Amursk Pressure Oxidation (POX) Hub Expansion Project

World’s largest, custom-designed pressure oxidation autoclave vessel

Amur Hydrometallurgical Plant LLP (Polymetal International Inc.) | Amursk, Khabarovsk Krai, Russian Federation | 2017-2023

240°C operating temperature and 52 bar(g) operating pressure

965 tonnes fabricated weight

5.95 m outside diameter and 50 m in length

Treatment capacity of refractory gold concentrate will double


  • Polymetal International Inc. is undertaking the Amursk POX Hub Expansion to recover gold from double-refractory (high carbon) sulphide concentrate from five of their mines in Siberia, Eastern Russia, and East Kazakhstan.
  • The project will double Polymetal’s concentrate treatment capacity to 250,000-300,000 t/a of refractory gold concentrate.
  • The centralized hub processing concept is unique, with concentrate from multiple mines being shipped to a central hydrometallurgical processing plant.
  • This is a technically challenging autoclave vessel constructed of high-strength carbon steel, with an explosion-bonded, titanium-clad (EXW Ti-clad) lining.
  • The vessel is 5.75 m inside diameter and 50 m in length, with a fabricated weight of 965 tonnes. It took 32 months for material order, fabrication and testing to be completed.


  • The autoclave vessel chemically oxidizes minerals such as pyrite and arsenopyrite, to liberate and recover sub-micron, solution-phase gold contained within the sulphide matrix. In six hours, the autoclave does what takes several hundreds of thousands of years to occur naturally in the earth.
  • Polymetal engaged Hatch to provide engineering and procurement services for the POX facility, utilities, off-gas treatment, heat recovery, and slurry conditioning areas.
  • Hatch are also supplying custom-designed process equipment for the facility, including flash vessels, gas cyclone, refractory linings, pressure letdown valves, vent gas condensers, dip pipes, and oxygen spargers.
  • Our scope of work includes basic and detailed engineering, procurement, quality management, project management, scheduling and project controls.


  • With an operating temperature of 240°C and 52 bar(g) operating pressure, the autoclave vessel is the heart of a new POX facility for treatment of double-refractory (high carbon) sulphide concentrates.
  • It was custom designed for extremely aggressive process conditions, including high temperature, high acidity, and elevated levels of chlorides and fluorides.
  • The design pressure is 50% higher than other POX autoclaves currently in operation.
  • This is the largest pressure oxidation autoclave vessel built to date in terms of overall size, volume, and weight. Read about the vessel's journey from Belgium to Russia, here. 

After travelling more than 25 000 kilometers, across 3 oceans and 8 seas, the 50-meter long, 965-tonne Amursk autoclave arrived at Polymetal’s hydrometallurgical plant in Amursk, Russia on July 21, 2020. Arrangements for ocean shipping, unloading and overland transport of the world’s largest autoclave from the manufacturing facility in Belgium to the client’s site took more than two years of logistics planning and preparation alone!

To unload the autoclave from the barge and deliver it to the site, a temporary berthing structure and new access road were built by Polymetal Construction in Amursk. From the pier to the plant, the vessel travelled on a unique road vehicle with 28 axles and 448 wheels to ensure that the load was evenly distributed over the roadway. Quite a feat! Read about the autoclave’s journey from Belgium to Russia! Click here.

For more information on our high-pressure metallurgy practice, click here.


Project numbers

  • Max. Operating Pressure: 52 bar(g)
  • Max. Operating Temperature: 240°C
  • Dimensions: 5.75 m ID X 50 m OAL
  • Operating Volume: 1095 m3
  • Shipping Weight: 965 t

Materials of construction:

  • EN10028-2 P355GH carbon steel
  • SB-265 Ti Gr 17 EXW cladding
  • SB-265 Ti Gr 12 internals

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