DD275997A3 - METHOD FOR THE SECURE DISPOSAL OF TOXIC HAERTERIAL SALT - Google Patents

Abstract

The invention relates to a method for the harmless disposal of toxic hard salts in the melt flow by combining several reactions with detoxifying agents specific for this purpose. The detoxifying agents used are iron compounds and alkali metal sulphates. The detoxification takes place by fusing the used salts with the detoxifying agents in the temperature range between 600 and 900C according to the following reaction equation: 6 NaCN FeSO4 BaCO3 Na2SO4 BaCl2 7 1/2 O2 2 BaSO4 3 Na2CO3 2 NaCl4 CO2 3 N2 FeODab there forms a readily deponendaehiges waste product. The process is carried out in the ongoing salt-water process in the existing salt bath facilities, observing the legal safety regulations in force in Haertereien.

Description

Characteristic of the known technical soundings

In the literature, a variety of methods and procedures for the detoxification of cyanides has been described.

In particular, the methods of detoxification in aqueous solutions with formaldehyde and alkaline chlorination have

proven with Kypochloriden, however, are associated with high investment costs and additional process steps and with a significant salinity of the wastewater.

In the detoxification dusch pressure hydrolysis according to DE-OS 2141294, the destruction of the cyanide by saponification occurs Increase of pressure and temperature, including a considerable investment is required. Also, the oxidative destruction of cyanide with hydrogen peroxide according to DE-OS 2109939 or various others Detoxification methods that rely on the reaction with oxygen, have so far no large-scale application

found.

The Verfahrenwelse of cyanide poisoning In the melt flow with nitrous salts according to DE-PS 2234171 and DE-PS 2318652

brings an increased risk of accidents due to explosive salt discharge in the event of errors in compliance with concentration values and the temperature and is therefore also not used on an industrial scale.

The Schmelzflußentgiftung with iron oxides at temperatures around 900 ° C according to DD-WP 11840 is because of the violence

the reaction reactions taking place at this temperature are not applied in practice. With the Vei drive to DD

WP 147769 and DD-WP 155978, in which a detoxification of cyanide old salts by heating with Fe (OH) ₃ -containing

neutral, puncture-resistant, chrome-free pickling or galvanic sludge is carried out to a temperature of 650-700 ⁰ C, one in the

Practice already applied detoxification option shown, but to very specific Quaiitätsanfordeningen the Detoxifying agent bound and in the case of a complete cyanide poisoning only with exact compliance with all technological Parameter is guaranteed. All these possibilities and methods of cyanide poisoning represent only a partial solution of environmental protection Problems of the harmless disposal of toxic salts of salts, because without exception only a Cyanidevitgiftung without

landfillable waste product result. On the other hand, there are no possibilities of eliminating other toxins contained in the salts which remain as harmful end products during the detoxification process or none

Change (such as barium kerateonate). The entire problem of the harmless disposal of toxic Härteroialts & lze is not through the underground storage

because this method is only a temporary solution in time, in which the toxicity of the aldehyde is maintained in the long term.

Object of the invention

The object of the invention is to develop a method for the harmless disposal of toxic hardening salts, in which all the toxic constituents contained therein are destroyed or converted so that a problem-free dep sniefähiges waste product is formed.

Explanation of the essence of the invention The technical task

The technical object underlying the invention is to carry out a complete detoxification of hardening salts without investment cost in existing plants by fusing with the appropriate gif * .offe specific detoxifying agents.

Features of the invention

Erfindungsgomäß this technical problem is solved in that the Altsalze be melted after the addition of the toxins contained therein specific detoxification agent in the required amount in the salt mixture in Härtereion depending on the consistency and composition of the used salt in the temperature range between 600 and 900 ⁰ C. With the intended as detoxification iron sulfate not only the Cyanld was known to be destroyed by the reaction with the iron but also in the used salts contained in different amounts of 8arlum carbonate with the sulfate of iron into completely aggressive barium sulfate werdon. However, the positive reaction of esterification was contrasted with the non-conversion of barium carbonate into barium sulphate.

Surprisingly, it has now been found that this reaction of the barium carbonate to barium sulfate in the melt flow takes place completely only in the presence of alkali metal sulphates, in particular with sodium sulphate.

In addition to the expected Cyanidentglftung at the same time, the barium carbonate is completely converted into the non-toxic compound barium sulfate by this combined fusion of the used salts with the detoxifying agents iron sulfate and sodium sulfate, so that as a result, the reacted melt represents a readily dumpable waste product. By this combination of several chemical reactions next to each other in a melt thus the disadvantages are eliminated, which are all known to all detoxification processes and in which there is always only a Cyanidentglftung. The detoxification process is carried out in detail in such a way that the used in dsr rule in uneven chunk form old salt is introduced in layers in the preheated to about BOO ⁰ C salt bath crucible with waste salt as a first layer. Initially, only about half of the altsaize weighed for detoxification and the entire amount of iron sulfate required for cyanide poisoning are added to the crucible. The sodium sulphate required for the reaction of the barium carbonate can be introduced into the liquid melt simultaneously with the sulphate sulphate or only after melting, for reasons of volume, depending on the amount required. The crucible is then further heated until the salt mixture begins to melt, with the crucible contents shrinking more or less depending on Altsalzstückengröße. Thereafter, the remaining amount of the used salt is added. During the entire melting process and up to about 30 minutes thereafter, the melt is repeatedly carried out in order to achieve the homogeneity of the melt and thus to ensure a complete detoxification.

Depending on the cyanide concentration, the cyanide detoxification reaction takes place in the lower temperature range (about 650-700 * 0) with more or less strong foaming of the melt, which means that the temperature should only be increased gradually during further heating in order to signal possible foaming of the bath After completion of foaming and existing bare bath surface at about 700-750 "C, the melt is heated for about 1 to 3 hours for complete conversion of the barium carbonate in barium sulfate to 90O ⁰ C. Thereafter, the entire detoxification process is completed, according to the following reaction equation expires:

6 NaCN + FeSO ₄ + BaCO ₃ + Na ₃ SO ₄ + BaCl ₃

2 BaSO ₄ + 3 Na ₂ CO ₃ + 2 NaGl + 4 CO ₂ + 3 N ₂ + FeO After the analytical control and determined absence of toxins, the waste product is dumpable.

Auffuhrungsbelsplel

In a gas-heated salt bath furnace with a size 50/80 crucible and a capacity of about 250 kg of salt with 80% empty crucible filling 200kg of used salt with a content of 4.6% NaCN and 26.6% BaCO _{1 were} detoxified. After the above

Reaction equation were required for cyanide poisoning 8.7 kg iron sulfate and for the conversion of barium carbonate in barium sulfate 38.2 kg of sodium sulfate.

Initially, about 120 kg of the tablet-form Altsalzes and the total amount of ferrous sulfate were introduced into the pre-heated to about 500 ⁰ C Salzbadtiegel, wherein the lowermost layer consisted of about 40 kg used salt. Due to the uneven shape of the piece of scrap salt, the iron sulfate distributed well in the existing interstices, so that at the same time all the sodium sulfate required for barium conversion could be added. After this filling of the crucible, the temperature was adjusted to 55O ⁰ C. When the temperature was reached, the contents of the crucible began to melt with moderate foaming and volume shrinkage. In the course of about 3 hours, the temperature was gradually increased to 700'C. During this time, the remaining about 80kg of used salt was replenished, with the melt was stirred several times until complete liquefaction of all salt components. After soaking the melt and existing bare bath surface, the temperature was raised to 900 ° C. and held for about 30 minutes.

The performed analysis gave cyanide-free. The detection of both water- and acid-soluble barium compounds (BaCl ₂ , BaCO ₃ ) was also negative. Thereafter, the melt was exhausted and the cooled waste product could easily be dumped.

The detoxification process lasted from the beginning of the salt input to the exhaustion β hours.

Compared with the landfill of hardeneroial salts currently in use as a disposal option, the decontamination costs according to the inventive method are only 10-20%, depending on the concentration of the poison constituents in the oil.

Claims (1)

Process for the harmless disposal of toxic hardening salts in a melt flow process, characterized in that the conversion of the barium carbonate contained therein to barium sulfate in the temperature range between 600 and 900 ⁰ C is achieved in the presence of alkali sulfates in an equivalent amount. Field of application of the invention The invention relates to a method for the complete detoxification of toxic hardening salts in salt bath plants present in hardening ooins, taking into account the regulations applicable to hardening operations.