GB822990A - Improvements relating to processes for the evaporation or distillation of sea water,brackish waters and like aqueous solutions - Google Patents

Abstract

<PICT:0822990/III/1> A process for the evaporation of sea water, estuarine water and aqueous solutions in which the formation of calcium carbonate and magnesium hydroxide containing scales is reduced or prevented by adjustment of the hydrogen ion concentration of the solution prior to or during evaporation comprises adding to the solution hydrogen ions which have been generated in the anode compartment of an electric cell operating in conjunction with the evaporator from a solution containing a sufficient concentration of ions such as sulphate, nitrate, or phosphate ions to result in principally hydroxyl ions being discharged at the anode of the cell with the liberation of oxygen and/or in the promotion of an oxidation reaction at the anode with the consequent generation of hydrogen ions. The cell preferably has 3 compartments and electrodes made from magnetite or platinum or graphite. Preferably the feed is pretreated with steam to remove air and carbon dioxide. In a preferred form of the invention, the solution of sodium chloride from which the magnesium and other metals having insoluble hydroxides have been precipitated by prior mixing with catholyte liquor is passed slowly through a centre compartment 21 from inlet 11 to outlet 14, a dilute solution of sulphuric acid being placed in the anode compartment 20 and oxygen being allowed to escape through line 13. Wash water is introduced into the cathode compartment 22 through line 12 and hydrogen and dilute caustic soda are removed through outlet 15. On passing a current, hydroxyl ions are discharged at the anode and hydrogen ions accumulate in the compartment 20. The current is carried across the membrane 5 by the migration of hydrogen ions into the centre compartment 21. At membrane 6 current is carried predominantly by the migration of sodium ions to the cathode compartment 22. In the central compartment there is a net gain in hydrogen ions.