The Electrolysis of Aqueous Sodium Sulfate

In the electrolysis of aqueous sodium sulfate using inert electrodes, we observe the following. 

Gaseous H2 is produced at one electrode. The solution becomes basic around that electrode. 

The net result is the electrolysis of water. This occurs because H2O is both more readily reduced than Na and more readily oxidized than S04 .The ions of Na2S04 conduct the current through the solution, but they take no part in the reaction. 

---

Section 23.4 Electrometallurgy is tire use of electrolytic methods to prepare or purify a metallic element. Sodium is prepared by electrolysis of molten NaCl in a Downs cell. Aluminum is obtained in the Hall process by electrolysis of AI2O3 in molten cryolite (NagAlFg). Copper is purified by electrolysis of aqueous copper sulfate solution using anodes composed of impure copper. 

Electrolysis of aqueous solutions of the following using inert electrodes sodium chloride, copper(n) sulfate, sodium sulfate and sodium hydroxide. 

The following example deals with the electrolysis of an aqueous solution of sodium sulfate (Na2S04). 

The question arises as to whether the formation of organometallic compounds during electrolysis of aqueous solutions of acrylonitrile is not due to cyanoethylation of hydrides formed initially at the electrode. In Table 5 data on the electrochemical reduction of tin, sulfur, selenium, and tellurium in aqueous solutions of sodium sulfate with and without acrylonitrile are compared [40]. 

The reduction of lactones of polyhydroxy carboxylic acids to the corresponding aldoses with sodium amalgam can be successfully achieved by electroreduction at a mercury cathode, provided that the catholyte contains salts of amalgam-forming metals. The electroreduction of the lactones of n-ribonic and n-arabinonic acids to n-ribose and n-arabinose, respectively, is performed at a mercury cathode, with sodium, potassium, or zinc sulfate (or their mixtures) as the catholyte, and platinum gauze as the anode, immersed in aqueous, 15% sulfuric acid. The electrolyzer compartments are separated by a diaphragm, and the electrolysis is performed with intensive stirring of the catholyte, which is maintained at a temperature of +5 to +12° and at a constant pH (adjusted by additions of dilute sulfuric acid). Yields of monosaccharide are increased by addition of boric acid to the reaction mixture. 

Reactions 7-Sl through 7-54 occur in the absorber. It is desirable that reaction 7-54 be maximized in order to capture as much SO2 as possible per unit of regenerated sodium hydroxide. Reaction 7-53 is an undesirable but unavoidable side reaction. However, oxidation of sulrite to sulfate is not as s ous in Ibis process as in many other aqueous systems since it does not interfere with the process chemistry or result in a loss of absorbent. Reactions 7-55 and 7-56 represent the SO2 release stq>. Both reactions result in the formation of sulfur dioxide gas and sodium sulfate in solution. The final reaction, 7-57, depicts the overall result of electrolysis. Sodium hydroxide and hydrogen are produced at the cathode, while sulfuric acid and oxygen are produced at the anode. The sodium hydroxide is recycled to the absorber, and the sulfuric acid is used to liberate SO2 from the rich solution. Sulfur dioxide represents the principal product of the process. 

Although silver is not treated by solvent extraction in any of the flow sheets, silver is recovered from aqueous solution in several other situations. For these processes, Cytec developed reagents with donor sulfur atoms to extract this soft element. For example, tri-isobutylphosphine sulfide (CYANEX 47IX) extracts silver from chloride, nitrate, or sulfate media selectively from copper, lead, and zinc [32]. The silver is recovered from the loaded organic phase by stripping with sodium thiosulfate, and the metal recovered by cementation or electrolysis. Silver can also be extracted from chloride solution by a dithiophosphinic acid (CYANEX 301) [33]. 

---