CS240917B1 - A method for recovering the proportion of nitrites and nitrates from waste tempering salts and disposing of the non-regenerable residue of these salts - Google Patents

Abstract

Method of recovering the proportion of nitrites by filtering them from the molten waste tempering salts in the temperature range of 190 to 210 °C and thermal disposal of the non-regenerable residue of these waste salts.

Description

Process for recovering the proportion of nitrites and nitrates from waste tempering salts and disposal of the non-regenerable residue of these salts

Process for recovery of nitrite fraction by filtering them from granulated waste tempering salts in the temperature range of 190 to 210 ° C and thermal disposal of non-regenerable residue of these waste salts ·

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The present invention relates to the recovery of a proportion of nitrites and nitrates from waste tempering salts and to the disposal of the irrecoverable residue of these salts by thermal destruction.

So far, the waste tempering salts have been disposed of in a wet way, producing both harmful or poisonous gases that have burdened the environment and wastewater, which has been heavily salinized after disposal. For this method of disposal, investment-intensive cleaning systems had to be built and, moreover, sludge was produced, the disposal or depositing of which constituted another problem for the engineering plants.

The described method of disposal of waste tempering salts is currently prohibited due to the strong salinisation of water discharged into the recipient.

At present, new ways of disposing of waste tempering salts are in the research stage and are mostly stored in engineering plants.

The present invention not only solves the problem of disposal of waste tempering salts, but also enables the recovery of their substantial fraction. It consists in melting the waste tempering salts, if cyanides are present, to remove them by heating to 400 ° C; at this temperature, the cyanides are quantitatively oxidized according to the equation

NaCN + 2 0 _{2 -} Na ₂ CO ₅ + CO ₂ + N _g

After the destruction of the cyanides, the melt is cooled to a temperature range of 190 to 210 ° C and filtered through a suitable ceramic filter or glass wool. The filtrate contains nitrites and nitrates which are reused in the preparation of the tempering salts. The unfiltered residue is destroyed by crushing the cooled melt into particles smaller than 1 mm, mixing it with coal in a weight ratio of 1 to 3 to 100, preferably adding 1 to 2 parts of calcium hydroxide, 240 917

- Λ so as to increase the melting point of the mixture so that the mixture cannot leak from the bed and grate of the combustion system before being exposed to high temperature and burn at a temperature of at least 600 ° C.

Example

In the engineering plant 50 kg of waste tempering salts containing 17.0 wt. % N, 21.0 wt. NOg, 2.1 wt% CN, 0.2 wt% CNO, 10 wt% CN; CO ^,

9.7 wt. Cl. The cations are essentially sodium and potassium.

The waste tempering salts are melted in a crucible in an electric furnace. The melt is heated to 400 ° C for 60 minutes and the cyanide content is checked. After reaching a negative cyanide test, the melt is cooled to a temperature range of 190 to 210 ° C and filtered through a glass wool filter. The filtrate contains 8.2 wt. % NOj and 4.34 wt. NOg, which returns to the production process. After cooling, the filter residue is crushed to particles of a maximum size of 1 mm, moistened in a mixer and mixed with calcium hydroxide in a 2: 1 weight ratio. The resulting mixture is re-moistened and mixed with fine coal at a weight ratio of 115 ° C. The mixture so treated is added to the solid fuel at a weight ratio of 1:10 to 20 and combusted at a minimum temperature of 600 ° C.

Claims (1)

OBJECT OF THE INVENTION _{24Q gi?} Process for recovering a proportion of nitrites and nitrates from waste tempering salts and disposing of a non-regenerable residue of these salts, characterized in that the waste tempering salts are melted, and if present, the cyanides are removed by heating the melt to 400 ° C at 190 to 210 ° C, the melt is filtered, the filtrate containing nitrites and nitrates is reused in the preparation of the tempering salts, and the unfiltered residue is destroyed by crushing the melt to a particle size of less than 1 mm after cooling, mixing with carbon in a 1 to 3 to 100 weight ratio. Preferably, 1 to 2 parts by weight of calcium hydroxide are added and combusted in a solid fuel combustion system at a temperature of at least 600 ° C.