Featured Story – New titanium application: industrial gold extraction

Coek Engineering (Belgium) has produced a carbon steel, explosion welded, titanium-clad industrial autoclave for Polymetal International PLC. Designed for extracting gold ore, the autoclave will be commissioned in early 2023 in Amursk, Russia. It represents a new industrial application area for titanium and a new generation in industrial autoclave design.

Tough operating conditions

Titanium Grade 17 was selected as the material of choice because of its superior chemical resistance, compared with refractory bricks typically used in autoclaves. The autoclave vessel is designed to extract the gold ore using highly corrosive chemicals (chlorides and fluorides) at high temperatures 240˚C (464˚F), with an operating pressure of more than 50 bar (725 psi). The autoclave interior diameter 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 or 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 USD 430 million. Van Roy did say that titanium Grade 17 used for the autoclave was sourced from Uniti Titanium, a joint venture of Allegheny Technologies Inc. and VSMPO-AVISMA Corp.

Explosion welded plates

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). It was selected to supply quality Detaclad™ explosion welding technology from their operations 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 according to the stringent project specification, such as automatic ultrasonic scanning, mechanical tests (shear and tensile), including flatness, and stress relief heat treatment. These next-generation vessels represent a major advancement for the gold processing industry, which currently operates approximately 30 brick-lined POX autoclaves worldwide.
“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.

Corrosion resistance paramount

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 lifetime 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 a fully recessed cover strip design on all bottom parts of the reactor. To increase safety, the cladding thickness was increased to the maximum that can be cladded without too many risks. This first of a kind autoclave employs some safety margins which, from a design perspective, will be optimized in the future based on the feedback during operation. From a cost point of view, we also learned that the overall price is very much dependent on the palladium price (key alloy element for titanium Grade 17), which is has been very volatile in the last six months.”

Growing interest

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 titanium use—at least for now. 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 maintain a brick lining), faster start-ups and quicker cooldowns (compared to brick-lined autoclaves), plus the gain 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.

All images were taken before the COVID-19 pandemic, or in compliance with social distancing.