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Extraction of chlorine and iodine

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Open-book: Extraction of chlorine and iodine In the membrane cell an electric current is passed through circulating brine, on one side the brine is in contact with an anode and chlorine is liberated from chlorine ions producing chlorine gas. 2Cl (aq) Cl2(g) + 2e Figure 1 (1) the reaction at the anode. Here the chlorine ions have been oxidised to form chlorine atoms and have produced free electrons. In the cathode reaction reduction occurs, the hydrogen atom in water is reduced at the electrode. A steel cathode supplies electrons to the water to liberate hydrogen gas and hydroxide ions. So the hydrogen gas produced has been oxidised and the hydroxide ions produced by reduction of water molecules. 2H2O(l) + 2e H2(g) + 2OH (aq) Figure 2 (2) the reaction at the cathode Both reactions show a redox reactions occurring, where by electrons are transferred from one species of an atom to another to become more positively charged (oxidised like the chlorine or Hydrogen). ...read more.


Also the chlorine ions also can't pass through the membrane, the sodium hydroxide solution is uncontaminated with salt and has a high purity. The membranes used are copolymers of tetrafluoroethene etc. consisting of chains of carbon atoms with fluorine atoms attached and side chains of acid groups. Chlorine is produced by the electrolysis of sodium chloride solution," brine." Thus, when sodium chloride is dissolved in water, it dissociates into sodium cations and chloride anions. The chloride ions are oxidized at the anode to form chlorine gas and water molecules are reduced at the cathode to form hydroxyl anions and hydrogen gas. The sodium ions in the solution and the hydroxyl ions produced at the cathode constitute the components of sodium hydroxide formed during the electrolysis of sodium chloride. Chlorine happens to be very abundant in the sea due to it being more reactive and therefore brine is a valuable source for the economy side of the process of extraction. ...read more.


Nevertheless the cost of extracting iodine is high due the high demands for energy and other resources involved. B Courtois discovered iodine in 1811AD. He treated the liquor obtained from the extraction of kelp (seaweed), which is now known to contain iodide salts, with sulphuric acid to produce a vapour with a violet colour. Figure 5 (4) the reaction, which led to iodine being discovered Iodine is extracted from kelp, which is obtained by burning seaweed. Salts such as sodium chloride, potassium chloride, and potassium sulphate are removed from the kelp by washing with water. This led to a large scale burning of kelp way back in the 19th century. However it later became possible to import barilla or other cheap readily available raw materials superior to kelp. It was also shown that the yield of iodine could be maximised by drying seaweed under cover and by burning it in a kiln to eliminate loss of iodine. But later in Chile sodium nitrate (Chile saltpetre), which contains a rich source of iodine, was discovered and from this, extraction methods were developed further. ...read more.

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