Pressure leaching atmospheric

Lower temperature and atmospheric pressure direct leaching of zinc sulphide concentrates has also been investigated in considerable detail (6), and there are two commercial facilities in operation, integrated with roast-leach-electrowin operations. The first is located at the Korea Zinc refinery in Onsan, Korea, and the second, at Outokumpu s zinc refinery in Kokkola, Finland (7). Similar to the pressure leach plant installations described above, both of these facilities were installed to expand zinc production. Table II summarizes the commercial zinc atmospheric pressure leach facilities. 

In the most common hydrometallurgical process for zinc manufacturing, the ore is leached with sulfuric acid to extract the lead/zinc. These processes can operate at atmospheric pressure or as pressure leach circuits. Lead/zinc is recovered from solution by electrowinning, a process similar to electrolytic refining. The process most commonly used for low-grade deposits is heap leaching. Imperial smelting is also used for zinc ores. 

Societe Le Nickel (SLN) employ similar chemistry at their operations to treat mattes obtained from the pyrometallurgical treatment of Ni-bearing oxidic laterite ores.104 It has demonstrated at laboratory scale that Ni-containing lateritic ores may be directly leached into HC1 acid solution without pyrometallurgical pre-concentration at atmospheric pressure and relatively low temperature (ca. 70 °C).105... 

The major drawback in the extended use of this catalyst system is its relatively short lifetime and ease of deactivation. An example for such a deactivation is shown in Table III, where reactions were carried out in a flow system, in the gas phase, and in the temperature range of 160-180°C at atmospheric pressure (49). Although the initial conversions were high, the catalyst was totally deactivated after a period of 6-8 h. A possible reason is leaching of the metal halide from the graphite layers by the feed. Three possible reasons for such a deactivation have been given by Heinermann and Gaaf in the case of the SbF, catalyst (40) ... 

Between 20 and 1100 kg of sulfuric acid is used per t ore. Acid leaching generally proceeds at atmospheric pressure. 

Leaching with alkali always takes place at high temperatures, either under pressure (5 to 6 bar, 95 to 120°C) or at atmospheric pressure (75 to 80°C). The leaching agent used is sodium carbonate, sodium hydrogen carbonate or ammonium carbonate. Uranium(Vl) oxide is converted in this process into uranyl tricarbonato-complexes ... 

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