Electrolytic production of elements

Many metals and some nonmetals are made by electrolytic methods. Hydrogen and oxygen are produced by the electrolysis of water containing an electrolyte. The alkali metals, alkaline-earth metals, magnesium, aluminum, and many other metals are manufactured either entirely or for special uses by electrochemical reduction of their compounds. 

The anode reaction involves the carbon of the electrodes, which is converted into carbon dioxide  

The cells operate at about 5 V potential difference between the electrodes. Bauxite is a mixture of aluminum minerals (AIHO2, AI(OH)3), which contains some iron oxide. It is purified by treatment with sodium hydroxide solution, which dissolves hydrated aluminum oxide, as the aluminate ion, AUOH) , but does not dissolve iron oxide  

The solution is filtered, and is then acidified with carbon dioxide, which reverses the above reaction by forming hydrogen carbonate ion, HC0.3  

The precipitated aluminum hydroxide is then dehydrated by ignition (heating to a high temperature), and the purified aluminum oxide is ready for addition to the electrolyte. 

---

Arsenic is sometimes used in the manufacture of its compounds, but more often in alloys. Small quantities, o-i to o 2 per cent, are added to lead for the production of shot (p. 196). Arsenical lead anodes are used in the electrolytic production of zinc. Alloys with antimonial lead containing 1 to 2 per cent of arsenic and sometimes other elements are used for sheaths for electric cables, etc. Arsenical coppers and bronzes are used for high temperature work such as locomotive fireboxes, etc. 

The desalination of brackish water by electrodialysis and the electrolytic production of chlorine and caustic soda are the two most popular processes using ion-exchange membranes. There are, however, many other processes such as diffusion dialysis, Donnan dialysis, electrodialytic water dissociation, etc. which are rapidly gaining commercial and technical relevance. Furthermore ion-exchange membranes are vital elements in many energy storage and conversion systems such as batteries and fuel cells. 

Production of HCl uses chlorine that otherwise could be recovered (at a cost) and so detracts from its net production. Where there is a reliable outlet for caustic, however, the best approach may be to increase electrolytic capacity, use HCl liberally in its in-plant applications, and reduce somewhat the severity of liquefaction. This improves the quality of the cell gas and allows more chlorine to appear in the tail gas, which is the raw material for HCl production. Both these changes reduce energy consumption in the liquefaction process. The gross production of elemental chlorine is preserved, all the benefits of acidification are obtained, and more caustic is available for use or sale. 

Tasaka A, Kobayashi H, Negami M, Hori M, OsadaT, Nagasaki K, Ozaki T, Nakayama H, Katamura K (1997) Effect of trace elements on the electrolytic production of NF3. J Electrochem Soc 144 192... 

The electrolytic cells used are very similar to the cells used for the production of elemental fluorine [4, 5, 7] cf. Fluorine Suppl. Vol. 2,1980, pp. 4/10. An electrolytic cell suitable for NF3 production on a pilot-plant scale having a capacity of about 25 kg of electrolyte was described by Massonne [5]. The cell and the gas separation skirt were made of Monel the cell cover and the cathode were made of mild steel. The anode was composed of nickel or carbon with an efficient surface of ca. 800 cm. Thus, a current density of 0.15 A/cm was possible at a current of 120 A. On the top of the cell cover there were holes for the release of Hg, the anode gas, inlets for HF, NH3, and Ng, and for the electrodes. The cell was electrically heated and a water-cooling system was attached to remove the heat at high current densities. 

Hevesy started as an electrochemist, since the topic of his dissertation was the production of alkali metals by melt electrolysis [12], He published several electrochemical papers on the electrolytic production of metals [13] but also on several other electrochemical topics, e.g., on the electrocapillarity [14], Nevertheless, we do not consider him as an electrochemist since he became famous as a discoverer of a new element, hafnium, and especially as a leading person in the area of radioactivity. He studied the electrochemistry of radioactive elements (Figs. 12.8,12.9, and 12.10) and used the electrochemical techniques successfully also in radiochemistry, ionic diffusion in electrolytes, and metals [15-19]. In 1913, he carried out the first radioactive tracer experiment with Friedrich Adolf Paneth in Vienna [20]. The use of tracer technique opened up new vistas also in electrochemistry. It provided a reliable method to investigate kinetics and equilibrium of electrode processes, e.g., adsorption dissolution, deposition, and underpotential deposition of metals. 

Since the production of elemental fluorine is only possible by anodic oxidation of fluoride ions, the electrolysis of HF mixed with KF as an electrolyte is the most important electrochemical application of AHF [5]. See below for additional information regarding the application of fluorine and its downstream product sulfur hexafluoride, SFg. 

A far more important application of potassium bifluoride is its use as electrolyte in the production of elemental fluorine in electrolysis cells [69]. The feed of additional HF into the reaction reduces the operating temperature of the cell to about 90 °C. The relation of HF to KF should not fall below KF-2HF. 

Salt was first electrochemicaHy decomposed by Cmickshank ia 1800, and ia 1808 Davy confirmed chlorine to be an element. In the 1830s Michael Faraday, Davy s laboratory assistant, produced definitive work on both the electrolytic generation of chlorine and its ease of Hquefaction. And ia 1851 Watt obtained the first Fnglish patent for an electrolytic chlorine production cell (11). 

It is easy to reduce anhydrous rare-earth hatides to the metal by reaction of mote electropositive metals such as calcium, lithium, sodium, potassium, and aluminum. Electrolytic reduction is an alternative in the production of the light lanthanide metals, including didymium, a Nd—Pt mixture. The rare-earth metals have a great affinity for oxygen, sulfur, nitrogen, carbon, silicon, boron, phosphoms, and hydrogen at elevated temperature and remove these elements from most other metals. 

Selective Reduction. In aqueous solution, europium(III) [22541 -18-0] reduction to europium(II) [16910-54-6] is carried out by treatment with amalgams or zinc, or by continuous electrolytic reduction. Photochemical reduction has also been proposed. When reduced to the divalent state, europium exhibits chemical properties similar to the alkaline-earth elements and can be selectively precipitated as a sulfate, for example. This process is highly selective and allows production of high purity europium fromlow europium content solutions (see Calcium compounds Strontiumand strontium compounds). 

Another approach for the production of phosphine is an aqueous electrolytic process, whereby nascent hydrogen reacts with elemental phosphoms (70). Phosphine is produced at the cathode. 

Several studies have been concerned with the chemistry of the + ni oxidation state of these elements, and the characterization of the first tantalum(iii) compounds has been claimed. The diamagnetic dimer [TaCl3(MeCN)2]2 has been prepared and used to obtain [TaClafphen)], [TaCljfbipy)], and tris-(dibenzoylmethanato)tantalum(ni). NbFa has been characterized as the product of the reaction of Nb and NbF (1 1) at 750 °C under pressure. Electrolytic reduction of niobium(v) in ethanol,formamide, and dimethylformamide can afford preparative concentrations of niobium(iii) and the new compound niobium(iii) trilactate has been obtained from ethanol. 

Bunsen is remembered chiefly for his invention of die laboratory burner umned after him. He engaged in a wide range of industrial and chemical research, including blast-furnace firing, electrolytic cells, separation of metals by electric current, spectroscopic techniques (with Kirchhoff). and production of light metals by electrical decomposition of their molten chlorides. He also discovered two elements, rubidium and cesium. 

---