ITMI20110837A1 - PROCEDURE AND RELATIVE PLANT FOR THE SAFE DECONTAMINATION OF NON-POROUS MATERIALS CONTAMINATED SUPERBALLY BY PCB OR OTHER TOXIC AND HARMFUL SUBSTANCES - Google Patents

Description

DESCRIPTION

PROCEDURE AND RELATED PLANT FOR THE SAFE DECONTAMINATION OF NON-POROUS MATERIALS SURFACELY CONTAMINATED BY PCB OR OTHER TOXIC AND HARMFUL SUBSTANCES

DESCRIPTION

Technical field of invention

The present invention refers to a process, and to the relative plant, for the decontamination in safe conditions of non-porous materials and objects, both large and minute, contaminated on the surface by toxic and harmful highly lyophobic and non-volatile substances, such as in particular the polychlorinated biphenyl.

State of the art

As the polychlorinated biphenyl (PCB) is known, it is a compound, or a mixture of homologous compounds, with a highly chlorinated aromatic base having characteristics of great chemical inertness, low volatility, thermal stability and excellent dielectric characteristics, which have spread its ™ application in electrical equipment as insulating / refrigerating fluids in condensers and transformers, as well as in other applications as hydraulic service fluids in operating machines and hydraulic systems.

However, due to its characteristics of toxicity towards humans and its non-degradability and persistence, which lead to its progressive accumulation in the environment and, therefore, also in the food chains with final accumulation effects in animal and human tissues , its use has been banned. Nevertheless, still today there are large quantities of materials, equipment and work surfaces (such as large appliances, racks and metal structures) contaminated by PCBs that must be decontaminated so that they can then proceed with the safe recovery and recycling of their metal components.

Among the decontamination methods currently in use, the most common are washing with solvent (used in both liquid and gaseous phases) of contaminated objects and materials which must therefore be forcibly treated in closed containers due to volatility, toxicity and, sometimes , flammability of the solvents normally used. Methods of this type are described, for example, in patent publications EP-A-0221028 and US-A-6423151.

If these solvent washing methods solve in an acceptable way the decontamination of objects and materials of relatively modest size, they are inapplicable for large pieces, surfaces and structures where the use of solvents could not be carried out in a safe way for the use. Environment and for operators, if not using closed spaces that would reach prohibitive dimensions, nor could contaminated elements be treated outdoors.

The same applies to the decontamination treatment of small parts or in any case of very small elements such as soil, fine sands, glass fiber or crushed rock wool, for which the solvent treatment is impractical and, in any case, uneconomical.

For this type of materials, it is preferable to resort to washing methods that use detergent solutions, as described for example in the patent publication WO-A-96/18464. Although effective, these methods lead to the generation of large quantities of contaminated effluents from which the solvent is not directly recoverable. Furthermore, these effluents must be disposed of by thermal destruction, with a considerable impact also from an economic point of view.

Another drawback of solvent-based decontamination systems is that these, for economic reasons, must always be recovered and recycled by separating them from the contaminant. This implies the need to have adequate equipment for the distillation / evaporation of the solvents themselves, avoiding their deterioration and escape into the atmosphere, with all the necessary precautions for the treatment of toxic substances.

There is therefore the need to have a process and a plant for decontamination from PCBs (or other contaminants with similar low volatility and solubility characteristics) that can be used safely, without having to resort to the use of inconvenient and fatiguing. safety equipment for operators and for the use of large closed containers, and which above all are suitable for treating both very small pieces, such as fine sand, and very large ones, not easily handled and / or transportable, possibly even on site.

Exhibition of the invention

The primary purpose of the present invention is therefore to remedy the disadvantages of the decontamination methods with solvents briefly described above.

A second purpose is to allow decontamination operations to be carried out in suitably equipped open places or containers, while at the same time allowing operators to work wearing only the ordinary personal protection systems used for handling chemical substances.

A third purpose again is that of being able to safely and at low cost decontaminate even extremely small contaminated elements such as fine sands or other similar material (for example, glass flakes, wires, etc.).

A fourth purpose is to allow the decontamination of contaminated places (floors, concrete or iron structures, etc.) in complete safety for operators and the environment, thanks also to the non-toxicity of the solvent used.

A fifth purpose is to avoid the formation of vapors harmful to the environment during decontamination operations, by using solvents with virtually zero vapor pressure at the working temperature.

A sixth purpose is to minimize the consumption of water used in decontamination operations, creating a simple and safe recovery and recycling system.

A seventh purpose is to generate process waste that is not toxic or harmful, as it does not contain PCBs, or other types of persistent organic pollutants, and that can be disposed of in landfills as inert solids or as fuels with heat recovery. .

These purposes are achieved with a process for the decontamination of materials having a non-porous surface, contaminated by toxic and noxious organic substances, comprising a pre-washing phase with a solvent and a rinsing phase with a detergent, characterized in that the solvent of the phase of pre-wash includes a mixture of refined mineral oils with a predominantly paraffinic base and the detergent of the rinsing phase consists of a detergent solution comprising, expressed as a percentage by weight of the solution: 5-10% of sodium hydroxide, 1-5% of ETDA tetrasodium, 5-15% dodecylbenzenesulfonic acid, 5-15% 2-butoxyethanol and 1-5% ethoxylated alcohol.

Brief description of the drawings

The present invention will be described in more detail below with reference to a preferred embodiment shown, by way of example only, in the attached drawing, where the single figure schematically shows a plant for carrying out the process of the invention for the decontamination of large non-porous materials and objects.

Preferred embodiment of the invention

With reference to the single figure of the drawing, a piece to be decontaminated 1 consisting of a large non-porous material, such as an element of a contaminated metal structure, is introduced and kept suspended on a basin which acts as a work 2 by means of an adequate transport and lifting system 3, for example of the monorail type.

Once in position, the person in charge of the decontamination operations sprays a pre-wash solvent on the entire surface of the piece that is able to adhere to the surface to be treated, whatever its orientation with respect to the ground.

According to the present invention, a product consisting of a mixture of refined mineral oils with a predominantly paraffinic base is used as the pre-wash solvent. It is a clear liquid, non-corrosive and, above all, not very toxic by inhalation, ingestion and contact with the skin. Its combination of thermal efficiency with its high temperature stability makes it particularly suitable for its total recovery by the process described here. This type of solvent has a fair, but sufficient solvent power towards PCB and / or other toxic, harmful, highly freeze-dried, non-volatile substances and is almost totally insoluble in water.

The chemical-physical characteristics of the pre-wash solvent are shown in the following Table I.

Table I.

CHARACTERISTICS METHOD U.D.M. VALUE Appearance - Clear Color ASTM D 1500 - 0.5 Viscosity at 60 ° C ASTM D 445 cSt 6 Flash point in open vessel ASTM D 92 ° C> 170 Self-ignition temperature ASTM D 659 ° C 360 Pour point ASTM D 97 ° C <-10 Distillation curve at 760 mmHg IBP ASTM D 2887 ° C 280 min 2% ° C 330 min ° C 390 max

98%

Vapor pressure at 20 ° C hPa <0.1 Solubility in water between 0 ° C and 100 ° C% by weight Insoluble

In comparison with the known solvents traditionally used for this purpose and described, for example, in the prior documents US-A-6423151 (solvent used: n-hexane) or EP-A-0221028 (solvent used: perchlorethylene), the solvent according to ™ invention is non-flammable, has a lower vapor pressure and is harmless. Consequently, the operator can safely work in an open environment near the piece to be treated wearing only normal protective clothing, so as not to come into direct contact with dripping of the product.

The solvent is in the liquid phase in a tank 9 from which it is sent, by means of a pump 5, to remote controlled sprayers 6 or directly controlled by the operator.

Any accidental drips and spills of the solution fall onto a drainable grid work surface 7 and from there into an underlying liquid collection hopper 8 from which they return through the diverter valve 4 to the tank 9.

Once the piece has been sprayed and covered with a layer of solvent, a time of about 15 minutes is allowed to elapse to allow it to drain and to allow the solvent to absorb and solubilize all the contaminant in itself.

Once this time has elapsed, the operator proceeds to rinse the piece using water mixed with a detergent additive contained in the tank 10. The rinsing takes place by means of the pump 11 and the sprayers 12 remotely controlled or directly controlled by the operator.

Any top-ups of detergent additive are carried out directly in line by means of a dosing pump 15 which takes the concentrated additive contained in a tank 16 from the storage tank.

According to the present invention, a mixture consisting of caustic alkalis, sequestrants, solvents and surfactants is used as the detergent solution. The excellent cleaning power of this solution allows to completely remove the residual solvent left on the contaminated piece.

The chemical-physical characteristics of the detergent solution are shown in the following Table II.

Table II

U.D.M. FEATURES VALUE Color Amber - brown pH (at 20 ° C) 12.6 /-0.3 sol. 2% Explosive properties Not explosive Oxidizing properties Non oxidizing Solubility in water Complete Vapor pressure at 60 ° C mmHg N.A.

The preferred composition of the cleaning solution is given in Table III. The concentration of the compounds in the detergent solution is expressed as a percentage by weight of the total weight of the mixture. Naturally, the percentages of the single compounds can vary in the corresponding ranges according to the degree of contamination and the type of material treated.

Table III

Name of the compound Conc. (% By weight) Sodium Hydroxide 5 â € “10

EDTA Tetrasodium 1 - 5

Dodecylbenzenesulfonic acid 5 â € “15 2â €“ Butoxyethanol 5 â € “15

Ethoxylated Alcohol 1 - 5

The solution of water and surfactants totally cleanses the piece, dragging the solubilized contaminant with it. This operation increases the solubility (initially practically zero) of the contaminating substance up to 10000Ã · 20000 times, in the specific example the PCB and the solvent that contains it.

The rinsing water with the surfactant solution, together with the contaminant substance absorbed and solubilized in it, ends up through the screen, the hopper and the diverter valve 4 into the washing liquid collection tank 10.

The recovery of the liquids contained in the tank 10 takes place by distillation and drying of the water in the distiller 18. From the distiller, the distilled and PCB-free water is condensed by means of the heat exchanger 17 and collected in the tank 14 kept in vacuum conditions from the pump 19.

The bottom residues of the evaporator 18 consisting of solvent, additives, detergents and PCBs, are extracted and sent to a dehalogenation unit 21 from which they are extracted by the pump 22 and subsequently sent to the tank 9 after filtration with filter 23.

The solid filtration residue is collected in a suitable container 24 to be managed as a material not containing PCBs to be disposed of in accordance with the law in force.

Some examples of application of the invention will be provided below. It is understood that these examples are given for illustrative purposes only, and do not constitute a limitation to the scope of the invention.

Example I.

No. 5 metal plates 300x300 mm in size were immersed in ASKARELâ „¢, extracted and left to drain for 2 hours. At this point one of these plates was analyzed with the US EPA 8082 method to evaluate its PCB content. The PCB concentration on the foil was 2.08 g / m2. Subsequently, the remaining 4 plates were immersed in the solvent at 60 ° C, and, after having dripped for 15 minutes, they were immersed in the solution of water and detergent additives for 5 minutes, after immersion in the aqueous solution, the plates they were left to drain for 2 minutes before being immersed in distilled water for the last wash. At the end of washing with distilled water, the plates were dried and the PCB content was evaluated using the US EPA 8082 method. The analysis carried out on the sheets thus treated gave a residual PCB content of 4.33 mg / m2.

Example II

An open tank used for the temporary storage of PCB-contaminated appliances 1.2x1.2m in size with 1m high walls (total internal surface plus external 8.48 square meters), kept raised on a drainage platform as described above à ̈ sprayed with solvent (0.5 mm thick on the piece) and then left covered internally and externally for about 15 minutes to allow the PCB to be detached, absorbed and solubilized in the solvent. Subsequently, the internal and external walls were carefully rinsed with a jet of water and surfactant under pressure using about 10 liters of solution. The aqueous phase drained from the grilled work surface containing the surfactant used was evaporated under vacuum at 60 ° 70 ° C. No trace of PCB was found in the water thus evaporated and condensed, while the analyzes carried out in several points of the tank walls gave PCB contents of 4.55 mg / m2.

Although a preferred embodiment of the invention has been illustrated, it is understood that a person skilled in the art could make various variations and modifications thereto, without thereby departing from the scope of the appended claims.

Claims (8)

CLAIMS 1) Process for the decontamination of materials having a non-porous surface, contaminated by toxic and noxious organic substances, comprising a pre-washing phase with a solvent and a rinsing phase with a detergent, characterized in that the solvent of the pre-washing phase comprises a mixture of refined mineral oils with a predominantly paraffinic base and the detergent of the rinsing phase is formed by a solution comprising, expressed as a percentage by weight of the solution: 5-10% of sodium hydroxide, 1-5% of ETDA tetrasodium, 5- 15% dodecylbenzenesulfonic acid, 5-15% 2-butoxyethanol and 1-5% ethoxylated alcohol. 2) Plant for carrying out the process of claim 1, characterized in that it comprises: a) a perforated grid or plate to support the contaminated materials to be treated, b) a first spraying device for spraying said solvent on the surface of the contaminated materials, c) a second spraying device for spraying said detergent on the surface of the contaminated materials, d) a first tank arranged below said grid or perforated plate for the collection of said solvent, and e) a second tank arranged below said grid or perforated plate for collecting said detergent. 3) Plant according to claim 2, characterized in that it comprises means for moving and / or manipulating the materials to be treated and / or treated. 4) Plant according to claim 2, characterized in that it includes means for treating and recirculating said detergent. 5) Plant according to claim 4, characterized in that said detergent treatment and recirculation means include an evaporator, a condenser, a distilled water storage tank, and means for circulating said detergent. 6) Plant according to claim 5, characterized in that said evaporator operates under vacuum conditions. 7) Plant according to claims 2-6, characterized in that the bottom residue of said evaporator can be totally recovered by means of a dehalogenation and filtration process. 8) Process for the decontamination of materials with a non-porous surface, contaminated by toxic and noxious organic substances, by means of treatment with a plant according to one or more of the preceding claims, characterized by the fact that the contaminating substance is formed by polychlorinated biphenyl or its homologs chemicals at different levels of chlorine content.