Cobalt electrorefining

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. 

Electrorefining in aqueous media is extensively applied for the production of copper, nickel, lead, tin, cobalt, silver, and gold, while in molten salt electrolytes it is practically limited to aluminum. 

In electrorefining, the metal to be refined is used as the anode whic dissolves in the electrolyte and is deposited as electrolytic-grade mett at the cathode. The impurities present in the anode remain on it, fall oi to the bottom of the cell as slime, or go into solution but are prevente. from moving toward the cathode by precipitation with some chemics reagent such as another metal added to the electrolyte. The buildup c metallic impurities that are dissolved but not deposited at the cathode i reduced by circulation of fresh electrolyte through the cells. Electrorefinin techniques are used in producing gold, silver, copper, nickel, cobalt, lead tin, antimony, bismuth, indium, and mercury. 

After solution purification, cobalt can be deposited as Co(II) or Co(III) hydroxide. The cobalt solutions are often too low in cobalt for direct electrowinning. In this case, cobalt hydroxide is precipitated, thickened, and redissolved to cobalt tankhouse electrolyte and then electrowon [77]. The cobalt hydroxide has been reduced in electric furnaces to an alloy with 80% Co, 18% Fe, and 0.8% Ni, cast to anodes, and electrorefined. The process was done in Flybinette cells, and the solution contained 60-120 g L 1 Co, pH was 3.3-48, and the temperature was 60 °C. The current density was 160-240 A m-2, cell voltage was 1.2-1.8 V, and the current efficiency was 95%. This process is not used anymore because of the lack of... 

At the time of writing this paper, three plant trials are currently underway with promising early signs. The sites selected for the trial are spread between Australia and the United States of America in the production of copper in electrowinning and electrorefining plants. Following the completion of these trials in early 2013, it is expected that commercial units will be available for sale by the end of Ql, 2013. All trials to date have been for copper with the next step to include commercial trials in nickel, cobalt and zinc operations. 

Many metals are now electrorefined but perhaps the most important are copper, tin, lead, nickel, cobalt, aluminium, silver and gold. 

It can be seen from the data in Table 4.3 that in order to obtain pure metals at the cathode, the current density is always low. On the other hand, with the exception of tin, the current efficiencies are good and the celt voltages can be low. fn electrorefining the cathode reaction is the reverse of that at the anode and therefore, in the ideal case, the celt voltage is only required to drive the current through the electrolyte. In practice, there may also be overpotemials associated with the anode and cathode reactions, and in the cases of nickel and cobalt these are considerable because the couples are very irreversible. 

Industrial liquors and effluents from electroplating or electrorefining industries often have considerably elevated cobalt and cadmium levels, which can be monitored routinely by the method described in this work for one week periods, without operator intervention or maintenance. The concept of using an exchange reaction with Zn(hedtc)2, instead of in situ complex formation with an excess of dithiocarbamate ligand or ex situ complex formation in the reaction chamber, offers a considerable improvement in reproducibility, stability, cost of reagents and safety. 

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