ZA200108580B

ZA200108580B - Method for treating metal-containing waste by pyrometallurgy.

Info

Publication number: ZA200108580B
Application number: ZA200108580A
Authority: ZA
Inventors: Jean-Luc Roth; Patrick Hutmacher; Emile Lonardi
Original assignee: Wurth Paul Sa
Priority date: 1999-05-03
Filing date: 2001-10-18
Publication date: 2003-01-20
Also published as: WO2000066796A1; EP1192288A1; AU5210800A; LU90395B1

Description

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LL 1 ® 20018580

WO 00/66796 PCT/EP00/039

P-PWU-418/WO

Method for the pyrometallurgical treatment of waste containing metals

Introduction

This invention relates to a method for the pyrometallurgical treatment of waste containing metals.

The treatment of waste is a fast-growing activity, often motivated by economic or ecological interests. It is of interest to treat waste containing metals in order to extract metals that can be recycled in a new production process, or simply to extract metals which present a risk to the environment.

The iron and steel industry is a sector which produces numerous types of metal waste, particularly in processes for manufacturing or processing metal parts: surface treatment, pickling, cleaning, metallisation or even tinplating. These processes generate waste containing metals, particularly in the form of dusts and siudges. The dusts derive from the filtration of gases discharged from the blast furnaces and steelworks furnaces. The sludges derive, for example, from the filtration of baths, and contain large quantities of water, as well as metals such as nickel (Ni) and/or iron (Fe), and heavy metals such as zinc (Zn) and lead (Pb) in an oxidised form. The tinplating sludges for their part contain essentially iron and tin (Sn) in the form of hydroxides.

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The chemical industry produces metal waste such as catalysts (e.g. nickel- based) or organometallic compounds (paints).

The pharmaceutical industry also generates waste containing various metals such as bismuth (Bi).

The electrical industry generates copper (Cu) based and silicon (Si) based waste, but this waste also contains other metals, including heavy metals (e.g.

Zn in batteries).

Finally, it would be desirable to treat some waste containing certain toxic metals, in order to extract the toxic metals so that they can be re-used and also to prevent the special and protected discharge of this waste. This applies particularly to waste containing heavy metals such as cadmium (Cd), antimony (Sb), arsenic (As), mercury (Hg) and even thallium (Tl), germanium (Ge) and selenium (Se).

These metals can be found in waste of different origins in varied concentrations and combinations. In most cases they are present in an oxidised form (in the context of oxido-reduction), rarely in their reduced form, thus we are speaking of waste containing metals generally in oxidised form.

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

The subject of this invention is to propose a method for the pyrometallurgical treatment of waste containing metals, generally in oxidised form. This objective is achieved according to the invention by a method as in Claim 1.

General description of the claimed invention, with its principal advantages.

The method according to the invention relates to the pyrometallurgical treatment of waste containing metals generally in oxidised form in a first zone comprising vertically spaced hearths of a multi-stage furnace, in which: (a) the waste containing metals, generally in oxidised form, is introduced on to the upper hearth of the first zone and is gradually transferred to the lower hearths; (b) conditions favouring volatilisation of metals in oxidised form are created in the first zone; (c) the gases containing the volatilised metals, in oxidised form, are extracted from the first zone.

This method utilises the capacity of the multi-stage furnace to create special atmospheres in particular zones and/or hearths according to a desired reaction.

It will be appreciated that according to this invention it is possible to treat waste containing metals pyrometallurgically and to extract from it at least a proportion of it, or at least some of these metals contained in the waste, by volatilising them in an oxidised form.

We are speaking here of metals that are generally in oxidised form, for it is assumed that the metals contained in this waste will in most cases be present in oxidised form, i.e. not in metallic form, but in ionic form, oxide, salts etc.

Some of the metals extracted from the waste may be recycled in new production processes, which is of interest in economic terms.

Waste with problematic discharge from the environmental viewpoint may be treated by the method according to the invention to extract the contaminating metals for disposal.” By carefully selecting the reaction conditions, the method according to the invention enables certain metals in oxidised form to be o 4 volatilised selectively, preferably in relation to the other metals contained, generally in oxidised form, in the same waste. It is therefore possible to achieve a selective extraction of some metals in oxidised form.

According to a first embodiment of the method, the waste containing metals, generally in oxidised form, is brought to a temperature of 1100°C in stage (b) in order to calcine them and bring about the volatilisation of metals in oxidised form. Such a method is particularly well suited for the selective extraction of metals such as Sb, As, Bi, Pb, Tl, Ge and Se contained in oxidised form in sludges or dusts, for example.

The first zone operates advantageously at co-current, and the so-called “co- current gases” are discharged from the bottom of the first zone. The gases and solids therefore circulate in the same direction, from the top to the bottom of the zone. Moreover, the co-current gases discharged may be cooled, filtered to separate the metals in oxidised form, and then re-introduced into the first zone, preferably after being heated. This enables the gas flow from the first zone to be increased. For a given steam pressure of a metal in oxidised form, the quantity of extracted metal in oxidised form is proportional to the gas flow.

According to a second embodiment of the method, waste containing metals, generally in oxidised form is brought to a temperature of 800°C in stage (b); waste containing metals is brought into contact with a carbonated reducer to obtain metals in reduced form, and a product containing chlorine and/or sulphur is introduced to bring about the reaction of metals with chlorine and/or sulphur, followed by their volatilisation in the chlorinated or sulphurised form. It is therefore possible to extract tin (Sn) by two extraction methods, one using chlorine in the form of HCI, chlorinated organic compounds, chlorine salts or a mixture of them, the other using sulphur in the form of H,S, sulphur in a solid state, sulphurised organic compounds, solid sulphides or a mixture of them.

One or other of the methods of extraction will be selected according to the other metals contained in the waste to be treated.

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According to another embodiment, the first zone may be operated at counter- current. The so-called “counter-current gases” are then discharged from the top of the first zone. These gases may then be treated in a post-burner, then cooled and filtered to separate the metals in oxidised form. This enables the energy properties of the gas to be used advantageously and a relatively clean gas to be released. The counter-current gases may also be re-introduced into the first zone after heating them.

According to another embodiment the remaining solid waste that may still containing metals, generally in oxidised form, is transferred after stage (c) into a second zone comprising vertically spaced hearths, the so-called “reduction zone’, located below the first zone, so that they can be gradually transferred to the lower hearths, brought into contact with a reducer and brought to a temperature that enables the metals present in oxidised form to be reduced. It is therefore possible, in the same multi-stage furnace, firstly to extract metals in oxidised form, then to reduce the oxidised metals not yet extracted. The temperature of the reaction that enables metals in oxidised form to be reduced may be between 800 and 1200°C, and preferably between 1000 and 1100°C.

At least a proportion of the reduced metals in the reduction zone are volatilised at the reaction temperature. They will therefore be advantageously extracted - from the reduction zone with the gases at the hearths on which they are formed.

This provides the possibility of extracting metals in reduced form from waste introduced into the furnace in the gaseous phase.

All the gases discharged from the reduction zone of the multi-stage furnace may be treated in a post-burner, cooled and filtered. The volatilised reduced metals are advantageously oxidised in the gaseous phase, cooled to condense them to dust, and filtered in order to be separated from the gases.

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Where the waste contains metals which cannot be extracted in gaseous form, either in the oxidised state or in the reduced state, the remaining waste will then be advantageously extracted from the multi-stage furnace after reaching the lower hearth of the reduction zone, and can then be sorted in order to separate the non-volatilised reduced metals. Among the metals which cannot be extracted in the gaseous phase, particular mention may be made of iron and/or nickel.

Carbon, solid or liquid petroleum products, synthetic materials such as plastic materials, rubbers, organic waste or their mixtures are used as the carburised reducer. In some cases plastic materials and/or rubbers containing chlorine and sulphur are used.

The waste containing metals, generally in oxidised form, may be dried on the upper hearths of the multi-stage furnace before being introduced into the first zone. This is of interest when the waste containing metals, generally in oxidised form, contain large quantities of water, sludges for example.

According to the gas flows and volatile metal concentrations, the hearths may be heated directly or indirectly.

All gases discharged from the multi-stage furnace, should preferably be dechlorinated and desulphurised.

Detailed Description by means of Figures

Other particularities and characteristics of the invention will be evident from the detailed description of some advantageous embodiments presented below, by way of illustration, with reference to the attached drawings. They show:

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Fig. 1: explanatory diagram of the method, in an embodiment for the treatment of waste containing metals of the type Sb, As, Bi, Hg, Pb, TI, Ge and Se, generally in oxidised form.

Fig. 2: variant of the method in fig. 1.

Fig. 3: explanatory diagram of the method in an embodiment for the treatment of tinplating bath waste.

Fig. 4: explanatory diagram of the method in an embodiment for the treatment of waste containing metals such as Fe, Ni, Zn and Pb, generally in oxidised form.

This method makes use of a multi-stage furnace for treating waste containing metals, generally in oxidised form. lt is important to note that the waste may contain a single metal only, thus the embodiment of the method should preferably be selected according to the metal to be treated. We speak here of waste containing metals generally in oxidised form, for the metals in the waste are rarely in a reduced state, and in most cases these are metal oxides and hydroxides. The term “oxidised form” must be interpreted here in its widest sense in terms of oxido-reduction: it is said that the metal is in oxidised form if it is not in the reduced state.

Fig. 1 is an explanatory diagram of this method in an embodiment that enables waste to be treated that contains metals of the type Sb, As, Bi, Pb, Hg, Tl, Ge and Se, generally in oxidised form. Use is made of a multi-stage furnace 10 consisting of vertically spaced annular hearths. Loading hearths 12 and unloading hearths 14 are arranged alternately. The former hearths 12 are provided with a peripheral opening, the peripheral openings of two consecutive loading hearths being diametrically opposed: the latter hearths 14 are provided with an open central circular section. In its central section the furnace is also provided with a vertical rotary shaft 16, to which are attached combs (not shown) extending throughout the radius of the hearths. Means of heating, direct (burners) or indirect (resistances) (not shown) enable each hearth to be o 8 heated individually in order to obtain different temperatures for certain zones and/or hearths.

The waste is fed in continuously through an opening 18 in the upper wall of the multi-stage furnace and falls onto the first loading hearth 12. The combs, driven by the vertical rotary shaft 16, spread the waste over loading hearth 12 and feed it to the peripheral opening through which it falls onto unloading hearth 14 located immediately below. The combs then feed the waste to the central opening, through which it falls onto the lower loading hearth. These stages are repeated until the waste reaches the lower hearth of the multi-stage furnace.

In the lower section of the multi-stage furnace a temperature of 1100°C should preferably prevail. At this temperature the waste is calcined and the metals Sb,

As, Bi, Pb, Hg, TI, Ge and Se are volatilised in oxidised form. As the dotted arrows indicate, the multi-stage furnace is operated under co-current conditions, i.e. the gases circulate in the same direction as the material: downwards. The gases containing the volatilised metals in oxidised form are then discharged from the multi-stage furnace in its lower section. The co-current operation enables the best use to be made of the gases, as all the gases are extracted at the level of the lower section of the multi-stage furnace, which provides a high gas flow in the lower stages of the multi-stage furnace, where the temperature conditions are the most suitable for volatilisation of the metals. The co-current gases discharged from the multi-stage furnace are fed to a treatment installation 20 in which they are cooled, then filtered, in order to recover the metals in oxidised form contained in the gases and release the gases. The remaining waste is discharged from the multi-stage furnace through an output port 22 once it has reached the lower hearth. The discharged waste is therefore deprived of the metals that have been volatilised in oxidised form.

Fig. 2 shows a variant of the method shown in Fig. 1, which enables the gas flow in the lower hedrths to be increased. To achieve this the co-current gases, once they have passed into treatment installation 20, are at least partially fed to iB 9 ® a heat exchanger 24 to be re-heated, then re-injected into the centre of multi- stage furnace 10. The quantity of metal in oxidised form extracted from the multi-stage furnace per unit of time is proportional to the gas flow through the furnace and to the steam pressure of the metal in oxidised form; the recovery of metal in oxidised form is accelerated by increasing the gas flow.

Fig. 3 shows an explanatory diagram of this method in another embodiment that enables waste to be treated that contains metals in oxidised form such as tin oxides or hydroxides, for example tinplating sludges containing essentially oxidised forms of iron and tin. A multi-stage furnace 10 similar to that described above is used, in which conditions suitable for volatilisation of the tin in oxidised form are created.

Waste containing iron and tin in oxidised form is fed into the multi-stage furnace through opening 18 and falls onto the first loading hearth 12. The combs push the waste gradually to the lower stages, aiternating between the loading and unloading hearths. In the central section of the furnace, where a temperature of approximately 800°C prevails, a reducer — arrow 26 — is introduced, preferably carbon with a fine granulometry. Through their sweeping action the combs then produce a compact mixture of the waste and carbon, bringing about the reduction of the tin oxides contained in the waste. At 800°C a selective reduction of the tin oxides is achieved because the temperature is too low to cause the reduction of iron oxides. In order to volatilise the tin, hydrochloric acid (HCI) is inserted in the hearths located below that on which the carbon has been fed in, arrow 28. It should be noted that the hydrochloric acid can be replaced by Cl,, or even by a volatile solid chlorinated product at the reaction temperature (e.g. NaCl, MgCl,, KCI, PVC, which have a steam pressure of over 0.01 atm. At 1000°C). The metallic tin formed by the reduction of the tin, in oxidised form, is then oxidised by HCI and is converted to SnCl,, a metal in oxidised form, which is volatilised at the reaction temperature. In terms of oxido-reduction, the-oxidation number (Noy) of the tin passes from Nox = 0 to Noy = +2, hence the expression “metal in oxidised form”. The gases containing the te 10 ) ® 20018584

SnCl,, dotted arrow 30, are discharged from multi-stage furnace 10 in its lower section, i.e. at the level of the hearths on which they are formed. These gases then pass into a cooling device 32 to condense the SnCl,, and recover it. The counter-current gases (ascending gases circulating typically in a multi-stage furnace), represented by dotted arrow 34, are discharged from the multi-stage furnace in its upper section and are fed to a post-burner 36. The gases discharged from cooling device 32 and post-burner 36 are then fed into a treatment installation 37 to be cooled, dechlorinated and desulphurised, then filtered, before being released. On reaching the lower hearth of multi-stage furnace 10, the waste is therefore deprived of the tin but the iron remains in oxidised form.

The method in Fig. 3 may also be provided by replacing the chlorine with a sulphur-based gas, e.g. H,S, or a solid sulphur which is volatile at the reaction temperature (pyrites, for example). A tin sulphide volatile at 800°C will then be formed. The choice of using chlorine or sulphur based products will then depend on the other metals contained in the waste. To extract Sn in the presence of iron or nickel, chlorine shouid preferably be used. On the other hand, sulphurisation is more appropriate for separating the Sn from metals such as Pb, Zn or Cd.

A final embodiment of the method according to this invention, illustrated in Fig. 4, enables waste containing a mixture of metals of the type Fe, Ni, Cu, Zn, Cd,

Sb, As, Bi, Pb, Hg, Tl, Ge and Se to be treated in a multi-stage furnace. Use is made of a multi-stage furnace 10 similar to that described above but which comprises two zones. These two zones aie essentially functional {they define reactional zones), and must not necessarily be structurally different in multi- stage furnace 10. In the first zone 38, the upper section of multi-stage furnace 10, metals are volatilised in oxidised form. In the second zone 40 — lower section of multi-stage furnace 10, metals are reduced: certain metals being solid and others volatile in the reduced state, at the temperature of the zone.

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To illustrate more specifically the method shown in Fig. 4, let us assume that the waste contains Fe, Ni, Zn and Pb in oxidised forms. The waste is fed into multi-stage furnace 10 through opening 18 and falls onto the first loading hearth 12, in the first zone 38. The combs push the waste gradually toward the lower stages, alternating between loading and unloading hearths. The waste is very quickly 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 volatilised; in this case PbO. The calcinations gases circulate in a counter- current direction, as illustrated by arrow 42, and are therefore discharged from multi-stage furnace 10 in its upper section, more precisely at the level of the first hearths of first zone 38; once extracted from multi-stage furnace 10 they are fed to a post-burner 36. After volatilised metals in oxidised form have been extracted from the first zone 38, waste is transferred to the second zone 40, located below the first zone 38. In the second zone 40 a reducer — arrow 44 — is injected, preferably carbon with a fine granulometry. Because of their sweeping action the combs thoroughly mix the waste with the carbon, 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 Zn oxides or hydroxides are reduced and the Zn is directly volatilised. The reduction gases — arrow 46 — containing the reduced metals in the gaseous phase are extracted from the multi-stage furnace in the lower section of the second zone 40, i.e. where they are formed. They are then fed to a post-burner 48, in which Zn is oxidised to ZnO for separation from the gas. All the gases discharged from multi-stage furnace 10 are then fed to a treatment installation 37 to be cooled, dechlorinated and desulphurised, then filtered before being released. It will be noted that it is advantageous to voiatiiise aii the iead oxide in the first zone 38, which enables the purity of the zinc oxide recovered in post- burner 48 to be increased.

It will be noted that this example is given for Fe, Ni, Zn and Pb. The Pb is extracted in oxidised form in a 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 reduced form, as would be the case with Cd, and must be oxidised in a post-burner. The iron and nickel are reduced in the second zone 40, but remain solid at the reduction temperature, which would also be the case for Cu.

The solid metals, in reduced form, i.e. the iron and nickel, are discharged from the furnace with the rest of the waste (an inert layer of sludge), and possibly an excess of reducer, through an outlet port. The iron and nickel, once cooled, can be sorted by manual or automated methods (e.g. magnetic sorting).

It will be noted that it is possible to add in each of the preceding methods a stage designed to dry the waste. The waste containing metals that are generally in oxidised form would then be dried in a drying zone comprising vertically spaced hearths, at the beginning of the multi-stage furnace. The first zone would then begin immediately below this drying zone.

The expert may obviously be directly inspired by the knowledge derived from this invention to modify the conditions prescribed in the methods described, particularly the temperatures and atmospheres, in order to extract other volatile metals in oxidised form from material introduced into a multi-stage furnace.

Claims

CC 13 P-PWU-418/WO CLAIMS

1. Method for the pyrometallurgic treatment of waste containing metals, generally in oxidised form, in a first zone comprising vertically spaced hearths of a multi-stage furnace, in which: a) the waste containing metals generally in oxidised form is introduced onto the upper hearth of the first zone, and gradually transferred to the lower hearths; b) conditions appropriate for the volatilisation of metals in oxidised form are created in the first zone; c) the gases containing the volatilised metals in oxidised form are extracted from the first zone.

2. Method according to claim 1, characterised in that in stage (b) the waste containing metals generally in oxidised form is brought to a temperature of up to 1100°C so that it is calcined and brings about the volatilisation of metals in oxidised form.

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

4. Method according to claim 2 or 3, characterised in that the first zone operates on a co-current basis, the gases all being discharged from the first zone in its lower section.

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5. Method according to claim 4, characterised in that the discharged co-current gases are cooled, filtered and then reintroduced into the first zone, preferably after being reheated.

6. Method according to claim 1, characterised in that in stage (b): - the waste containing metals generally in oxidised form is brought to a temperature of up to 800°C; - the waste containing metals generally in oxidised form is brought into contact with a carbonated reducer to obtain metals in reduced form; - a product containing chlorine and/or sulphur is introduced to bring about the volatilisation of metals in chlorinated and/or sulphurised form.

7. Method according to claim 6, characterised in that the volatilised metal in chlorinated and/or sulphurised form is tin in chlorinated and/or sulphurised form.

8. Method according to claim 6 or 7, characterised in that the product containing chlorine is selected from the group consisting of hydrochloric acid (HCI), chlorine (Cy) or of organic chlorinated compounds and/or of chlorine salts or of their mixtures, that can be volatilised at the temperature of the first zone, and in that the product containing sulphur is selected from the group consisting of hydrogen sulphide (H,S), sulphur in the solid state, sulphurised organic compounds, solid sulphides or their mixtures, that can be voiatiiised at the temperature of the first zone.

9. Method according to any of claims 2, 3 and 6 to 8, characterised in that the first zone operates in a counter-current direction, and in that the counter- current gases are discharged from the upper section of the first zone.

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10. Method according to claim 9, characterised in that the discharged counter- current gases are treated in a post-burner, then cooled and filtered, and are re-introduced into the first zone, preferably after being reheated.

11.Method according to any of the preceding claims, characterised in that the gases containing the volatilised metals in oxidised form, from stage (c), are cooled and filtered in order to separate the metals in oxidised form from the remaining gases.

12.Method according to any of the preceding claims, characterised in that the waste containing metals generally in oxidised form are transferred, after stage (c), to a second zone comprising vertically spaced hearths, the so- called reduction zone, located below the first zone, in order to be transferred gradually from there to the lower hearths, brought into contact with a reducer, and brought to a temperature which enables metals in oxidised form to be reduced.

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

14. Method according to claim 12 or 13, characterised in that at least a proportion of the reduced metals in the reduction zone are volatilised at the reaction temperature.

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

16. Method according to claim 14, characterised in that the volatilised reduced metals are extracted from the reduction zone level with the hearths on which they are formed."

’ R 16 ®

17.Method according to any of claims 12 to 16, characterised in that all the gases discharged from the reduction zone of the multi-stage furnace are treated in a post-burner, cooled and filtered, and in that the volatilised reduced metals are oxidised in the gaseous phase, cooled to condense them to dusts, and filtered to separate them from the gases.

18. Method according to any of claims 12 to 17, characterised in that at least a proportion of the reduced metals in the reduction zone are not volatilised at the reaction temperature.

19. Method according to claim 18, characterised in that the waste is extracted from the multi-stage furnace after reaching the lower hearth of the reduction zone.

20.Method according to claim 19, characterised in that the waste discharged from the reduction zone is sorted after being extracted from the multi-stage furnace in order to separate the non-volatilised reduced metals.

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

22 Method according to any of the preceding claims, characterised in that the waste containing metals generally in oxidised form are dried in a drying zone comprising vertically spaced hearths of the multi-stage furnace, before being introduced onto the upper hearth of the first zone, the drying zone being located above the first zone.

23. Method according to any of claims 1 to 10, characterised in that the first zone extends over the entire area of the multi-stage furnace.

24. Method according to any of the preceding claims, characterised in that the hearths are heated directly or indirectly.

od PCT/EP00/03954

25. Method according to claim 19, characterised in that the reduced metals discharged from the furnace are separated by magnetic sorting of the remainder of the content of the reduction zone.

25. Method according to any of the preceding claims, characterised in that all the gases discharged from the multi-stage furnace are dechlorinated and desulphurised.

27. A method as claimed in claim 1, substantially as herein described and illustrated.

28. A new pyrometallurgical treatment method, substantially as herein described. AMENDED SHEET