Our two-stage roasting plants are mainly used for treating double-refractory gold concentrates. A two-stage roasting process combines partial roasting in the first stage with dead roasting in the second stage. The first stage is used as a de-arsenifying process step in an oxygen-deficient roasting atmosphere, while the second stage operates in an oxidizing atmosphere to fully transform the metals into their oxide form. When roasting sulfur-bearing minerals, their iron content can form hematite (Fe2O3) or magnetite (Fe3O4), depending on the partial pressure of the oxygen in the roaster gas. In the first roasting stage, pyrites with a grain size of up to 6 mm are roasted in a fluidized bed of iron sulfide, where the arsenic is volatized. The partly roasted solids are then transferred to the second stage and dead roasted. De-arsenifying roasting can also be applied when processing gold-bearing concentrates or ores, or copper concentrates.
• Elimination of impurities such as arsenic and antimony • Substantially arsenic-free calcine • Autothermic process