Solid/liquid separation filter presses

It is well Icnown that the solid-liquid separation characteristics of residues become a problem when zinc concentrates with high silica content are treated in a hydrometallurgical process. Once treated improperly, the silica dissolved in the sulfuric acid solution turns to a gel which significantly reduces the solid-liquid separation characteristic of the residue. As a consequence, larger capacity solid-liquid separation facilities such as thickeners, filter presses and others are required. In some cases, the slurry may completely turn into a gelatinous form, which cannot be treated. For this purpose, a technology to settle the dissolved silica in a form easy for solid-liquid separation becomes necessary. 

Howard, G.W. and Nickolaus, N., 1986, Cartridge Filters, in Solid/Liquid separation equ ment scale-up, D.B.Purchas and RJ.Wakeman, (Eds.) Uplands Press, Croydon. 

These are used for quick solid-liquid separation, generally for easily separable crystals/suspended solids. However, difficulties have been experienced in use of centrifuge in case of sticky pastes for which press leaffilter may be used with appropriate additions of filter aid powders. 

Pharmaceutical Removal of suspended matter is a frequent application for MF. Processes may be either clarification, in which the main product is a clarified liquid, or solids recovery. Separating cells or their fragments from broth is the most common application. Clarification of the broth in preparation for product recovery is the usual objective, but the primary goal may be recovery of cells. Cross-flow microfiltration competes w l with centrifugation, conventional filtration by rotary vacuum filter or filter press and decantation. MF delivers a cleaner permeate, an uncontaminated, concentrated cell product... 

While T. Weyl, J. A. Joannis, and H. Moissan consider that the soln. of the alkali metals in liquid ammonia contain compounds of ammonia and the metal, C. A. Seely, C. A. Kraus, and 0. Ruff and E. Geisel say that the soln. are soln. of the metal in ammonia or mixtures of the metal with a soln. of the metal in liquid ammonia. If the copper-coloured substances be squeezed between folds of cloth in a filter-press, 0. Ruff and E. Geisel separated solid metal, and a sat. soln. of the metal in liquid ammonia. 

In the laboratory, the dye chemist uses a suction funnel and flask to separate solid materials from liquids. In the plant, however, such equipment is suitable only for filtering coarse precipitates which, even in thick layers, do not offer too much resistance to passage of the liquid. Fine precipitates — and this includes the great majority of dyes — must be filtered through a filter press in large scale operations (see Fig. 56, page 376, and schematic drawing in Fig. 42a-4i). 

In the filtration process, a liquid containing suspended solids is passed through a porous medium. The solids are trapped against the medium, and the separation of solids from liquids results. For large solid particles, a thick barrier such as sand may be used for smaller particles, a fine filter such as a filter cloth is preferable. Fluid passage may be induced by gravity, positive pressure, or a r acuum. A few of the more popular filter fypes are the plate and frame filter press, and shell and leaf and cartridge filters. 

The liquid fat or oil coming from the press contains 2% to as much as 15% fat-free solids, which is usually separated out in a two-step procedure. First, the bulky solids are separated in a settling chamber equipped with a drag that collects the solids, passes them over a drainage screen, and then drops them into the conveyor taking fresh material to the screw-presses. The second step is to clarify the liquid in a manual or automatic plate-and-frame filter press. 

Filtration and drying are important steps in the production of dyes. They require time and labor, and filter presses. In the case of vat dyes the presses separate suspended solids, usually the desired product, from liquids, generally in the form of a slurry. This is achieved by forcing the reaction mixture through a suitable filter medium, that supports the solid, under applied pressure. For an acidic slurry, wooden plates and frames are used. The vat dye press cake is washed with water, though in a number of cases organic solvents are used. After filtering, the solids are dried. 

Separation of Crystals.—The separation of crystals from the mother-liquor is effected by filtration under diminished pressure. A funnel is attached to a filter-bottle by means of a rubber stopper. A perforated plate about 4 cm. in diameter is placed in the funnel and covered with a circular piece of filter-paper the diameter of which is about 6 mm. greater than that of the plate. This paper is moistened with the solvent. The bottle is connected with the suction-pump, and air is drawn through the apparatus. The paper is fitted into place so that it covers the joint between the filter-plate and funnel. If a crust has formed around the beaker at the surface of the liquid from which the crystals to be separated have formed, it should be carefully removed, as it will probably contain some of the impurities present. The remaining solution and crystals are then poured into the funnel, and the suction applied. When all the liquid has been drawn off the solid should be pressed down tightly with a spatula. The connection with the pump is broken, and the solid on the funnel is moistened with some of the pure solvent used for crystallization. The crystals are allowed to absorb the solvent and to stay in contact with it for about half a minute. The suction is then applied and the crystals drained as fully as possible from the liquid. The filter-bottle is again disconnected from the pump, and the crystals covered again with the solvent, and washed as before. Crystals should never be... 

The WRS includes two clarifiers, two thickeners, two filter presses, and auxiliary equipment. The ICB effluent is transferred to the WRS clarifiers, where a polymer will be injected to provide chemical coagulant for enhancing removal of suspended solids. The clarified effluent will be transferred to the BRS. The clarifier sludge will be pumped to the WRS thickeners, where a polymer may be added to enhance thickening. Thickener overflow is recycled to the clarifiers, and underflow is pumped to the dewatering filter presses. The Alter press separates the solids from the liquid stream. The liquid is recirculated to the clarifiers, and the filter cake, containing 20-25 percent dry weight sohds, is a secondary waste. 

Dry Fractionation—is the simplest fractionation technique because no additives or posttreatment of the end product is involved. Fractionation is basically a two-stage process. First the oil is crystallized by cooling the oil in a controlled manner to the required temperature in a crystallizer. The oil is then filtered to separate the liquid from the solid fraction by means of a vacuum filter or membrane filter press. Recent developments of new and more efficient crystallizers and reliable high-pressure membrane filters moved dry fractionation from a third choice to a good alternative for solvent fractionation in many cases. 

This unit operation covers a wide range of mechanical methods designed to separate solids from liquids or gases. In a simple filter (Fig. 4.4) the mixture of solid and liquid, or solid and gas, is pressed against one side of a porous bed called the filter medium, allowing only the liquid or gas to pass, leaving the solid in the form of a cake on the surface of the filter medium. 

Pressure filtration differs fi-om vacuum filtration in that the liquid is forced through the filter medium by a positive pressure instead of a vacuum. Among the most widely used in Che chemical process industry (and widely used in Europe for wastewater treatment) is Che filter press. As shown in Figure 3, Che filter press operates by pumping the sludge between plates that are covered with a filter cloth. The liquid seeps throu Che filter cloth leaving the solids bdiind between the plates. Whoi the spaces between the plates are filled, the treatment plant operator separates the plates and removes the solids. 

Typically mechanical separators Hke filter centrifuges, vacuum or pressure filters, decanters, filter presses or simple static thickeners are used to isolate the solids from the liquid. 

Separation of the solid particles from the liquid is most likely to be done by a filter press or belt filter, although decantation can be used for washing, as the product settles well. Soluble sulfate and /or nitrate salts, depending on the acid used to dissolve the cadmium, will also need washing out. This step is important, as the retention of excessive amounts of salts can have a detrimental effect on the product. 

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