Method for determining metal content in potassium tetracyanopalladate

Abstract

The invention relates to a method for determining the metal content of a potassium tetracyanopalladate chemical. The method comprises the steps of sample pretreatment, reaction precipitation, aqua regia dissolution and ICP-OES testing. The core of the method is to construct a two-stage digestion mechanism based on potassium thiocyanate induced precipitation-aqua regia / hydrogen peroxide synergistic oxidation. Palladium in the finally obtained clear solution exists in the form of a single and stable Pd (II)-chlorine complex, and completely meets the sample introduction and excitation requirements of ICP-OES (Inductively Coupled Plasma-Optical Emission Spectrometer). The whole process from sample weighing to result output can be completed within 40 minutes, which is far better than the operation period of several hours required by the traditional gravimetric method or titration method, and the dependence of the X-ray fluorescence method on the uniformity and surface state of the solid sample is avoided.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of analytical chemistry, in particular to a method for determining the metal content of potassium tetracyanopalladate. BACKGROUND

[0002] Potassium tetracyanopalladate is an important chemical with wide applications in electroplating, catalysts, and other fields. Accurate determination of its palladium content is crucial for product quality control and process optimization. However, due to the strong stability of cyanide compounds in potassium tetracyanopalladate, traditional digestion methods (such as aqua regia or nitric acid digestion) often take a long time (more than 1 hour) and are difficult to completely decompose the sample. Palladium elements are prone to precipitation, which limits the accuracy of the determination results.

[0003] Chinese patent CN119178765B discloses a method for determining the metal content of palladium ash. This patent melts and decomposes palladium ash with a mixed oxidizing agent, precipitates and separates palladium elements using dimethylglyoxime, and then uses an inductively coupled plasma optical emission spectrometer (ICP-OES) for determination. This method enhances the decomposition ability of the sample, solving the problems of limited palladium capture ability and incomplete impurity separation in existing methods. However, this technical solution is mainly aimed at palladium ash samples and does not address the handling of cyanide compounds such as potassium tetracyanopalladate. Due to the special chemical properties of potassium tetracyanopalladate, complete sample digestion may not be achieved using this method, which can affect the accuracy of the determination results. In addition, this method has complex operation steps, and the melting and decomposition and precipitation separation processes may increase experimental errors.

[0004] Chinese patent CN114354579B discloses a method for simultaneously detecting silver and palladium elements in a silver-palladium mixture. This patent digests silver-palladium mixture samples with nitric acid and aqua regia in steps, and simultaneously determines the contents of silver and palladium using inductively coupled plasma optical emission spectrometry (ICP-OES). This method overcomes the problem of silver chloride precipitation in hydrochloric acid systems, avoids the loss caused by separate determination of silver and palladium, and improves the stability and accuracy of the determination results. However, this technical solution is mainly suitable for silver-palladium mixture samples and is not suitable for cyanide compounds such as potassium tetracyanopalladate. Due to the strong stability of potassium tetracyanopalladate, longer time may be required for digestion with nitric acid and aqua regia, and precipitation may occur, affecting the accuracy of subsequent determination. In addition, this method does not consider the release of toxic gases during the digestion process of cyanide compounds, which poses a certain safety risk.

[0005] Therefore, it is necessary to design a palladium content determination method with faster speed and higher accuracy to avoid the above problems. SUMMARY

[0006] The application aims to provide a method for determining the metal content of potassium tetracyanopalladate, which can quickly and accurately detect the palladium content in potassium tetracyanopalladate.

[0007] To achieve the above-mentioned application purposes, the application provides a method for determining the metal content of potassium tetracyanopalladate, which comprises the following steps: S1, sample pretreatment: dry the potassium tetracyanopalladate sample to be measured in an oven, and then transfer it to a vacuum dryer containing a drying agent and cool it to room temperature; S2, reaction precipitation: weigh the dried sample and place it in a volumetric flask, then add sufficient potassium thiocyanate solution, heat the reaction until black precipitates appear in the solution, and filter out the precipitates; S3, aqua regia dissolution: add sufficient aqua regia to the precipitates and drop in hydrogen peroxide, heat the reaction until the precipitates disappear, and obtain a red-brown clear sample solution to be measured; S4, ICP-OES testing: measure the emission intensity of the blank solution, standard series solution and sample solution to be measured under preset conditions in sequence, deduct the blank, and automatically calculate the concentration of each element according to the standard curve by the built-in program of the instrument, with the concentration in ppm; in the data processing step, the mass fraction ω of palladium is calculated according to the formula ω = m / (m+0.5) ×100%, wherein m is the palladium concentration displayed by ICP.

[0008] Specifically, the temperature control accuracy of the oven used in step S1 is ±1℃, and the oven is dried at 105℃ for 1.5 hours.

[0009] Specifically, the weighing operation of the sample in step S2 is performed in an environment with a relative humidity of less than 40%, and an electronic balance with a resolution of 0.01mg is used to accurately weigh the sample within the range of 0.05±0.005g, accurate to the fourth decimal place.

[0010] Specifically, the molar concentration of the potassium thiocyanate solution in step S2 is 0.5mol / L, the amount of potassium thiocyanate used is 20 times the molar amount of potassium tetracyanopalladate, and the heating temperature is 200℃.

[0011] Specifically, the test conditions in step S4 are as follows: test stabilization time: 30s, integration time: 5s, integration times: 3 times, atomizer flow rate: 0.7L / min, plasma gas flow rate: 15L / min, back pressure: 280kPa.

[0012] Specifically, the method for drawing the standard curve of palladium is as follows: ​Using a 1000 mg / L palladium standard solution, take 100 μL, 500 μL, 1 mL, 2 mL, 5 mL, 10 mL, and 20 mL respectively into seven 100 mL volumetric flasks. Add 10 ppm Y 1 mL as an internal standard to each flask and dilute to volume with 15% hydrochloric acid (v / v). The detection wavelength of palladium is 340.458 nm. Subtract the intensity of the blank solution from the emission intensity of palladium, and plot the palladium mass concentration on the x-axis and the emission intensity on the y-axis to obtain the palladium standard curve.

[0013] Furthermore, the method for plotting the standard curve of impurity elements is as follows: Using standard solutions of 1000 mg / L Ag, As, Cd, Co, Cr, Cu, Fe, Ni, Pb, Ti, and Zn, 50 μL, 100 μL, 200 μL, 500 μL, and 1 mL were respectively poured into five 100 mL volumetric flasks. 10 ppm Y 1 mL was added as an internal standard to each flask. The solutions were then diluted to volume with 5% nitric acid. The detection wavelengths for each element were: Ag 328.068 nm, As 228.812 nm, Cd 226.502 nm, Co 236.380 nm, Cr 284.325 nm, Cu 327.393 nm, Fe 259.939 nm, Ni 231.604 nm, Pb 220.353 nm, and Zn 213.857 nm. The emission intensity of each impurity element was subtracted from the intensity of the blank solution. A standard curve for the impurity elements was plotted with the mass concentration of each impurity element on the x-axis and the emission intensity on the y-axis.

[0014] The beneficial effects of the technical solution of this invention are: The core of this invention lies in constructing a two-stage digestion mechanism based on potassium thiocyanate-induced precipitation and aqua regia / hydrogen peroxide synergistic oxidation. First, KSCN hydrolyzes at 200℃ to generate S. 2- This anion reacts with [Pd(CN)4] 2- Slow-release Pd 2+ The formation of PdS precipitate essentially disrupts the strong coordination protection of palladium by the original cyanide ion, transforming the stable complexed palladium into a sulfide form that is easily attacked by strong oxidizing agents; secondly, aqua regia provides a high concentration of Cl... - and strong oxidizing NO3 - / Cl2 oxidizes and dissolves PdS into soluble H2 [PdCl4], while the introduction of hydrogen peroxide not only enhances the oxidation potential of the system, but also effectively decomposes intermediate reduction products (such as NO, Cl) that may be generated during the reaction. -The free radical complex prevents palladium from forming colloids or secondary precipitation; the final clear solution contains palladium in a single, stable Pd(II)-chlorine complex form, perfectly suited to the injection and excitation requirements of ICP-OES. The entire process, from sample weighing to result output, can be completed within 40 minutes, far superior to the several hours required by traditional gravimetric or titration methods, and avoids the dependence of X-ray fluorescence methods on the homogeneity and surface condition of solid samples. Attached Figure Description

[0015] Figure 1 This is a schematic flowchart of a method for determining the metal content of potassium tetracyanopallate chemical according to the present invention. Detailed Implementation

[0016] The present invention will be further described in detail below with reference to specific embodiments.

[0017] Example: like Figure 1 As shown, a method for determining the metal content of potassium tetracyanopallate is performed according to the following steps: S1. Sample pretreatment: The potassium tetracyanopallate sample to be tested was placed in an oven and dried completely, and then transferred to a vacuum desiccator containing a desiccant and cooled to room temperature.

[0018] Because potassium tetracyanopallate (K2Pd(CN)4) is highly hygroscopic, the actual content measured may be lower than expected. Therefore, it needs to be dried first and kept dry in a vacuum dryer. In step S1, the oven temperature control accuracy is ±1℃, and the product is dried at a constant temperature of 105℃ for 1.5 hours.

[0019] S2. Reaction Precipitation: Weigh the dried sample and place it in a volumetric flask. Add sufficient potassium thiocyanate solution and heat the reaction until a black precipitate appears in the solution. Filter out the precipitate.

[0020] The sample weighing operation in step S2 is performed in an environment with a relative humidity below 40%. An electronic balance with a resolution of 0.01 mg is used to accurately weigh the sample within the range of 0.05 ± 0.00 g, accurate to four decimal places, i.e., within the range of 0.0450 g to 0.0550 g. Since the sample inevitably comes into contact with air during the weighing process, it must be done in an environment with low relative humidity. As long as the sampling process is short, it will not significantly affect the accuracy of the measurement.

[0021] When potassium tetracyanopallate comes into contact with water in a potassium thiocyanate solution, it undergoes a hydrolysis equilibrium reaction: [Pd(CN)4]. 2- Pd 2+ +4CN -Potassium thiocyanate undergoes a hydrolysis reaction when heated to 200°C: SCN - +H2O→HS - +HOCN, generated HS - It can be further hydrolyzed at high temperature to obtain S2 - HS - →S 2- +H + S 2- It will react with Pd produced by hydrolysis 2+ The precipitate immediately combines to form a black palladium sulfide (PdS) ​​precipitate, and the hydrolysis equilibrium reaction continues to move to the right. The precipitate has a loose structure and higher chemical activity than the original cyanide, creating conditions for subsequent oxidation and digestion.

[0022] S3, Dissolving in aqua regia: Add the precipitate (a solid mainly composed of PdS) to a sufficient amount of aqua regia (the molar ratio of nitric acid to hydrochloric acid is 1:3), and add hydrogen peroxide (H2O2) dropwise. Heat the mixture until the precipitate disappears, and a clear, reddish-brown solution of the sample to be tested is obtained.

[0023] The main reaction that occurs in this step is the dissolution reaction between palladium sulfide and aqua regia: PdS + 2HNO3 + 6HCl → H2 [PdCl4] + H2SO4 + 2NOCl + 2H2O.

[0024] Hydrogen peroxide forms a synergistic oxidation system with nitric acid and hydrochloric acid in aqua regia, which can oxidize any low-valent palladium species (such as Pd). 0 or Pd + Completely oxidized to Pd 2+ And ensure that all palladium elements exist stably in solution in the form of soluble chloropalladium acid, avoiding precipitation regeneration caused by reducing byproducts.

[0025] S4, ICP-OES test: Under preset conditions, the emission intensity of blank solution, standard series solutions and test sample solution are measured sequentially. After subtracting the blank, the palladium concentration is automatically calculated by the instrument's built-in program based on the standard curve.

[0026] The test conditions in step S4 are as follows: test stabilization time: 30s, integration time: 5s, number of integrations: 3, atomizer flow rate: 0.7L / min, plasma gas flow rate: 15L / min, back pressure: 280kPa.

[0027] A blank solution is a solution prepared under identical experimental conditions, using a blank sample (such as pure water or a blank solvent) that does not contain the analyte (palladium) instead of the actual sample. Its purpose is to eliminate background interference (such as reagent impurities and instrument noise).

[0028] The most important metal content in potassium tetracyanopallate is palladium. However, during the testing process, it is often necessary to test whether the content of impurity metals (such as Ag, As, Cd, Co, Cr, Cu, Fe, Ni, Pb, Ti, Zn) exceeds the standard. Therefore, the same testing equipment can be used to complete the content test.

[0029] Method for plotting the ICP-OES standard curve: ① Standard curve of palladium: Using a 1000 mg / L palladium standard solution, take 100 μL, 500 μL, 1 mL, 2 mL, 5 mL, 10 mL, and 20 mL respectively into 100 mL volumetric flasks numbered 2-8. Flask number 1 is the blank solution. Add 10 ppm Y and 1 mL as an internal standard to each of the following flasks, and dilute to volume with 15% hydrochloric acid (v / v).

[0030]

[0031] ②Standard curves for other impurity elements Using standard solutions of 1000 mg / L Ag, As, Cd, Co, Cr, Cu, Fe, Ni, Pb, Ti, and Zn, respectively, take 50 μL, 100 μL, 200 μL, 500 μL, and 1 mL and pour them into 100 mL volumetric flasks numbered 9-13, with flask number 1 serving as the blank solution. Add 10 ppm Y and 1 mL as an internal standard to each of the following flasks, and dilute to volume with 5% nitric acid (v / v).

[0032]

[0033] The wavelengths selected for each element are as follows:

[0034] The measurements were performed under optimal instrument operating conditions. The emission intensity of each element was subtracted from the intensity of the blank solution in the series of solutions. A working curve was plotted with the mass concentration of each element on the x-axis and the emission intensity on the y-axis. The correlation coefficient of the working curve equation was not less than 0.9999.

[0035] The detected concentration m of each element is in ppm. In the data processing steps, the mass fraction ω of each element is calculated using the formula ω= Calculated by multiplying by 100%.

[0036] The core of this invention lies in constructing a two-stage digestion mechanism based on potassium thiocyanate-induced precipitation and aqua regia / hydrogen peroxide synergistic oxidation. First, KSCN hydrolyzes at 200℃ to generate S. 2- This anion reacts with [Pd(CN)4] 2- Slow-release Pd 2+The formation of PdS precipitate essentially disrupts the strong coordination protection of palladium by the original cyanide ion, transforming the stable complexed palladium into a sulfide form that is easily attacked by strong oxidizing agents; secondly, aqua regia provides a high concentration of Cl... - and strong oxidizing NO3 - / Cl2 oxidizes and dissolves PdS into soluble H2 [PdCl4], while the introduction of hydrogen peroxide not only enhances the oxidation potential of the system, but also effectively decomposes intermediate reduction products (such as NO, Cl) that may be generated during the reaction. - The free radical complex prevents palladium from forming colloids or secondary precipitation; the final clear solution contains palladium in a single, stable Pd(II)-chlorine complex form, perfectly suited to the injection and excitation requirements of ICP-OES. The entire process, from sample weighing to result output, can be completed within 40 minutes, far superior to the several hours required by traditional gravimetric or titration methods, and avoids the dependence of X-ray fluorescence methods on the homogeneity and surface condition of solid samples.

[0037] Extended applications include the analysis of other cyanide-containing noble metal complexes, such as potassium tetracyanoplatinate (K₂Pt(CN)₄) and potassium tetracyanoalloy (KAu(CN)₂). Preliminary verification shows that using the same digestion process, complete dissolution of platinum and gold can be achieved with a recovery rate greater than 99%, indicating that the technology of this invention has universal potential.

[0038] The above descriptions are merely some embodiments of the present invention. Those skilled in the art can make various modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. A method for determining the metal content of potassium tetracyanopalladate, characterized by the steps of Comprise: S1, sample pretreatment: the potassium tetracyanopalladate sample to be tested is completely dried in an oven, and then transferred to a vacuum dryer containing a drying agent and cooled to room temperature; S2, reaction precipitation: the dried sample is weighed and placed in a volumetric flask, and then sufficient potassium thiocyanate solution is added. The heating reaction continues until black precipitate appears in the solution, and the precipitate is filtered out; S3, aqua regia dissolution: the precipitate is added to sufficient aqua regia, and hydrogen peroxide is added dropwise. The heating reaction is carried out until the precipitate disappears, and a red-brown clear sample solution to be tested is obtained; S4, ICP-OES testing: the emission intensity of blank solution, standard series solution and sample solution to be tested is determined in turn under preset conditions, the concentration of each element is automatically calculated by the built-in program of the instrument according to the standard curve after deducting the blank, and the concentration is in ppm unit; in the data processing step, the mass fraction ω of palladium is calculated according to the formula ω = m / 100%, wherein m is the palladium concentration displayed by ICP. ×100% calculates, wherein m is the palladium concentration displayed by ICP.

2. The method for determining the metal content of potassium tetracyanopalladate according to claim 1, characterized in that: The temperature control accuracy of the oven used in step S1 is ±1℃, and the constant temperature drying is carried out at 105℃ for 1.5 hours.

3. The method of claim 1, wherein the method is characterized by: The weighing operation of the sample in step S2 is carried out in an environment with a relative humidity of less than 40%. The sample in the range of 0.05±0.005g is accurately weighed using an electronic balance with a resolution of 0.01mg, and the fourth decimal place is accurate.

4. The method of claim 1, wherein the method is characterized by: The test conditions in step S4 are: test stabilization time: 30s, integration time: 5s, integration times: 3 times, atomizer flow rate: 0.7L / min, plasma gas flow rate: 15L / min, back pressure: 280kPa.

5. The method of claim 1, wherein the method is characterized by: The method for drawing the standard curve of palladium is: 1000mg / L palladium standard solution is taken 100ul, 500ul, 1ml, 2ml, 5ml, 10ml, and 20ml into seven 100ml volumetric flasks, respectively. In each of the following bottles, 10ppm Y 1ml is added as an internal standard, and is filled with 15% volume ratio hydrochloric acid; the detection wavelength of palladium element is 340.458nm, the emission intensity of palladium element is subtracted from the intensity of blank solution, and the standard curve of palladium element is drawn with the mass concentration of palladium element as the abscissa and the emission intensity as the ordinate.

6. The method for determining the metal content in potassium tetracyanopallate according to claim 5, characterized in that: The method for drawing the standard curve of impurity elements is: 1000mg / L Ag, As, Cd, Co, Cr, Cu, Fe, Ni, Pb, Ti, Zn standard solution is taken 50ul, 100ul, 200ul, 500ul, and 1ml into five 100ml volumetric flasks, respectively. In each of the following bottles, 10ppm Y 1ml is added as an internal standard, and is filled with 5% volume ratio nitric acid; the detection wavelengths of each element are: Ag 328.068nm, As 228.812nm, Cd 226.502nm, Co 236.380nm, Cr 284.325nm, Cu 327.393nm, Fe 259.939nm, Ni 231.604nm, Pb 220.353nm, Zn 213.857nm; the emission intensity of each impurity element is subtracted from the intensity of blank solution, and the standard curve of impurity elements is drawn with the mass concentration of each impurity element as the abscissa and the emission intensity as the ordinate.

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