Filtration laboratory testing

Note that filter aid selection must be based on planned laboratory tests. Guidelines for selection may only be applied in the broadest sense, since there is almost an infinite number of combinations of filter media, filter aids, and suspensions that will produce varying degrees of separation. The hydrodynamics of any filtration process are highly complex filtration is essentially a multiphase system in which interaction takes place between solids from the suspension, filter aid, and filter medium, and a liquid phase. Experiments are mandatory in most operations not only in proper filter aid selection but in defining the method of application. Some general guidelines can be applied to such studies the filter aid must have the minimum hydraulic resistance and provide the desired rate of separation an insufficient amount of filter aid leads to a reduction in filtrate quality — excess amounts result in losses is filtration rate and it is necessary to account for the method of application and characteristics of filter aids. 

In selecting cloths made from synthetic materials, one must account for the fact that staple cloths provide a good retentivity of solid particles due to the short hairs on their surface. However, cake removal is often difficult from these cloths - more than from cloths of polyfilament and, especially, monofilament fibers. The type of fiber weave and pore size determine the degree of retentivity and permeability. The objective of the process, and the properties of particles, suspension and cake should be accounted for. The cloth selected in this maimer should be confirmed or corrected by laboratory tests. Such tests can be performed on a single filter. These tests, however, provide no information on progressive pore plugging and cloth wear. However, they do provide indications of expected filtrate pureness, capacity and final cake wetness. 

Worch E, Grischek T, Bomick H, Eppinger P (2002) Laboratory tests for simulating attenuation processes of aromatic amines in riverbank filtration. J Hydrol 266 259-268... 

A slurry containing 40 per cent by mass solid is to be filtered on a rotary drum filter 2 m diameter and 2 m long which normally operates with 40 per cent of its surface immersed in the slurry and under a pressure of 17 kN/m2. A laboratory test on a sample of the slurry using a leaf filter of area 200 cm2 and covered with a similar cloth to that on the drum, produced 300 cm3 of filtrate in the first 60 s and 140 cm3 in the next 60 s, when the leaf was under pressure of 84 kN/m2. The bulk density of the dry cake was 1500 kg/m3 and the density of the filtrate was 1000 kg/m3. The minimum thickness of cake which could be readily removed from the cloth was 5 mm. 

Abnormal clearance may be anticipated when there is major impairment of the function of the kidney, liver, or heart. Creatinine clearance is a useful quantitative indicator of renal function. Conversely, drug clearance may be a useful indicator of the functional consequences of heart, kidney, or liver failure, often with greater precision than clinical findings or other laboratory tests. For example, when renal function is changing rapidly, estimation of the clearance of aminoglycoside antibiotics may be a more accurate indicator of glomerular filtration than serum creatinine. 

Figure 11.3. Laboratory test data with a vacuum leaf filter, (a) Rates of formation of dry cake and filtrate, (b) Washing efficiency, (c) Air flow rate vs. drying time, (d) Correlation of moisture content with the air rate, pressure difference AP, cake amount W Ib/sqft, drying time 6d min and viscosity of liquid Dahlstrom and Silverblatt, 1977).

The method most commonly used to stabilize a wine, once instability is determined, is to chill the wine to -5° C and hold it until stability is achieved, usually seven to fourteen days. Addition of fine potassium bitartrate crystals during chilling (30 mg/L) helps seed the formation of potassium bitartrate crystals. When laboratory tests have shown the wine to be stable, the wine goes through a tight diatomaceous earth or pad filtration to remove the crystals. 

Lithium Recovery. The melt used in this process is relatively inexpensive except for the lithium carbonate which comprises approximately 84% of the salt cost. Therefore it is desirable to recover the lithium from the process filter cakes. An aqueous process has been developed for this purpose. The filter cakes are slurried with water and filtered to extract the very soluble sodium and potassium carbonates lithium carbonate remains with the ash because it is relatively insoluble under these conditions. The ash-lithium carbonate cake is slurried in water and the lithium is solubilized by conversion to the bicarbonate. The ash is removed by filtration and the soluble bicarbonate in the filtrate is precipitated as the carbonate. The lithium carbonate is separated by filtration and returned to the process stream the saturated lithium carbonate filtrate is recycled to conserve lithium. Laboratory tests have demonstrated that more than 90% of the lithium can be recovered by this technique. 

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