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 has also established a new continuous pilot plant at its research center in Frankfurt, Germany, to test customers’ concentrates with the new process. During the tests it is possible to collect reliable and necessary 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 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.

Outotec’s partial roasting process depends on concentrate composition and plant capacity. The process can either be run in a stationary fluidized bed or in a circulating fluidized bed. The partial roasting process for copper concentrates is a single-stage roasting process. The impurities are volatilized and the process produces calcine, which is rich in copper sulfide, but has a low impurity content. The calcine is mixed and 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 sulfur are removed in the second stage. All sulphur, iron and carbon are fully oxidized in the process and calcine suitable for actual gold leaching is produced.