Inprotec was approached by SPMP and Australian engineering contractor Worley to work on the project, which involved the construction of two refining converters that remove impurities in the final antimony refining stage, according to a report in regional British newspaper, Yorkshire Times.

"Over the last two years we've worked closely with SPMP to design, supply and commission a world-leading plant that enables them to cost-effectively, efficiently and safely refine antimony," Inprotec MD Chris Oldroyd told the publication.

Inprotec also developed an ancillary plant that supports the two refining converters. This includes a trough-like molten metal launder system that carries molten alloys from one location to another using gravity, and an air lancing system used in the refining process.

The Sohar plant can produce more than 50,000 oz/yr of gold and 20,000 t/yr of antimony.

SPMP, which is 40% owned by London-listed Tri-Star Resources, sold and shipped its first consignment of antimony from the plant, comprising 60 tonnes of antimony metal ingots, in May.

Management expects the plant to be operating at full capacity by the end of the year.

David Fourie, smelting manager at SPMP, told the paper: "Not only is this the first antimony roaster to be built outside of China in the last 30 years, but it's also the world's first ‘clean plant', designed and built to the highest environmental standards."