Anode slimes

Anode slimes Anodization Ano diz ed aluminium Anodizing Anodizingaluminum... 

In both the sulfuric and nitric acid processes, the dorn metal must be in shot form prior to treatment to secure a reasonably rapid reaction. A number of steps also may be required in processing the dorne metal to remove miscellaneous impurities, particularly in treating material from copper-anode slime (31). 

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. 

R. K. Manahan and F. Loewen, "Treatment of Anode Slimes at the INCO Copper Refinery," paper presented at CIMMeeting, Halifax, Nova Scotia, 1972. 

An electrorefining plant may operate with either an acid or an alkaline bath. The acid bath contains stannous sulfate, cresolsulfonic or phenolsulfonic acids (to retard the oxidation of the stannous tin in the solution), and free sulfuric acid with P-naphthol and glue as addition agents to prevent tree-like deposits on the cathode which may short-circuit the cells. The concentration of these addition agents must be carefliUy controlled. The acid electrolyte operates at room temperature with a current density of ca 86—108 A/m, cell voltage of 0.3 V, and an efficiency of 85%. Anodes (95 wt % tin) have a life of 21 d, whereas the cathode sheets have a life of 7 d. Anode slimes may be a problem if the lead content of the anodes is high the anodes are removed at frequent intervals and scmbbed with revolving bmshes to remove the slime (7). 

The Sperry process for making white lead ia an electrolytic cell recovers bismuth as a by-product ia the anode slimes. 

Anode impurities either dissolve in the electrolyte or fall to the bottom of the electrolytic cell as anode slime. These slimes contain silver, gold, selenium, and tellurium and represent a very significant value. Thus, the recovery of by-products from the anode slime is an important operation. 

The series system was used in the past as an alternative to the multiple system. In this system only anodes were charged and a potential was maintained between the ends of each cell so that copper dissolved from one anode was plated on the adjacent anode. After a sufficient period of time, all the original anode copper was replaced by a cathodic deposit and the impurities were either in the form of anode slime or in solution. The series system demanded highly uniform anodes, a requirement that was difficult to meet with horizontal equipment. 

By-Product Recovery. The anode slime contains gold, silver, platinum, palladium, selenium, and teUurium. The sulfur, selenium, and teUurium in the slimes combine with copper and sUver to give precipitates (30). Some arsenic, antimony, and bismuth can also enter the slime, depending on the concentrations in the electrolyte. Other elements that may precipitate in the electrolytic ceUs are lead and tin, which form lead sulfate and Sn(0H)2S04. 

The mud or slime is coUected from the bottom of the electrolytic ceUs and pumped to the sUver refinery, where it is processed for recovery of copper, precious metals, selenium, and, in many cases, teUurium. The anode slime contains 2—20% selenium as copper and sUver selenides, whereas gold exists as the metal and in combination with teUurium. A flow diagram is shown in Figure 8. 

Cathodic protection with impressed current, aluminum or magnesium anodes does not lead to any promotion of germs in the water. There is also no multiplication of bacteria and fungi in the anode slime [32,33]. Unhygienic contamination of the water only arises if anaerobic conditions develop in the slurry deposits, giving rise to bacterial reduction of sulfate. If this is the case, HjS can be detected by smell in amounts which cannot be detected analytically or by taste. Remedial measures are dealt with in Section 20.4.2. 

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... 

The major part of this blister copper is further purified electro lytic ally by casting into anodes which are suspended in acidified CUSO4 solution along with cathodes of purified copper sheet. As electrolysis proceeds the pure copper is deposited on the cathodes while impurities collect below the anodes as anode slime which is a valuable source of Ag, Au and other precious metals. 

AnnulUeren, v.t. annul, cancel, strike out. Anoden-batterie, /. anode battery, B battery, -dichte, /. anode density, anodic density, -raum, m. anode region, space around the Anode, -schlamm, m. anode slime, anode... 

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. 

Silver was formerly extracted by cyanide solution of Ag2S, the resulting Ag(CN)2 being treated with zinc to afford the metal roasted ores could also be extracted with mercury to give silver amalgam. Presently much silver is extracted by workup of the anode slime from the preparation of non-ferrous metals (Pb, Cu) pure silver is obtained by electrolysis of AgN03. 

Selenides and tellurides Anodic slimes from copper electrolysis... 

The anode potential is so positive, due principally to the activation overpotential, that the majority of the impurity metals (Fe, Cu, Co, etc.) in the anode dissolve with the nickel sulfide. In addition, some oxygen is evolved (2 H20 = 02 + 4 H+ + 4 e ). The anodic current efficiency reduced to about 95% on account of this reaction. Small amounts of selenium and the precious metals remain undissolved in the anode slime along with sulfur. The anolyte contains impurities (Cu, Fe, Co) and, due to hydrogen ion (H+) liberation, it has a low pH of 1.9. The electrolyte of this type is highly unfit for nickel electrowinning. It is... 

The slime is recovered and heated in a brick-lined tank to melt the sulfur. The molten sulfur is filtered in a heated stainless-steel pressure filter to separate remaining nickel sulfide pieces and insoluble precious metals, and cast into moulds. The residue is remelted and cast into anodes, the resulting anode slime is now a relatively concentrated precious metal residue and is treated for the extraction of individual metals. 

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. 

Moebius An electrolytic process for removing gold and platinum from silver. The crude metal, known as Dore, is used as the anode. The cathodes are of silver or stainless steel. The electrolyte is a diluted solution of silver nitrate and nitric acid. Gold and other metals collect as anode slimes. Invented in Mexico by B. Moebius, first operated there in 1884, and subsequently widely operated in Germany and the United States. See also Balbach, Thum, Wohlwill. 

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. 

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