Method and plant for removing arsenic and/or antimony from flue dusts

Abstract

A method for the treatment of flue dusts containing arsenic and/or antimony from pyrometallurgical methods, wherein a reducing agent is added to the flue dusts, the flue dusts are heated together with the reducing agent, and volatile components are separated from a slag. The reducing agent is a carbonaceous compound.

Claims

1. A method for the treatment of flue dusts containing 2 to 10% w/w arsenic and/or antimony from pyrometallurgical methods, wherein a reducing agent is added to the flue dusts, where the flue dusts mainly have a diameter of less than 10 m, the flue dusts are heated together with the reducing agent in a reductive atmosphere, whereby volatile components are separated, wherein the reducing agent is a carbonaceous compound, characterized in that heating is effected in a fluidized bed, and further characterized in that the flue dusts are granulated before heating with a size of 100 to 500 m, based on 60 to 100 wt % of the particles, during a microgranulation stage, and used to form the fluidized bed, and further characterized in that the carbonaceous compound is admixed to the flue dusts during granulating.

2. The method according to claim 1, characterized in that in the fluidized bed is a circulating fluidized bed.

3. The method according to claim 1, characterized in that a binder is admixed to the flue dusts during granulating.

4. The method according to claim 1, characterized in that granulating is effected at temperatures between 20 and 200 C.

5. The method according to claim 1, characterized in that heating is effected at temperatures between 500 and 1200 C.

6. The method according to claim 1, characterized in that at least a part of the heat is recovered after heating and supplied to a granulating process and/or the heating.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) In the drawings:

(2) FIG. 1 shows the method according to the invention with a downstream cooling for increasing the energy efficiency, and

(3) FIG. 2 schematically shows a representation of the complete waste gas after-treatment.

DETAILED DESCRIPTION OF THE INVENTION

(4) In FIG. 1, the flue dust containing arsenic and/or antimony is introduced into an apparatus for the microgranulation 10 via conduit 11. Via conduit 12, a carbonaceous reducing agent in solid form, such as coal or biomass, can be added. Via conduit 13, further binders can be supplied to the microgranulation 10. It is of course also possible to realize the supply of several components via a common supply conduit, so that intermixing already is effected in advance. If no carbonaceous reducing agent is introduced here, this addition must be effected later on.

(5) The particles obtained in the microgranulation 10, of which 60 to 100 wt-% have a diameter of 100 to 500 m, are introduced into the reactor 20 via conduit 14 and/or into venturi dryer 93 via conduit 34. Via conduit 94, the stream loaded with solids flows into a second separating means 96, e.g. a cyclone. From the second separating means 96 the feed material is conveyed to the reactor via conduit 15. The reactor 20 preferably is designed as circulating fluidized bed. In the reactor 20, the granules are heated to a temperature between 650 and 1000 C., preferably 750 to 950 C. The fluidizing gas is introduced into the reactor via conduit 21. Resulting process gas is discharged via conduit 24.

(6) Via conduit 23, gaseous carbonaceous reducing agent, such as CO and/or methane, can also be introduced. At the same time, it is also possible to introduce a carbonaceous solid material as reducing agent into the reactor 20 via a non-illustrated conduit.

(7) The input of energy for heating into the reactor 20 can be effected in the usual way, in that for example the fluidizing gas at the same time acts as fuel gas, reactant and/or as energy carrier.

(8) Via conduit 24, the solids obtained, namely the calcine, is withdrawn together with at least considerable parts of the waste gas or also the complete waste gas stream and supplied to a first cyclone 90.

(9) In this cyclone 90, the solids of the waste gases and the calcine are at least partly recirculated into the reactor 20 via conduit 92. Part of the solid stream is discharged via conduit 22 into calcine cooler 30 where the heat of the calcine is partially transferred to the fluidizing gas 21. The final product is discharged via conduit 25.

(10) Via conduit 91, the hot waste gas which still is loaded with fine dusts, in particular with particles with a diameter50 m, is supplied to a Venturi drier 93. In the Venturi drier 93, further cooling of the waste gas and a separation of solids and waste gas is effected. Heat contained in the waste gas can be transferred to the microgranulation stage 10 via a non-illustrated heat stream.

(11) FIG. 2 shows the complete aftertreatment of the resulting waste gas stream together with a corresponding energy concept.

(12) Via conduit 11 the flue dust, via conduit 12 a carbonaceous solid reducing agent, and via conduit 13 further binders (bentonite and/or other anorganic binders, cellulose compounds and/or other organic binders) are introduced into the microgranulation 10. Here as well, a combined supply and/or the omission of the addition of the reducing agent and/or the binder is possible.

(13) After granulating 60 to 100 wt-% of the introduced material to particles with a diameter between 100 and 500 m, the granules obtained are introduced into the reactor 20 via conduit 14 and/or into the venturi drier 93 via conduit 34 as explained at FIG. 1.

(14) The reactor 20 preferably is designed as a circulating fluidized-bed reactor. Via conduit 24, hot waste gas which also contains fine dust is withdrawn and supplied to a post-combustion 40.

(15) Via conduit 42, most of the waste gases are supplied to a waste gas cooling with a heat recovery system and/or a quench 50. Parts of the recovered heat can be employed elsewhere in the method, e.g. to reduce the energy demand of roasting in the reactor 20. Via conduit 51, the hot waste gas stream which still contains flue dusts is supplied to a hot electrostatic precipitator, for example an electric filter 60. In the same, the fine dusts are separated and for example can be recirculated into the microgranulation 10 in a non-illustrated form. Via conduit 61, the waste gas cleaned and cooled in this way flows into a further, wet gas cleaning 70. In this way, the sulfur compounds contained in the waste gas can be separated and via conduits 71 and 72 finally be supplied to an apparatus for producing sulfuric acid 80, from which sulfuric acid can be withdrawn via conduit 81.

(16) Via conduit 73, parts of the gas stream from the wet gas cleaning 70 are supplied to a heat recovery system 74 and via conduit 75 recirculated into the reactor via a non-illustrated conduit. Due to this recycling loop, the sulfur content in the system is enriched continuously, so that with a corresponding control the downstream plant for producing sulfuric acid can be operated highly profitably in particular with educts with a sulfur content high enough for operation of a sulfuric acid plant (>5 Vol-% SO.sub.2).

(17) Finally, parts of the solids, the calcine, can be withdrawn from the reactor 20 after a successful heat treatment and be supplied to a cooling device 30 via conduit 23 and/or from the recirculated stream as explained in FIG. 1 via a non-illustrated conduit. Preferably, the cooling device 30 is designed as fluidized-bed cooler, as it has turned out to be favorable to use the resulting hot gas for pre-heating in the microgranulation 10, to which it is supplied via conduit 31. Correspondingly, the hot gas obtained, preferably hot air, also can be fed into the fluidizing conduit 21 of the reactor 20 via conduit 32.

(18) The cooled calcine is withdrawn from the cooling stage 30 via conduit 33. It can now be fed to the smelter to extract the contained valuable metals as Cu, Ni etc.

LIST OF REFERENCE NUMERALS

(19) 10 microgranulation 11-15 conduit 20 reactor 21-26 conduit 30 cooling device 31-34 conduit 40 post-combustion reactor 41, 42 conduit 50 heat recovery means 51 conduit 60 gas-solids separating means 61 conduit 70 wet gas cleaning 71-73 conduit 74 heat exchanger 75 conduit 80 sulfuric acid plant 81 conduit 93 Venturi drier 94-95 conduit 96 cyclone 97 conduit