Flocculation cationic flocculants

The repulsion between oil droplets will be more effective in preventing flocculation Ae greater the thickness of the diffuse layer and the greater the value of 0. the surface potential. These two quantities depend oppositely on the electrolyte concentration, however. The total surface potential should increase with electrolyte concentration, since the absolute excess of anions over cations in the oil phase should increase. On the other hand, the half-thickness of the double layer decreases with increasing electrolyte concentration. The plot of emulsion stability versus electrolyte concentration may thus go through a maximum. 

The carboxylated units, ionized, decrease adsorption on subterranean substrates (23), ia proportion to the number of units, an important parameter ia petroleum recovery processes. In waste treatment processes cationic acrylamide comonomer units are often used (31) to iacrease adsorption and thereby flocculation of soHds ia wastewater (see Acrylamide POLYMERS Flocculating agents). The favorable and characteristics of acrylamide facilitate the... 

Cationic monomers are used to enhance adsorption on waste soHds and faciHtate flocculation (31). One of the first used in water treatment processes (10) is obtained by the cyclization of dimethyldiallylammonium chloride in 60—70 wt % aqueous solution (43) (see Water). Another cationic water-soluble polymer, poly(dimethylarnine-fi9-epichlorohydrin) (11), prepared by the step-growth... 

Starch is a polysaccharide found in many plant species. Com and potatoes are two common sources of industrial starch. The composition of starch varies somewhat in terms of the amount of branching of the polymer chains (11). Its principal use as a flocculant is in the Bayer process for extracting aluminum from bauxite ore. The digestion of bauxite in sodium hydroxide solution produces a suspension of finely divided iron minerals and siUcates, called red mud, in a highly alkaline Hquor. Starch is used to settle the red mud so that relatively pure alumina can be produced from the clarified Hquor. It has been largely replaced by acryHc acid and acrylamide-based (11,12) polymers, although a number of plants stiH add some starch in addition to synthetic polymers to reduce the level of residual suspended soHds in the Hquor. Starch [9005-25-8] can be modified with various reagents to produce semisynthetic polymers. The principal one of these is cationic starch, which is used as a retention aid in paper production as a component of a dual system (13,14) or a microparticle system (15). 

In the area of municipal and iadustrial wastewater treatment, the principal environmental issue is the toxicity of residual flocculating agents ia the effluent. Laboratory studies have shown that cationic polymers are toxic to fish because of the iateraction of these polymers with giU. membranes. Nonionic and anionic polymers show no toxicity (82,83). Other studies have shown that ia natural systems the suspended inorganic matter and humic substances substantially reduce the toxicity of added cationic polymer, and the polymers have been used successfully ia fish hatcheries (84—86). Based on these results, the EPA has added a protocol for testing these polymers for toxicity toward fish ia the presence of humic acids (87). The addition of anionic polymers to effluent streams containing cationic polymers to reduce their toxicity has been mentioned ia the patent Hterature (83). 

Flocculation. The interaction of the cationic PEIs with anionic substrates leads to substrate flocculation. AppHcations of this property include the coagulation of latex (434), commercial appHcation in effluent treatments (435—437), and stabiHzation of highly loaded coal—water mixtures in mining (438). 

Low molecular cationic polymers or alum can also be used to flocculate pitch, ie, bind up the pitch so that it is retained in the sheet, to minimize pitch deposition on machine surfaces and fabrics (35,36). Alum is used commonly in newsprint operations (34). The addition of a nonionic surfactant with a hydrocarbon solvent to the wet end has shown some utility in preventing deposits of adhesive recycled furnish contaminants from forming on the paper... 

Two types of immobilization are used for immobilizing glucose isomerase. The intracellular enzyme is either immobilized within the bacterial cells to produce a whole-ceU product, or the enzyme is released from the cells, recovered, and immobilized onto an inert carrier. An example of the whole-ceU process is one in which cells are dismpted by homogenization, cross-linked with glutaraldehyde, flocculated using a cationic flocculent, and extmded (42). 

The hot-water separation process involves extremely compHcated surface chemistry with interfaces among various combinations of soUds (including both silica sand and alurninosilicate clays), water, bitumen, and air. The control of pH is critical. The preferred range is 8.0—8.5, achievable by use of any of the monovalent bases. Polyvalent cations must be excluded because they tend to flocculate clays and thus raise viscosity of the middlings in the separation cell. 

Polymeric flocculants are available in various chemical compositions and molecular weight ranges, and they may be nonionic in character or may have predominantly cationic or anionic charges. The range of application varies but, in general, nonionics are well suited to acidic suspensions, anionic flocculants work well in neutral or alkaline environments, and cationics are most effective on organic material and colloidal matter. 

DETERMINATION OF THE RESIDUAL CONTENTS OF CATIONIC FLOCCULANTS IN WATERS... 

Cationic flocculants are widely used in clearing oil-water, waste, natural and drinking water. At the sarue time they ar e moderately toxic substances which have cumulative properties. For the majority of flocculants, prodused and used in Ukraine, limit admission concentration is 0,l-t-0,4 mg/dm for drinking water and 0,01 mg/dm and less - for natural waters. 

Chemical pretreatment is often used to improve the performance of contaminant removal. The use of chemical flocculants is based on system efficiency, the specific DAF application and cost. Commonly used chemicals include trivalent metallic salts of iron, such as FeClj or FeSO or aluminum, such as AISO. Organic and inorganic polymers (cationic or anionic) are generally used to enhance the DAF process. 

The Jordi polyethyleneimine phase has been developed in an attempt to block adsorptive effects of the PDVB surfaces toward cationic polymers such as chitosan and quaternary water-soluble flocculants (Fig. 13.17). 

In previous works [18-20,23,102] water-soluble polymers such as polyacrylamide (pAM), polysodium acrylate (pAA Na), poly(acrylamide-sodium acrylate) (pAM-AA Na), poly(acrylamide-diallyethylamine-hy-drochloride) (pAM-DAEA-HCl), and poly(acrylamide-sodium acrylate-diallyethylamine-hydrochloride) (pAM-AANa-DAEA-HCl) were used in the recovery of cations and some radioactive isotopes from aqueous solutions. It was found that the floe is formed between the added polymer and ions of the solution in the flocculation process with the formation of a crosslinked structure. The formed cross-linked structure is characterized by [103-105] ... 

The efficiency of flocculation of these polyelectrolytes was investigated at different pH and polymer concentrations, valency of cations, and weight-average molecular weight of the polymer. The results are shown in Figs. 12-16,... 

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