HAZARDOUS OR NON HAZARDOUS? A STUDY OF THE CLASSIFICATION OF WASTE ENAMEL SLIPS
Emil Barta - Lampart Vegyipari Gépgyár RT, Hungary

Abstract
Waste classification is an integral part of waste management. Classification of waste enamel slip can make it possible for the owner of the waste to obtaina more favourable hazard classification. The method in which the waste is stored can influence the resultant classification.
The development of a single waste management technology requires careful consideration to obtain a "non hazardous waste" classification.

Introduction
One requirement of joining the European Community is that Hungarian companies must meet their environmental regulations.
Due to this, the standards applied have become more strict, as to ignore these directives may involve serious consequences. It has now become necessary to deal with environmental protection in Hungary.
The management of the Lampart company took a decision to impose rules on the management of waste enamel slip.
The aim was to classify waste from pre- privatisation according to the present regulations and also that waste enamel slip from current production should be classified according to the current regulations.
As waste enamel slip is included in the hazardous waste material list without any classification, it is classified as "Class II hazardous waste", as a result of its most hazardous constituent.
Waste classification is an integral part of waste management, as collection, storage, treatment, transport and potential recycling of the waste material are closely related to its hazard classification, with reference to re-classification as "non-hazardous waste".
The classification of waste enamel slip will make it possible to gain a more favourable classification.
This may result in a "non-hazardous waste" classification where favourable test results are obtained, instead of the automatic "Class II hazardous waste" classification.
We, as enamellers with professional knowledge, anticipate that waste enamel slip will be classified as "non-hazardous waste" (except for Cd and Pb containing enamels).
It was for this reason that we commenced classification of our waste slip.

First study
The first waste enamel slip selected for classification was from preprivatisation.
This was partially dried frit.
Its composition was a fine ground mixture of ground coat frits, chemical enamel frits, clays and set-up salts together with other finely ground materials.
This waste under investigation came from manufacturing, repairing or reenamelling of coated chemical vessels during the process shown in figure 1.

Steps of the classification

figure 1 - Enamelling process of coated chemical vessels

Test results
For the purposes of this investigation, extractions were made using the following solvents: distilled water, pH 4.5 acetate buffer and 2M Nitric acid.
The first two model the effects of live water, subsoil water, acid rain and discharges from public waste deposits.
The last gives information about the total metal content of the waste.
The results determined are evaluated in comparison to the concentration limits applied to drinking water, sludges and soil (Table 1).

Results of the investigations of physical and chemical properties
Table 2 shows results of original sample investigations in comparison with the relevant limits.

There are no unacceptable values among the results from this initial investigation.
Table 3 shows results of investigations of distilled-water extract.

The pH value of 9.5 for the distilled water extraction is the only value which is excessive. None of the other values are of concern.

Investigation of influence of the quantity and of the environmental effects of mobile components
Table 4 shows the results of the distilled water and acetate buffer extractions compared to the relevant limits for metals.

The drinking water limit in the distilled water extraction is exceeded by more than ten times for the mobile metals B, Cr, Co, Ni, Fe and Zn.
The aluminium exceeds the limit by more than one hundred times. The results of the acetate buffer extraction are generally smaller than those of the distilled water extraction and no single result exceeds the one hundred times threshold given as the limit for drinking water.
The high concentration of aluminium in the distilled water extraction was fairly surprising.
The amount of aluminium oxide in the waste mixture is 1-2% on average, according to our recipes and even the total amount does not exceed 4%, partially introduced from the clay in the mill addition.
Table 5 shows the results of toxic metal releases in the 2M nitric acid extraction compared to the relevant limits.

The relevant sludge limits are exceeded only by Co and Ni. The ten times limit for soils is exceeded by Ba, B, Co and Ni.
I will not go into details regarding the toxicological and mutagenetical investigations, as the results were negative in all cases. Daphnia and alga tests show slight ecotoxicological effect.
On the basis of the test results of the toxic metal investigations, the waste enamel slip could be classified as a Class III hazardous waste, if we exclude aluminium.
However, the evaluation committee classified as a Class II hazardous waste, as aluminium ions can contribute to Alzheimer's disease.
During the evaluation, there was a professional debate relating to the high value obtained for aluminium and as a result we took the opportunity toinvestigate the effect of aluminium from fresh waste enamel slip.
It was considered that it was probable that this aluminium came not from our technology, but had been introduced as a result of unsuitable storage conditions.

Second study
The high aluminium content, found during the classification, is not typical of the current waste.
Even though the waste contains finely ground clay as a suspending agent, it is only present as a low amount and does not account for the high results.
To clarify these doubts, a determination of the aluminium content was made of enamel waste from the past few years, which had been collected in containers and deposited in an enclosed space.
The investigations show (Table 6) that the aluminium content in the distilled water extraction does not exceed the ten times limit for drinking water.
In the acetate buffer extraction a 126 -140 times value was obtained, exceeding the limit and giving a Class III hazardous waste classification.
The 2M nitric acid extraction of this sample gave a lower average aluminium content (3297 mg/kg) compared to the first sample (5113 mg/kg)-(Table 6).

In comparison to this decrease, the solution into water was smaller. This shows that aluminium is found in other chemicals associated with fresh waste.
The higher solution into the acetate buffer seems to confirm this.
Aluminium was present in the second sample, but the solution into water is below the limit and the value typified by Class III hazardous wastes only occurred with the acetate buffer extraction.
As a result of these investigations, the current waste enamel slip was classified as a Class III hazardous waste.

Third study
Although we had managed to classify the waste into the lowest class as a result of the latest investigations, the conclusions arrived at did not satisfy me, since it is contradictory that aluminium bound onto a clay material would have any effect on the environment, despite the fact that the current waste enamel was classified as hazardous on the basis of the other components.
The second sample was subjected to further investigation. It was proposed that in addition to dissolved Al ions, Al ions from the fine clay particles were also being measured causing a false result.
Two samples were prepared. One was centrifuged at a rotation frequency of 4500 min-1 for 10 minutes before filtration.
The level of aluminium in the centrifuged sample was approximately one tenth of that in the un-centrifuged sample (Table 7).

Test results show that the aluminium content of the sample is decreased by centrifuging.
It thus seems likely, that in the first sample, the hundred times excess of the limit was due, not to aluminium ions, but derived from measurement of aluminium in covalent crystalline bonds in the clay particles.

Solid particles of size less than 1 μm introduced into the Ar plasma during nebulisation of the sample solution were dissociated into atoms at a temperature of 6000 - 7000 K.
Thus, when determined by the ICP-AES technique, without centrifuging, the amount of aluminium included both aluminium bonded into the solid clayparticles and also the aluminium dissolved as ions; while in the centrifuged sample only the aluminium dissolved as ions was included.
Frit particles with a size less than 1 μm may also pass through the filter leading to a false result.
Future work will include the proving of this supposition and correction of the standard.

Fourth study
We would like to know if it is possible to transform the waste enamel, which has already been classified as a "Class III harzardous waste" into a waste classified as "non- hazardous waste". The obvious route to us was to smelt the waste slip after drying and homogenising. From this procedure we obtained an enamel frit of an unknown composition with a reduced surface area compared with the surface area after grinding.
During this work the first study was repeated with the transformed waste enamel. Centrifuging before filtration was also carried out.

Test results
Results of the investigations of physical and chemical properties
Table 8 shows results of the resmelted sample investigations in comparison with the untreated waste results.

There are no unacceptable values among the results of this resmelted sample.
Table 9 shows the results of the distilled water extraction.
There are no constituent values which exceed the hazardous limit (ten times the value for drinking water) in the distilled water extraction.
The pH value meets the requirements.

Investigation of the influence of the quantity and of the environmental effects of mobile components
Table 10 shows the comparison of results of toxic metal determinations for the resmelted and untreated waste in distilled water and acetate buffer extractions.
None of the mobile metals exceeded the limit for hazardous waste i.e ten times the drinking water limit in the distilled water extraction and one hundred times in the acetate buffer extraction.
Table 11 shows a comparison of the results of 2M nitric acid extractions of the toxic metal investigations with those of the untreated waste.
No results exceeded the ten times limit for sludge and soils.

We can summarise these findings by stating that the waste enamel frit treated by re-smelting meets all of the criteria of a "non hazardous waste" on the basis of the physical and chemical investigations.
The test results show that for waste treated by re-smelting nearly all of the values are lower than those for the untreated waste.
Hazardous constituents are strongly bonded within the glass matrix due to the trasformation, the surface area is significantly decreased and leaching is no longer significant (from the pH value).

Conclusion

Note
The classifications obtained for waste enamel slip by Lampart Rt. does not necessarily imply that the waste enamel slip of other companies can be classified in the same category. Each waste has to be classified individually.