ITVE980036A1 - PROCEDURE FOR INERTIFICATION OF HAZARDOUS AND NON-HAZARDOUS INORGANIC WASTE THROUGH PARTIAL OR TOTAL GLAZING OF A MIXTURE WITH - Google Patents

Description

"DESCRIPTION OF THE INVENTION WITH THE TITLE: Process of inerting hazardous and non-hazardous inorganic waste, through partial or total vitrification of a mixture containing at least 95% and up to 100% of inorganic waste, and products obtainable from this process."

Inorganic hazardous waste are substances that are harmful to humans and the environment and as such must be segregated or appropriately inerted; their confinement is becoming extremely problematic given the quantity involved. Finding an inexpensive way to neutralize them is also important to prevent illegal solutions to the problem. According to recent legislation, solutions must be sought within the boundaries of the Province and / or Region of belonging and this places further limits on the vitrification or inertization process if conceived as a treatment of a single type of waste. In the scientific literature the vitrification of one waste or at most two waste has been extensively dealt with. There are also numerous patents among which the most significant are:

• Italian Patent N ° 48.313 A / 89 of 07/07/87;

• Italian Patent N ° 000884/95 of 28/08/89;

• US Patent N ° 4,678,493 of 07/07/87;

• EPO Patent N ° 84308001.1 dated 19/11/84,

However, the inertization through vitrification of a restricted type of waste represents a non-economic solution to the problem in the sense that even if the vitrification system is suitable for treating a single type of waste, it is nevertheless difficult to amortize for various reasons; for example, a vitrification plant that treats a limited quantity of waste has high energy and plant costs. In this regard, figure 1 illustrates the specific consumption and daily production in a typical electric glass furnace (fossil fuel furnaces also have similar diagrams): the advantages obtained by increasing the size are evident.

Fig. 1 - specific consumption and production as a function of the sole size.

Furthermore, in the event that vitrification is to be carried out using only one waste, the composition of the obtainable product hardly allows its processing and must be disposed of only in landfills, unless other raw materials are added (siliceous sands, soda, feldspar, etc.) available on the market but at high costs.

Table 1 shows the chemical compositions of some types of asbestos, the only material for which vitrification was initially considered advantageous. In general, however, asbestos is used in conjunction with other materials such as gypsum, calcite, cements and various dressings etc, from which separation is not possible. Table 2 shows the indicative chemical compositions of a typical material containing asbestos and other wastes that can be used in the vitrification or inertization process.

Table 1- Composition of asbestos (% by weight).

The materials indicated in table 2 with a capital letter in the first row are defined in the following legend:

A. composite material containing asbestos (defined as hazardous);

B. ashes from MSW incinerator (defined as dangerous);

C. waste from a MSW incinerator (defined as dangerous);

D. fly ash of the thermoelectric power station (defined as dangerous);

E. bottom ash thermoelectric power station;

F. excavated channel mud (defined as dangerous);

G. zinc processing slag (defined as dangerous);

H. inert feldspar processing;

I. inert granite processing;

J. calcined slag for leather processing (defined as dangerous);

K. slag steel processing;

L. purposes of glass cullet processing.

The vitrification process includes the following operations:

- characterization and preparation of waste as summarized below: chemical analysis, crushing, possible washing to eliminate soluble salts, dehumidification; reduction of the organic and metallic part, dangerous for the refractories making up the furnace; in particular, a value lower than 400 ppm for metals and 1000 ppm for organic residues is considered acceptable;

- homogenization of the waste and its mixing in order to obtain a suitable vitrifiable mixture whose composition is determined by the product to be obtained; the pelletizing of the mixture is an unnecessary process but which can be useful in many cases;

- melting of the batch in a combustion or electric glass furnace; the second system is preferable because it is easier to control as regards emissions; in any case, the oven must be equipped with a suitable emission abatement system and also with a drainage system for the vitreous material in correspondence with the sole;

- forming of the product (stretching for fibers, pressing for tiles, casting between rollers or in water for granulates, etc.) and its eventual annealing;

- quality control of the product obtained with, for example, evaluation of chemical resistance, mechanical properties, etc.

Table 2 - Examples of composition of inorganic industrial waste (% by weight).

Table 2 follows - Examples of composition of inorganic industrial waste (% by weight)

The advantage of the present invention is based on the construction of a plant capable of treating the hazardous and non-hazardous inorganic waste present in the territory after suitable treatment and mixing; this allows to:

1. considerably reduce transport costs, also taking into account the legislative limits relating to the transport of waste;

2. obtain from the appropriate mixing of such waste and their fusion, a series of glassy products of different composition depending on the use and / or destination;

3. reduce or eliminate the use of high-cost raw materials such as silica sands, soda, feldspar, etc.

4. reduce the volume of starting waste to a minimum given that with this procedure it is intended to vitrify a mixture with over 95% of waste;

5. obtain commercial products with their own added value; this result also depends on the stability of the composition of the material produced which can only be obtained if the waste is “cultivated” in these plants in order to regulate the flows of materials; in this sense it is possible to proceed for production campaigns.

6. have a wide range of widely used glass products, the chemical composition of which can be varied according to the forming parameters and the required properties.

The main constituents of a glass are the lattice-forming oxides (SiO2, A12 O3, P2 O5, B2 O3, etc) responsible for the chemical and mechanical stability of the glass and the modifying, fluxing oxides (Na2O, K2 O, etc) and stabilizers (CaO, MgO, BaO, etc), on which the fusibility of the mixture and also the chemical stability of the glass produced depend. When a vitrifiable mixture is designed, it is necessary to properly dose the vitrifying raw materials that bring these oxides. Having a variety of waste available in which the various oxides are present in different percentages, it is necessary to make a careful choice and dosage among the various waste in order to obtain a chemically stable glass in order to block the toxic elements and with physical and mechanical properties that allow processing and use. For example, waste A - B - F - J - K can be considered as raw materials that bring stabilizing oxides such as dolomite and limestone; waste C - D - E - H - I consisting mainly of forming oxides give high chemical stability such as sand, feldspar and nepheline. Finally, the waste L is important as it ensures a significant supply of fluxing oxides which contribute to reducing the melting temperature. On the basis of these considerations, some examples of vitrifiable mixtures obtained using the previous wastes are provided according to their role:

EXAMPLE 1 - 70 parts of waste B with 20 parts of waste C and 10 parts of waste J. A glass is obtained with the chemical composition described below and suitable for the production of insulating glass fiber (equivalent to the chemical composition of commonly used basalts for the production of rock wool).

Table 3 - Chemical composition of the glass of example 1.

EXAMPLE 2 - 50 parts of waste A with 20 parts of waste D and 30 parts of waste H. A glass is obtained with the chemical composition described below and suitable for the production of exterior cladding material in building. By subsequent heat treatment, the glass obtained takes on the characteristics of a ceramic glass.

Table 4 - Chemical composition of the glass of example 2.

EXAMPLE 3 - 20 parts of waste A with 40 parts of waste D, 10 parts of waste F and 30 parts of waste L. A glass with the chemical composition described below and suitable for the production of glass - foam for insulation is obtained.

Table 5 - Chemical composition of the glass of example 3.

EXAMPLE 4 - 20 parts of waste A, 30 parts of waste L and 50 parts of phosphating sludge. A glass is obtained with the chemical composition described below and suitable for the production of nutritive glass for agriculture.

Table 6 - Chemical composition of the glass of example 4.

It is clear that, in all the various examples, instead of individual waste A or B etc it is convenient to use a mixture of different waste in order to stabilize the mixture within the composition of glass to be obtained.

Claims (9)

CLAIMS 1. The process as per title, as a whole, suitable for vitrifying at least 95% of inorganic waste. 2. The process referred to in point 1 which produces glass that can be used as a raw material in the ceramic, cement and glass industry. 3. The process described in point 1 which produces glass for use as a fiber. 4. The process described in point 1 producing glass or glass ceramic for tiles. 5. The procedure referred to in point 1 which produces glass to be used as a fertilizer for agriculture. 6. The process of point 1 which produces glass for use as a filler. 7. The process referred to in point 1 producing glass for glass-ceramic products. 8. The procedure referred to in point 1 which produces glass - foam; 9. The procedure referred to in point 1 for obtaining glassy products for any other possible application.