Coagulation basics

In addition to inducing relative velocities between dust particles, gas turbulence will also lift dust particles that have already settled toward the mid-plane and return them to the disk surface. Particles that have been lifted up will be allowed another pass at settling down to the disk mid-plane while sweeping up smaller dust particles in their path. 

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The earhest frothing process developed was the Dunlop process, which made use of chemical gelling agents, eg, sodium fluorosiUcate, to coagulate the mbber particles and deactivate the soaps. The Talalay process, developed later, employs freeze-coagulation of the mbber followed by deactivation of the soaps with carbon dioxide. The basic processes and a multitude of improvements are discussed extensively in Reference 3. A discussion more oriented to current use of these processes is given in Reference 115. 

Solids present in oil and synthetic muds must be kept wet with the nonaqueous phase to prevent coagulation and settling and mud instabiUty. Oil-wetting agents are normally incorporated in the basic mud package. These materials are typically amines or quaternary ammonium salts having hydrocarbon chains of 10 or more carbon atoms. They also render clays or lignites oil-wet for use in viscosity and filtration control (128). 

Food. Food-grade calcium chloride is used in cheese making to aid in rennet coagulation and to replace calcium lost in pasteurization. In the canning iadustry it is used to firm the skin of fmit such as tomatoes, cucumbers, and jalapenos. It acts as a control in many flocculation, coagulation systems (37). Food-grade calcium chloride is used in the brewing iadustry both to control the mineral salt characteristics of the water and as a basic component of certain beers (see Beer). 

Emulsion Polymerization. In this method, polymerization is initiated by a water-soluble catalyst, eg, a persulfate or a redox system, within the micelles formed by an emulsifying agent (11). The choice of the emulsifier is important because acrylates are readily hydrolyzed under basic conditions (11). As a consequence, the commonly used salts of fatty acids (soaps) are preferably substituted by salts of long-chain sulfonic acids, since they operate well under neutral and acid conditions (12). After polymerization is complete the excess monomer is steam-stripped, and the polymer is coagulated with a salt solution the cmmbs are washed, dried, and finally baled. 

Control philosophies for clarifiers are based on the idea that the overflow is the most important performance criterion. Underflow density or suspended sohds content is a consideration, as is optimal use of flocculation and pH control reagents. Automated controls are of three basic types (I) control loops that optimize coagulant, flocculant, and pH control reagent additions (2) those that regulate underflow removal and (3) rake drive controls. Equahzation of the feed is provided in some installations, but the clarifier feed is usually not a controlled variable with respect to the clarifier operation. 

At the pH = Jt there is a balance of charge and there is no migration in an electric field. This is referred to as the isoelectric point and is determined by the relative dissociation constants of the acidic and basic side groups and does not necessarily correspond to neutrality on the pH scale. The isoelectric point for casein is about pH = 4.6 and at this point colloidal stability is at a minimum. This fact is utilised in the acid coagulation techniques for separating casein from skimmed milk. 

Either the Mohr titration or the adsorption indicator method may be used for the determination of chlorides in neutral solution by titration with standard 0.1M silver nitrate. If the solution is acid, neutralisation may be effected with chloride-free calcium carbonate, sodium tetraborate, or sodium hydrogencarbonate. Mineral acid may also be removed by neutralising most ofthe acid with ammonia solution and then adding an excess of ammonium acetate. Titration of the neutral solution, prepared with calcium carbonate, by the adsorption indicator method is rendered easier by the addition of 5 mL of 2 per cent dextrin solution this offsets the coagulating effect of the calcium ion. If the solution is basic, it may be neutralised with chloride-free nitric acid, using phenolphthalein as indicator. 

Problems which arise with certain precipitates include the coagulation or flocculation of a colloidal dispersion of a finely divided solid to permit its filtration and to prevent its re-peptisation upon washing the precipitate. It is therefore desirable to understand the basic principles of the colloid chemistry of precipitates, for which an appropriate textbook should be consulted (see the Bibliography, Section 11.80). However, some aspects of the colloidal state relevant to quantitative analysis are indicated below. 

With lower heat-flux ratings and higher ratios of internal water volume to heating surface than is the norm today, complex external treatment was not always necessary where deemed necessary, it was often limited to basic sedimentaion or filtration techniques employing inorganic coagulants and flocculants, typically followed by the use of natural zeolites (see sections 9.2.3.1 and 9.2.5 for additional information). 

Basic aspects of the proteins of the blood coagulation system and of fibrinolysis are described in this chapter. Some fundamental aspects of platelet biology are also presented. Hemorrhagic and thrombotic states can cause serious medical emergencies, and thromboses in the coronary and cerebral arteries are major causes of death in many parts of the world. Rational management of these conditions requires a clear understanding of the bases of blood clotting and fibrinolysis. 

Over the past decade there has been an explosion of knowledge on the mechanisms of both coagulation and fibrinolysis that has contributed to our appreciation of the basic concepts of these two pathways. 

The basic unit operations/processes required for treating the acid pickling wastewater are (a) neutralization with NaOH and/or lime to increase the pH and (b) physicochemical methods, such as chemical coagulation, precipitation, clarification (sedimentation or DAF), and filtration to remove BOD5, COD, and iron. 

Hambleton, J. and O Reilly, R.A., Drugs used in disorders of coagulation, in Basic and Clinical Pharmacology, 8th ed., Katzung, B.G., Ed., Lange Medical Books/McGraw-Hill, New York, 2001, chap. 34. 

Filtration is analogous to coagulation in many respects. This is illustrated by juxtaposing the basic kinetic equations on particle removal ... 

Basically, crystallization occurs either by monomer addition to a growing crystal or by coagulation of smaller crystals unto larger crystals. Monomer addition produces more uniform and regular crystals and a narrower crystal size distribution. Coagulation produces irregularly shaped crystals with a wide range in crystal sizes. These processes are obviously addition crystallization and condensation crystallization, respectively. We will not consider these kinetics in any more detail here, but save them for a homework problem. 

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