A method for controlling the homogenization of precious metals

Abstract

The present invention belongs to the field of precious metals, and specifically relates to a method for controlling the homogenization of precious metals. Aiming at the special needs of precious metal processing, the present invention applies granulation processing to the primary non-standard gold homogenization processing, and has achieved success, and has expanded the scope of precious metals (silver, platinum group metals) in the whole domain, providing a new method for the batch processing of non-standard purity precious metal products and recycled precious metals, which has important promoting significance for the processing of precious metals and has great commercial value and economic benefits. In addition, the method described in the present invention has low energy consumption and no harmful gas emissions during the operation process, which has positive significance for green environmental protection.

Description

Technical Field

[0001] The invention belongs to the field of precious metals, and in particular relates to a method for controlling the homogenization of precious metals. Background Art

[0002] Precious metals mainly refer to eight metal elements, including gold, silver and platinum group metals (ruthenium, rhodium, palladium, osmium, iridium and platinum). Most of these metals have beautiful colors, are highly resistant to chemicals, and are not prone to chemical reactions under normal conditions. They are widely used in jewelry, handicrafts, and aerospace chemical and electronic industries. Their excellent antioxidant capacity and high-temperature miscibility are irreplaceable by other metals. These excellent characteristics are all based on the later fusion and proportioning processing of pure precious metals. Taking gold as an example, it has a unique and brilliant luster and excellent ductility. It is easy to eutectic with a variety of metals to form alloys, and exhibits good castability after alloying. With the gradual opening of the gold processing market, more and more non-standard purity precious metal products and batch processing of recycled precious metal materials have been carried out. The determination of metal content has brought great pressure to refineries. A large number of recycled gold materials with uneven purity cannot obtain specific content parameters after merging, and they have to accept the fact of data judgment after purification.

[0003] Homogenization has long been a headache. For example, the biggest problem in melting gold alloys is that it is difficult to achieve the ideal state of homogenization of the melt ingredients. This is because the mass of gold is much greater than that of non-ferrous metals, and its melting point is often greater than several hundred degrees. The melting process often results in the deposition of elements in layers, and the aggregation and precipitation of low-melting-point elements along the grain boundaries during the solidification process. Mechanical stirring has little effect. Taking 18k gold as an example, it is impossible to achieve homogenization by hot melting and stirring alone. In order to avoid disputes caused by uneven color, the jewelry industry often deliberately adds excessive gold content to ensure that the gold content is not less than 75%. In the market, the standard gold samples for testing are all imported, and the price is high, generally three times the price of ordinary gold, which greatly increases the testing cost and also restricts the orderly development of the precious metal content industry. Particle metallurgy technology is an advanced process technology for hot melt casting. It is widely used in the production and processing of special alloys. The finished materials completely eliminate gravity segregation and solid solution segregation, and the material body reaches the ideal state of no segregation. A large number of literature and materials have been consulted, but no cases of particle metallurgy technology application for precious metals such as gold and silver have been found. How to keep the added elements evenly distributed as long as possible? Industry experts have made unremitting efforts for a long time and have their own opinions and measures. Here is a brief list of different treatment processes:

[0004] Technology mechanism Effect Market application status Melting and mechanical stirring Forced mechanical stirring and mixing Effective, blind area cannot be removed. Slow condensation with back segregation Mainstream Magnetic vortex stirring High frequency magnetic eddy current has strong stirring function There is magnetic eddy current skin effect, and the equipment requirements are high. The internal homogeneity of the material is poor, and overheating is prone to occur. Semi-replacement of mechanical stirring Vacuum multiple feeding in temperature sections Controlling the relationship between temperature and solubility High difficulty in process control, domestic multi-element low-K gold preparation is a shortcoming Long-term technical shortcomings below 18K Pre-alloying treatment Pre-melting of refractory elements and secondary melting of main elements Auxiliary mechanical stirring has been improved, but the control is difficult. Pre-alloy preparation is difficult. High requirements for equipment and staff quality Summary of the invention

[0005] The present invention provides a method for controlling the homogenization of precious metals. The non-standard precious metals can be treated by rapid solidification of liquid flow by particle metallurgy method to achieve homogenization of precious metal materials with different contents, which can save energy and reduce consumption, reduce carbon emissions, and has positive significance for green environmental protection.

[0006] The technical solution of the present invention is achieved in this way:

[0007] A method for controlling the homogenization of precious metals comprises the following steps:

[0008] a. Cleaning

[0009] Degreasing: The precious metal raw materials are cleaned and degreased in a closed container with trichloroethylene or ultrasonic water-soluble degreasing agent to remove residual fat-soluble and separable impurities on the surface of the precious metal raw materials;

[0010] Rinsing: Ultrasonic cleaning with 60-80℃ pure water once, rinse twice, and clean once with deionized water;

[0011] Drying: vacuum heat drying method is adopted;

[0012] b. Detection

[0013] Pre-test the metal content of the primary metal raw materials one by one, and pre-grade them according to the metal content;

[0014] c. Classification

[0015] The metal content is determined by grade, and the predetermined value of the primary metal raw material is calculated according to the metal content of the final product. The primary metal raw material is packaged in batches according to the predetermined value range of + / -1%;

[0016] d. Merge and fusion (one-time homogenization)

[0017] The mixture is melted according to a predetermined ratio, and after the fusion is completed, it is cast into a graphite cavity mold to form a single ingot; achieving the first homogenization;

[0018] e. Granulation (secondary homogenization)

[0019] The single charge weight is configured by presetting the balanced metal content, the material embryos are combined, remelted and mixed again under the protection of inert gas, and the fused metal flow is atomized into 0.05-0.15 mm diameter particles under the shearing action of low-pressure jet injection, and cooled and recovered;

[0020] f. Dry mixing (three times homogenization)

[0021] The particles are mechanically mixed to achieve the third component homogenization;

[0022] g. Detection

[0023] Determine the metal content by sampling in different areas and layers, and verify the difference between the measured metal content of the particles and the expected metal content;

[0024] h. Hot Press Fusion

[0025] The particles that pass the test are hot pressed and fused, and the particle densification process is completed under heating and pressure.

[0026] Furthermore, the precious metal is gold, silver and / or platinum group metal.

[0027] Furthermore, in the step a, during the rinsing operation, the resistance of the deionized water is R>2MΩ; during the drying operation, vacuum drying is performed at 130°C for 30 minutes, and the vacuum is maintained at -0.095 to -0.1MPa.

[0028] Furthermore, in the step d, the amount of the required metal raw material is calculated in units of 80-100 kg, the weight of a single ingot is 3-5 kg, and the melting and casting temperature is no more than 1120°C.

[0029] Furthermore, in the step d, a tiltable medium frequency induction crucible furnace is added for fusion.

[0030] Furthermore, in the step d, depending on the impurity content of the metal raw material, slag can be formed to remove it if necessary. The slag forming method is hot-melt slag forming, and the specific operation is: in an aerobic atmosphere, the easily oxidized low-density metal will float to the surface as slag after hot melting, which can be removed by melting with sodium tetraborate, and lead oxide can be removed by soot blowing; the organic matter is oxidized and burned in an aerobic atmosphere to form slag to remove it; the impurity slag is properly stored as a basis for the total amount.

[0031] Furthermore, in the step e, the remelting temperature is 1100-1150° C., and the jet pressure is 0.03-0.05 MPa; and the inert gas is argon or high-purity nitrogen.

[0032] Furthermore, in the step f, the mechanical stirring is natural mixing in a closed barrel with overall tumbling; all the materials are filled with argon gas for protection, the speed is 15-20r / m, the mixing time is 20 minutes, the pressure is 1-5KPa, and the pressure is released and collected out of the cavity.

[0033] Furthermore, in step g, 3-5 points are sampled to determine the metal content, and the difference between the measured value and the predetermined metal content is less than 0.3%.

[0034] Furthermore, in the step h, the temperature is set to be 5-7°C below the solid-liquid phase line, and the pressure is 30-50 MPa for 30-60 seconds.

[0035] Beneficial effects of the present invention:

[0036] This research invention adopts particle metallurgy technology to solve the problem of chemical purification pre-stage component prediction by dispersing particle distribution in tons of processing units, and fundamentally solves the problem of non-standard metal homogenization. Benefiting from the rapid development of industrial technology, the present invention applies particle processing to primary non-standard gold homogenization processing for the special needs of precious metal processing, and has achieved success, and has expanded the scope of precious metals (silver, platinum group metals), providing a new method for batch processing of non-standard purity precious metal products and recycled precious metals, which has important promotion significance for the processing of precious metals and has great commercial value and economic benefits. In addition, the method described in the present invention has low energy consumption and no harmful gas emissions during the operation process, which has positive significance for green environmental protection. For example, the method described in the present invention can replace the acid purification method to process non-standard gold, which can save energy and reduce consumption and reduce carbon emissions. The financial strategic attributes of gold are well known. The homogenization technology described in the present invention solves two basic problems: 1. Most of the crude gold is imported in small pieces with uneven gold content, and the customs manual cannot calibrate the code. The measurement results after homogenization can supplement the customs code, which is ahead of the customs inspection. The inspection results reversely verify the customs import declaration verification; 2. The atomized particle powder making pressure is increased, and the particle diameter is controlled between 0.05-0.15 mm. The component elements are highly dispersed and distributed. Through hot isostatic pressing and sintering densification, a completely segregation-free gold alloy blank is made, which can fill the long-term domestic low-K gold self-configuration component distribution uneven distribution and long-term dependence on imports. The weak passive situation.

[0037] The mean distribution of components in the alloy state (solid solution) of multi-component precious metals is still a difficult problem. Of course, it can be achieved by investing in special equipment (hot isostatic pressing) at all costs, but the high cost makes many manufacturers difficult to move forward. Whoever masters the low-cost process technology first will rewrite the processing history and seize business opportunities. The method described in the present invention controls the process cost to no more than 1 yuan / gram, which is within the acceptable range of customers, fills the gap in the processing of multi-component gold precious metal materials in China, and the application market demand is huge. The method described in the present invention realizes low-cost pollution-free operation, and the whole process is pollution-free. Waste discharge meets environmental protection requirements. Compared with the current treatment results of non-segregated multi-component precious metal materials in Germany, Switzerland, Italy, etc., homogenization achieves the same effect, and the grain size is slightly larger than the isostatic pressing product. The cost can be controlled to no more than one-fifth of it, reaching the economically affordable range of users. This process is also suitable for highly dispersed gold and platinum products, which has a good effect on maintaining the lasting physical and chemical properties of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0039] Figure 1 Schematic diagram of granulation.

[0040] Figure 2 The relationship between density and time and temperature. In the figure, T is the temperature change curve, and D is the density change curve; the left side of the vertical axis is temperature T (℃), the right side is pressure P (n), and the horizontal axis T (m) is the processing time (min).

[0041] Figure 3 Relative density (vertical axis) versus applied pressure (horizontal axis).

[0042] Figure 4 Schematic diagram of hot pressing fusion. DETAILED DESCRIPTION

[0043] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0044] Example 1

[0045] A method for controlling the homogenization of precious metals comprises the following steps:

[0046] The raw material is gold.

[0047] a. Cleaning

[0048] (1) Degreasing: After polishing and multiple processing, the polishing wax and compound grease silicate oxide impurities remaining on the surface of primary gold products must be thoroughly removed; use trichloroethylene or ultrasonic water-soluble degreasing agent to clean and degrease in a closed container to remove impurities on the surface;

[0049] Trichloroethylene has low toxicity, is highly volatile, and can be deeply condensed, recovered, and recycled;

[0050] (2) Rinse: Ultrasonic clean once with 60-80℃ pure water, rinse twice, and clean once with deionized water (water resistance R>2MΩ);

[0051] (3) Drying: Dry in a vacuum oven at 130°C for 30 minutes, with the vacuum maintained at -0.095 to -0.1 MPa;

[0052] b. Detection

[0053] Portable X-ray spectrometer (Japanese Olympus portable X-ray fluorescence spectrometer, model: MIX5PRO, weight about 2 kg, lithium battery powered, for on-site detection) pre-tests the gold content of the primary gold to be processed one by one, and pre-grades it according to the content: those with a content less than 95% are pre-graded according to a 5% gradient; those with a content greater than 95% are pre-graded according to a 1% gradient. The operation process complies with the practical safety regulations of radiation instruments;

[0054] c. Classification

[0055] The gold raw materials are graded according to the predetermined gold content, and the amount V of primary gold raw materials with different gold contents is calculated according to the predetermined gold content. The primary gold raw materials are packed in batches within the range of V+ / -1%.

[0056] d. Merge and fusion (one-time homogenization)

[0057] 80-100 kg is taken as a unit and added into a tilting medium frequency induction crucible furnace for melting according to a predetermined ratio. After the melting is completed, it is cast into a graphite cavity mold to form a 3-5 kg ​​single ingot; the melting temperature is not more than 1120°C; depending on the primary gold impurity content, slag can be made to remove it when necessary; the impurity slag is properly preserved as a basis for the total amount; the slag making method is hot melt slag making, and the specific operation is: in an oxygen atmosphere, the easily oxidized low-density metal will become slag and float on the surface after hot melting, which can be removed by melting with sodium tetraborate, and lead oxide can be removed by soot blowing; the organic matter is oxidized and burned to form slag to be removed.

[0058] e. Granulation (secondary homogenization)

[0059] The combined raw materials are configured with a single furnace weight according to the preset balanced concentration content, and are remelted and mixed again under the protection of inert gas (argon or high-purity nitrogen). The remelting temperature is 1100-1150℃. The stopper rod of the low-pressure jet particle forming machine is turned on, and the fused metal solution flows in under natural gravity. Under the shearing action of the low-pressure jet (jet pressure 0.03-0.05MPa), the liquid metal flow is atomized into particles with a diameter of 0.05-0.15 mm, which are cooled and recovered in a water tank. Figure 1 shown.

[0060] f. Dry mixing (three times homogenization)

[0061] The supported particles are forced to be mechanically mixed (naturally mixed by overall tumbling in a closed barrel) to complete the third component homogenization; all the materials are filled with argon for protection, the speed is 15-20r / m, the mixing time is 20 minutes, the pressure is 1-5KPa, and the pressure is released and collected out of the cavity;

[0062] g. Detection

[0063] The sample was taken at 3-5 points in different zones and stratified, and the gold content was verified by a desktop spectrometer. The difference between the measured gold content in the particles and the predetermined gold content should be less than 0.3%. The verification of the dispersion was completed on a desktop spectrometer (SPECTROMAXx70, wavelength 160-670nm, channel 128, excitation mode: spark, charge coupled device: CCD, German Spark direct reading spectrometer).

[0064] h. Hot pressing fusion

[0065] The hot pressing fusion of qualified particles is a micro-fusion process in the super-solid phase region. The temperature is set 5-7°C below the solid-liquid phase line, and the particle full densification process is completed under the action of 30-50MPa continuous pressure; ( Figure 2-4 shown)

[0066] i. Surface treatment

[0067] According to user requirements, the surface can be deburred, ground and polished.

[0068] j. Terminal detection

[0069] The results of the entire homogenization process will be based on this measurement standard.

[0070] k. Weighing and storage

[0071] Routine operations, data entry, product warehousing.

[0072] The whole process is as follows:

[0073] Cleaning - testing - grading - merging and fusing - granulation - dry mixing - testing - hot pressing and fusing - surface treatment - terminal testing - weighing - product storage.

[0074] The gold products made by the above method have a gold dispersion of less than 0.1% according to terminal multi-point detection, which is much lower than the value of 0.3% obtained by ordinary hot melt method (the mainstream melting + mechanical stirring on the market).

[0075] Comparison of the effects of different homogenization methods

[0076] Using the same batch of recycled gold jewelry raw materials, 18K gold products were prepared by different methods. The obtained particles were sampled at 5 points by the method in "g. Detection" of Example 1 to detect the gold content of the particles. The preparation method and detection results of the particles are shown in Table 1.

[0077] Table 1

[0078] Serial number Preparation method Discreteness 1 The method described in Example 1 <0.1% 2 Refer to the method in Example 1, except that the "d. merging and fusion (one-time homogenization)" process is not performed. Multiple domain values ​​will appear 3 Refer to the method in Example 1, except that the "e. Granulation (secondary homogenization)" process is not performed. <0.15% 4 Refer to the method in Example 1, except that the "f. dry mixing (three times homogenization)" process is not performed <0.12%

[0079] As can be seen from Table 1, the preparation method of Example 1, i.e., three homogenization operations, produces a particle discreteness of <0.1%, while Method 2 does not perform the first homogenization, and the obtained particles have multiple domain values, which does not meet the homogenization requirements at all. Method 3 does not perform the second homogenization, and the particle discreteness is <0.15%, and Method 4 does not perform the third homogenization, and the particle discreteness is <0.12%, both lower than <0.1% of Example 1. Therefore, the homogenization control method described in the present invention can reduce the discreteness of gold and improve the homogenization level of gold through three homogenization operations.

[0080] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for controlling the homogenization of precious metals, characterized in that: The following steps are involved: a. Cleaning Degreasing: The precious metal raw materials are cleaned and degreased in a closed container with trichloroethylene or ultrasonic water-soluble degreasing agent to remove residual fat-soluble and separable impurities on the surface of the precious metal raw materials; Rinsing: Ultrasonic cleaning with 60-80℃ pure water once, rinse twice, and clean once with deionized water; Drying: vacuum heat drying method is adopted; b. Detection Pre-test the metal content of the primary metal raw materials one by one, and pre-grade them according to the metal content; c. Classification The metal content is determined by grade, and the predetermined value of the primary metal raw material is calculated according to the metal content of the final product. The primary metal raw material is packaged in batches according to the predetermined value range of + / -1%; d. Merge and fusion The mixture is melted according to a predetermined ratio, and after the melting is completed, it is cast into a graphite cavity mold to form a single ingot; thus achieving the first component homogenization; e. Granulation The single charge weight is configured by presetting the balanced metal content, the material embryos are combined, remelted and mixed again under the protection of inert gas, and the fused metal flow is atomized into 0.05-0.15 mm diameter particles under the shearing action of low-pressure jet injection, cooled and recovered; the second component homogenization is completed; f. Dry Mixing The particles are mechanically mixed to achieve the third component homogenization; g. Detection Determine the metal content by sampling in different areas and layers, and verify the difference between the measured metal content of the particles and the expected metal content; h. Hot pressing fusion The particles that pass the test are hot pressed and fused, and the particles are fully densified under heat and pressure. The precious metal is gold and / or silver.

2. A method for controlling the homogenization of precious metals according to claim 1, characterized in that: In the step a, during the rinsing operation, the resistance of the deionized water is R>2MΩ; during the drying operation, vacuum drying is performed at 130°C for 30 minutes, and the vacuum is maintained at -0.095 to -0.1MPa.

3. A method for controlling the homogenization of precious metals according to claim 1, characterized in that: In the step d, the amount of the required metal raw material is calculated in units of 80-100 kg, and the weight of a single ingot is 3-5 kg.

4. A method for controlling the homogenization of precious metals according to claim 1, characterized in that: In the step d, a tiltable medium frequency induction crucible furnace is added for fusion.

5. A method for controlling the homogenization of precious metals as claimed in claim 1, characterized in that: In the step d, depending on the impurity content of the metal raw material, slag can be formed to remove it. The slag forming method is hot-melt slag forming. The specific operation is: in an oxygen atmosphere, the easily oxidized low-density metal will float on the surface as slag after hot melting, which can be removed by melting with sodium tetraborate, and lead oxide can be removed by soot blowing; slag is formed by oxidation and burning of organic matter in an oxygen atmosphere to remove it; the impurity slag is properly stored as a basis for the total amount.

6. A method for controlling the homogenization of precious metals as claimed in claim 1, characterized in that: In the step e, the remelting temperature is 1100-1150° C., and the jet pressure is 0.03-0.05 MPa; and the inert gas is argon or high-purity nitrogen.

7. A method for controlling the homogenization of precious metals as claimed in claim 1, characterized in that: In the step f, the mechanical mixing is natural mixing in a closed barrel with overall tumbling; all the materials are filled with argon gas for protection, the speed is 15-20r / m, the mixing time is 20 minutes, the pressure is 1-5KPa, and the pressure is released and collected out of the cavity.

8. A method for controlling the homogenization of precious metals as claimed in claim 1, characterized in that: In step g, 3-5 points are sampled to determine the metal content, and the difference between the measured value and the predetermined metal content is less than 0.3%.

9. A method for controlling the homogenization of precious metals as claimed in claim 1, characterized in that: In the step h, the temperature is set to be 5-7°C below the solid-liquid phase line, and the pressure is maintained at 30-50 MPa for 30-60 seconds.

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