Pretreatment chemicals

Pretreatment Chemicals Even though the suspended solids concentration of the slurry to be tested may be correct, it is frequently necessary to modify the sluriy in order to provide an acceptable filtration rate, washing rate, or final cake moisture content. The most common treatment, and one which may provide improvement in all three of these categories, is the addition of flocculating agents, either inorganic chemicals or natural or synthetic polymers. The main task at this point is to determine which is the most effective chemical and the quantity of chemical which should be used. 

Annual operating cost of pretreatment (chemicals) - 0,03/m of feed. 

Care must be taken here not to confuse acid cleaners with the high-strength, phosphoric acid-based chemical polishes and chemical brighteners, which are used specifically to obtain the surface finish which such materials produce. Also in the category of acid cleaners could be considered the lightweight alkali-metal phosphating cleaner-coater solutions, but a discussion on such materials is best left to specialist publications on metal pretreatment chemicals. 

All membrane exposures were carried out by soak testing under equilibrium conditions at fixed concentrations and constant pH. Pretreatment chemicals were added to buffer solutions at pH 3.0, 5.8 and 8.6. These buffers, representing an arbitrary pH range were prepared according to directions given by Perrin and Dempsey... 

The two lower pH levels were phosphate buffers whereas the 8.6 buffer consisted of a boric acid, sodium borate system. The buffers showed no reaction with pretreatment chemicals used, and had sufficient buffer capacity to maintain constant pH during experiments of long duration. 

Products Finishing. March 1982. "Cyclonic Separator Saves Pretreatment Chemicals." Pp. 88-90. 

The pretreating chemical is a surfactant, usually a cationic polyelectro-lyte. 

Mintova et al. studied deposition of zeolite A on various cellulose fibers pretreated chemically and/or mechanically [151]. It was shown that the amount of zeolite deposited was controllable by suitable fiber pretreatment with ball-milling or with diethyl ether under ultrasonic action. The reactive high-concentration hydroxyl groups on the structurally loosened celluloses seem to interact with aluminosilicate species and thus promote the formation of nuclei for zeolite crystallization. Pretreatment of natural cellulose fibers with alkali provides another simple route for anchoring preformed zeolite crystallites onto the cellulose surface. 

Other pretreatment chemical feeds These include coagulants and flocculants. What is the nature of the chemical(s) being fed, the dosage, and how is the dosage controlled ... 

The components in adhesives and pretreatment chemicals are characterized and differentiated in terms of their volatility, Table 2. 

The solid support for the liquid phase should be chemically inert and stable at the operating temperatures, and should have a large surface area. The importance of uniform particle-size to facilitate even packing has already been emphasized (see Section 11,1, p. 96). Materials in most common use as inert supports are diatomaceous earth and glass beads, both of which are often pretreated chemically to minimize adsorption effects. Preparations of diatomaceous earth are available commercially, in narrow ranges of particle size, pretreated with acid, alkali, or dichlorodimethyl-silane. A coating of silver has been used for diminishing adsorption on the inert support it probably enhances heat transfer in the columns, as well. 

MF may be used to remove these heavy metals provided pretreatment chemicals are added to precipitate the metals to particles of filterable size. The chemical pretreatment step is crucial since it will affect the performance of the membrane and the resultant sludge volume as well as the contaminant removal efficiency. Reduction/oxidation, absorption/oxidation, and/or catalytic reactions are utilized along with pH adjustment to provide the optimum precipitation. Although conventional methods of waste water treatment may use a similar pretreatment chemistry, the final solid/liquid separation by gravity settling is usually not as effective as membrane filtration. 

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