Electrorefining of metals

In the field of electrowinning and electrorefining of metals, titanium has an advantage as a cathode, upon which copper particularly can be deposited with finely balanced adhesion that allows the electrodeposited metal to strip easily when required. Titanium anodes are also being employed as a replacement for lead or graphite in the production of electrolytic manganese dioxide. 

As a matter of fact, this is the basis for the electrorefining of metals. The impure metal electrode (say, Cu) is used as the positive electrode, and a piece of pure Cu metal is used as the negative electrode the solution is CuS04. The composition of the solution is so designed, and the applied voltage so chosen, that the impurities stay in solution or precipitate out, and only copper plates out at the negative electrode ... 

Cook, G. M. Twenty-five years progress in electrowinning and electrorefining of metals. J. Electrochem. Soc., 125 49C, 1978. 

The electrolytic production of materials is one of the oldest branches of electrochemical technology. Electrowinning and electrorefining of metals, electroplating, and electrolytic gas production are but a few examples. While still at an evolutionary stage, electroprocessing of materials presents enormous potential opportunities and could well have a significant commercial impact. A few examples are described below and are not intended to be all inclusive. 

Production of Aluminum Electrorefining of Metals Metal Plating Electrolysis of Sodium Chloride... 

The need for a different approach to overcome the environmental constraints of pyrometallurgical processes led to the CX-EWS technology, which is the direct electrorefining of metallic lead (grids and poles) obtained from the CX breaker. It is based on fluoborate technology, and when introduced into primary and secondary lead operations, can eliminate all the drawbacks present in lead production. 

The current distribution on a macroprofile is very important in technical metal electrodeposition. In electroplating, the current distribution determines the local variations in the thickness of the coating. In electrowinning and electrorefining of metals, a non-homogeneous current distribution can cause a short circuit with the counter electrode and the comer weakness effect in electroforming. This is very important in the three-dimensional electrodes, as well as in some storage batteries. In all the cited cases, a uniform current density distribution over the macroprofile is required. 

The major application areas of electrochemical reactors In metal recovery are electrowinning of metals from ores and primary sources, electrorefining of metals from aqueous solutions or molten salts and electrochemical pollution control or detoxificatlon/removal of metals from Industrial effluents and other liquid wastes. Although cell designs for electrorefining of metals are usually quite specific, many cell designs used for both electrowinning and... 

Electrolytic cells are used for technical processes such as electrolytic syntheses, electrorefining of metals, and electroplating. 

Electrorefining in aqueous solution is used for purifying metals and for electroplating, for example, for corrosion protection by zinc coating of steel. Electrorefining of metals is only possible for those metals with a positive standard potential (Ag, Au, Cu, Table 6.19.1) or if H2 formation at the cathode (which competes with deposition of the metal) is hindered by a high overpotential (Zn, Ni). For electrochemically very non-noble metals such as aluminum with a very negative standard potential, fused salt electrolysis is needed (Section 6.19.4.2). 

Electrorefining of metals in aqueous solution for purifying metals and for electroplating is only possible for those metals with a positive standard potential (Ag, Au, Cu) or if H2 formation at the cathode is hindered by a high overpotential (Zn, Ni). 

Illustration 3.2 Electrorefining of Metals, Concentration Polarization and the Limiting Current Density... 

The term used at head of this section needs definition. Let it include in this context all those commercial processes which use electrical current for the production of materials. The chlor-alkali industry clearly comes under this heading, as does electrowinning and electrorefining of metals. Production of fluorine and fluorinated organic compounds will also be dealt with here. Other uses of electrode processes, such as electrochemical machining and electroforming are not included in this section. 

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