Precipitates impurities

Brine Preparation. Sodium chloride solutions are occasionally available naturally but they are more often obtained by solution mining of salt deposits. Raw, near-saturated brines containing low concentrations of impurities such as magnesium and calcium salts, are purified to prevent scaling of processing equipment and contamination of the product. Some brines also contain significant amounts of sulfates (see Chemicals FROMBRINe). Brine is usually purified by a lime—soda treatment where the magnesium is precipitated with milk of lime (Ca(OH)2) and the calcium precipitated with soda ash. After separation from the precipitated impurities, the brine is sent to the ammonia absorbers. 

Aeration must be avoided since it can oxidize and resolubiUze the cemented (precipitated) impurities. Filter presses are used after each step and the cakes are leached to recover various values. For example, cadmium is dissolved, recemented with zinc, and recovered on site either electrolyticaHy or by distillation. A copper residue of 25—60% copper is sold for recovery elsewhere. The other impurities cannot be recovered economically with the exception of cobalt in some plants. 

Modem manufacturing processes quench the roast by continuous discharge into the leach water held in tanks equipped with agitators. At this point the pH of the leach solution is adjusted to between 8 and 9 to precipitate aluminum and siHcon. The modem leaching operations are very rapid because no or htde lime is used. After separation of the ore residue and precipitated impurities using rotary vacuum filters, the cmde Hquid sodium chromate may need to be treated to remove vanadium, if present, in a separate operation. The ore residue and precipitants are either recycled or treated to reduce hexavalent chromium to Cr(III) before disposal. 

The crude extract needs to be further purified for HPLC analysis. Direct injection of the crude extract into the HPLC would clog the frit and analytical column with precipitated impurities (i.e., proteins). 

Unless the reagent has been recently purchased it may contain substantial amounts of toluene-p-sulphonic acid. The most satisfactory procedure for the purification of the chloride involves dissolving it in the minimum amount of chloroform (about 2.5 ml per g) and diluting with 5 volumes of light petroleum (b.p. 40-60 °C), which precipitates impurities. The filtered solution is treated with decolourising charcoal, filtered and concentrated to small volume when colourless crystals of the pure reagent, m.p. 68 °C, are obtained these should be washed with chilled light petroleum (b.p. 40-60 °C). 

In production of chlorine by the diaphragm cell process (Fig. 1), salt is dissolved in water and stored as a saturated solution. Chemicals are added to adjust the pH and to precipitate impurities from both the water and the... 

If air or gases are drawn through filter cake, evaporation of solvent may precipitate impurities onto crystals. 

One part by wei t of KgPtCls is suspended in water and treated with a concentrated solution of 10 parts by weight of NaNOg. The mixture is then heated with stirring. The yellow KgPtClg first dissolves giving a dark solution, and then nitric oxide is liberated as fine bubbles while the solution clears to a pale greenish yellow. When no further gas evolves the solution is cooled and, if necessary, the precipitated impurities are filtered off. 

Purification upon prolonged standing the material develops impurities of p-toluenesulfonic acid and HCl. Tosyl chloride is purified by dissolving 10 g in a minimum volume of CHCI3 (ca. 25 mL), filtering, and diluting with five volumes (ca. 125 mL) of petroleum ether (bp 30-60 °C) to precipitate impurities (mostly tosic acid, mp 101-104 °C). The solution is filtered, clarified with charcoal, and concentrated to ca. 40 mL by evaporation. Further evaporation to a very small volume gives 7 g of pure white crystals (mp 67.5-68.5 °C). ... 

An example of bulk defects are voids where there are simply no structural atoms. Another example consists of impurities that can cluster together to form small regions of a different phase such as precipitates. Impurities and precipitates also play an important role in the corrosion resistance of metals. 

The important supplies to the cells from outside the electrolysis area are brine and electrical energy. The most basic operations in brine treatment are those of precipitating impurities and removing the resulting suspended particles. New filters are available that give improved performance (Section 9.4.4.3) and offer the promise of one-step removal of suspended solids. Section 17.3.1 describes these. 

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