Pressure leaching

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Pressurised leaching is one of several leaching methods.

Pressure leaching is the chemical dissolution of soluble minerals within a solid ore or concentrate carried out at elevated pressures and giving rise to a solution containing metals to be recovered. The process is carried out in closed autoclaves which permit higher temperatures (>220°C) and pressures (>20 atm) than are possible with open tanks. The increased pressure improves the solubility rate of solids and increases the speed of dissolution into the leach solution (Figureā€¦). Because of the very fast kinetics, the duration of the leaching is short - from 30 minutes up to 24 hours depending on the concentrate being leached and conditions applied.

  • The high pressure makes the method ideal for oxidative leaching of sulfides since the content of dissolved oxygen in the leaching solution is directly proportional to the pressure.
  • Also in acid leaching of sulfides it can be chosen if the sulfide should be converted to elemental sulfur (S°) or sulfate (SO42-). At temperatures below 120-150°C elemental sulfur is formed which in many cases is a preferred form and also requires less oxidant to be added.
  • Pressure leaching is applied in the leaching of Co and Ni sulfides with ammonia as leaching reagent, in the so-called Sherrit Gordon process.
  • Another considerable application of pressure leaching is the Bayer process where bauxite is leached with sodium hydroxide to produce alumina (Al2O3), which is used as raw material for aluminium production by smelt electrolysis.
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