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Autoclave pressure oxidation (POX) is an effective pre-treatment option when extracting gold from refractory ore bodies, such as pyrite and arsenopyrite. While gold processing plants are the most common utilizers of POX technology, the process can also be applied to other metals, like copper, zinc and uranium. Metso has a wide range of valves and services for POX process.
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Valves control various liquid and gaseous flows in gold autoclave pressure oxidation process
Autoclave POX operations include several different types of valves to control both liquid and gaseous flows.
Slurry feed and discharge valves, pump isolation valves, depressurization valves, steam supply and steam drum isolation valves, as well as oxygen feed valves, among others, make sure that the POX process works optimally and efficiently.
In the autoclave, valves are subjected to a high-temperature and an oxygen-rich environment, so the right selection of valves can potentially make a significant positive impact on the operation’s reliability.
Valves for slurry feed
The conditions that valves face in the POX process require the highest possible resistance against corrosion and erosion as well as against the deterioration caused by solids. The right material, seat and coating choices play an important role in maintaining the sealing abilities of slurry feed valves.
Valves for oxygen feed
Controlling oxygen feed is one of the essential jobs in the POX process.
In the event they are called upon, these valves need to provide absolute isolation. Valve materials need to be carefully selected, and cleanliness is of paramount importance because of the inherent danger of oxygen reacting with any grease, oil, or combustible material left in a piping system.
The evaluation of valves for an oxygen application requires an understanding of metallurgy as well as valve geometries.
Valves for depressurization
In an operational disturbance, emergency or maintenance event, autoclave processes are sometimes depressurized. During depressurization, a vent line is used to reduce the pressure and temperature inside the autoclave.
When selecting the right valve for this service, Metso combines the knowledge of experts in process technology, metallurgy and field service to deliver the most reliable and economical solution.
Autoclave POX for the extraction of refractory gold
In the POX process, the ore is crushed and mixed with water to create aqueous slurry that is then heated and fed into an autoclave.
Oxygen is added to the vessel to react with the slurry. The POX process uses high temperatures (approximately 200 °C/400 °F) and high pressures (10-35 bar/150-500 psi) to facilitate the leaching process.
After the autoclave processing step, the slurry is returned to atmospheric condition by taking it through two or more flashing letdown stages.
Once at atmospheric condition, the slurry is washed and separated, at which point the metal can be recovered from the liquid portion in the downstream processing circuits.
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