Degussa Aktiengesellschaft

Degussa Aktiengesselschaft

Hubert Wolf

Joachim Fischer

Manfred Diehl

Edgar Bilger

Friedhelm Brandner

Klaus Stuetzel

A method for controlling the detoxification of aqueous solutions containing cyanides and/or cyano complexes, in particular zinc cyano complexes, with the use of a source for formaldehyde for glycolnitrile formation and a source for hydrogen peroxide for perhydrolysis of the glycolnitrile is disclosed. During the addition of the source for formaldehyde at a pH value in the range from 8.5 to 12 the pH value is kept constant by addition of an acid. The addition of the source for formaldehyde is discontinued if the pH value no longer increases.

Method for controlling the detoxification of cyanidic waste waters

Reduction of the nitrite content of aqueous solutions by treatment with hydrogen peroxide in the acidic pH range can be controlled by measurement of the redox potential. Contrary to the teaching of the prior art, addition of the hydrogen peroxide in the process according to the invention is terminated not at the highest redox potential, but only after lowering of the potential to a value of 650.+-.10 mV. In this way, nitrite contents below 1 mg/l can be obtained even when the solutions additionally contain fluctuating amounts of various compounds oxidizable by H.sub.2 O.sub.2.

Process for automatically controllable reduction of the nitrite content

A process is disclosed for the detoxication of aqueous solutions which contain cyanohydrins, in particular glycol nitrile, and/or nitriles and in addition contain decomposition catalyst for peroxide compounds, in particular manganese compounds, by perhydrolysis of the cyano compounds at temperatures of from 5.degree. to 80.degree. C. and pH values of from 8 to 12 by means of one or more peroxide compounds which are alkali metal percarbonates and perborates of alkali metals and alkaline earth metals and alkaline earth metal peroxides. The peroxide compounds are added as such to the solution to be detoxified or formed in situ in the solution to be detoxified. Sodium percarbonate is preferably used.

Process for the detoxification of aqueous solutions containing

A process is disclosed for the separation of hydrogen cyanide from gases and waste gases by a throughflow or circulation scrubbing, in which formaldehyde is added at a controlled rate to the aqueous scrubbing liquid to form glycol nitrile. This addition is controlled by measuring the HCN tension in a measuring stream which has been branched off and which is first treated with hydrogen peroxide so that free H.sub.2 O.sub.2 is still detectable after 1 to 100 seconds and the pH is adjusted to a constant value before measurement of the HCN tension is carried out. The process prevents overdosing with formaldehyde which could not always be prevented in previously known processes in which the addition of formaldehyde was regulated by measuring the cyanide specific redox potential.

Process for the separation of hydrogen cyanide from gases and waste gases

The content of halo-organic pollutants in water is lowered to residual AOX values below 1 mg/l, preferably below 0.1 mg/l by adjusting the Fe.sup.2+ comtent of the water to 20 to 1000 mg/l, adding a precipitated or pyrogenic silicic acid, converting 20 to 1000 mg of the Fe.sup.2+ into Fe.sup.3+ by adding in an oxidation agent, preferably hydrogen peroxide, and separating the iron (III) hydroxy complexes formed and the silicic acid, which contain the halo-organic pollutants in an adsorbed state, at pH 5-10. The method can be controlled in a simple manner as regards the addition of Fe.sup.2+ and oxidation agent via the Fe.sup.2+ /Fe.sup.3+ redox potential.

Method of lowering the AOX content in water

According to the invention, cyanide concentrations of approximately 0.001 to 5 mg cyanide/1 are colorimetrically determined in a continuous manner by means of the known cyanidepicric acid color reaction. The solution containing free cyanide and/or cyanide releasable from cyanocomplexes is converted in a system enclosed in a gas-tight manner in the presence of chelate complexing agents, picric acid and alkaline buffer systems in 1-60 minutes at 50.degree.-120.degree. C. to the color complex and the absorbency is measured spectrophotometrically. The method avoids the extraction step which was previously necessary under 0.2 mg CN/1, avoids errors due to HCN gas evolution losses, is easy to manage, not prone to trouble and suitable for the continuous monitoring of waste-water streams or for controlling cyanide detoxification methods.

Growing community of inventors

Hammersbach, Germany

Hubert Wolf