Pressure leaching elevated

One of the most important developments in the field of hydrometallurgy has been the application of elevated pressures and temperatures to complex sulfide and oxide ores (B21, F8, G8, M5, M6). The pressure-leaching of bauxite ores by the Bayer process (E3) is probably the first successful commercial application of this technique. The bauxite ore is leached with sodium hydroxide solution with a specific gravity of 1.36-1.4 at 160-170°C for 1 2 hr under a working pressure of 100 psig. The alumina is produced by calcining the aluminum hydrate precipitated from the leach liquor. 

The direct leaching of metal sulfide minerals by dilute sulfuric acic under an oxygen partial pressure at elevated pressures and temperaturei... 

Cobalt can be recovered from nickel-sulfide concentrates or nickel matte by the Sherritt-Gordon ammonia leaching process in Fort Saskatchewan, Alberta, Canada, and it is also recovered from sulfuric-acid pressure leaching of laterites. In both cases, cobalt is obtained in nickel-free liquor by reduction with hydrogen under elevated pressure and temperature (Section 2.2). 

HydrometaUurgical refining can be applied both to laterite ore and sulfide ore or sulfide ore concentrates. Soluble nickel amines are formed during pressure leaching of the sulfide ore concentrate with strong anunoniacal solution at a moderately elevated temperature. The saturated solution is boiled to drive off ammonia and precipitate copper as sulfide. Sulfur is oxidized. Nickel and cobalt are recovered as pure metal powders by reduction with hydrogen under pressure. 

In the acid-leaching process, the oxide ore is leached with sulfuric acid at elevated temperature and pressure, which causes nickel, but not iron, to enter into solution. The leach solution is purified, foHowed by reaction with hydrogen sulfide and subsequent precipitation of nickel and cobalt sulfides. 

Australian Vanadium—Uranium Ore. A calcareous camotite ore at YeeHrrie, AustraHa, is iU-suited for salt roasting and acid leaching. Dissolution of vanadium and uranium by leaching in sodium carbonate solution at elevated temperature and pressure has been tested on a pilot-plant scale... 

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

Two other refining processes are also frequently employed. One involves hydrometallurgical refining in which sulfide concentrates are leached with ammonia solution to convert the copper, nickel, and cobalt sulfides into their complex amines. Copper is precipitated from this solution upon heating. Under such conditions, the sulfide-amine mixture of nickel and cobalt are oxidized to their sulfates. The sulfates then are reduced to metalhc nickel and cobalt by heating with hydrogen at elevated temperatures under pressure. The metals are obtained in their powder form. 

But lead is poisonous. Lead poisoning can cause elevated blood pressure, pain, mental disorders, irritability, and infertility. The Romans were not completely unaware of the dangers of lead, for they noted the poor health of the unfortunate men who produced and worked with the metal. Yet this warning may not have been enough. Perhaps the Romans believed that their exposure to lead leaching from pipes or cooking vessels would not be serious. 

The use of inorganic ion exchangers to solidify liquid radioactive waste followed by pressure sintering to produce a ceramic waste form appears to be a viable alternative to calcina-tion/vitrification processes. Both the process and waste form are relatively insensitive to changes in the composition of the waste feed. The stability of the ceramic waste form has been shown to be superior to vitrified wastes in leaching studies at elevated temperatures. Further studies on the effects of radiation and associated transmutation and the influence of temperature regimes associated with potential geologic repositories are needed for a more definitive comparison of crystalline and amorphous waste forms. 

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