Process for obtaining metal oxide and SO.sub.2 -containing gases essentially free of SO.sub.3 and H.sub.2 SO.sub.4 from ferrous sulphate containing salt

A process for obtaining metal oxides and SO.sub.2 -containing exhaust gases essentially free of SO.sub.3 and H.sub.2 SO.sub.4 from feed salt which contains ferrous sulphate in an amount of 40 to 85% by weight ferrous sulphate calculated without water of crystallization through thermal decomposition in a circulating fluidized bed;

• the fluidized state of which is maintained by oxygen-containing fluidized gas which has been preheated and by oxygen-containing secondary gas and which has been preheated and fed above the inlet for the fluidizing gas, with fuel being fed into the zone between inlets for the fluidizing gas and secondary gas;
• wherein a major part of the resulting metal oxide is discharged together with the exhaust gases from the top part of a shaft and is separated from the exhaust gases in a recycling cyclone and is recycled at least in part to the fluidized bed;
• comprising contacting the exhaust gases from the fluidized bed reactor, which exhaust gases contain SO.sub.2 and are essentially free of SO.sub.3 and H.sub.2 SO.sub.4, with said feed salt which feed salt contain at least 1 mol of water of crystallization for a time sufficient to insure oxidation of the divalent iron to trivalent iron in a single suspension type exchanger, introducing the contacted feed salt into the circulating fluidized bed reactor to effect decomposition thereof into metal oxide and removing the metal oxide and exhaust gases through the top of said shaft;
• characterized in that the exhaust gases used to contact the feed salt result from the reaction of the oxygen containing gases with said fuel and contacted feed salt in the fluidized reactor, the fluidized gas and at least a partial stream of the secondary gas stream are heated by an indirect heat exchange in a fuel-heated heat exchanger, and the quantity of oxygen introduced via the fluidizing gas and the secondary gas is controlled dependent on the quantity of fuel in order to receive an exhaust from the suspension type exchanger with a free oxygen content of 1-6% by volume and a temperature of 300.degree.-450.degree. C.