GB1576067A

GB1576067A - Method of and apparatus for de-toxifying nitrite and/or cyynide containing aqueous solutions

Info

Publication number: GB1576067A
Application number: GB1211177A
Authority: GB
Original assignee: UTZINGER VERFAHRENSTECH
Current assignee: UTZINGER VERFAHRENSTECH
Priority date: 1976-03-24
Filing date: 1977-03-22
Publication date: 1980-10-01
Also published as: FR2345397B3; CH598142A5; ATA150377A; AT353194B; DE2709722A1; FR2345397A1

Description

(54) METHOD OF AND APPARATUS FOR DE-TOXIFYING NITRITE AND/OR CYANIDE CONTAINING AQUEOUS SOLUTIONS (71) We, VERFAHRENSTECHNISCHES BUERO VALENTIN UTZINER A.G., a Swiss Body Corporate of Kolliken, Switzerland, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention concerns a method for de-toxifying nitrite- and/or cyanidecontaining aqueous solutions, especially waste water, and in particular waste water from metal-hardening workships which, in the hardening of small parts or with the application of modern methods of rinsing adopted so as to use as little rinsing water as possible, yield waste water in which toxic compounds are increasingly concentrated.

Such waste water may contain more than 20 grams per litre of nitrite radical and up to a few grams per litre of cyanide radical.

Waste waters of such high concentrations can be de-toxified by conventional chemical methods only by an enormous expenditure of chemicals and additionally in accordance with the formerly known methods the nitrite is usually oxidised to nitrate, which burdens the clarifying plant almost as much as nitrite. In addition, attempts are already being made to limit the amount of nitrate, so that in the long view methods of nitrite oxidation can no longer be employed. The individual chemical methods of nitrite-detoxification without the formation of nitrate that are already known (using amino sulphamic acid) cannot on economic grounds be employed for high concentrations or large quantities. Nitrite can also be reduced to nitrogen by bio]ogical means, but this is possible, however, only with waste waters that also contain organic impurities.

According to the present invention there is provided a method for the detoxification of a nitrite- and/or cyanide-containing aqueous solution, wherein the pH value of the solution is adjusted so that the nitrous acid and/or hydrogen cyanide is released, these compounds are driven off and the nitrogen oxides resulting upon contact of the nitrous acid with the oxygen of the air and/or the hydrogen cyanide are reduced or oxidised respectively in a flame.

Less concentrated waste waters can first of all be concentrated by known methods, e.g. reverse osmosis or evaporation, and the concentrate then detoxified by the method of the invention. Likewise very dilute waste water mayi be deionized by an ion exchange method and the eluant (regenerating liquid) de-toxified in accordance with the method of the invention.

The fact that the method is especially suitable for concentrated solutions makes it also appear suitable for the neutralisaflon of solid hardening,-plant wastes (used salt melts) when these are previously dissolved in water.

To carry out the method the waste water can be acidified in an evacuable container and de-gassed by the application of vacuum, that is, by reducing the ambient pressure above the solution. The escaping gases are preferably led to an oil or gas burner, so that the nitrogen oxides are reduced to nitrogen and the hydrogen cyanide is burnt to carbon dioxide, water and nitrogen: A burner with recirculation of the exhaust gases is advantageously employed.

The rate of extraction of the gases is as a rule dependent upon the pH value, upon pressure, upon the temperature and upon the applied kinetic energy. It is therefore advantageous to provide the evacuable container with a stirring mechanism or to circulate the contents by means of a pump and possibly spray nozzles in the evacuated container. The de-gassing temperature should preferably be held between 10 and 400C, and the pH value should in general be below 5, preferably about 2. To acidify the solutions, which as a rule exhibit a pH value of about 9, any acids whatever may be used, e.g. hydrochloric acid or sulphuric acid.

In accordance with this method the nitrite content can be reduced extremely efficiently to less than 1 gram per litre and the cyanide content to less than 1 milligram per litre.

The major portion of the toxic compounds are thus convcrted into completely non-toxic gases.

Finally, such a preliminary detoxification may be advantageously followed by a subsequent detoxification by known methods, so that low amounts of nitrate result at small cost in chemicals.

WHAT WE CLAIM IS: 1. A method for the detoxification of a nitrite and/or cyanide-containing aqueous solution, wherein the pH value of the solution is adjusted so that the nitrogen oxides and/or hydrogen cyanide are released, these compounds are driven off by reducing the ambient pressure above the solution and the nitrogen oxides and/or the hydrogen cyanide are reduced or oxidised respectively in a. flame.

2. A method in accordance with claim 1 wherein a dilute solution to be detoxified is concentrated by reverse osmosis or evaporation.

3. A method in accordance with claim 1 or 2 wherein the gases are driven off by circulating and spraying the solution under said reduced pressure.

4. A method in accordance with any of claims 1 to 3 wherein the temperature of the solution is held at a temperature in the range of 100 to 400C.

5. A method in accordance with any of claims 1 to 4 wherein the pH value of the solution is brought to a value not exceeding 5..

6. A method in accordance with claim 5 wherein the pH value of the solution is approximately 2.

7. A method in accordance with any of claims 1 to 6 when applied to the detoxification of waste water.

8. A method in accordance with any of claims 1 to 6 when applied to the detoxification of hardening-plant waste water.

9. A method in accordance with any of claims 1 to 6 when applied to the detoxification of ion exchange regenerating liquid resulting from the deionization of a dilute toxic solution.

10. A method in accordance with any of claims 1 to 6 when applied to the detoxification of used hardening compounds dissolved in water.

11. Detoxifying apparatus when used for carrying out the method in accordance with any of claims 1 to 10 and including an evacuable container and means whereby gases withdrawn from the container are passed to a burner.

12. Apparatus in accordance with claim 10 wherein said burner is an oil or gas burner.

13. Apparatus in accordance with claim 10 wherein said burner is arranged to recirculate the combustion gases.

14. Apparatus in accordance with claim 10 wherein a stirring mechanism is provided in the evacuable container.

15. Apparatus in accordance with claim 10 wherein a circulating pump is provided in the evacuable container.

16. Apparatus in accordance with claim 15 wherein liquid discharged by said pump is led to spray nozzles.

17. A method for the detoxification of an aqueous solution containing nitrite and/ or cyanide, in accordance with claim 1 and substantially as hereinbefore described.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. The major portion of the toxic compounds are thus convcrted into completely non-toxic gases. Finally, such a preliminary detoxification may be advantageously followed by a subsequent detoxification by known methods, so that low amounts of nitrate result at small cost in chemicals. WHAT WE CLAIM IS:

1. A method for the detoxification of a nitrite and/or cyanide-containing aqueous solution, wherein the pH value of the solution is adjusted so that the nitrogen oxides and/or hydrogen cyanide are released, these compounds are driven off by reducing the ambient pressure above the solution and the nitrogen oxides and/or the hydrogen cyanide are reduced or oxidised respectively in a. flame.