HU201716B - Process for making unharmful salt baths of toxic effect - 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

The present invention relates to a process for the disposal of toxic salts. The procedure can be used to render exhausted exercise baths harmless in existing salt bath equipment, subject to compliance with applicable safety regulations.

Numerous methods have already been described in the literature to render cyanide baths harmless. Among the various methods used are mainly disposal of formaldehyde in aqueous solution and alkaline chlorination with hypochlorite. However, these methods require very high investment, high investment and additional procedural steps, and impose a considerable amount of salt on the waste water.

German Patent Publication No. 2,141,294 describes pressurized hydrolysis wherein the cyanide is saponified at elevated temperature and elevated pressure. This procedure is also device-intensive.

U.S. Patent Application Publication No. 2,109,939 proposes oxidative destruction of cyanide with hydrogen peroxide, but neither this method nor many other oxygen-based detoxifications have been commercially implemented.

According to U.S. Patent Nos. 2,334,171 and 2,318,652, cyanide is decomposed by melt-salt formation; the process is dangerous because if the concentration and temperature are not accurately maintained, the salt will explode out of the cauldron. The procedure is not used in practice.

The process of reacting the melt with iron oxides at a temperature of about 900 ° C is also not practiced due to the violent nature of the reaction, as disclosed in GD 11,840. In U.S. Patent Nos. 147,769 and 155,978, it is proposed to detoxify a depleted cyanide bath at 650-700 ° C with a ferric hydroxide-containing, neutral chromium-free sludge, which is the residue of marinating baths and electroplating baths. The process is used in practice, but its application is subject to the sludge quality requirements and other technological parameters strictly adhered to.

A common disadvantage of the processes outlined above is that the detoxification of cyanide baths is not satisfactorily protected from the environmental point of view, since the final products cannot be deposited or vomited because they are cyanide-free, but other toxic components (or cyanide decomposition products barium carbonate).

Underground storage is not a satisfactory solution to the complex problem of rendering toxic salt baths harmless; this can only be a temporary and temporary solution, since the toxic effect of the salts has remained.

It is an object of the present invention to provide a process by which each toxic component of a toxic salt bath can be degraded or converted so that the resulting end product can be safely deposited.

In the present invention, it has been assumed that complete detoxification of exhausted salt baths with existing equipment is best accomplished without the need for investment by melting the bath with detergents specific to the particular toxic components.

This is accomplished in accordance with the present invention by melting the salt bath in a salt bath in each training workshop after adding the appropriate detoxifying agent, depending on the consistency and composition of the depleted salt at a temperature between 600 ° C and 900 ° C. The detoxifying agent used is iron sulfate, which is reacted with cyanide in a known manner to decompose it. The aim was to react the iron sulfate with various amounts of barium carbonate present in the salt bath to form completely harmless barium sulfate, but this reaction does not take place under the conditions commonly used in the treatment of salt baths.

Surprisingly, it has been found that barium carbonate in the melt still reacts to barium sulfate when alkali metal sulfate, preferably sodium sulfate, is added to the melt.

Bulk salt baths are bulk melted with ferrous sulfate and sodium sulfate, and on the one hand, barium carbonate reacts fully to harmless barium sulfate and the reacted melt can be deposited. Combining other chemical reactions eliminates the drawbacks of known detoxification processes; it renders not only cyanide but barium carbonate harmless.

The procedure is described in more detail below. The salt bath cauldron is preheated to about 500 ° C and filled with salt, usually in the form of irregularly shaped pieces, and detoxifying agents, so that the first, lowest layer is bath salt. Thus, about half of the previously measured cyanide salt and all of the ferrous sulfate is filled into the pan. The sodium sulphate required for the conversion of barium carbonate may be added to the vessel together with the ferrous sulphate, but if it is too full, it may be waited until the portion so far has melted and the sodium sulphate added to the melt. The pan is heated further until the salts are completely melted, which results in a volume reduction depending on the size of the pieces. Thereafter, the remainder of the cyanide bath salt is added to the pan. During the entire melting process and for about 30 minutes thereafter, the contents of the kettle are occasionally stirred to homogenize the melt and complete the reaction.

The reaction to render the cyanide harmless takes place in the lower temperature range (about 550-700 ° C) and results in more or less strong foaming, depending on the cyanide concentration in the salt bath. Therefore, during further heating, the temperature should be raised gently to prevent the contents of the pan from leaking. Once the foam has ceased and the reflection of the melt is clear, the temperature is raised from 700-750 'C to 900' C and the temperature is maintained for 1-3 hours at this temperature. During this time, the detoxification process is complete according to the following reaction equation:

BaSO ₄ +3 Na 2 CO 3 + 2 NaCl + 4 CO 2 + 3 N 2 + FeO The cooled melt is analyzed and deposited after its safety has been established.

HU 201716 Β

Execution example

In a 50/80 gas heated salt bath furnace capable of accepting about 250 kg of depleted salt in a 50/80 capacity, we detoxify 200 kg of depleted salt bath containing 4.61% sodium cyanide and 26.5% barium carbonate. The chemical requirement calculated according to the above equation is 8.7 kg iron sulfate and 38.2 kg sodium sulfate.

To the pan heated to about 500 ° C was added about 120 kg of salt and all ferrous sulfate; the lowest layer is 40 kg of salt. Iron sulphate is well distributed in the gaps between the soda lumps, so the sodium sulphate needed to convert the barium carbonate is already added to the pan. The temperature is adjusted to 550 ° C. The contents of the cauldron begin to melt with moderate frothing and volume reduction. The temperature was continuously raised to 700 ° C over three hours. During this time, the remaining 80 kg of salt is added to the pan in smaller portions. During melting, the contents of the cauldron are sometimes stirred. After the melt has calmed, its mirror is clear, and the bath temperature is raised to 900 ° C for about 30 minutes.

According to the analysis, the melt is cyanide-free and contains no water-soluble or acid-soluble barium compounds (BaCh). The melt is exhausted and the cooled final product can be deposited without problems.

From the addition of the salt to the depletion, the whole process took 6 hours.

Relative to the cost of depositing cyanide salts so far with poison storage, the cost of the process of the invention, depending on the cyanide content of the salt, is only 10-20%.

Claims (1)

PATIENT PERSONALITY A process for rendering poisonous salt baths in a molten iron sulphate safe, characterized in that an alkali metal sulfate, preferably an equivalent amount of sodium sulfate, is added to the insert and the melt is heated to 900 ° C.