FR2737428A1 - PROCESS FOR THE TREATMENT OF WASTE CONTAINING METAL CONTAMINANTS - Google Patents

Abstract

A method for processing waste material containing metallic contaminants in the form of carbon-, oxygen-, phosphor-, or sulphur-modified metals includes the steps of mixing the waste material in powder form with aluminium nitride and, if desired, an additional silica and alumina-based vitrification mineral filler; melting the mixture until a first nitrogen vitreous leaching-resistant phase and a second metal phase are obtained; and separating and solidifying the two phases for the disposal or temporary storage of the first and recycling of the second phase. The invention is useful for inactivating or recycling metallic contaminant containing waste material.

Description

 The subject of the invention is a method for treating waste containing metallic contaminants. It also relates to applications of this process, in particular in the steel, automobile industry or in the field of household waste recovery.

 The metallic contaminants in question in the context of the present invention are in particular metals modified with carbon, oxygen, phosphorus or sulfur, with a view to their inerting and to their recovery for their recovery.

 Methods are already known for treating waste containing metallic contaminants.

By way of example, mention may be made of pyrometallurgical treatment processes based on a reduction of metallic contaminants by carbon at high temperature, such as the IMS - Tetronics processes or
Waelz.

 However, these methods are not entirely satisfactory insofar as they are essentially expensive, difficult to implement and do not always allow all the recoverable metals to be recovered.

 There is therefore a need to provide a process for treating such waste which is more economical, simpler to operate and more profitable than those which already exist, this process further guaranteeing the inerting of metallic contaminants in a safe manner.

 The object of the invention is to provide a process for treating waste containing metallic contaminants, which combines the above-mentioned advantages and by which it is also possible to recover most of the recoverable metals.

This is achieved, according to the invention, by carrying out the following operations: mixing said waste in the pulverulent state with
aluminum nitride (AlN) and where appropriate a
additional mineral filler based on vitrification
silica (SiO2) and / or alumina (Al203),. melting the mixture until a first
glassy nitrogen phase resistant to leaching and
a second metallic phase, and. separation and solidification of the two phases with a view
the landfill or temporary storage of the
first and recycling the second.

The process according to the invention reveals the metal or the metallic phase by reaction in the liquid phase between metal cations of the waste and nitride ions of aluminum nitride. The reaction scheme is as follows

The metal Me can be, for example V, Cr, Mn, Fe,
Co, Ni, Cu and Ag. In the particular case of titanium, the predominant reaction is written

These chemical reactions can also be written in schematic form

The metal oxide reduction reactions (3) can be written, for example,

 This more traditional notation, which does not appeal to ionic formalism, has the advantage of facilitating the determination of the free energy of the reaction AG. Indeed, we refer to the thermodynamic quantities already calculated for defined compounds.

The variation of standard free energy AGo of reaction (3) is negative over a wide temperature range for many metals such as V, Cr, Mn,
Fe, Co, Ni, Cu and Ag. The theory therefore predicts the appearance of the metal by reaction of aluminum nitride and metal oxide in a temperature range.

Furthermore, the calculation of the variation of standard free energy AGo of reaction (4) as a function of temperature has shown that the values of AGo are always negative in a wide range of temperatures between 1000 and 2000 K. The values of AGo for these two temperatures are respectively close to -70 and -80 kcal.mole-1. The values used for these determinations are indicated for example by Elliot and
Gleiser (Thermochemistry for Steelmaking-Massachussetts
Institute of Technology - Addison Wesley publishing-London 1960). The main sources of these tables are the
National Bureau of Standards and the US Bureau of Mines.

 The method according to the invention gives rise either to obtaining a vitreous substrate on the surface of which a metallic layer Me migrates, or to obtaining a true two-phase material comprising a metallic phase and an amorphous phase. In the event that the waste contains several metals, it can give rise, depending on the value of the free energy relating to each of the metals, to the formation of one or more more or less complex metallic phases.

 Furthermore, it is possible that all these metallic phases are produced on the surface of the glassy substance. It is also conceivable that they are all contained or else trapped in the glass network. After a certain time, due to the differences in density between the metallic phase and the glassy phase, the appearance of the metallic phase will generally be observed at the bottom of the reactor. In all cases, these phases will be separated by means known to those skilled in the art, such as flotation, centrifugation or any other suitable process.

 According to a preferred embodiment of the method according to the invention, the aluminum nitride is added to the said mixture in stoichiometric excess relative to the metallic contaminants. On the one hand, the probability of reducing all of the metal oxides involved is thus increased. On the other hand, the formation of the second phase, that is to say of a nitrogenous glass, is facilitated in this way. This second phase retains the metallic contaminants which, possibly, did not give rise to the formation of a metallic phase. In sum, the method according to the invention guarantees the inerting of metallic contaminants, these being anyway trapped, in the nitrogenous glass in the case where there is no formation of a metal.

 According to the process according to the invention, it is not necessarily useful to provide a mineral load of vitrification. In fact, if the waste itself contains sufficient SiO2 and Al203, the use of such a charge is absolutely superfluous.

 Preferably, the melting of said mixture is obtained by bringing said mixture to a temperature of the order of 1200 to 16000C. This heating is maintained for a period of the order of 15 minutes. This temperature is accessible with most ovens available in the industry. It is therefore not necessary, for the implementation of this process, to use special means.

 However, it is also possible to use a localized heating mode. In general, these modes are more complex to implement. For example, the mixture of waste and aluminum nitride is heated using a LASER or an electron gun.

 More preferably, the pulverulent mixture of the waste is used with a particle size between 0.5 and 200 μm.

 In this way, the contact surface between the waste and the mineral filler is optimal and the yield of the reaction is optimized.

 The process according to the invention can be carried out in an atmosphere free of oxygen and water, in order to avoid any parasitic oxidation reaction. This neutral atmosphere can for example be constituted by an inert gas, such as argon, or even by nitrogen.

 Furthermore, still with a view to avoiding parasitic phenomena resulting from oxidation reactions, the mixture of reaction products can be deposited in a molybdenum basket. The heating of the reaction products can obviously be carried out by any suitable means, for example in a high-frequency oven.

 Advantageously, the second metallic phase is recovered by flotation, in the form of an alloy, in particular based on chromium and nickel.

 Preferably, the additional mineral charge for vitrification based on silica and alumina is constituted by another waste such as a clinker for the incineration of household refuse or other glass waste such as discarded glass cullet.

 A combination of these wastes can also be used. For example, a combination based on Household Waste Incineration Fumes (REFIOM) containing calcium and ashes from thermal power plants can be used. This waste is mixed with an alloy based on SiO2 and Al203.

 This method can still be advantageously used for the purpose of treating dust comprising transition elements.

The process according to the invention can be used preferentially for the treatment of steel waste such as dust from electric or thermal power stations. It can also be used more preferably for the treatment of exhaust catalysts of motor vehicles or other catalysts based on metals such as: V, Cr, Co, Ni, Cu,
Ag, Mo, W in the form of oxides or sulphides on supports such as SiO2, Al203 and ZrO2.

 It is also possible to treat metal oxides or sulfides of the M1M2PONH type, in which M1 and M2 are metals, such as in particular Cr, Zr, Al, Ga. This process can also be used to separate, for example, vanadium, in AlVONH. In short, the process according to the invention can be used either with the sole objective of treating waste, or else with the dual objective of treating waste and recovering metallic substances.

 The method according to the invention can advantageously be used for the treatment of cathode ray tubes with a view to their inerting, by separation of a metallic phase based on lead and of a nitrogenous glass resistant to leaching.

 It can also be used advantageously for the treatment of Household Waste Incineration Smoke Residues (REFIOM) with a view to their inerting, by obtaining a nitrogenous glass with high resistance to leaching.

 The invention can be better understood using the nonlimiting example which follows and which constitutes an advantageous embodiment of the method according to the invention.

This example is described with reference to the appended figures 1 and 2.

 FIG. 1 represents an X-ray energy dispersion spectrum of a metallic phase FeNiCr obtained according to the method according to the invention.

 FIG. 2 represents an X-ray emission diagram of a glassy phase obtained according to the method according to the invention, this phase being associated with the metallic phase represented in FIG. 1.

 FIG. 3 represents an X-ray energy dispersion spectrum of a metallic phase based on lead obtained according to the method according to the invention.

 FIG. 4 represents an X-ray emission diagram of a glassy phase obtained in accordance with the method according to the invention, this phase being associated with the metallic phase represented in FIG. 3.

Example
The method according to the invention is used to treat waste from the steel industry. This waste includes dust from steelworks smoke as well as steel slag.

The composition of the dust from steelworks is as follows:
CaO 6.06%
MgO 5.27%
SiO2 6.69%
A1203 0.85%
Cr203 17.98%
MnO 3.69%
FeO 39.30%
TiO2 0.22%
P205 0.21%
ZnO 6.29%
PbO 1.06%
NiO 3.36%
CuO 0.39%
SnO 0.33%
MoO3 0.15%
Na2O 1.64%
K2O 1.26%
CoC 0.07%
F 1%
The composition of the steel slag is as follows
CaO 35-60%
MgO 4-12%
SiO2 27-37%
A1203 2-6%
Cr203 1-8%
MnO 1-3%
FeO 0.5-4%
Tio2 1-2% P2O5 0-0.02%
To treat this waste, a mixture is produced, the mass composition of which is as follows
i) 20 to 30% of the steelworks smoke dust from
composition indicated above,
ii) 55 to 70% steel slag of composition
indicated previously,
iii) 9 to 10% of SiO2,
iv) 5 to 7% AlN.

 It is observed that the compositions of steelworks dust and steelworks slag are complementary from the point of view of their contribution in SiO2 and Al203. In fact, the dust provides essentially SiO2 and little Al203 while the slag provides the complement of Au203 necessary to avoid having to resort to a mineral load of vitrification.

 This mixture is brought to fusion at a temperature between 1200 and 12500C. A solid is thus obtained, which examination under a scanning microscope reveals that it consists of two distinct phases, namely a first apparently glassy phase and a second metallic phase. These two phases are separated from each other, the metallic phase being found at the bottom of the reactor.

 The X-ray energy dispersion spectrum of the metallic phase, represented in FIG. 1, reveals that the latter essentially comprises iron and, to a lesser extent, nickel and chromium.

 The composition of the metal phase is determined by micro-analysis. It is reported in Table I below.

Table I
Element Percent Percent
atomic mass
Cr 9.21 9.87
Fe 80.79 80.63
Ni 10.01 9.50
The spectrum of energy dispersion of X-rays of the glassy phase, represented in FIG. 2, shows that this essentially comprises silicon and calcium. It includes, to a lesser extent, magnesium, aluminum, titanium, chromium, manganese and iron.

Its composition, also determined by microanalysis, is given in Table II below
Table II
item Percent Percent
atomic mass
Mg 5.48 7.44
Al 10.39 12.72
If 34.32 40.36
Ca 41.97 34.58
Ti 0.92 0.64
Cr 3.30 2.10
Mn 2.65 1.59
Fe 0.96 0.57
It is observed that the glassy phase is enriched with aluminum. The spectrum has the same appearance as that of a calcium silicate CaSiO3 or an aluminosilicate of calcium and magnesium containing traces of Cr, Mn, Fe and Ti.

 We also note that this glassy phase appears homogeneous.

 Consequently, the method according to the invention gives rise to the transformation of the metallic elements in the form of oxides, into metallic elements.

 We can therefore take advantage of this not only for the simple treatment of waste, but also to recover or recycle metals.

 In addition, the use of aluminum nitride gives rise to the formation of a nitrogenous glass. This has the advantage of having a very low tendency to leach. Thus, traces of contaminants which have not passed through the metallic phase separated from the glass will remain trapped in the mass of the nitrogenous glass. Excellent inerting is thus obtained, which constitutes one of the major objectives of the present invention.

The method according to the invention has also been implemented on glasses originating from lead-based cathode-ray tubes. it is a CORNING glass type 0138 of composition
SiO2 54%
A1203 2%
Na2O 6%
K2O 8%
CaO 3.5%
MgO 2.5%
PbO 2.3%
Tio2 1-2%
Sb203 0.1%
The x-ray emission diagram corresponding to the sample of lead-based glass treated according to the invention is shown in FIG. 3. The spectrum of x-ray energy dispersion of the corresponding metal phase is mentioned in Figure 4.

 Analysis of these two diagrams reveals excellent inerting.

Claims (13)

 1. Process for treating waste containing metallic contaminants, in the form of metals modified with carbon, oxygen, phosphorus or sulfur, with a view to their inerting and their recovery for their recovery, characterized in that it involves the following operations:. mixing of said waste in pulverulent state with  aluminum nitride (AlN) and where appropriate a  additional vitrification mineral filler based on  silica (SiO2) and / or alumina (au203),. melting of the mixture until a first phase is obtained  glassy nitrogen resistant to leaching and a  second metallic phase-,. separation and solidification of the two phases with a view to  the landfill or temporary storage of the  first and recycling the second.  2. Method according to claim 1, characterized in that the aluminum nitride (AlN) is added to said mixture in stoichiometric excess relative to the metallic contaminants.  3. Method according to one of claims 1 and 2, characterized in that the melting of said mixture is obtained by bringing said mixture to a temperature of the order of 1200 to 1600 "C.  4. Method according to one of claims 1 to 3, characterized in that the pulverulent mixture of waste is implemented with a particle size between 0.5 and 200 Hm.  5. Method according to one of claims 1 to 4, characterized in that the second metallic phase is recovered by flotation, in the form of an alloy, in particular based on chromium and nickel.  6. Method according to one of claims 1 to 5, characterized in that the additional mineral load of vitrification based on silica and alumina is constituted by another waste such as a clinker for incineration of household waste or other glass waste such as rejected glass cullet.  7. Method according to one of claims 1 to 6, characterized in that said mixture, subjected to fusion, is obtained from a following mass composition  i) 20 to 30% of a dust from steelworks smoke  ii) 55 to 70% steel slag  iii) 9 to 10% SiO2  iv) 5 to 7% AlN.  8. Method according to claim 7, characterized in that the steel smoke smoke responds to the following composition  CaO 6.06%  MgO 5.27%  SiO2 6.69%  A1203 0.85%  Cr203 17.98%  MnO 3.69%  FeO 39.30%  TiO2 0.22%  P2O5 0.21%  ZnO 6.29%  PbO 1.06%  NiO 3.36%  CuO 0.39%  SnO 0.33%  MoO3 0.15%  Na2O 1.64%  K2O 1.26%  CoC 0.07%  F 1%  9. Method according to claims 7 or 8, characterized in that the steel slag corresponds to the following composition  CaO 35-60%  MgO 4-12%  SiO2 27-37%  A1203 2-6%  Cl203 1-8%  MnO 1-3%  FeO 0.5-4%  Tio2 1-2%  P205 0-0.02%.  10. Application of the method according to one of claims 1 to 9 to the treatment of iron and steel wastes such as dust from electric or thermal power plants.  11. Application of the method according to one of claims 1 to 6 to the treatment of exhaust catalysts of motor vehicles or other catalysts based on metals such as: V, Cr, Co, Ni, Cu, Ag, Mo, W in the form of oxides or sulphides on supports such as SiO2, Al2O31 and ZrO2.  12. Application of the method according to one of claims 1 to 6 to the treatment of cathode ray tubes with a view to their inerting, by separation of a metallic phase based on lead and of a nitrogenous glass resistant to leaching.  13. Application of the method according to one of claims 1 to 6 to the treatment of Household Waste Incineration Smoke Residues (REFIOM) with a view to their inerting, by obtaining a nitrogen glass with high resistance to leaching.