Copper electrolytic purification

SPILL CLEAN-UP use water spray to cool and disperse vapors may be removed from process-ventilated exhaust air from copper electrolytic purification cells by counter-current wet scrubbing remove all ignition sources. 

Use of on-stream XRE analysis for monitoring liquid process streams has been reported for a number of applications including measurement of Fe, Cu, Co, Ni and Mo from five different points in a solution purification process of a cobalt refinery [28] analysis of Cu, As and S in copper electrolyte purification solutions [29] control of a solvent extraction process for La and Nd [30, 31] continuous monitoring of catalyst elements (Mn, Co and Br) in terephthalic acid process solutions [32] and measurement of various elements (particularly sulfur) in petroleum product and refinery streams [33, 34]. 

The precipitated copper from this reaction is an important constituent of the slime that collects at the bottom of the electrolytic cells. The accumulation of copper as well as of impurities such as nickel, arsenic, antimony, and bismuth is controlled by periodic bleed-off and treatment in the electrolyte purification section. 

Other references in Table in discuss applications in precipitation of metal.compounds, gaseous reduction of metals from solution, equilibrium of copper in solvent extraction, electrolyte purification and solid-liquid equilibria in concentrated salt solutions. The papers by Cognet and Renon (25) and Vega and Funk (59) stand out as recent studies in which rational approaches have been used for estimating ionic activity coefficients. In general, however, few of the studies are based on the more recent developments in ionic activity coefficients. 

Preparation. Industrially, silver is usually a by-product of processes of extraction of other metals such as copper, lead, zinc. The so-called anode slimes from the electrolytic purification of copper contain silver and the involved process is often finished by an electrolysis of a nitrate solution containing silver. 

Polonium may be purified by various processes. Such purification methods include precipitation of polonium as sulfide and then decomposing the sulfide at elevated temperatures spontaneous decomposition of polonium onto a nickel or copper surface and electrolysis of nitric acid solutions of polonium-bismuth mixture. In electrolytic purification polonium is electrodeposited onto a platinum, gold, nickel, or carbon electrode. 

Selenium and tellurium are much less abundant than sulfur and no ores are rich in these elements. They are recovered from the anode slime deposited in the electrolytic purification of copper (having been present as impurities in the copper sulfide ores), as by-products in other sulfide ore processing, and in sulfuric acid manufacture. 

Q Outline the chemical steps of a process for separating the rare metals Ru, Os, Rh, Ir, Pd, Pt, Ag and Au present in the wastes ( anode slimes ) formed during the electrolytic purification of nickel or copper. 

Electrolytic purification of smelted copper removes contaminants which adversely affect electrical conductivity, malleability, and other properties. It also permits recovery of the precious metal content of the fire-refined product. 

TABLE 13.2 Standard Reduction Potentials for a Series of Elements of Importance to Electrolytic Purification of Copper"... 

Gkrld is also recovered from the anode sludge from electrolytic purification of copper Section 21-7. Gktld is so rare that it is also obtained from very low-grade ores by the cyanide process. Air is bubbled through an agitated slurry of the ore mixed with a solution of NaCN. This causes slow oxidation of the metal and the formation of a soluble complex compound. 

Only weakly electropositive metals can, obviously, be purified by electrorefining, since the concerned metal must not react with water and must be easily oxidized (at anode) and reduced (at cathode) relative to hydrogen. Beside copper, some other metals for which electrorefining has been employed are Silver, gold, tin and lead. In the electrolytic purification of these metals the relevant electrolyte is the one listed below against each metal ... 

In the electrolytic purification of copper, the anodes are blister copper bars and the cathodes are made of pure copper. As electrolysis proceeds, copper is oxidized at the anode, moves through the solution as Cu ions, and is deposited on the cathode. The voltage of the cell is regulated so that more active impurities (such as iron) are left in the solution, and less active ones are not oxidized at all. The less active impurities include gold and silver, which collect as anode slime, an insoluble residue beneath the anode. The anode slime is subsequently treated to recover the valuable metals. 

APPLYING CONCEPTS Copper ore contains zinc metal, which is oxidized along with Cu during the electrolytic purification process. However, the Zn + ions are not then reduced when the Cu + ions are reduced to Cu at the cathode to obtain purified copper metal. Explain how Zn can be oxidized with Cu, but their ions not be reduced together. 

Electrolytic purification by dummy plating to remove undesirable metallic impurities, such as copper, is frequently employed in conjunction with filtration equipment, by either pumping from a separate tank or weir filled with overflow solution, or by recirculating through the slurry tank for this purpose. 

The cementation of gold and the purification of the ziac electrolyte ate usually carried out ia cylindrical vessels usiag mechanical agitation. The cementation of copper is carried out ia long narrow tanks called launders, ia rotating dmms, or ia an iaverted cone precipitator (see Copper). 

Electrorefining. Electrolytic refining is a purification process in which an impure metal anode is dissolved electrochemicaHy in a solution of a salt of the metal to be refined, and then recovered as a pure cathodic deposit. Electrorefining is a more efficient purification process than other chemical methods because of its selectivity. In particular, for metals such as copper, silver, gold, and lead, which exhibit Htfle irreversibHity, the operating electrode potential is close to the reversible potential, and a sharp separation can be accompHshed, both at the anode where more noble metals do not dissolve and at the cathode where more active metals do not deposit. 

Metals less noble than copper, such as iron, nickel, and lead, dissolve from the anode. The lead precipitates as lead sulfate in the slimes. Other impurities such as arsenic, antimony, and bismuth remain partiy as insoluble compounds in the slimes and partiy as soluble complexes in the electrolyte. Precious metals, such as gold and silver, remain as metals in the anode slimes. The bulk of the slimes consist of particles of copper falling from the anode, and insoluble sulfides, selenides, or teUurides. These slimes are processed further for the recovery of the various constituents. Metals less noble than copper do not deposit but accumulate in solution. This requires periodic purification of the electrolyte to remove nickel sulfate, arsenic, and other impurities. 

Purification actually starts with the precipitation of the hydrous oxides of iron, alumina, siUca, and tin which carry along arsenic, antimony, and, to some extent, germanium. Lead and silver sulfates coprecipitate but lead is reintroduced into the electrolyte by anode corrosion, as is aluminum from the cathodes and copper by bus-bar corrosion. 

In many refineries, nickel is the principal impurity (up to 20 g/L) in the electrolyte. The nickel remains in the electrolyte as the copper is stripped out in the purification section and is recovered from the resulting acid solution by precipitation as the sulfate in evaporators. 

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