Determination method of bismuth content

Abstract

The invention discloses a determination method of bismuth content. The method comprises the following steps: (1) mixing a bismuth raw material with a nitric acid solution for first heating, then mixing with a hydrochloric acid solution for second heating, and then adding hydrochloride to obtain an electrolyte, the mass of the bismuth raw material being M; (2) an anode electrode and a cathode electrode of an electrolysis instrument are inserted into the electrolyte for electrolysis, so that the cathode electrode deposited with elemental bismuth and residual electrolyte are obtained, the increased weight of the cathode electrode is M1, and the mass of bismuth in the residual electrolyte is M2; (3) treating the cathode electrode deposited with the bismuth elementary substance with a nitric acid solution so as to obtain a bismuth-tellurium mixed solution, and determining that the mass of tellurium in the bismuth-tellurium mixed solution is M3; and calculating the bismuth content in the bismuth raw material according to the following formula: Bi (%) = (M1 + M2-M3) / M * 100%. According to the method, the content of the bismuth in the pure bismuth is directly measured by adopting an electrolytic method, and a brand new detection method for detecting the main grade content of the bismuth in the pure bismuth is provided.

Description

Technical Field

[0001] The invention belongs to the technical field of electrochemical analysis, and particularly relates to a method for determining bismuth content. Background Art

[0002] Bismuth (Bi) is a metallic element with a metallic luster, but is brittle and has poor electrical and thermal conductivity. It is also the most diamagnetic metal, with its resistivity increasing while its thermal conductivity decreases in the presence of a magnetic field. Bismuth has the lowest thermal conductivity of any metal, except for mercury. Bismuth exhibits a thermoelectric effect, expanding in volume upon solidification, with an expansion rate of 3.3%. Unlike other heavy metals, bismuth is relatively less toxic than lead or antimony. Bismuth is not easily absorbed by the body, is non-carcinogenic, does not damage DNA structure, and can be excreted through urination. For these reasons, bismuth is often used to replace lead in applications such as lead-free bullets, lead-free solder, and even in pharmaceuticals and cosmetics. Bismuth is also used in alloying and is an ideal superconducting material. It is also used in batteries, semiconductors, and nuclear industry materials. China is the world's largest producer and exporter of bismuth. Due to bismuth's wide range of uses and excellent properties, direct purity testing of pure bismuth is essential.

[0003] Standard testing methods for bismuth materials include: GB / T15926-2010, Chemical Analysis of Bismuth Ores, Determination of Bismuth Content, with a detection range of 0.10%-5.25%; YS / T240.1-2007, Chemical Analysis of Bismuth Concentrates, Determination of Bismuth Content by Na2EDTA Titration, with a detection range of 10%-40%; and EDTA Titration for Continuous Determination of Lead and Bismuth in Crude Lead-Bismuth Alloys, with values ​​reported in the literature being around 25%. All of these testing methods use Na2EDTA titration.

[0004] While searching for bismuth content testing methods, it was discovered that there are currently no national or industry standards for crude bismuth with a bismuth content below 98%, and companies generally agree to use the EDTA method for testing. Furthermore, there are no national or industry-standard methods for testing the main bismuth content of pure bismuth with a bismuth content of 98.0% to 99.8%. While there are national and industry-standard testing methods for pure bismuth with a content above 99.8%, these methods are often subtractive. For example, the YS / T536 chemical analysis method for bismuth uses a subtraction method for main bismuth content, subtracting the total amount of substantial impurities (such as copper, lead, zinc, iron, silver, arsenic, tin, cadmium, magnesium, chromium, aluminum, gold, and nickel) from 100%. This method does not allow for direct detection of the main bismuth content, and the subtraction method suffers from poor selectivity and significant detection risks and loopholes. While the EDTA method is acceptable for testing crude bismuth or bismuth alloys with a bismuth content below 98%, it suffers from issues such as limited accuracy and poor reproducibility when testing pure bismuth with a bismuth content above 98%. In view of this, conducting research on the determination method of the main grade bismuth content in pure bismuth has important practical significance and can fill a gap in detection methods. Summary of the Invention

[0005] The present invention aims to at least partially address one of the technical problems in the related art. To this end, one object of the present invention is to provide a method for determining bismuth content. This method uses electrolysis to directly determine the bismuth content in pure bismuth, avoiding the risks and scientific inaccuracies associated with inferring the bismuth content by measuring the total impurity content in the sample. It also reduces the risk of bias associated with indirect measurement and provides a novel method for detecting the main grade of bismuth in pure bismuth. Furthermore, the electrolysis apparatus employed in this method is simple and easy to operate, enabling rapid detection.

[0006] In one aspect of the present invention, the present invention provides a method for determining bismuth content. According to an embodiment of the present invention, the method comprises:

[0007] (1) mixing a bismuth raw material with a nitric acid solution, performing a first heating, then mixing it with a hydrochloric acid solution, performing a second heating, and then adding hydrochloride to obtain an electrolyte, wherein the mass of the bismuth raw material is M;

[0008] (2) inserting the anode electrode and cathode electrode of the electrolyzer into the electrolyte for electrolysis to obtain a cathode electrode on which bismuth is deposited and an electrolyte residue, wherein the increased weight of the cathode electrode is M1 and the mass of bismuth in the electrolyte residue is M2;

[0009] (3) treating the cathode electrode on which bismuth is deposited with a nitric acid solution to obtain a bismuth-tellurium mixed solution, and measuring the mass of tellurium in the bismuth-tellurium mixed solution as M3;

[0010] The bismuth content in the bismuth raw material is calculated according to the following formula:

[0011] Bi(%)=(M1+M2-M3) / M×100%.

[0012] According to the method for determining the bismuth content of an embodiment of the present invention, the bismuth raw material is mixed with a nitric acid solution for a first heating and then mixed with a hydrochloric acid solution for a second heating to convert the matrix into hydrochloride. The bismuth raw material is mixed with the nitric acid solution for a first heating to dissolve the bismuth, and then mixed with the hydrochloric acid solution for a second heating to drive away the nitric acid through the hydrochloric acid. Specifically, hydrochloric acid and nitric acid react as follows in the solution: HNO3+HCl→NOCl+H2O. In this process, nitric acid decomposes into nitrogen subchloride (NOCl), which is an unstable compound, which further decomposes into chlorine (Cl2) and nitric oxide (NO), thereby achieving the purpose of "driving away" nitric acid, and then the electrolyte is converted from a nitric acid matrix to a hydrochloric acid matrix, and then hydrochloride is added to the above solution to obtain an electrolyte. The mass of the bismuth raw material is M. The anode electrode and cathode electrode of the electrolyzer are inserted into the above electrolyte for electrolysis. Specifically, the following reaction occurs. Bismuth is deposited and precipitated at the cathode electrode: Bi 3+ +3e=Bi, chlorine precipitation occurs at the anode electrode: 2Cl - -2e=Cl2, thus obtaining a cathode electrode deposited with elemental bismuth and an electrolyte residue. Bismuth ions in the electrolyte are not completely deposited on the cathode electrode, resulting in trace amounts of bismuth ions in the electrolyte residue. Because bismuth is deposited on the cathode electrode, the weight of the cathode electrode increases by M1, and the mass of bismuth in the electrolyte residue is M2. During the deposition of bismuth on the cathode electrode, only tellurium is simultaneously deposited on the cathode electrode (during the bismuth refining process, only a few elements, such as Zn, Ca, Sn, Te, Pb, and As, are enriched in the bismuth matrix, a phenomenon determined by the chemical properties of bismuth and the refining process). Other metal elements are not deposited. Therefore, the cathode electrode deposited with elemental bismuth is treated with a nitric acid solution, dissolving both bismuth and tellurium to obtain a bismuth-tellurium mixed solution. The mass of tellurium in the bismuth-tellurium mixed solution is measured as M3. Finally, the bismuth content in the bismuth raw material is calculated according to the following formula: Bi (%) = (M1 + M2 - M3) / M × 100%. Therefore, the method uses an electrolysis method to directly determine the bismuth content in pure bismuth (the bismuth content is not less than 98wt%), avoiding the detection risks and scientific inaccuracies caused by measuring the total impurity content in the sample and then inferring the bismuth content (differential subtraction method), reducing the risk of bias in indirect measurement, and providing a new detection method for detecting the main grade content of bismuth in pure bismuth. The electrolysis device used in this method is simple and easy to operate, and the detection work can be completed in a short time (within 8 hours).

[0013] In addition, the method for determining bismuth content according to the above embodiment of the present invention may also have the following technical features:

[0014] In some embodiments of the present invention, in step (1), the bismuth content in the bismuth raw material is not less than 98 wt%.

[0015] In some embodiments of the present invention, in step (1), the acidity of the electrolyte is 20 g / L to 40 g / L, based on the mass of hydrochloric acid. This allows bismuth to be deposited on the cathode electrode, thus preventing bismuth from being hydrolyzed.

[0016] In some embodiments of the present invention, the concentration of hydrochloride in the electrolyte is 40 g / L to 80 g / L, thereby increasing the density of bismuth deposition on the cathode electrode and the deposition rate of bismuth ions in the electrolyte.

[0017] In some embodiments of the present invention, the concentration of bismuth in the electrolyte is 0.6 g / L to 1.0 g / L, thereby increasing the density of bismuth deposition on the cathode electrode and improving the deposition rate of bismuth ions in the electrolyte.

[0018] In some embodiments of the present invention, the concentration of the nitric acid solution is 68 wt % to 71 wt %.

[0019] In some embodiments of the present invention, the first heating temperature is 200° C. to 300° C., and the first heating time is 10 min to 15 min. Thus, the bismuth raw material is fully dissolved.

[0020] In some embodiments of the present invention, the concentration of the hydrochloric acid solution is 31 wt% to 37 wt%.

[0021] In some embodiments of the present invention, the second heating temperature is 200° C. to 300° C., and the second heating time is 3 minutes to 5 minutes. Thus, nitric acid can be removed as much as possible.

[0022] In some embodiments of the present invention, the hydrochloride comprises at least one of sodium chloride, potassium chloride, magnesium chloride and zinc chloride.

[0023] In some embodiments of the present invention, in step (2), the current density of the electrolysis is 0.1 A / m 2 ~0.3A / m 2 Thus, the density of bismuth deposition on the cathode electrode can be increased, and the deposition rate of bismuth ions in the electrolyte can be increased.

[0024] In some embodiments of the present invention, in step (2), the electrolysis temperature is 40° C. to 55° C. This can increase the density of bismuth deposition on the cathode electrode and improve the deposition rate of bismuth ions in the electrolyte.

[0025] In some embodiments of the present invention, the electrolysis time is 6 hours to 10 hours.

[0026] In some embodiments of the present invention, in step (2), stirring is performed during the electrolysis at a speed of 250 rpm to 500 rpm, thereby increasing the density of bismuth deposition on the cathode electrode and the deposition rate of bismuth ions in the electrolyte.

[0027] In some embodiments of the present invention, the anode electrode includes a platinum electrode, a graphite electrode, or a gold electrode.

[0028] In some embodiments of the present invention, the cathode electrode comprises a platinum electrode or a gold electrode.

[0029] In some embodiments of the present invention, atomic absorption spectrophotometry is used to determine the mass of bismuth in the residual electrolyte, thereby improving the accuracy of measuring the mass of bismuth in the residual electrolyte.

[0030] In some embodiments of the present invention, in step (3), the mass of tellurium in the bismuth-tellurium mixed solution is determined using inductively coupled plasma-mass spectrometry, thereby improving the measurement accuracy of the mass of tellurium in the bismuth-tellurium mixed solution.

[0031] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. DETAILED DESCRIPTION

[0032] The embodiments of the present invention are described in detail below, which are intended to explain the present invention but are not to be construed as limiting the present invention.

[0033] In one aspect of the present invention, the present invention provides a method for determining bismuth content. According to an embodiment of the present invention, the method comprises:

[0034] S100: Mix the bismuth raw material with the nitric acid solution for the first heating, then mix it with the hydrochloric acid solution for the second heating, and then add the hydrochloride

[0035] In this step, the bismuth raw material is mixed with a nitric acid solution for a first heating, and then mixed with a hydrochloric acid solution for a second heating, converting the matrix into a hydrochloride. The bismuth raw material is mixed with the nitric acid solution for the first heating to dissolve the bismuth, and then mixed with the hydrochloric acid solution for a second heating, and the hydrochloric acid is used to drive away the nitric acid. Specifically, hydrochloric acid and nitric acid react in the solution as follows: HNO3 + HCl → NOCl + H2O. In this process, nitric acid decomposes into nitrogenous chloride (NOCl), an unstable compound, which further decomposes into chlorine (Cl2) and nitric oxide (NO), thereby achieving the purpose of "driving away" nitric acid. The electrolyte is then converted from a nitric acid matrix to a hydrochloric acid matrix, and hydrochloride is added to the above solution to obtain an electrolyte. The mass of the bismuth raw material is M. Furthermore, the bismuth content in the bismuth raw material is not less than 98wt%.

[0036] According to an embodiment of the present invention, the first heating temperature is 200°C to 300°C, and the first heating time is 10 to 15 minutes. The inventors have found that controlling the first heating temperature and time within these ranges can fully dissolve the bismuth raw material. Furthermore, the concentration of the nitric acid solution is 68wt% to 71wt%.

[0037] According to an embodiment of the present invention, the second heating temperature is 200°C to 300°C, and the second heating time is 3 minutes to 5 minutes. The inventors have found that controlling the second heating temperature and time within the above ranges can remove nitric acid as much as possible. Furthermore, the concentration of the hydrochloric acid solution is 31wt% to 37wt%.

[0038] According to an embodiment of the present invention, the acidity of the electrolyte is 20 g / L to 40 g / L, measured by mass of hydrochloric acid. The inventors have discovered that controlling the acidity of the electrolyte within this range can have the following effects: (1) preventing the bismuth ions in the electrolyte from hydrolyzing during the entire electrolysis process; and (2) achieving a minimum bismuth ion content in the electrolyte after approximately 7 hours of electrolysis. This content range facilitates accurate detection using the AAS method and also indicates that the more densely packed bismuth metal is on the cathode plate, the higher the accuracy and operability of the method.

[0039] According to an embodiment of the present invention, the concentration of hydrochloride in the electrolyte is 40 g / L to 80 g / L. The inventors found that (1) because the anions in the hydrochloride participate in the anode reaction, the concentration of hydrochloride is controlled within the above range, which can ensure that during the entire electrolysis process, the decrease in the chloride ion content during the electrolysis process will not affect the changes in the entire electrolytic medium system, thereby affecting the entire detection process. (2) At the same time, when controlled within the above range, the bismuth ion content remaining in the electrolyte after about 7 hours of electrolysis is also the lowest. It should be noted that hydrochloride is a conventional material in this field, and those skilled in the art can choose it according to actual conditions. For example, hydrochloride includes but is not limited to at least one of sodium chloride, potassium chloride, magnesium chloride and zinc chloride.

[0040] According to an embodiment of the present invention, the bismuth concentration in the electrolyte is 0.6 g / L to 1.0 g / L. The inventors have found that controlling the bismuth concentration in the electrolyte within this range not only meets the weighing accuracy of the electronic balance and the representativeness of the sample, but also ensures that the entire detection process is completed within 7 hours. It should be noted that the bismuth ion concentration here is obtained by dividing the mass of the weighed bismuth raw material by the volume of the electrolyte.

[0041] S200: Insert the anode electrode and cathode electrode of the electrolyzer into the electrolyte for electrolysis

[0042] In this step, the anode electrode and cathode electrode of the electrolyzer are inserted into the above electrolyte for electrolysis. Specifically, the following reaction occurs, and bismuth is deposited and precipitated at the cathode electrode: Bi 3+ +3e=Bi, chlorine precipitation occurs at the anode electrode: 2Cl - -2e=Cl2, thereby obtaining a cathode electrode deposited with elemental bismuth and an electrolyte residue. The bismuth ions in the electrolyte are not completely deposited on the cathode electrode, so trace amounts of bismuth ions exist in the electrolyte residue. Because elemental bismuth is deposited on the cathode electrode, the increased weight of the cathode electrode is M1, and the mass of bismuth in the electrolyte residue is M2. It should be noted that the electrolyzer is a conventional instrument in the art, and those skilled in the art can select a specific model based on actual needs, which will not be described in detail here.

[0043] According to an embodiment of the present invention, the anode electrode comprises a platinum electrode, a graphite electrode, or a gold electrode; and the cathode electrode comprises a platinum electrode or a gold electrode. The inventors have discovered that using electrodes made of the aforementioned materials for the anode and cathode electrodes not only allows bismuth ions to be densely deposited on the cathode electrode in the form of metallic bismuth, but also allows the deposited metal to be easily dissolved by acid without dissolving the cathode electrode material itself.

[0044] According to an embodiment of the present invention, the current density of the electrolysis is 0.1A / m 2 ~0.3A / m 2 The inventors found that when the electrolysis current density is within the above range, the entire electrolysis process can be smooth, bismuth ions are densely deposited on the cathode electrode in the form of metallic bismuth, and the entire electrolysis process is completed within 7 hours.

[0045] According to an embodiment of the present invention, the electrolysis temperature is 40° C. to 55° C. The inventors have discovered that controlling the electrolysis temperature within this range can maintain the balance of the entire electrolysis system, ensure an appropriate migration speed of bismuth ions throughout the electrolysis process, improve metallic luster and density, thereby reducing operational difficulty and improving measurement accuracy.

[0046] According to an embodiment of the present invention, the electrolysis time is 6 hours to 10 hours. The inventors have found that controlling the electrolysis time within the above range can ensure that the metallic bismuth deposited on the cathode mesh maintains its metallic luster, avoids overoxidation, and improves the accuracy of the detection results.

[0047] According to an embodiment of the present invention, stirring is performed during electrolysis at a speed of 250 rpm to 500 rpm. Stirring during electrolysis can eliminate concentration polarization, allowing bismuth ions to be densely deposited on the cathode mesh and exhibit a metallic luster.

[0048] According to an embodiment of the present invention, atomic absorption spectrophotometry is used to determine the mass of bismuth in the residual electrolyte. The inventors have discovered that the bismuth content in the residual electrolyte is relatively low, and atomic absorption spectrophotometry can accurately determine the bismuth content in the residual electrolyte. It should be noted that the equipment used for atomic absorption spectrophotometry is conventional in the art, and the specific testing method is also conventional in the art. Those skilled in the art can select the specific equipment and test data parameters based on actual circumstances.

[0049] S300: Treating the cathode electrode deposited with bismuth with a nitric acid solution

[0050] During this step, only tellurium is deposited simultaneously on the cathode electrode during the deposition of bismuth. Other metal elements (such as Zn, Ca, Sn, Te, Pb, and As, which may be introduced during the bismuth refining process) are not deposited. Therefore, after the cathode electrode with the deposited bismuth is treated with a nitric acid solution, both bismuth and tellurium dissolve, resulting in a bismuth-tellurium mixed solution. The mass of tellurium in the bismuth-tellurium mixed solution is measured as M3. Finally, the bismuth content in the bismuth raw material is calculated according to the following formula: Bi (%) = (M1 + M2 - M3) / M × 100%.

[0051] According to an embodiment of the present invention, inductively coupled plasma-mass spectrometry is used to determine the mass of tellurium in a bismuth-tellurium mixed solution. The inventors have discovered that the tellurium content in the bismuth-tellurium mixed solution is very low. Therefore, using inductively coupled plasma-mass spectrometry to determine the mass of tellurium in the bismuth-tellurium mixed solution can improve the accuracy of tellurium mass determination. It should be noted that the equipment and process used in inductively coupled plasma-mass spectrometry are conventional in the art, and those skilled in the art can select the equipment model and operating process based on actual conditions.

[0052] Therefore, the method uses an electrolysis method to directly determine the bismuth content in pure bismuth (the bismuth content is not less than 98wt%), avoiding the detection risks and scientific inaccuracies caused by measuring the total impurity content in the sample and then inferring the bismuth content (differential subtraction method), reducing the risk of bias in indirect measurement, and providing a new detection method for detecting the main grade content of bismuth in pure bismuth. The electrolysis device used in this method is simple and easy to operate, and the detection work can be completed in a short time (within 7 hours).

[0053] The present invention is described below with reference to specific examples. It should be noted that these examples are merely illustrative and do not limit the present invention in any way.

[0054] Example 1

[0055] (1) Pure bismuth sample: Pure bismuth samples produced by Chizhou smelter were selected for testing.

[0056] (2) Electrolysis equipment: HDJ-60 fast dual-unit controlled potential electrolyzer, including two sets of positive and negative platinum electrodes (platinum mesh).

[0057] (3) Determination of bismuth content in pure bismuth samples

[0058] Place the platinum cathode and platinum anode in a nitric acid solution (concentration 68wt%) and boil for 4-5 minutes, take out and rinse with water, boil in boiling water for 1-2 minutes, take out and soak twice with anhydrous ethanol, put in an oven at about 105℃ to dry, and set aside.

[0059] a. Preparation of electrolyte

[0060] Weigh 0.2 g of pure bismuth sample (accurate to 0.0001 g, the mass of the pure bismuth sample is M) into a 250 ml tall beaker, add 2 ml of nitric acid solution (concentration 68 wt%), heat to 250 ° C and dissolve for 12 min, then add 20 ml of hydrochloric acid (concentration 37 wt%) and heat to 200 ° C for 3 min, remove the nitric acid and cool, finally add 10.0 g of sodium chloride and dilute with water to 250 ml to obtain an electrolyte.

[0061] b Electrolysis - Determination of the mass M1 of the cathode electrode deposition weight gain

[0062] Install the platinum anode and a precisely weighed platinum cathode on the electrolyzer, immerse the platinum mesh in the electrolyte, and cover the tall beaker with a split Teflon dish or glass dish. Adjust the current density, voltage and potential, electrolysis temperature, and stirring speed to conduct the electrolysis. After the electrolysis is completed, do not cut off the power supply. Slowly raise the electrode or lower the beaker. Immediately rinse the electrode with about 100ml of water 2-3 times. Quickly remove the platinum cathode and immerse it in two cups of anhydrous ethanol in turn. Remove and immediately place it in a constant temperature drying oven heated to 105℃ to dry for 3-5 minutes. Remove and place in a desiccator. Cool to room temperature and weigh (accurate to 0.0001g).

[0063] c Determine the mass M2 of bismuth in the residual electrolyte

[0064] Bismuth Standard Stock Solution (1g / L): Weigh 1.0000g of bismuth powder (≥99.99%) into a 250mL Erlenmeyer flask. Slowly add 50mL of nitric acid. Cover with a watch glass. Heat on a hot plate at low temperature until completely dissolved. Boil to remove nitrogen oxides. Remove the solution, rinse the watch glass and beaker with water, and cool to room temperature. Transfer the solution to a 1000mL volumetric flask. Rinse the beaker with water, add the washings to the flask, dilute to the mark with water, and mix thoroughly.

[0065] Bismuth standard solution (Bi 100.0 μg / mL): Pipette 50.00 mL of bismuth standard stock solution into a 500 mL volumetric flask, add 25.0 mL of hydrochloric acid and 25.0 mL of nitric acid, dilute to the mark with water, and mix thoroughly.

[0066] Establishment of bismuth standard curve: Pipette 0.00mL, 1.00mL, 2.00mL, 5.00mL, and 10.00mL of Bi standard solution into a set of 200mL volumetric flasks, add 10.0mL of hydrochloric acid and 10.0mL of nitric acid, dilute to the scale with water, and mix well.

[0067] After electrolytically precipitating bismuth, the residual electrolyte solution was transferred to a 200-ml volumetric flask, diluted to the mark with water, and shaken well. The bismuth concentration in the residual electrolyte solution was measured by AAS at a wavelength of 223.1 nm, and the mass of bismuth in the residual electrolyte solution, M2, was calculated.

[0068] d The mass of tellurium deposited on the platinum cathode M3

[0069] Place a weighed platinum cathode with deposited bismuth metal in a 250ml tall beaker. Rinse the deposited bismuth metal from the platinum cathode with nitric acid until it is completely removed. Pour the eluent from the beaker into a 100ml glass volumetric flask, dilute to volume with water, and shake well. Measure the tellurium concentration in the solution using ICP-MS using the following test parameters: sampling depth 5mm, power 1.55kW, cooling gas flow 14.0L / min, auxiliary gas flow 0.80L / min, and nebulizer flow 1.0L / min. The tellurium mass is calculated as M3.

[0070] Calculate the bismuth content (rounded to the second decimal place) using the following formula:

[0071] Bi(%)=(M1+M2-M3) / M×100%

[0072] (4) Test results at different electrolysis temperatures

[0073] The electrolysis current density was 0.1A / ㎡, the voltage was 0.15V, and the potential was 0.370mV. The acidity of the electrolyte was 60g / L, and the concentration of sodium chloride in the electrolyte was 40g / L. Stirring was performed at 350rpm. Five sets of tests were conducted, namely, electrolysis for 8 hours at 30℃, 35℃, 40℃, 50℃, and 60℃. Specific test results are shown in Table 1.

[0074] Table 1

[0075] Electrolyte temperature (℃) 30 35 40 50 60 Bismuth content of cathode electrode (%) 97.38 98.03 98.16 98.48 98.02 Bismuth content in residual electrolyte (%) 1.24 0.73 0.54 0.27 0.77 Final bismuth content determination results (%) 98.62 98.76 98.70 98.75 98.79

[0076] As can be seen from Table 1, when the electrolysis time is equivalent, the density of bismuth deposited on the platinum mesh meets the detection requirements, but as the electrolyte temperature increases, the bismuth ion content in the electrolyte residual liquid gradually decreases, reaching a low value (0.27%) at 50°C, and then gradually increases. According to the principle of electrolysis, it is hoped that bismuth ions are deposited on the platinum cathode as much as possible, and the lower the bismuth ion content remaining in the electrolyte, the better. Based on this, it is determined that 50°C is selected as the optimal electrolysis temperature. It should be noted that the density is perceived by visual inspection, and when the cathode mesh is subsequently tapped and cleaned with anhydrous ethanol after the deposited metal bismuth is deposited, there is no obvious metal bismuth powder falling. If the density is not high, bismuth powder will continue to fall during the subsequent operations of the cathode mesh (cleaning, drying, weighing, etc.), which will seriously affect the accuracy and precision of the detection and increase the difficulty of the operation.

[0077] Example 2

[0078] The main difference between Example 2 and Example 1 is that the electrolysis temperature in Example 2 was 50°C, and five sets of tests were conducted, i.e., the concentrations of sodium chloride in the electrolyte were 10 g / L, 20 g / L, 40 g / L, 60 g / L, and 80 g / L, respectively. The test results of the five sets of tests in Example 2 are shown in Table 2.

[0079] Table 2

[0080] Sodium chloride concentration (g / L) 10 20 40 60 80 Bismuth content of cathode electrode (%) 97.29 97.42 97.90 97.87 97.86 Bismuth content in residual electrolyte (%) 0.90 0.86 0.65 0.66 0.57 Final measurement results (%) 98.19 98.28 98.55 98.53 98.43

[0081] Table 2 shows that, given a comparable electrolysis time, the density of bismuth deposited on the platinum mesh meets detection requirements. However, as the sodium chloride concentration in the electrolyte increases, the bismuth ion content in the residual electrolyte gradually decreases. After reaching 40 g / L, the bismuth content stabilizes at a low value between 0.57% and 0.66%. Therefore, based on the principles of electrolysis and the density of bismuth deposited on the platinum mesh, a sodium chloride concentration of 40 g / L was selected as the optimal concentration.

[0082] Example 3

[0083] The main difference between Example 3 and Example 1 is that the electrolysis temperature in Example 3 was 50° C., the electrolysis time was 7.6 h, and four sets of tests were performed, i.e., the acidity of the electrolyte was 10 g / L, 20 g / L, 40 g / L, and 60 g / L, respectively. The test results of the four sets of tests in Example 3 are shown in Table 3.

[0084] Table 3

[0085] Hydrochloric acid concentration (g / L) 10 20 40 60 Bismuth content of cathode electrode (%) 97.06 97.82 97.75 97.73 Bismuth content in residual electrolyte (%) 0.90 0.42 0.39 0.47 Final measurement results (%) 97.96 98.24 98.14 98.20

[0086] Table 3 shows that, given a similar electrolysis time, the density of bismuth deposited on the platinum mesh meets the testing requirements. However, as the hydrochloric acid concentration increases, the bismuth ion content in the residual electrolyte gradually decreases, reaching a low value of 0.39% to 0.47% after reaching 20 g / L. Therefore, based on the principles of electrolysis and the density of bismuth deposited on the platinum mesh, 20 g / L hydrochloric acid concentration was selected as the optimal electrolyte hydrochloric acid concentration.

[0087] Example 4

[0088] The main difference between Example 4 and Example 1 is that the electrolysis temperature in Example 4 is 50° C., the electrolysis time is 7.6 h, and three sets of tests are performed, namely, the rotation speeds during electrolysis are 250 rpm, 350 rpm, and 500 rpm, respectively. The test results of the three sets of tests in Example 4 are shown in Table 4.

[0089] Table 4

[0090]

[0091]

[0092] Table 4 shows that as the stirring speed increases, the density of the bismuth deposited on the platinum mesh meets the testing requirements. When the stirring speed reaches 350 rpm, the bismuth content in the residual electrolyte remains stable at a low value between 0.41% and 0.42%. Therefore, based on the principles of the electrolysis method and the density of bismuth deposited on the platinum mesh, 350 rpm is selected as the optimal stirring speed.

[0093] Example 5

[0094] The main difference between Example 5 and Example 1 is that the electrolysis temperature in Example 5 is 50°C, the electrolysis time is 8h, and three groups of experiments are performed, that is, the current density during electrolysis is 0.1A / m 2 , 0.2A / m 2 , 0.3A / m 2 The test results of the three groups of experiments in Example 5 are shown in Table 5.

[0095] Table 5

[0096] Current density (A / ㎡) 0.1 0.2 0.3 Bismuth content of cathode electrode (%) 97.82 97.88 97.86 Bismuth content in residual electrolyte (%) 0.42 0.40 0.37 Final measurement results (%) 98.24 98.28 98.23

[0097] Table 5 shows that when the current density is gradually increased from 0.1A / ㎡ to 0.3A / ㎡, the amount of bismuth deposited on the platinum mesh increases, while the electrolysis time is equivalent. The measurement results are stable from 0.1A / ㎡ to 0.3A / ㎡, and the metallic bismuth deposited on the platinum mesh has good density. Considering that the current density of 0.3A / ㎡ has the lowest bismuth content in the residual electrolyte, effectively shortens the electrolysis time, and densely enriches bismuth on the platinum mesh, 0.3A / ㎡ was selected as the optimal current density.

[0098] Example 6

[0099] The main difference between Example 6 and Example 1 is that the electrolysis temperature in Example 6 is 50° C., and four groups of tests are performed, namely, the electrolysis time is 6 h, 7 h, 8 h, and 10 h respectively. The test results of the four groups of tests in Example 6 are shown in Table 6.

[0100] Table 6

[0101] Electrolysis time (h) 6 7 8 10 Bismuth content of cathode electrode (%) 99.14 99.80 99.95 99.95 Bismuth content in residual electrolyte (%) 0.20 0.16 0.17 0.21 Final measurement results (%) 99.34 99.96 100.12 100.16

[0102] Table 6 shows that the bismuth content in the residual solution gradually decreases with increasing electrolysis time. When the electrolysis time exceeds 6 hours, the bismuth content in the residual solution remains stable at 0.16% to 0.21%. However, when the electrolysis time reaches 8 hours or longer, the metallic bismuth accumulated on the platinum mesh begins to turn black, indicating oxidation. Considering factors such as the bismuth content in the residual solution and whether the platinum mesh is oxidized, 7 hours is selected as the optimal electrolysis time.

[0103] Example 7

[0104] The electrolysis test was conducted for approximately 7 hours using the optimal operating parameter conditions (i.e., current density of 0.3 A / m2, voltage of 0.15 V, potential of 0.370 mV, 20 g / L hydrochloric acid solution, 40 g / L sodium chloride solution, electrolysis temperature of 50°C, and stirring speed of 350 rpm). Two groups (A and B) of pure bismuth samples were measured, with five parallel tests performed in each group.

[0105] The spike recovery test method is as follows: weigh 0.1000g of sample A (the spike recovery test procedure for sample B is the same as A) and then weigh 0.1000g of pure bismuth, and place them in a 250ml tall beaker. The sample is tested according to the aforementioned sample dissolution procedure and optimal operating parameters. The amount of bismuth is determined to be 0.19744g. The spike recovery rate is: [(0.19744-0.1000*99.25%) / 0.1000]*100%=98.19%.

[0106] The test results of Example 7 are shown in Table 7.

[0107] Table 7

[0108]

[0109] As can be seen from Table 7, the recovery rate of this detection method is between 98% and 102%, and the relative standard deviation (RSD) is within 0.10%, indicating that this detection method can accurately determine the bismuth content in pure bismuth samples.

[0110] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0111] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A method for determining bismuth content, characterized in that: include: (1) mixing a bismuth raw material with a nitric acid solution, performing a first heating, then mixing it with a hydrochloric acid solution, performing a second heating, and then adding hydrochloride to obtain an electrolyte, wherein the mass of the bismuth raw material is M; (2) inserting the anode electrode and cathode electrode of the electrolyzer into the electrolyte for electrolysis to obtain a cathode electrode on which bismuth is deposited and an electrolyte residue, wherein the increased weight of the cathode electrode is M1 and the mass of bismuth in the electrolyte residue is M2; (3) treating the cathode electrode on which bismuth is deposited with a nitric acid solution to obtain a bismuth-tellurium mixed solution, and measuring the mass of tellurium in the bismuth-tellurium mixed solution as M3; The bismuth content in the bismuth raw material is calculated according to the following formula: Bi(%)=(M1+M2-M3) / M×100%.

2. The method according to claim 1, characterized in that In step (1), the bismuth content in the bismuth raw material is not less than 98 wt%.

3. The method according to claim 1, characterized in that In step (1), the acidity of the electrolyte is 20 g / L to 40 g / L based on the mass of hydrochloric acid; Optionally, the concentration of hydrochloride in the electrolyte is 40 g / L to 80 g / L; Optionally, the concentration of bismuth in the electrolyte is 0.6 g / L to 1.0 g / L.

4. The method according to claim 1 or 3, characterized in that The concentration of the nitric acid solution is 68wt% to 71wt%; Optionally, the temperature of the first heating is 200° C. to 300° C., and the time of the first heating is 10 min to 15 min; Optionally, the concentration of the hydrochloric acid solution is 31 wt% to 37 wt%; Optionally, the second heating temperature is 200° C. to 300° C., and the second heating time is 3 min to 5 min; Optionally, the hydrochloride comprises at least one of sodium chloride, potassium chloride, magnesium chloride and zinc chloride.

5. The method according to claim 1, characterized in that In step (2), the current density of the electrolysis is 0.1A / m 2 ~0.3A / m 2 .

6. The method according to claim 1, characterized in that In step (2), the electrolysis temperature is 40° C. to 55° C.; Optionally, the electrolysis time is 6 h to 10 h.

7. The method according to claim 1, characterized in that In step (2), stirring is performed during the electrolysis, and the stirring speed is 250 rpm to 500 rpm.

8. The method according to claim 1, characterized in that In step (2), the anode electrode includes a platinum electrode, a graphite electrode or a gold electrode; Optionally, the cathode electrode comprises a platinum electrode or a gold electrode.

9. The method according to claim 1, characterized in that The mass of bismuth in the residual electrolyte solution is determined by atomic absorption spectrophotometry.

10. The method according to claim 1, characterized in that In step (3), the mass of tellurium in the bismuth-tellurium mixed solution is determined by inductively coupled plasma-mass spectrometry.

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