Selenium, pressure leaching

Some of the important but expensive rare metals are usually extracted as by-products of other metal separation processes. Selenium and tellurium are recoverable from copper refinery slime by pressure leaching (M40), scandium from uranium plant iron sludge (R15), uranium from gold cyanida-tion residues (G3), silver from aqueous chlorination process for the treatment of slimes, and gravity concentrates from gold ores (V2). A host of other processes are in use. 

Final solutions from both pressure and atmospheric leach tests were submitted for chemical analysis, and the results are presented in Table VIA. The concentrations of cobalt, nickel and selenium in the final solutions were not significantly different. Arsenic, antimony and tellurium levels were about the same or lower in the solution generated in pressure leaching (the arsenic concentration was substantially lower in the pressure leach liquor for... 

The sulphidic portions of the leach residues were subjected to sulphur melting and hot filtration. The arsenic and mercury contents of the elemental sulphur byproducts originating from the pressure leach treatment of the concentrates were consistently lower than the arsenic and mercury contents of the elemental sulphur originating fi om atmospheric leaching. The selenium content was about the same or lower in the elemental sulphur originating from pressure leaching compared to atmospheric leaching. 

The impurity content of the elemental sulphur filtrate produced from the pressure leach residues was slightly lower than that produced from the atmospheric leach residues. The elemental sulphur produced from the pressure leach residues contained less arsenic and mercury and about the same level of selenium in comparison to the elemmtal sulphur produced from the atmospheric leach residues. 

These cast allo5 utilize bismuth and bismuth-selenium as a substitute for lead to fru ilitate machinability and pressure tightness in fluid carrying applications. Lead is not added intentionally to these alloys to minimize the amount that may leach in potable water systems and in other applications such as daily product processing. 

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