CZ310591A3 - 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

manufacture of imitation jewelery and the like to improve the functional properties, corrosion resistance and / or appearance of the articles.

BACKGROUND OF THE INVENTION

So far, the most common component of chemical pickling and polishing baths is nitric acid, or its salts, and nitrates, where they are used as an oxidizing component. However, the use of nitric acid-containing baths 3 usually leads to intensive development of corrosive and highly toxic nitrous gases, essentially 3 months of nitrogen oxides, with a negative impact on the occupational and environmental environment. For this reason, the use of nitric acid baths worldwide has been abandoned and efforts have been made to replace it with other oxidizing agents, such as hydrogen peroxide and its derivatives, but which are unfavorable in terms of cost.

Many techniques are known in the art to dispose of unsafe gaseous products by trapping them, for example, with low-carbon activated carbon or by absorbing them in hydroxide solutions or a lime pan. The disadvantage of these processes is that there are additional operating and investment costs associated with the need for intensive aspiration of the bath astronomy and the collection and treatment of the diluted gas mixture. For these reasons, PCD devices have only taken over in large-scale operations.

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From a logical point of view, however, the amount of addition of nitric acid in the bath according to stoichiometry, however, is already at a significantly lower level. In baths operating at normal or slightly elevated temperatures, the additions of these substances can be realized gradually, that is, they are added to the bath as they dissolve therein and are more effective in chemical reaction, and the solubility of urea or hydrazine is low. at low temperature, it is relatively low and can thus be regenerated quite efficiently from the exhausted bath, which is consumed by mechanical yield to the component and passes through the rinses into waste water.

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- V, r- - - cast iron, z ylo do typical 1 ďi ZC obozhu 55 11 .. 0 u · / - acid fo -5 b; t without k water ky seliny oc to v o i čně nu by 10 «, y i, 4 1, work /. -x 9 k. U. * j added 20 g ni urine loss ovi. rozpuč melting was , y in roz flow ruse n. r »» »»

The content of nitrous gases formed on dissolution, calculated as nitrous oxide, was 3.2% by volume at 60 ° C. After cooling to 20 ° C, 73% of the urea nitrate crystallized out of the solution.

Example 2

In the treatment of a nickel polishing bath, a typical nickel chemical polishing bath containing 65 wt. % anhydrous acetic acid, 35 wt. h of nitric acid having a density of 1.44 g / ml and 0.5 wt. 1 g of hydrochloric acid was added 20 g of hydrazine hydrate (SO 3). per liter of finished bath. The nitrogen oxide content, calculated at 20, was 1.2 cc. n at 30 ° 0. The melting of the bath used crystallizes part of the present hyarnine nitrate together with the nicotine salt.

Claims (2)

A method for treating polishing and scouring baths based on nitric acids and for chemical treatment of metal surfaces, to which a treatment group 3 is added to the bath with a free amino group, for example urea and / or amidosulphuric acid and / or hydroxyarsine and / or not more than the nitric acid content in 2. The method of claim 1 including that the addition of substances having a free amino group to the bath is performed oo portions by a ^ d ¹² ^ · soctřebování dissolution and chemical reaction with the nitrogen oxides.