Pressure Filtration Tests Research Articles

Filtration resistance during pressure filtration tests of liquid aluminium alloys

Abstract Prefil Footprinter, a portable pressure filtration instrument, is usually employed to detect liquid metal quality. However, no investigations have ever been done to determine overall filtration resistance and resistance of the “clean” filter media. Based on the identification of flow behaviour using the derivative methods, classic filtration equations have been effectively used to estimate total filtration resistance for the first time. The variations of overall resistance during filtration provide a new approach to understand filtration behaviour. The resistance values of the “clean” filter media have been obtained for the first time. An innovative method has been developed to obtain the resistance of the “clean” filter media through the backward extrapolation of the overall filtration resistance versus filtrate weight or filtration time curves over the steady stages operating in incompressible cake mode.

Examination and verification of the filtration mechanism of cake mode during the pressure filtration tests of liquid Al–Si cast alloys

The filtration equations at constant pressure were used to examine and verify the filtration mechanism of cake mode during the Prefil Footprinter ® tests of liquid Al–Si cast alloys. Although cake mode is the dominant mechanism, the conventional equations have not well described the Prefil curves. The inverse mass flow rate deviates from the linearity with filtrate weight at the initial and terminal transient stages. The deviation at the initial transient stage is probably due to the lack of well-formed cakes. In the terminal transient stage the occurrences of partial and/or complete clogging may cause the deviation. If both the initial and terminal transient stages disappear, the linear relationship tends to hold true over the whole course. For some low filtrate weight melts, however, the deviations from the linearity occur at the steady stage probably due to the compressibility of the formed cake caused by oxide films and non-uniform cake thickness.

Rapid determination of compressive yield stress of dense suspensions by a mean-phi ( ϕ¯) model of high pressure filtration

The compressive yield stress plays a crucial role in consolidation of concentrated suspensions in sedimentation and thickening, filtration under pressure or vacuum, shaping of ceramic bodies by slip casting, and in disposal of mining and industrial particulate wastes. Measurement of compressive yield stress is ordinarily a time consuming undertaking. Fast and demonstrably reliable techniques for measuring compressive yield stress are needed for screening dispersant/flocculent reagents and establishing their optimum dosage for improving the dewatering characteristics. Fast characterization of yield rheology is also essential in case of biologically active sludges whose rheological behavior changes with time and in monitoring of slurry characteristics for on-line control of industrial dewatering processes in face of fluctuating feeds. We propose rapid methods for determining compressive yield stress from truncated single pressure or truncated step pressure test data by a recently proposed mean-phi ( ϕ¯) model of high pressure filtration. Because filtration rate slows down drastically as the end point is approached, considerable saving in measurement time is possible in truncated tests where the experiment is terminated in single pressure tests or pressure is stepped up to next higher level in multi pressure tests before the filtration system reaches equilibrium or steady state. Based on a recently proposed ϕ¯-model, we derive and validate a mathematical model for simulation of conventional and truncated step pressure filtration tests. In the former case, the process is permitted to run to equilibrium before the pressure is stepped up. The simulation model is employed to extract compressive yield stress as a function of solid volume fraction from truncated single pressure and step pressure test data. The proposed fast technique is used to demonstrate the effect of pH, polymers and surfactants on compressive yield stress of flocculated and dispersed suspensions.

Pressure filtration tests of liquid Al–Si cast alloys: II. Best-fitted equations for filtrate weight versus filtration time curves

Though the cake mode generally dominates the Prefil Footprinter ® tests, the filtrate weight versus filtration time curves deviate, to some extent, from conventional filtration equations at constant pressure. This work attempts to seek other models for the Prefil Footprinter ® curves. It is interesting to find that there is a good linear relationship between ln(weight, in grams) and ln(time, in seconds) over the whole course of the filtration period, i.e. filtrate weight can be best expressed as a power function of filtration time. In the presence of the complete blockage stage, the filtrate weight or ln(weight) appears to be a line paralleling to X-axis at this substage. The physical mechanism for the model is not known at the moment. The Prefil Footprinter ® filtrate weight versus filtration time curves will never be convex, i.e. they appear as concave and/or straight lines.

Empirical Correlations for Estimating Filtrate Volume of Water Based Drilling Fluids

Standard American Petroleum Institute (API) filter press is generally used for identifying the filtrate volume of drilling fluids and works only at very low pressures. In fact, during a drilling operation, at downhole conditions, the pressures encountered are significantly higher than what is used during standard API filter press tests. A relationship between the well-known fluid properties and the filtrate volume test is developed. In this study, experiments have been conducted for different water-clay mixtures with varying concentrations at different pressure values by using standard API filter press and HP&HT (high-pressure high-temperature) filter press. The relationship between physical and chemical properties of water-clay mixtures and filtrate volume is analyzed. An empirical correlation has been developed for estimating filtrate volume using basic information of the mud (i.e., rotational viscometer readings, density, pressure, cation exchange capacity, and chemical composition). The developed correlation can estimate filtrate volume with an error less than 20% for a wide range of pressure values.

A new analysis of pressure filtration curves for liquid aluminum alloys

The filtrate weight versus filtration time curves of the pressure filtration tests are analyzed for the first time using the first and second derivative methods to investigate the flow behaviors of liquid metal. Three stages, i.e. initial transient, steady and terminal transient, are found during the course of the filtration.

Evaluation of Metal Attenuation through Paper Clay Utilized for Containment of Contaminated Groundwater

Paper clay has several properties that make its use in vertical barriers very promising. In this paper the characteristics of two paper sludges (which will also be referred to as paper clays) one from the Erving Paper Company and one from the International Paper Company are considered. To determine the feasibility of paper clay for heavy metal attenuation, batch tests, column tests, hydraulic conductivity tests, and pressure filtration tests were performed. Batch testing showed that the metal, the distribution coefficient (Kd) ranged from as low as 0.002 L/g for manganese to as high as 6.7 L/g for lead in International paper clay. In the Erving paper clay the Kd ranged from 0.007 L/g for manganese to 1.9 L/g for cadmium, while the International paper clay Kd ranged from 0.002 L/g for manganese to 6.7 L/g for lead. Chemisorption was established as the predominant metal binding mechanism in both clays with the only exceptions being manganese adsorption on International paper clay that indicated a constant p...

Effect of precipitation and sedimentation of primary α-Fe phase on liquid metal quality of cast Al–11.1Si–0.4Mg alloy

A novel approach, the heat treatment of liquid metal, was initiated to investigate the possibility of removing oxide films and primary intermetallics from aluminium melts and its effectiveness. The concept was to remove oxide cracks from liquid metal by precipitation of primary intermetallics onto oxide films, causing them to sink under the weight of the particles. The sedimentation of primary α-Fe particles was investigated at 600°C using an Al–11·1Si–0·4Mg alloy. The liquid metal quality was assessed by reduced pressure and pressure filtration tests. After sedimentation processing there is a clear improvement in liquid metal quality due to the sedimentation and separation of primary α-Fe particles, causing the removal of some oxide films from aluminium melts. Thus the heat treatment of liquid metal has the potential to improve liquid metal quality. Primary α-Fe phase seems to precipitate onto the wetted sides (i.e. the outer interfaces) of double oxide films. However, the gap between the two dry sides of a double film constitutes a crack, thus explaining the common observation of cracks in and around such intermetallics. Hydrogen precipitation into the central oxide films in intermetallics may open the oxide films, or even expand and convert the cracks into open porosity. The oxide films may further open during a later stage of freezing because of shrinkage and cooling stress in the solid state.

Testing procedures to assess the viability of dewatering with geotextile tubes

Geotextile tubes are finding increasing market acceptance for dewatering high water content materials. The success of this application depends on the filtration compatibility between the high water content materials and the geotextiles used to make the tubes. In this paper, 26 pressure filtration tests using four woven geotextiles of various materials were conducted to study soil retention and permeability of the sludge/geotextile system and the possible controlling factors. Based on the test results, the filter cake is not only the major contributor to the retention of fine particles, but also causes a decrease in permeability. Controlling the formation of the filter cake on the inside of the geotextiles tube and thus achieving a balance between soil retention and permeability is vital to a successful project. Surprisingly, initial water content may have a significant effect on the dewatering efficiency and dewatering rate. More testing is recommended to gain a deeper understanding into this relationship.

Determining Hydraulic Conductivity of Soil-Bentonite Using the API Filter Press

AbstractThe American Petroleum Institute (API) filter press is commonly used to measure the hydraulic conductivity of soil-bentonite, both during mix design and as a part of construction quality assurance and quality control. However, interpretation of the test results is complicated by the fact that, during the test, the soil-bentonite specimen is consolidated by seepage forces, which produce a variation in effective consolidation stress from the top of the specimen to the bottom. This paper presents the results of a laboratory investigation undertaken to illustrate that seepage consolidation theory provides a logical way to interpret filter press test results. A description of seepage consolidation theory, which relates stress, compressibility, and hydraulic conductivity in soil consolidated by seepage forces, is presented. Following this is a description of the laboratory testing program that involved comparing the hydraulic conductivity of two soil-bentonite mixes, as measured in rigid wall consolidometer permeameter cells, a flexible wall permeameter, and an API filter press. Using seepage consolidation theory to interpret the filter press tests produces hydraulic conductivities consistent with those obtained from the other tests. The filter press test results are used to illustrate a method for estimating the hydraulic conductivity of soil-bentonite in a cutoff wall by taking backfill consolidation pressures into account.

Effect of Cations on Permeant Flow-Through Bentonite Clays using a Rapid Filter Press Test

The relative effects of different cations on permeant flow through two commercially available Wyoming bentonite clays have been assessed using a rapid filter press (RFP) test. The clays were exposed to test solutions of sodium, potassium, calcium, ammonium and zinc ions, all added as acetates at different molarities, so that the relative effects on flow rates could be determined. Results showed that ammonium and potassium had particularly deleterious effects on permeant flow for both clays, while solutions of sodium and zinc acetate permeated at much lower rates. Of the two materials tested, the modified bentonite, which had been treated with surface-active additives, had significantly improved performance compared to the untreated clay. XRD has been used to identify changes in interlayer spacing (d001) associated with exposure to the different acetate solutions.

Water flow in filter paper and capillary suction time

Flow of water in Whatman #17 chromatography paper and the interpretation of the capillary suction time method for determining filterability of suspensions is examined. Filter paper water flow is described by well-established theory of water flow in porous media. This theory is based on material balance for the water and Darcy’s law. Assuming that the matric potential or suction (arising from the interaction of water with the solid surfaces and their geometry) and the hydraulic conductivity of both the filter paper and the suspension are well-defined functions of the water content, one-dimensional capillary suction time is analysed from considerations of material balance and continuity of water potential on the paper/suspension interface. Experiments agree with theory and illustrate that flow in the paper is unsaturated, with the advance of a wetting front in paper a function of the interaction of the sorptivity-matric potential functions of both the paper and the suspension. Extension of the approach to radial flow in the filter paper is too complicated to permit simple interpretation of wetting front advance. The capillary suction time method must remain a useful empirical tool for practicing engineers. Its weaknesses should be recognised, however, and constant pressure filtration tests, for example, which provide both sorptivity-, and equilibrium water content– pressure relations simply and accurately must ultimately be preferable.

Batch crystallization of a photochemical: Modeling, control, and filtration

AbstractModel identification and control were studied for the seeded batch crystallization of an organic, industrial photochemical. The growth and nucleation kinetics are described by empirical power‐law expressions in relative supersaturation, and an additional model describing crystal shape dynamics is proposed. The parameters in the kinetic models are estimated from on‐line measurements of solute concentration and transmittance. Parameter uncertainty is assessed, and optimal experimental design techniques are used to construct experiments to diminish uncertainty. Given the identified model, optimal open‐loop temperature schedules are designed to improve the filtration of final‐time slurries. The profiles minimize the mass of nucleated crystal relative to seed crystal mass, subject to supersaturation and yield constraints. Filtration improvements are verified using constant pressure filtration tests to determine the flow resistance of the filter cake. The best control experiment gives a cake resistance 25% lower than the best identification experiment.

New Concept for Simulating Particle Packing in Colloidal Forming Processes

A new simulation concept based on the discrete element method (DEM) has been developed for studying particle‐packing dynamics during colloidal forming processes. Long‐range potential interactions, medium influences, solid‐body contact, and adhesion are considered. DEM regards each particle as an individual element and enables the observation of the spatially and temporally resolved microscopic details. The importance of different competitive interaction forces is compared. The electrostatic repulsion constrains the Brownian motion for all particle sizes. The simultaneous, competitive influences of the colloidal chemical and process parameters on the particle‐packing structure during pressure filtration and centrifugal casting have been simulated and analyzed. In the pressure filtration test, the well‐stabilized monomodal particles form a close‐packed hexagonal structure, and this regularity is strongly dependent on the filtration rate. The higher the filtration rate, the more packing defects are formed. Although well‐stabilized suspensions with high zeta‐potential tend to form particle chains, suspensions with low zeta‐potential form agglomerate structures. The limitations of the long‐range interaction functions derived from the Hamaker theory and from the electrostatic Poisson‐Boltzmann equation are discussed.

An Improved Contaminant Resistant Clay for Environmental Clay Liner Applications

AbstractTesting shows that many of the present commercially available bentonite products used for clay liner/soil sealant applications may be susceptible to chemical degradation by certain contaminants. Testing also confirms that a recently developed contaminant resistant clay (CRC) is resistant to various contaminants that would otherwise attack and degrade the present commercially available products. The tests that were used to determine its effectiveness were American Petroleum Institute (API) fluid loss, rigid wall hydraulic conductivity, flexible wall hydraulic conductivity and a newly developed top loading filter press (TLFP) test (LSK method).

Geotechnical properties of fresh cement grout—pressure filtration and consolidation tests

This technical note examines the effects of removing water from a fresh cement suspension by pressure filtration, which turns the slurry into a material having significant effective stresses; it also clarifies some aspects of the consolidation behaviour of this filtered material. The test series covered: (1) a sulphate-resisting Portland cement (SRC); (2) an ordinary Portland cement (OPC); and (3) a super-fine Portland cement (MFC). They were all normal cements, obtained in 25kg batches. The experiments were like one-dimensional consolidometer tests with top drainage only, but used a slurry as starting material. The usual assumptions for one-dimensional consolidation analysis were made, and the filter cake was also treated as a stiff uniform layer. In the experimental procedure, the grout was mixed for a time in a high-shear disperser, then transferred to a consolidometer tube lubricated with mould release oil, with one layer of tissue and two layers of filter paper placed carefully on top of the grout. A displacement transducer measured the piston movement. Charts and tables are presented for the results of the filtration and consolidation tests. The analysis and data are required for quantitative assessment of construction effects, due to cement grouting or concrete placement in the ground.

Sealing Properties of Bentonite Suspensions

AbstractSealing with waterborne clays is a rapid and low cost method of controlling seepage through porous media whenever the clay source is within economical shipping distance of the sealing site. But more must be learned about this method of sealing before it can be fully utilized.Water impedance of waterborne bentonites, as measured by water loss in the filter press test, was correlated with their physical, chemical and mineralogical properties. A multiple linear regression analysis showed clay content and exchangeable sodium percentage (ESP) were most highly correlated with water impedance. Swelling, viscosity and gelation of these clays play only a secondary role in forming a water barrier when used as dilute waterborne sealants as suggested by these and other data.There were strong positive correlations between water loss and samples high in silt-sized cristobalite, quartz and feldspar; and negative correlations between water loss and samples high in clay-sized montmorillonite, chlorite and illite.Predicted minimum clay contents (of prospective sealers) were found to be 65–75 per cent clay at 70 and 20 per cent exchangeable sodium, respectively.