RU2285070C2 - Method of cleaning diamond - Google Patents

Abstract

FIELD: production of diamonds of jewelry property; high-quality cleaning of diamonds.

SUBSTANCE: proposed method includes stage-by-stage treatment of diamond by mixture of acids under action of microwave radiation; at first stage, use is made of nitric acid and hydrogen peroxide at volume ratio of components of 10:1, respectively; at second stage, volume ratio of mixture of concentrated nitric acid, hydrochloric acid and hydrofluoric acid is 6:2:1, respectively; diamond is treated at temperature not higher than 210°C, pressure of 35 atm as set by loading ratio of autoclave equal to 1:10 at power of oven of microwave radiation of 1200 W; duration of each phase does not exceed 40 min. Proposed method ensures perfect cleaning of diamonds from contamination of mineral and organic nature including bitumen compounds on surface and in cracks of diamond.

EFFECT: enhanced efficiency; reduction of time required for process.

Description

The invention relates to improving the purity and color characteristics of gem-quality diamonds and can be used for high-quality cleaning of diamonds simultaneously from surface contaminants and deposits of mineral and organic origin inside diamond cracks.

On the surface and in fissures of natural diamonds, there are often contaminants resulting from the deposition of diamonds from the fluid and melt phases of various minerals and bitumen on the surface and in cracks of diamonds, moreover, the contaminants are often of overlapping nature.

The presence of contaminants on the surface and in the cracks of crystals of jewelry diamonds complicates the sorting of raw materials by color and imperfection, which leads to significant economic losses.

Various methods are known for cleaning the surface of diamonds, for example, by electron beam or ionizing radiation treatment and supersonic treatment (JP 6183893 A, Sumitomo Electric Ind. Ltd., 07/05/94), supersonic treatment in solutions of alkali, hydrogen peroxide, organic or inorganic acids (US 4339281 A, RCA Corp., 07/13/82), autoclaving with concentrated nitric acid at elevated temperature (RU 2163222 C2, Ilyich Abrasive Plant OJSC, 02.20.2001). However, these methods provide cleaning only the surface of the diamond or metal impurities and residues of graphite, or organic contaminants during the extraction of diamonds, or clean the surface to improve the fastening of diamonds in jewelry.

A known method of universal cleaning of diamonds, which consists in sequential processing of diamonds in autoclaves with organic solvents and hydrogen peroxide, alkaline reagents, a mixture of concentrated sulfuric, hydrochloric and nitric acids at a temperature of 250-500 ° C and high vapor pressure, followed by washing with distilled water and final processing with a mixture nitric and hydrofluoric acids. (US 5133792 A, Anshal Inc., 07.28.92, US 5346090 A, Anshal Inc., 09/13/94.) This method is characterized by low productivity due to the multi-stage process, associated with the need for special equipment for carrying out reactions at high temperatures and vapor pressure (US 5 346 090 A 09/13/94).

The disadvantages of the known methods is that each of these methods has a narrow application and is used for very specific types of pollution. Full purification, regardless of the type of impurities, is achieved only in the method described in US Pat. No. 5,133,792, but the process involves many steps.

Closest to the invention is a method for the chemical cleaning of diamonds, including the processing of natural diamonds when heated to 220-250 ° C and at high pressure in an autoclave with a reaction vessel of fluoroplastic for 1.5-3 hours with a mixture of concentrated nitric, hydrochloric and hydrofluoric acids at their volume ratio of 3: 1: (1-2), respectively (SU 1104791 A, GOKHRAN and GPI of the rare metal industry "GIREDMET", 12/20/2000).

This method allows you to clean jewelry diamonds only from impurities contained on the surface of the crystals and formed as a result of enrichment of diamond-bearing rocks, which are presented in the form of traces of metal, inorganic compounds and oils. The method 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. Bitumens screen the access of the reaction mixture to mineral contaminants, and therefore this method does not allow to dissolve mixed types of contaminants, where the mineral phases formed during crystal growth, such as garnets, rutiles, spinels are interbedded with bitumen contaminants.

The objective of the invention is to obtain diamonds of gem quality, and the technical result that can be obtained by carrying out the claimed invention is to ensure complete cleaning of natural diamonds from mixed contaminants of mineral and organic origin, including bitumen compounds on the surface, in cracked diamonds, and reducing the duration of the cleaning process.

The effect is achieved by the fact that in a method for cleaning diamonds, including autoclaving diamonds with a mixture of concentrated nitric, hydrochloric and hydrofluoric acids at elevated temperatures and pressures, the acid mixture is processed stepwise under the influence of microwave radiation, while the mixture of nitric acid is used in the first stage and hydrogen peroxide at a volume ratio of components of 10: 1, respectively, and on the second - the volume ratio of a mixture of concentrated nitrogen, hydrochloric, hydrofluoric acid the slot is 6: 2: 1, respectively.

The processing process is carried out at a temperature of not more than 210 ° C, the pressure is set by the autoclave filling factor equal to 1:10, and is 25 atm with a microwave oven power of 1200 watts. The processing time at each stage is not more than 40 minutes.

It is widely known that powerful high-frequency electromagnetic radiation with a centimeter and sub-centimeter wavelength can accelerate the course of many chemical reactions. The modern interpretation of this phenomenon associates an increase in the reaction rate not only with an increase in the thermal exponential factor in the Arrhenius equation describing the kinetic constant of the reaction, but also with the influence of harmonic vibrations of a certain frequency on the preexponential factor. As a result of this, both molecular energetic excitation and the energy of atomic bonds increase due to the transition of electrons to high-energy orbitals that are unusual for them under normal conditions.

The selected modes of the reaction of dissolution of contaminants under microwave radiation in a mixture of nitric acid and hydrogen peroxide allow the bitumen to be oxidized in deep cracks to carbon dioxide and water in no more than 40 minutes, freeing the surface of mineral contaminants for further reaction with a mixture of nitric, hydrochloric and hydrofluoric acids .

The experimentally found volumetric ratios of the mixture — nitric acid: hydrogen peroxide, equal to 10: 1, as well as a three-component mixture of concentrated acids — nitric: hydrochloric: hydrofluoric, equal to 6: 2: 1, when exposed to microwave radiation with a microwave oven power of 1200 W, make it possible in two stages of the process to dissolve compounds of different mineralogical composition not only on the surface, but also in diamond cracks, without first sorting the crystals according to the type of pollution. At a heating temperature of not more than 210 ° C and a pressure range from 15 to 40 atm, the proposed method allows you to remove contaminants with an efficiency close to 100%.

Examples of carrying out the invention.

Natural diamond crystals containing contaminants with varying degrees of ironization and bituminization in open deep cracks were selected for purification. The total weight of the selected diamonds amounted to 77.92 carats, a total of 119 samples from the classes of size groups: +1.8 ct., 4-6 gr, 3 gr, 2gr, +11. Each diamond was examined for contamination visually using an MBS-10 optical microscope. Diamonds were placed in a fluoroplastic beaker of a 100 ml autoclave and poured into a reaction mixture prepared as follows: 100 ml of concentrated nitric acid was poured into a polyethylene measuring container, then 10 ml of 30% hydrogen peroxide was added, maintaining a volume ratio of 10: 1. The reaction mixture was added at a rate of 10 ml for every 50 carats (or 10 grams) of diamonds, which corresponded to an autoclave fill factor of 1:10, then the reaction vessel was closed with a lid. Then the autoclave was placed in a microwave oven to dissolve the samples. For processing, laboratory equipment for microwave sample preparation of the MARS 5 type with a set of high pressure autoclaves was used. The microwave radiation furnace power was set equal to 1200 W and a temperature of 210 ° C. Temperature changes were controlled using a standard instrument control unit. The pressure was measured by a pressure sensor and reflected on the display. The processing time was also set on the display of the device and was 40 minutes.

Upon completion of heating, the autoclave was cooled to 35 ± 5 ° С, the diamonds were washed with double distillate and filled with a second reaction mixture consisting of 60 ml of concentrated nitric acid, 20 ml of concentrated hydrochloric acid and 10 ml of concentrated hydrofluoric acid, corresponding to a volume ratio of 6: 2: 1. The second cleaning cycle was carried out according to the same parameters, after which the crystals were washed repeatedly with redistillate, while 10 ml of water was added and acid residues were replaced by crystal cracks with water for 15 minutes at a temperature of 150 ° C. Then the crystals were removed from the autoclave and dried in air. The quality and degree of cleaning the surface of diamonds was determined visually using an MBS-10 optical microscope.

The proposed method provided the following results:

1. Improving the visual color perception of the total mass of rough diamonds (77.92 ct., 119 pieces).

2. 3 pollution in the size class of +1.8 ct. were excluded completely.

3. In the size class 4-6 gr of 10 crystals with the presence of petroleum products (bitumen contaminants) 6 pieces were completely cleaned, in the others the degree of purification reached 94-96%.

4. Among the ferruginized diamonds of size groups 3 gr, 2 gr, +11 absolute purification reached 90% of the crystals, in the remaining insignificant residues were noticed.

5. The proposed cleaning method allows with an efficiency close to 100% to clean the tar and iron fill in the cracks.

6. Since the standard set of working autoclaves for the microwave oven of the used MARS 5 device is 11 pieces and one control, when loading one autoclave with 50 carats of diamonds, it is possible to simultaneously clean about 500 carats (100 grams) of natural diamonds for no more than 1.5 hours .

Claims (1)

A method for purifying a diamond, including autoclaving it at an elevated temperature and pressure with a mixture of nitric, hydrochloric, and hydrofluoric acids, characterized in that the treatment with a mixture of acids is carried out step by step under the influence of microwave radiation, and in the first stage a mixture of nitric acid and hydrogen peroxide is used in a volume ratio components 10: 1, respectively, and in the second stage, the volume ratio of the mixture of concentrated nitric, hydrochloric, hydrofluoric acids is 6: 2: 1, respectively, while lmaz treated at a temperature not exceeding 210 ° C, a pressure of 25 atm, given by the coefficient of filling of the autoclave is 1:10, oven microwave power 1200 W radiation, and the duration of each step is not more than 40 minutes.