Filters diatomaceous silica

Filter aids should have low bulk density to minimize settling and aid good distribution on a filter-medium surface that may not be horizontal. They should also be porous and capable of forming a porous cake to minimize flow resistance, and they must be chemically inert to the filtrate. These characteristics are all found in the two most popular commercial filter aids diatomaceous silica (also called diatomite, or diatomaceous earth), which is an almost pure silica prepared from deposits of diatom skeletons and expanded perhte, particles of puffed lava that are principally aluminum alkali siheate. Cellulosic fibers (ground wood pulp) are sometimes used when siliceous materials cannot be used but are much more compressible. The use of other less effective aids (e.g., carbon and gypsum) may be justified in special cases. Sometimes a combination or carbon and diatomaceous silica permits adsorption in addition to filter-aid performance. Various other materials, such as salt, fine sand, starch, and precipitated calcium carbonate, are employed in specific industries where they represent either waste material or inexpensive alternatives to conventional filter aids. 

Diatomaceous Silica Filter aids of diatomaceous silica have a dry bulk density of 128 to 320 kg/m (8 to 20 Ib/fU), contain paiiicies mostly smaller than 50 [Lm, and produce a cake with porosity in the range of 0.9 (volume of voids/total filter-cake volume). The high porosity (compared with a porosity of 0.38 for randomly packed uniform spheres and 0.2 to 0.3 for a typical filter cake) is indicative of its filter-aid ability Different methods of processing the crude diatomite result in a series of filter aids having a wide range of permeability. 

The filter cake is stirred with 3.1 liters of acetone. The volume of acetone used is about 1.5 times the weight of the cake resulting in about a 65% acetone concentration. The benzoic acid dissolves in the acetone and the urokinase flocculates out. Sodium benzoate, about 1% of the weight of the cake, or 21 grams, is added to speed up the formation of the precipitate. The suspension of crude urokinase in acetone Is filtered on a Buchner funnel using filter paper precoated with a diatomaceous silica product (Celite 505). The precipitate is washed with acetone until the filtrate is water clear. The precipitate is then washed with ether and air dried. The yield of powder so obtained is 2.3 grams. 

Gas chromatography (GC) employs a gaseous mobile phase, known as the carrier gas. In gas-liquid chromatography (GLC) the stationary phase is a liquid held on the surface and in the pores of a nominally inert solid support. By far the most commonly used support is diatomaceous silica, in the form of pink crushed firebrick, white diatomite filter aids or proprietary variants. Typical surface areas of 0.5-4 m2/g give an equivalent film thickness of 0.05-1 pm for normal liquid/support loadings of 5-50 per cent by mass. 

Celite, a Johns-Manville registered trademark for a diatomaceous silica product. It is used as a filter aid. Supplier Fisher. Bernstein recommends that a water-washed benzene extract of a reaction product be filtered through a small pad of Celite and evaporated without further drying. 

For amorphous materials, sludges or other poor filtering products, improved filtration characteristics and/or filtrate clarity are enhanced with the use of filter aids. Slurry additives such as diatomaceous silica or perlite (pulverized rock), are employed to aid filtration. Diatomite is a sedimentary rock containing skeletons of unicellular plant organisms (diatoms). These... 

Celite . [Celite] Diatomaceous silica filter aids, catalyst carriers, filler, extender pigment, grinding aid, conditioner, processing aid, flatting agent for paints, agric. chonicals, paper, rubber, polishes, cleaners. 

FILTER AIDS. Slimy or very fine solids that form a dense, impermeable cake quickly plug any filter medium that k fine enough to retain them. Practical filtration of such materials requires that the porosity of the cake be increased to permit passage of the liquor at a reasonable rate. This is done by adding a filter aid, such as diatomaceous silica, perlite, purified wood cellulose, or other inert porous solid, to the slurry before filtration. The filter aid may subsequently be separated from the filter cake by dissolving away the solids or by burning out the filter aid. If the solids have no value, they and the filter aid are discarded together. 

The most important filter aids from a volume standpoint are the diatomaceous silica type (90% or better silica). These are manufactured from the siliceous fossil remains of tiny marine plants known as diatoms. 

Concentrates containing up to 80 per cent uranium are first dissolved by nitric acid in stainless-steel, steam-heated, stirred vessels. The slurry is then fed to a bank of rotary vacuum filters where silica and small amounts of other insoluble impurities are removed. These filters are of the pre-coat type, the filter medium being a 2 in. layer of diatomaceous earth filter-aid, supported on cloth and removed to the extent of a few thousandths of an inch at each revolution. Washing takes place on the drum, the washings being mixed with the main filtrate to provide a clear hquor for TBP extraction at a uranium concentration of 300 g/1. and a free acidity of up to 3N. 

Diatomaceous earth, widely-known and long-used as a filteraid in process and waste filtrations, has a high microcrystalline silica content. As well as being a respiratory hazard in the workplace, the silica is being scrutinized in some jurisdictions as a potentially hazardous dust in landfills in which spent filter cakes are deposited. 

Diatomaceous earth A fine, siliceous (made of silica) "earth" composed mainly of the skeletal remains of diatoms (single cell microscopic algae with rigid internal structure consisting mainly of silica). Tests prove that DE leaches unacceptable amounts of silicate into the water for fish health. If used as a filter substance, a silicone removing resin should be employed afterwards. 

Diatoms are single-celled algae that produce a hard skeleton made of hydrous silica (opal). The rock that forms from consolidated layers of diatom skeletons is called diatomite. This material has many common and commercial names, including diatomaceous earth, Fuller s earth, kieselgur, and tripo-lite. Diatomite is mined and used as building material, in filters, as insulation, as a mild abrasive, and as a filler in dry chemicals. 

Nowadays, precoated filters with diatomaceous earth are mainly used for the separation of yeast. For overseas exportation, the product is pasteurized after prior adsorptive elimination of on-heat-resisting colloids through treatment with bentonite, silica gel etc. Essential for the quality of the beer is the elimination of temperature fluctuations during storage and transport. 

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