Novel Autoclave for Extracting Gold Ore Showcases Titanium Properties for a New Industrial Application

By Michael C. Gabriele

Coek Engineering, Geel Belgium, has produced a carbon steel explosion welded titanium-clad, industrial autoclave for Polymetal International PLC, which will be used for extracting gold ore. The unit, expected to be commissioned in early 2023, will operate at a facility in Amursk, Russia, and represents a new industrial application area for titanium and a new generation in the design of industrial autoclaves.

Titanium Grade 17 was selected as the material of choice because of its superior chemical resistance, compared with refractory bricks, which are the typically used in autoclaves. The autoclave vessel has been designed to use highly corrosive chemicals (chlorides and fluorides) at high temperatures 240˚C (464˚F), with an operating pressure of more than 50 bar (725 psi), to extract the gold ore. The interior diameter of the autoclave is over 5 meters (16 feet) and the vessel is around 50 meters long (164 feet).

Patrick Van Roy, chief sales officer for Group Coek, said Hatch Ltd., based in Mississauga, Ontario, Canada, provided the design and process conditions for the autoclave, while Coek manufactured the vessel and worked out the mechanical design. The spokesman would not reveal the projected annual processing capacity for the autoclave and would not confirm the capital investment for the equipment. Several online news outlets reported the design and production of the autoclave represents a capital investment in excess of $430 million. He did say that the titanium Grade 17 used for the autoclave was sourced from Uniti Titanium, a joint venture of Allegheny Technologies Inc. and VSMPO-AVISMA Corp.

NobelClad Europe GmbH, a global leader in cladding technology, and having a long-term close collaboration relationship with both Coek and Hatch in providing titanium clad plates for autoclaves (i.e. high pressure acid leach [HPAL] for nickel), was selected to supply quality Detaclad™ explosion welding technology from theiroperations in Liebenscheid, Germany, for this first titanium-clad pressure oxidation (POX) Autoclave.

NobelClad supplied approximately 1,000 tons of quality explosion welded plates. This alone was a transport and logistics challenge and required a coordinated supply chain approach. All plates were produced and tested in accordance to the stringent project specification, such as automatic ultrasonic scanning, mechanical tests (shear and tensile), including flatness, and stress relief heat treatment. These nextgeneration vessels represent a major advancement for the gold processing industry, which currently operates approximately 30 brick-lined POX autoclaves around the world.

“Looking back on this project I am proud of the global team effort as well as the partnership with leading engineering and fabricating players in this exciting and challenging industry,” Antoine Nobili, NobelClad president, said.

When asked to offer insights regarding the selection of titanium for the autoclave, Van Roy explained that the primary issue is long-term corrosion resistance for extracting the gold ore. “There is no corrosion on the titanium lining,” he said. “The main issue that can influence the lifetime of such equipment is metal erosion (of the autoclave’s interior). Given the fact that we have put a lot of effort into our design, to avoid erosion as much as possible, the expected life time of this equipment can be long as 20 years, with a limited requirement on maintenance and downtime as compared with brick-lined autoclaves.”

He continued by citing long-term maintenance cost-saving advantages through the use of titanium.

“Given the experience on erosion issues for previous nickel extraction autoclaves, it was decided to use full recessed cover strip design on all bottom parts of the reactor. And in order to increase maximum safety, also the cladding thickness was increased to the maximum that can be cladded without too many risks. This first of a kind autoclave for the gold mining industry is using some safety margin from a design perspective, which will be optimized in the future based on the feedback during operation. We also learned that from a cost point of view, the overall price is very much depending on the palladium price (key alloy element for titanium Grade 17), which is very much fluctuating in the last six months.”

According to Coek, new orders from Polymetal for similar equipment are expected. Coek also indicated they are involved in discussions with a separate Russian gold mining company for another titanium-lined autoclave. However, Van Roy was cautious not to overplay the notion that this represents a major new trend in the design and production of autoclaves and the use of titanium—at least fornow. He did acknowledge that titanium-clad autoclaves have gained attention in the gold mining industry. He also cited safety advantages and cost efficiencies as part of the interest in these autoclaves.

“The substantial advantage of a much longer cycle time (no regular shutdowns to be scheduled to do maintenance on the brick lining), faster start-ups and quicker cool downs (compared to brick-lined autoclaves), and the fact that you gain a lot in volume, makes the alternative of titanium cladding much more cost efficient.”

It’s also possible that, based on the success of the Polymetal operation, titanium-lined autoclaves might gain currency in other areas of metal mining and extraction. Autoclaves also are used for other industrial applications involving corrosive production environments and these applications can benefit from the reliability of titanium-clad construction.