Pyrometallurgical methods

The lead bullion is refined using pyrometallurgical methods to remove any... 

The U.S. is the world s third largest primary lead producer, with one-seventh of all production reserves. Over 80% of the lead ore mined domestically comes from Missouri. The majority of lead ore mined in the U.S. is smelted in conventional blast furnaces and refined using pyrometallurgical methods. 

Preparation. Antimony metal is obtained by pyrometallurgical methods. The sulphide is converted into the oxide, which can be directly reduced by carbon. 

The classical pyrometallurgical method of processing metal sulphide concentrate is to heat the material in air and drive off the sulphur as sulphur dioxide. This process is becoming increasingly unacceptable from an environmental point of view. 

Metals that have been produced by pyrometallurgical methods, such as copper, silver, nickel, and tin, are too impure for many purposes, and electrorefining is used to purify them further. Crude metallic copper is cast into slabs, which are used as anodes in electrolysis cells that contain a solution of CUSO4 in aqueous H2SO4. Thin sheets of pure copper serve as cathodes, and the copper that dissolves at the anodes is deposited in purer form on the cathodes (Fig. 17.18). Impurities that are more easily oxidized than copper, such as nickel, dissolve along with the copper but remain in solution elements that are less easily oxidized, such as silver and gold, do not dissolve but fall away from the anode as a metallic slime. Periodically, the anode slime and the solution are removed and further processed for recovery of the elements they contain. 

A conceptual pyrometallurgical method for the reprocessing of thorium-based fuels is presented in Fig. 1. It is responsive to the constraints described previously, being operable with either oxide or metal alloy fuel, and producing product streams consisting of enriched uranium/thorium and plutonium/thorium. 

The pyrometallurgical method this involves separating the PGM by melting the (ceramic) substrate in a furnace together with a collector metal which is subsequently processed. 

T.R.A. Davey, Pyrometallurgical Methods for Refining Metals , Chapter 12 in Techniques of Materials Prenaration and Handling. Part 2, Interscience Publishers, N.Y., 1968, 549-581. 

This section reviews the studies related to the rare-earth recycling from the Sm-Co and Nd-Fe-B magnets in terms of the physical separation, and hydro-and pyrometallurgical methods including molten salt electrolysis. 

Pyrometallurgical methods, magnet separation gas-solid and solid-liquid reaction chlorination examination, 176-178 nonmetallic elements control, 178 processes, Vllf on vapor pressure basis, 176 molten salts... 

Copper is widely used to make electrical wiring and in other applications fliat utilize its high electrical conductivity. Crude copper, which is usually obtained by pyrometallurgical methods, is not suitable to serve in electrical applications because impurities greatly reduce the metal s conductivity. 

Electrorefming involves the transfer of lead from an impure anode sheet, through an electrolyte to a high purity lead cathode. Crude bullion, after copper, arsenic and antimony ranoval, is cast into anodes, which are placed in tank cells. The electrolyte commonly used in the Betts Process is a solution of lead fluorosilicate and free fluorosilicic acid. Lead is deposited on lead starter sheets, which are removed from the cells and melted to high purity refined lead. Impurities are contained in the anode slimes and are collected and processed by pyrometallurgical methods for recovery of precious metals, bismuth and copper. 

One of the pyrometallurgical methods used is the Imperial Smelting Technique. A roasted zinc concentrate is charged together with coke into a blast furnace. At 1000°C zinc is reduced and its vapor passes from the top of the furnace into a condenser. Here the zinc vapor is cooled by molten lead and the two metals form a molten alloy, which is allowed to cool to 44f)°C. At this temperature the metal system has separated into a lead phase and a zinc phase. The lead is circulated for continued cooling purposes. Crude zinc produced by this process contains about 2% Pb, 0.3% Cd and 0.05% Fe. It is refined by distillation in two columns [33.5]. In the first one, zinc is purified from lead and iron. The separation is based on the fact that the boiling point of zinc is 907°C, while lead boils at 1749°C and iron at 2861°C. In the second column, zinc is separated from cadmium (boiHng point 767°C). Zinc metal with 99.9% purity is obtained. 

The pyrometallurgical methods were developed based on the differences between zirconium and hafnium in oxidation and reduction characteristics [11, 12] volatility [13-16] electrochemical properties [17-19] and molten metal-molten salt equilibrium [20, 21], The extractive distillation process, using carbochlori-nation of zircon [13], is in operation by CEZUS in France. Both chlorides are sublimated and run through a vertical distillation column containing molten aluminium chloride and potassium chloride. Both hafnium and zirconium tetrachloride chlorides dissolve, but hafnium tetrachloride has a higher vapour pressure and is therefore condensed from the top of the column in a hafnium-enriched mixture. The zirconium tetrachloride is partitioned to a liquid phase and recovered from a salt, typically containing less than 50 ppm hafnium. 

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