Method for decontamination of explosives production process waste water

Technical Field

The invention deals with a method of disposal of azides and selected organic substances contained in wastewater from the production of explosives, blasting explosives and raw materials used for their production.

Background Art

Industrial production of explosives is often based on the use of a precipitating reaction, which mainly holds good for synthesis of explosives on the basis of lead salts. Precipitating reactions are used e.g. within the production of lead azide, lead trinitroresorcinate and lead picraminate. Preparation of explosives by precipitation always involves production of wastewater. This wastewater typically contains residues of precipitated explosives (e.g. from rinsing of equipment, filtration cloths) and a dissolved fraction of explosives corresponding to the solubility of the corresponding salt. The wastewater further contains surplus reagents, salt produced by the precipitation reaction, usually nitrate based. Other components of the wastewater are rinsing and cleaning solutions.

The first step of disposal of concerned water is typically decomposition of the solid fractions of the explosive. Lead azide is usually decomposed with acids with the formation of azoimide and the corresponding lead salt, very often nitrate. Salts based of trinitroresorcinate or pieraminate are usually converted with sodium carbonate to less soluble lead carbonate and the corresponding salt of the organic substance.

The second step is disposal, i.e. decomposition of the anion and the third step is the removal of the lead cation from the wastewater by its precipitation in the form of an insoluble salt. The resulting precipitate is removed

mechanically from the wastewater, e.g. by filtration or sedimentation. This invention deals with the disposal, i.e. decomposition of the anion and therefore the text below concerns the current state of the art of solving this issue. For the decomposition of azides patent no. CS 245689 suggests a solution of sodium nitrite. In this step the toxic azoimide is converted to the slightly harmful azoxide. A disadvantage of this solution is the formation of nitrogen dioxide due to the reaction of sodium nitrite with the present nitric acid. Another disadvantage is that this method can be used for reliable disposal of azoimide, but it cannot be used to decompose the other above mentioned substances contained in wastewater.

Thus, other methods must be used for disposal of wastewater from the production of lead trinitroresorcinate and picraminate. One of them is described in patent no. CS 245688 and it consists of adsorption of anions on active carbon, which precedes conversion of lead salts with the use of sodium carbonate. This method enables separation of the concerned anions, but it does not lead to their chemical decomposition.

It can be achieved e.g. by oxidation of the organic component of the explosive in an acidic solution with the use of a hypochlorite solution. A disadvantage of this method is that during chlorination of the aromatic core substituted with nitro-grόups toxic chloropicrin is produced as tertiary waste. Another disadvantage & strong corrosive stress of the equipment with chlorine, which is manifested through increased costs of its purchasing and operation. Therefore, disposal of the above mentioned substance with UV radiation in the presence of hydrogen peroxide described in the article of Alnaizy R., Akgerman A.: Oxidative treatment of high explosives contaminated wastewater, Water Research, 33, 9, 2021-2030 (1999) appears to be more suitable from the environmental point of view. In this case intensively stirred and heated mixture of wastewater with hydrogen peroxide is exposed to the

effect of UV light wijth the predominant wavelength of 254 nm. A disadvantage of this method consists in relatively high losses of hydrogen peroxide and the resulting, high consumption.

An alternative solution is the use of potassium hyperoxide, which is described in the US patent no. US 6.118.039 (2000). With regard to strong oxidation effects of potassium hyperoxide the concerned substances are decomposed in a few minutes;

The US patent no. 5.558.783 (1996) called "Supercritical oxidation reactor" describes the possibility of destruction of explosives and rocket fuel by their oxidation in water in the supercritical condition, i.e. at a high temperature and pressure by spraying of gaseous oxygen. This method is very demanding for the equipment, which is disadvantageous mainly in case of processing of higher volumes of wastewater.

Disclosure of Invention

The principle of the invention is that wastewater containing the concerned substances is acidified to the pH value 3 and less, beneficially to pH 1 and less in the first step. The solution can be suitably acidified with addition of diluted nitric acid. In the second step the component forming the anion of the explosive, usually an azide, trinitroresorcinate or picraminate is decomposed by addition of a solution containing permanganate ions.

Compared to the existing methods of disposal of wastewater from the production of explosives this method shows several advantages while the combination of these advantages may be significant in a number of cases.

The first advantage is its versatility, i.e. the possibility to use the same method and the same reagents for the disposal of liquid waste from the production of all the above mentioned explosives. This fact allows e.g. simultaneous disposal of waste from the production of different explosives or the use of the same equipment for gradual disposal of wastewater from the

production of different explosives. In the case of separate disposal of different explosives it provides the advantage of the possibility of common preparation or dosing of the used reagents. The versatility certainly has a positive impact on enhancing work safety during wastewater disposal. Another advantage is the fact that the oxidation reaction used for the disposal is relatively quick, it takes several minutes, and enables a high degree of oxidation of the disposed components of the wastewater, which is very important from the environmental point of view. The balanced status of the reaction is substantially shifted towards the products due to the redox potential value of the used reagent while the products of the reduction of permanganate are slightly toxic or not toxic at all. These products can be easily removed from wastewater in the form of hardly soluble substances, mostly as oxides, hydrated oxides and hydroxides. If they are removed together with lead ions, they act as flocculants and improve capturing of the lead precipitate which is generally the hydroxide, hydrated oxide, carbonate or sulphide, namely during the filtration of the treated wastewater.

Another advantage is simple and easy monitoring of the course of disposal. A suitable instrumental technique is potentiometric indication, i.e. observing the moment of a significant increase of the redox potential. The course of the reaction can also be checked visually as the addition of permanganate dyes the treated water violet. In the course of the disposal - oxidation of the substances in the wastewater the colour is quickly lost as the violet colour disappears and at the same time the intensity of wastewater coloration with the disposed substances is reduced. At the end of the disposal the wastewater is virtually colourless. After addition of a super- stechiometric quantity of permanganate the wastewater becomes brown due to the produced manganese dioxide.

The samples described below illustrate, but do not limit the scope of the subject matter of the invention in any way. Experts involved in this area will find advantages of the present solution obvious and they would certainly find

other possibilities of embodiments of the invention within the specified patent claims.

Description of the Preferred Embodiment

Sample 1

Wastewater from the production of lead azide was drawn. This wastewater contained solid fractions of lead azide and a solution of lead azide corresponding to the solubility of this salt. Besides the above mentioned monitored and disposed components the wastewater contained sodium nitrate generated during, the synthesis of the explosive, unreacted super- stechiometric fraction of dissolved lead nitrate, nitric acid used for rinsing of the equipment and possible products of its reaction with the above mentioned substances.

In the first step 10% solution of nitric acid was added to this wastewater during continuous stirring until pH 1 value was achieved. In the second step 2% solution of permanganate was added to this acidified wastewater. At the beginning approx. 60% of the volume of the permanganate solution that is theoretically necessary for complete oxidation of all the present azide ions was added all at once while the rest was dosed gradually.

The end of oxidation of azide ions and consequently the end of addition of permanganate was indicated with the used of the potentiometric method on the basis of an increase of the redox potential value. The end of disposal, i.e. oxidation of azide ions is also perceivable visually since the surplus of permanganate reacts with the resulting manganese salt. The product of their reaction is the insoluble manganese dioxide, which gives the originally colourless solution brown colour. Completeness of disposal of azide ions in the wastewater was further verified and confirmed photometrically on the basis of the creation of a complex with a ferrous salt.

Sample 2

Wastewater from the production of lead trinitroresorcinate was drawn. This wastewater contained solid fractions of lead trinitroresorcinate, a solution of lead trinitroresorcinate corresponding to the solubility of this salt and unreacted super-stechiometric fraction of dissolved magnesium trinitroresorcinate. Besides the above mentioned monitored and treated components the wastewater further contained magnesium nitrate produced during the synthesis of the explosive, a solution of acetic acid, a solution of sodium carbonate used for rinsing of the equipment and possible products of reaction of these reagents with the above mentioned substances.

This wastewater was treated in the same way as in sample 1. The end of oxidation of organic substances in the wastewater and thus the end of addition of permanganate was indicated with the potentiometric method, on the basis of an increase of the redox potential value.

The course of gradual disposal of the trinitroresorcinate can also be checked visually on the basis of dropping intensity of yellow coloration of the solution until its discoloration. Surplus of permanganate in the solution was visually manifested in the same way as in sample 1. Completeness of disposal of trinitroresorcinate was evaluated on the basis of consumption of permanganate until the point of equivalence and further verified with an analysis of an extract from the treated wastewater with the use of the mass spectroscopy method.

Sample 3

Wastewater from the production of lead picraminate was drawn. This wastewater contained solid fractions of lead picraminate, a solution of lead picraminate corresponding to the solubility of this salt unreacted super- stechiometric fraction of dissolved lead nitrate. Besides the above mentioned

monitored and treated components the wastewater further contained sodium nitrate produced during the synthesis of the explosive a solution of sodium carbonate used for rinsing of the equipment and possible products of reaction of these reagents with the above mentioned substances. This wastewater was treated in the same way as in samples 1 and 2. The end of oxidation of organic substances in the wastewater, i.e. the end of addition of the permanganate solution was indicated with the potentiometric method, on the basis of an increase of the redox potential.

The course of gradual disposal of the picraminate can be monitored similarly to the above mentioned samples, just the original colour of the solution was reddish brown.

Completeness of disposal of the picraminate was evaluated on the basis of the consumption of permanganate to the point of equivalence and it was further verified with an analysis of an extract from the treated wastewater with the use of the mass spectrometry method.

Industrial Applicability

The method of disposal of wastewater based on the invention can be used for disposal of wastewater from the production of explosives on the basis of lead azide, lead trinitroresdrcinate and lead picraminate and the production of raw materials necessary for the synthesis of the above mentioned explosives. It can be also used for disposal of the above mentioned groups of substances in wastewater from other kinds of production.