WO1995002471A1

WO1995002471A1 - Removal of paint, lacquer and other coatings from metal and alloy materials

Info

Publication number: WO1995002471A1
Application number: PCT/AU1994/000399
Authority: WO
Inventors: Peter James Mcallister; Ian Roy; Warwick Arthur Hoffmann; Susan Meryl Beaupeurt
Original assignee: Technological Resources Pty. Ltd.
Priority date: 1993-07-16
Filing date: 1994-07-15
Publication date: 1995-01-26
Also published as: CA2166864A1; JPH09500420A; KR960703686A; EP0715549A1; ZA945173B; TW278054B; EP0715549A4; NZ268852A

Abstract

This invention relates to novel methods for removing paint, lacquers and other coatings from metal and alloy materials, in particular metallic cans. One method of the present invention involves a combination of steps including: (i) a pre-treatment step to alter the structure of the paint, lacquer or other coating, such pre-treatment preferably involving heat, making the coating more amenable to biostripping; and (ii) contacting the metal or alloy material with a bacterial culture capable of removing said coating. In an alternative method the combination of steps includes: (i) a heat treatment step to alter the structure of the paint, lacquer or other coating; and (ii) an abrasive treatment involving contacting the heat treated coated metal or alloy material in step (i) with a similarly heated material and/or with an untreated and/or uncoated like metal or alloy material, wherein the contact is caused by rolling in a rolling reactor. The abrasion step makes the paint, lacquer or coating of the metal or alloy in step (2) amenable to stripping with a fluid which fluid is either present in the rolling reactor or is jet sprayed onto the heat treated and abraded coated metal or alloy material. The removed paint, lacquer or other coating, and/or the liquid used to remove the coating is treated with orgamisms such as bacteria, capable of degrading said coating, before subsequent disposal.

Description

REMOVAL OF PAINT, LACQUER AND OTHER COATINGS FROM METAL AND ALLOY MATERIALS

Field of The Invention This invention relates to novel methods for removing paint, lacquers and other coatings from metal and alloy materials in particular metallic cans.

Background of The Invention Many products including foods, beverages and non- edible products are distributed in metallic and alloy containers coated on the interior or exterior surfaces with substances including paints, lacquers or polymers. Other metallic and alloy materials are also coated in a similar manner. These coatings may function in preventing the contents from being contaminated by the container, or may be for aesthetic reasons or for advertisements.

For environmental and economical reasons, it is desirable to recycle these containers which may or may not involve recovery of the metal. Particularly, advantageous techniques are energy efficient, inexpensive, and environmentally friendly.

Aluminium containers, and in particular cans for drinks such as beer, soft drinks and food products are the most common metallic containers presently in use which are desirably recycled. Most technologies for the removal of coatings such as lacquer and paints from such cans are generally thermal involving incineration of the coating prior to remelting and recovery of the metal. Such thermal delacquering steps to remove the coating occur at high temperatures of approximately 536°C and are thus energy inefficient, and produce gases which have detrimental environmental effects. Furthermore, in D.L. Stewart, Jr., and J.H.L. van Linden, "Measurement of Residual Carbon on Used Beverage Containers To Monitor Delacquering

Effectiveness", Light Metals, 1992, 1143-1145, it is disclosed that there are also two factors affecting melt loss and thus the recovery of aluminium. One is the carbon content of the coating, and the second is metal oxidation. Longer incineration times are required to produce lower carbon material. However, this results in an increase in the level of metal oxidation and the loss of aluminium as oxides. Therefore, in the recovery of aluminium, a compromise is required between the two factors of temperature and time.

In order to overcome these problems, biological stripping has been proposed and demonstrated on some can types. Biological stripping is disclosed in PCT/US90/04938 to G.L.A. Bowers-Irons et al, the contents of which are wholly incorporated by this reference.

This patent discloses the process of contacting coated metallic beverage containers with bacteria capable of removing such coatings, where the bacteria are applied in admixture with a nutrient medium capable of sustaining viability of the bacteria, and contacting said mixture for a sufficient amount of time to allow the bacteria to remove the coating from the metallic surface.

However, this process is not effective in removing all types of coatings. In particular, "green" coated cans are stripped far more slowly than "red" coated cans, and "yellow" coated cans are not stripped at all. Importantly, the stripping rates with these cultures are uneven and slow compared to those required for commercial use.

We have been exploring potential methods of increasing the slow rates of stripping such coatings when using bacteria, and generally to increase the viability of commercial application of this technique to include a broader range of coatings.

We have also been exploring alternative methods of reducing the temperature and time of stripping coatings such as lacquers and paints, so as to overcome one or more of the above-identified problems associated with conventional thermal delacquering. Summary of the Invention

According to one aspect of the present invention there is provided a method of removing a coating from a coated metal or alloy material involving a two stage process comprising initial pre-treatment of the container to alter the structure of the coating and/or make it more amenable to biostripping, followed by the step of biostripping. Preferably the first step to alter the structure of the coating and to make it more amenable to biostripping involves thermal treatment. The thermal pre-treatment may for example be carried out at 250°C to 300°C for periods of up to one hour.

The second step of biostripping is preferably carried out by bacteria capable of removing said coating. The invention also provides for enriched cultures of living organisms or bacteria capable of degrading coatings. The enriched cultures can be used to provide pure cultures of individual bacterial strains, using well-known bacteriological methods. Alternatively, the bacteria ATCC 53922 first described in PCT/US90/04938 can be used. It will also be understood that variants of any of the above- identified bacteria can be used as well as other life forms containing all or part of the DNA that encodes for the protein or the ability to perform the biodegradative function. Most preferably the nutrient medium capable of maintaining said bacteria also helps in the removal of said coating. Alternatively the protein or agent per se capable of performing this degradative function isolated in substantially pure form from cultures may be used. According to a further aspect of the invention, there is provided a method for isolating organisms or enriching for organisms useful in degrading the carbon based coatings comprising the steps of selection of bacteria capable of growth utilising said coating, said bacteria originating from a source comprising coatings in the presence of essential elements.

Preferably the method of the invention is used to isolate organisms capable of rapidly degrading the more difficult to degrade "green" coloured coatings at a high pH, most preferably at a pH of 8.5.

The process of removing the coating may also be enhanced by subjecting the coated metal or alloy material to further processing including jet spray action, ultra sound, abrasive treatment or detergent.

After the coating has been removed from the metal or alloy material, the item may then be processed for recovery or recycling of the metal.

According to a further aspect of the invention where it is the intention to recover the metal after the coating has been removed, before pre-treatment to alter the structure of the coating in order to make it more amenable to biostripping, the item is shredded.

According to a further aspect, the invention also relates to products resulting from the above described processes.

According to a further aspect of the invention there is provided a method of removing a coating from a coated metal or alloy material including the steps of:

(i) initial heat treatment of the coated metal or alloy material; (ii) abrasive treatment of the heat treated coated metal or alloy material in step (i) using as the abrasive a similar heat treated surface and/or an unheated and/or uncoated like metal or alloy material; and (iii) agitation of the heat treated and abraded coating with a fluid to enhance the stripping of the paint or lacquer or coating from the metallic or alloy surface of step (ii) .

Preferably where it is the intention to recover the metal or alloy, the coated metallic or alloy material to be treated is shredded before heat treatment. For example, the item may be shredded such that 60-70% of the shredded material passes through a 19 mm screen.

Preferably the abrasive treatment step (ii) and the solution agitation step (iii) are performed simultaneously in a rolling reactor. Most preferably the fluid used in the agitation is water. The abrasion and agitation step may be for example carried out for a period of up to four hours. Alternatively the abrasive treatment step (ii) occurs in a rolling reactor in air and the paint, lacquer or coating of the metal or alloy material is removed in step (iii) by jet spray action with a fluid such as water and/or air.

It will be understood that the thermal pre-treatment step (i) depends on a trade-off between temperature and time. Preferably the thermal pre-treatment is above 100°C since we have found that thermal pre-treatment below this temperature does not degrade the organic coatings. More preferably the thermal pre-treatment is between 120°C and below 536°C, which latter temperature is a typical temperature used in thermal delacquering. Even more preferably the temperature is between 200° and 400°C. Preferably the thermal pre-treatment is performed in a rotary kiln although other devices may be used such as for example a fluidised bed reactor or conveyor drier.

While it is desirable to remove all of the coating it will be appreciated that any degree of removal of the coating will improve the eventual metal recovery.

The stripped paint, lacquer or coating and/or fluid used to remove the coating may be treated with organisms such as bacteria, capable of degrading the coating before disposal by conventional means. The biodegradative function may be performed with the bacteria capable of removing or stripping said coating as described in one of the aspects of the invention above.

Detailed Description of the Invention

The invention will now be described in detail by way of reference only, to the following non-limiting examples, and to the drawings in which:

Figure 1 shows photographs of flasks with can material and other material incubated with microbial cultures from different sources. Figures 2a and 2b are photographs showing the difference in susceptibility to biostripping of a variety of can material.

Figure 3a shows the temperature profile in the rotary kiln used in the thermal pre-treatment step of the water abrade method of examples 9 and 10.

Figure 3b shows the effect of varying pre-treatment temperature on the percent carbon stripped in a 200 litre rolling reactor.

Figure 4 shows a comparison of carbon levels obtained after thermal treatment alone and thermal treatment with water abrade. The bars represent standard error of the mean.

Example 1. Biodegradation Of Lacquer From VB And Coke Cans A standard can fragment has been chosen. This consists of a 15 mm diameter button punched from an unused VB can body.

VB buttons (50) were added to an orbital shaker flask, bacteria were added and the system incubated at 28°C. Samples of button were removed periodically. Little degradation of the coating was observed after 18 days. At this point 10 coke can fragments were placed in the flask, and allowed to incubate for 7 days. Considerable degradation was noted of the coating on the coke can. It is clear that the different coloured fragments differ in their susceptibility with respect to microbial attack. However biostripping can not be accomplished in a commercially useful imeframe.

Example 2. Culture Development Work

In order to develop microbial cultures a variety of can types were cut into small fragments, and used as a source of bacteria for culture flasks containing samples of lacquers and varnishes used in can manufacture.

In order to develop the bacteria, model coatings were prepared by curing paints, lacquers and varnishes onto conical flasks under simulated process conditions.

Standard microbial growth medium (100 mL) was added to 5 flasks containing each coating either from inside the can (IC), outside the can lid (OCL) or inside the can lid (ICL) . Four different sources of bacteria were used to develop microbial cultures. These were (1) used beverage cans from a burial test, (2) polyurethane foam from a burial test, (3) rotted plastic coated wood and canvas, and (4) garden soil. The fifth flask of the series had can fragments added and a biocide (sodium azide Θ 0.1 % w/v) to distinguish between biological and abiotic removal. The flasks were photographed initially, and incubated at 28°C for 4 weeks, at a shaking rate of 150-200 oscillations/minute (opm) .

Some of the cultures clearly showed microbial attack of the lacquers and varnishes. After four weeks it was apparent that there had been microbial attack of the model surfaces. This varied from some bubbling of the material, to total breakdown of the lacquer material. Photographs of the flask bottoms at 4 weeks are shown in Figure 1. In all cases the poisoned control is on the extreme right.

The process was repeated except green ink was added to all systems in order to select for green ink degrading bacteria. After four weeks, the cultures were evaluated, and the most promising continued. The studies were targeted to the green coloured cans, as the results of the biodegradation rate studies in Example 1 showed that this material was the most difficult to attack. This may relate to the copper phthalocyanin content of the dyes and further investigation is required. However, a literature review on copper phthalocyanin indicates it exists in two forms, the more stable of which (the β form ) is green. The material has been approved by the Food and Drug Administration (FDA) for use in sutures, which implies a low toxicity.

The development of new microbial cultures resulted in 16 cultures. These appear to be capable of removing lacquer from VB buttons.

Cultures obtained from international culture collections have also been tested against lacquer cured onto flasks. One culture (Penicillin Chrysogrenum, IMI314384) was able to remove the lacquer off a flask in approximately 24 hrs. However this did not translate to increased stripping of lacquer from can fragments. Delacquering may be limited by the properties of the overvarnish rather than the dye.

Example 3. Biodegradation Of Lacquer From Different Coloured Cans

In order to understand better the effect of colour on stripping rates, tests were conducted on nine different can types: - Tooheys Red

Solo Fosters VB

Fanta - Tooheys Blue

Fosters Lite Coke

Diet Coke Fragments were isolated from recycled washed cans, placed into shake flasks and incubated with the mixed culture.

The stripping of a variety of can types was investigated. Stripping was monitored photographically. The results are shown in the attached photos in Figures 2a and 2b. It is clear that Tooheys cans are very amenable to biostripping and other can types less so. The results indicate that Coke cans are mid range with respect to biostripping amenability. The range is shown as a continuum below.

Amenable —_ ^- Recalcitrant

Tooheys Diet Coke Coke Solo VB Fosters Light

Posters Fanta

The difference between the stripping of Coke and VB cans is thought to be due to the resin types included, with Coke containing more biodegradable glycol residues.

Example 4. The Effect Of pH And Media On Delacquering Rates

Experiments were performed to test the effect of pH and medium composition on stripping Coke fragments.

Significant stripping was observed with a two day contact time. The system was sampled at 2, 5 and 8 days. Carbon contents of the fragments were also evaluated.

Small scale tests have shown the Leco analyser is suitable for determining the carbon content of can fragments. A standard can fragment was chosen. This consisted of a 15 mm diameter button punched from an unused coke can body. A minimum of 5 fragments per analysis was tested to reduce the variability to an acceptable level. Standard can lid fragments consist of VΛ lids, and the mass is such that acceptable variation is achieved with one fragment.

Experiments on the effect of pH and medium composition on stripping coke fragments were carried out first. Long contact times were required (up to 32 days), and it was found that pH had a significant effect on the rate of biodegradation.

The results of tests carried out over a wider range of pH's and yeast extract (YE) concentration are shown in Table 1.

Table 1: Carbon Removal Rate (% C/day) under Various Conditions pH 8.0 pH 8.5 pH 9.0 pH 9.5

Mineral Salts (MS) 0.08 0.07 0.08 0.02

MS + 2.5 g/L YE* 0.07 0.11 0.11 0.04

MS + 5.0 g/L YE* 0.05 0.12 0.06 0.05

MS + 7.5 g/L YE* 0.05 0.05 0.05 0.05

*YE = Yeast Extract

These results show that pH 8.5 and 5 g/L of yeast extract are the best conditions for biostripping.

Again these rates are significantly faster than the rates measured for VB fragments (0.015% C/day). The addition of a surfactant (Tween 20) did not aid stripping rates.

Example 5. Effect Of Other Pre-treatment Steps On Rates of Biodegradation

Five factors pre attrition acid washing caustic washing solvent washing (acetone) pre-heating (250°C, 1 hr) were tested to study the effect of pre-treatment of cans on the rates of biodegradation of the coating. These were investigated along with the addition of abrasives to the culture media. The abrasives tested are sand fragments and 3μm diamond slurry. These tests were performed in shake flasks.

The four other pre-treatments were tested as methods of making the material more amenable to stripping. The effect of attrition during incubation was also tested.

The following effects were observed: (1) The addition of sand at 1% to the mixture resulted in good stripping, irrespective of the presence or absence of bacteria.

(2) Heat treatment at 250°C for 1 hour resulted in total stripping. The measured rate was 0.08 % C/day. However this does not indicate the true rate, as the data was generated from one initial and one final sample. The rate could be much higher if stripping occurred in the first few hours or days.

(3) Pre-treatment with 1M HC1, acetone or scratching made no difference to stripping rates.

(4) Diamond fragments were not effective stripping agents.

(5) NaOH attacked the aluminium and made it brittle, and was not tested further.

Example 6. Degradation Rate improved By Pre-treatment In order to increase the rates of stripping of coatings, a two stage process was tested. Initial thermal treatment 250°C, 1 hour, was carried out, followed by biostripping. This two stage process was found to strip green material in a total time of 5.5 hours, compared to approximately two weeks without thermal pre-treatment. The temperature and time regime used was much less than thermal processing alone, which is typically greater than 550°C, resulting in less off gas production and little aluminium oxidation. The heating step in the two stage process of the present invention appears to alter the structure of the lacquers and varnishes, making them more amenable to biostripping, the residual carbon content being less than 0.01% carbon. This may or may not be as a result of thermal destruction of inhibitors to the growth of the bacteria.

The two stage process does not appear to be as sensitive to ink pigment which is the case in biostripping alone. The net result is a lower dross production, resulting in a decreased waste disposal problem and an increased level of recovery of saleable metal.

Heat treatment 250°C for 1 hr resulted in total stripping in 2 days. The heat treatment resulted in some loss of carbon (1.4% to 0.6%) with the remainder removed at a rate of 0.3% C/day. Repeat tests were carried out with both Coke buttons and VB buttons. The stripping rate measured for coke buttons was found to be 0.07%C/hr (1.6%C/day). This rate, along with the initial loss of carbon in the furnace (1.4% - 0.8%) resulted in almost complete stripping in 8 hrs, and total stripping within 24 hrs.

Tests with VB buttons showed total stripping in 4.5 hrs from a carbon content of 0.4% (0.09% C/hr) . These results indicate that thermal pre-treatment will give stripping rates in the order of magnitude that is desired for commercial application.

Thermal pre-treatment darkens both the varnish on the can exterior, and the lacquer on the interior. The exterior material is removed rapidly after this treatment, with the lacquer removal appearing to be the rate limiting step.

Example 7. Degradation Rate After Pre-treatment And The Effects Of Bacterial Metabolism On Biodegradation

An evaluation of the biodegradation rates of lacquer on cans was assessed.

To observe the effect of metabolism of the bacteria on the biodegradation, coke cans and VB cans were heat treated for 1 hr at 300°C prior to further treatment in the following solutions: (1) Distilled water (sterile)

(2) Growth media (sterile)

(3) Growth media and bacteria in the presence and absence of the metabolic growth inhibitor hibitane (4) Bacterial cultures after sterilisation in an autoclave. The data are shown in Table 2. The data shown are the carbon content as a percentage of the total weight of a can, and the percentage of lacquer left after 4, 8 and 24 hrs of incubation in the above-defined solutions. As can be seen, the initial carbon content of coke cans is more than two times higher than the carbon content of VB cans. The addition of water or media alone decreased the percent of lacquer left to an amount similar to that obtained with the microorganisms in the presence of a metabolic inhibitor, or when the bacterial cultures were sterilised. In contrast, cultures in the same media decreased the percent of lacquer to almost negligible levels within 4 hrs for coke cans.

Table 2:

Can Buttons (300°C 1 hr)

Coke initial = 0.661% C

Innoculum Hibitane Sterile Media dH₂0 Autoclaved Culture

4 hr <0.01 0.235 0.203 0.404 0.360

8 hr <0.05 0.170 0.215 0.332 0.168

CO 24 hr <0.01 0.085 <0.01 <0.01 <0.01

VB initial = 0 .251% C

Example 8. Large Scale Lacquer Removal And Preparation For Remelt Tests

For the remelt testwork, a 20 L reactor (working column 15 L) was established at pH 8.5 and 5.0 g/L yeast extract. This is a stirred tank system, containing 2 kg of can fragments. These were biostripped in batches to generate material for remelt testwork. Metal was added into a 5 kg molten heel of aluminium with mixing. The dross was allowed to float to the surface, and recovered. The dross make was expressed as % of metal added that was recovered as dross. The data is shown in Table 3. This shows that the biostripped material has a lower dross make than thermally delacquered or untreated cans.

Table 3: Remelt Test Results

Mass Added Gross Dross Net (grams) Dross Metal Dross Make (%) Content Make (%) (%)

Untreated Cans 3000 52 91 4.7

Thermally Delacςuered Material 5000 47 76 11.2

Biologically Delacquered Material 6000 22 91 2.0

Canstock 5000 3 77 1.0

Example 9. Thermal Treatment And Water Abrade

A rotary kiln 0.6 m in diameter and 10.7 m long was operated with a countercurrent flow of hot gases. A typical kiln temperature profile is shown in Figure 3a. A series of trials was performed in the kiln at varying operating temperatures ranging from 340°C to 400°C at the gas burner end, ie. the product end. Used beverage containers (UBC) were shredded in a hammer mill to a sizing of 70% passing through a 19 mm screen and fed into the kiln. The residence time of the cans in the kiln was about 14 minutes. Heat treated UBC could be produced at a rate of 0.5-1 tonne per hour. Samples of thermally pre-treated UBC were then removed and stripped in a baffled, 200 litre rolling reactor. Approximately 7 kg of treated cans were added with 30 litres of water to the reactor and rolled at 30 rpm for a period of 4 hours. The kiln throughput rate was 4 kg/min. The effect of kiln temperature on percent stripping obtained in the 200 litre rolling reactor are shown in Figure 3b. To obtain a clean exposed can surface within 4 hours rolling, it was found that the cans had to be pre-treated at a temperature of at least 380°C for 14 minutes; stripping was 85% at 360°C, and 90% at 370°C. A total of 15 tonnes of pre-treated UBC was prepared under these conditions.

Example 10. Intermediate Scale Pilot Plant For Thermal Pre-Treatment and Water Abrade

A 0.5 tonne per day pilot plant was constructed to treat the 15 tonnes of thermally pre-treated UBC material generated in the rotary kiln in example 9 above. The dimensions of the rolling stripping reactor were 0.75 m in diameter by 3 m long. The rolling reactor rotated at the speed of 9.5 rpm, and was fed continuously at a rate of approximately 20 kg per hour of pre-treated cans. The reactor had an inventory of approximately 85 kg of cans and 300 litres of water. Can residence time was 4 hours.

Stripped cans were washed in the integrated trommel with fresh water.

The reactor was run for a period of 21 days and the stripping results after thermal pre-treatment and after water abrasion are shown in Figure 4. Results are expressed as a percentage of residual carbon levels. Carbon levels of approximately 0.74% were achieved in cans that had undergone heat treatment followed by water abrasion. It will be understood that lower residual carbon levels would be obtained if the method of can shredding was altered to generate a can with more exposed surface area. Thus thermal treatment and washing on a large scale produces a can which had total stripping of lacquers from the exposed surfaces.

Further modifications may be made to the invention as would be apparent to persons skilled in the art. These and other modifications may be made without departing from the ambit of the invention, the nature of which is to be determined from the foregoing description.

Claims

CLAIMS :

1. A method of removing a coating from a coated metal or alloy material including the steps of:

(i) initial heat treatment of the coated metal or alloy material;

(ii) abrasive treatment of the heat treated coated metal or alloy material in step (i) using as the abrasive a similar heat treated material and/or an unheated and/or uncoated like metal or alloy material; and

(iii) agitation of the heat treated and abraded coating with a fluid to enhance stripping of the paint or lacquer or coating from the metal or alloy material of step (ii) .

2. A method according to claim 1 wherein the coated metal or alloy material to be treated is shredded to substantially enhance exposure of the coated surfaces before the heat treatment.

3. A method according to any one of the preceding claims wherein the abrasive treatment step (ii), and the fluid agitation step (iii) are performed simultaneously.

4. A method according to claim 3 wherein the abrasive treatment step and the agitation step are performed in a rolling reactor.

5. A method according to claim 4 wherein the fluid used in the agitation is water.

6. A method according to any one of claims 1 to 3 wherein the abrasive treatment step (ii) occurs in a rolling reactor and the paint, lacquer or coating of the metal or alloy material is removed by jet spray action with a fluid such as air and/or water.

7. A method according to any one of the preceding claims wherein the thermal treatment is above 100°C.

8. A method according to any one of the preceding claims wherein the thermal treatment is between 120°C and below 536°C.

9. A method according to any one of the preceding claims wherein the thermal treatment step is between 200°C and 400°C.

10. A method according to any one of the preceding claims wherein the thermal treatment is performed in a rotary kiln.

11. A method of treating the stripped coating produced by the method according to any one of claims 1 to 10 wherein the stripped coating is treated in fluid medium with organisms capable of degrading the stripped coating.

12. A method for removing paint, lacquers and other coatings from coated metal and alloy materials, involving a combination of steps including:

(i) a pre-treatment step to alter the structure of the paint, lacquer or other coating making the coating more amenable to biostripping; and

(ii) contacting the metal or alloy material with an organism capable or removing and/or degrading said coating or with the protein or agent capable of performing the degradative or removing function isolated in substantially pure form from the organism.

13. A method according to claim 12 wherein the step to alter the structure of the coating and to make it more amenable to biostripping involves thermal treatment.

1 . A method according claim 12 and claim 13 wherein the thermal treatment is above 100°C.

15. A method according to claim 12 and claim 13 wherein the thermal treatment is between 120°C and below 536°C.

16. A method according to claim 12 and claim 13 wherein the thermal treatment step is between 200°C and 400°C.

17. A method according to claim 12 wherein the second step of biostripping is carried out by bacteria capable of removing said coating.

18. A method according to claim 17 wherein the bacteria are ATCC 53922.

19. A method according to any one of claims 12 to 18 wherein the nutrient medium capable of maintaining said organisms also helps in the removal of said coating.

20. A method according to any one of claims 12 to 19 wherein removal of the coating is enhanced by subjecting the metal or alloy material to further processing including jet spray action, ultrasound, abrasive treatment, or detergent.

21. A method according to claim 20 wherein the abrasive step is carried out in a rolling reactor.

22. A method according to any one of claim 12 to 21 wherein the coated metal or alloy material is shredded before pre-treatment of the material to alter the structure of the coating.

23. A method according to any one of the claims 12 to 22 wherein after the coating has been removed from the metal or alloy material, the item is further processed for recovery or recycling of the metal.

2 . A method for isolating or enriching organisms useful in degrading the carbon based coatings comprising the steps of selection of bacteria capable of growth utilising said coating, said bacteria originating from a source comprising coatings in the presence of essential elements.

25. A method according to claim 24 wherein the organisms are selected for their ability to rapidly utilise green coloured coatings at a high pH.

26. A method according to claim 25 wherein the organisms are capable of utilising said green coloured coatings at a pH of 8.5.