Parkes process

Pemoval of Other Impurities. After softening, the impurities that may stiU remain in the lead are silver, gold, copper, tellurium, platinum metals, and bismuth. Whereas concentrations may be tolerable for some lead appHcations, the market values encourage separation and recovery. The Parkes process is used for removing noble metals and any residual copper, and the KroU-Betterton process for debismuthizing. 

In the Parkes process, a quantity (1—2%) of 2inc is added to lead which is in excess of the saturation value. This creates insoluble intermetaUic compounds consisting of 2inc and the noble metals that precipitate from the lead on cooling (22). 

The cmsts from the Parkes process are then treated to recover the 2inc contained in the dross for reuse in desi1veri2ing This is done by distillation (qv) and more commonly by vacuum technology. A continuous adaptation of the Parkes process is carried out at The Broken Hill Associated Smelters Pty. (Port Pide, AustraUa). The chemistry of this operation is the same as that for batch desi1veri2ing (22,23). 

Precipitation can also occur upon chemical reaction between the impurity and a precipitating agent to form a compound insoluble in the molten metal. The refining of cmde lead is an example of this process. Most copper is removed as a copper dross upon cooling of the molten metal, but the removal of the residual copper is achieved by adding sulfur to precipitate copper sulfide. The precious metals are separated by adding zinc to Hquid lead to form soHd intermetaHic compounds of zinc with gold and silver (Parkes process). The precious metals can then be recovered by further treatment (see Lead). 

Parkerveriahien, n. (Metal.) Parker process, parkesieren, v.t. (Meial.) subject to the Parkes process. 

Reich-schaum, m. (Metal.) the zinc crust, rich in silver, etc., formed in the Parkes process, -schlacke, /. rich slag, -schmelzen, n. smelting of precious metals. 

Liquid metal-liquid metal Parkes process, (molten Zn is... 

The problem of the separation of zinc and lead from each other is encountered not only in the refining of zinc but also in the refining of lead. When lead is subjected to refining by the Parkes process, a certain amount of zinc, which is not insignificant, is introduced into the refined lead bullion. This zinc impurity may be removed by distillation. 

Brittania A process for removing silver from lead, operated by Brittania Refined Metals in England, using ore from the Mount Isa mine in Australia. After initial concentration by the Parkes process, and removal of the zinc by vacuum distillation, the mixture, which contains silver (70 percent), lead, and some copper is treated in a bottom blown oxygen cupel in which lead and copper are removed by the injection of oxygen through a shielded lance. 

Davey A modification of the Parkes process for removing silver from lead. A water-cooled tray is floated on the molten lead. Invented by T. R. A. Davies in 1970 and operated by Penarroya in Brazil, France, Greece, and Spain. 

Pattinson (1) A process for extracting silver from lead by selective crystallization. When molten lead is cooled, the first crystals of lead contain less silver than the residual melt. Repetition of this process a number of times yields a silver concentrate which is further purified by cupellation. Invented in 1833 by H. L. Pattinson. Largely superseded by the Parkes process, except for metals containing bismuth for which the Pattinson is the preferred process. See also Luce-Rozan. 

Sulfide ores of silver and lead are also treated by the Parkes process, which is described later, in discussion of the metallurgy of lead. 

Of interest also is the high-temperature liquid-liquid extraction of molten silver dissolved in molten lead, the extraction solvent being molten zinc (Parkes process) this process is analogous to the familiar extraction of bromine from water using carbon tetrachloride, and is used to recover silver from lead ores. 

The pig lead contains about 2 per cent, of silver, and there are three processes for its desilverization, the final stage of each being cupellation. In the almost obsolete PaUinson process the lead is melted and then allowed to crystallize. The first fractions consist of almost pure lead, and the crystals are removed by means of perforated ladles. The crystallization is continued until the residual lead contains about 1 per cent, of silver. In the Rozan process the molten metal is agitated by revolving paddles or jets of steam, and the concentration continued up to 2 per cent. In the Parke process the silver is extracted from the... 

Silver is often removed from lead by the Parkes process, described in Chapter 27. Some pure lead is made by electrolytic refining. 

Ores of silver native silver, argentite, cerargyrite (horn silver). Metallurgy of silver cyanide process, amalgamation process, Parkes process. O mpoimds of silver silver oxide, silver chloride, silver bromide, silver iodide, silver ammonia complex, silver cyanide complex, silver thiosulfate complex, silver nitrate. 

Silver occurs in lead ores and appears in metal from the smelter its removal and recovery is usually worthwhile. Parkes process is based on the low solubility of Zn in molten Pb and the very high distribution coefficient for silver between the zinc and lead layers. After stirring zinc into the molten lead, the Zn-Ag alloy which floats to the top is skimmed off and treated for the recovery of silver. 

Method of purification Desilvering (Parkes process), electrolytic refining (Betts process), pyrome-tallurgical refining (Harris process). Bismuth is removed by Betterton-Kroll process. 

Parkes process. A standard process for the separation of silver from lead. From 1 to 2% molten zinc is added to the lead-silver mixture, heated to above the melting point of zinc. A scum containing most of the silver and zinc forms on the surface this is separated and the silver recovered. The separation of silver is not complete, and the process is repeated several times. 

---