Nickel electrorefining

The energy consumption in electrowinning depends on the thermodynamical voltage, electrode polarization, and electrolyte resistivity. The conductivity of nickel electrowinning electrolytes (catholyte) at 60 °C is typically 120mScm 1 and for nickel electrorefining electrolytes at 60 °C it is about 200 mS cm-1 [47]. The sulfate electrolyte conductivity can be estimated using Eq. (26)... 

Fite refining adjusts the sulfur and oxygen levels in the bhster copper and removes impurities as slag or volatile products. The fire-refined copper is sold for fabrication into end products, provided that the chemistry permits product specifications to be met. Some impurities, such as selenium and nickel, are not sufficiently removed by fire refining. If these impurities are detrimental to fabrication or end use, the copper must be electrorefined. Other impurities, such as gold, silver, selenium, and tellurium, are only recovered via electrorefining. Virtually all copper is electrorefined. 

Calcining, sintering or smelting of nickel copper matte or acid leaching or electrorefining of roasted matte Coal soots, coal tar, pitch and coal tar fumes Hardwood dusts... 

Electrorefining has been used for the purification of many common as well as reactive metals. It has been seen that the emf or the potential required for such a process is usually small because the energy needed for the reduction of the ionic species at the cathode is almost equal to that released by the oxidation of the crude metal at the anode. Some metals, such as copper, nickel, lead, silver, gold, etc., are refined by using aqueous electrolytes whereas molten salt electrolytes are necessary for the refining of reactive metals such as aluminum,... 

Alternatively, nickel sulfide is roasted to nickel oxide, which then is reduced to crude nickel and is electrorefined as above. 

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 ... 

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. 

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. 

Copper electrorefining plays a major role in the production and recycling of copper. In the production of copper, copper-bearing sulfide concentrates are first smelted to copper matte. The molten matte is oxidized to blister copper by a Peirce-Smith converter and the blister copper is fire refined and cast to copper anodes. Blister copper contains about 99% copper and impurities such as arsenic, bismuth, iron, nickel, lead, antimony, selenium, tellurium, and precious metals. It is cast into flat anodes, most often on a rotating horizontal wheel. The mold shape includes lugs by which the anodes are... 

World nickel metal production in 2002 was 678000 tons [39]. Hydrometallurgy has typically been applied to the treatment of nickel-copper mattes, anode nickel, and reduced laterite ore. The sulfide concentrates are usually oxidized by roasting and then smelted to copper-iron-nickel sulfide matte (75-80% Cu-Ni), which is refined or used directly to make M onel metal. Cathode nickel can be produced from a variety of electrolytes, including chloride, sulfate, or a mixed chloride-sulfate. The former two are acid systems used in leaching and electrowinning. Mixed chloride-sulfate electrolytes are used for electrorefining the nickel sulfide matte from the traditional matte-smelting operations. 

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... 

Electrorefining Nickel Metal Anodes In the refining of nickel metal anodes, the principal reaction at the anode is the dissolution of nickel metal as nickel ions. The principal cathodic reaction is the reduction of nickel ions from solution. Nickel anodes are made by reducing nickel oxide with coke at temperatures up to 1550 °C and casting in molds. The practice is designed to obtain anodes with the desired strength and crystal size. 

Fig. 19 Hybinette cell for the electrorefining of nickel. 1 - the cell, 2 - anode, 3 - cathode,...

Insoluble impurities fall to the floor of the cell as anode slime. Despite the derogatory name, this material contains precious metals such as gold, silver, and platinum. Anode slime from the electrorefining of nickel at Sudbury, Ontario, is a significant source of platinum and palladium as byproducts ( 0.34 g Pt and 0.36 g Pd per metric ton of ore), whereas deposits in the Bushveld complex (Transvaal, South Africa) are so rich in platinum-group metals (Ru, Os, Rh, Ir, Pd, Pt) that the associated Co, Ni, and Cu recovered are considered to be by-products of the lucrative platinum production (4.78 g Pt and 2.03 g Pd per metric ton of ore). ... 

In both the electrorefining (ER) and electrowinning (EW) processes, the primary product is a pure cathode sheet. Although similar processes, ER and EW differ only in the source of the metal ions that are reduced at the cathode. In electrorefining, impure, solid metal anodes are suspended in the electrolytic cell and oxidized to metal ions by the current. The metal ions are, in turn, reduced at the cathode. The net result is that metal ions are formed at the anode and removed at the cathode. Nickel, copper, and other metals can be cast in the impure form as anodes, which serve as the metal ion source during electrorefining. 

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