Matte anodes

Figure 6.28 Electroextraction of nickel from nickel matte anodes (principally based on Thompson Refinery Plant practice).

Several processes for the extraction of copper by electrometallurgical methods have been devised. The Marchese patent2 aimed at the decomposition of copper matte and deposition of the copper simultaneously in a sulphuric-acid electrolyte with a copper-matte anode and a copper cathode. In Siemens and Halske s patent3 the copper of the ore was oxidized to the cupric state by an acid solution of ferric sulphate, and the copper deposited electrolytically in a second vessel with a diaphragm separating the cathode and the anode. Neither process has been commercially successful. 

Fig. 9. Cutaway view of Inco s matte anode electrowinning tank. Boldt and Queneau (B25).

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... 

The current efficiency at the matte anodes is only about 95%, so that a deficiency of nickel and an increase in acidity develop in the electrolyte. The chemical treatment of the latter must therefore correct for this as well as remove impurities. The electrolyte at pH 1.5 is first treated with H2S, which precipitates copper and arsenic(IH) sulphides copper is recovered from the precipitate. The electrolyte then flows to a series of agitated aeration tanks and finely ground anode scrap is added. Metallic nickel dissolves and the sulphide undergoes the reaction... 

In the anodizing stage electrolytic reactions produce a uniform aluminum oxide layer across the aluminum surface. This anodic film is transparent and porous. The underlying matte or bright surface can be seen. After anodizing, the aluminum part can be colored or sealed. 

The matte can be treated in different ways, depending on the copper content and on the desired product. In some cases, the copper content of the Bessemer matte is low enough to allow the material to be cast directly into sulfide anodes for electrolytic refining. Usually it is necessary first to separate the nickel and copper sulfides. The copper—nickel matte is cooled slowly for ca 4 d to faciUtate grain growth of mineral crystals of copper sulfide, nickel—sulfide, and a nickel—copper alloy. This matte is pulverized, the nickel and copper sulfides isolated by flotation, and the alloy extracted magnetically and refined electrolyticaHy. The nickel sulfide is cast into anodes for electrolysis or, more commonly, is roasted to nickel oxide and further reduced to metal for refining by electrolysis or by the carbonyl method. Alternatively, the nickel sulfide may be roasted to provide a nickel oxide sinter that is suitable for direct use by the steel industry. 

Pyrometa.llurgica.1 Processes. Nickel oxide ores are processed by pyrometaHurgical or hydrometaHurgical methods. In the former, oxide ores are smelted with a sulfiding material, eg, gypsum, to produce an iron—nickel matte that can be treated similarly to the matte obtained from sulfide ores. The iron—nickel matte may be processed in a converter to eliminate iron. The nickel matte then can be cast into anodes and refined electrolyticaHy. 

As already noted (p. 1073), the platinum metals are all isolated from concentrates obtained as anode slimes or converter matte. In the classical process, after ruthenium and osmium have been removed, excess oxidants are removed by boiling, iridium is precipitated as (NH4)2lrCl6 and rhodium as [Rh(NH3)5Cl]Cl2. In alternative solvent extraction processes (p. 1147) [IrClg] " is extracted in organic amines leaving rhodium in the aqueous phase to be precipitated, again, as [Rh(NH3)5Cl]Cl2. In all cases ignition in H2... 

A crack count of 30-80 cracks/mm is desirable to maintain good corrosion resistance. Crack counts of less than 30 cracks/mm should be avoided, since they can penetrate into the nickel layer as a result of mechanical stress, whilst large cracks may also have a notch effect. Measurements made on chromium deposits from baths which produce microcracked coatings indicate that the stress decreases with time from the appearance of the first cracks . It is more difficult to produce the required microcracked pattern on matt or semi-bright nickel than on fully bright deposits. The crack network does not form very well in low-current-density areas, so that the auxiliary anodes may be necessary. 

The metals are obtained from the metallic phase of the sulphide matte or the anode slime from electrolytic refining of nickel. In the traditional process for the platinum metals, their separation was facilitated by their solubility in aqua regia and convertibility into PdCl - or PtCl - salts. Nowadays, substantial amounts are obtained using solvent extraction. 

Aqueous electrolysis using matte as soluble anode... 

Hybinette A process for extracting nickel from sulfide ores. The nickel ore that occurs in Canada is a mixture of the sulfides of nickel, copper, and iron. Several methods have been used to separate these metals. In the Hybinette process, the ore is first smelted in a blast furnace, yielding a nickel-copper matte (i.e., a mixture of their lower sulfides). This is roasted to remove sulfur and leached with dilute sulfuric acid to remove copper. The resulting crude nickel oxide is used as the anode of an electrochemical cell. The nickel deposits on the cathode, which is contained in a cloth bag. Precious metals collect in the anode slime. The process was invented by N. V Hybinette in 1904 and operated at the Kristiansand refinery, Norway, from 1910. 

INCO [International Nickel Company] An electrolytic process for extracting nickel from nickel sulfide matte. The matte is melted and cast into anodes. Electrolysis with an aqueous electrolyte containing sulfate, chloride and boric acid dissolves the nickel and leaves the sulfur, together with precious metals, as an anode slime. Operated in Manitoba by International Nickel Company of Canada. 

Copper-nickel matte obtained in this stage is allowed to cool slowly over a few days to separate mineral crystals of copper sulfide, nickel sulfide and nickel-copper alloy. The cool matte is pulverized to isolate sulfides of nickel and copper by froth flotation. Nickel-copper alloy is extracted by magnetic separation. Nickel metal is obtained from the nickel sulfide by electrolysis using crude nickel sulfide cast into anodes and nickel-plated stainless steel cathodes. 

Native copper ore is crushed, concentrated by washing with water, smelted, and cast into bars. Oxide and carbonate ores are treated with carhon in a smeller. Sulfide ore treatment is complex, hut. in brief, consists of smelling to a matte of cuprous sulfide, ferrous sulfide, and silica, which molten matte is treated in a converter by the addition of lime and air is forced under pressure through the mass. The products are blister copper, ferrous calcium silicate slag, and SO . Refining is conducted by electrolysis, and the anode mud is treated to obtain the gold and silver. See Fig. I. 

Polished, matt, and brushed finishes may be obtained and, in addition, other decorative effects from embossed, oxidized, and etched foils. The surface may be lacquered, anodized, or chromium-plated to prevent oxidation, and can be coloured to simulate other metals like brass and bronze. 

The Savelsberg-Wannschaff Process2 consists in treating with chlorine an intimate mixture of nickel matte and water or calcium chloride solution. The matte employed contains some 65 to 70 per cent, of nickel and some iron, but is, commercially speaking, free from copper. The solution thus obtained contains iron and nickel in the form of their chlorides. Sulphuric acid produced by the oxidation of the sulphur is thrown out as insoluble calcium sulphate. The liquid is filtered free from suspended matters, heated to about 65° C., and fresh powdered ore is added. A blast of air is now blown through, whereby the iron is oxidised and precipitated as insoluble ferric hydroxide. The clear solution containing nickel chloride is separated by filtration and electrolysed between graphite anodes and sheet metal cathodes, at a cathodic current density of 1-0 to 1-2 amperes persq. dem., and with a potential difference of from 4-0 to 4-5 volts. 

Browne s Process,3 which is made use of by the Canadian Copper Company, consists in desulphurising copper-nickel-iron matte, whereby a product, containing 54 per cent, of copper and 43 per cent, of nickel, together ivith small quantities of iron and sulphur, results. Half of this is cast into anodes and the remainder is treated with chlorine in brine, whereby the metals are obtained in solution as chlorides. On electrolysing, copper is deposited on to cathodes of the sa,me metal until the proportion of copper to nickel is reduced to 1 in 80. Addition... 

The early work on electropolishing silicon was done in largely nonaqueous solutions because it was believed that silicon could not be polished in aqueous HF solutions. Uhlir (7), for example, anodized silicon in 24 to 48% by weight aqueous solutions of HF at current densities up to 500 ma/cm and obtained only a matte black, brown, or red deposit. Later Turner (29) showed that silicon could be electropolished in aqueous HF solutions if a critical current density was exceeded. 

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