Anode sludge

The impure copper from either process is refined electrolytically it is made into anodes and plated onto cathodes of pure copper. Other metals may be present in the impure copper and those with highly positive electrode potentials also are reduced. The rare metals—most notably, platinum, silver, and gold—obtained from the anode sludge are sold to recover much of the cost of the electricity used in the electrolysis. 

Ruthenium is derived from platinum metal ores. Method of production depends on the type of ore. However, the extraction processes are simdar to those of other nohle metals (see Platinum, Rhodium and Iridium). Ruthenium, like Rhodium, may he obtained from accumulated anode sludges in electrolytic refining of nickel or copper from certain types of ores. Also, residues from refining nickel by Mond carbonyl process contain ruthenium and other precious metals at very low concentrations. The extraction processes are very lengthy, involving smelting with suitable fluxes and acid treatments. 

Each industrial chemical process has as its objective the economical production of a particular primary product. It is frequently true that, in attaining this objective, one or more by-products may become available. If these by-products can be disposed of at a profit, this serves to decrease the overall cost of operation and to permit the sale of the primary product at a lower, more favorable, competitive price. Thus, the cost of electrolytically refined copper is dependent on the recovery and sale of the by-products—silver, gold, platinum, and palladium. These precious metals are recovered in large quantities from accumulated anode sludges. Fully one-fourth of the total production of silver, about one-eighth of the gold, and lesser quantities of platinum and palladium are obtained as by-products of the electrolytic refining of copper. 

The abundance of tellurium in earth s crust is ca. 0.01 ppm. Tellurium is found free in nature and over 100 tellurium-containing minerals are known (for some examples, see Table 1), but because of their low abundance, it is economically not viable to recover the element from its mineral ores. Since, like selenides, tellurides generally occur together with the sulfide ores, the element is commercially obtained from the anode sludge produced during the refining of copper from CuSep2. 

Copper is refined electrolytically, the silver and gold present separating as an anode sludge. The last two metals are also recovered during the purification of both lead (p. 310) and nickel (p. 502). Silver and gold are extracted by aqueous sodium cyanide which reduces the oxidation potential of the metals so that atmospheric oxygen brings them, or their salts, into solution as soluble complexes ... 

Impurities such as Zn and other active metals also dissolve as cations. But they are not reduced at the cathode. Inactive metals, such as Au and Ag, fall to the bottom as an anode sludge. This sludge is a valuable source of these more-expensive metals in the industrial process. 

Anode sludge Copper(II) sulfate/ sulfuric acid solution... 

The INCO, Thompson plant in Manitoba, Canada, electrolyzes 240 kg sulfide anodes in a sulfate-chloride electrolyte. The approximate composition of the electrolyte is 60 g L x Ni2+, 95 g L 1 SC>42, 35 g L 1 Na+, 60 g L 1 Cl-, and 16 g L 1 H3BO4, and the temperature is 60 °C. Nickel, cobalt, and copper dissolve from the anode, while sulfur, selenium, and the noble metals form an insoluble sludge or slime, from which they can be recovered. The anode sludge contains 95% elemental sulfur, sulfide sulfur, nickel, copper, iron, selenium, and precious metals. Nickel is deposited on to pure nickel starting sheets. The anode cycle is 15 days and the cathode cycle is 5 to 10 days. Electrolysis is carried out at a current density of 240 A m-2 giving a cell voltage of 3 to 6 V [44, 46]. 

Selenium and tellurium are found in sulfide ores they are also recovered from the anode sludge formed during the electrolytic refining 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. 

The studies of the use of the ion exchanger Metalfix Chelamine of tetraethylenepentamine ligands (1,4,7,10,13 - pentaazatridecane) in the process of recovery, concentration and separation of platinum metal ions, gold and their accompanying elements from the environmental samples, anodic sludges from the electrorefining of copper ores, spent car exhaust gas catalysts, etc. [93-98]. 

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