RU2367601C1 - Method for diamonds purification - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method includes stagewise diamonds treatment in autoclave at increased temperature and pressure under the action of microwave radiation: in the first stage -with mixture of nitric acid and hydrogen peroxide, in the second stage- with mixture of concentrated nitric, chlorhydric and hydrofluoric acids. The treatment in both stages is carried out in acids gas phase at autoclave filling 45-55%, in the first stage the volume ratio nitric acid/hydrogen peroxide is 4:1 respectively, the treatment is carried out at temperature 215-250°C during 15-60 min. In the second stage the volume ratio nitric acid/chlorhydric acid/hydrofluoric acid is 5:4:1 respectively; the treatment is carried out at the same temperature during 15-150 min. In the third stage the mixture is treated with 5% solution of chlorhydric acid/ during 5-15 min and temperature not more than 160°C.

EFFECT: efficiency enhancing of diamonds purification process along with increase of the used equipment productivity and decrease of reagents consumption.

2 ex

Description

The invention relates to the purification of diamonds and diamond powders and can be used for high-quality purification of natural diamonds from surface contamination and removal of foreign impurities.

A known method for cleaning diamond (No. 1104791, publ. 12/20/2000, Bull. No. 35, C01B 31/06), including processing the diamond when heated with a mixture of nitric and hydrochloric acids at elevated pressure in a reaction vessel made of fluoroplastic, and the mixture is additionally hydrofluoric acid is introduced at a volume ratio of concentrated nitric, hydrochloric and hydrofluoric acids

3: 1: (1-2), respectively, at 220-250 ° C for 1.5-3 hours.

This method allows you to clean diamonds only from impurities contained on the surface of the crystals and resulting from the enrichment of diamond-bearing rocks, which are presented in the form of traces of metal, inorganic compounds and oils.

The disadvantage of this method is that it does not provide high-quality purification from contaminants of mixed origin that appeared during diamond growth or later as a result of various secondary reactions, since the redox potential of the reaction mixture used is insufficient for the oxidation of bitumen. In addition, the disadvantages of this method can be attributed to the duration of the cleaning process - up to 3 hours and a large consumption of acids.

The closest technical solution is a method for cleaning diamond (RU No. 2285070 A1, 04/27/06, С30В 33/04), which includes multi-stage autoclaving at elevated temperature and pressure under the influence of microwave radiation with a mixture of hydrochloric, nitric, and hydrofluoric acids, with the first the stages use a mixture of nitric acid and hydrogen peroxide at a volume ratio of 10: 1, respectively, and in the second stage, the volume ratio of the mixture of concentrated nitric, hydrochloric and hydrofluoric acids is 6: 2: 1 s responsibly, the duration of each step is not more than 40 minutes. The temperature maintained in the autoclave is not more than 210 ° C, the pressure is 25 atm, the microwave oven power is 1200 W, the duration of each stage is not more than 40 minutes with an autoclave fill factor of 1:10. When implementing this method, a sufficiently effective cleaning of diamonds from bitumen contaminants is carried out. However, only 57% of the diamonds in need of refining are completely refined, 31% partially. In 12% of the crystals, with the complete removal of bitumen impurities, transparent red-brown spots (pollution in cracks) appear in their place, shifting the color of the crystals to the region of brown colors, which reduces the price of diamonds. On a number of crystals, some of the red color contaminants (presumably iron oxides) were removed from the cracks as a result of cleaning, but were located on the surface of diamond crystals, which required the introduction of an additional cleaning stage.

The disadvantages of this method should also include a large amount of highly toxic oxidizing mixture for disposal. In addition, the need to completely fill diamonds with a reagent increases the consumption of an acid mixture, limits the volume of simultaneously processed crystals in autoclaves to 3-5 cm ³ and reduces the equipment life several times due to the high pressures that develop in the reaction chamber during acid evaporation. All this, respectively, reduces the productivity and service life of the installation, requires a lot of manual labor, which ultimately makes this method not effective enough when used in production conditions for processing large batches of diamond crystals.

The technical problem solved by the invention is to increase the efficiency of the diamond cleaning process while increasing the productivity of the equipment used and reducing the consumption of reagents.

The specified technical result is achieved in that in a method for cleaning diamonds, which includes stepwise processing of diamonds in an autoclave at elevated temperature and pressure under the influence of microwave radiation: in the first stage, with a mixture of nitric acid and hydrogen peroxide, in the second, with a mixture of concentrated nitric, hydrochloric and hydrofluoric acids , the processing in the first and second stages is carried out in the gas phase of the acids when filling the volume of the autoclave 45-55%, nitric acid and hydrogen peroxide for the first stage are taken in a volume ratio 4: 1, respectively, and the treatment is carried out for 15-60 minutes at a temperature of 215-250 ° C, nitric, hydrochloric and hydrofluoric acids for the second stage are taken in a volume ratio of 5: 4: 1, respectively, and the treatment is carried out at the same temperature for 15-150 minutes, after which, in the third stage, they are treated with 5% hydrochloric acid at a temperature of not more than 160 ° C for 5-15 minutes.

Processing of rough diamonds not in a liquid reagent, but in a gaseous environment created by the evaporation of acids and the formation of highly active compounds (gases: chlorine, nitrosyl, nitrosyl chloride, nitrosyl fluoride), which are more effective oxidizing agents than the starting acids, allows the process to be activated, while the gaseous medium is formed by molecules with higher kinetic energy compared to molecules in solution, and, accordingly, the process is carried out more efficiently.

The total pressure of saturated steam (gas) in the autoclave during heating is created due to the partial pressure of the reagent components and the newly formed chemical components. The pressure generated by saturated steam is the highest pressure exerted by the vapor of the reactant at a given temperature. In order to withstand the required temperature conditions, it is necessary to reduce the amount of reagents used. Moreover, in the case of its complete evaporation, the gas pressure will be less than saturated. Thus, due to the process of cleaning diamond crystals in a gaseous medium created by the evaporation of acids, it becomes possible to create the necessary temperature regime at a lower pressure inside the autoclave.

Carrying out the processing process in a gaseous medium also allows to increase the filling of the autoclave up to 45-55% (compared with 9% in the prototype), and therefore, increase the productivity of the equipment used, volumes of autoclaves for cleaning large batches of diamond crystals. In addition, the processing of diamond crystals in a gaseous medium reduces the consumption of acids used for processing by 15-20 times. The degree of filling of the autoclave 45-55% was tested experimentally and corresponds to 60-85 ml of the bulk volume of processed diamonds for autoclaves with a capacity of 100 ml.

Additional processing of diamonds with a weak (5%) hydrochloric acid solution at a temperature of not more than 160 ° C for 5-15 minutes allows you to effectively clean them from acid residues in the cracks.

The volume ratios of a two-component mixture of nitric acid and hydrogen peroxide in the first stage of processing, equal to 4: 1, and a three-component mixture of nitric, hydrochloric and hydrofluoric concentrated acids, equal to 5: 4: 1, used in the second stage of purification of diamond crystals, are most rational for use in full-fledged operation of components, exposure to microwave radiation at a microwave oven power of 1200 watts and make it possible to dissolve compounds of various mineralogical composition. In this case, an increase in the ratio of acids of the amount of hydrochloric acid increases the effect of purification of diamond crystals from ironing (inclusions of metallic impurities).

The time of the first stage of processing (15-60 min) and the second stage of processing (15-150 min) are selected experimentally depending on the degree and type of diamond contamination (individually for each deposit).

The temperature of the first and second processing stages is maintained equal to 215-250 ° C. The temperature range was chosen based on the fact that above 250 ° С the fluoroplastic loses its physical and mechanical properties and is deformed, and at a temperature of less than 215 ° С the surface purity of diamond crystals does not exceed 85% (according to the GOKHRAN and GIREDMET patent, see No. 1104791 , published on December 20, 2000, Bull.No. 35, С01В 31/06).

The set of features of this technical solution is not identified from the patent documentation and scientific and technical information, which indicates the inventive step of the claimed technical solution.

Concrete implementation example

To fully disclose the technical nature and advantages of the present invention, examples are given where the initial data for the implementation of the proposed method are adopted as follows. A batch of rough diamonds was subjected to

-6.7 + 4.7 mm from two deposits (primary and placer). In this case, both problematic diamond crystals (having cracks with impurities) and diamond crystals without visible impurities were processed. The crystals of each deposit were processed separately.

For processing diamonds, the Speedwave MWS-3 + microwave pressure decomposition system was used. This system is equipped with 8 autoclaves

DAK-100 is made of TFM fluoroplastic with a capacity of 100 ml each with a maximum heating temperature of 250 ° C, allowing a total processing of up to 5000 carats of diamonds. For washing the diamonds, DAP-240 autoclaves with a capacity of 250 ml with a maximum heating temperature of 160 ° C were used.

Processing with a mixture of acids was carried out in three stages under the influence of microwave radiation using a microwave oven. The power of the microwave oven does not exceed 1200 watts (during cleaning, the power varies depending on the volumes of the processed crystals and the set temperature).

The processing regimes for primary and placer diamonds are somewhat different. The differences lie in the longer processing time in the second stage of cleaning for diamonds from placer deposits. This is due to the greater degree of contamination of these diamonds with ironing.

The first stage is mainly used to clean diamonds from bitumen and process fats. In our case, a mixture of concentrated nitric acid and hydrogen peroxide is used. Concentrated nitric acid partially dissolves bitumen with the formation of a red-brown solution. Hydrogen peroxide is used to enhance the oxidizing properties of nitric acid and to break down hydrocarbon molecules. In the latter case, the formation of oxygen-containing substances, mainly organic acids. A typical mixture composition used for the decomposition of hydrocarbons is HNO ₃ : H ₂ O ₂ = 4: 1.

The second stage is used to clean the diamonds from ironing and various types of greases located on the surface and in the cracks of diamonds. In order to increase the purification of diamonds from ironing, the composition of the reagent used was changed in the direction of increasing the volume of hydrochloric acid. The volumetric ratios of the new composition were as follows: nitric acid: hydrochloric acid: hydrofluoric acid = 5: 4: 1. A further increase in this ratio of the volume of hydrochloric acid was impractical due to the development of the maximum allowable pressure in the autoclaves used. Since according to the results of experiments with these acids, it was found that the greatest partial pressure in the autoclave is created due to hydrochloric acid.

1. Processing of diamonds from a primary deposit

In the first stage, diamond crystals were placed in a fluoroplastic beaker of the autoclave over the entire height of the reaction chamber (bulk volume 60 cm ³ ), and filled with a small volume portion of the reaction mixture of nitric acid and hydrogen peroxide at a volume ratio of components 4: 1 to create a gas medium (6 ml of reagent) , and covered with a lid.

Autoclaves were placed in the microwave. The temperature was set at 230 ° C. Cleaning was carried out within 60 minutes At the end of heating, the autoclave was cooled, the diamonds were washed with double distillate and poured with a mixture of concentrated nitric, hydrochloric and hydrofluoric acids at a volume ratio of 5: 4: 1 and treated similarly to the first stage at the same temperature for 60 minutes. The amount of the concentrated acid mixture solution was 6 ml.

After re-cooling the autoclave and washing the diamonds with double distillate in the third stage, the diamonds were loaded into the DAP-240 autoclave, the crystals were completely filled with the reagent - 5% hydrochloric acid solution and kept at 160 ° С for 15 min in the liquid phase. The amount of reagent per 60 cm ³ sample crystals was 40 ml. At the end of the third stage of processing, diamonds were dried and viewed under the binoculars by mineralogists.

It is possible to increase the number of heating-cooling cycles within each stage of cleaning diamond crystals, depending on the degree of contamination.

As a result of mineralogical estimates, it was found that with these modes of processing diamonds of a primary deposit with a grain size of -6.7 + 4.7 mm, 94.3% was completely purified.

2. Diamond processing from placer deposits

Diamonds from alluvial deposits are characterized by a greater degree of contamination: ironization, compared with crystals from primary deposits.

In the first stage, diamond crystals were placed in a fluoroplastic beaker of the autoclave over the entire height of the reaction chamber (bulk volume 60 cm ³ ), and filled with a small volume portion of the reaction mixture of nitric acid and hydrogen peroxide at a volume ratio of components 4: 1 to create a gas medium (6 ml of reagent) , and covered with a lid.

Autoclaves were placed in the microwave. The temperature was set at 230 ° C. Cleaning was carried out within 60 minutes At the end of heating, the autoclave was cooled, the diamonds were washed with double distillate and poured with a mixture of concentrated nitric, hydrochloric and hydrofluoric acids at a volume ratio of 5: 4: 1 and treated similarly to the first stage at the same temperature for 120 min. The amount of the concentrated acid mixture solution was 6 ml.

After re-cooling the autoclave and washing the diamonds with double distillate in the third stage, the diamonds were loaded into the DAP-240 autoclave, the crystals were completely filled with the reagent - 5% hydrochloric acid solution and kept at 160 ° С for 15 min in the liquid phase. The amount of reagent per 60 cm ³ sample crystals was 40 ml. At the end of the third stage of processing, diamonds were dried and viewed under the binoculars by mineralogists.

It is possible to increase the number of heating-cooling cycles within each stage of cleaning diamond crystals, depending on the degree of contamination.

As a result of mineralogical assessments, it was found that under these processing conditions for diamonds from an alluvial deposit with a grain size of -6.7 + 4.7 mm, 77.01% was completely cleaned.

The reagent consumption does not depend on the type of deposits, and for 10,000 carats of diamond products during three-stage cleaning, the following was obtained: nitric acid - 145.6 ml; hydrochloric acid - 67.7 ml; hydrofluoric acid - 11.2 ml and hydrogen peroxide - 22.4 ml, while the prototype: 3160 ml, 440 ml, 240 ml and 180 ml, respectively.

A comparative analysis of the cost estimates of crystals before and after cleaning showed that the cost of problem stones increased by 10-14%, and the entire batch increased from 1.0 to 1.5% (depending on deposits).

Claims (1)

The method of cleaning diamonds, including the stepwise processing of diamonds in an autoclave at elevated temperature and pressure under the influence of microwave radiation: in the first stage - with a mixture of nitric acid and hydrogen peroxide, in the second - with a mixture of concentrated nitric, hydrochloric and hydrogen fluoride acids, characterized in that the processing at the first and second stages, 45-55% of the acids are carried out in the gas phase when the autoclave is filled, nitric acid and hydrogen peroxide for the first stage are taken in a volume ratio of 4: 1, respectively, and the treatment is carried out at a temperature of 215-250 ° C for 15-60 minutes, nitric, hydrochloric and hydrofluoric acids for the second stage are taken in a volume ratio of 5: 4: 1, respectively, and the treatment is carried out at the same temperature for 15-150 minutes after which, in the third stage, they are treated with a 5% hydrochloric acid solution for 5-15 minutes at a temperature of not more than 160 ° C.