Process and apparatus for roasting of metal sulfide concentrates and/or residues

1. A process for roasting of metal concentrate, wherein concentrate particles are fed into a roaster where they are thermally treated at a temperature in a range of 500 and 1200° C. in a fluidized bed to form a calcine, at least parts of the calcine are withdrawn from the roaster together with a gas stream as a solid fraction, particles are gained in another hydrometallurgical step as other particles, at least parts of the other particles are pelletized, whereby at least 80% of pellets feature a diameter of at least 80% of an average diameter of the concentrate particles and the pellets are fed into the roaster so that the metal concentrate contains at least 45 wt.-% zinc, whereby the average diameter of the concentrate particles is between 5 and 40 μm, the metal concentrate contains at least 60 wt.-% pyrite, whereby the concentratc particles' average diameter of the concentrate particles is between 5 and 90 μm, the metal concentrate contains at least 2 g/t gold, whereby the average diameter of the concentrate particles is between 5 and 100 μm, the metal concentrate contains at least 15 wt.-% copper, whereby the concentrate particles' average diameter of the concentrate particles is between 10 and 50 μm, the metal concentrate contains at least 1 wt.-% cobalt, whereby the average diameter of the concentrate particles is between 5 and 40 μm, or the metal concentrate contains at least 100 g/t Platinum-Group Metals (PGMS), whereby the average diameter of the concentrate particles is between 20-100 μm.

2. The process according to claim 1 , wherein concentrate particles with a diameter at least 50% smaller than the average diameter of the concentrate particles are separated as small particles and pelletized together with the other particles, and/or small calcine particles, which are particles from a gas-solid-fraction separated in at least one step, are separated in a waste heat boiler, an evaporative cooler, a cyclone, and/or an electrostatic precipitator.

3. The process according to claim 1 , wherein particles from a gas-solid-fraction are separated in at least one step as small calcine particles and are pelletized together with the other particles.

4. The process according to claim 1 , wherein small particles, which are concentrate particles with a diameter at least 50% smaller than the average diameter of the concentrate particles, and/ or at least part of small calcine particles, which are particles from a gas-solid-fraction separated in at least one step, and/or at least parts of the other particles are pelletized such that at least 70 wt.-% are bigger than 500 μm or that at least 70 wt.-% are smaller than 90 μm.

5. The process according to claim 1 , wherein an amount of sulfur and/or carbon in the concentrate particles is between 0.5 and 60 wt.-% and/or an amount of sulfur and/or carbon in small particles, which are concentrate particles with a diameter at least 50% smaller than the average diameter of the concentrate particles, is more than 20% higher than in the concentrate particles and/or an amount of sulfur and/or arsenic in small calcine particles, which are particles from a gas-solid-fraction separated in at least one step, is more than 15% higher than an average amount in all calcine particles and/or the small calcine particles contain at least 2 wt.-% sulfur.

6. The process according to claim 1 , wherein secondary air is injected into the roaster which is heated to a temperature of at least 200° C.

7. The process according to claim 6 , wherein at least parts of the calcine are cooled in a fluid bed cooler, whereby air used as direct and/ or indirect cooling medium is used as secondary air and/or fluidizing medium in the roaster.

8. The process according to claim 1 , wherein small particles, which are concentrate particles with a diameter at least 50% smaller than the average diameter of the concentrate particles, and/or at least part of small calcine particles, which are particles from a gas-solid-fraction separated in at least one step, and/or at least part of the other particles and/or further particles are pelletized by mixing with a liquid binder comprising water or an aqueous solution containing sulfates, said further particles comprising calcine particles and/or sand and/or unseparated concentrate particles.

9. The process according to claim 1 , wherein small particles, which are concentrate particles with a diameter at least 50% smaller than the average diameter of the concentrate particles, and/or at least part of small calcine particles, which are particles from a gas-solid-fraction separated in at least one step, and/or at least part of the other particles and/or further particles are pelletized by mixing with further particles, said further particles comprising calcine particles and/or sand and/or unseparated concentrate particles.

10. The process according to claim 1 , wherein downstream of the roaster at least parts of the calcine are leached in leaching solution with an acid content leading to pH value of 2 or less and/or are leached in a cyanide solution or are smelted or introduced into an electric furnace.

11. The process according to claim 1 , wherein not recirculated calcine particles are milled and/or grinded.