Chlorinity, seawater

Sedimentary basins and oil flelds. Despite their similarity with seawater chlorine-isotopic composition, enough variability between fluids exists locally (and the precision of the analytical method is fine enough) to distinguish the sources of chloride contributing to... 

Figure 16.30. (a) Absorbance spectra of coastal seawater chlorinated at varying chlorine doses, (b) Differential absorbance spectra of coastal seawater chlorinated at varying reaction chlorine doses. Reaction time 168h (Fabbricino and Korshin, 2005). 

Experiences with seawater chlorination on copper alloys and stainless steels Working party report on marine corrosion of stainless steels chlorination... 

Occurrence. Magnesium bromide [7789-48-2] MgBr2, is found in seawater, some mineral springs, natural brines, inland seas and lakes such as the Dead Sea and the Great Salt Lake, and salt deposits such as the Stassfurt deposits. In seawater, it is the primary source of bromine (qv). By the action of chlorine gas upon seawater or seawater bitterns, bromine is formed (see Chemicals frombrine). 

Preparation and Manufacture. Magnesium chloride can be produced in large quantities from (/) camalhte or the end brines of the potash industry (see Potassium compounds) (2) magnesium hydroxide precipitated from seawater (7) by chlorination of magnesium oxide from various sources in the presence of carbon or carbonaceous materials and (4) as a by-product in the manufacture of titanium (see Titaniumand titanium alloys). 

Chlorine. Chlorine, the material used to make PVC, is the 20th most common element on earth, found virtually everywhere, in rocks, oceans, plants, animals, and human bodies. It is also essential to human life. Eree chlorine is produced geothermally within the earth, and occasionally finds its way to the earth s surface in its elemental state. More usually, however, it reacts with water vapor to form hydrochloric acid. Hydrochloric acid reacts quickly with other elements and compounds, forming stable compounds (usually chloride) such as sodium chloride (common salt), magnesium chloride, and potassium chloride, all found in large quantities in seawater. 

The chlorinity. Cl (%e), is determined by the titration of seawater with AgNO. It was defined as the chlorine equivalent of the total hahde concentration ia g kg seawater it is now defined as the mass ia grams of Ag necessary to precipitate the halogens (Cl and Br ) ia 328.5233 g of seawater. It has been adequately demonstrated that the relative composition of the major (greater than 1 m kg seawater) components of seawater is nearly constant. By measuriag one constituent of seawater, the composition of other components can be characterized. The constituent normally selected is the chlorinity. Cl... 

Saline Water for Municipal Distribution. Only a very small amount of potable water is actually taken by people or animals internally, and it is quite uneconomical to desalinate all municipally piped water, although all distributed water must be clear and free of harmful bacteria. Most of the water piped to cities and industry is used for Htfle more than to carry off small amounts of waste materials or waste heat. In many locations, seawater can be used for most of this service. If chlorination is requited, it can be accompHshed by direct electrolysis of the dissolved salt (21). Arrayed against the obvious advantage of economy, there are several disadvantages use of seawater requites different detergents sewage treatment plants must be modified the usual metal pipes, pumps, condensers, coolers, meters, and other equipment corrode more readily chlorination could cause environmental poUution and dual water systems must be built and maintained. 

Another possible modification is the use of seawater as the regenerant. Even though it contains calcium and magnesium, but only 2.7 wt % NaCl, it sometimes can be purified by coagulation, filtration, and chlorination less expensively than salt can be purchased. The lower concentration reduces the regeneration efficiency by 40—50%. 

Reaction with Other Halides. Bromide ion is oxidi2ed by chlorine to bromine. This is the basic reaction in the production of bromine from seawater, brines, or bitterns. 

Bromine occurs ia the form of bromide ia seawater and ia natural brine deposits (see Chemicals frombrine). Chloride is also present. In all current methods of bromine production, chlorine, which has a higher reduction potential than bromine, is used to oxidize bromide to bromine. 

Calcium chloride is found in the marine environment. The elemental composition of seawater is 400 ppm calcium, 18,900 ppm chlorine, and many organisms and aquatic species are tolerant of these concentrations. Toxicity arises either from the invasion of freshwater in otherwise saltwater environments or possible toxic doses of calcium chloride from spills, surface mnoff, or underground percolation into typically freshwater streams or aquifers. Various agencies have guidelines for calcium and chloride in potable water (41). The European Economic Community (EEC) is the only agency to have a minimum specification for calcium in softened water. 

Water Tests. In colorfastness to water, ISO 10S-E01, the test specimen is placed in contact with the chosen adjacent fabrics, immersed in water, and placed wet between glass plates and left for 4 h at 37°C. After drying, the effect on the test specimen and stain on adjacents are assessed. The test, colorfastness to seawater, ISO 10S-E02, is the same as EOl but uses 30 g/L anhydrous sodium chloride solution instead of water. To test for colorfastness to chlorinated seawater/swimming baths water, ISO 10S-E03, the specimen is immersed in sodium hypochlorite solution containing either 100, 50, or 20 mg of active chlorine per Hter at pH 7.5 for 1 h at 27°C, rinsed, dried, and assessed. 

Aromatic polyamide (aramid) membranes are a copolymer of 1-3 diaminobenzene with 1-3 and 1-4 benzenedicarboxylic acid chlorides. They are usually made into fine hollow fibers, 93 [Lm outer diameter by 43 [Lm inner diameter. Some flat sheet is made for spirals. These membranes are widely used for seawater desalination and to some extent for other process applications. The hollow fibers are capable of veiy high-pressure operation and have considerably greater hydrolytic resistance than does CA. Their packing density in hoUow-fiber form makes them veiy susceptible to colloidal fouling (a permeator 8 inches in diameter contains 3 M fibers), and they have essentially no resistance to chlorine. 

Chlorine is desirable as a bulk pretreatment biocide for inlet water, but its subsequent removal upstream of the membrane is absolutely necessary ana difficult. NaHSO,3 is a common additive to dechlorinate before membranes. It is customarily added at 3-5 mg/1, an excess over the stoichiometric requirement. NH3 is sometimes added to convert the chlorine to chloramine, a much less damaging biocide. Heavy metals present in seawater seem to amplify the damaging effects of chlorine and other oxidants. 

For the solubility in seawater of oxygen, nitrogen and carbon dioxide at various temperatures and chlorinities refer to Tables 21.21 and 21.22. 

If all the oxygen produced were to combine with the carbon the maximum theoretical wastage rate would be of the order of 1 kg A" y However, in practice the rate is usually of the order of 0-2 kg A y and in coke breeze may be as low as 0-05 kg A" y ". In seawater, where chlorine is the predominant gas produced, to which carbon is immune, any oxygen formed will be quickly removed and the corrosion rate may be very low. 

The performance of graphite in seawater, where chlorine is the principal gas evolved, is considerably better than in fresh water where oxygen is produced. Graphite is immune to chlorine and has a long history in the chemical industry in this and similar applications . 

Platinum Platinum-coated titanium is the most important anode material for impressed-current cathodic protection in seawater. In electrolysis cells, platinum is attacked if the current waveform varies, if oxygen and chlorine are evolved simultaneously, or if some organic substances are present Nevertheless, platinised titanium is employed in tinplate production in Japan s. Although ruthenium dioxide is the most usual coating for dimensionally stable anodes, platinum/iridium, also deposited by thermal decomposition of a metallo-organic paint, is used in sodium chlorate manufacture. Platinum/ruthenium, applied by an immersion process, is recommended for the cathodes of membrane electrolysis cells. ... 

Titanium has an unusually high ratio of strength to weight. It is considerably stronger than either aluminum or steel, two metals with which it competes (for special purposes). Its density (4.5 g/cm3) is intermediate between that of Al (2.7 g/cm3) and that of Fe (7.9 g/cm3). Titanium is extremely resistant to corrosion by air, soil, seawater, and even such reactive chemicals as nitric acid and chlorine gas. Like aluminum, it forms a thin, tightly adherent oxide layer that protects the metal from further attack. 

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