Patent GB-459823-A (GB)
Title: Improvements relating to the roasting of mineral sulphides in gaseous suspension
IPC: C22B1/10
Filed: 1936-03-12
Abstract: Mineral sulphides are roasted in gaseous suspension, and part or all of the solid combustion products are introduced into a sulphating chamber wherein they are exposed to the action of sulphur dioxide-bearing gases at a temperature below the decomposition temperature of the sulphates formed.  The term "solid combustion products" includes the roasted material falling to the bottom of the combustion chamber, and also the dust particles separated from the combustion gases.  Reference is made to the roasting of zinc, copper, iron and lead sulphides.  The temperature of the hearth of the combustion chamber is about 1700 DEG  F., and that of the sulphating chamber, when zinc sulphate is to be formed, about 900 DEG  F. Ferric oxide produced acts catalytically in the sulphating operation. In the furnace shown in Fig. 1, <PICT:0459823/III/1> <PICT:0459823/III/2> which is adapted to produce oxides or sulphates or any desired proportion of each, the sulphide ore is passed by rabble arms A through drop holes 3 from the first drying hearth 2 to a second drying hearth 5, and thence by rabble arms B to pulverizer 17.  It then passes through conduits 18, 30 to nozzle 20 from which it is blown by fan 21 into the combustion chamber 8.  The hot combustion gases are used in part to dry the ore, being passed by conduit 22 to the hearth 5, finally escaping through conduit 6.  A setting hearth 9 is disposed at the bottom of the chamber 8 and communicates with a second setting hearth 11 by opening 10. Conduits 13, 14 communicate with storage bin 15, and the valves 73, 72 may be opened so that the product is wholly oxidic.  A cast iron or steel hearth 57 having a lute ring 70 is arranged below hearth 11, and forms the sulphating chamber.  Drop holes 65 are provided in hearth 11 through which the roasted material is passed by rabble arms D. The drop holes 65 are formed with adjustable closure means working in conjunction with valves 72, 73 to enable any desired percentage of the oxidic material to pass to the sulphating chamber.  Sulphur dioxide gases pass to the sulphating chamber via holes 69.  The material being sulphated is agitated by rabble arms 58 and is finally discharged through drop hole 66. Sulphur dioxide gases from the lower settling hearth and any desired percentage from the sulphating chamber pass through valved conduits 61, 59 to dust-collecting chambers 28, from which the separated dust is passed either to the combustion chamber 8 via conduit 64, or to the sulphating chamber, or to storage bin 15 via conduit 67.  The gases from the collecting chamber may be voided, or passed via conduit 26 and blower 21 to the combustion chamber to maintain the temperature therein.  Air from a heat-exchange device 29 passes to the drying chamber 12, which communicates with blower 21 through conduit 25.  In the furnace shown in Fig. 2, an additional sulphating hearth 57a is provided, and is formed with holes 65a, 69a for the passage of the product being sulphated and the sulphur dioxide gases respectively.  The latter are evacuated from the lower chamber through conduit 59, but the dust particles from the separators are returned to the upper sulphating chamber.