Preparation method of high-purity cobalt

Abstract

The invention discloses a preparation method of high-purity cobalt, and relates to the technical field of high-purity metal purification, and the preparation method is technically characterized by comprising the following steps: pretreatment reagent purification: analytically pure hydrogen peroxide passes through a filter containing organic carbon, is filtered at the rate of 8-10 L / h, and is rectified and refluxed for 5 hours at the normal pressure of 54 DEG C to obtain electronic-grade hydrogen peroxide; the method comprises the following steps: crushing analytically pure sodium phosphate, adding pure water, heating to 70-80 DEG C, dissolving, filtering, adding 5L of high-quality pure acetic acid, washing with pure water to obtain a sodium phosphate precipitate, adding 50L of pure water, and re-dissolving for later use; through collaborative optimization of front-end chemical deep impurity removal and rear-end ion exchange and electro-deposition processes, the strict requirements of the high-end field on the impurity content are accurately met; the optimal dosage window of hydrogen peroxide / sodium phosphate of 0.3-0.5 L / 100kg and the balance control of the electrolysis voltage of 4-5V are adopted.

Description

Technical Field

[0001] The present invention relates to the technical field of high-purity metal purification, and in particular to a method for preparing high-purity cobalt. Background Art

[0002] Currently, the production of high-purity cobalt generally requires ion exchange resins with outstanding properties and controlled electrodeposition conditions. The resin is used to adsorb specific impurity ions and the precipitation rate of metal ions is controlled by adjusting the current and voltage for purification. The impurity content of the electrolyte produced by this method is still very high, and controlling the electrolysis rate inevitably sacrifices output. This method has high production costs, low efficiency and poor stability. Summary of the Invention

[0003] In response to the shortcomings of the existing technology, the present invention provides a method for preparing high-purity cobalt. The preparation method effectively purifies the cobalt salt at the front end, ensures the fault tolerance of the back end, and improves the electrolysis yield.

[0004] To achieve the above object, the present invention provides the following technical solution: a method for preparing high-purity cobalt, comprising the following steps: Step (1) Pretreatment reagent purification: Analytical grade hydrogen peroxide was filtered through a filter containing organic carbon at a rate of 8-10 L / h, and then distilled and refluxed at 54°C and atmospheric pressure for 5 hours to obtain electronic grade hydrogen peroxide. After grinding analytical grade sodium phosphate, add pure water and heat to 70-80℃ to dissolve, filter and add 5L of high-grade pure acetic acid, wash with pure water to obtain sodium phosphate precipitate, add 50L of pure water to dissolve again for later use; Step (2) chemical deep impurity removal: Dissolve the cobalt chloride crystals in 50-60°C pure water, filter, add 0.3-0.5L / 100kg of cobalt chloride obtained in step (1) of electronic grade hydrogen peroxide, and stir for 10 minutes; Add 0.3-0.5 L / 100 kg of cobalt chloride to the sodium phosphate solution obtained in step (1), stir for 10 minutes, let it stand and cool for 1 hour, and then filter; Step (3) ion exchange to remove copper: The filtrate from step (2) is passed through an ion exchange column loaded with a copper-removing chelating resin at a flow rate of 3-5 L / h; Step (4) Preparation of high-purity cobalt by electrodeposition: The solution obtained in step (3) was supplemented with 50 ml each of hydrogen peroxide and sodium phosphate, and the mixture was diluted and transferred to the electrolytic cell; High-purity cobalt is obtained by electrolytic deposition at a cell voltage of 4-5V using a titanium plate as the cathode and a ruthenium mesh as the anode.

[0005] Preferably, the sodium phosphate in step (1) is at least one of trisodium phosphate, sodium metaphosphate, sodium tripolyphosphate or sodium pyrophosphate.

[0006] Preferably, in step (2), hydrogen peroxide oxidizes Fe²⁺ to Fe³⁺ (wherein, hydrogen peroxide has the ability to adsorb organic impurities and oxidize, and can oxidize Fe²⁺ to Fe³⁺, the reaction formula is as follows: Fe²⁺+H2O2→Fe³⁺+H2O+O2, Fe³⁺ is easier to precipitate and remove), and sodium phosphate forms a precipitate or complex with at least one of Fe³⁺, Mg²⁺, Cu²⁺, Ag⁺, Pb²⁺, Cd²⁺, Hg²⁺, and Cr³⁺, which has an excellent effect on Fe that is difficult to remove in the preparation of high-purity cobalt. The relevant reaction is as follows: 3(PO4)³⁻+Fe³⁺→

Fe(PO4)3

[0007] Preferably, the dilution ratio of the solution before electrolysis in step (4) is 300 L of electrolytic cell volume for every 100 kg of raw material cobalt chloride.

[0008] High-purity cobalt, wherein the purity of the high-purity cobalt is ≥99.9995%, Fe is ≤0.2ppm, Pb, Zn, Ag, Al, Mg, Mn are ≤0.1ppm, and Ni is ≤0.5ppm.

[0009] Compared with the existing technology, the present invention provides a method for preparing high-purity cobalt with the following beneficial effects: first, the present invention precisely meets the stringent requirements of high-end fields for impurity content through the coordinated optimization of front-end chemical deep impurity removal and back-end ion exchange and electrodeposition processes; second, through the balanced control of the optimal dosage window of hydrogen peroxide / sodium phosphate of 0.3-0.5L / 100kg and the electrolysis voltage of 4-5V, it avoids the problems of insufficient impurity removal or sodium contamination, and achieves a shortened production cycle and increased output. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 A histogram of the cycles is generated for the embodiments of the present invention and the comparative example. DETAILED DESCRIPTION

[0011] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention. Purity and impurity content analysis Glow discharge mass spectrometry (GD-MS): Refer to GB / T25934-2010 Chemical analysis method of high purity gold - Determination of impurity element content by glow discharge mass spectrometry, suitable for full element analysis of high purity metals above 99.999%. Inductively coupled plasma mass spectrometry (ICP-MS): Refer to GB / T 23364-2009 Chemical analysis method of high-purity indium hydroxide - Determination of magnesium, aluminum, silicon, chromium, manganese, iron, nickel, copper, zinc, arsenic, cadmium, tin, antimony, tungsten, lead and bismuth by inductively coupled plasma mass spectrometry to assist in verifying ppm-level impurity content.

[0012] Atomic Absorption Spectrophotometry (AAS): Refer to GB / T 15072.6-2008 Chemical Analysis Methods for Precious Metal Alloys - Determination of Copper, Manganese, Nickel, Aluminum, Iron, Zinc, Tin, Lead and Silicon in Silver Alloys - Atomic Absorption Spectrophotometry for precise calibration of specific elements (e.g., Cu and Fe). Production capacity parameter determination Production cycle timing: Refer to the "test duration recording" principle in "GB / T3354-2014 Test method for tensile properties of oriented fiber reinforced plastics" to accurately record the continuous time from the start to the end of electrolysis.

[0013] Output weighing: Refer to the sample weighing specifications in "GB / T223.1-2008 Steel and Alloy - Determination of Carbon Content - Gravimetric Method" and use an electronic balance with an accuracy of 0.1g to measure the mass of the cobalt product after electrolysis. High-purity cobalt purity and impurity content test (GD-MS method) Sample pretreatment: Cut a 10 mm × 10 mm × 2 mm sample block from the electrolytically obtained high-purity cobalt product and ultrasonically clean it with anhydrous ethanol for 15 minutes to remove surface oil and debris. Rinse it three times with deionized water and dry it in a vacuum drying oven (60°C, -0.1 MPa) for 2 hours. Cool it to room temperature and set aside.

[0014] Instrument preparation: Start the glow discharge mass spectrometer and preheat it for 1 hour to ensure that the instrument vacuum reaches above 5×10^-7Pa. The instrument was calibrated using standard samples (cobalt standard samples with a purity of 99.9999%), and the calibration elements covered the target elements involved in this application, such as Fe, Pb, Zn, Ag, Al, Mg, Mn, Ni, Cu, and Na.

[0015] Test condition settings: discharge voltage: 700 V, discharge current: 30 mA, argon carrier gas flow rate: 450 mL / min. Mass spectrometry resolution: 5000 (10% peak-to-valley ratio), scanning range: 1-250 amu (atomic mass unit).

[0016] Each sample was scanned 3 times, each scanning time was 60 seconds, and the average value was taken as the test result.

[0017] Data collection and calculation The ion intensity of each impurity element was recorded and converted into mass fraction (unit: %) using the calibration curve.

[0018] Purity calculation formula: Purity of high-purity cobalt (%) = 100% minus the sum of the mass fractions of all impurity elements (%). Calculation of impurity content (ppm): Impurity content of a certain element (ppm) = mass fraction of the element (%) multiplied by 10^6. Auxiliary verification of impurity content (ICP-MS method) Sample Dissolution: Weigh 0.5 g (accurate to 0.0001 g) of high-purity cobalt sample into a polytetrafluoroethylene beaker. Add 10 mL of ultra-pure nitric acid and heat at low temperature until completely dissolved. After cooling, transfer to a 100 mL volumetric flask, dilute to the mark with deionized water, and shake well to obtain the test solution (concentration approximately 5 mg / mL). Instrument parameters: RF power: 1550 W, plasma gas flow: 18 L / min, auxiliary gas flow: 1.2 L / min, nebulizer flow: 0.9 L / min, sampling depth: 8 mm, integration time: 0.1 s / element.

[0019] Calibration and testing: Prepare multi-element standard solutions at concentrations of 0.1 ppb, 1 ppb, 10 ppb, and 100 ppb and plot a calibration curve (correlation coefficient ≥ 0.999). Dilute the test solution 100-fold and inject it into the instrument. Measure the signal intensity of each element and calculate the concentration based on the calibration curve. Result conversion: Impurity content of a certain element (ppm) = (element concentration in the test solution (μg / L) × constant volume (L)) ÷ sample mass (g). Capacity parameter test Production cycle measurement: Start timing from the moment the electrolytic cell is powered on and stop timing when electrolysis is completed (when the cobalt deposition thickness reaches the preset value). The recorded time is the production cycle (unit: hours). Use an electronic stopwatch with an accuracy of 0.1 second. Repeat the test three times in parallel and take the average value. Yield Determination: After electrolysis, remove the cobalt product from the cathode titanium plate, rinse with deionized water until neutral, and vacuum dry at 60°C for 2 hours. Weigh the mass of the dried cobalt product using an electronic balance with a precision of 0.1g to obtain the single-shot yield (unit: kg). Calculate the output corresponding to every 100kg of cobalt chloride raw material: Output (kg / 100kg of raw material) = (actual output ÷ amount of cobalt chloride raw material used) × 100.

[0020] Example 1: A method for preparing high-purity cobalt, comprising the following steps: Purification of pretreatment reagents: Analytical grade hydrogen peroxide is passed through a filter containing organic carbon, filtered at a rate of 8 L / h, and then distilled and refluxed at 54°C and normal pressure for 5 hours to obtain electronic grade hydrogen peroxide; analytical grade sodium phosphate (trisodium phosphate is used) is crushed, added to pure water and heated to 70°C to dissolve, filtered, and then 5 L of high-grade pure acetic acid is added. The sodium phosphate precipitate is washed with pure water to obtain a sodium phosphate precipitate, and 50 L of pure water is added to dissolve it again for later use. Chemical deep impurity removal: Weigh 100 kg of cobalt chloride crystals and dissolve them in 50°C pure water. After filtering, add 0.3 L of electronic-grade hydrogen peroxide obtained in step 1 and stir for 10 min. Add 0.3 L of sodium phosphate solution obtained in step 1 and stir for 10 min. After standing and cooling for 1 h, filter at a rate of 10 L / h using a 1 μm pore size filter membrane. Ion exchange copper removal: The filtrate from step 2 was passed through an ion exchange column filled with copper-removing chelating resin at a flow rate of 3 L / h. Preparation of high-purity cobalt by electrodeposition: Add 50 ml each of hydrogen peroxide and sodium phosphate to the solution obtained in step 3, dilute to a volume of 300 L per 100 kg of raw material, and transfer to an electrolytic cell. Electrolytic deposition is performed at a cell voltage of 4 V using a titanium plate as the cathode and a ruthenium mesh as the anode to obtain high-purity cobalt.

[0021] Example 2: Purification of pretreatment reagents: Analytical-grade hydrogen peroxide was passed through a filter containing organic carbon, filtered at a rate of 9 L / h, and then distilled and refluxed at 54°C under normal pressure for 5 hours to obtain electronic-grade hydrogen peroxide; analytical-grade sodium phosphate (a mixture of sodium metaphosphate and sodium tripolyphosphate) was crushed, added to pure water and heated to 75°C to dissolve, filtered, and then 5 L of high-grade pure acetic acid was added. The sodium phosphate precipitate was washed with pure water to obtain a sodium phosphate precipitate, which was then redissolved in 50 L of pure water for later use. Chemical deep impurity removal: Weigh 100 kg of cobalt chloride crystals and dissolve them in 55°C pure water. After filtering, add 0.4 L of electronic-grade hydrogen peroxide obtained in step 1 and stir for 10 min. Add 0.4 L of sodium phosphate solution obtained in step 1 and stir for 10 min. After cooling for 1 h, filter through a 0.8 μm pore size filter membrane at a rate of 15 L / h. Ion exchange copper removal: The filtrate from step 2 was passed through an ion exchange column filled with copper-removing chelating resin at a flow rate of 4 L / h. Preparation of high-purity cobalt by electrodeposition: Add 50 ml each of hydrogen peroxide and sodium phosphate to the solution obtained in step 3, dilute to a volume of 300 L per 100 kg of raw material, and transfer to an electrolytic cell. Electrolytic deposition is performed at a cell voltage of 4.5 V using a titanium plate as the cathode and a ruthenium mesh as the anode to obtain high-purity cobalt.

[0022] Example 3: Purification of pretreatment reagents: Analytical grade hydrogen peroxide was passed through a filter containing organic carbon, filtered at a rate of 10 L / h, and then distilled and refluxed at 54°C and normal pressure for 5 hours to obtain electronic grade hydrogen peroxide; analytical grade sodium phosphate (sodium pyrophosphate was selected) was crushed, added with pure water and heated to 80°C to dissolve, filtered, and then 5 L of high-grade pure acetic acid was added, and the sodium phosphate precipitate was washed with pure water to obtain a sodium phosphate precipitate, which was then redissolved in 50 L of pure water for later use.

[0023] Chemical deep impurity removal: Weigh 100 kg of cobalt chloride crystals and dissolve them in 60°C pure water. After filtering, add 0.5 L of electronic-grade hydrogen peroxide obtained in step 1 and stir for 10 min. Add 0.5 L of sodium phosphate solution obtained in step 1 and stir for 10 min. After standing and cooling for 1 h, filter through a 0.5 μm pore size filter membrane at a rate of 20 L / h.

[0024] Ion exchange copper removal: The filtrate from step 2 was passed through an ion exchange column filled with copper-removing chelating resin at a flow rate of 5 L / h.

[0025] Preparation of high-purity cobalt by electrodeposition: Add 50 ml each of hydrogen peroxide and sodium phosphate to the solution obtained in step 3, dilute to a volume of 300 L per 100 kg of raw material, and transfer to an electrolytic cell. Electrolytic deposition is performed at a cell voltage of 5 V using a titanium plate as the cathode and a ruthenium mesh as the anode to obtain high-purity cobalt.

[0026] Comparative Example 1: Except for using unpurified analytical grade hydrogen peroxide and sodium phosphate, the remaining steps are the same as those of Example 2. Comparative Example 2: Except for not adding hydrogen peroxide, the remaining steps are the same as those of Example 2. Comparative Example 3: Except for not adding sodium phosphate, the remaining steps are the same as Example 2. In Comparative Example 4, except for omitting the ion exchange step, the remaining steps were the same as those in Example 2. In Comparative Example 5, the dosage of the reagent was 0.2 L / 100 kg, and the rest was the same as in Example 2. In Comparative Example 6, the dosage of the reagent was 0.6 L / 100 kg, and the rest was the same as in Example 2. Comparative Example 7: voltage 3V, and the rest are the same as in Example 2. Comparative Example 8: voltage 6V, and the rest are the same as in Example 2. The high-purity cobalt obtained in Examples 1, 2, and 3 and Comparative Examples 1, 2, 3, 4, 5, 6, 7, and 8 were grouped as GCG-01, GCG-02, GCG-03, GCG-04, GCG-05, GCG-06, GCG-07, GCG-08, GCG-09, GCG-10, and GCG-11, respectively. Production cycle and yield tests were performed on the examples and comparative examples, and impurity tests (unit: ppm) were performed on the high-purity cobalt obtained in the examples and comparative examples. Specific test results are shown in Tables 1 and 2.

[0027] Table 1

[0028] Table 2

[0029] The present invention uses the "three-stage impurity removal + optimized electrodeposition" process to stably prepare high-purity cobalt with a purity of ≥99.9995%, wherein Fe≤0.2ppm, Pb, Zn, Ag, Al, Mg, Mn≤0.1ppm, and Ni≤0.5ppm; the present invention removes impurities in advance through front-end chemical impurity removal, and the back-end ion exchange and electrodeposition pressure is greatly reduced, the purity is increased from 99.99% to above 99.9995%, and the impurity control accuracy is improved by 2 orders of magnitude; 4-5V The electrolysis cycle under high voltage is only 6-8h, and the output reaches 85-95kg / 100kg of raw materials, which is more than 150% higher than the traditional method, achieving the synergy of high purity and high production capacity; 0.3-0.5L / 100kg of hydrogen peroxide / sodium phosphate is the optimal window: below 0.3L, impurities are not completely removed, and above 0.5L, sodium contamination is introduced. This range can stably ensure that the impurity indicators meet the standards; 4-5V voltage achieves balance: below 4V, the rate is halved, and above 5V, impurities are precipitated. This range takes into account both production capacity and purity.

[0030] By using cheap reagents after purification, the cost is not only reduced, but also the purity fluctuation is smaller in continuous production and the stability is excellent.

[0031] The above are only specific embodiments of the present invention, but the technical features of the present invention are not limited thereto. Any simple changes, equivalent substitutions, or modifications based on the present invention to solve substantially the same technical problems and achieve substantially the same technical effects are all included in the scope of protection of the present invention.

Claims

1. A method for preparing high-purity cobalt, characterized in that: The following steps are involved: Step (1) Pretreatment reagent purification: Analytical grade hydrogen peroxide was passed through a filter containing organic carbon at a rate of 8-10 L / h, and then distilled and refluxed at 54°C and atmospheric pressure for 5 hours to obtain electronic grade hydrogen peroxide. After grinding analytical grade sodium phosphate, add pure water and heat to 70-80℃ to dissolve, filter and add 5L pure acetic acid, wash with pure water to obtain sodium phosphate precipitate, add 50L pure water to dissolve again for later use; Step (2) chemical deep impurity removal: Dissolve the cobalt chloride crystals in 50-60°C pure water, filter, add 0.3-0.5L / 100kg of cobalt chloride obtained in step (1) of electronic grade hydrogen peroxide, and stir for 10 minutes; Add 0.3-0.5 L / 100 kg of cobalt chloride to the sodium phosphate solution obtained in step (1), stir for 10 minutes, let it stand and cool for 1 hour, and then filter; Step (3) ion exchange to remove copper: The filtrate from step (2) is passed through an ion exchange column loaded with a copper-removing chelating resin at a flow rate of 3-5 L / h; Step (4) Preparation of high-purity cobalt by electrodeposition: The solution obtained in step (3) was supplemented with 50 ml each of hydrogen peroxide and sodium phosphate, and the mixture was diluted and transferred to the electrolytic cell; High-purity cobalt is obtained by electrolytic deposition at a cell voltage of 4-5V using a titanium plate as the cathode and a ruthenium mesh as the anode.

2. The method for preparing high-purity cobalt according to claim 1, wherein: The sodium phosphate in step (1) is at least one of trisodium phosphate, sodium metaphosphate, sodium tripolyphosphate or sodium pyrophosphate.

3. The method for preparing high-purity cobalt according to claim 1, wherein: In step (2), hydrogen peroxide oxidizes Fe²⁺ to Fe³⁺, and sodium phosphate forms a precipitate or complex with at least one of Fe³⁺, Mg²⁺, Cu²⁺, Ag⁺, Pb²⁺, Cd²⁺, Hg²⁺, and Cr³⁺.

4. The method for preparing high-purity cobalt according to claim 1, wherein: The filtration in step (2) uses a filter membrane with a pore size of ≤1 μm and a filtration rate of 10-20 L / h.

5. The method for preparing high-purity cobalt according to claim 1, wherein: The dilution ratio of the solution before electrolysis in step (4) is 300 L of electrolytic cell volume for every 100 kg of raw material cobalt chloride.

6. A high-purity cobalt prepared by the method according to any one of claims 1 to 5, characterized in that: The high-purity cobalt has a purity of ≥99.9995%, Fe ≤0.2ppm, Pb, Zn, Ag, Al, Mg, Mn ≤0.1ppm, and Ni ≤0.5ppm.

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