Methods of Purifying Water

For chemical work water is purified by distillation. Pure tin vessels and pipes are often used for storing and transporting distilled water. Glass vessels are not satisfactory, because the alkaline constituents of glass slowly dissolve in water. Distilling apparatus and vessels made of fused silica are used in making very pure water. 

The impurity which is hardest to keep out of distilled water is carbon dioxide, which dissolves readily from the air. 

Ionic impurities can be effectively and cheaply removed from water by an interesting process that involves the use of giant molecules — n o QC-ular structures that are so big as to constitute visible particles. A crystal of diamond is an example of such a giant molecule (Chapter 7). Some complex inorganic crystals, such as the minerals called zeolites, are of this nature. These minerals are used to soften hard water, to remove the heavy metal ions from the water. Such a process is termed ion exchange. 

The reactions that occur when a solution containing salts passes through tank A may be written as 

That is, sodium ions and calcium ions are removed from the solution by the acidic framework, and hydrogen ions are added to the solution. The solution is changed from a salt solution (Na+, C, etc.) to an acid solution (H+, Cl, etc.). 

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The following technologies are among the most commonly used physical methods of purifying water ... 

An alternative method of purifying water is by reverse osmosis. Under normal conditions, if an aqueous solution is separated by a semi-permeable membrane from pure water, osmosis will lead to water entering the solution to dilute it. If, however, sufficient pressure is applied to the solution, i.e. a pressure in excess of its osmotic pressure, then water will flow through the membrane from the solution the process of reverse osmosis is taking place. This principle has been... 

Shevchenko MA, Taran PH, Marchenko PV. 1982. Modem methods of purifying water from pesticides. Soviet J Water Chem Technol 4 53-71. 

The Addition of Chemical Agents to Water. —This head includes several proposed methods of purifying water, which consist in the addition cf certain chemical agents to this liquid, by whioh its composition is altered. 

USP XXII (published 1990) purified water standards remain the same as USP XXI. Purified water is essentially equal to deionized water, at least chemically (not necessarily biologically). Figures 1 and 2 outline the most common methods of purified water generation. After the deionization process, water is collected in a storage tank. A distribution loop takes water from the storage tank to all use points and then back to the storage tanks. 

The use of filtration of water in modem water plants is another illustration of the adoption of one of nature s methods of purifying water. When water passes through a considerable thickness of fine... 

The following is an alternative method of purifying the crude aspirin. Dissolve the solid in about 30 ml. of hot alcohol and pour the solution into about 75 ml. of warm water if a sohd separates at this point, warm the mixture until solution is complete and then allow the clear solution to cool slowly. Beautiful needle-like crystals will separate. The yield is 13 g. The air-dried crude product may also be recrystallised from benzene or from ether - light petroleum (b.p. 40-60°). 

Treatment of a water supply is a safety factor, not a corrective measure. There are a number of ways of purifying water. In evaluating the methods of treatment available, the following points regarding water disinfectants should be eonsidered ... 

Sulfolane (TMS) [22] Main impurities are water and 3-sulfolene (decomposed to S02 and 1,3-dibutadiene at >70°C), but 2-sulfolene and isopropyl sulfolanyl ether may also be present. For fairly pure commercial products, two vacuum distillations, the second of which is from solid NaOH, can give a distillate applicable for most general purposes. The water level is <5 mM. The distillate should be stored in the dark under a nitrogen atmosphere. For a method of purifying fairly contaminated products, see Ref. [22]. 

Leidi6 1 recommends the following method of purifying iridium as obtained by the process first described. The metal in a fine state of division is heated to dull redness with twice its weight of fused sodium chloride in a current of dry chlorine. On cooling, the mass is extracted with water containing a little hydrochloric acid. The solution is filtered, raised to 50° C., and sodium nitrite added until nitrous fumes cease to be evolved. Sufficient sodium carbonate 1 Leidie, Cornet, rend., 1899, 129, 214. 

Purification by Sulphuric Acid. Hot sulphuric acid, 100 per cent concentrated, possesses the property of dissolving all three classes of the nitrotoluenes. Upon cooling such a solution, the trinitrotoluene crystallizes, but the mono- and dinitrotoluenes remain in solution. This property of Sulphuric acid forms the basis of another method of purifying TNT. The solution of the TNT in the sulphmic acid is effected in steam-heated, lead-lined vats. The liquor is then filtered and cooled. The recrystallized TNT must be washed with several changes of water to remove the acid. This method... 

Materials. The method of purifying distilled water has been described (6, 13, 14). Except for Baker and Adamson s 70% perchloric acid and Baker s inhibitor-free hydrogen peroxide, all chemicals used in stoichiometric experiments were reciystallized at least once from purified water. Buffer solutions were prepared by adding purified KH2PO4 or Na4P207 to solutions of HCIO4 in purified water. 

Hemodialysis (HD) is the method of extracorporeal drug removal most commonly used in the treatment of poisoning [1]. The apparatus consists of a blood circuit, an electronic and mechanical device (with pumps and pressure monitors), a dialyzer cartridge (containing hollow permeable fibers), and a dialysate circuit (of purified water with added electrolytes). In practice, a double-lumen catheter is first placed in a central vein. 

Giles C H and Greczek J J, A review of methods of purifying and analyzing water-soluble dyes . Textile Research Journal, 1962, 32, 506. 

Sven Palitzsch suggests the following method of purifying commercial preparations Heat 4 g. of methyl red with 30 c.c. of glacial acetic acid. After filtration, add sufficient water to produce a slight turbidity. Warm until the turbidity disappears, and then cool rapidly. If the quantity of water added is not too great, methyl red will separate out in the form of well-defined crystals. H. Wales finds it more satisfactory to recrystallize the compound from toluene. 

Among the methods of purifying protein, precipitation is the most useful and typical for both small and large scale procedures. The precipitation methods are classified into 4 types, salting-out, organic solvent precipitation, pH changing precipitation and water-soluble precipitation. The precipitation is usually carried out early and the total protein concentration should be >0.1 mg/mL. 

An obvious method of purifying salty water is by distillation. Because of the large energy requirement (AH° of vaporization for water = 44 kJ moP at 25 °C), the cost is high, about US 1 per 1000 L. The technology is practical in Middle East countries, where energy costs are low. 

The electroflotation method employs fine oxygen and hydrogen bubbles formed during electrolysis of purified water suspensions. 

Those methods of purifying vinyl acetate which involve washing of the monomer usually seem to be concerned with the removal of hydroquinone, acetic acid, and acetaldehyde. The use of aqueous solutions for these procedures actually is somewhat questionable in view of the ease of hydrolysis of vinyl acetate (comparable in rate to the hydrolysis of ethyl acetate). In aqueous alkali, the hydrolysis rate of this monomer is said to be 370 times as fast as in water [2]. Nevertheless, such procedures have been suggested and are given here for information only as a typical example of this method. 

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