Degussa Aktiengesellschaft

Deutsche Gold- Und Silber-scheideanstalt Vormals Roessler

Degussa Gmbh

Deutsch Gold-und Silber-scheideanstalt

Degussa Aktiengesselschaft

Joachim Fischer

Helmut Knorre

Hubert Wolf

Manfred Diehl

Gerhard Pohl

Andrew Griffiths

Klaus Stutzel

Juergen Loroesch

Klaus Stuetzel

Friedhelm Brandner

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 described for leaching gold and/or silver from ores or ore concentrates using an aqueous alkaline cyanide solution with addition of hydrogen peroxide. The addition of the aqueous H.sub.2 O.sub.2 solution is regulated and controlled through the concentration of the oxygen dissolved in the leaching solution, the leaching solution containing from 2 to 20 mg O.sub.2 and preferably from 7 to 13 mg O.sub.2 per liter. 0.5 to 5% by weight H.sub.2 O.sub.2 solutions are preferably added. The process is applicable both to leaching by agitation and to heap leaching, the addition of H.sub.2 O.sub.2 being regulated and controlled through measurement of the O.sub.2 concentration in the leaching solution and can also involve measurement in a measuring stream. Despite low consumptions of H.sub.2 O.sub.2 and NaCN, the gold yield is even increased in some cases and the leaching time shortened.

Process for the leaching of gold and silver with cyanidic leaching

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

In purifying gas wash waters containing cyanide with formaldehyde, the exact dosing of formaldehyde presents a problem, especially with strongly fluctuating cyanide contents. By continuous potentiometric measurement in a side stream which is regulated to a pH of 7 to 10, while the pH of the main stream remains unchanged, the formaldehyde can be adjusted safely to any cyanide content.

Process for the purification of industrial gases or waste gases

There is provided a continuous process for the lowering of the content of toxic materials in waste waters which also contain other oxidizable materials by quickly and continuously ascertaining the requirement of hydrogen peroxide, namely by potentiometric determination of the oxidizing agent requirement in a branched-off side-stream using a strong oxidizing agent, such as peroxymonosulfate, peroxydisulfate, permanganate, hypochlorite or ozone, which acts more quickly than hydrogen peroxide under comparable conditions.

Process for the treatment of continuous waste water streams having

In the detoxification of waste waters containing nitrite ions by means of hydrogen peroxide the addition of hydrogen peroxide is automatically controllable by adding the hydrogen peroxide continuously or in portions with continuous measurement of the pH and stopping the addition when no further reduction of the pH is caused by it. By control of the hydrogen peroxide addition through the change of the pH it is guaranteed that sufficient hydrogen peroxide is added to reach a complete detoxification of the waste water while on the other hand there is not wasted hydrogen peroxide unnecessarily.

Process for automatically controlling the detoxification of waste waters

Caking of industrial alkali metal chlorides and mixtures containing them in storage is prevented and a flowable product is obtained by adding a hydrophilic and/or a hydrophobic material, in combination with a complex iron cyanide, on a hydroxyl group containing carrier to produce a permanent moisture content of at least 0.01 weight percent of water on the salt.

Process for preventing caking and obtaining flowability of alkali

Preventing caking and obtaining flowability of alkali chlorides and salt

Silver coatings in photographic tanks are dissolved with an aqueous solution of an alkali mono or di peroxysulfate, an alkali bisulfate and thiourea.

Method of dissolving a silver coating in a photo tank

There is prepared a powdery anticaking agent for inorganic salts based on (A) an iron cyanide complex, (B) a water insoluble inorganic, inert, finely divided hydroxyl group containing material or a material able to form this in the production of the anticaking agent, (C) hydrophobizing and/or (D) hydrophilizing materials in which (A), (C) and/or (D) are employed on component (B) as a carrier together with (E) water in an amount of 20 to 50 weight percent, preferable 35 to 45 weight percent. The composition is prepared by intensively mixing the carrier (B) in the corresponding ratio in the dry state with the active materials at room temperature and then adding to this mixture so much water that the active components go into solution and as such are absorbed on the carrier and regulating the pH to 7 to 9, preferably 7 to 8.

Anticaking agent for inorganic salts

Waste water containing cyanides, cyanohydrins and/or organic nitriles are detoxified by adding a peroxide compound in the presence of iodide ion or free iodine, in a given case in the presence of silver ions.

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Rodenbach, Germany

Joachim Fischer