Autoclave leaching

Most commercial tellurium is recovered from electrolytic copper refinery slimes (8—16). The tellurium content of slimes can range from a trace up to 10% (see Seleniumand selenium compounds). Most of the original processes developed for the recovery of metals of value from slimes resulted in tellurium being the last and least important metal produced. In recent years, many refineries have changed their slimes treatment processes for faster recovery of precious metals (17,18). The new processes have in common the need to remove the copper in slimes by autoclave leaching to low levels (<1%). In addition, this autoclave pretreatment dissolves a large amount of the tellurium, and the separation of the tellurium and copper from the solution which then follows places tellurium recovery at the beginning of the slimes treatment process. 

Braginsky LN (1964) The study of aeration characteristics of impellers for autoclave leaching processes. Scientific Report on Research Project, Research and Design Institute NIIKhIMMASH, Leningrad, Russia, cf. Zundelevich (1979). 

Carbonate leaching under ambient conditions is extremely slow with poor recoveries. Therefore, the ore is typically leached in an autoclave with air providing most of the needed oxygen. The leach Hquor is separated from the soHd in a countercurrent—decantation system of thickeners, and the uranium is precipitated from the clarified sodium carbonate solution with addition of sodium hydroxide (eq. 9) (23). 

The cmde oxide is pressure-leached in a steam-heated autoclave using water or circulating mother hquor. The arsenic trioxide dissolves, leaving behind a residue containing a high concentration of heavy metal impurities and sihca. The solution is vacuum-cooled and the crystallisation is controUed so that a coarse oxide is obtained which is removed by centrifuging. The mother hquor is recycled. The oxide (at least 99% purity) is dried and packaged in a closed system. 

Agitated autoclaves These systems are used for leaching under conditions of elevated temperatures and pressures... 

Rubisov, D. H. Papangelakis, V. G. Sulphuric acid pressure leaching of laterites—a comprehensive model of a continuous autoclave. Hydrometallurgy 2000, 58, 89-101. 

Demopoulos, G. P., Parisien-La Salle, J.-C., Blais, D. (2012). The mobilization and potential in-autoclave recovery of gold during pressure oxidation and leaching of auriferrous sulfide materials. In 51st Conference of Metallurgists COM 2012 (pp. 15-29). MetSoc. 

An effective catalyst recycling with no loss of catalytic activity was accomplished by removing the liquid phase via the liquid sampling valve and re-charging the autoclave with a solution containing the substrate. In all cases, no rhodium leaching occurred. Remarkably, the hydrogenation activity of the 1,3-bis-... 

Hydrometallurgical methods are normally employed for recovery of gold from oxidized deposits (heap leach), low-grade sulphide ores (cyanidation, CIP, CIL) and refractory gold ores (autoclave, biological decomposition followed by cyanidation). 

Leaching (mixing and solid/liquid separation)—dissolution with acid, alkali, or bacteria, using redox, pressure (autoclave), etc. 

Niacin is relatively stable to most food-processing operations. It is stable to exposure to air and resistant to autoclaving (and is therefore stable to pasteurization and UHT treatments). The amide linkage of nicotinamide can be hydrolysed to the free carboxylic acid (nicotinic acid) by treament with acid but the vitamin activity is unaffected. Like other water-soluble vitamins, niacin can be lost by leaching. 

Reactions were carried out in batch autoclaves and in a continuous trickle bed reactor. In the latter experiments at 55-95°C a Bi2.39Ru1.61°7-y catalVst gave no evidence of deactivation, leaching by the alkaline solution, or change in bulk structure after 180 hours of operation. Adipic acid selectivities were of the order of 81-877. at complete conversion. In contrast, we have not observed, in initial experiments42, any cleavage with carbohydrates under the same conditions. 

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