Electrowinning processes

The electrowinning process developed by Ginatta (34) has been purchased by M.A. Industries (Atlanta, Georgia), and the process is available for licensing (qv). MA Industries have also developed a process to upgrade the polypropylene chips from the battery breaking operation to pellets for use by the plastics industry. Additionally, East Penn (Lyons Station, Pennsylvania), has developed a solvent-extraction process to purify the spent acid from lead—acid batteries and use the purified acid in battery production (35). 

Fig. 6. Roast-Leach electrowinning process for the production of zinc metal from a sulfide concentrate.

Copper. Copper is economically extracted by smelting of a chalcopyrite concentrate. A copper electrowinning process was developed commercially in 1912 for the treatment of lean ores. It is also suitable for treatment of copper oxide or sulfate obtained by roasting of the concentrate. 

For operations producing 30,000 tons or less of copper annuaHy, hydrometaHurgy offers an alternative to smelting that avoids problems associated with sulfur dioxide recovery and environmental controls. Techniques include the Anaconda oxygen—ammonia leaching process, the Lake Shore roast-leach-electrowin process, and ferric chloride leaching processes for the treatment of copper sulfides. AH the facHities that use these techniques encountered serious technical problems and were shut down within a few years of start-up. 

ELECTROCHEMICAL DETERMINATION OF GUAR IN COPPER ELECTROWINING PROCESS... 

In the case of molten salts, the functional electrolytes are generally oxides or halides. As examples of the use of oxides, mention may be made of the electrowinning processes for aluminum, tantalum, molybdenum, tungsten, and some of the rare earth metals. The appropriate oxides, dissolved in halide melts, act as the sources of the respective metals intended to be deposited cathodically. Halides are used as functional electrolytes for almost all other metals. In principle, all halides can be used, but in practice only fluorides and chlorides are used. Bromides and iodides are thermally unstable and are relatively expensive. Fluorides are ideally suited because of their stability and low volatility, their drawbacks pertain to the difficulty in obtaining them in forms free from oxygenated ions, and to their poor solubility in water. It is a truism that aqueous solubility makes the post-electrolysis separation of the electrodeposit from the electrolyte easy because the electrolyte can be leached away. The drawback associated with fluorides due to their poor solubility can, to a large extent, be overcome by using double fluorides instead of simple fluorides. Chlorides are widely used in electrodeposition because they are readily available in a pure form and... 

A number of electrolytic processes are used for the industrial production of metals. Some metals such as zinc, copper, manganese, gallium, chromium, etc. are electrowon from aqueous baths. Another common electrolytic process used is molten salt electrolysis. The most important application of molten salt electrolysis till now has been in the electrowinning of metals. Today aluminum, magnesium, lithium, sodium, calcium, boron, cerium, tantalum, and mischmetal are produced in tonnage quantities by molten salt electrolysis. As a representative example, the electrowinning process for aluminum is taken up. 

In the aluminum electrowinning process a phenomenon called the anode effect is normally encountered when the alumina content in the electrolyte falls below 2%. The anode gets partially covered with a gas blanket and as a consequence, sparking occurs and the cell voltage fluctuates considerably due to frequent breaking and reestablishment of local contact between the anode and the electrolyte. A heavy current passes through the anode area... 

The electrowinning processes essentially use anodes that do not dissolve anodically. In electrorefining, however, an impure metal is anodically dissolved as metal ions and subsequently these ions are reduced at the cathode to yield the pure metal the cell reactions are ... 

In comparison to electrorefining, the electrowinning process of copper, when using a copper sulfate-sulfuric acid electrolyte, presents an interesting situation. In the electro-... 

To establish the economic feasibility of producing wire bar-grade copper by a combined SX-EW (EW = electrowinning) process... 

The electrowinning process is connected with higher power consumption but, on the other hand, the electrolytically produced zinc has higher purity. Therefore, further investigations are in progress. The main factors that must be considered in electrowinning process are (1) the electrochemical properties of the cathode materials, (2) the effect of ionic impurities in the electrolyte, and (3) the cohesion strength between the deposited metal and its substrate. 

The liquor from the first reaction is used as a pregnant liquor to be fed to electrowinning cells. An important electrical current benefit is realized in that it is only necessary to convert cuprous copper (Cu+) to copper rather than the conventional electrowinning process where cupric copper ( - ) is converted to copper. In an alternative process developed by Cymet (6), the cuprous chloride is crystallized from this liquor by cooling. The cuprous chloride is later reduced to copper in a furnace using hydrogen. 

In tills method a known copper deposit would be injected in several locations with a solution of dilute sulfuric acid, This acid would percolate through Ihe veins of the ore-bearing rock (usually copper oxidel. The copper would go into solution as copper sulfide and be pumped to the surface by way of several recovery wells. At the surface the copper would be plated onto cathodes (electrowinning process). It is proposed that the dilute solution, when free oF copper, could be returned and circulated up lo several limes. An automatic analytical system would maintain the required strength of the acid solution. Proponents elaim that the cost of Ihe system would be less per ton of copper produced and would increase miner safely. One factor that must he carefully tested is the possible percolation of acid solution into nearby groundwater. 

Speciation of metal ions and complex ions in ionic liquid solution prior to electrodeposition is also clearly an important issue in understanding and developing electrowinning processes. Little is known about the stoichiometry and structure of... 

Table 4 shows examples of the energy consumption of some electrorefining and electrowinning processes [5, p. 163],... 

The copper electrowinning process requires concentrated solutions to improve mass transport and increase the solution conductivity. The pregnant leach solutions from leaching are too dilute and too impure for the direct production of high-purity cathodes. Electrowinning from these solutions would give impure, dendritic deposits. Solvent extraction provides the means for producing pure,... 

Fig. 18 General flowsheet of copper leaching, solvent extraction, and electrowinning process. 

The first electrolytic nickel refinery plant, treating nickel metal anodes, was built by Hybinette in Kristiansand, Norway, in 1910, and this plant was acquired by Falconbridge in 1928. INCO developed electrorefining of nickel sulfide matte anodes in the 1950s. In a typical electrowinning process, the raw material is first smelted to a matte and then leached in a sulfate or chloride solution. The sulfur of the raw material is oxidized to insoluble elemental sulfur or soluble sulfate. The nickel contents of the mattes treated hydrometallurgically are in the... 

The electrowinning processes use nickel sulfide matte, which is dissolved. To prevent the deposition of impurities, the... 

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