Flocculants, starch derivatives

The optimum pH for flocculation is about 6.5 to 7.5 for aluminum salts and about 8.5 for iron salts. If the natural alkali content of the untreated water is insufficient to neutralize the acid formed, alkali has to be added (e.g. calcium hydroxide or sodium hydroxide). In addition flocculation aids such as poly(acrylamide) or starch derivatives may be added (not in the case of potable water production). When aluminum sulfate Al2(S04)3 I8H2O is used 10 to 30 g/m- is added. The very fine hydroxide flakes which precipitate are positively charged and adsorb the negatively charged colloidal organic materials and clay particles. 

Silylated starch derivatives were tested with limited success as flocculants in the production of beet sugar.1873... 

Haack V, Heinze T, Oehneyer G (2002) Starch derivatives of high degree of functionalization, 8 - synthesis and flocculation behaviour of cationic starch polyelectrolytes. Macromol Mater Eng 287 495... 

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. 

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. 

The various industrial uses of starch depend in large measure on the properties of the individual fractions. A starch paste may function in two ways it may be used for its flocculating, its adsorptive, or its gel qualities or it may act as a sol or protective colloid. These properties derive directly from the A and B fractions, respectively. In many instances, it appears that only one action is required, and that the presence of the other starch component may even be detrimental. Thus, Hixon and Sprague have reported superior qualities for waxy maize starch in those applications for which stability and protective colloid action are requisite. 

Protective colloids n. Materials such as gums, starches and proteins, polyacrylates and cellulose and cellulose derivatives, which are effective agents for protecting charged colloidal particles in aqueous media against flocculation. 

Natural and synthetic polyelectrolytes are used in causing small suspended particles to flocculate to larger settleable particles. Among the natural compounds so used are starch and cellulose derivatives, proteinaceous materials, and gums composed of polysaccharides. More recently, selected synthetic polymers, including neutral polymers and both anionic and cationic polyelectrolytes that are effective flocculants, have come into use. 

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