Electrolysis of seawater

Chlorine is the most abnndant of the halogens having a concentration of 19.87 parts per thousand (ppt) by weight in seawater and an average of 0.17 ppt in Earth s crust. It is produced commercially by electrolysis of seawater and brines. Sodinm chloride (NaCl), or common table salt, can be obtained from seaside evaporation pools or mined from undergronnd deposits. 

Baboian et alP examined the anodic reaction of electrolysis of seawater as a means of preventing fouling. They used current density in excess of 50 mA cm . ... 

Tschaikowski obtained a British patent for developing a method to prevent rusting and fouling of ship s bottoms by continuous formation of molecular hydrogen and caustic soda formed by the electrolysis of seawater. The author mentions a current density of 6.5/iAcm in the electrochemical cell formed by graphite anode and the underwater part of the vessel, cathode, and at a cell potential of 4.0 V. ... 

Littauer and Jenningsexamined the cathodic electrolysis of seawater as a means of fouling prevention at various current densities, and obtained partial protection. However, at current densities greater than 1 mAcm , calcareous deposits formed on the electrode. 

R. Baboian, G. S. Haynes, B. S. Ryskiewich, and B. J. Freedman, Biofouling Prevention of Flat Surfaces Using in situ Electrolysis of Seawater, Mater. Perform. 19(10), 42-46 (1980). 

Oh BS, Oh SG, Hwang YY et al (2010) Formation of hazardous inorganic by-products during electrolysis of seawater as disinfection process for desalination. STOTEN 408 5958-5965... 

Another approach towards reducing global atmospheric CO2 attempts to isolate the surplus CO2 from the biosphere, by permanently fixing it as an insoluble mineral onto the sea bottom. This method is based on the concept that insoluble CaCOs can be formed by the direct electrolysis of seawater, which yields the hydroxide ions reacting according to Equation 1.2. 

The basic problems are in finding a cheap source of hydrogen and an effective means of storing it. One possibility is to use hydrogen made by the electrolysis of seawater. This possibility requires an abundant energy source, however—perhaps nuclear fusion energy if it can be developed. Another alternative is the thermal decomposition of water. The problem here is that even at 2000 °C, water is only about 1% decomposed. What is needed is a thermochemical cycle, a series of reactions that have as their overall reaction ... 

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. 

Fluorine comes from the minerals fluorspar, CaF, cryolite, Na3AlF6 and the fluorapatites, Ca,F(P04)3. The free element is prepared from HF and KF by electrolysis, but the HF and KF needed for the electrolysis are prepared in the laboratory. Chlorine primarily comes from the mineral rock salt, NaCl. The pure element is obtained by electrolysis of liquid NaCl. Bromine is found in seawater and brine wells as the Br ion it ts also found as a component of saline deposits the pure element is obtained by oxidation of Br (aq) by Cl,(g). Iodine is found in seawater, seaweed, and brine wells as the I" ion the pure element is obtained by oxidation of I (aq) by Cl,(g). 

The alkali metals (Group 1A) and the alkaline earth metals (Group 2A) are not found free in nature because they are so easily oxidized. Their primary sources are seawater, brines of their soluble salts and deposits of sea salt. The metals are obtained from the electrolysis of their molten salts. 

Chlorine is produced commercially by the electrolysis of a liquid solution of sodium chloride (or seawater), through which process an electric current is passed though the solution (electrolyte). 

In the process used by Norsk Hydro, magnesium hydroxide extracted from seawater with the aid of calcined dolomite is mixed with charcoal and magnesium chloride brine and is heated to 1000-1200°C in the presence of chlorine produced during subsequent electrolysis of magnesium chloride. The main reactions are [266]... 

Chlorine occurs in Nature mainly as sodium chloride in seawater and in various inland salt lakes, and as solid deposits originating presumably from the prehistoric evaporation of salt lakes. Chlorine is prepared industrially mainly by electrolysis of brine ... 

Seawater is evaporated by concentrating the seawater in the first evaporation pool transporting to the next evaporation zone, in which calcium sulfate precipitates out and finally crystallizing sodium chloride in a further evaporation zone. The residual brine is rich in potassium and magnesium salts. The salt obtained is too impure to be used in electrolysis. Washing in special units is sufficient to increase the sodium chloride content to > 99%. I m- of seawater yields ca. 23 kg of sodium chloride. 

The final step in the production of magnesium from seawater is the electrolysis of molten magnesium chloride, in which the overall reaction is... 

Derivation (1) Electrolysis of fused magnesium chloride (Dow seawater process) (2) reduction of magnesium oxide with ferrosilicon (Pidgeon process). 

The principal source of the other halides is seawater (natural brines). Chlorine is liberated by the electrolysis of aqueous NaCl (the chloialkali process) ... 

Similar problems arise in connection with the electrolysis of dilute NaCl solutions (seawater). NaOCl produced by electrolysis is used to kill marine life in cooling systems in industrial plants using seawater. Interestingly, amorphous Pd-Ir-P alloys have lower activity in dilute solutions, and Pd-Rh-P samples prove to be more suitable under these conditions (102,103). In order to further increase their activity, surface activation by the Zn deposition-heat treatment-Zn leaching method was used (63). 

Extraction of Mg by electrolysis of fused MgCl2 is also important and is applied to the extraction of the metal from seawater. The first step is precipitation (see Table... 

Electrolysis of molten MgCL is the final production step in the isolation of magnesium from seawater. Assuming that 35.6 g of Mg metal forms,... 

The effect of the cost of the ion exchange membrane on the total cost of electrodialysis or electrolysis is large because the membrane is relatively expensive. The lifetime of the membrane depends on the purpose and conditions of electrodialysis or electrolysis. A membrane for the electrodialytic concentration of seawater to produce sodium chloride has a lifetime of over 10 years, and that in the chlor-alkali membrane process, which is operated at ten times or more higher current density than that of seawater concentration, is over 5 years. However, in applications for food industries, the lifetime of the membrane is relatively short due to periodical sanitary cleaning of the electrodialyzer by acid or alkali solution, and sometimes oxidizing agents. 

The metal is now principally obtained in the U.S. by electrolysis of fused magnesium chloride derived from brines, wells, and seawater. 

Sodium occurs widely as NaCl in seawater and as deposits of halite in dried up lakes etc. (2.6% of the lithosphere). The element is obtained commercially by electrolysis of NaCl melts in which the melting point is reduced by the addition of calcium chloride sodium is produced at the iron cathode (the Downs cell). The metal is extremely reactive. It reacts vigorously with the halogens, and also with water to give hydrogen and sodium hydroxide. The chemistry of sodium is very similar to that of the other members of group 1. 

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