Cationic pretreatment

Surface charge Anionic (limits use of cationic pretreatment coagulants) Neutral (no limitations on pretreatment coagulants)... 

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. 

Provision of pretreatment The initial fill volume and MU supply is almost always pretreated in some manner. Because of the large volume of water in these systems, even low-hardness waters can produce sufficient quantities of calcium carbonate scale to severely impede heat transfer thus, for MTHW pretreatment, the use of ion-exchange softeners is the norm. For HTHW, some form of demineralization such as reverse osmosis (RO) or deionization by cation-anion exchange is typically preferred. 

Where hardness removal is required, the simplest pretreatment method for smaller, lower pressure boiler plants (below 200-300 psig) is to use a cation-exchange softener. This removes the calcium and magnesium at source and converts the bulk of temporary hardness salts into sodium bicarbonate (NaHC03), which decomposes to form sodium carbonate (soda ash) but does not scale under normal boiler operating conditions. 

The N2-physisorption characterisation results show that, no significant variations (less than 5%) are observed on the BET surface area, the total pore volume and the micropore volume of the different Pd-ZSM-5 catalysts, when the preparation method, the pretreatment gas, the charge-balancing cations and the palladium loading are modified. This result suggests that the ZSM-5 texture is stable with respect to the preparative parameter variations and that the observed activity differences are not related to any... 

The efficacy of CE separation depends considerably on the type of capillary. Fused-silica capillaries without pretreatment are used most frequently. Its outside is coated with a polymer layer to make it flexible and to lessen the occurrence of breakage. The polymer coating has to be dissolved with acid or burned away at the detection point. Capillaries with an optically transparent outer coating have also found application in CE. The objectives of the development of chemically modified capillary walls were the elimination of electro-osmotic flow and the prevention of adsorption on the inner wall of the capillary. Another method to prevent the adsorption of cationic analyses and proteins is the use of mobile phase additives. The modification of the pH of the buffer, the addition of salts, amines and polymers have all been successfully employed for the improvement of separation. 

In summary, the overall successful effect has been assigned to the fact that any pretreatment of either the electrode surface (use of promoters, use of specific carbon electrodes, with the eventual generation of functional COO groups) or the solutions (addition of multicharged cationic species, proper choice of pH) creates at the bare electroinactive surface more and more specific microscopic active sites able to favour the exchange of electrons with proteins.10 This means that, in the absence of proper pretreatments, the electrode surface does not possess specific sites... 

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