WO2000066796A1

WO2000066796A1 - Method for treating metal-containing waste by pyrometallurgy

Info

Publication number: WO2000066796A1
Application number: PCT/EP2000/003954
Authority: WO
Inventors: Jean-Luc Roth; Emile Lonardi; Patrick Hutmacher
Original assignee: Paul Wurth S.A.
Priority date: 1999-05-03
Filing date: 2000-05-03
Publication date: 2000-11-09
Also published as: ZA200108580B; AU5210800A; EP1192288A1; LU90395B1

Abstract

The invention concerns a method using pyrometallurgy for treating waste containing metals generally in oxidised form, in a first zone including vertically spaced hearths, of a multistage furnace, which consists in: introducing the waste containing metals generally in oxidised form on the top hearth of the first zone and gradually transferring it towards the lower hearths; creating in the first zone conditions favourable for volatilising the metals in oxidised form; extracting from the first zone the gases containing the volatilised metals in oxidised form.

Description

Method for pyrometallurgical treatment of waste containing metals

Introduction

The present invention relates to a method of pyrometallurgical treatment of waste containing metals.

Waste treatment is a booming activity, often motivated by economic or ecological interests. It is interesting to treat waste containing metals in order to extract the metals which can be recycled in a new manufacturing process, or simply to extract metals which present a risk for the environment.

The steel industry is a sector that produces a lot of metallic waste, in particular in processes for the preparation or treatment of metallic parts: surface treatment, pickling, cleaning, metallization or tinning. These processes generate waste containing metals, in particular in the form of dust and sludge. The dust comes from the filtration of gases from blast furnaces and steel furnaces. The sludge comes, for example, from the filtration of baths, and contains large quantities of water, with in addition metals such as nickel (Ni) and / or iron (Fe), and heavy metals such as zinc (Zn) and lead (Pb) in an oxidized form. Tin sludge, on the other hand, contains mainly iron and tin (Sn) in the form of hydroxides.

The chemical industry rejects metallic waste such as catalysts (eg nickel-based) or organometallic compounds (paints).

The pharmaceutical industry also produces waste containing various metals such as Bismuth (Bi).

The electrical industry produces waste based on copper (Cu) and silicon (Si), but also containing other metals, including heavy metals (eg Zn in batteries)

Finally, it would be desirable to treat certain wastes containing certain toxic metals, in order to extract toxic metals for reuse, and also to avoid the special and protected landfill of the waste. These include wastes containing heavy metals such as cadmium (Cd), antimony (Sb), arsenic (As), mercury (Hg), even even thallium (Tl), germanium ( Ge) and selenium (Se).

These metals can be found in waste of various origins in various concentrations and combinations. They are most generally present in an oxidized form (in the sense of redox), rarely in their reduced form, so we speak of waste containing metals generally in oxidized form.

Object of the invention (Problem to be solved by the invention)

The object of the present invention is to provide a process for the pyrometallurgical treatment of waste containing metals generally in oxidized form. According to the invention, this objective is achieved by a method according to claim 1.

General description of the claimed invention with its main advantages.

The process according to the invention relates to the pyrometallurgical treatment of waste containing metals generally in oxidized form, in a first zone comprising vertically spaced hearths, of a multi-stage oven, in which:

(a) waste containing metals generally in oxidized form is introduced onto the upper floor of the first zone and gradually transferred to the lower floors;

(b) conditions favorable to the volatilization of metals in oxidized form are created in the first zone; (c) extracting from the first zone the gases containing the volatilized metals in oxidized form.

The present method takes advantage of the capacity of the multi-stage oven to create particular atmospheres by zones and / or by floors, according to a reaction which it is desired to carry out. It will be appreciated that according to the present invention, it is possible to pyrometallurgically treat waste containing metals, and to extract at least part of it, respectively some of these metals contained in the waste by volatilizing it in an oxidized form. We are talking here about metals generally in oxidized form, because it is assumed that the metals contained in this waste will most often be present in oxidized form, that is to say not in metallic form but in ionic form, of oxide, salts etc.

Some of the metals extracted from the waste can be recycled in new manufacturing processes, which is interesting from an economic point of view.

Waste whose landfill is problematic from an environmental point of view can be treated by the method according to the invention, in order to extract the troublesome metals for landfill. By choosing the reaction conditions well, the method according to the invention makes it possible to selectively volatilize certain metals in oxidized form, preferably with respect to the other metals generally in oxidized form contained in the same waste. It is therefore possible to carry out a selective extraction of certain metals in oxidized form. According to a first embodiment of the process, in stage (b) the waste containing metals generally in oxidized form is brought to a temperature up to 1100 ° C. so as to calcine them and to cause the volatilization of metals under a oxidized form. Such a process is particularly suitable for the selective extraction of metals such as Sb, As, Bi, Pb, Tl, Ge and Se contained in oxidized form in eg sludge or dust.

Advantageously, the first zone operates co-current, and the gases said “co-current gas” are evacuated from the first zone at its lower part. The gases and the solids therefore flow in the same direction, from the top of the zone to the bottom of the zone. In addition, the evacuated cocurrent gases can be cooled, filtered to separate the metals in oxidized form, and then reintroduced into the first zone, preferably after having been reheated. This increases the gas flow from the first zone. For a given vapor pressure of a metal in oxidized form, the quantity of metal in oxidized form extracted is proportional to the gas flow rate.

According to a second embodiment of the process, in step (b) the waste containing metals generally in oxidized form is brought to a temperature up to 800 ° C; the metal-containing waste is brought into contact with a carbonaceous reducing agent so as to obtain metals in reduced form, and a product containing chlorine and / or sulfur is introduced to cause the reaction of metals with chlorine and / or sulfur , then their volatilization in chlorinated and or sulfur form. It is thus possible to extract the tin (Sn) by two extraction routes, one of which uses chlorine in the form of

HCI, chlorinated organic compounds, chlorine salts or their mixture, and the other uses sulfur in the form of H ₂ S, sulfur in the solid state, organic sulfur compounds, solid sulfur or their mixture . One or the other of the extraction routes will be chosen according to the other metals contained in the waste to be treated.

According to another embodiment, the first zone can be operated against the current. The gases known as “counter-current gases” are then evacuated from the first zone at its upper part. These gases can then be treated in an afterburner, then cooled and filtered to separate the metals in oxidized form. This makes it possible to take advantage of the energy properties of the gas, and to release a relatively clean gas. It is also possible to reintroduce the counter-current gases into the first zone after having reheated them.

According to another embodiment, the solid waste remaining possibly still containing metals generally in oxidized form are transferred after step (c) into a second zone comprising soles vertically spaced, called the "reduction zone", located below the first zone, to be gradually transferred there to the lower sole, brought into contact with a reducing agent and brought to a temperature allowing the reduction of the metals present in oxidized form. It is thus possible, in the same multi-stage oven, to extract metals first in oxidized form, then to proceed to the reduction of the oxidized metals not yet extracted. The reaction temperature allowing the reduction of metals in oxidized form can be between 800 and 1200 ° C, and is preferably between 1000 and 1100 ° C. At least part of the reduced metals in the reduction zone are volatilized at the reaction temperature. They will then advantageously be extracted from the reduction zone with the gases at the level of the sole on which they are formed. This reveals the possibility of extracting waste introduced into the furnace, metals in reduced form in the gas phase. All gases from the reduction zone of the multi-stage oven can be treated in an afterburner, cooled and filtered. Advantageously, the volatilized reduced metals are oxidized in the gas phase, cooled to condense them into dust, and filtered to be separated from the gases.

If the waste contains metals which cannot be extracted in gaseous form, either in the oxidized state or in the reduced state, the remaining waste will then advantageously be extracted from the multi-stage oven after reaching the bottom floor of the reduction zone, then can be sorted, so as to separate the non-volatilized reduced metals. Among the metals which cannot be extracted in the gas phase, there is in particular iron and / or nickel. As carbonaceous reducing agent, coal, solid or liquid petroleum products, synthetic materials such as plastics, gums, organic waste or mixtures thereof are used. In some cases, plastics and / or gums containing chlorine and sulfur can be used. Waste containing metals generally in oxidized form can be dried on the upper floors of the multi-stage oven before being introduced in the first zone. This is interesting when the waste containing metals generally in oxidized form contains large quantities of water, such as for example sludge.

Depending on the gas flow rates and the volatile metal concentrations, the heating of the hearths can be carried out directly or indirectly.

Preferably, all the gases from the multi-stage oven are dechlorinated and desulfurized.

Detailed Description using Figures

Other features and characteristics of the invention will emerge from the detailed description of some advantageous embodiments presented below, by way of illustration, with reference to the accompanying drawings. These show:

Fig.1: schematic diagram of the process, in an embodiment for the treatment of waste containing metals of the Sb, As, Bi, Hg, Pb, Tl, Ge and Se type, generally in oxidized form. Fig.2: variant of the process of Fig.1.

Fig.3: schematic diagram of the process, in an embodiment for the treatment of tin bath waste. Fig.4: schematic diagram of the process, in an embodiment for the treatment of waste containing metals such as Fe, Ni, Zn, and Pb generally in oxidized form.

The present method uses a multi-stage furnace to treat waste containing metals generally in oxidized form. It is important to note that the waste can contain only one metal, the embodiment should therefore be chosen preferably according to the metal to be treated. We speak of waste containing metals generally in oxidized form because the metals in the waste are rarely in a reduced state, and they are most often oxides and hydroxides of metals. The term “oxidized form” must be considered here in its broadest sense, at the level of redox: it is said that the metal is in oxidized form if it is not in the reduced state. Fig.1 shows a block diagram of the present method in an embodiment allowing the treatment of waste containing metals of the Sb, As, Bi, Pb, Hg, Tl, Ge and Se types generally in oxidized form. A multi-stage oven 10 composed of vertically spaced annular soles is used. Loading 12 and unloading sole 14 are arranged alternately. The first 12 have a peripheral orifice, the peripheral orifices of two consecutive loading decks being diametrically opposite; the seconds 14 have an open central circular part. The oven is also provided, in its central part, with a vertical rotation shaft 16 to which are attached rakes (not shown) extending over the entire radius of the hearths. Direct (burners) or indirect (resistors) heating means (not shown) make it possible to heat each hearth individually, in order to obtain different temperatures by zones and / or by hearths. The waste is introduced continuously through an opening 18 in the upper wall of the multi-stage oven and falls on the first loading floor 12. The rakes, driven by the vertical rotation shaft 16, spread the waste on the loading floor 12 and bring them back to the peripheral opening through which they fall on the unloading deck 14 located just below. The rakes then direct the waste to the central orifice, through which they fall on the lower loading floor. These steps are repeated until the waste reaches the bottom of the multistage oven.

In the lower part of the multi-stage oven, there is preferably a temperature of 1100 ° C. At this temperature, the waste is calcined and the metals Sb, As, Bi, Pb, Hg, Tl, Ge, Se are volatilized in oxidized form. As indicated by the dotted arrows, the multi-stage oven is operated cocurrently, that is to say that the gases circulate in the same direction as the material: downwards. The gases containing the volatilized metals in oxidized form are therefore removed from the multi-stage oven at its lower part. The co-current operation makes the best use of the gases since all the gases are extracted at the bottom of the multi-stage oven, which makes it possible to obtain a large gas flow rate in the lower stages of the multi oven stages where temperature conditions are most conducive to the volatilization of metals. The co-current gases evacuated from the multi-stage oven are led to a treatment installation 20 in which they are cooled and then filtered, in order to recover the metals in oxidized form contained in the gases and to release the gases. The rest of the waste is evacuated from the multi-stage oven by an outlet orifice 22 once it has reached the lower floor. The evacuated waste is therefore freed from metals which have been volatilized in oxidized form.

Fig. 2 proposes a variant of the method of FIG. 1, making it possible to increase the gas flow in the lower floors. To do this, the co-current gases once passed through the treatment installation 20 are at least partially led to a heat exchanger 24 to be reheated, then reinjected into the middle of the multi-stage oven 10. The amount of metal in oxidized form extracted from the multi-stage oven per unit of time is proportional to the gas flow through the oven and to the vapor pressure of the metal in oxidized form; by increasing the gas flow, the recovery of metal in oxidized form is accelerated.

Fig.3 shows a block diagram of the present method in another embodiment allowing the treatment of waste containing metals in oxidized form such as tin oxides or hydroxides, such as for example tinning sludges which contain essentially oxidized forms of iron and tin. A multi-stage oven 10 similar to that described above is used; conditions are created there which are suitable for the volatilization of tin in oxidized form.

Waste containing iron and tin in oxidized form is introduced into the multi-stage oven through the opening 18 and falls on the first loading floor 12. The rakes advance them towards the lower stages, alternating between loading and unloading decks. In the central part of the furnace, where there is a temperature of about 800 ° C., a reducer - arrow 26 is introduced, preferably fine-grained coal. The rakes by their sweeping then realize an intimate mixture of waste and coal, causing the reduction of the tin oxides contained in the waste. At 800 ° C., a selective reduction of the tin oxides is carried out, since the temperature is too low to cause the reduction of the iron oxides. In order to volatilize the tin, hydrochloric acid (HCl) is introduced at the level of the sole placed below that on which the coal has been introduced. Arrow 28. It should be noted that hydrochloric acid can be replaced by Cl ₂ , or by a solid chlorine product volatile at the reaction temperature (eg NaCI, MgCI ₂ , KCI, PVC which have a vapor pressure greater than 0.01 atm at 1000 ° C). The metallic tin formed by the reduction of the tin in oxidized form is then oxidized by HCI and is transformed into SnCl ₂ , metal in oxidized form which is volatilized at the temperature of the reaction. In terms of redox, the number of oxidation (N _ox ) of tin goes from N _ox = 0 to N _ox = + 2, hence the expression "metal in oxidized form". The gases containing SnCI ₂ , dotted arrow 30, are evacuated multi-stage oven 10 at its lower part, that is to say at the level of the sole on which they are formed. These gases then pass through a cooling device 32 to condense the SnCI ₂ and recover it. The counter-current gases (ascending gases typically circulating in a multi-stage oven), represented by the dotted arrow 34, are discharged from the multi-stage oven at its upper part and are brought to an after-burner 36. The gases from the cooling device 32 and the post-burner 36 are then sent to a treatment installation 37 to be cooled, dechlorinated and desulfurized, then filtered, before being released. On reaching the bottom floor of the multi-stage oven 10, the waste is therefore freed from the tin, but the iron remains in oxidized form. The process in Fig. 3 can also be carried out by replacing the chlorine with a sulfur-based gas, e.g. H ₂ S, or a solid sulfide volatile at the reaction temperature (pyrite, for example). A volatile tin sulfide will then be formed at 800 ° C. The choice between using chlorine or sulfur products depends on the other metals contained in the waste. To extract Sn in the presence of iron or nickel, chlorine is preferably used. On the other hand, sulphurization is more suitable for separating Sn from metals such as Pb, Zn or Cd. A final embodiment of the process of the present, illustrated with the aid of FIG. 4, makes it possible to treat in a multi-stage oven waste containing a mixture of metals of the Fe, Ni, Cu, Zn, Cd type, Sb, As, Bi, Pb, Hg, Tl, Ge, Se. A stage oven 10 similar to that described above is used, but which comprises two zones. These two zones are essentially functional (they define reaction zones), and do not necessarily have to be structurally distinct in the multi-stage oven 10. In the first zone 38, the upper part of the multi-stage oven 10, metals are volatilized in oxidized form. In the second zone 40 - lower part of the multistage oven 10, metals are reduced: certain metals being solid and others volatile in the reduced state, at the temperature of the zone.

In order to illustrate the process in Fig. 4 concretely, consider that the waste contains Fe, Ni, Zn, and Pb in oxidized forms. The waste is introduced into the multi-stage oven 10 through the opening 18 and falls on the first loading floor 12, in the first zone 38. The rakes make it progress towards the lower floors, alternating between loading floors and unloading. Very quickly, the waste is brought to the temperature of 1100 ° C. in this first zone 38, the temperature at which it is calcined and the metals with volatile oxides are volatilized; in this case it is PbO. The calcination gases flow against the current, as illustrated by arrow 42, and are therefore evacuated from the multi-stage oven 10 at its upper part, more precisely at the level of the first hearths of the first zone 38; once extracted from the multi-stage oven 10 they are led to a post-burner 36. After the extraction of volatilized metals in oxidized form in the first zone 38, the waste is transferred to the second zone 40, located below the first zone 38. In the second zone 40, a arrow reducer 44 is injected, preferably fine-grained carbon. The rakes, by their sweeping, intimately mix the waste with coal, causing the reduction of metals. The iron and nickel oxides are reduced, and continue their progression towards the bottom of the multi-stage furnace 10. The oxides or hydroxides of Zn are reduced and the Zn is directly volatilized. Reduction gases - arrow 46, containing metals reduced in phase gas, are extracted from the multi-stage oven in the lower part of the second zone 40, that is to say where they are formed. They are then sent to an afterburner 48, in which Zn is oxidized to ZnO, in order to be separated from the gas. All the gases from the multi-stage oven 10 are then led to a treatment installation 37 to be cooled, dechlorinated and desulfurized, and filtered, before being released. It will be noted that it is advantageous to volatilize all of the lead oxide in the first zone 38, which makes it possible to increase the purity of the Zinc oxide recovered in the post-burner 48.

It will be noted that this example is given for Fe, Ni, Zn, and Pb. The Pb is extracted in oxidized form in the first zone 38, as would be the case with Sb, As, Bi, Hg, Tl, Ge or Se. The Zn is extracted in the reduction gases of the second zone because it is volatile in its reduced form, as would be the case with Cd, and must be oxidized in a post-burner. Iron and Nickel are reduced in the second zone 40, but remain solid at the temperature of reduction, this would also be the case for Cu.

Solid metals in reduced form, that is to say iron and nickel, are removed from the oven with the rest of the waste (an inert gangue) and possibly an excess of reducing agent, through an outlet orifice. Iron and nickel, once cooled, can be sorted by manual or automated methods (eg magnetic sorting).

It will be noted that it is possible to add in each of the preceding processes a step intended for drying the waste. Waste containing metals generally in oxidized form would then be dried in a drying zone, comprising vertically spaced hearths, at the start of the multi-stage oven. The first zone would then start directly below this drying zone.

Those skilled in the art will obviously be able to draw directly from the teaching of the present to modify the conditions prescribed in the processes presented, in particular the temperatures and atmospheres, in order to extract other volatile metals in oxidized form, from of material introduced into a multi-stage oven.

Claims

claims

1. A process for the pyrometallurgical treatment of waste containing metals generally in oxidized form, in a first zone comprising vertically spaced hearths, of a multi-stage oven, in which:

(b) conditions favorable to the volatilization of metals in oxidized form are created in the first zone;

(c) extracting from the first zone the gases containing the volatilized metals in oxidized form.

2. Method according to claim 1, characterized in that in step (b) the waste containing metals is generally carried in oxidized form at a temperature up to 1100 ° C so as to calcine them and cause the volatilization of metals in oxidized form.

3. Method according to claim 2, characterized in that the metals generally in oxidized form are chosen from the group consisting of: Sb, As, Bi, Pb, Tl, Ge, Se, or their mixtures.

4. Method according to claim 2 or 3, characterized in that the first zone operates co-current, the gases being all evacuated from the first zone at its lower part.

5. Method according to claim 4, characterized in that the evacuated cocurrent gases are cooled, filtered and are reintroduced into the first zone, preferably after having been reheated.

6. Method according to claim 1, characterized in that in step (b): - the waste containing metals is generally brought in oxidized form at a temperature up to 800 ° C;

- we put waste containing metals generally in the form oxidized in contact with a carbon reducer so as to obtain metals in reduced form,

- Introducing a product containing chlorine and / or sulfur to cause the volatilization of metals in chlorinated and or sulfur form.

7. Method according to claim 6, characterized in that the metal volatilized in chlorinated and or sulfur form is tin in chlorinated and or sulfur form.

8. Method according to claim 6 or 7, characterized in that the product containing chlorine is chosen from the group consisting of hydrochloric acid (HCl), chlorine (Cl ₂ ), or chlorinated organic compounds and / or chlorine salts or their mixtures, volatilizable at the temperature of the first zone; and in that the sulfur-containing product is chosen from the group consisting of hydrogen sulfide (H ₂ S), sulfur in the solid state, sulfur-containing organic compounds, solid sulfides or their mixtures, volatilizable at temperature of the first zone.

9. Method according to any one of claims 2,3 and 6 to 8, characterized in that the first zone operates against the current, and in that the counter-current gases are evacuated from the first zone at its upper part.

10. Method according to claim 9, characterized in that the evacuated counter-current gases are treated in a post-burner, then cooled and filtered, and are reintroduced into the first zone, preferably after having been reheated.

11. Method according to any one of the preceding claims, characterized in that the gases containing the volatilized metals in oxidized form from step (c) are cooled and filtered so as to separate the metals in oxidized form from the rest of the gas.

12. Method according to any one of the preceding claims, characterized in that the waste containing metals generally in oxidized form is transferred after step (c) into a second zone comprising both vertically spaced sole, called reduction zone, located below the first zone, to be gradually transferred there to the lower sole, brought into contact with a reducing agent and brought to a temperature allowing reduction of metals in oxidized form.

13. Method according to claim 12, characterized in that the reaction temperature allowing the reduction of metals in oxidized form is between 800 and 1200 ° C, and is preferably between 1000 and 1100 ° C.

14. The method of claim 12 or 13, characterized in that at least a portion of the metals reduced in the reduction zone are volatilized at the reaction temperature.

15. Method according to claim 14, characterized in that the volatilized reduced metals are extracted from the reduction zone with the gases.

16. Method according to claim 14, characterized in that the volatilized reduced metals are extracted from the reduction zone at the level of the sole on which they are formed.

17. Method according to any one of claims 12 to 16, characterized in that all the gases coming from the reduction zone of the multi-stage oven are treated in a post-burner, cooled and filtered; and in that the volatilized reduced metals are oxidized in the gas phase, cooled to condense them into dust, and filtered to be separated from the gases.

18. Method according to any one of claims 12 to 17, characterized in that at least part of the metals reduced in the reduction zone are not volatilized at the reaction temperature.

19. The method of claim 18, characterized in that the waste is extracted from the multi-stage oven after reaching the bottom floor of the reduction zone.

20. The method of claim 19, characterized in that the waste from the reduction zone is sorted after being extracted from the multi-stage oven, so as to separate the reduced non-volatilized metals.

21. Method according to any one of claims 12 to 20, characterized in what the reducer is carbon, and the reduced metals are Fe and / or Ni.

22. Method according to any one of the preceding claims, characterized in that the waste containing metals generally in oxidized form is dried in a drying zone comprising vertically spaced floors, of the multi-stage oven, before being introduced on the upper floor of the first zone, the drying zone being located above the first zone.

23. Method according to any one of claims 1 to 10, characterized in that the first zone extends over the entire multi-stage oven.

24. Method according to any one of the preceding claims, characterized in that the heating of the floors is carried out directly or indirectly.

25. The method of claim 19, characterized in that the reduced metals from the furnace are separated by magnetic sorting from the rest of the content of the reduction zone.

26. Method according to any one of the preceding claims, characterized in that the all gases from the multi-stage oven are dechlorinated and desulfurized.