Determination method of rhodium content in platinum-rhodium alloy

Abstract

The invention provides a method for measuring the content of rhodium in a platinum-rhodium alloy, which comprises the following steps: completely dissolving the platinum-rhodium alloy, then mixing and reacting with nitrite, adjusting the pH value, and carrying out solid-liquid separation to obtain a platinum-rhodium mixed solution; and mixing the platinum-rhodium mixed solution with a coordination precipitator and a polar solvent in sequence, carrying out solid-liquid separation to obtain rhodium precipitate, and calculating the rhodium content in the platinum-rhodium alloy according to the mass of the rhodium precipitate. According to the determination method, measurement errors caused by introduction of metal impurities in the platinum-rhodium alloy are avoided, trace residues of rhodium precipitates in the solution and co-precipitation of other interference metals are also avoided, procedures and used reagents are simple, operation is safe, efficiency is high, use of high-cost and complex precipitants such as metal elementary substances or cobalt hexammine nitrate in the prior art is avoided, and the method is suitable for large-scale popularization and application. Rhodium precipitation is complete, the determination result is accurate, the relative standard deviation is especially smaller than 0.21%, meanwhile, dependence on expensive analysis equipment is not needed, and the method has great application value.

Description

Technical Field

[0001] The invention belongs to the technical field of metal material testing, and relates to a method for determining a precious metal element, in particular to a method for determining the rhodium content in a platinum-rhodium alloy. Background Art

[0002] The precious metal rhodium and its alloys and compounds are widely used in the fields of petrochemicals, glass fiber, electronic electroplating, green catalysis and jewelry. In the process of rhodium metal resource application and recycling, its weight percentage needs to be accurately measured.

[0003] At present, the main methods for detecting the rhodium content in rhodium alloys and compounds are spectroscopy, titration, and weight methods. The spectroscopy method generally dissolves the rhodium alloy or compound and uses a spectrometer to determine the rhodium content in the solution, such as atomic absorption spectroscopy (AAS), X-ray fluorescence spectroscopy (XRF), inductively coupled plasma atomic emission spectroscopy (ICP-AES), etc., such as CN111999150A, CN115452807A, CN117054401A, etc., but the spectroscopy method often relies on expensive analytical equipment, the result analysis is more complicated, and there are problems such as element interference. The titration method usually has the problem of endpoint judgment, and the error of human judgment is large. The weight method mainly uses the method of liquid phase reduction or coordination compound to calculate the rhodium content through the precipitation of rhodium element or rhodium complex. The weight method has a wide measurement range, high measurement accuracy, and low equipment dependence. It is a widely recognized measurement method.

[0004] The industry standard method YS / T 561-2009 (Chemical analysis of precious metal alloys - determination of rhodium content in platinum-rhodium alloys) uses hexaammine cobalt nitrate and rhodium to generate a complex salt precipitation for determination. This method is generally applicable to samples with a single system, but not suitable for the analysis of samples with a high impurity content. In addition, the preparation process of the raw and auxiliary material hexaammine cobalt nitrate requires the use of explosive chemicals, which has the disadvantages of complex preparation process and low yield. The rhodium complex has a certain solubility in the solution, and the precipitation cannot be guaranteed to be complete. CN113075200A discloses a method for determining the content of platinum and rhodium in a platinum-rhodium mixed solution. The platinum-rhodium mixed solution is repeatedly precipitated and calcined with a saturated ammonium chloride solution to first obtain sponge platinum, then reduced with magnesium powder to obtain rhodium precipitate, and then calcined and reduced with hydrogen to obtain a single rhodium substance, which is weighed and calculated separately. The process of this method is relatively complicated, and there are problems such as the metal reducing agent is easily wrapped in the rhodium precipitate, the ammonium chloride precipitation separation of platinum easily leads to rhodium co-precipitation, and multiple rhodium dissolutions lead to rhodium evaporation loss.

[0005] Therefore, based on the deficiencies of the prior art, the present invention provides a method for determining rhodium content based on a precipitation method with high measurement accuracy and simplified procedures. Summary of the invention

[0006] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a method for determining the rhodium content in a platinum-rhodium alloy, which determines the rhodium content in the platinum-rhodium alloy based on the weight method, effectively eliminates the interference of impurity metals in the platinum-rhodium alloy, and has high determination accuracy.

[0007] To achieve this object, the present invention adopts the following technical solutions: The present invention provides a method for determining the rhodium content in a platinum-rhodium alloy, the method comprising the following steps: (1) completely dissolving the platinum-rhodium alloy to obtain a metal chloric acid solution; (2) mixing the metal chlorate solution obtained in step (1) with nitrite, adjusting the pH, standing for reaction, and then performing a first solid-liquid separation to obtain a platinum-rhodium mixed solution; (3) The platinum-rhodium mixed solution obtained in step (2) is mixed with a coordination precipitant for precipitation, and then mixed with a polar solvent. After standing for precipitation, a second solid-liquid separation is performed to obtain a rhodium precipitate. The rhodium precipitate is dried to a constant weight, and the rhodium content in the platinum-rhodium alloy is calculated based on the mass of the rhodium precipitate.

[0008] The determination method provided by the present invention dissolves the platinum-rhodium alloy, and after obtaining the solution, first uses nitrite to react the impurity metal ions in the platinum-rhodium alloy such as iron, copper and nickel in the solution to generate feasible nitroso complexes to form precipitation, separate and remove, and eliminate the interference of subsequent impurity metals; then uses a coordination precipitant to form a rhodium compound into a rhodium complex hexanitrorhodate (potassium hexanitrorhodate or ammonium hexanitrorhodate) to selectively precipitate rhodium, at this time, the platinum compound is in a dissolved state, and then by adding a polar solvent, the solubility difference of the rhodium complex in the solution and the polar solvent is used to completely precipitate the rhodium complex remaining in the solution, and finally all rhodium is converted into a rhodium complex precipitate and separated, and the rhodium content in the platinum-rhodium alloy is calculated by the total mass of the final rhodium complex precipitate. The determination method of the present invention has simple procedures and reagents, safe operation, high efficiency, avoids the use of high-cost and complex precipitants such as metal elements or hexaammine cobalt nitrate in the prior art, platinum and rhodium are completely separated, rhodium is completely precipitated, loss is small, and the determination result is accurate. At the same time, it does not need to rely on expensive analytical equipment, and has great application value.

[0009] Preferably, the dissolving method in step (1) comprises: mixing the platinum-rhodium alloy powder with a mixed acid, performing microwave digestion, and then fixing the volume with water.

[0010] Preferably, the mixed acid comprises hydrochloric acid and hydrogen peroxide.

[0011] In the present invention, the mass concentration of the hydrochloric acid is 36%.

[0012] Preferably, the volume ratio of hydrochloric acid to hydrogen peroxide is (1-3):1, for example, 1:1, 1.5:1, 2:1, 2.5:1 or 3:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0013] Preferably, the mass ratio of the platinum-rhodium alloy powder to the mixed acid is (1-50):400, for example, it can be 1:400, 5:400, 10:400, 20:400, 30:400, 40:400 or 50:400, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0014] Preferably, the temperature of the microwave digestion is 100-200°C, for example, it can be 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C or 200°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0015] Preferably, the microwave digestion time is 0.5-2 days, for example, 0.5 days, 1 day, 1.5 days or 2 days, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0016] Preferably, the mass ratio of the mixed acid to water is (1-10):50, for example, 1:50, 2:50, 3:50, 4:50, 5:50, 6:50, 7:50, 8:50, 9:50 or 10:50, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0017] Preferably, the mass ratio of the nitrite to the platinum-rhodium alloy in step (2) is (10-50):1, for example, it can be 10:1, 15:1, 20:1, 25:1, 30:1, 35:1, 40:1, 45:1 or 50:1, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0018] Preferably, the nitrite in step (2) comprises sodium nitrite.

[0019] Preferably, the mixing temperature in step (2) is 50-90°C, for example, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C or 90°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0020] Preferably, the pH value in step (2) is adjusted to 6-10, for example, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5 or 10, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0021] Preferably, the adjusting agent used for adjusting the pH in step (2) comprises any one of sodium carbonate, sodium hydroxide or sodium bicarbonate, or a combination of at least two of them. Typical but non-limiting combinations include a combination of sodium carbonate and sodium hydroxide, a combination of sodium hydroxide and sodium bicarbonate, a combination of sodium carbonate and sodium bicarbonate, or a combination of sodium carbonate, sodium hydroxide and sodium bicarbonate.

[0022] Preferably, the standing reaction time in step (2) is 0.5-3 h, for example, 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h or 3 h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0023] Preferably, in step (2), the first solid-liquid separation is performed using a glass frit funnel.

[0024] Preferably, the coordination precipitant in step (3) comprises any one of ammonium chloride, potassium chloride, potassium carbonate, ammonium carbonate or potassium hydroxide, or a combination of at least two thereof. Typical but non-limiting combinations include a combination of ammonium chloride and potassium chloride, a combination of potassium chloride and potassium carbonate, a combination of potassium carbonate and ammonium carbonate, a combination of ammonium carbonate and potassium hydroxide, a combination of ammonium chloride, potassium chloride and potassium carbonate, or a combination of potassium carbonate, ammonium carbonate and potassium hydroxide.

[0025] Preferably, the mass ratio of the coordination precipitant to the platinum-rhodium alloy in step (3) is (10-50):1, for example, it can be 10:1, 15:1, 20:1, 25:1, 30:1, 35:1, 40:1, 45:1 or 50:1, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0026] Preferably, the precipitation temperature in step (3) is 60-100°C, for example, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C or 100°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0027] Preferably, the polar solvent in step (3) comprises any one of anhydrous ethanol, acetonitrile or methanol, or a combination of at least two thereof. Typical but non-limiting combinations include a combination of anhydrous ethanol and acetonitrile, a combination of acetonitrile and methanol, a combination of anhydrous ethanol and methanol, or a combination of anhydrous ethanol, acetonitrile and methanol.

[0028] Preferably, the volume ratio of the polar solvent to the platinum-rhodium mixed solution in step (3) is 1:(5-20), for example, it can be 1:5, 1:8, 1:10, 1:12, 1:15, 1:18 or 1:20, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0029] Preferably, the temperature of the static precipitation in step (3) is 0-20°C, for example, 0°C, 2°C, 5°C, 8°C, 10°C, 12°C, 15°C, 18°C ​​or 20°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0030] Preferably, the static sedimentation time in step (3) is 0.5-3 h, for example, 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h or 3 h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0031] Preferably, the drying temperature in step (3) is 70-150°C, for example, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C or 150°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0032] Preferably, the calculation formula of the rhodium content in step (3) is as follows:

[0033] in, oh is the rhodium content in the platinum-rhodium alloy; m 1 is the weight of rhodium precipitate, in g; m is the weight of platinum-rhodium alloy, in g; α Factor for converting rhodium precipitate into rhodium element.

[0034] In the present invention, when the rhodium is precipitated as a rhodium complex potassium hexanitrorhodate, α is 0.20736; when rhodium is precipitated as rhodium complex ammonium hexanitrorhodate, α It is 0.23761.

[0035] As a preferred technical solution of the determination method provided by the present invention, the determination method comprises the following steps: (1) mixing platinum-rhodium alloy powder with a mixed acid for microwave digestion, wherein the mixed acid comprises hydrochloric acid and hydrogen peroxide, wherein the volume ratio of the hydrochloric acid to the hydrogen peroxide is (1-3):1, and the mass ratio of the platinum-rhodium alloy powder to the mixed acid is (1-50):400. The microwave digestion temperature is 100-200° C., and the microwave digestion time is 0.5-2 days. After microwave digestion, the digested solution is fixed to volume with water, wherein the mass ratio of the mixed acid to water is (1-10):50, to obtain a metal chloride solution; (2) mixing the metal chlorate solution obtained in step (1) with sodium nitrite, wherein the mass ratio of the sodium nitrite to the platinum-rhodium alloy powder is (10-50):1, the mixing temperature is 50-90° C., adding a pH adjuster to adjust the pH to 6-10, wherein the pH adjuster comprises any one of sodium carbonate, sodium hydroxide or sodium bicarbonate or a combination of at least two thereof, standing the reaction for 0.5-3 h, and the impurity metals in the platinum-rhodium alloy generate nitroso complex precipitation, and then using a glass sand core funnel for solid-liquid separation to obtain a platinum-rhodium mixed solution; (3) mixing the platinum-rhodium mixed solution obtained in step (2) with a coordination precipitant, wherein the coordination precipitant includes any one of ammonium chloride, potassium chloride, potassium carbonate, ammonium carbonate or potassium hydroxide or a combination of at least two thereof, and the mass ratio of the coordination precipitant to the platinum-rhodium alloy powder is (10-50):1, and performing coordination reaction at 60-100°C to obtain a mixture; and then mixing the mixture with a polar solvent, wherein the polar solvent includes any one of anhydrous ethanol, acetonitrile or methanol or a combination of at least two thereof, and the volume ratio of the polar solvent to the platinum-rhodium mixed solution is 1:(5-20), and after mixing, standing and settling at 0-20°C for 0.5-3h, and after the standing and settling is completed, performing solid-liquid separation to obtain a precipitate, and drying the precipitate to constant weight at a drying temperature of 70-150°C to obtain a rhodium precipitate; (4) Weigh the rhodium precipitate obtained in step (3), and calculate the rhodium content in the platinum-rhodium alloy based on the mass of the rhodium precipitate. The calculation formula is as follows:

[0036] in, oh is the rhodium content in the platinum-rhodium alloy; m 1 is the weight of rhodium precipitate, in g; m is the weight of platinum-rhodium alloy, in g; α Factor for converting rhodium precipitate into rhodium element.

[0037] Compared with the prior art, the present invention has the following beneficial effects: The determination method of the present invention avoids the measurement error introduced by metal impurities such as copper and iron in the platinum-rhodium alloy, and also avoids trace residues of rhodium precipitate in the solution and co-precipitation of other interfering metals. The process and reagents used are simple, the operation is safe, and the efficiency is high. The use of high-cost and complex precipitants such as metal elements or hexaamminecobalt nitrate in the prior art is avoided. The rhodium precipitation is complete, the determination result is accurate, and the relative standard deviation is especially less than 0.21%. At the same time, there is no need to rely on expensive analytical equipment, and the method has great application value. DETAILED DESCRIPTION

[0038] The technical solution of the present invention is further illustrated below through specific implementation methods. Embodiment 1

[0039] This embodiment provides a method for determining the rhodium content in a platinum-rhodium alloy, the method comprising the following steps: (1) 0.2 g of platinum-rhodium alloy powder was placed in a microwave digestion apparatus, and a mixed acid of 15 mL of hydrochloric acid and 5 mL of hydrogen peroxide was added, wherein the volume ratio of hydrochloric acid to hydrogen peroxide was 3:1, and the mass ratio of platinum-rhodium alloy powder to mixed acid was 1:126. The mixture was heated to 160° C. for digestion until the material was completely dissolved, and then 300 mL of pure water was added to make up the volume, wherein the mass ratio of mixed acid to pure water was 1:12, to obtain a metal chloride solution; (2) Weigh 8 g of sodium nitrite and add it to a metal chloric acid solution, with the mass ratio of sodium nitrite to platinum-rhodium alloy powder being 40:1. Heat to 50° C., stir, add sodium hydroxide to adjust the pH to 8, and allow to react for 3 h. (3) Filter the solution after the reaction using a G4 glass sand core funnel to remove metal impurities, repeat this step twice until no precipitate remains in the solution to obtain a platinum-rhodium metal filtrate; (4) Weigh 10 g of potassium chloride as a coordination precipitant, add the platinum-rhodium metal filtrate, the mass ratio of the coordination precipitant to the platinum-rhodium alloy powder is 50:1, heat to 90° C. until no more precipitate continues to precipitate, and then cool to room temperature; (5) Measure 20 mL of polar solvent anhydrous ethanol and add it to the solution of step (4), the volume ratio of the polar solvent to the platinum-rhodium mixed solution is 1:20, stir evenly, control the solution temperature at 0°C, and let it stand for 0.5 h; (6) All materials in step (5) are filtered to obtain a precipitate, which is placed in an oven at 150° C. and dried to constant weight. The weight of the rhodium precipitate after drying is weighed. The composition of the rhodium precipitate is potassium hexanitrorhodate. The rhodium content is calculated according to the formula:

[0040] in, oh is the rhodium content in the platinum-rhodium alloy; m 1is the weight of rhodium precipitate, in g; m is the weight of platinum-rhodium alloy, in g; 0.20736 is the factor for converting rhodium precipitate into rhodium. Embodiment 2

[0041] This embodiment provides a method for determining the rhodium content in a platinum-rhodium alloy, the method comprising the following steps: (1) 0.2 g of platinum-rhodium alloy powder was placed in a microwave digestion apparatus, and a mixed acid of 20 mL of hydrochloric acid and 15 mL of hydrogen peroxide was added, wherein the volume ratio of hydrochloric acid to hydrogen peroxide was 1.3:1, and the mass ratio of platinum-rhodium alloy powder to mixed acid was 1:228. The mixture was heated at 200° C. for digestion until the material was completely dissolved, and then 300 mL of pure water was added to make up the volume, wherein the mass ratio of mixed acid to pure water was 1:6.6, to obtain a metal chloride solution; (2) Weigh 3 g of sodium nitrite and add it to a metal chloric acid solution, with the mass ratio of sodium nitrite to platinum-rhodium alloy powder being 15:1. Heat to 85°C, stir, add sodium hydroxide to adjust the pH to 10, and allow to react for 1 hour. (3) Filter the solution after the reaction using a G4 glass sand core funnel to remove metal impurities, and repeat this step 4 times until no precipitate remains in the solution to obtain a platinum-rhodium metal filtrate; (4) Weigh 4 g of potassium hydroxide as a coordination precipitant, add the platinum-rhodium metal filtrate, the mass ratio of the coordination precipitant to the platinum-rhodium alloy powder is 20:1, heat to 100° C. until no more precipitate continues to precipitate, and then cool to room temperature; (5) Measure 20 mL of polar solvent anhydrous ethanol and add it to the solution of step (4), the volume ratio of the polar solvent to the platinum-rhodium mixed solution is 1:15, stir evenly, control the solution temperature at 5°C, and let it stand for 2 hours; (6) All materials in step (5) are filtered to obtain a precipitate, which is placed in an oven at 100° C. and dried to constant weight. The weight of the rhodium precipitate after drying is weighed. The composition of the rhodium precipitate is potassium hexanitrorhodate. The rhodium content is calculated according to the formula:

[0042] in, oh is the rhodium content in the platinum-rhodium alloy; m 1 is the weight of rhodium precipitate, in g; m is the weight of platinum-rhodium alloy, in g; 0.20736 is the factor for converting rhodium precipitate into rhodium. Embodiment 3

[0043] This embodiment provides a method for determining the rhodium content in a platinum-rhodium alloy, the method comprising the following steps: (1) 0.2 g of platinum-rhodium alloy powder was placed in a microwave digestion apparatus, and a mixed acid of 20 mL of hydrochloric acid and 10 mL of hydrogen peroxide was added, wherein the volume ratio of hydrochloric acid to hydrogen peroxide was 2:1, and the mass ratio of platinum-rhodium alloy powder to mixed acid was 1:192. The mixture was heated to 120° C. for digestion until the material was completely dissolved, and then 300 mL of pure water was added to make up the volume, wherein the mass ratio of mixed acid to pure water was 1:7.8, to obtain a metal chloride solution; (2) Weigh 10 g of sodium nitrite and add it to a metal chloric acid solution, with the mass ratio of sodium nitrite to platinum-rhodium alloy powder being 50:1. Heat to 90° C., stir, add sodium hydroxide to adjust the pH to 6, and allow to react for 0.5 h. (3) Filter the solution after the reaction using a G4 glass sand core funnel to remove metal impurities, repeat this step twice until no precipitate remains in the solution to obtain a platinum-rhodium metal filtrate; (4) Weigh 2 g of potassium chloride as a coordination precipitant, add the platinum-rhodium metal filtrate, the mass ratio of the coordination precipitant to the platinum-rhodium alloy powder is 10:1, heat to 60° C. until no more precipitate continues to precipitate, and then cool to room temperature; (5) Measure 20 mL of polar solvent anhydrous ethanol and add it to the solution of step (4), the volume ratio of the polar solvent to the platinum-rhodium mixed solution is 1:15, stir evenly, control the solution temperature at 20°C, and let it stand for 3 hours; (6) All materials in step (5) are filtered to obtain a precipitate, which is placed in an oven at 70° C. and dried to constant weight. The weight of the rhodium precipitate after drying is weighed. The composition of the rhodium precipitate is potassium hexanitrorhodate. The rhodium content is calculated according to the formula: in, oh is the rhodium content in the platinum-rhodium alloy; m 1 is the weight of rhodium precipitate, in g; m is the weight of platinum-rhodium alloy, in g; 0.20736 is the factor for converting rhodium precipitate into rhodium. Embodiment 4

[0044] This embodiment provides a method for determining the rhodium content in a platinum-rhodium alloy. Compared with Example 1, the coordination precipitant in step (4) is replaced by ammonium chloride by the mass of potassium chloride, and the rest is the same as Example 1. The composition of the rhodium precipitate is ammonium hexanitrorhodate. The rhodium content is calculated according to the formula, which is as follows:

[0045] in, oh is the rhodium content in the platinum-rhodium alloy; m 1 is the weight of rhodium precipitate, in g; mis the weight of platinum-rhodium alloy, in g; 0.23761 is the factor for converting rhodium precipitate into rhodium. Embodiment 5

[0046] This embodiment provides a method for determining the rhodium content in a platinum-rhodium alloy. Compared with Embodiment 1, the polar solvent in step (5) is replaced by an equal volume of anhydrous ethanol with acetonitrile, and the rest is the same as Embodiment 1. Embodiment 6

[0047] This embodiment provides a method for determining the rhodium content in a platinum-rhodium alloy. Compared with Embodiment 1, the pH value in the control step (2) is adjusted to 11, and the rest is the same as Embodiment 1. Embodiment 7

[0048] This embodiment provides a method for determining the rhodium content in a platinum-rhodium alloy. Compared with Embodiment 1, the heating temperature in step (4) is controlled to be 50° C., and the rest is the same as Embodiment 1. Comparative Example 1

[0049] This comparative example provides a method for determining the rhodium content in a platinum-rhodium alloy. Compared with Example 1, sodium nitrite is not added in step (2), and the rest is the same as Example 1. Comparative Example 2

[0050] This comparative example provides a method for determining the rhodium content in a platinum-rhodium alloy. Compared with Example 1, no polar solvent is added in step (5), and the rest is the same as Example 1. Comparative Example 3

[0051] This comparative example provides a method for determining the rhodium content in a platinum-rhodium alloy. Compared with Example 1, the coordination precipitant in step (4) is replaced by sodium chloride by an amount equal to that of potassium chloride, and the rest is the same as Example 1. Comparative Example 4

[0052] This comparative example provides a method for determining the rhodium content in a platinum-rhodium alloy. Compared with Example 1, the filtering in step (3) is not performed, and the rest is the same as Example 1. Comparative Example 5

[0053] This comparative example provides a method for determining the rhodium content in a platinum-rhodium alloy. According to the Chemical Analysis Method for Platinum-Rhodium Alloys, GB1485-79, the hexaammine nitrate cobalt complex precipitation method is used for determination. The specific steps are as follows: (1) According to step (1) of Example 1, the platinum-rhodium alloy powder is completely dissolved to obtain a sample solution; (2) The sample solution is heated to 60°C, sodium nitrite is added, and the solution is heated to a boil. A saturated solution of hexaammine cobalt nitrate is added under vigorous stirring, and the solution is aged on a sand bath. After cooling, the solution is filtered, washed and dried to obtain a double salt precipitate of rhodium. The percentage of rhodium is calculated based on the mass of the double salt precipitate.

[0054] Three parallel experiments were performed using the test methods of the embodiments and comparative examples, and the average values ​​were calculated. The results are listed in Table 1.

[0055] Table 1

[0056] “-” in the table means no data.

[0057] As can be seen from Table 1, the method for determining the rhodium content provided by the present invention has a simple procedure, and the results of three parallel determinations are accurate and reliable, with a small standard deviation. In Examples 1-5, the standard deviation is controlled below 0.036. Compared with Example 1, in Example 6, the pH is adjusted too high in step (2), so that part of the rhodium forms a hydroxide precipitate, resulting in a large loss of rhodium elements when removing metal impurities, and the deviation of the determination result is large; in Example 7, the heating temperature in step (4) is low, so that the rhodium complex salt reacts slowly, resulting in incomplete rhodium precipitation, affecting the accuracy of the determination result.

[0058] In Comparative Examples 1 and 2, rhodium cannot be completely precipitated, and therefore, accurate measurement results cannot be obtained; in Comparative Example 3, sodium chloride cannot be used to generate hexanitrorhodium salt precipitate, and rhodium element cannot be precipitated, so measurement cannot be performed; in Comparative Example 4, no filtration is performed, and the interference of impurity metals in the platinum-rhodium alloy is not eliminated, and the impurity metals and rhodium complex salts are co-precipitated, resulting in inaccurate measurement results; in Comparative Example 5, a standard rhodium content measurement method is used, and the measurement result has a slightly increased deviation compared with the present invention, and hexaammine cobalt nitrate is used, and the preparation process is complicated and inconvenient to operate.

[0059] In summary, the determination method of the present invention avoids the measurement error introduced by metal impurities such as copper and iron in the platinum-rhodium alloy, and also avoids trace residues of rhodium precipitate in the solution and co-precipitation of other interfering metals. The process and reagents used are simple, the operation is safe, and the efficiency is high. It avoids the use of high-cost and complex precipitants such as metal elements or hexaamminecobalt nitrate in the prior art. The rhodium precipitation is complete, the determination results are accurate, and the relative standard deviation is especially less than 0.21%. At the same time, there is no need to rely on expensive analytical equipment, and it has great application value.

[0060] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific 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 protection scope of the present invention.

Claims

1. A method for determining the rhodium content in a platinum-rhodium alloy, characterized in that: The determination method comprises the following steps: (1) completely dissolving the platinum-rhodium alloy to obtain a metal chloric acid solution; (2) mixing the metal chlorate solution obtained in step (1) with nitrite, adjusting the pH, standing for reaction, and then performing a first solid-liquid separation to obtain a platinum-rhodium mixed solution; (3) The platinum-rhodium mixed solution obtained in step (2) is mixed with a coordination precipitant for precipitation, and then mixed with a polar solvent. After standing for precipitation, a second solid-liquid separation is performed to obtain a rhodium precipitate. The rhodium precipitate is dried to a constant weight, and the rhodium content in the platinum-rhodium alloy is calculated based on the mass of the rhodium precipitate.

2. The measuring method according to claim 1, characterized in that The dissolving method in step (1) comprises: mixing platinum-rhodium alloy powder with a mixed acid, wherein the mixed acid comprises hydrochloric acid and hydrogen peroxide, performing microwave digestion, and then fixing the volume with water; The mass ratio of the platinum-rhodium alloy powder to the mixed acid is (1-50):400; The volume ratio of hydrochloric acid to hydrogen peroxide is (1-3):1; The temperature of the microwave digestion is 100-200°C; The microwave digestion time is 0.5-2 days; The mass ratio of the mixed acid to water is (1-10):

50.

3. The measuring method according to claim 1, characterized in that The mass ratio of the nitrite to the platinum-rhodium alloy in step (2) is (10-50):1; The nitrite in step (2) includes sodium nitrite; The mixing temperature in step (2) is 50-90°C.

4. The measuring method according to claim 1, characterized in that Step (2) wherein the pH is adjusted to 6-10; The pH regulator used in step (2) includes any one of sodium carbonate, sodium hydroxide or sodium bicarbonate, or a combination of at least two of them.

5. The measuring method according to claim 1, characterized in that The standing reaction time in step (2) is 0.5-3h.

6. The measuring method according to claim 1, characterized in that The mass ratio of the coordination precipitant to the platinum-rhodium alloy in step (3) is (10-50):1; The coordination precipitant in step (3) includes any one of ammonium chloride, potassium chloride, potassium carbonate, ammonium carbonate or potassium hydroxide, or a combination of at least two thereof; The precipitation temperature in step (3) is 60-100°C.

7. The measuring method according to claim 1, characterized in that The volume ratio of the polar solvent to the platinum-rhodium mixed solution in step (3) is 1:(5-20); The polar solvent in step (3) includes any one of anhydrous ethanol, acetonitrile or methanol, or a combination of at least two of them.

8. The measuring method according to claim 1, characterized in that The temperature of the static precipitation in step (3) is 0-20°C; The static sedimentation time in step (3) is 0.5-3h.

9. The measuring method according to claim 1, characterized in that The calculation formula of the rhodium content in step (3) is as follows: ;in, ω is the rhodium content in the platinum-rhodium alloy; m 1 is the mass of rhodium precipitate, in g; m is the mass of platinum-rhodium alloy, in g; α Factor for converting rhodium precipitate into rhodium element.

10. The measuring method according to claim 1, characterized in that The determination method comprises the following steps: (1) mixing platinum-rhodium alloy powder with a mixed acid for microwave digestion, wherein the mixed acid comprises hydrochloric acid and hydrogen peroxide, wherein the volume ratio of the hydrochloric acid to the hydrogen peroxide is (1-3):1, and the mass ratio of the platinum-rhodium alloy powder to the mixed acid is (1-50):

400. The microwave digestion temperature is 100-200° C., and the microwave digestion time is 0.5-2 days. After microwave digestion, the digested solution is fixed to volume with water, wherein the mass ratio of the mixed acid to water is (1-10):50, to obtain a metal chloride solution; (2) mixing the metal chlorate solution obtained in step (1) with sodium nitrite, wherein the mass ratio of the sodium nitrite to the platinum-rhodium alloy powder is (10-50):1, the mixing temperature is 50-90° C., adding a pH adjuster to adjust the pH to 6-10, wherein the pH adjuster comprises any one of sodium carbonate, sodium hydroxide or sodium bicarbonate or a combination of at least two thereof, standing for reaction for 0.5-3 h, and the impurity metals in the platinum-rhodium alloy generate nitroso complex precipitates, and then using a glass sand core funnel for solid-liquid separation to obtain a platinum-rhodium mixed solution; (3) mixing the platinum-rhodium mixed solution obtained in step (2) with a coordination precipitant, wherein the coordination precipitant includes any one of ammonium chloride, potassium chloride, potassium carbonate, ammonium carbonate or potassium hydroxide or a combination of at least two thereof, and the mass ratio of the coordination precipitant to the platinum-rhodium alloy powder is (10-50):1, and performing coordination reaction at 60-100°C to obtain a mixture; and then mixing the mixture with a polar solvent, wherein the polar solvent includes any one of anhydrous ethanol, acetonitrile or methanol or a combination of at least two thereof, and the volume ratio of the polar solvent to the platinum-rhodium mixed solution is 1:(5-20), and after mixing, standing and settling at 0-20°C for 0.5-3h, and after the standing and settling is completed, performing solid-liquid separation to obtain a precipitate, and drying the precipitate to constant weight at a drying temperature of 70-150°C to obtain a rhodium precipitate; (4) Weigh the rhodium precipitate obtained in step (3), and calculate the rhodium content in the platinum-rhodium alloy based on the mass of the rhodium precipitate. The calculation formula is as follows: ;in, ω is the rhodium content in the platinum-rhodium alloy; m 1 is the weight of rhodium precipitate, in g; m is the weight of platinum-rhodium alloy, in g; α Factor for converting rhodium precipitate into rhodium element.

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