METHOD FOR THE RECOVERY OF ZINC

Abstract

A method for the recovery of zinc from zinc containing materials using a smelting apparatus for smelting a metalliferous feed material, wherein the smelting apparatus includes a smelting vessel, a smelt cyclone mounted on the smelting vessel and in connection with the inside of the smelting vessel and an off-gas duct connected to the smelt cyclone, and wherein the method includes the steps of: injecting the feed material with a carrier gas into the smelt cyclone, injecting an oxygen containing gas into the smelt cyclone, injecting coal with a carrier gas into the smelting vessel, injecting an oxygen containing gas into the smelting vessel, optionally injecting fluxes with a carrier gas into the smelting vessel, wherein the zinc containing materials are injected into the smelt cyclone and/or into the smelting vessel.

Claims

1. A method for the recovery of zinc from zinc containing materials using a smelting apparatus for smelting a metalliferous feed material, wherein the smelting apparatus comprises a smelting vessel, a smelt cyclone mounted on the smelting vessel and in connection with the inside of the smelting vessel and an off-gas duct connected to the smelt cyclone, wherein the method comprises the steps of: injecting the feed material with a carrier gas into the smelt cyclone, injecting an oxygen containing gas into the smelt cyclone, injecting coal with a carrier gas into the smelting vessel, injecting an oxygen containing gas into the smelting vessel, optionally injecting fluxes with a carrier gas into the smelting vessel, wherein the zinc containing materials are injected into the smelt cyclone and/or into the smelting vessel.

2. The method according to claim 1, wherein the zinc containing materials injected into the smelting vessel are injected above and/or in a slag layer on the liquid feed material in the smelting vessel.

3. The method according to claim 2, wherein the zinc containing materials injected into the smelting vessel are injected at a first and/or a second level wherein the first level is between the smelt cyclone and the slag layer on the liquid metal in the smelting vessel and wherein the injection at the second level is carried out through a supply lance into the slag layer.

4. The method according to claim 1, wherein the particle size of the zinc containing materials injected into the smelt cyclone are in a range of at most 2.0 mm.

5. The method according to claim 1, wherein the particle size of the zinc containing materials injected into the smelt vessel at the first level have a particle size of at most 15 cm.

6. The method according to claim 1, wherein the particle size of the zinc containing materials injected at the second level into the slag layer have a particle size of at most 50 m.

7. The method according to claim 1, wherein the off-gas is guided through an inclined off-gas duct part downstream of the smelting vessel and the smelt cyclone.

8. The method according to claim 1, wherein the off-gas is cooled/quenched in an upright off-gas duct part downstream of the inclined off-gas duct part.

9. The method according to claim 8, wherein the off-gas is cooled/quenched to a temperature of 1200 C.

10. The method according to claim 1, wherein the off-gas is passed through a cooling tower followed by a cold dust cyclone.

11. The method according to claim 1, wherein the off-gas is passed through a high temperature dust cyclone.

12. The method according to claim 1, wherein the off-gas is used to drive a steam driven electric generator.

13. The method according to claim 1, wherein at least part of the zinc oxide containing dust recovered from the off-gas is injected into the smelting vessel.

14. The method according to claim 1, wherein the off-gas from the smelting apparatus is controlled by controlling the amount of oxygen injected into the smelt cyclone and/or into the smelting vessel.

15. The method according to claim 1, wherein the off-gas from the smelting apparatus is controlled by controlling the amount of oxygen injected into the process such that the conditions in the off-gas are oxidising.

16. The method according to claim 1, wherein a controlled amount of oxygen is injected into the off-gas upstream of the inclined off-gas duct part.

17. The method according to claim 1, wherein the particle size of the zinc containing materials injected into the smelt cyclone are in a range of at most 1.5 mm.

18. The method according to claim 1, wherein the particle size of the zinc containing materials injected into the smelt cyclone are in a range of at most 1.0 mm.

19. The method according to claim 1, wherein the particle size of the zinc containing materials injected into the smelt vessel at the first level have a particle size of at most 10 cm.

20. The method according to claim 1, wherein the particle size of the zinc containing materials injected into the smelt vessel at the first level have a particle size of at most 5 cm.

21. The method according to claim 1, wherein the particle size of the zinc containing materials injected at the second level into the slag layer have a particle size of at most 30 m.

22. The method according to claim 1, wherein the particle size of the zinc containing materials injected at the second level into the slag layer have a particle size of at most 20 m.

23. The method according to claim 8, wherein the off-gas is cooled/quenched to a temperature of 1050 C.

24. The method according to claim 8, wherein the off-gas is cooled/quenched to a temperature of 900 C.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0033] The invention will be further explained with the example shown in the drawing, in which schematically a smelting apparatus with off-gas handling devices is shown.

DETAILED DESCRIPTION OF THE DRAWING

[0034] In the drawing a smelting apparatus 1 is shown which has a smelt cyclone 2 and below the smelt cyclone a smelting vessel 3. The smelt cyclone is provided with injections lances 4 to feed a metalliferous feed material such as iron ore into the smelt cyclone together with flux as far as necessary by means of an conveying gas. For the heating and partial melting of the injected iron ore oxygen is injected into the smelt cyclone 2 by means of a set of oxygen lances 5.

[0035] The smelting vessel 3 is provided with oxygen lances as well (not shown) to inject oxygen above the slag level when the smelting apparatus is in operation to adjust heating and reduction requirements of the process. Further lances 6 are provided to inject coal and/or additives in the slag layer 7. The molten iron 8 produced in the smelting reduction process is continuously discharged from the vessel 3 through a forehearth 9. The slag 7 resulting from the process is discharged from smelting vessel 3 by sequential tapping through a slag tap hole 10.

[0036] The smelting apparatus 1 is further designed for the injection of zinc containing materials at different levels in the apparatus. A first level of injection is the smelt cyclone 2 where the zinc containing materials are injected at the level where the metalliferous feed material is injected and/or just below that level. Injections through separate lances is an option but because the size of the zinc containing material injected at this level is within the range of the metalliferous feed material it is preferably injected in the smelt cyclone 2 together with the metalliferous feed material.

[0037] A second level for the injection of zinc containing materials is higher up in the smelting vessel 3, in this example in a roof portion 11 of the smelting vessel 3 through injection devices 12. At this level larger pieces of zinc containing materials are injected into the vessel. In this respect the term inject could mean a number of different methods to bring the zinc containing material into the vessel, for instance by means of a conveying gas or by means of a mechanical conveying system. Such systems are typically provided with a gas lock system to prevent that process gas escapes the vessel through the injection system or device.

[0038] A further injection level is just above the slag layer 7 or directly in slag layer 7 through injection lances 13. Injection of zinc containing materials at this level is for the finest fraction.

[0039] These different levels of injection of the zinc containing materials is to ensure that the zinc will melt and evaporate before the zinc containing materials reaches the liquid iron bath in the smelting vessel.

[0040] The zinc vapour will flow upward into the off-gas duct 14. The off-gas duct is provided with an inclined off-gas duct part 15 in which liquid iron or metalliferous droplets present in the off-gas will end up against the inner wall of the inclined off-gas duct part 15 and flow back into the smelting vessel 3. In this manner the off-gas will practically free from any iron components. This is important because the formation of Franklinite a zinc iron oxide is suppressed totally or to a very large extent. With Franklinite present in the zinc bearing dust makes the recovery of zinc from the dust more difficult and costly.

[0041] The temperature in the inclined off-gas duct part 15 is in a range of 1600-1900 C. at which temperature the zinc vaporised in the vessel under reductive conditions will remain vaporised. In the temperature range of 1600-1900 C. it is irrespective of whether the conditions are reductive or oxidising, the zinc will remain vaporised.

[0042] The inclined off-gas duct part 15 is followed by a cooling/quenching device 16 in the off-gas duct 14 with which the temperature of the off-gas is lowered to a temperature of 1200 C. or lower. At about 1000 C. the zinc vapour is changed to zinc oxide which is a solid with a fine to ultrafine particle size.

[0043] The off-gas with the dust and the zinc oxide is further cooled by means of heat exchange with a steam driven electric generator device 17 further downstream of the cooling/quenching device 16. After passing the steam driven electric generator 17 the off-gas goes through a cold cyclone dust separator 18 wherein the off-gas is at least partially cleaned. Instead of a cold dust cyclone 18 also a high temperature dust cyclone could be used which should be positioned upstream of steam driven electric generator 17 and downstream of the cooling/quenching device 16, for instance at the horizontal duct portion at the top of duct 14.

[0044] After passing through hot or cold dust cyclone and steam driven electric generator the off-gas goes through the bag filter 19 wherein most if not almost all dust and zinc oxide is removed from the off-gas.

[0045] Downstream of the bag filter or bag house 19 a desulphurisation unit 21 is provided for the removal of SOx compounds. Part of the cleaned off-gas after the desulphurisation unit 21 is used as cooling gas for the cooling/quenching device 16 for which a return duct 23 with compressor is provided. Another part of the cleaned off-gas after the desulphurisation unit 21 is used as carrier gas for injecting iron ore through lances 4 into cyclone 2 and/or injecting coal and/or additives through lances 6 into the slag layer 7, for which a return duct 24 with compressor is provided.

[0046] In order to pass the off-gas through the off-gas duct 14, cooling/quenching device 16, steam driven electric generator 17, cold dust cyclone 18, and bag filter 19 a fan 20 is provided in the off-gas duct 14 downstream of the bag filter 20. The fan 20 is not necessary if the smelting vessel 3 is operated at sufficient pressure.

[0047] Before the off-gas is discharged through stack 22 the NOx in the off-gas is removed as far as possible at location 25.