Brine purification sulfate

With this wide variety of sources, one would expect to find great variations in the type and abundance of impurities in salt. Still, there are a number of useful generalizations. Table 7.6 shows that calcium, magnesium, and sulfate ions are the other major components of seawater and therefore the major impurities in most salts [63], and the removal or eontrol of these constituents is a primary objective of the brine purification process. The most widespread impurity in NaCl deposits is CaS04. Magnesium compounds, and to a lesser extent iron compounds, also are present in most natural salts. Oxides of silicon and aluminum are also found, as well as traces of other metals and sometimes anions such as iodide. The importance of these impurities depends greatly on the type of cell in use, and the methods used for purification of brine reflect all the above factors. 

The first step in brine purification is chemical treatment to remove certain impurities. The elements of hardness (calcium and magnesium) must be removed, along with iron and heavy metals. This is done by precipitation, adding a source of carbonate ion to remove calcium and a source of hydroxide ion to remove the other metals. Sulfate ion also can be removed by precipitation, using either calcium or barium ion. Precipitation processes cannot usefully be considered in isolation. The nature of the solids formed in this way determines how they will behave in the later processes that are designed for their physical removal. The subsections that follow therefore describe in a general way the flow behavior and settling rates of precipitated particles. Later sections of the chapter cover the details of sedimentation and filtration of the solids. 

Brine Purification. In mercury cells, traces of heavy metals in the brine give rise to dangerous operating conditions (see p. 32), as does the presence of magnesium and to a lesser extent calcium (521. In membrane cells, divalent ions such as Ca or Mg are harmful to the membrane. The circulating brine must be rigorously purified to avoid any buildup of these substances to undesirable levels [7]. Calcium is usually precipitated as the carbonate with sodium carbonate magnesium and iron, as hydroxides with sodium hydroxide and sulfate, as barium sulfate. 

Recovery Process. The process for making sodium sulfate [7757-82-6] is different at each faciUty extracting it from brine. One step common to all facihties is a cooling step to form Glauber s salt followed by a purification and recrystallization step to form anhydrous sodium sulfate. 

Upon cooling to room temperature, a gray precipitate forms and the reaction is quenched with 220 mL of saturated, aqueous ammonium chloride. The resulting mixture is poured into a 1-L separatory funnel and extracted with 220 mL of diethyl ether. The organic fraction is washed two times with 100 mL of water, and once with 100 mL of brine, dried over magnesium sulfate, filtered, and concentrated under reduced pressure to provide 44.1 g of crude product as a pale yellow oil. Purification of this material by bulb-to-bulb distillation (140-145°C, 0.5 mm) (Note 11) into a chilled (-78°C) receiving flask yields 41.0 g (92%) of 2 as a clear, colorless oil (Note 12). 

The mixture of alcohols is placed in a 1000-mL round-bottomed flask, dissolved in 300 mL of ether, and cooled to 0°C. To this solution is added via an addition funnel over a 30-min period a mixture of sodium dichromate dihydrate (27.5 g, 0.092 mol), 100 mL of water, and 10.2 mL of coned sulfuric acid. The mixture is stirred at 0°C for 1 hr, warmed to room temperature where stirring is maintained overnight, diluted with 200 mL of water, and poured into a separatory funnel. The layers are separated and the aqueous phase is extracted with ether (3 x 200 mL). The combined organic layers are washed with saturated sodium bicarbonate solution (200 mL) and brine (200 mL), dried over anhydrous magnesium sulfate, filtered, and concentrated by rotary evaporation to give 16.8-17.8 g (61-65%) of verbenone (Note 7). Final purification is achieved by distillation of the oil through a 5-in Vigreux column at reduced pressure (dry ice-acetone cooled receiver) 13.1 g (47%), bp 108-110°C (5 mm) (Note 8). 

The mixture was extracted with ethyl acetate (twice) and the combined organic layers were washed with brine and dried over sodium sulfate. Evaporation of solvent gave a crude mixture of epoxides. After purification by silica gel flash column chromatography (hexane/ethyl acetate 100/1-50/1), the corresponding a, S-epoxy ester 3a was obtained (212.7mg, 1.11 mmol, 89%) as a colourless oil. The enantiomeric excess of 3a was determined by chiral stationary-phase HPLC analysis Daicel Chiralpak AD-H, /-PrOH/ hexane 2/98, flow rate 0.4mL min-1, r 31.5 min [(25,5/ )-isomer] and 38.0 min [(2/ ,35)-isomer], detection at 254 nm. [oc]r> —158.8° [c= 1.06, CHCI3 (99% ee)]. 

To a stirred solution of (+)-6-ethyl-5-methyl-2-(4-sulfotolyl-l,3-dimethyl-but-l-ene)-yl-3,6-dihydro-2H-pyran (54.4 mg, 0.15( mmol) in dry Et20 (1 ml) cooled to 0°C was added dropwise a solution of nBuLi (1.5 M in hexane, 0.18 mmol). The yellow solution was stirred at 0°C for 10 min, then at -42°C for 15 min. Dry hexane (0.5 ml) was added, and a solution of the methyl (8E,10S,llS,12S)-2,3-di-O-benzyl-l,4-dideoxy-ip-[ll-methyl-12-formylcyclopropylethenyl]-D-glucoheptopyranuronate (60.0 mg, 0.125 mmol) in Et20 (0.5 ml) was added dropwise. The reaction mixture was stirred at -42°C for 2 h, then quenched with ammonium chloride, and extracted with EtOAc several times. The combined organic extracts were washed with brine, dried over sodium sulfate, and the solvent removed in vacuum. The residue was chromatographed over silica gel (hexane-EtOAc, 8 2) to give 53.7 mg (51%) of a mixture of diastereomers. The mixture was used in the next reaction without further purification. 

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