Starch flocculants

Polyaluminum chloride flocculant, paper wet end applies. (3-Chloro-2-hydroxypropyl) trimethylammonium chloride modified starch flocculant, petroleum PEG-14M... 

The raw juice is neutralized and passes through various purification steps. Proteins and lipids from starch flocculate at a suitable pH value and are separated as sludge. Pigments are eliminated with activated carbon and minerals with ion exchangers. The purified juice is evaporated under vacuum (falling-film evaporator) up to a solids content of 70—85%. 

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). 

Guar gum [9000-30-0] derived from the seed of a legume (11,16), is used as a flocculant in the filtration of mineral pulps leached with acid or cyanide for the recovery of uranium and gold (16). It is also used as a retention aid, usually in a chemically modified form (14,17). Starch and guar gum are subject to biological degradation in solution, so they are usually sold as dry powders that are dissolved immediately before use. Starch requires heating in most cases to be fully dissolved. 

Thus, at a concentration of 0.95 g Na2S /100 g solution, the solubihty of mercuric sulfide has increased to 2100 ppm. It is customary to use no greater than a 20% excess of the alkah sulfide. Because the particle size of the precipitated mercuric sulfide is so small, it is helpful to add a ferric compound such as ferric chloride or ferric sulfate to effect flocculation. Sometimes other flocculating agents (qv) may also be added, eg, starch or gum arabic. 

Dispersants andfloeculants. These are important for the control of slimes that sometimes interfere with the selectivity and increase reagent consumption. For example, soda ash, lime sodium silicate, and lignin sulfonates are used as dispersants, and starch and polyacrylamide are used as flocculants. 

Star-branched butyl rubber, 4 437-438 copolymers, 4 445-446 Starch(es), 4 703-704, 20 452-453 as blood substitute, 4 111-112 cationic, 18 114-115 in cereal grains, 26 271-274 in cocoa shell from roasted beans, 6 357t compression effects in centrifuges, 5 513 depolymerization, 4 712 in ethanol fermentation, 10 534—535 etherified, 20 563 as a flocculant, 11 627 high-amylose, 26 288 Mark-Houwink parameters for, 20 558t modified and unmodified, 12 52-53 in paper manufacture, 18 122-123 performance criteria in cosmetic use, 7 860t... 

Cationic starch in a paper mill furnish can have additional benefits beyond ash retention and strength. Properly added cationic starch can improve formation in a sheet. With an even distribution of fibers, the natural attraction of water for ionized anionic groups can be counteracted by the addition of cationic counter ions in the form of cationic starch. The flocculation effect that occurs produces much improved drainage on the paper machine. The result is increased speed on the machine yielding greater production rates and overall efficiency. To a paper mill, increased production means increased profitability. 

It is postulated that the main thermodynamic driving force for particle adsorption at the liquid-liquid interface is the osmotic repulsion between the colloidal particles and hydrophilic starch polymer molecules. This leads to an effective depletion flocculation of particles at the boundaries of the starch-rich regions. At the same time, the gelatin has a strong tendency to adsorb at the hydrophobic surface of the polystyrene particles, thereby conferring upon them some degree of thermodynamic... 

Cationic starch -as flocculating agent [FLOCCULATING AGENTS] (Vol 11)... 

Chanamai, R. and McClements, D.J. 2001. Depletion flocculation of beverage emulsions by gum arabic and modified starch. J. Food Sci. 66 457-463. 

Cationic starches to coagulate or flocculate materials during wastewater treatment... 

Cationic starch ethers are used in the paper industry to increase the cohesion and rigidity of cellulose fibres and as a flocculant for the selective separation of negatively charged particles. 

Combinations of cationic starch and anionic microparticles are useful commercial systems. Shear-sensitive flocculation occurs, allowing microscale reflocculation in the formed paper sheet, which improves dewatering and retention.63,75,76 The microparticles can be colloidal silica, aluminum silicate, poly(silicic acid) or bentonite of specific size and surface area.77 79 Cationic, anionic or polymeric aluminum-containing compounds can be additional components. A three-part coacervate system uses a high molecular weight anionic polyacrylamide, cationic starch and silica.80 Cooking cationic starch in the presence of an anionic silica hydrosol was reported to improve drainage and retention.81... 

New starch products might be derived from emulsion copolymerization with synthetic monomers and the replacement of all-synthetic polymers. Potential applications could be in flocculation, sizing, modified rheological characteristics, bonding to a wide range of substrates, film formation and in effluent treatment. A critical requirement will be the removal of hazardous residuals and Food and Drug Administration (FDA) approval for use in specific paper grades. 

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