CS243274B1 - A method for the removal of hexavalent Cr6 + chromium when disposing of alkaline-oxidative type tempering salts - Google Patents

Abstract

The purpose of the solution is to remove hexavalent chromium Cr6+ contained in waste tempering salts of the alkaline-oxidation type, which are otherwise disposed of by storage, while in the presence of hexavalent chromium CrB+ during their storage there is always a risk of an ecological accident. The essence of the solution is that an aqueous solution of waste tempering salts of the alkaline-oxidation type is treated with an aqueous solution of hydrazine waste product from nuclear power, in a stoichiometric ratio of chromium Cre+ : : hydrazine N2H4 at a pH value of 11 to 14 at room temperature and atmospheric pressure, and the chromium hydroxide Cr(OH)3 precipitated by the reaction is separated, for example by filtration, and after neutralization, for example with calcium chloride CaCl2, it is disposed of in concentrations corresponding to standards.

Description

(54) Cr ⁶⁺ chromium removal method for the disposal of alkali-oxidation-type tempering salts waste

2

The purpose of the solution is to remove the hexavalent Cr ⁶⁺ contained in the waste of alkali-oxidation-type tempering salts, which are otherwise disposed of by their storage, while in the presence of hexavalent Cr ^{B +} chromium during storage there is always a danger of ecological accident. The essence of the solution is that the aqueous solution of waste tempering salts of the alkali-oxidation type is treated with an aqueous solution of the hydrazine waste product from nuclear power, in a stoichiometric ratio of Cr ^{e +} :

The hydrazine N2H4 at pH 11-14 at room temperature and atmospheric pressure and Cr (OH) 3 precipitated by reaction is separated off, for example by filtration, and after neutralization, for example with calcium chloride, CaCl2 is discarded at concentrations corresponding to standards.

The invention relates to the removal of hexavalent Cr ⁸⁺ from the alkali-oxidation-type tempering salt waste containing sodium hydroxide and potassium nitrate.

For some types of high-speed steel products, such as twist drills, a tempering salt is preferably used in their technological tempering. After the tempering, some of the chromium contained in the high-speed steel becomes part of the waste after tempering and, by its toxicity, influences the disposal of these waste tempering salts.

A major drawback of this method is that the Cr content of stored waste tempering salts still poses a potential ecological accident due to accidental water leakage, which can never be excluded under these conditions. The object of the invention is to avoid this danger.

This is achieved by a process for the removal of hexavalent chromium in the disposal of alkali-oxidation-type tempering salts according to the invention by treating an aqueous solution of alkali-oxidation-type waste tempering salts with an aqueous solution of a hydrazine waste product from nuclear power in stoichiometric Cr ^{B +} The hydrazine N2H4 at pH 11-14 at room temperature and atmospheric pressure and Cr (OH) 3 precipitated by reaction with chromium hydroxide is separated, for example by filtration, and after neutralization, for example with calcium chloride, CaCl2 is discarded at concentrations corresponding to standards.

The advantage of the solution according to the invention is the simplicity of the process, easy feasibility, unpretentiousness 11 and the necessary working equipment. Another advantage is that the reduction process proceeds spontaneously, without interphases, even under normal conditions, and the reduction of hexavalent chromium is complete. Another advantage of using N2H4 waste hydrazine is its cheapness. It is also advantageous that the reduction proceeds continuously even in a strongly alkaline medium, so that it is not necessary to change the reaction medium with additional auxiliaries.

Exemplary embodiment

To one tuna, waste salts with chromium waste such as 15% insoluble matter, 55% potassium nitrate KN03, 5% sodium hydroxide, 1.5% potassium chromate K2CO3, 1% potassium nitrite KNO2 and 13% potassium carbonate K 2 CO 3 (all in% by weight) is added to 3 m ^{3 of} water, stirred and the insoluble matter is separated. A stoichiometric amount of 9.6 kg of N2H4 hydrazine coming from nuclear waste is added to produce 41.2 kg of Cr (OH) 3 chromium hydroxide, which is separated and neutralized, for example, with chlorine lime CaCl2. e.g., discharges to flow while maintaining acceptable concentrations třímocného chromium Cr ^3+. the solution remaining after separation of the chromium hydroxide can be processed by known methods, whose essence is the conversion of nitrites to nitrates and use solution, such as liquid fertilizers.

Claims (1)

Subject A process for the removal of hexavalent Cr ³⁺ in the disposal of alkaline-oxidation-type waste salts by reduction thereof with hydrazine, characterized in that an aqueous solution of alkali-oxidation-type waste salts is treated with an aqueous solution of a hydrazine waste product from nuclear power in stoichiometric chromium Cr ⁶⁴ '; Hydrazine N2H4 at pH 11-14 at room temperature and atmospheric pressure and Cr (OH) 3 precipitated by reaction with chromium hydroxide is separated, for example by filtration, and, after neutralization with, for example, calcium chloride, CaCl2 is discarded at concentrations corresponding to standards.