Solids Flocculating

Paddle reel/stator-rotor gentle mechanical mixing for coagulation, viscosity 20 mPa s, volumes large. Size increase for particles, with details in Section 9.3. 

Gentle mechanical mixing, such as paddle reel or stator-rotor for flocculation, 

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For adsorption on flocculated particles, the polymer was added in a drop-by-drop-wise manner from a burette containing a 50 cc solution to a 50 cc solution containing the solids. Flocculation was performed in an unbaffled vessel, 58 ram in diameter. Agitation was achieved with a 3-bladed propeller, 35 mm in... 

The polymers manufactured are high molecular weight acrylamide derivatives used in water purification, enhanced oil recovery and solid flocculation. 

The effect of pressure shown earlier is modified in most industrial flltrations in which cake compressibility usually lies between 0.1 and 0.8. Furthermore, the resistance of the filter reduces the effects of the respective variables. It has been found, however, that an increase in pressure causes a nearly proportionate increase in the flow rate in the filtration of granular or crystalline solids. Flocculent or slimy precipitates, on the other hand, have their filtration rates increased only slightly by an increase in pressure. Some materials have a critical pressure above which a further increase results in an actual decrease in flow rate. 

Sections 7.3.1 to 7.3.4 consider solids suspension, solids dispersion, solids dissolving, and solids flocculating respectively. General issues related to mixing using a fluidized bed are given in Section 7.3.5. 

These can be clarified relatively easily in separation equipment such as corrugated plate separators, flotation units, hydrocyclones or centrifuges. An example, the Compact Clarifier, is shown in Figure 6.18. The efficiency of the equipment is usually enhanced by the application of flocculants/coagulants which draw the finely dispersed oil droplets and suspended solids together into larger particles which are separated more effectively, in a manner that is akin to suspended-solids flocculation. The oil droplets have a substantially... 

Feed rate Feed solids Flocculant rate Polymer concentration Centrate solids Cake solids... 

Assists in solid flocculation in liquids used in the treatment of wastewater Soil conditioner. Can absorb up to 400 times its own weight of water, slow release watering system for plants. 

A mixture of polymethylene glycols of the type (CH20) ,xH20 where n is 6- 50. It is a white, amorphous powder having the odour of meth-anal, m.p. I20-130°C. The commercial product contains 95% methanal and is obtained in while flocculent masses when solutions of methanal are evaporated or allowed to stand. When heated it is converted to methanal. Used as a convenient solid substitute for methanal. 

In a 500 ml. wide-mouthed reagent bottle place a cold solution of 25 g. of sodium hydroxide in 250 ml. of water and 200 ml. of alcohol (1) equip the bottle with a mechanical stirrer and surround it with a bath of water. Maintain the temperature of the solution at 20-25°, stir vigorously and add one-half of a previously prepared mixture of 26-5 g. (25 -5 ml.) of purebenzaldehyde (Section IV,115) and 7 -3 g. (9-3 ml.) of A.R. acetone. A flocculent precipitate forms in 2-3 minutes. After 15 minutes add the remainder of the benzaldehyde - acetone mixture. Continue the stirring for a further 30 minutes. Filter at the pump and wash with cold water to eliminate the alkali as completely as possible. Dry the solid at room temperature upon filter paper to constant weight 27 g. of crude dibenzalacetone, m.p. 105-107°, are obtained. Recrystallise from hot ethyl acetate (2-5 ml. per gram) or from hot rectified spirit. The recovery of pure dibenzalacetone, m.p. 112°, is about 80 per cent. 

An interesting example of a large specific surface which is wholly external in nature is provided by a dispersed aerosol composed of fine particles free of cracks and fissures. As soon as the aerosol settles out, of course, its particles come into contact with one another and form aggregates but if the particles are spherical, more particularly if the material is hard, the particle-to-particle contacts will be very small in area the interparticulate junctions will then be so weak that many of them will become broken apart during mechanical handling, or be prized open by the film of adsorbate during an adsorption experiment. In favourable cases the flocculated specimen may have so open a structure that it behaves, as far as its adsorptive properties are concerned, as a completely non-porous material. Solids of this kind are of importance because of their relevance to standard adsorption isotherms (cf. Section 2.12) which play a fundamental role in procedures for the evaluation of specific surface area and pore size distribution by adsorption methods. 

Removal of Solids. Sohds incorporated in the mud during drilling generally are separated mechanically, reduced by dilution, or removed chemically by flocculation. It is desirable to maintain a low concentration of drill sohds (4—8 vol %) and in some cases total removal is required. In the latter case, the drilling fluid is clear, consisting of fresh water or brine, and high drilling rates can be achieved. Polymeric flocculants added in small (0.03—0.06 kg/m (0.01—0.02 Ib/bbl)) quantities maintain a clear hquid (139). 

A colloid is a material that exists ia a finely dispersed state. It is usually a solid particle, but it may be a Hquid droplet or a gas bubble. Typically, coUoids have high surface-area-to-volume ratios, characteristic of matter ia the submicrometer-size range. Matter of this size, from approximately 100 nm to 5 nm, just above atomic dimensions, exhibits physicochemical properties that differ from those of both the constituent atoms or molecules and the macroscopic material. The differences ia composition, stmcture, and iateractions between the surface atoms or molecules and those on the iaterior of the colloidal particle lead to the unique character of finely divided material, specifics of which can be quite diverse (see Flocculating agents). 

There is a gradual transition from particulate setthug into the zone-settling regime, where the particles are constrained to settle as a mass. The principal characteristic of this zone is that the setthug rate of the mass, as observed in batch tests, will be a function of its solids concentration (for any particular condition of flocculation, particle density, etc.). 

Detention Test This test utihzes a 1- to 4-L beaker or similar vessel. The sample is placed in the container, flocculated by suitable means if required, and allowed to settle. Smah samples for suspended-sohds analysis are withdrawn from a point approximately midway between liquid surface and settled solids interface, taken with sufficient care that settled solids are not resuspended. Samphng times may be at consecutively longer intei vals, such as 5, 10, 20, 40, and 80 min. 

The method is apphcable for unflocculated pulps or those in which the ionic characteristics of the solution produce a flocculent structure. If polymeric flocculants are used, the floccule size will be highly dependent on the feed concentration, and an approach based on the Kynch theoiy is preferred. In this method, the test is carried out at the expec ted feed solids concentration and is continued until underflow concentration is achieved in the cyhnder. To determine the unit area, Talmage and Fitch (op. cit.) proposed an equation derived from a relationship equivalent to that shown in Eq. (18-45) ... 

The factors which may make CCD a preferred choice over other separation systems include the following rapidly settling solids, assisted by flocculation relatively high ratio of solids concentration between underflow and feed moderately high wash ratios allowable (2 to 4 times the volume of hquor in the thickened underflows) large quantity of sohds to be processed and the presence of fine-size sohds that are difficult to concentrate by other means. A technical feasibihty and economic study is desirable in order to make the optimum choice. 

Pretreatment Chemicals Even though the suspended solids concentration of the slurry to be tested may be correct, it is frequently necessary to modify the sluriy in order to provide an acceptable filtration rate, washing rate, or final cake moisture content. The most common treatment, and one which may provide improvement in all three of these categories, is the addition of flocculating agents, either inorganic chemicals or natural or synthetic polymers. The main task at this point is to determine which is the most effective chemical and the quantity of chemical which should be used. 

With any chemical treatment system, the main task is one of getting the chemical thoroughly mixed with the solids without degrading the floes which are formed. For those slurries that are relatively fluid, the chemical can frequently be added and mixed satisfactorily using a relatively wide spatula. However, for those thick, relatively viscous slurries, a power mixer will be required. In this case, the mixer should be stopped about one second after the last of the flocculant is added. Should this approach be required, it means that a suitably designed addition system must be supplied with the full-scale instaUation in order to do an effective job of flocculation. 

Particle surface characteristics Type of solid (in terms of internal liquid content) gel, flocculated, hard particle Strength of particle (resistance to deformation under pressure) compressibility over time expressed cake... 

Modification of Process Conditions Relatively small changes in process conditions often markedly affect the performance of specific solids-liquid separators, makiug possible their application when initial test results indicated otherwise or vice versa. Flocculating... 

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