Outotec has developed a two-stage partial roasting process to remove impurities such as arsenic, antimony and carbon from copper and gold concentrates as a pre-treatment to actual extraction processes.

The company said it also installed a new continuous pilot plant at the company’s research center in Frankfurt, Germany, to test customers’ concentrates with the new process. Testing will allow Outotec to collect reliable data for industrial process scale-up.

“This new process complements our portfolio of sustainable technologies for the minerals and metals industry. With Outotec roasting technology the harmful elements can be removed in an environmentally sustainable way. We are currently building the world’s largest arsenic-removing roasting furnace at Codelco’s Mina Ministro Hales mine in Chile, where the new partial roasting process will be used. More than 90% of the arsenic contained in the concentrate can be removed to produce clean copper calcine,” said Outotec CEO Pertti Korhonen.

Depending on concentrate composition and plant capacity, the process can either be run in a stationary fluidized bed or in a circulating fluidized bed, according to Outotec.

The partial roasting process for oxide copper concentrates is a single-stage roasting process. The impurities are volatilized and the process produces calcine, which is rich in copper sulphide. The calcine can be further processed in copper smelters. The partial roasting process is also combined with post-combustion of process gas to convert all volatile compounds into oxides.

The roasting process for refractory gold concentrates contaminated with arsenic and carbon is a two-stage process. Arsenic is removed in the first roasting stage while carbon and remaining sulphur are removed in the second stage. The sulphur, iron and carbon are fully oxidized in the process and calcine suitable for actual gold leaching is produced.