volume of particles that could be stored in the bulk of the filter media. The results showed that the more angular the media, the wider the range of particle sizes that could be strained in the bulk of the filter. The stepwise model was applied only to individual particles; trapping of colloidal particles was not considered. However, when individual particles are too small to be strained, the same pore throat trapping contributes to the physical capture of avalanches and flocculates. Thus the findings of this work are relevant to deep bed filtration applications where headloss results from straining, such as storm-water best management practices or soil filters.     

钛白粉生产中钛液过滤的影响因素分析

在硫酸法金红石型钛白粉的生产工艺中,钛液的质量对产品的质量有着较大的影响,残渣是钛液质量的一个主要指标。在实验室条件下,分别讨论了物料的残渣、胶体、滤布、温度、助滤剂、TiO2含量等因素对钛液过滤的影响。     

洗煤浮选压滤系统改造

通过对洗煤现状的分析,阐述了洗煤浮选、压滤系统改造的必要性。采取新增压滤机、刮板机、更换精煤压滤机等措施进行改造,改造后运行效果良好,洗煤水实现闭路循环,减少了环境污染,提高了精煤收得率,降低了生产成本。     

Larox Pressure Filters in Filtration and Washing of Non-Ferrous Minerals Concentrates and Metallurgical Slurries

Automatic pressure filter with horizontally positioned filtration chambers and one endless filter cloth was first introduced in the late 1960s. Actual product development and process adaptation was done during the 1970s. During the next decade this type of dewatering equipment established a firm position in a wide range of applications in mining, metallurgical, and chemical industries worldwide. More than 320 of these first generation LAROX PF filters are in operation in many types of dewatering applications. The maximum unit size has been 35 m². In many cases, particularly in mining applications, the size of one unit has not been enough. For large production capacities in mining and mineral processing LAROX introduced in 1992 the big PF filter with maximum filtering area up to 144 m², the second generation PF filter. The big 144 has 24 filter plates (filter chambers) and all mechanical operations are performed hydraulicaly. The normal size PF filters (below 38 m²) are also available with hydraulic operation devices. The second generation PF and big PF filters considerably increase the application range of this type of dewatering equipment.

There are many processes in the mining, mineral and metallurgical industries, where improved efficiency in the solid/liquid separation would help achieve significant savings in energy consumption, affluent treatment costs, capital cost by simplifying the process, operation costs and especially labor costs. In most cases the efficiency can be improved by replacing the existing solid/liquid separation process with pressure filtration.     

Filtration efficiency in casting of a complexly alloyed nickel melt

The use of a cellular ceramic filter is shown to be effective for casting nickel superalloys in vacuum, including superalloys cast using wastes. As a result of filtration, the volume fraction of nonmetallic inclusions and their sizes and quantity in a metal decrease.     

Dynamic Modeling of Bentazon Removal by Pseudo-Moving-Bed Granular Activated Carbon Filtration Applied to Full-Scale Water Treatment

A model for the removal of pesticides by granular activated carbon (GAC) filtration in full-scale water treatment is presented. The model describes GAC filtration in a pseudo-moving-bed configuration, where two filters are operated in series and after breakthrough the first filter is regenerated and becomes the second filter. The influent of the second filter is changing due to gradual breakthrough of the first filter. Therefore, a dynamic model is developed based on kinetics, equilibrium, and mass balance equations. The model is calibrated and validated on data of full-scale and pilot plants. Operational strategies are evaluated of two different cases. From this study it can be concluded that a dynamic mathematical model can be successfully used to evaluate the performance and operation of full-scale GAC filters for pesticide removal and can be used for operational decision support. Data obtained from practice can be used for calibration without additional laboratory work.     

Arsenic Removal from Water by Moving Bed Active Filtration

Arsenic (As) in drinking water was removed by a combined co-precipitation, active filtration process. A serpentine prereactor for ferric chloride (FeCl3) reagent mixing was combined with a moving bed active filter, followed by separation of waste residuals from clean water discharge. Waste effluent, using 10% of influent for transport, was retained in a clarifier for settling prior to water recycling. Process residuals passed leach tests for landfill disposal. The pilot-scale apparatus was tested at a small community, public drinking water system in Fruitland, Id. In a 49?hour test, influent groundwater averaging 40.2±1.0?μg/L total As (n = 17) was fed at 38?L/min?(10?gpm) and FeCl3 solution was added at an optimized Fe to As molar ratio of 133:1. Arsenic concentrations were reduced to 3.3±1.4?μg/L(n = 49) over the test period. Research observations support the hypothesis that the formation and renewal of iron oxide-coated sand in the active filter is a viable mechanism for high efficiency As removal. Further testing is underway to optimize long-term operating performance and to characterize the chemical processes of the system.