Washing of filter cake

The three types of washing are washing of filter cakes by displacement, washing by reslurrying of cakes or sludges, and washing by successive dilution. 

It is common practice to exclude from consideration as leaching the elution of surface-adsorbed solute. This process is treated instead as a special case of the reverse operation, adsorption. Also usually excluded is the washing of filter cakes, whether in situ or by reslurrying and refiltration. 

The washing of filter cake is carried out to remove liquid impurities from valuable solid product or to increase recovery of valuable filtrates from the cake. Wakeman (1990) has shown that the axial dispersion flow model, as developed in Sec. 4.3.6, provides a fundamental description of cake washing. It takes into account such situations as non-uniformities in the liquid flow pattern, non-uniform porosity distributions, the initial spread of washing liquid onto the topmost surface of the filter cake and the desorption of solute from the solid surfaces. 

The washing of filter cake is carried out to remove liquid impurities from the valuable solid filter cake or to increase the recovery of valuable filtrate. Wake-man (1990) has shown that the axial dispersion flow model, as developed in... 

These filters (Fig. 9) have the advantages of low cost, near indestructibility, and ease of internal inspection. They have the lowest liquid volume-to-area ratio, which makes them most efficient for the washing of filter cakes. Because of this low ratio, they will also have the smallest unfiltered heel remaining at the end of the cycle. 

By convention, elution of a surface-adsorbed solute is treated as a special case of adsorption, rather than leaching. The washing of filter cakes is also excluded. 

Filtration and washing of filter cake on a flat disc rotary vacuum filter ... 

Section 7.5.4.2 discusses filter aids, washing of filter cake to remove occluded liquors, removal and handling of filter cake, and the backwashing of packed bed filters to remove and recover deposited solids. 

Countercurrent washing offers a great saving on the quantity of wash liquid together with many other important advantages listed below. Consequently, its application in industry is spreading quickly. Even washing of filter cakes by displacement, where the wash liquid requirement in the co-current mode is not excessive, is in some cases performed countercurrently if the additional cost of equipment needed for the separate collection of filtrates can be justified. 

Figure App. 15.1 A schematic diagram of leaf testing for countercurrent washing of filter cakes ...

C. Big secret 2...Quack ...One MUST filter this 600+ ml of ether...but a duck can t do this all at once...so one must fitter in vacuum filter in 200 ml portions...changing the duck paper every time and wash the filter cake with ether...Dr. Quack thinks a vacuum filter (apirator) at this stage is a must..Quack ... 

Mercuric Sulfate. Mercuric s Af2iX.e.[7783-35-9] HgSO, is a colorless compound soluble ia acidic solutions, but decomposed by water to form the yellow water-iasoluble basic sulfate, HgSO 2HgO. Mercuric sulfate is prepared by reaction of a freshly prepared and washed wet filter cake of yellow mercuric oxide with sulfuric acid ia glass or glass-lined vessels. The product is used as a catalyst and with sodium chloride as an extractant of gold and silver from roasted pyrites. 

For the purpose of washing, the filter cake on the funnel is covered with ice water. After being allowed to remain in contact for a few seconds, the liquid is quickly drained under reduced pressure. The second portion of washing water should no longer be acid to Congo red. 

When eontaminated, polluted, or valuable suspension liquors are present, it becomes necessary to wash the filter cake to effect clean separation of solids from the mother liquor or to recover the mother liquor from the solids. The operation known as dewatering involves forcing a clean fluid through the cake to recover residual liquid retained in the pores, directly after filtering or washing. Dewatering is a complex process on a microscale, because it involves the hydrodynamics of... 

This family of filters consist of a vertical pressure vessel with a horizontal filter plate at the bottom. The filtrate from this equipment flows out a nozzle on the bottom of the filter. These devises are usually used for slurries where large amounts of solids are being collected. Variations of this equipment include equipment with removable lower heads for easy cake removal, ability to pressure or vacuum filter, ability to wash the filter cake, an agitator to break-up and rewash the filter cake, and heating or cooling jackets for the whole vessel. The Nutsche filter is the industrial version of the well known laboratory scale Buchner Funnel with the exception that it is designed to operate under either on vacuum or pressure. 

Blinks used a different method to dislodge the particles of active material from the strips cut off from the jellyfish (Blinks et al., 1978). The strips are shaken in cold seawater, and the particles dislodged are harvested by filtration on a Buchner funnel with the aid of Celite. The filter cake is first washed with 50 mM EDTA, pH 8.0, containing (NH4)2S(>4 at 75% saturation, to remove seawater. Then, the particles are cytolyzed and aequorin is extracted in situ by washing the filter cake with cold 50 mM EDTA, pH 8.0. The filtrate is clear and slightly greenish. The active matter in the filtrate is precipitated by saturation... 

A significant improvement in yield (to about 74%) and purity (approx 98%) was realized by the substitution of methanol for chlf and crystn of the product from the soln without neutralization, residual acid being removed, by washing the filter cake with w... 

The bis-acylation byproduct (Me3CCONHNHCOCMe3) was removed by filtration 20 mL of water was used for washing the filter cake. 

Shake 25 g (dry weight equivalent) of soil with 100 mL of methanol with a mechanical shaker for 30 min. Filter the mixture through a filter paper into a 300-mL round-bottom flask. Wash the filter cake with 80 mL of methanol, combine all the filtrates in the round-bottom flask and remove the methanol by rotary evaporation. 

When separating solid particles from a liquid filtrate, if the solid filter cake is a product, rather than a waste, then it is usual to wash the filter cake to remove the residual filtrate from the filter cake. The washing of the filter cake after filtration takes place by displacement of the filtrate and by diffusion. 

A slurry containing 100 kg of whiting/m3 of water, is filtered in a plate and frame press, which takes 900 s to dismantle, clean and re-assemble. If the filter cake is incompressible and has a voidage of 0.4, what is the optimum thickness of cake for a filtration pressure of 1000 kN/m2 The density of the whiting is 3000 kg/m3. If the cake is washed at 500 kN/m2 and the total volume of wash water employed is 25 per cent of that of the filtrate, how is the optimum thickness of cake affected The resistance of the filter medium may be neglected and the viscosity of water is 1 mN s/m2. In an experiment, a pressure of 165 kN/m2 produced a flow of water of 0.02 cm3/s though a centimetre cube of filter cake. 

Pour the contents of the flask into a Buchner funnel and rinse the flask with 300 ml of anhydrous ethyl ether. Pour this into the funnel. Filter with vacuum from an aspirator equipped with a dry ice/acetone trap. Wash the filter cake with two 300ml portions of anhydrous ethyl ether. The filter cake is X, n-diethyaniline hydrochloride and is not used in this process. It may be saved and converted back to its original form for reuse. 

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