DE2318652A1 - Common destruction of metal hardening waste - by reacting cyanides and cyanates with nitrates and nitrites - Google Patents

Abstract

Pollution by waste from melts used in hardening, carburising and nitriding steel, and from heat-treatment melts contg. alkali nitrite/nitrate, is prevented by common destruction of (1) cyanides, cyanates and complex cyanides (I)and of (2) nitrates and nitrites (II). Powdery mixts contg (I) and (II) are reacted with one another, in molten or sinter sintered conditions, using a wt. ratio (II):(I)>2.1(>4), and reducing excess (II) by reaction with C or C-contg. substances in molten phase. Mixts of powdered salts are heated at least to formation of melt, partic. when C is added after reaction of (I) and (II), or powdered salts contg. (I) or (II) may be introduced into stirred melt of the other cpd gp. Reduction with C may be effected also during reaction of salt mixts. esp. at 50 degrees C above their melting temp.

Description

"Procedure for the joint destruction of # Cya; # iden / Oyanaten1 complexes Cyanides as well as nitrates and nitrites as waste materials in used hardening salts " The invention relates to a method for the joint destruction of cyanides and cyanates and complex cyanides on the one hand and nitrates, nitrites on the other hand, as described in the hardening technique in Alt salzen at all.

In the case of Stalil refinement, hardening, carburizing and nitriding are used Cyanide-containing sodium, potassium and balium chloride melts are used. For heat treatment Alkali nitrite / nitrate melts are used.

The former baths lose their effectiveness when they are consumed Cyanide; for regeneration, part of the weld pool is skimmed off and the bath cyanide added again. The skimmed off parts represent so-called cyanidic Used salt is, depending on the type of bath, up to approx. 8% cyanide and up to approx. 3% cyanate and traces of heavy metal cyanides, in the special case of a pure alkali cvanide cyanate bath contains approx. 19% cyanide and 24% cyanate and 20% carbate.

Nitrate-nitrite heat treatment baths are caused by the entrained alkali and alkaline earth chlorides which settle as sludge. This mud is separated off and contains, in addition to chlorides and those introduced by oxidation Cyanide formed carbonates approx. 50% nitrate-nitrite.

The methods practiced so far to destroy these toxic residues are difficult and time-consuming. Methods practiced are oxidation of the aqueous solution Cyanides and cyanates with hydrogen peroxide, hypochlorite or catalytic. oxidation with oxygen. A prerequisite for these procedures is usually sufficient great dilution, resulting in a large amount of wastewater. Another method is the alkali see Yerkochen of the cyanide or cyanate; the one with it The ammonia produced, however, represents an impermissible waste water pollution and must therefore separated and isolated by distillation. This procedure is thereby uneconomical.

The destruction of the nitrates-nitrites takes place mostly through joint Incineration with industrial and / or municipal waste. This creates nitrous gases, which are difficult to destroy due to their great dilution. Aqueous methods, e.g. oxidation of the toxic nitrite content to nitrate or decomposition of the nitrite with Amidosulfonic acid or joint reduction of the two substances with aluminum to ammonia, lead to wastewater pollution with nitrate or ammonia.

It has been found that the disadvantages of the method described of the prior art can avoid and a satisfactory destruction of the polluting ingredients of the two types of baths can get if you use them Powdered mixtures containing substance groups in the melted or sintered state reacting with each other, with at least 2.1, preferably over 4 parts by weight of nitrate / nitrite, based on 1 part by weight of the first group of substances, are used and the excess on the second group of substances by carbon or carbon-containing substance is reduced in the melting phase.

The method-a avoids that known from inorganic chemistry explosive reaction of mixtures of pure cyanides / cyanates with nitrates / itrites at elevated temperature.

The procedure also takes into account the fact that the for a stoichiometric reaction of the ingredients of the two types of bath is required Unrelated analytical and preparative effort is avoided. this happens by using an excess of nitrate / nitrite, its unreacted portion destroyed after / or during the reaction with carbon as a reducing agent will.

One embodiment of the method according to the invention provides that Mixtures of the powdered salts at least until the melt has formed to heat up. This variant is used in particular when the carbon is only added after the conversion between the two types of waste baths.

One can also use powdered salts, which are one of the two groups of substances contained in a stirred melt of the other group of substances. So that will achieved that the reaction only begins when a liquid phase is present, what in some cases by avoiding foam formation. Advantage is.

The reduction with carbon can be carried out after the salt mixtures have reacted carry out. But you can also reduce with carbon during the implementation of the salt mixtures, preferably at least 50 ° C. above their melting temperature lying temperature to achieve a sufficient to incorporate the carbon low viscosity, perform.

It is important that the carbon material is not too finely divided use to keep the reactivity of its surface low. In this way it is achieved that the oxidizing agent nitrate / nitrite all the cyanide / cyanate can convert and only the proportion in the absence of carbon material would remain is reduced. When using coke, one grain is sufficient on the order of 2 - 10 mm in diameter.

Variants of this mode of operation are that you have a powder Mixing of the three reactants in an inert alkali metal alkali metal chloride carbonate melt enters or highly concentrated cyanide-cyanate-containing salts in an inert alkali-earth alkali chloride-carbonate melt dissolves and by adding nitrate-nitrite-containing Converts used salts and carbon.

Another embodiment of the method provides that one salt mixtures reaction sintered in the presence of carbon at temperatures below their melting point and then to a preferably at least 500C above the melting temperature the Mixture temperature achieved.

In this case, the two types of used salt react at first at temperatures below the melting point of the mixture with oxidation of Cyån. 1 / cyanate. Thereafter is heated to a temperature above the melting point in the melt then the reduction of the remaining nitrate-nitrite excess.

In the process according to the invention mostly and appropriately, in moderation Used salts of the first group of substances are used, their sum of cyanide, cyanate and complex Cyanides not more than 20, preferably 10 to 15, in particular approx. 10 percent by weight amounts to. Waste salts with a content of salts of the first group in excess of 20% by weight are best made by mixing with inert salt or low-percentage waste salt rediluted.

In all of the above variants, the cyanides, cyanates, Nitrites and nitrates in an equivalent amount of carbonate.

The method according to the invention allows effective destruction for the first time highly toxic and environmentally harmful waste materials from hardening technology in equipment minimal space requirements and under particularly economical conditions. The at the salt reaction only produces small quantities of nitrous gases (per 1 t of salts mixture approx. 150 Nm3 exhaust gas with approx. 50 vol.% NQx) are highly concentrated and are accordingly easy to destroy. There is no wastewater pollution.

The following examples illustrate the present invention, without restricting them.

Example 1 A mixture consisting of 10 g of a 30% nitrate and 26% nitrite-containing Ilärterei old salt and 10 g of a 3.2% cyanide and 0.6 % Cyanate containing old salt was in the nickel Crucible over open Flame heated. At around 20,000 an exothermic reaction set in under gases Rapid heating to approx. 550 - 600 ° C. It was then heated to 65,000 and in portions 1.5 g of powdered coke was added. a. 10 minutes after the addition there was no more gassing to observe. The cooled melt was taken up in aqueous form and analyzed.

In addition to alkali-alkaline earth chlorides and carbonates, it only contains: 0.0009% ON 0.0014% CRO 0.0007% NO2 0.0006% N03 Example 2 10 g of a nitrate-nitrite-containing Used salt of the above composition was heated to 60,000 in the crucible. In the melt became a powdered oyanide-oyanate-containing waste salt according to the composition Example 1 charged, then heated to 67,000 and 1.5 g of powdered coke admitted.

About 8 minutes after the addition, no more gases could be observed.

In addition to chlorides and carbonates, the melt contained.

0.0012% CN 0.0010% NO 0.0009 ° / ° NO2, 0.0010% NO3 Example 3 In a 50 g melt of an old salt containing 20.0% nitrate and 15.6% nitrite, was at 70,000 a mixture of 100 g of a cyanide-cyanate-containing old salt of the Composition according to Example 1 and 6 g of granulated charcoal (approx. 4 mm particle diameter ) registered. After the end of the gassing, the melt contained, in addition to A. potassium, alkaline earth chlorides and carbonates: 0.0017% CN 0.0020% CNO 0.0003% NO2 0.0010% NO3 Example 4 10 g of an approx. 19.2% cyanide, 24 0% cyanate in addition to carbonate as alkali salts (sodium-potassium salt) containing used salt were with 70 g of a used salt with a composition ground and mixed according to example 1. For this purpose, 200 g of a nitrate-nitrite-containing Used salt with a composition as in Example 1 and 20 g of powdered coke given. This mixture was then sintered for 10 minutes in a muffle furnace at 2000C Maintained in the melt flow at 750 ° C. for 10 min.

In addition to alkali and alkaline earth metal chlorides and carbonates, the slag contained: 0.0012% CN 0.0020% CNO-0.0002% NO, 0.0009% NO, example 5 In a 5 kg melt Alkali-alkaline earth chlorides and carbonates became a mixture at 6300C 2.5 kg of a used salt containing 4.4% cyanide and 3.6% cyanate with a 10.45 % Nitrate and 24.6% nitrite containing old salt and 0.25 kg of coke under vigorous Stirring entered. After the end of the gassing, the melt contains alkali-alkaline earth chlorides in addition to and carbonates: 0.0019% CN 0.0100% CNO 0.0008% NO2 0.0004- to NO, Example 6 In a 5 kg melt of alkali and alkaline earth chlorides and carbonates were at 630 0C 1 kg of a highly concentrated old salt with 19.2% cyanide and 24% cyanate dissolved. Thereafter, 3 kg of a mixture of a salt became in 3 hours with 26% nitrite and 30.2% nitrate dosed with 0.25 kg of coke. The melt contains after the end of the gassing in addition to alkali and alkaline earth chlorides and carbonates: 0.0013% CN 0.0020% CNO 0.0007% NO2 0.0003% NO,

Claims (10)

Claims 1. Process for the joint destruction of cyanides, Cyanates and complex cyanides on the one hand and nitrates, nitrites on the other, as they occur in the hardening technology in waste salts, characterized in that powder mixtures containing these groups of substances in the melted or sintered state reacting with each other, where # at least 2.1, preferably over 4 parts by weight of nitrate / nitrite, based on 1 part by weight of the first group of substances, and the excess on the second group of substances by carbon or carbon-containing substance is reduced in the melting phase. 2. The method according to claim 1, characterized in that the Mixtures of the powdered salts are heated at least until the melt is formed. 3. The method according to claim 15, characterized in that one is powdery Salts that contain one of the two groups of substances in one melt the other. " Entries a substance group. 4. The method according to claims 1 to 3, characterized in that that one carries out the reduction with carbon after reaction of the salt mixtures. 5. The method according to claims 1 to 3, characterized in that that the reduction with carbon during the reaction of the salt mixtures, preferably at a temperature at least 500C above its melting point, performs. 6. The method according to claim 5, characterized in that one powdery mixture of the three reactants in an inert alkali-alkaline earth chloride -Carbonate melt enters. 7. The method according to claim 1, characterized in that one highly concentrated Cyanide-cyanate-containing salts in an inert alkali-earth alkali chloride-carbonate melt dissolves and converts salts and carbon by adding nitrate-nitrite-containing aluminum. 8. The method according to claims 1 to 3, characterized in that that one salt mixtures in the presence of carbon at temperatures below their Melting point reaction asintert and then to a preferably at least 50 0C The temperature is above the melting temperature of the mixture. 9. The method according to claims 1 to 8, characterized in ## that the sum of cyanide, cyanate and complex cyanide in the old salts of the first Substance group maximum 20, preferably 10 to 15, in particular approx. 10 percent by weight amounts to. 10. The method according to claims 1 to ~), characterized in that that one aluminum salts with a 20 wt.% Exceeding content of salts of the first Group of substances diluted back by blending with inert salt or low-percentage waste salt.