Kalciums och magnesiums inverkan på arsenikavdrivningen i virvelbäddsugnen
The influence of calcium and magnesium on the expellation of arsenic in the fluidized bed furnace
In the fluidized bed furnace at Rönnskärsverken, Skelleftehamn, sulphur-containing ore concentrates are roasted in order to remove about 50% of the sulphur in the incoming ore concentrate. This occurs in order to reach the goal of a matte containing 55% of copper in the following smelting process. At the same time as the ore concentrate is partially roasted pollutions as arsenic, antimony and bismuth are expelled. Earlier made thermodynamic calculations of equilibrium suggested that calcium and magnesium form stable compounds with arsenic and thereby inhibit expellation of arsenic in the fluidized bed furnace, an element that is undesired. The purpose of this thesis work was to gain knowledge of the mechanisms behind the formation of these stable arsenic compounds. In order to yield an increased expellation of arsenic in the fluidized bed furnace. Thermodynamic calculations were made by the computer programme FactSage and roasting experiments with ore concentrates were performed on a laboratory scale. Simple particle size measurements were performed as well. It could be ascertained that raising the temperature increased the cupellation of arsenic and that magnesium carriers bind less arsenic than calcium carriers. The expellation of arsenic was also affected by the form of calcium carriers as well as their particle size. Calcium oxide binds the most arsenic while limestone and calcium silicate bind it the least. Smaller particles reacted in a larger extent with arsenic. When roasting ore concentrates with high arsenic levels in the fluidized bed furnace, the addition of slurry from the lead kaldo furnace should be avoided. The slurry, which is normally added during roasting, contains large amounts of calcium oxide which has proven to be an inhibitor of the expellation of arsenic. Future roasting experiments focusing on the slurry?s effect on the expellation of arsenic should be made. For these experiments another roasting furnace should be used since the one used in this thesis work didn?t give conditions homogenous enough. It would also be interesting to investigate at what levels calcium in a given mineral form starts to give a substantial expellation of arsenic.