Water-softening methods

Condensate drainage devices, 70 148 Condensate polishing ion exchange in, 74 417 in steam-generating systems, 23 227 water softening method for, 26 122-123 Condensate return, in heat pipes, 73 226 Condensate return systems, 70 147-148 Condensate systems, in industrial water treatment, 26 136-137 Condensation, 9 281-282. See also Polycondensation control of VOCs by, 26 679-680 ketone, 74 570... 

Demethyl-6-deoxytetracycline, 24 600 6-Demethylchlortetracycline, 24 592 Demigras coal grade (France), 6 713t Deminerahzation water softening method, 26 122, 123... 

Limestone-gypsum roasting lithium recovery process, 15 126, 127 Lime water softening methods, 26 116-119 Liming, in beet juice purification, 23 459-462... 

Municipal solid waste (MSW), 25 864 as biomass, 3 684 cadmium in, 4 489-490 characteristics of leachates in, 25 867t characterizing, 25 866-869 collection of, 25 869-870 composition analysis for, 27 365t ferrous scrap in, 27 411 incineration of, 25 872-873 mixed, 27 367-369 preparation of, 27 367-369 processing, 27 364-371 quantity and composition of, 27 362-364 recovery rates for, 27 364, 366-367t recycled, 27 360, 362-371 toxic chemicals in, 25 875-876 Municipal waste sludge, as biomass, 3 684 Municipal water, for aquaculture, 3 198 Municipal water softening methods,... 

Silica receiving layers, in instant photography, 79 281 Silica reduction water softening method, 26 121... 

Lime-soda process a water-softening method in which lime and soda ash are added to water to remove calcium and magnesium ions by precipitation. (7.6)... 

Softening refers to removing calcium and magnesium hardness by chemicals. However, sihea, alkahnity and other constituents are also removed during lime softening. Other water softening methods include ion exchange and NF membrane separation. 

Ring-and-ball method (ASTM D36-26). In the United States, two other softening point methods ate employed cube-in-air (35) and cube-in-water (36). Cube-in-air softening point = R-and-B softening point +4 C. Cube-in-water softening point = R-and-B softening point +10 C. 

Scale prevention methods include operating at low conversion and chemical pretreatment. Acid injection to convert COs to CO2 is commonly used, but cellulosic membranes require operation at pH 4 to 7 to prevent hydrolysis. Sulfuric acid is commonly used at a dosing of 0.24 mg/L while hydrochloric acid is to be avoided to minimize corrosion. Acid addition will precipitate aluminum hydroxide. Water softening upstream of the RO By using lime and sodium zeolites will precipitate calcium and magnesium hydroxides and entrap some silica. Antisealant compounds such as sodium hexametaphosphate, EDTA, and polymers are also commonly added to encapsulate potential precipitants. Oxidant addition precipitates metal oxides for particle removal (converting soluble ferrous Fe ions to insoluble ferric Fe ions). 

NaCl(s) + X2+(aq) XCl2(aq) + 2Na+(aq) Water softened by this method contains extra sodium ions. Explain why people with hypertension (high blood pressure) should avoid drinking water softened by this type of ion exchange. 

An alternative method of water softening involves adding chemical compounds known as chelators or sequestrants. Many household and institutional cleaners as well as personal care products contain glycolic acid (HOCH2COOH), also... 

Conductivity sensors are most commonly used for safety purposes in household appliances. Presence and absence of washing liquor, detergency, and water softener can be easily measured and proper operation ensured [71]. The various applications mainly differ by their design of electrode geometry and methods for electrical measurement. Due to the close relation between ionic conductivity and water hardness, the automatic water softener in an automatic dishwasher can be controlled by a conductivity sensor [72]. To isolate the transmission of the measured value from the process controller, the conductivity sensor could incorporate an opto-electronical coupling [73]. Thus, protective insulation of the electrodes in a washer-dryer could be ensured. 

The most common method to treat hard water is through a process called ion-exchange water softening, in which the hardness ions, magnesium and caicium, are exchanged with either sodium or occasionally potassium ions. 

Ethylenediamine tetraacetic acid (EDTA) was introduced originally as a water-softener and as a textile dyeing assistant because of its ability to form very stable, water soluble complexes with many metal ions, including calcium and magnesium. The equilibria involved in chelation of metal ions by EDTA and related ligands have been exhaustively studied, notably by G. Schwarzenbach and his colleagues, and provide the basis for complexometric methods of chemical analysis. EDTA and its metal complexes have also become probably the most familiar examples of agents used in chelation therapy. 

Lime-soda process. Combination of the use of slaked lime for the removal of temporary hardness and sodium carbonate for the removal of permanent hardness constitutes the lime-soda process for softening natural waters. This method is commonly used in municipal water-treatment plants and is a cheap and yet fairly effective process. If sufficient time can be allowed, the insoluble carbonates may be permitted to settle out in settling basins, or they may be more rapidly removed by means of filters. Frequently, iron or aluminum salts are added, and these hydrolyze to form gelatinous precipitates of ferric or aluminum hydroxides. As these precipitates slowly settle, they carry with them the insoluble normal carbonates, as well as any other suspended matter such as sand, clay, or organic matter which is sometimes slow in settling otherwise. 

Ion-exchange chromatography Has a wide range of uses in the food industry, medicine and life and health sciences. This technique has been extensively used in the food industry as a quality control measure and to detect contamination with metals and organic acids. Another important use of this method is in the purification of blood products such as human albumin, growth factors and enzymes. Perhaps the most common application of this technique is the deionization of water and water softening/purification. 

The need for conunercial water softeners prompted attempts to synthesize zeolites. These were not successful, although St Claire DeviUe (1862) claimed to be able to make levyne. The early attempts at zeohte synthesis have been extensively reviewed by Merely and Ingersoll (1937). Lack of available, definitive, characterization methods makes it difficult to confirm their work. 

Slaked lime is also widely used in water treatment plants for softening hard water, which involves the removal of ions such as Ca2+ and Mg2+, ions that hamper the action of detergents. The softening method most often used in water treatment plants is the lime-soda process, in which lime (CaO) and soda ash (Na2C03) are added to the water. As we will see in more detail later in this chapter, the C032- ion from soda ash reacts with water to produce the HC03 ion. When the lime is added to the hard water, it forms slaked lime,... 

One novel method for scale control is magnetic and electrostatic technology suggested by US Department of Energy [22]. This nonchemical technology is recommended for scale and hardness control as a reliable energy saver in certain applications that can be used as a replacement for most water-softening equipment. 

The process is reversible and the bed (Na Z) can be regenerated by passing concentrated salt solution. This method of water softening yields a very soft water (0.5-1 hardness). 

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