DE2318652C3 - Process for the joint destruction of cyanides / cyanates, complex cyanides as well as nitrates and nitrites as waste materials in used hardening salts - Google Patents

Description

the destruction of the environmentally harmful ingredients in both types of baths is possible a process for the joint destruction of cyanides, cyanates and complex cyanides on the one hand and nitrates, nitrites on the other hand, as they occur in hardening technology in waste salts Oxidation of the cyanide / cyanate by an excess of nitrite / nitrate and reduction of the excess of nitrate / nitrite by carbonaceous substances, which is characterized in that pulverulent mixtures containing these groups of substances in the melted or sintered state with one another implemented, with at least 2.1, preferably 4 parts by weight of nitrate / nitrite, based on 1 part by weight of the first group of substances, and a Excess of the second group of substances is reduced in the melt phase.

The process avoids those from the inorganic Chemistry known explosive reaction of mixtures of pure cyanides / cyanates with nitrates / Nitrites 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 required uneconomical analytical and preparative effort is avoided. This is done by employing an excess Nitrate / nitrite, whose unreacted portion after or during the reaction with carbon as Reducing agent is destroyed.

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

Powdered salts containing one of the two groups of substances can also be introduced into a stirred melt of the other group of substances. This ensures that the reaction does not start until a liquid phase is present, which in some cases is advantageous because it avoids foam formation. The reduction with carbon can be carried out after the salt mixtures have reacted. However, the reduction with carbon can also be carried out during the reaction of the salt mixtures, preferably at a ^{temperature which is at least 50 °} C. above their melting temperature in order to achieve a viscosity which is low enough to incorporate the carbon. It is important not to use the carbon material in too finely divided form in order to keep the reactivity of its surface low. In this way it is achieved that the oxidizing agent nitrate / nitrite can convert all of the cyanide / cyanate and only the proportion that would remain in the absence of carbon material is reduced. When using coke, a grain size of the order of 2 to 10 mm in diameter is sufficient.

Variants of this procedure consist in that one mixes the three reactants in powder form enters an inert alkali-alkaline earth chloride-carbonate melt or contains highly concentrated cyanide cyanate Salts in an inert: alkali-alkaline-earth-chloride-carbonate melt dissolve una by entering of nitrate-nitrite-containing old salts and carbon.

Another embodiment of the process provides that one salt mixtures in the presence of Carbon is reaction sintered at temperatures below its melting point and then preferably to one heated at least 50 ° C above the melting point of the mixture temperature.

In this case, the two types of old salt react at first at temperatures below the melting point the mixture with oxidation of cyanide / cyanate. Thereafter, a temperature above the Melting point heated; The remaining nitrate-nitrite excess is then reduced in the melt.

In the process according to the invention, used salts of the first group of substances are mostly and expediently used are used, the sum of cyanide, cyanate and complex cyanides a maximum of 20, preferably 10 to 15, in particular about 10 percent by weight. Used salts with a weight percent exceeding 20 Salt content of the first material limit is best determined by blending with inert salt or low-percentage Used salt rediluted.

In all of the above variants, the cyanides, cyanates, nitrites and nitrates in equivalent amount of carbonate. The method according to the invention allows effective destruction for the first time

»5 highly toxic and environmentally harmful waste materials from hardening technology in apparatus that require little space and under particularly economical conditions. The nitrous gases that are only produced in small quantities from the salt reaction (about 150 Nm ³ exhaust gas with about 50 percent by volume of NO _x per 1 t of salt mixture) are highly concentrated and can therefore be easily destroyed. There is no wastewater pollution.

The following examples illustrate the present invention without restricting it.

example 1

10 g of a nitrate-nitrite-containing Altsalzes with a content of 30 weight percent and 26 weight percent nitrate nitrite was heated in the crucible to 600 ⁰ C. In the melt a powdered cyanidcyanathaltiges used salt with a content of 3.2 percent by weight of cyanide and 0.6 weight percent cyanate was charged, then heated to 670 ⁰ C and 1.5 g of powdered coke added.
About 8 minutes after the addition had taken place, no more gassing could be observed. In addition to chlorides and carbonates, the melt contained:

0.0012% CN-0.0010% CNO-0.0009% NO ₂
0.0010% NO ₃ ".

Example 2

To a 50 g of a melt Altsalzes containing 20.0 weight percent and 15.6 weight percent nitrate nitrite was at 700 ⁰ C a mixture of 100 g of a cyanide-cyanate Altsalzes with a content of 3.2 percent by weight of cyanide and 0.6 Percent by weight of cyanate and 6 g of granulated charcoal (about 4 mm particle diameter) entered. After the

Gasens, the melt contained alkali-alkaline earth chlorides and carbonates:

0.0017% CN-0.0020% CNO-0.0003% NO ₂ -0.0010% NO ₃ -.

Example 3

10 g of a used salt containing about 19.2 percent by weight cyanide, 24 percent by weight cyanate in addition to carbonate as alkali metal salts (sodium-potassium salt) were ground and mixed with 70 g of a used salt containing 3.2 percent by weight cyanide and 0.6 percent by weight cyanate. 200 g of a nitrate-nitrite-containing old salt with a content of 30 percent by weight of nitrate and 26 percent by weight of nitrite and 20 g of pulverized coke were added. This mixture was sintered in a muffle furnace at 200 ^° C. for 10 minutes, then kept in the melt flow ^{at 750 ° C. for 10 minutes.}

In addition to alkali and alkaline earth metal chlorides and carbonates, the slag contained:

0.0012% CN-0.0020% CNO-0.0002% NO ₂ -0.0009% NO ₃ ".

Example 4

In a 5-kg-melt of alkali-alkaline earth carbonates and was at 630 ⁰ C a mixture of 2.5 kg of a 4.4 weight percent and 3.6 weight percent of cyanide-containing cyanate Altsalzes with a 10.45 percent by weight nitrate and 24, 6 percent by weight of nitrite-containing old salt and 0.25 kg of coke entered with vigorous stirring. After the end of the gassing, the melt contains alkali-alkaline earth chlorides and carbonates as well as:

0.0019% CN-0.0100% CNO-0.0008% NO ₂ "
0.0004% NO ₃ ".

Example 5

In a 5 kg melt of alkali and alkaline earth ^{chlorides and carbonates were at 630 0} C 1 kg of a highly concentrated old salt with 19.2 weight

^ao percent cyanide and 24 percent by weight cyanate dissolved. Then 3 kg of a mixture of a salt with 26 percent by weight of nitrite and 30.2 percent by weight of nitrate with 0.25 kg of coke were dosed in 3 hours. After the end of the gassing, the melt contains alkali and alkaline earth chlorides and carbonates:

0.0013% CN-0.0020% CNO-0.0007% NO ₂ -0.0003% NO ₃ -.

Claims (10)

The invention relates to a method for common claims: seed destruction of cyanides, cyanates and complex cyanides on the one hand and nitrates, nitrites 1. Process for joint destruction on the other hand, as used in hardening technology in waste salts of cyanides, cyanates and complex cyan-5. iden on the one hand and nitrates, nitrites on the other hand- In steel finishing, hardening, car- on the one hand, as they are in hardening technology in waste salts and nitriding, cyanide-containing sodium, ca- incurred by oxidation of the cyanide / cyanate üum- and bariumchloiidschmelzen used. To the due to an excess of nitrite / nitrate and re-heat treatment, alkali metal nitrite-nitrate melts Reduction of the excess of nitrate / nitrite by ™ »n used. Carbon-containing substances, the first-named baths as a result, lose their effectiveness indicates that one of these substance groups by consumption of the cyanide; for regeneration containing powdery mixtures skimmed off in one part of the molten bath and the bath Melted or sintered state reacted with each other, cyanide added again. The skimmed tea wherein at least 2.1, preferably 4 weight 15 ^constitutes a so-called n cyanide used salt which, depending parts nitrate / nitrite, based on 1 part by weight of the bath type, up to about 8% cyanide and up to about the former group of substances, and a ³ % cyanate and traces of SchwermetaUcyaniden, im Excess of the second group of substances in the special case of a pure alkali-cyanide-cyanate bath Melting phase is reduced. about 19% cyanide and 24% cyanate and 20% carbon 2. The method according to claim 1, characterized in that it contains ^{ao na} *>. draws that the mixtures of powder nitrate-nitrite heat treatment baths are f shaped salts of at least up to the formation of the alkali metal and heats ^by introduced Erdalkalichlonde melt. contaminated, which settle as sludge. This 3. The method according to claim 1, characterized marked sludge is separated and contains in addition to the fact that powdered salts containing a »5 chlorides and two groups of substances entrained by oxidation, in a melt ^anids resulting carbonates about 50% nitrate / the other substance group. Nitrite. 4. The method according to claims 1 to 3, that ^{the blshe} r practiced methods of destruction characterized in that the reduction with ^these toxic residues are difficult and agile on-carbon after conversion of the salt mixtures 3o. Practiced methods are carried out by oxidation of the aqueous dissolved cyanides and cyanates with hydrogen 5. The method according to claims 1 to 3, da- peroxide, hypochlorite or catalytic oxidation with characterized in that the reduction with atmospheric oxygen. A prerequisite for this process is carbon during the conversion of the salt ^{- usually a} sufficiently large dilution, from which mixtures, preferably at least 35, result in a high amount of wastewater. Another method, which is 50 "C above its melting temperature, is the alkaline boiling of the cyanide temperature, which carries out the cyanate; the ammonia produced in the process represents 6. The method according to claim 5, characterized in that it represents an inadmissible waste water pollution and shows that a powdery mixture ^{must therefore} be separated and isolated by distillation, the three reactants in an inert alkali-alkaline earth 4o This process is uneconomical.
chloride-carbonate melt enters. ^The destruction of the nitrate-nitrites usually takes place 7. The method according to claim 1, characterized ^by joint combustion with industrial and / characterized in that one highly concentrated cyanide ° ^de 'municipal waste. This creates nitrous gases, cyanate-containing salts in an inert alkali earth - ^{which, due} to their great dilution, dissolves alkali chloride-carbonate melt only with difficulty and can be destroyed by 45. Aqueous methods, e.g. B. Oxidation Entry of nitrate-nitrite-containing old salts and ^the Nitnt component went to nitrate or decomposition of the carbon. Nitrites with sulfamic acid or common re- 8 Process according to claims 1 to 3, production of the two substances with aluminum to form ammo characterized in that one salt mixtures in ^niak . ^lead n to wastewater pollution with nitrate or Presence of carbon at temperatures 5 »ammonia. below their melting point reaktionssintert ^Another known method provides the essential and then ^union to a preferably at least 50 ° C common disposal and / or Aufarbeiüber the melting temperature of the mixture ^do lying g ^v ° n optionally banumhaltigen hardness salt-temperature heated fall based on nitnwnitrathaltigen drop 9. The method according to claims 1 to 8, da- 55 on the one hand and cyanide / cyanate-containing waste andurch characterized in that the sum of cyanide, on the other hand by oxidation of the cyanide / cyanate cyanate and complex cyanide in the old ^{salts by} nitrite / nitrate before, the latter group of substances being used in the first group of substances not more than 20, preferably excess, and the oxidation of the 10 to 15, in particular about 10 percent by weight, optionally carbon-containing mixture is ^{60 m} dry state at temperatures above 10. The method according to claims 1 to 9, da- ¹ SO ⁰ C takes place. The reaction mixture is characterized in that old salts are left to their own devices with an ignition. The reaction proceeds 20 percent by weight in excess of content from uncontrollably, can be very severe and salts of the first group of substances by blending conditions before complete conversion to Stillmit inert salt or low-percentage used salt rear ⁶ 5 come ^stan d. diluted. Subject of the invention, by which one the Disadvantages of the described procedures of the state technology and to a satisfactory