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INVENTION
Patent of the Russian Federation RU2013459

METHOD OF REFINING SILVER

METHOD OF REFINING SILVER

Name of the inventor: Lapitskaya EV .; Slotintseva MG; Rytvin EI; Slotintsev NM; Vasekin VV; Bychkov EM; Trofimov NN; Nikitin V.P.
The name of the patentee: Research and Production Complex "Supermetall"
Address for correspondence:
Starting date of the patent: 1991.10.18

The invention relates to metallurgy and can be used in the purification of silver. The purpose of the invention is to reduce silver losses and additional purification from iron, magnesium, silicon. This goal is achieved by the fact that the refining of silver, including heating to 700 - 1200C, melting, blowing into the melt of oxygen-containing gas and simultaneous introduction of caustic alkali and boric acid, melting is carried out in two stages: first - in the air to 99.8% purity; Second - in an atmosphere of oxygen up to purity of 99.9% and higher in the presence of a flux of composition, %: Potassium fluoride 30 - 35; Potassium hydroxide 15 - 25; Boric acid the rest.

DESCRIPTION OF THE INVENTION

The invention relates to metallurgy and can be used in the processing and purification of silver.

A method for dry refining of silver in the remelting in the presence of oxygen and a melt of sodium or potassium hydroxide is known. Thus, silver is purified from copper and tellurium [1]. The verification of the method showed that there are significant losses of silver due to its transition into flux in the form of oxide, purification from silicon, magnesium, and iron does not occur.

The object of the invention is to provide a method for purifying silver from base metals during remelting, which excludes large silver losses.

The aim is achieved by the fact that in the method for refining silver, which includes melting, blowing an oxygen-containing gas into the melt, and simultaneous introduction of caustic alkali and boric acid, the melting is carried out in two stages: first, in the air to 99.8% purity; The second in an oxygen atmosphere to a purity of 99.9% and higher in the presence of a flux of the composition, %: Potassium fluoride 30-35; Potassium hydroxide 15-25; Boric acid the rest.

The flux was prepared as follows.

In a bath of Pt Rh-10 alloy, potassium fluoride was mixed in accordance with GOST 20848-75 and boric acid according to GOST 18704-78 in the required ratio, the moisture formed was evaporated and dried in the same bath on an electric plate covered with asbestos. Dry salts were crushed and stored in tightly closed polyethylene bags. Directly before refining, the flux was mixed with potassium hydroxide in accordance with GOST 24363-80 in the required ratio.

Silver refining was carried out in a quartz crucible in an induction furnace. The silver was loaded into the crucible, the prepared flux was poured in the amount of 1/100 of the weight of the metal to be cleaned, the temperature was raised and the metal with the flux was molten in the molten state for 5 minutes. The crucible was covered from above with a lid, through which a stream of oxygen was fed to the surface of the melt, if necessary. Due to induction currents, intensive melt mixing took place. The flux gradually spread on the surface of the molten metal.

Liquid metal along with the flux was poured into the ingot, and another hot ingot was lowered into the water. The flux was easily detached from the ingot. The metal was analyzed for the content of impurities of copper, iron, lead, etc. by atomic absorption method. In the flux, the silver content was determined by the atomic-adsorption method.

The results of testing the silver refining method are shown in the table.

The use of the proposed composition as a flux (examples 1, 2, 3, 10, 11, 12) makes it possible to achieve a good purification of silver from copper, iron, magnesium, silicon. With an excess of hydroxide or potassium fluoride in the flux, there is a sharp increase in the destruction of the crucible walls during the melting of silver (examples 5, 9), and the lack of these components leads to a deterioration in the purification of silver. And with a lack of potassium fluoride flux is worse than iron, silicon and magnesium (example 4), and with a lack of potassium hydroxide, copper purification deteriorates (Example 8).

When silver is refined in the air atmosphere (examples 2, 3, 10), the loss of silver and flux is lower than when melting in an oxygen atmosphere (examples 11, 6). When refining in the air atmosphere, it is not possible to completely completely get rid of copper even for six melts (example 10), the use of oxygen during refining makes it possible to obtain pure silver (example 11). Only the refining with the flux of the claimed composition first in the air atmosphere, and then in the atmosphere of oxygen, makes it possible to obtain sufficiently pure silver (99.96%) with a minimum of its flux transition (example 12).

CLAIM

A method for refining SILVER, comprising melting, introducing into a melt a flux containing caustic alkali and boric acid and injecting into the melt an oxygen-containing gas, characterized in that the flux further comprises potassium fluoride at the following component ratio,% wt. :

Potassium fluoride 30 - 35

Potassium hydroxide 15 - 25

Boric acid Other

And the melting is carried out in two stages, in the first stage - in the air atmosphere to a purity of silver of 99.8% and in the second stage - when the oxygen-containing gas is injected into the melt to a purity of silver of not less than 99.9%.

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Date of publication 14.03.2007gg