A method for rapidly dissolving rhodium powder

Abstract

The present invention relates to a method for rapid dissolution of rhodium powder, and mainly relates to the particle size of rhodium powder, the concentration and dosage of hydrochloric acid, and the selection of cosolvent type, dosage, and concentration. The method is specifically as follows: after the rhodium powder is reduced by hydrogen, it is ground to a particle size of less than 100 μm, hydrochloric acid is added and heated at 65°C-90°C, a cosolvent is added, hydrogen peroxide is added dropwise, and the mixture is dripped at a uniform speed for 2 hours. Stirring and dissolving are continued for 2-4 hours. The rhodium powder can be dissolved by more than 95% at one time and can be completely dissolved twice. The cosolvent is a rare earth metal element solution, including lanthanum, neodymium, cerium, samarium, gadolinium, dysprosium solution and a combination thereof. The method solves the problem of difficulty in dissolving rhodium powder, the dissolved solution has few impurities, and the rhodium content in the rhodium solution is obtained to be more than 7%. The subsequent synthesis of rhodium products does not require impurity removal, saving cost and time; it is processed at normal pressure, and the process flow is simple and easy to operate.

Description

Technical Field

[0001] The invention relates to a method for quickly dissolving rhodium powder, which is mainly used in the precious metal industry, and in particular relates to the quick dissolution of finished rhodium powder and rhodium powder produced in the recycling industry. Background Art

[0002] The dissolution of precious metal powders is crucial in the precious metal production industry, as the purification of materials is tedious and complex, which limits the output in batch production. Pure metal powders can dissolve quickly, which greatly meets the raw material requirements in production. Rhodium powder is the most difficult to dissolve among precious metal powders. It is very chemically inert and difficult to completely dissolve even after several months of dissolution in aqua regia. Therefore, the efficient, clean and rapid dissolution of rhodium powder is an important cutting-edge technology and a recognized problem in the scientific and technological development of the precious metals industry. Currently, there are several main methods for the dissolution of rhodium powder:

[0003] Alkali fusion method: Weigh a certain amount of rhodium powder into a crucible, add a certain proportion of sodium hydroxide, sodium peroxide and rhodium to mix, melt at high temperature, and dissolve the solid with acid after melting. However, this method is only suitable for dissolving a small amount of rhodium powder and is used in sample analysis. Large-scale applications in production are not easy to achieve because it will bring in a large amount of impurities and will need to be purified later.

[0004] Dry chlorination method: Rhodium powder and sodium chloride are mixed in proportion, and chlorine gas is introduced at high temperature. This method can be industrialized, but the dissolution time is very long, the processing volume is small, the dissolution rate is not high, multiple dissolutions are required, the equipment is difficult to seal, and chlorine gas is also relatively dangerous.

[0005] High-temperature fragmentation method: base metals need to be added to form an alloy and then chlorinated with aqueous solution. This method introduces a large amount of base metals, which has a great impact on the purity of the product.

[0006] Electrochemical dissolution method: In a hydrochloric acid system, the rhodium material is placed at the anode, and with the help of electrode reaction, the anode is oxidized and dissolved into the solution system. The advantage is that the dissolution process does not introduce new impurities, and the electrolyte can directly enter the subsequent refining process. The disadvantage is that the dissolution rate is slow.

[0007] Patent CN113087027A provides a method for dissolving rhodium powder. The specific steps for rhodium powder activation are: after mixing rhodium powder with pure water, add hydrazine hydrochloride solution under stirring, stir evenly, let it stand for 5-24 hours, and then filter. Filtration may be required multiple times. Then, 30-37% hydrochloric acid is added, heated to 80-100°C, and hydrogen peroxide is added. After the hydrogen peroxide is added, stirring and dissolving are continued for 2-8 hours. Heating and stirring are stopped, and filtering is performed to obtain a chlororhodium acid solution. Rhodium powder is very difficult to reduce. In this method, adding pure water during rhodium powder activation results in a poor reduction effect, resulting in a long and inefficient process. Multiple filtration and washing are required. Incomplete washing can cause the rhodium powder in the solution to be reduced to a solid state, significantly increasing the amount of waste liquid and the difficulty of handling, increasing costs, and easily causing rhodium powder loss. Hydrazine hydrochloride is highly hygroscopic, and improper storage can also reduce the reduction effect.

[0008] The above methods generally have problems such as poor operating environment, long dissolution time, high equipment requirements, small processing volume, and introduction of impurities. Summary of the Invention

[0009] In order to solve the above problems, the present invention provides a method for quickly dissolving rhodium powder.

[0010] The present invention is achieved by the following technical solutions, which are as follows:

[0011] (1) Grind the rhodium powder after hydrogen reduction to less than 100 μm, preferably 75 μm;

[0012] (2) The reduced rhodium powder is mixed with hydrochloric acid solution and co-solvent solution in a mass ratio of 100:500~1000:0.3~5 in a reaction flask, and the mass percentage concentration of the hydrochloric acid solution is 15%~40%;

[0013] (3) Stirring under normal pressure, heating to 65℃-90℃ and reflux;

[0014] (4) Use a peristaltic pump to add hydrogen peroxide solution to the reaction bottle. The amount of hydrogen peroxide solution is 1 / 4 of the amount of hydrochloric acid. The solution should be evenly added within 2 hours. Stir and dissolve for 2-4 hours. The mass concentration of hydrogen peroxide is 27%-35%.

[0015] (5) Stop heating and stirring to obtain a solution of chlororhodium acid;

[0016] (6) Filter the solution in the reaction flask and wash the filter cake with water. The remaining filter cake can be dissolved by repeating the above steps once or used as the raw material for dissolving the next batch of rhodium powder.

[0017] Furthermore, in step 2, the hydrochloric acid has a mass fraction of 15% to 40%; preferably, the mass percentage concentration of the hydrochloric acid is about 25%, which is not easy to volatilize too quickly when heated.

[0018] Furthermore, in step 3, due to the high volatility of hydrochloric acid, the temperature should not be too high; the heating temperature cannot be higher than 90° C., otherwise the hydrochloric acid will not be easily cooled and refluxed;

[0019] Furthermore, in step 4, the amount of hydrogen peroxide solution added is 1 / 4 of the amount of hydrochloric acid solution, and the amount of hydrogen peroxide added is evenly added within 2 hours. The mass concentration of hydrogen peroxide is 27%-35%.

[0020] Furthermore, in step 6, the filtrate is a chlororhodium acid solution with few impurities, and the filter residue can be dissolved again or inserted into the raw material for dissolving the next batch of rhodium powder.

[0021] The present invention has the following beneficial effects:

[0022] (1) Rhodium powders produced by different manufacturers have different freshness and particle sizes, resulting in different dissolution effects. Reducing the freshness by hydrogen and grinding the powder to less than 100 μm increases the contact area of ​​the rhodium powder and increases the dissolution rate.

[0023] (2) The addition of a co-solvent greatly increases the dissolution rate of rhodium powder. Several kilograms of rhodium powder can be dissolved in one day. More than 95% of the rhodium powder can be dissolved in one treatment and all of it can be dissolved in two treatments. The purity of the resulting chlororhodium acid solution is more than 99.96%, and the content of a single metal impurity is less than 3 ppm.

[0024] (3) The reaction is carried out under normal pressure, the reaction temperature is not very high, the container does not need to be sealed, there is no pressure, and the operating conditions are simple;

[0025] (4) No dangerous chlorine gas is used, which greatly reduces the risk. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with 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.

[0027] Example 1, comparative experiment on the effect of particle size:

[0028] (1) Weigh 2 kg of rhodium powder and reduce it with hydrogen in a tube furnace;

[0029] (2) After the reduction, 1 kg of the rhodium powder was not ground, and 1 kg of the rhodium powder was placed on a grinder and ground to 75 μm;

[0030] (3) Transfer the unground and ground rhodium powders to two 10 L reaction bottles, add 5.7 L of hydrochloric acid (25%) and 4 g of lanthanum chloride solution (3 ppm lanthanum concentration) to each bottle, start stirring, and slowly heat to 75 °C and reflux.

[0031] (4) Use a peristaltic pump to uniformly add 1.4 L of hydrogen peroxide to the reaction bottle, and drip it evenly within 2 hours. Continue stirring and dissolving for 2 hours. The mass concentration of hydrogen peroxide is 30%.

[0032] (5) Stop stirring and heating, and filter. Rinse the filter cake five times with 1000 ml of water, and transfer the washing liquid to the filtrate. The ground filter cake yields 8.2 L of filtrate, and the unground filter cake yields 8.15 L of filtrate. After testing, the rhodium powder ground to 75 μm yields about 116.63 g / L of rhodium, with a rhodium content of 9.88%. The unground filter cake yields about 12.63 g / L of rhodium, with a rhodium content of 1.07%. Dry the filter cakes separately and weigh the remaining mass. The remaining mass of the filter cake ground to 75 μm is 4%, while the remaining mass of the unground filter cake is 90%, which is much less than that of the unground filter cake. The remaining filter cake of the ground filter cake can be completely dissolved after another dissolution. The remaining solids of the unground filter cake remain after another dissolution.

[0033] Example 2, comparative experiment with and without adding co-solvent:

[0034] (1) Weigh 2 kg of rhodium powder and reduce it with hydrogen in a tube furnace;

[0035] (2) The reduced rhodium powder is placed on a grinder and ground to 75 μm;

[0036] (3) Rhodium powder was divided into two 1 kg portions and transferred to two 10 L reaction bottles. 5.7 L of hydrochloric acid (25%) was added to each of the two bottles. 4 g of lanthanum chloride solution (3 ppm lanthanum concentration) was added to the first bottle, while no lanthanum chloride solution was added to the second bottle. Stirring was started and the temperature was slowly raised to 75 °C and refluxed.

[0037] (4) Use a peristaltic pump to uniformly add 1.4 L of hydrogen peroxide to the reaction bottle and drip it evenly within 2 hours. Continue stirring and dissolving for 2 hours. The mass concentration of hydrogen peroxide is 30%.

[0038] (5) Stop stirring and heating, and filter. Rinse the filter cake five times with 1000 ml of water, and transfer the washing liquid into the filtrate. When a cosolvent is added to No. 1, 8.25 L of filtrate is obtained. After testing, the rhodium content is about 115.64 g / L, the rhodium content is 9.80%, the solubility of rhodium powder is 95.4%, the purity of chlororhodic acid is 99.96%, and the single impurity is 3 ppm. When no cosolvent is added, 8.2 L of filtrate is obtained. The rhodium content in the filtrate is about 20.73 g / L, the rhodium content is 1.76%, and the solubility of rhodium powder is 17%, which is much lower than the solubility rate when a cosolvent is added.

[0039] Example 3, comparative experiment using different co-solvents:

[0040] (1) Weigh 2 kg of rhodium powder and reduce it with hydrogen in a tube furnace;

[0041] (2) The reduced rhodium powder is placed on a grinder and ground to 75 μm;

[0042] (3) Divide the rhodium powder into four 500g portions and transfer them to four 5L reaction bottles respectively. Add 3L of hydrochloric acid (25%) to each of the four 5L reaction bottles. Add 3g of the co-solvent lanthanum chloride solution (3ppm lanthanum concentration) to bottle No. 1, add 3g of the co-solvent samarium chloride solution (3ppm samarium concentration) to bottle No. 2, add 3g of the co-solvent cerium chloride solution (3ppm cerium concentration) to bottle No. 3, and add 3g of the co-solvent dysprosium chloride solution (3ppm dysprosium concentration) to bottle No. 4. Start stirring and slowly heat the mixture to 75°C and reflux.

[0043] (4) Use a peristaltic pump to uniformly add 0.75 L of hydrogen peroxide to the reaction bottle and drip it evenly within 2 hours. Continue stirring and dissolving for 2 hours. The mass concentration of hydrogen peroxide is 30%.

[0044] (5) Stop stirring and heating, filter, rinse the filter cake with 500 ml of water 5 times, and transfer the washing liquid to the filtrate. 4.20 L of filtrate was obtained from No. 1. After testing, the rhodium content was about 114.28 g / L, and the rhodium content was 9.69%. 4.25 L of filtrate was obtained from No. 2. The rhodium content in the filtrate was about 112.70 g / L, and the rhodium content was 9.55%. 4.20 L of filtrate was obtained from No. 3. The rhodium content in the filtrate was about 113.93 g / L, and the rhodium content was 9.65%. 4.22 L of filtrate was obtained from No. 4. The rhodium content in the filtrate was about 113.51 g / L, and the rhodium content was 9.62%. The dissolution rate of rhodium powder in one step was: 96.0% for No. 1, 95.8% for No. 2, 95.7% for No. 3, and 95.8% for No. 4. After testing, the purity of chlororhodium acid was all above 99.96%, and other impurities were below 2 ppm. After the filter cake is dried, it is weighed and dissolved for the next time. All of No. 1 to No. 4 can be dissolved. In addition, experiments were also conducted on other rare earth elements such as neodymium and gadolinium, which also have a solubility-promoting effect, and the one-time dissolution rate can reach 95%. However, lanthanum chloride still has the best effect.

[0045] Example 4, comparative experiment of different concentrations of cosolvent:

[0046] (1) Weigh 2 kg of rhodium powder and reduce it with hydrogen in a tube furnace;

[0047] (2) The reduced rhodium powder is placed on a grinder and ground to 75 μm;

[0048] (3) Divide the rhodium powder into two 1kg portions and transfer them to two 10L reaction bottles. Add 5.7L of hydrochloric acid (25%) and 5g of cosolvent, respectively. Use 10ppm lanthanum chloride solution and 3ppm lanthanum chloride solution as cosolvents, respectively. Start stirring and slowly heat to 75℃ and reflux. These are No. 1 and No. 2 respectively.

[0049] (4) Use a peristaltic pump to uniformly add 1.43 L of hydrogen peroxide to the reaction bottle and drip it evenly within 2 hours. Continue stirring and dissolving for 2-4 hours. The mass concentration of hydrogen peroxide is 30%.

[0050] (5) Stop stirring and heating, and filter. Rinse the filter cake 5 times with 1000 ml of water, and transfer the washing liquid into the filtrate. 8.2 L of filtrate was obtained in No. 1. After testing, the rhodium content was about 116.88 g / L, the rhodium content was 9.82%, and the rhodium powder dissolution rate was 95.8%. 8.26 L of filtrate was obtained in No. 2. The rhodium content in the filtrate was about 116.10 g / L, the rhodium content was 9.84%, and the rhodium powder dissolution rate was 95.9%. The purity of chlororhodic acid was greater than 99.96%, and other impurities were all below 3 ppm. There was not much difference in the rhodium powder dissolution rate. In order to use a small amount of co-solvent, a 3 ppm co-solvent solution was selected.

[0051] Example 5, comparative experiment of different co-solvent combinations:

[0052] (1) Weigh 2 kg of rhodium powder and reduce it with hydrogen in a tube furnace;

[0053] (2) The reduced rhodium powder is placed on a grinder and ground to 75 μm;

[0054] (3) Divide the rhodium powder into two 1 kg portions and transfer them to two 10 L reaction bottles. Add 5.71 L of hydrochloric acid (25%) to each of them. Add 1.7 g of the co-solvent lanthanum chloride solution (3 ppm lanthanum solution) and 1.7 g of the co-solvent cerium chloride solution (3 ppm cerium solution) to the No. 1 reaction bottle. Add 1.7 g of the co-solvent samarium chloride solution (3 ppm samarium solution) and 1.7 g of the co-solvent neodymium chloride solution (3 ppm neodymium solution) to the No. 2 reaction bottle. Start stirring and slowly heat the mixture to 75 °C and reflux.

[0055] (4) Use a peristaltic pump to uniformly add 1.42 L of hydrogen peroxide to the reaction bottle and drip it evenly within 2 hours. Continue stirring and dissolving for 2 hours. The mass concentration of hydrogen peroxide is 30%.

[0056] (5) Stop stirring and heating, filter, rinse the filter cake with 1000 ml of water 5 times, and transfer the washing liquid into the filtrate. No. 1 obtained 8.15 L of filtrate. After testing, the rhodium content was about 117.55 g / L, the rhodium content was 9.96%, and the rhodium powder dissolution rate was 95.8%. No. 2 obtained 8.24 L of filtrate. The rhodium content in the filtrate was about 116.5 g / L, the rhodium content was 9.87%, and the rhodium powder dissolution rate was 96.0%. The purity of chlororhodic acid was greater than 99.96%, and other impurities were all below 3 ppm. The rhodium powder dissolution rate was basically the same. In addition, other types of co-solvents were mixed and used, and the effect difference was not obvious, indicating that rare earth metal elements have a certain solubility effect on the dissolution of rhodium powder.

[0057] 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 principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for rapidly dissolving rhodium powder, characterized in that: The steps include: (1) Grind the rhodium powder after hydrogen reduction to less than 100 μm; (2) The reduced rhodium powder is mixed with a hydrochloric acid solution and a co-solvent solution in a mass ratio of 100:500-1000:0.3-5 in a reaction flask. The mass percentage concentration of the hydrochloric acid solution is 15%-40%. The co-solvent is a hydrochloric acid solution of a rare earth metal element. (3) Stirring under normal pressure, heating to 65℃-90℃ and reflux; (4) Add hydrogen peroxide solution dropwise. The amount of hydrogen peroxide solution is 1 / 4 of the amount of hydrochloric acid solution. Add the solution evenly within 2 hours. Continue stirring and dissolving for 2-4 hours. The mass concentration of hydrogen peroxide solution is 27%-35%. (5) Stop heating and stirring, and the resulting solution is chlororhodium acid; (6) Filter the solution in the reaction flask and wash the filter cake with water. The remaining filter cake can be dissolved by repeating the above steps once or used as the raw material for dissolving the next batch of rhodium powder.

2. The method according to claim 1, characterized in that In step 1, the rhodium powder after hydrogen reduction is ground to a particle size of less than 75 μm.

3. The method according to claim 1, characterized in that In step 2, the mass percentage concentration of the hydrochloric acid solution is 25%.

4. The method according to claim 1, wherein In step 2, the co-solvent solution is selected from hydrochloric acid solutions of lanthanum, neodymium, cerium, samarium, gadolinium, dysprosium, and combinations thereof.

5. The method according to claim 1, wherein In step 2, the concentration of the co-solvent solution is 3ug / ml~10ug / ml.

6. The method according to claim 1, characterized in that In step 4, the reaction time is 4-6 hours.

7. The method according to claim 1, characterized in that In step 6, the solution is cooled and then filtered.

8. The method according to claim 1, characterized in that Rhodium powder can be dissolved by more than 95% in one time and completely dissolved in two times; the purity of the obtained chlororhodium acid solution is greater than 99.96%, and the impurities are less than 3ppm.