Coagulation salts

Like nitric oxide, the discovery of the eicosanoid signalling molecules was a significant event in twentieth century physiology, due largely to research led by Sir John Vane (Nobel Prize 1982). The diverse actions of the eicosanoids include roles in muscle contraction, blood coagulation, salt and fluid homeostasis, inflammatory responses and pain sensitivity. 

The range of steric thickness plus electrostatic screening increases as the pH is reduced from 11 to 6 and decreases as the layers bind more Na+ as the total coagulating salt concentration is increased above 0.15 M. 

The major use of coagulating diemicals is the production of potable water, where ftie task is usually to remove very smafl concentrations of suspaided solids and organic materials such as humic adds which impart odour, taste, and colour to the water and because of the low concentrations of particles present, the initial coagulation rates may be slow. However, if they are used at the correct pH, ftie common coagulating salts produce insoluble hydrolysis products vriudt increase the particle concentration and improve the coagulation rate. 

With the advent of flotation as a useful treatment process in water and waste water treatment, made possible by the creation of finer bubbles by dissolved air precipitation, and electrolysis, the concept of bubble flocculation can be reconsidered. In the flotation process in water treatment, flocculation takes place prior to bubble flotation, usually by mechanical (paddle) flocculator with a coagulant salt (such as alum). It seems possible that the flocculation and flotation processes could be combined with the bubbles providing the flocculating power. 

The removal of colloidal solids from water usually requires coagulation. Salts of aluminum and iron are the coagulants most often used in water treatment. Of these, alum or filter alum is most commonly used. This substance is a hydrated aluminum sulfate, Al2(S04)3-18H20. When this salt is added to water, the aluminum ion hydrolyzes by reactions that consume alkalinity in the water, such as... 

The overall regeneration process consists of three different mechanisms the chemical regeneration (elimination of CS2), the coagulation (salting-out effect), and the compound formation (by insoluble Zn-salts). 

For a more complete understanding of colloid stability, we need to address the kinetics of aggregation. The theory discussed here was developed to describe coagulation of charged colloids, but it does apply to other cases as well. First, we consider the case of so-called rapid coagulation, which means that two particles will aggregate as soon as they meet (at high salt concentration, for instance). This was considered by von Smoluchowski 1561 here we follow [39, 57]. 

After the washing, the fiber is dried, and then is heat-drawn in the same manner as in the case of dehydration—coagulation with salt but to a much higher draw ratio. As a result the finished fiber has high strength and modulus and is, without acetalization, sufficientiy resistant to boiling water. Figure 3 shows schematic fiber stmctures (17). 

Fig. 3. Schematic comparison of the stmctures of PVA fibers formed by salt coagulation and alkaU coagulation, (a) Low orientation, low crystallinity (b)...

The correct viscose age or ripeness for spinning varies according to the type of fiber being made. Ripeness can be assessed by estabHshing the salt concentration necessary to just coagulate the viscose dope. The preferred test uses sodium chloride (salt figure) although ammonium chloride is the basis of the alternative method (Hottenroth number). 

Water Treatment Industrial CleaningPipplications. Boiler and cooling tower waters are treated with lignosulfonates to prevent scale deposition (78). In such systems, lignosulfonates sequester hard water salts and thus prevent their deposition on metal surfaces. They can also prevent the precipitation of certain iasoluble heat-coagulable particles (79). Typical use levels for such appHcatioas range from 1—1000 ppm. 

Vitamin A (845 RE/L) and vitamin D (913 RE/L) may be added to fortify evaporated milk. Other possible ingredients are sodium citrate, disodium phosphate, and salts of carrageenan. Phosphate ions maintain an appropriate salt balance to prevent coagulation of the protein (casein) during sterilization. The amount of phosphate added depends on the amount of calcium and magnesium present. 

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). 

Poly(ethylene oxide) associates in solution with certain electrolytes (48—52). For example, high molecular weight species of poly(ethylene oxide) readily dissolve in methanol that contains 0.5 wt % KI, although the resin does not remain in methanol solution at room temperature. This salting-in effect has been attributed to ion binding, which prevents coagulation in the nonsolvent. Complexes with electrolytes, in particular lithium salts, have received widespread attention on account of the potential for using these materials in a polymeric battery. The performance of soHd electrolytes based on poly(ethylene oxide) in terms of ion transport and conductivity has been discussed (53—58). The use of complexes of poly(ethylene oxide) in analytical chemistry has also been reviewed (59). 

The product of an emulsion polymerization is a latex ie, polymer particles on the order of 0.5—0.15 p.m stabilized by the soap. These form the basis for the popular latex paints. SoHd mbber is recovered by coagulating the latex with ionic salts and acids (see Latex technology). 

Sodium alumiaate is used ia the treatment of iadustrial and municipal water suppHes and the use of sodium alumiaate is approved ia the clarification of drinking water. The FDA approves the use of sodium alumiaate ia steam generation systems where the steam contacts food. One early use of sodium alumiaate was ia lime softening processes, where it iacreases the precipitation of ions contributing to hardness and improves suspended soHds removal from the treated water (17). Sodium alumiaate reacts with siHca to leave very low residual concentrations of siHca ia hot process water softeners. Sodium alumiaate is often used with other chemicals such as alum, ferric salts, clays, and polyelectrolytes, as a coagulant aid (18,19). 

Disposal of the solutions of aluminum salts generated in the Eriedel-Crafts process presents an environmental problem unless use can be found for them as coagulants in a water treatment plant. 

---