METHOD OF DECOMPOSING ASBESTOS-CONTAINING WASTES

Abstract: The invention relates to a method for neutralizing asbestos waste. According to the method, the waste is contacted with an acid capable of dissolving the asbestos, or with a salt thereof. According to the method, a hydrochloric acid solution is used as the acid, containing a suitable potassium salt in an amount of about 0.5 to 10 % based on the amount of the hydrochloric acid, in particular potassium sulphate, potassium chloride, potassium nitrate, potassium carbonate or potassium phosphate, and possibly a small amount of nitric acid and/or phosphoric acid. In order to enhance the dissolution of the asbestos, the waste is first wetted with water which may contain a surface activity reducing agent. The invention also relates to a method for disposing of the asbestos material in acetylene cylinders, whereby the acetylene cylinder is cut in two and the material is removed by hydrostatic pressure. Next, the wetted material is treated with a hydrochloric acid solution. The invention can also advantageously be applied to demolition waste from buildings.

Description: Method of decomposing asbestos-containing wastes The present invention relates to a method according to the preamble of claim 1 for disposing of and neutralizing asbestos-containing waste. According to such a method, asbestos-containing waste is contacted with an acid capable of dissolving the asbestos, or with a salt thereof. Asbestos has been found to cause serious pulmonary diseases all over the world. Today, the use of asbestos is forbidden everywhere and in almost all products, but the disposal of old products has given rise to considerable problems relating to occupational hygiene. This is because there is a great deal of asbestos in the thermal and electric insulation systems of buildings, in electrical appliances and in discarded storage cylinders for acetylene welding gas, which explains why asbestos has proved a complicated problem when old asbestos-containing constructions, machines, isolations and acetylene cylinders are taken down or dismantled. Solvay Umweltchemie GmbH has applied for a patent for a method for the disposal of asbestos, the method being based on dissolving the asbestos in acidic saline solutions containing hydrofluoric acid and/or fluorine (Published EP Application No. 0,559,051). The publication also discloses a method for emptying an acetylene cylinder of acetone and residual acetylene, whereby gases and fumes are sucked through a particle filter and a gas conditioner into the ambient air using a vacuum pump. Next, a hydrofluoric acid compound or derivative capable of dissolving asbestos and cement is introduced into the cylinder. After dissolution, the cylinder is emptied of dissolved material and acid suspension by pumping. The cylinder metal is recovered and recycled. An economically attractive system for the disposal ofthe asbestos in acetylene cylinders must understandably be functional and environmentally friendly, preferably such that the cylinders remain undamaged. However, the above-described solution provides environmentally detrimental fluorine-containing waste. According to the method, the cylinders remain undamaged but are not used as pressure vessels; instead, they are scrapped. Furthermore, it has proved difficult to scrape the bottles empty in the manner suggested in the prior art method. The present invention seeks to remove the drawbacks hampering the prior art and to provide a novel method for the disposal of asbestos-containing waste. It is well known within analytic chemistry that asbestos is soluble in hydrochloric acid and forms silicon dioxide crystals which are partly acicular or have the form of flakes but are harmless after dissolution. In our tests for the comparison of various inorganic acids we found that asbestos rapidly and completely dissolves in the hydrofluoric acid suggested in the above-cited solution. Dissolution in hydrochloric acid, on the contrary, takes more than twice as much time as dissolution in hydrofluoric acid, and even then, the dissolution is not complete. In the present context it has, however, surprisingly been found that the dissolution of asbestos in hydrochloric acid can be greatly accelerated by introducing potassium ions into the hydrochloric acid in the form of a potassium compound or salt. The present invention is based on the concept of dissolving the asbestos in hydrochloric acid, whereby a suitable potassium salt has been added to the hydrochloric acid in an amount of about 0.1 to about 20 %, preferably about 0.5 to about 10 % calculated on the basis of concentrated (100 %) hydrochloric acid. The amount of potassium in the solution varies according to the salt, but generally speaking, the molar ratio (M K M C1) of the potassium and the chlorine in the hydrochloric acid should be in the range 0.001 to 0.01, preferably about 0.002 to 0.05. More specifically, the invention is characterized by what is stated in the characterizing part of claim 1. The invention can be applied to, e.g. taking apart acetylene cylinders and neutralizing the asbestos/cement material in the cylinders. Thus, according to the invention, the treatment of acetylene cylinders containing asbestos comprises the following steps: - the cylinder is cut in two using a lathe or the like, such that the tool cuts through the metal casing only, - a dust-retaining, elastic sleeve is passed over the cylinder which is cut in two, - a catheter which fits inside the central cavity within the material in the cylinder is passed through the sleeve and the absorption mass contained in the cylinder is pushed out through the catheter and directly into the sleeve covering the cylinder by means of pressure fluid, and - the material removed from the bottle is brought to the above-described hydrochloric acid solution directly using the sleeve or via an intermediate storage step. The characterizing features of this alternative and other advantageous embodiments ofthe invention are described in the dependent claims 2 to 10. The hydrochloric acid (HCl) used for dissolving the asbestos is advantageously fairly concentrated; typically, the aqueous solution contains at least 10 % by weight of hydrochloric acid. Preferably, a hydrochloric acid of as high a concentration as possible is used, in particular a concentration of approximately 20 to 40 %. A potassium salt or compound is added into the hydrochloric acid at a suitable treatment stage. Inorganic potassium salts of advantage comprise potassium sulphate, potassium chloride, potassium nitrate, potassium carbonate and potassium phosphate. The potassium salt can be added to the hydrochloric acid prior to the outset ofthe treatment or during the treatment. As stated above, adding a potassium compound (that is, potassium ions) into the acid enhances the dissolution ofthe asbestos, but it has also been found that adding other mineral acids further accelerates the dissolution ofthe asbestos fibres. Such other mineral acids comprise, among others, phosphoric acid and nitric acid. They are (each) typically present in an amount of about 0.1 to 10 % by weight based on the amount of hydrochloric acid (calculated as 100 % hydrochloric acid). In addition to the above, it has surprisingly been found that the dissolution can be greatly enhanced by wetting the waste prior to the hydrochloric acid treatment. This is particularly true for the material in a gas cylinder which hardly dissolves at all in the acid unless the material is first wetted with water. If need be, soap admixtures or similar agents reducing surface activity can be added to the water for improved wetting. In the case of an asbestos sheet used in a building, wetting has no major effect, but even here, wetting with water accelerates the effect ofthe acid on the material. Thus, in both cases, it is of advantage that, once the material or waste has been removed or taken apart, it is kept wetted until the hydrochloric acid treatment is initiated. The dissolution of asbestos-containing waste is advantageously carried out at an elevated temperature of about 30 to 95 °C, preferably about 40 to about 80 °C, under stirring. The treatment time depends on the amount of asbestos but, generally speaking, a treatment of 1 min to 24 hrs, preferably about 10 min to 4 hrs, will suffice. The present method can be applied to the treatment of asbestos-containing waste from different sources, including, for instance, asbestos waste from thermal and electric insulation in buildings, electric devices and discarded gas cylinders. According to an advantageous embodiment, the method ofthe invention is applied expressly to emptying acetylene cylinders and to rendering the asbestos contained therein harmless. This type of asbestos material usually contains some cement which is readily soluble in hydrochloric acid. According to the invention, the gas cylinder is evacuated by means of underpressure, the valve is removed and the cylinder is cut in two in a lathe or a corresponding device. Next, a plastic sleeve or a coπesponding elastic obstruction fully blocking the advance of dust is pulled over the longer half of the cylinder. All acetylene cylinders are equipped with an 8 to 9 mm gas collector hole in the middle. A catheter pipe the size of said hole is inserted through the elastic dust obstruction, and the pressurized water is slowly allowed to reach the other end ofthe cylinder through the pipe. The water has a wetting and lubricating effect and it will pack the edge between the cylinder and the material, and the pressure will push the material straight into the elastic dust shield. At the same time, the cylinder walls are left moist such that no dust will rise into the ambient air during later phases either. The mass removed by the inventive method is left moist, this being of relevance for lates phases. Next, the cylinder which is wet inside is brushed slowly with a rotating brush using a small amount of additional water. The removed asbestos-containing mass in a bag is then taken to asbestos dissolution either directly or via intermediate storage. The asbestos is then dissolved in hydrochloric acid in the manner described above, whereby the temperature during the treatment is kept at a value not allowing the plastic or other material used to melt yet, such that said material is available for possible reuse for the same purpose. The invention can also be applied to the treatment of asbestos-containing waste from buildings. Thus, the taking down in buildings can be performed with water, as explained above for acetylene cylinders, but preferably, a high-pressure water jet is used which functions as a shearing and tearing medium. All dust is then moist and will settle easily. According to the method, dry dust is not generated at all. Detached asbestos-containing pieces can be removed from the site of dismantling by using either a dry suction machine or a wet suction machine to forward the pieces directly into an acid bath. The ventilation air at the building demolition site can be sucked through an acid washer before it is let out. The mediod according to the invention for taking down and treating asbestos waste from a building comprises using water or an aqueous solution as the medium for taking down and the detached waste can be brought to an acid treatment directly by suction. Even in this case the asbestos can be pre-wetted by means of the water used for the taking down, which greatly enhances its dissolution in hydrochloric acid. The invention provides considerable benefits. Thus, the asbestos can be fully and completely dissolved in the hydrochloric acid solution. The dissolution of the asbestos will neutralize the hydrochloric acid solution, and the neutralized solution which mainly consists of a solution of CaCl 2 and MgC can be used as anti-icing salt. The silicon dioxide fluff and fibres separated from the salt solution by filtering can advantageously be used for reinforcing ϋhe matrix of concrete. When neutral (pH 5 to 9), the salt solution can also be used for, e.g., emptying and washing acetylene cylinders more advantageously than clean additional water. When the method is applied to expressly the treatment ofthe asbestos mass in acetylene cylinders, the cylinder cut open in the above-explained manner can be forwarded to further use fit for use, and the remaining waste can also be exploited futher. The idea is that since the cylinders face scrapping in any case, it is of advantage to start by cutting the cylinder such that it will serve as a blank for a new product. Used gas cylinders can be utilized to obtain various structurally useful products, and it is not profitable to waste good material by scrapping it for melting in the first place. The use of hydrochloric acid and the cutting open ofthe cylinder before it is emptied and the mounting and use of a dust-proof sleeve as steps of one method make the solution according to the present invention clean and safe and also economically advantageous as regards the production of follow-up products. The corresponding benefits are gained in the treatment of waste from buildings in accordance with the invention. Below, the invention is examined in more detail in the light of a working example. The example refers to the annexed photographs, wherein Fig. 1 is a microscopic photograph of asbestos waste treated with hydrochloric acid at an early stage of dissolution, and Fig. 2 is a coπesponding photograph ofthe end result ofthe treatment. Example A 5 g sample was extracted from a gas cylinder having contained acetylene. The sample was comprised of asbestos fibres and cement. The sample was wetted with a small amount of water whereafter it was suspended into 55 ml of 33 % hydrochloric acid under stirring. The temperature was 60 °C. After a few minutes of stirring, the cement was completely dissolved. The asbestos fibres began to swell into a slimy thick mass which was partly covered by colloidal material. Next, a small amount (approximately 0.5 g) of potassium sulphate was added into the suspension, whereby the swelling ofthe fibres continued and the colloidal phase began to dissolve. In order to accelerate the dissolution, 3 ml of concentrated nitric acid was added. The colloidal phase disappeared and the fibres were bared again. As a result of continued stirring, the fibres began to break and became thinner (Fig. 1 ). After the addition of phosphoric acid (about 2 ml of concentrated acid) and 15 minutes of stirring, the fibres were completely dissolved. This is also clear from Fig. 2 which shows some silicon dioxide fluff.

Claims: Claims: 1. A method for neutralizing asbestos-containing waste, wherein the waste is contacted with an acid capable of dissolving the asbestos, or with a salt thereof, characterized by using as said acid hydrochloric acid containing a small amount of potassium ions. 2. The method according to claim 1 , wherein a hydrochloric acid solution is used containing a suitable potassium salt, in particular potassium sulphate, potassium chloride, potassium nitrate, potassium carbonate or potassium phosphate, in an amount of approximately 0.5 to 10 % based on the amount of hydrochloric acid. 3. The method according to claim 1 or 2, wherein the hydrochloric acid solution also comprises small amounts of other mineral acids, particularly nitric acid and/or phosphoric acid. 4. The mediod according to any one of claims 1 to 3, wherein d e waste is first wetted with water which may contain a surface activity reducing agent. 5. The method according to any one of uhe previous claims, wherein the hydrochloric acid treatment is carried out at an elevated temperature, preferably at about 30 to 95 °C, in particular at about 40 to 80 °C. 6. The method according to any one ofthe previous claims, wherein the asbestos- containing waste treated comprises the asbestos mass contained in acetylene cylinders. 7. The method according to claim 6, wherein the asbestos mass is separated from the acetylene cylinder by the steps of - cutting the cylinder in two, - fitting a dust-retaining elastic sleeve over the open end of the cylinder cut in two, - passing a tube through the sleeve, - leading water under pressure into the cylinder through the tube, - gathering the material detached from the cylinder into the elastic sleeve, and - subjecting the gathered material to a dissolution treatment using hydrochloric acid. 8. The meϋhod according to any one of claims 1 to 5, wherein the asbestos waste treated is obtained from a building or the like. 9. The method according to any one ofthe previous claims, wherein the solution obtained from the treatment with hydrochloric acid is neutralized and used as anti- icing salt. 10. The method according to any one ofthe previous claims, wherein silicon dioxide matter is separated by filtering from the solution obtained from the hydrochloric acid treatment and used as an admixture in concrete.

Inventors: AHONEN HEIKKI JUHANI, KARHUMAEKI MARKKU KALEVI, PUSA MARKKU PETE JUHANI, AHONEN, HEIKKI, JUHANI, KARHUMAEKI, MARKKU, KALEVI, PUSA, MARKKU, PETE, JUHANI
Applicants: AHONEN HEIKKI JUHANI, HJA ENG OY, KARHUMAEKI MARKKU KALEVI, PUSA MARKKU PETE JUHANI, AHONEN, HEIKKI, JUHANI, HJA-ENGINEERING OY, KARHUMAEKI, MARKKU, KALEVI, PUSA, MARKKU, PETE, JUHANI
Application year: 1997
Main classification: A62D3
IPC codes: A62D3, A62D101, B09B3, C04B14, C04B18