CZ278402B6 - Process of treating picking and polishing baths based on nitric acid - Google Patents

Abstract

The process of treating, picking and polishing baths based on nitric acid for metals consists in adding substances to the baths with a free amino group. These substances could be urea and/or amidosulfuric acid and/or hydrazine and/or hydroxylamine and/or their dissolvable salts in the highest quantity corresponding to the content of nitric acid in the bath. Part of the total quantity of these materials can be added to the bath gradually at the rate to which they are consumed in the bath.

Description

Technical field. _z ·.

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This invention relates to treatment of pickling and polishing bath based on acid or nitrates Nitrate used for _r finishes. Chemical surface treatments of metals and metal alloys are widely used in final operations in mechanical engineering, jewelery manufacturing and the like to improve performance, corrosion resistance and / or product appearance. . .

BACKGROUND OF THE INVENTION

So far, the most common component of chemical pickling and polishing baths is nitric acid, or its salts, nitrates, where they are used as an oxidizing component. However, the nitric acid content used typically results in the intensive development of corrosive and very toxic nitrosous gases, in a mixture of nitrogen oxides, with a negative impact on the working and the environment. For this reason, the nitric acid poultices have been withdrawn worldwide and efforts have been made to replace them with other oxidizing agents, such as hydrogen peroxide and its derivatives, which, however, are unfavorable in terms of price.

There are many procedures known in the technical practice that you aim ”! to dispose of hazardous gaseous products by saturating them, for example, on activated carbon or by absorption in hydroxide or lime milk solutions. The disadvantage of these processes is that there are additional operating and investment costs associated with the need for intensive extraction of the bath space and the collection and processing of the diluted gas mixture. For these reasons, similar devices have only been taken up in large plants and their efficiency is not very high. rí

The essence of the invention

These deficiencies are eliminated by the method of treating nitric acid-based thioicides and pickling baths for the chemical treatment of metals by adding substances to the bath with an amino group, for example urea and / or amodosulfuric acid and / or hydrazine and / or hydroxylamine and / or or a salt thereof. ^r Their effect consists in reacting with the nitrogen oxides at the time of their occurrence in the bath fluid, which are converted into free nitrogen, respectively, and y. _{in the} case of urea, to a 'mixture' of nitrogen and carbon dioxide, ie substances which are not harmful from a health or environmental point of view. The amount of addition of these substances corresponds to the content of nitric acid in the bath according to stoichiometry, but they work at a substantially lower level. Thus, in baths operating at normal or slightly elevated temperatures, the addition of these substances can be realized gradually, i.e., they are added to the bath as much as they dissolve therein and are consumed by a chemical reaction. The solubility of urea or hydrazine nitrates is relatively low at reduced temperature and can therefore be efficiently recovered from the depleted bath by crystallization. In practice, however, before the bath is exhausted, it is consumed by mechanical yield on the surface of the components and passes through the rinses into the waste water.

The main advantages of the process according to the invention include that. In a simple procedure, the nitrous gas content is lowered to less than one tenth of the original amount, without altering the pickling or polishing properties of the bath, which has a beneficial effect on. working and living environment. In the case of urea, the procedure ⁵ cost far more advantageous than the way of additional disposal nitroshích ^c 'plyhů from this perspective it can be recommended for smaller ^fi facility and where would the construction Apparatus for nitrogen likvidacíoxidů met with great difficulties. / cq

DETAILED DESCRIPTION OF THE INVENTION iri

Example i

In the treatment of the polishing bath for the chemical polishing of copper and its alloys, there was a dotty bath for chemical polishing of copper containing 55 hmbtl; ·% Phosphoric acid density 1.75 g / ml; 25 wt. % anhydrous acetic acid and 20 wt. % of nitric acid having a density of 1 ~ 4 ^: g / ml operating at a temperature range of 55 to 80 DEG C. was added 90 g of triturate per liter of bath and after dissolution, ² copper objects were polished in solution for 90 s. Vjžmiklýčh gas during dissolution converted to carbon dioxide was 3.2 otrj ¹ -. After cooling to 20 DEG C., 75% of the original amount of urea nitrate crystallized from the solution. -'s ffiXÍW 'ζ.ε.Ί'. Λ- ~:

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.. ~ š. p ^ p ^ pi _rav g nickel polishing bath was a typical polishing bath prtPchémické nickel content of 65 wt. % anhydrous acetic acid, 3-5 wt. % nitric acid of 1.44 g / ml and 0.5 wt. % hydrochloric acid added 20 g hydrazine hydrate (80%) per liter of finished bath. The nitrogen oxide content, calculated as NO ₂ , was

1.8 vol% at 30 ° C. On standing from the bath used, some of the hydrazine nitrate present crystallizes together with the nickel salt.

VV «. '? ·' O '. SX'v · 'tPrůmyslová APPLICABILITY _£ .Λ RIC / method of the invention can be used wherever it to a chemical etching and / or polishing metal articles using baths containing nitric acid · and / or for the purpose of .dusičnanů MPROVING' functional properties appearance, or corrosion resistance of the products, to all sectors of mechanical engineering, electrical engineering, mechanical engineering, in the manufacture / surgical instruments, industries.week, goods 2a imitation jewelery - more ..... ;. ' .. '. 1' / .. ''. '''

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-2GB 278402 B6

Claims (2)

PATENT REQUIREMENTS 1. A method for treating polishing and pickling baths based on nitric acid for chemical treatment of metal surfaces, characterized in that substances containing free amino groups are added to the bath, for example urea and / or amidosulphuric acid and / or hydrazine and / or hydroxylamine and / or a salt thereof in an amount at most equal to the nitric acid content of the bath. Process according to claim 1, characterized in that the addition of the free amino group substances to the bath is carried out in portions, according to their dissolution and consumption by chemical reaction with nitrogen oxides.