Starch adsorption

Calorimetric investigations of hydrous metal oxide suspensions are more scarce. A study of starch adsorption on hematite revealed that the adsorption process became less exothermic as surface coverage increased (25). This was attributed to a rearrangement of starch molecules to less favorable configurations. 

Iodide can be determined spectrophotometrically (after oxidation to iodine), either as the blue iodine-starch adsorption compound, or as coloured organic extracts containing iodine. Iodide is oxidized to iodine with nitrite or iron(III). 

Cationic starch is the major wet-end starch. The phenomena involved in starch adsorption and the selection of cationic starch need careful consideration, as do the proper preparation and application of starch. The criteria for the use of native, anionic and amphoteric starches are also considered. 

Polyelectrolytes with molecular weight between 5,000 and 10,000 are able to enter most fibre pores, but starch molecules are too large to penetrate into the fibres. So only the surface charge on the fibres is available for interaction with cationic starch. The accessible fibre surface for cationic starch (the hydrodynamic surface) is estimated to be about 6 mVg, which is only 10% of the combined hydrodynamic and internal surface area accessible to small ions [6]. Papermaking fibres become surface saturated at 16-25 kg/t starch on fibre [8]. For large polymers such as starch, adsorption increases linearly with hydrodynamic surface area. 

Starch adsorption decreases with increasing specific conductivity and is sensitive to the type of salt cation. The bivalent cations Ca " and Mg " appear to be ten times as effective as Na" in suppressing the adsorption of cationic polymers. 

Acknowledgements Particular reference is made to the following authors J.J.W. Swinkels for information on native starches and fundamental structure and chemistry, H.G.M. van de Steeg for her dissertation on starch adsorption, P.H. Brower for the development of starch application in the wet-end. Professor T. Lindstorm for fundamental wet-end chemistry. 

Figure 10.33. Schematic illustrating the mechanism of starch adsorption through binuclear complexation with Fe sites on the surface of haematite (after ref. (6)). ( Reprinted from International Journal of Mineral Processing, 58, S. Mathur, P. Singh and B. M. Moudgil, Advances in selective flocculation technology for solid-solid separations, Page 218, Copyright (2000), with permission from Elsevier Science )...

A large number of columns are available for SEC, but this part of the system needs the most careful selection. All packing materials so far evaluated show different degrees of starch adsorption. This can... 

Enzymatic properties of the respective CGTases such as optimum pH, pH stability, optimum temperature, thermal stability, behavior on starch adsorption, molecular weight by SDS-PAGE and isoelectric point were compared. The result of the starch adsorption is shown in Table I (9). 

Repeat the above precipitation of lead chromate. No need to use a weighed dried crucible. After filtration and washing the precipitate, place it in a 250 cm beaker, add 1 1 HNO3 to dissolve the chromate followed by 20 cm of 10% KI solution, stir to liberate iodine, add water and titrate with standardised 0.05 M thiosulphate solution until the colour of iodine fades. Then add 2 cm of freshly prepared starch solution until the dark iodine/starch adsorption complex disappears, leaving a green Cr(Ill) solution. Alternatively, filter through a GF filter paper, transfer it quantitatively and carefully, after washing, to a conical flask and continue as above. 

Place each mixture in a shaking thermostat at 25"C (or a large 2-4 dm beaker containing water at room temperature) as quickly as possible after mixing and note the time on a stopwatch when the blue colour of iodine/starch adsorption complex appears. Plot the time against l/[A][B]. 

Filter aids should have low bulk density to minimize settling and aid good distribution on a filter-medium surface that may not be horizontal. They should also be porous and capable of forming a porous cake to minimize flow resistance, and they must be chemically inert to the filtrate. These characteristics are all found in the two most popular commercial filter aids diatomaceous silica (also called diatomite, or diatomaceous earth), which is an almost pure silica prepared from deposits of diatom skeletons and expanded perhte, particles of puffed lava that are principally aluminum alkali siheate. Cellulosic fibers (ground wood pulp) are sometimes used when siliceous materials cannot be used but are much more compressible. The use of other less effective aids (e.g., carbon and gypsum) may be justified in special cases. Sometimes a combination or carbon and diatomaceous silica permits adsorption in addition to filter-aid performance. Various other materials, such as salt, fine sand, starch, and precipitated calcium carbonate, are employed in specific industries where they represent either waste material or inexpensive alternatives to conventional filter aids. 

The performance of several Sephacryl gel combinations is illustrated by results achieved for glucans from different types of starch granules. The applied Sephacryl gels of Pharmacia Biotech (15) are cross-linked copolymers of allyl dextran and N,N -methylene bisacrylamide. The hydrophilic matrix minimizes nonspecific adsorption and thus guarantees maximum recovery. Depending on the pore size of the beads, ranging between 25 and 75 im in diameter, aqueous dissolved biopolymers up to particle diameters of 400 nm can be handled. 

Starches can be separated into two major components, amylose and amylopectin, which exist in different proportions in various plants. Amylose, which is a straight-chain compound and is abundant in potato starch, gives a blue colour with iodine and the chain assumes a spiral form. Amylopectin, which has a branched-chain structure, forms a red-purple product, probably by adsorption. 

Ridomil, with which the treatment with starch solution was not carried out, is said to yield brown chromatogram zones on a pale yellow background [14]. Hence, it may be assumed that this detection is based not on the iodine azide reaction but on the physical adsorption and enrichment of iodine in the lipophilic chromatogram zones (cf. Iodine Reagents ). 

In addition to these three treatments, there are several alternative treatment technologies applicable to the treatment of common metals wastes. These technologies include electrolytic recovery, electrodialysis, reverse osmosis, peat adsorption, insoluble starch xanthate treatment, sulfide precipitation, flotation, and membrane filtration.1516... 

Figure 4.15 Selective adsorption synthesis of a-cyclodextrin from starch applying a hatch process using a sequence of stirred-tank reactor, heat exchanger modules and adsorption step...

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