Electrolysis electrorefining

Electroplating Creation of an adherent metal layer on some substrate by electrolysis. Electrorefining Increasing the purity of a metal by electrolysis. 

Other Meta.Is, Although most cobalt is refined by chemical methods, some is electrorefined. Lead and tin are fire refined, but a better removal of impurities is achieved by electrorefining. Very high purity lead is produced by an electrochemical process using a fluosiUcate electrolyte. A sulfate bath is used for purifying tin. Silver is produced mainly by electrorefining in a nitrate electrolyte, and gold is refined by chemical methods or by electrolysis in a chloride bath. 

Electrolytic Processes. The electrolytic procedures for both electrowinning and electrorefining beryUium have primarily involved electrolysis of the beryUium chloride [7787-47-5], BeCl2, in a variety of fused-salt baths. The chloride readUy hydrolyzes making the use of dry methods mandatory for its preparation (see Beryllium compounds). For both ecological and economic reasons there is no electrolyticaUy derived beryUium avaUable in the market-place. 

Besides copper passing into the solution as ions, the total concentration of the solution in respect of S04 ions (not discharged) and Cu2+ ions (copper is depositing on the cathode) remains constant. The electrolysis merely transfers copper from the anode to the cathode. With a platinum or a carbon anode, it is found that the color of the solution fades as copper is deposited, whereas with copper electrodes, the color does not change. The two situations, in fact, represent respectively the electrowinning and the electrorefining processes introduced later in the section on process classification. 

With the progress of electrolysis the concentration of aluminum (and of other base impurities) increases as a result of this the contamination of the cathode deposit also increases. A stage may be reached when the contamination exceeds acceptable limits, thereby calling for a premature termination of electrolysis. It is for this reason that it is desirable to purify and recycle the electrolyte wherever possible so that electrorefining could be conducted for extended periods, without having to contend with the problem of excessive contamination. 

Methods have been developed (75) to prepare actinide metals directly from actinide oxides or oxycompounds by electrolysis in molten salts (e.g., LiCl/KCl eutectic). Indeed, the purest U, Np, and Pu metals have been obtained (19, 24) by oxidation of the less pure metal into a molten salt and reduction to purer metal (electrorefining. Section III,D). 

If an actinide metal is available in sufficient quantity to form a rod or an electrode, very efficient methods of purification are applicable electrorefining, zone melting, and electrotransport. Thorium, uranium, neptunium, and plutonium metals have been refined by electrolysis in molten salts (84). An electrode of impure metal is dissolved anodically in a molten salt bath (e.g., in LiCl/KCl eutectic) the metal is deposited electrochemically on the cathode as a solid or a liquid (19, 24). To date, the purest Np and Pu metals have been produced by this technique. 

Most metals found in nature exist as ores in combination with other elements such as oxygen and sulfur. Electrolysis can be used to separate metals from their ores and remove impurities from the metals. The general process is known as electrorefining. Other electrolytic processes are used to obtain a number of important chemicals. 

Electrorefining purification of a metal using electrolysis Electrostatic charge at rest Element see Chemical Element Elementary Particle collectively the smallest units of matter, electrons, protons, quarks, and so on. 

Electroplating movie The purification of a metal by means of electrolysis is called electrorefining. For... 

Closely related to electrorefining is electroplating, the coating of one metal on the surface of another using electrolysis. For example, steel automobile bumpers are plated with chromium to protect them from corrosion, and silver-plating is commonly used to make items of fine table service. The object to be plated is carefully cleaned and then set up as the cathode of an electrolytic cell that contains a solution of ions of the metal to be deposited. 

Electrolysis, the process of using an electric current to bring about chemical change, is employed to produce sodium, chlorine, sodium hydroxide, and aluminum (Hall-Heroult process) and is used in electrorefining and electroplating. 

T Flotation Roasting T Electrolysis or chemical treatment T Electrorefining or distillation... 

Nickel, used to make stainless steel, can be purified by electrorefining. The electrolysis cell has an impure nickel anode, a pure nickel cathode, and an aqueous solution of nickel sulfate as the electrolyte. How many kilograms of nickel can be refined in 8.00 h if the current passed through the cell is held constant at 52.5 A ... 

Pure copper for use in electrical wiring is obtained by electrorefining. How many hours are required to transfer 7.50 kg of copper from an impure copper anode to a pure copper cathode if the current passed through the electrolysis cell is held constant at 40.0 A ... 

Metals that have been produced by pyrometallurgical methods, such as copper, silver, nickel, and tin, are too impure for many purposes, and electrorefining is used to purify them further. Crude metallic copper is cast into slabs, which are used as anodes in electrolysis cells that contain a solution of CUSO4 in aqueous H2SO4. Thin sheets of pure copper serve as cathodes, and the copper that dissolves at the anodes is deposited in purer form on the cathodes (Fig. 17.18). Impurities that are more easily oxidized than copper, such as nickel, dissolve along with the copper but remain in solution elements that are less easily oxidized, such as silver and gold, do not dissolve but fall away from the anode as a metallic slime. Periodically, the anode slime and the solution are removed and further processed for recovery of the elements they contain. 

The metal deposition rate from aqueous solutions can be expressed as a current density (A m-2 of electrode surface) as the rate is linked to the current density by Faraday s law (1). In modern copper electrorefining and electrowinning, the current density is 300-350 Am-2, while in zinc operations it is greater, 450-500Am-2 or more. According to Faraday s law, enormous amounts of electricity are needed for the tens or hundreds of kilotons of metal produced in a typical electrolysis plant per year. 

The major technical factors in electrorefining are cathode purity, production rate, and specific energy consumption. These factors are influenced primarily by anode quality, electrolyte conditions, and cathode current density. The electrolysis is performed in a solution of copper sulfate and sulfuric acid with a nominal composition of40-45 g L-1 copper and 160-200 g L-1 sulfuric acid at 60-66 °C with a current... 

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