The recovery of metal from waste that contains metal polluted by organic material is an important activity for the present industry. Such waste comprises, among others, aluminium foil contain- ing packaging for beverages and food, metal boxes, scrap from the metal processing industry, etc. Thereby oil, paints, adhesives, paper and food residues form the most common polluting constituents. The cost effectiveness of the process for the recovery of the metal depends to a large extent on the amount of metal which may be recovered as metal from the waste, and as such may further be processed. In this process there is a need to prevent as much as possible oxidation of the metal, since this decreases the metal yield. Preventing oxidation of the metal is particularly important if the metal is present in the form of thin layers of foil.

From WO 92/01825 a process is known for the recovery of metal from waste of metal contaminated by organic compounds. In the process disclosed in WO 92/01825, metal polluted by organic material, particularly aluminium or aluminium alloys, is heated in a fluidised bed of granules to a temperature which is sufficiently high to remove the organic material, but which is below the melting point of the metal. In order to prevent oxidation of the metal, the metal is heated in the presence of anorganic and organic fluorine

compounds.

This known process however has the disadvan- tage that the addition of such fluorine compounds involves an additional metering, which has to be controlled, causing the cost price of the process to be undesirably increased.

Moreover the possibility exists that the gases released during the combustion contain fluoride compounds. In order to meet the European emission standards, these gases will have to be subjected to an additional wet flue gas purification, causing the cost price to be further increased.

The aim of this invention consists in providing a process for the recovery of metal from waste of material polluted by organic material, whereby oxidation of the metal may mainly be prevented, without thereby necessitating the use of said fluorine compounds.

This is achieved according to the invention in that.

for maintaining the fluidised bed an oxidising gas is used that contains 6-21 volume percent of oxygen, and that the residence time of the waste in the fluidised bed is kept shorter than 15 minutes.

Surprisingly it has namely been found that when using such an amount of oxidising gas, such a residence time of the waste, and such a temperature range, the organic material is mainly gasified in the fluidised bed, and combustion of the organic material, whereby undesirable ash is formed which pollutes the metal, as well as oxidation of the metal may substantially completely be prevented.

The above described control of the reaction circumstances further allows to keep the temperature in the reactor mainly constant and to limit the formatlon of flue gases (NO, CO). On the other hand, the above described process provides an economically profitable process, because the gasificatiorl of the organic contami- nating material proceeds sufficiently fast.

Because of the absence of above said fluoride compounds, moreover the plant is to a much lesser extent subject to corrosion.

The invention is suitable for the recovery of the most common metals, for example iron, copper, aluminium, and alloys of these metals. The invention is mainly intended for the recovery of aluminium or alloys thereof, from waste. Aluminium is namely a metal that is very easily oxidised and has a low melting point. so that a careful control of the temperature and the oxidation circumstances is required.

According to the invention, the gasificatlon is preferably carried out at a temperature between 400 and 600 "C, depending on the nature of the organic contaminants which have to be gasified. In any case, the temperature shall be below the melting point of the metal. According to the invention the temperature is preferably between 400 and 550 "C. At temperatures below 400 "C, the rate at which the organic material is gasified is low, and the process is economically little profitable. At temperatures above 600 "C, there is a risk that the aluminium starts to melt. Because of the presence of contaminants, a decrease of the melting point may namely occur.

In order to maintain aoove said temperatures of the fluidised bed, the fluidised bed may, if required, be heated, for example by heating the gas for fluidising the bed. With the process of this invention, this will mostly not be required, since the organic waste which is gasified is mostly highly calorific waste. The heat which is released in the gasification of the organic contaminants, is absorbed by the bed, so that the gas which is responsible for the fluidisation of the fluidised bed, is heated in the fluidised bed. This provides an economically profitable process, in which extra energy costs required for heating the fluidised bed can be minimised.

The fluidised bed preferably contains granules of an inert material, for example sand, silica, aluminium oxide and/or zirconium oxide granules, or mixtures thereof. Preferably silica or alumina is used. The granules have preferably an average particle size between 20 p and 2 mm, more preferably between 100 and 1000 ijm, in order to simultaneously obtain a stable fluldised bed and realise an optimal heat transfer from the fluldised bed to the waste. The heat transfer is namely associated to the surface-volume ratio of the granules. which has to be as large as possible. With large granules a

well fluidising bed may be obtained, but the heat transfer is insufficiently effective. With small granules on the other hand, an effective heat transfer may be obtained, but it is more difficult to obtain an effective fluidisation and to prevent the formation of sluggish flows.

Preferably an amount cf 5 to 20 wt % in relation to the total weight of the fluidised bed, of a porous, inert material is added.

The porous material is preferably an expanded clay, for example Argex(, and has preferably a grain size of 8-16 mm. Such a material may also be kept in movement by the fluidised bed, and is capable of maintaining an improved movement of the waste in the fluidised bed. In this way it is possible to prevent that organic waste starts to float above the fluidised bed, and is not gasified. Through the addition of such a material, it is also possible to prevent the occurrence of the encapsulation of the waste by the organic material present in the waste. Such an encapsulation is undesirable, since the accessibility of the encapsulated material for the oxidising gas is decreased, which may result in an incomplete gasification.

The residence time which is needed for the removal of the organic material varies with the nature and amount of organic material that has to be gasified, and the nature and form of the waste, i.e. whether the waste has been compacted or not and/or is shredded. The residence time mostly varies between 3 and 15 minutes.

If required, the gases formed in the gasification of the organic material may be post-burned above the fluidised bed. This may be required, for example for the oxidation of CO to C02. Thereto, preferably an amount of a secundary oxygen containing gas is metered above the fluidised bed.

The invention is further elucidated by means of the attached figures and description of the figures.

Figure 1 shows a cross section of a fluidised bed that is suitable for use in the process according to the invention.

Figure 2 gives a schematic overview of the device for the recovery of metal from waste. connected to a device for the recovery of energy.

The device shown in figure 1 comprises a reactor 21. At the bottom, the reactor contains a first layer of silica 22, onto which a perforated plate 4 is applied. Onto the perforated plate a second layer of silica 23 is applied. The reactor 21 also comprises a gas inlet 2, 3, at the position of the first silica layer 22. By the combination of such silica layers 22, 23 with a perforated plate 4, an optimal distribution of the gas and an optimal fluidisation of the fluidised bed 1 may be obtained. The reactor 21 further comprises a basket 8 in which the waste 10 is fed and a gas outlet for the discharge of the gases 12 being released during the reaction. If so desired, the gases may be transferred to a post-burner and/or dry gas scrubbing 18 for the purification of the flue gases. The basket 8 may at the bottom comprise a sealable funnel- shaped outlet for the removal of the purified metal. The basket 8 is preferably movably, i.e. can be moved up and down, mounted in the reactor 21.

it is also possible to connect the fluidised bed with a shaftiess screw for the metering of the waste. This allows a conti- nuous feed of the waste to the fluidised bed and thus provides a continuous process for the waste processing. With such a shiftless screw. it is moreover possible to adjust the rate of metering the waste to the fluidised bed.

In the process according to the invention, gas, preferably air, is fed through the gas inlet 2. 3 into the reactor 21. The gas is distributed through the first silica layer 22, the perforated plate 4 and the second silica layer 23, through which the fluidised bed 1 starts to fluidise and the waste 10 in the basket 8 is heated to a temperature between 400 and 600 "C.

Through the gas inlet 2, 3 an oxidising gas is metered, comprising 6-21 vol. % of oxygen. The residence time of the waste in the fluidised bed is preferably maximum 15 minutes. In these conditions, the organic material present in the waste is mainly gasified, and combustion of the waste can be substantially prevented. Moreover, it is also possible to avoid an oxidation of the metal. The gases 12 originating from the gasification are discharged to a post-burner 24 at the top of the reactor. where the eventually formed flue gases are post-

burned by feeding of secondary air to the reactor (11), in order to completely oxidise the CO present. If so required, the off gases may also be dedusted.

In such a way it is possible to completely strip 120 kg of waste in 20 minutes from organic material and to obtain mainly pure aluminium, the surface of which is hardly oxidised, and which may be used without further special treatment for further processing. With the process according to the invention, it is possible to recover more than 80 % of the metal present in the waste for further use.

Due to the high temperature effectiveness of the fluidised bed, it is also possible to recover the energy intrinsically present in the waste, which involves an important economical advantage. This may be carried out by connecting a hot water boiler or a low pressure flow boiler to the fluidised bed, as is shown in figure 3.

If so required, the recovered metal may be purified by removal of the sand originating from the fluidised bed. for example by sieving.

Example 5 g of metal waste polluted by organic material was charged to a closed round basket with a diameter of 450 mm and fed to a reactor with a volume of 750 I. The reactor contained a fluidised bed of 1100 kg of silica to which 100 kg of Argex( has been added. The temperature of the fluidised bed was held at 500 "C. Through the gas inlet, air containing alternately between 21 and 6 % of oxygen was fed.

The residence time of the waste in the reactor was 15 minutes. The composition of the recovered fraction was (all % are wt %): Al = 91.4 %, of which 86.5 % pure metallic Al; Fe = 0.53 %; Zn = 0.1 %. Mg = 0.03 %. Cu - 0.001 %; S = 0.009 %; Mn = 0.06 %; Ni = 0.003 %.

List of used references 1. fluidised bed 2. air feed 3. gas feed 4. gas-air distribution plate 5. safety bumer 6. ventilating fan 7. combustion chamber 8. basket for recovery of metal 9. process gases 10. recovered metal 11. secundary gas feed 12. flue gases 13. engine room 14. stack 15. recovered metal 16. metal container 17. boiler for heat recovery 18. dry gas scrubbing 19. (ceramic) filter 20. waste feed 21. reactor 22. first silica layer 23. second silica layer 24. post-burner