Method for simultaneously determining contents of oxides of lithium, sodium, potassium, calcium and magnesium elements in lithium ore based on inductively coupled plasma emission spectrometry

Abstract

The invention discloses a method for simultaneously determining the contents of oxides of lithium, sodium, potassium, calcium and magnesium elements in lithium ore based on inductively coupled plasma emission spectrometry, which is characterized by comprising the following steps: adding hydrochloric acid, nitric acid, hydrofluoric acid and perchloric acid into a lithium ore sample, heating and dissolving the sample at 100-120 DEG C, steaming to be nearly dry, and measuring the content of the oxides of the lithium, sodium, potassium, calcium and magnesium elements in the lithium ore sample; adding dilute nitric acid formed by mixing nitric acid and water in equal volume, and adding distilled water to a constant volume to obtain a to-be-detected sample solution; detecting the to-be-detected sample solution by adopting an inductively coupled plasma emission spectrometer to obtain emission intensity of each element under corresponding detection wavelength; and finally, calculating the concentration of each element in the to-be-detected sample solution according to the standard curve, and calculating the content of oxides of lithium, sodium, potassium, calcium and magnesium elements in the lithium ore. The method has the advantages of high accuracy, low detection limit, wide linear range and short detection time.

Description

Technical Field

[0001] The present invention relates to a lithium ore detection method, in particular to a method for simultaneously determining the contents of lithium, sodium, potassium, calcium and magnesium oxides in lithium ore based on inductively coupled plasma emission spectrometry. Background Art

[0002] Lithium and its alloys are widely used in high-tech fields. The rapid development of new energy vehicles in recent years has further increased China's demand for lithium. Currently, lithium ore imports are increasing annually, reaching 5.5624 million tons in 2024, a year-on-year increase of 26%. Therefore, accurate measurement of the content of key elements in lithium ore is crucial for guiding lithium ore imports. Current standards for testing lithium in lithium ore include "GB / T 17413.1-2010 Methods for Chemical Analysis of Lithium, Rubidium, and Cesium Ores - Part 1: Determination of Lithium Content," and the YS / T 509 series of standards for testing spodumene and lepidolite concentrates. The content of lithium oxide, sodium oxide, potassium oxide, calcium oxide, and magnesium oxide in spodumene and lepidolite concentrates is determined using atomic absorption spectrometry. This method requires multiple sample dissolutions and the spectrometer must be equipped with lamps for these elements. Each time an element is detected, a lamp must be replaced, resulting in the same solution needing to be measured five times. This is relatively inefficient and unsuitable for large-scale sample testing. X-ray fluorescence spectrometry is complex to establish calibration curves and requires high sample matrix consistency. It also suffers from insufficient sensitivity for detecting light elements such as lithium and sodium. Inductively coupled plasma optical emission spectrometry, on the other hand, does not require an element lamp and can detect these elements in a single dissolution, significantly accelerating detection speed and making it widely used in the testing of imported ores. While there are reports on the determination of elemental content in lithium ores using inductively coupled plasma optical emission spectrometry (ICP-AES), there are few reports on the simultaneous determination of lithium, sodium, potassium, calcium, and magnesium in lithium ores using ICP-AES.

[0003] Currently, the methods for dissolving lithium ore generally include acid dissolution and alkaline fusion. Since the alkaline fusion method is not friendly to the instrument and will introduce a large amount of salt, the sodium ions in the salt will make the matrix effect more serious. The large amount of salt introduced will also be deposited on the atomizer, causing signal attenuation and even clogging the atomizer. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for simultaneously determining the lithium, sodium, potassium, calcium and magnesium contents in lithium ore based on inductively coupled plasma emission spectrometry with high accuracy, low detection limit, wide linear range and short detection time.

[0005] The technical solution adopted by the present invention to solve the above technical problems is: a method for simultaneously determining the content of lithium, sodium, potassium, calcium and magnesium oxides in lithium ore based on inductively coupled plasma optical emission spectrometry, which is characterized by comprising the following steps:

[0006] Step 1: Sample pretreatment

[0007] Weigh a dried lithium ore sample with a particle size of less than 105 μm, add hydrochloric acid, nitric acid, hydrofluoric acid and perchloric acid, and heat at 100-120°C to dissolve the sample. After dissolution is complete, evaporate to near dryness, add dilute nitric acid prepared by mixing equal volumes of nitric acid and water, add distilled water to the volume, and let it stand for 20-40 minutes to obtain a sample solution to be tested;

[0008] Step 2: Sample testing

[0009] The sample liquid to be tested obtained in step 1 is detected by inductively coupled plasma emission spectrometry, and the emission power is set to 1-1.3 kW, the integration time is 5 s, the plasma gas flow rate is 12-16.5 L / min, the atomizing gas flow rate is 0.65-0.95 L / min, the pump speed is 10-18 rpm, and the observation height is selected to be 6-10 mm. The emission intensity of each element of lithium, sodium, potassium, calcium and magnesium in the lithium ore is detected at the corresponding detection wavelength;

[0010] Step 3: Concentration calculation

[0011] The concentrations of lithium, sodium, potassium, calcium and magnesium in the lithium ore sample standard solution were used as the horizontal axis and the emission intensity was used as the vertical axis to draw a standard curve. The concentrations of each element in the sample solution to be tested were calculated according to the standard curve. The content of lithium, sodium, potassium, calcium and magnesium oxides in the lithium ore was further calculated according to formula (1).

[0012]

[0013] Where:

[0014] w i ---The content of oxide of the element to be measured, in mass fraction %;

[0015] P---oxide conversion coefficient, the P value of Li2O is 2.1527, the P value of Na2O is 1.3480, the P value of K2O is 1.2046, the P value of CaO is 1.3992, and the P value of MgO is 1.6582;

[0016] m---sample quantity, in grams (g);

[0017] c1---the concentration of the element to be measured in the sample solution, in micrograms per milliliter;

[0018] c0---the concentration of the element to be tested in the blank sample, in micrograms per milliliter;

[0019] 100---The initial fixed volume of the sample solution, in milliliters;

[0020] f---Dilution factor of the sample solution.

[0021] Furthermore, in step 1, the ratio of the lithium ore sample, hydrochloric acid, nitric acid, hydrofluoric acid, perchloric acid, dilute nitric acid and constant volume is 0.1 g: 10 mL: 3 mL: 3 mL: 2 mL: 5 mL: 100 mL.

[0022] Further, the detection wavelengths of lithium in the lithium ore described in step 2 are selected as 670.783nm and 610.365nm, the detection wavelengths of sodium are selected as 588.995nm and 589.592nm, the detection wavelength of potassium is selected as 766.491nm, the detection wavelength of calcium is selected as 315.887nm, and the detection wavelength of magnesium is selected as 285.213nm and 279.553nm.

[0023] Furthermore, the parameters of the inductively coupled plasma emission spectrometer in step 2 were set as follows: emission power of 1.2 kW, integration time of 5 s, plasma gas flow rate of 12 L / min, atomizing gas flow rate of 0.75 L / min, pump speed of 17 rpm, and observation height of 6 mm.

[0024] Furthermore, the standard curves of each element in step 3 are as follows:

[0025]

[0026] Compared with the prior art, the advantages of the present invention are: the present invention is based on the method for simultaneously determining the content of lithium, sodium, potassium, calcium and magnesium in lithium ore by inductively coupled plasma optical emission spectrometry, and selects 10 mL of hydrochloric acid, 3 mL of nitric acid, 3 mL of hydrofluoric acid and 2 mL of perchloric acid to dissolve the lithium ore sample by low-temperature heating in an open system, so that each element is dissolved more thoroughly, no other reagents are introduced, and the influence of the matrix effect is reduced. The parameters of the inductively coupled plasma optical emission spectrometer were optimized, and the optimal analytical lines for each element were selected. Li (670.783nm, 610.365nm), K766.491nm, Na (588.995nm, 589.592nm), Ca315.887nm, and Mg (285.213nm, 279.553nm) were selected as analytical lines. The detection limit of the method was calculated to be 0.0047μg / mL-0.067μg / mL. Taking 3 times the detection limit as the lower detection limit, the quantification limit of the oxides of the five elements was calculated to be 0.0030%-0.027%. Under the selected instrument conditions, the method's precision and accuracy were verified for reference materials GBW07152 and GBW07733. The method's precision (RSD, n=10) for the five oxides ranged from 0.63% to 2.85%. Spike recovery experiments for each element revealed recoveries ranging from 96% to 104%. This method, with its high accuracy, low detection limit, wide linear range, and short detection time, meets the requirements for testing imported lithium ores and is therefore suitable for widespread use. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is the element spectrum diagram in Example 3. DETAILED DESCRIPTION

[0028] The present invention will be described in further detail below with reference to the accompanying drawings and embodiments.

[0029] Example 1: A method for simultaneously determining the contents of lithium, sodium, potassium, calcium, and magnesium oxides in lithium ore based on inductively coupled plasma optical emission spectrometry, comprising the following steps:

[0030] Step 1: Sample pretreatment method

[0031] Prepare the sample according to GB / T 2007.2-1986. The sample particle size is less than 105μm. Pre-dry the sample in an oven at 105℃~110℃ for 2 hours, remove it, and place it in a desiccator for later use. Accurately weigh 0.10g of lithium ore sample, add 10mL hydrochloric acid (analytical grade), 3mL nitric acid (analytical grade), 3mL hydrofluoric acid (analytical grade), and 2mL perchloric acid (analytical grade). Heat at 100-120℃ to dissolve the sample. After dissolution is complete, evaporate to near dryness, add 5mL of dilute nitric acid prepared by mixing nitric acid (analytical grade) and water in a volume ratio of 1:1, add distilled water to 100mL, and let it stand for 30 minutes to obtain the sample solution to be tested.

[0032] Step 2: Sample testing

[0033] After the inductively coupled plasma emission spectrum stabilized, the experimental conditions were optimized, and the standard solution, sample, and standard substance were tested. The optimal spectral line of each element was selected. The emission power was 1.2 kW, the integration time was 5 s, the plasma gas flow rate was 12 L / min, the atomizing gas flow rate was 0.75 L / min, the pump speed was 17 rpm, the observation height was 6 mm, and the sampling was performed three times. The detection wavelengths of the optimal spectral lines of each element were 670.783 nm and 610.365 nm for lithium, 588.995 nm and 589.592 nm for sodium, 766.491 nm for potassium, 315.887 nm for calcium, and 285.213 nm and 279.553 nm for magnesium.

[0034] Step 3: Concentration calculation

[0035] The element concentration and emission intensity in the calibration solution are used as the horizontal and vertical coordinates to draw a calibration curve, and the emission intensity of each element in the sample solution to be tested at the corresponding wavelength is measured. The concentration of the sample solution to be tested is calculated according to the calibration curve, and the oxide content of the five elements is further calculated. The calculation formula is shown in formula (1):

[0036]

[0037] Where: w i --- Oxide content of the element to be measured, in mass fraction (%);

[0038] P---oxide conversion coefficient. The oxide content in the sample is calculated according to formula (2), formula (3), formula (4), formula (5), and formula (6). The value is expressed in percentage. According to formula (2), formula (3), formula (4), formula (5), and formula (6), the P value of Li2O is 2.1527, the P value of Na2O is 1.3480, the P value of K2O is 1.2046, the P value of CaO is 1.3992, and the P value of MgO is 1.6582.

[0039] m---sample quantity, in grams (g);

[0040] c1---the concentration of the element to be tested in the sample solution, in micrograms per milliliter (μg / mL);

[0041] c0---the concentration of the element to be measured in the blank sample, in micrograms per milliliter (μg / mL);

[0042] 100---The initial fixed volume of the sample solution, in milliliters (mL);

[0043] f---Dilution factor of the sample solution.

[0044]

[0045] ω (CaO) =ω (Ca) ×1.3992 (5);

[0046] ω (MgO) =ω (Mg) ×1.6582 (6).

[0047] Example 2: Selection of Dissolving Acid Type in Lithium Ore Sample Pretreatment

[0048] Five different combinations of mixed acids were selected for sample digestion, as shown in Schemes 1-5.

[0049] Solution 1: Accurately weigh 0.10 g of lithium ore sample, add 15 mL of hydrochloric acid, heat and dissolve at 100-120°C for 10 minutes, then add 3 mL of nitric acid and 2 mL of perchloric acid, and heat and dissolve the sample at 100-120°C;

[0050] Solution 2: Accurately weigh 0.10 g of lithium ore sample, add 10 mL of hydrofluoric acid and 2 mL of sulfuric acid, and heat at 100-120°C to dissolve the sample.

[0051] Solution 3: Accurately weigh 0.10 g of lithium ore sample, add 10 mL of hydrochloric acid, 3 mL of nitric acid, 3 mL of hydrofluoric acid and 2 mL of perchloric acid, and heat at 100-120°C to dissolve the sample.

[0052] Solution 4: Accurately weigh 0.10 g of lithium ore sample, add 10 mL of nitric acid, 3 mL of hydrofluoric acid, and 2 mL of perchloric acid, and heat at 100-120°C to dissolve the sample.

[0053] Solution 5: Accurately weigh 0.10 g of lithium ore sample, add 10 mL of hydrofluoric acid and 2 mL of perchloric acid, and heat at 100-120°C to dissolve the sample.

[0054] The sample solutions obtained by dissolving the samples in different mixed acids according to the above schemes 1-5 were tested using the method of Example 1. The results are shown in Table 1.

[0055] Table 1 Comparison of different mixed acid dissolution methods

[0056]

[0057] The test results show that the dissolving acid type selected in Scheme 3 can completely dissolve all standard substances and the test results are consistent with the standards. Therefore, the dissolving acid type in Scheme 3 is the optimal choice.

[0058] Example 3: Selection of measurement conditions for inductively coupled plasma optical emission spectrometry

[0059] Different spectral lines, RF power, plasma gas flow, auxiliary gas flow, peristaltic pump speed and observation height parameters were optimized.

[0060] 1. Selection of analysis lines

[0061] The principle of selecting the analytical spectrum line is that the element to be measured is least affected by the matrix, and at the same time the wavelength with the strongest intensity within the measurement range, that is, the analytical wavelength with high sensitivity and little interference is selected as the first analytical quantitative wavelength as much as possible.

[0062] The spectrum of the standard sample GBW07733 was selected for investigation. Figure 1 The standard sample was tested using the method in Example 1, and the results were as follows: Figure 1 As shown by Figure 1 It can be seen that the corresponding intensity of each element in the standard sample at different wavelengths is determined by comprehensively considering sensitivity, signal-to-background ratio and stability factors. The recommended analysis spectral lines for each element are shown in Table 2.

[0063] Table 2 Element analysis spectral lines

[0064]

[0065] 2. Selection of RF power

[0066] Different emission powers were selected and the experimental standard solution 3 (STD3) in Table 8 was measured using the method of Example 1. The corresponding signal intensities were recorded. The results are shown in Table 3.

[0067] Table 3 RF power test results

[0068]

[0069] Experimental results show that as the transmission power increases, the spectral line intensity of the measured elements gradually increases, while the background intensity also increases. Because this method measures multiple trace and major elements, the major elements are present in high concentrations in the sample, so the signal intensity should not be too high. Trace elements, however, are present in lower concentrations in the sample, so high spectral line intensity and low background intensity are required. Therefore, considering all factors, the RF power selected was 1.2 kW.

[0070] 3. Selection of plasma gas flow

[0071] Different plasma gas flow rates were selected, and the experimental standard solution 3 (STD3) in Table 8 was measured using the method of Example 1. The corresponding signal intensities were recorded. The results are shown in Table 4.

[0072] Table 4 Plasma gas flow experimental results

[0073]

[0074]

[0075] The test results show that when the plasma gas flow rate is 12L / min, the intensity of most elements reaches the maximum value. Taking into account the simultaneous determination of multiple elements in this experiment, the plasma gas flow rate of 12L / min is selected in this experiment.

[0076] 4. Selection of auxiliary gas flow

[0077] Different auxiliary gas flow rates were selected and the experimental standard solution 3 (STD3) in Table 8 was measured using the method of Example 1. The corresponding signal intensities were recorded. The results are shown in Table 5.

[0078] Table 5 Auxiliary gas flow rate experimental results

[0079]

[0080] The test results show that: with the increase of auxiliary gas flow rate, considering the simultaneous determination of multiple elements in this experiment, the atomizing gas flow rate is selected as 0.75L / min.

[0081] 5. Selection of peristaltic pump speed

[0082] Different peristaltic pump speeds were selected, and the experimental standard solution 3 (STD3) in Table 8 was measured using the method of Example 1. The corresponding signal intensities were recorded. The results are shown in Table 6.

[0083] Table 6 Peristaltic pump speed experimental results

[0084]

[0085] The test results show that as the pump speed increases, the change trend of the spectral intensity value of the measured element is not obvious. Therefore, the pump speed selected in this experiment is the instrument recommended value: 17 rpm.

[0086] 6. Observation height

[0087] Different observation heights were selected and the experimental standard solution 3 (STD3) in Table 8 was measured using the method of Example 1. The corresponding signal intensities were recorded. The results are shown in Table 7.

[0088] Table 7 Observation height test results

[0089]

[0090] From the results in Table 7 above, the observation height is selected as 6 mm.

[0091] In summary, the optimal working conditions for this instrument were finally determined as follows: RF power of 1.2 kW, plasma flow rate of 12 L / min, nebulizer flow rate of 0.85 L / min, auxiliary gas flow rate of 0.75 L / min, observation height of 6 mm, and pump speed of 17 rpm.

[0092] Example 4. Determination of the detection limit and measurement range of the method of Example 1.

[0093] 1. Establishment of standard curve and linear correlation

[0094] Ten mixed standard curves were prepared according to Table 8. The multi-element standard solution series were measured using the method established in Example 1. Working curves were plotted with the mass concentration of the analyzed element as the abscissa and the emission intensity as the ordinate. The regression equations and correlation coefficients for each element are shown in Table 9.

[0095] Table 8 Li, K, Na, Ca, Mg in standard solutions (μg / mL)

[0096]

[0097]

[0098] Table 9 Standard curves and correlation coefficients of each element

[0099]

[0100] 2. Determination of detection limit

[0101] A full-process laboratory blank was prepared according to the sample analysis procedures. Eleven consecutive measurements were performed using the conditions of Example 1. The standard deviation of the intensity results for each element was calculated. The detection limit for each element was calculated by dividing three times the standard deviation by the slope of the working curve. The limit of quantification was determined as three times the detection limit. The upper limit of detection was determined based on the highest point of the working curve and the dilution factor. The results are shown in Table 10.

[0102] Table 10 Method detection limit and quantification limit

[0103]

[0104] According to the detectable range of the working curve, the lower limit of detection of each element oxide was determined to be 0.003-0.027%. The upper limit of detection was calculated based on the highest point of the curve, combined with a sample weight of 0.1 g, a fixed volume of 100 mL, and a maximum dilution of 5 times, which were 21.5%, 12.0%, 13.4%, 13.9%, and 16.5%, respectively.

[0105] Example 5. Determination of the precision and accuracy of the method of Example 1.

[0106] 1. Precision determination

[0107] Precision refers to the degree of agreement between indications or measured values obtained from repeated measurements of the same or similar measured objects under specified conditions. It is a prerequisite for characterizing accuracy. The precision of test results obtained from 10 consecutive measurements of two standards is shown in Table 11.

[0108] Table 11 Precision and accuracy of the method

[0109]

[0110] 2. Spike recovery experiment

[0111] 0.1000 g of each of the imported lithium ore samples 1# and 2# were weighed, treated with mixed acid and added with a standard solution, and detected by the ICP-AES method established in Example 1. Each sample was tested three times, and the average value was taken to calculate the test results. The specific results are shown in Table 12.

[0112] Table 12 Spike recovery

[0113]

[0114] As shown in Table 12, the recovery rate of the spiked lithium ore samples is between 96% and 104%, which meets the requirement of 90% to 110% recovery rate of mineral products.

[0115] The above description is not intended to limit the present invention, and the present invention is not limited to the above examples. Any changes, modifications, additions or substitutions made by persons of ordinary skill in the art within the spirit and scope of the present invention shall also fall within the scope of protection of the present invention.

Claims

1. A method for simultaneously determining the content of lithium, sodium, potassium, calcium and magnesium oxides in lithium ore based on inductively coupled plasma optical emission spectrometry, characterized in that The following steps are involved: Step 1: Sample pretreatment Weigh the dried lithium ore sample, add hydrochloric acid, nitric acid, hydrofluoric acid and perchloric acid, heat at 100-120 ° C to dissolve the sample, evaporate to dryness, add dilute nitric acid prepared by mixing equal volumes of nitric acid and water, add distilled water to make up to volume, and let it stand for 20-40 minutes to obtain the sample solution to be tested; Step 2: Sample testing The sample liquid to be tested obtained in step 1 is detected by inductively coupled plasma emission spectrometry, and the emission power is set to 1-1.3 kW, the integration time is 5 s, the plasma gas flow rate is 12-16.5 L / min, the atomizing gas flow rate is 0.65-0.95 L / min, the pump speed is 10-18 rpm, and the observation height is selected to be 6-10 mm. The emission intensity of each element of lithium, sodium, potassium, calcium and magnesium in the lithium ore is detected at the corresponding detection wavelength; Step 3: Concentration calculation The concentrations of lithium, sodium, potassium, calcium and magnesium in the lithium ore sample standard solution were used as the horizontal axis and the emission intensity was used as the vertical axis to draw a standard curve. The concentrations of each element in the sample solution to be tested were calculated according to the standard curve. The content of lithium, sodium, potassium, calcium and magnesium oxides in the lithium ore was further calculated according to formula (1). Where: w i ---The content of oxide of the element to be measured, in mass fraction %; P---oxide conversion coefficient, the P value of Li2O is 2.1527, the P value of Na2O is 1.3480, the P value of K2O is 1.2046, the P value of CaO is 1.3992, and the P value of MgO is 1.6582; m---sample quantity, in grams; c1---the concentration of the element to be measured in the sample solution, in micrograms per milliliter; c0---the concentration of the element to be tested in the blank sample, in micrograms per milliliter; 100---The initial fixed volume of the sample solution, in milliliters; f---Dilution factor of the sample solution.

2. The method for simultaneously determining the contents of lithium, sodium, potassium, calcium and magnesium oxides in lithium ore based on inductively coupled plasma optical emission spectrometry according to claim 1, characterized in that In step 1, the ratio of lithium ore sample, hydrochloric acid, nitric acid, hydrofluoric acid, perchloric acid, dilute nitric acid and constant volume is 0.1g:10mL:3mL:3mL:2mL:5mL:100mL.

3. The method for simultaneously determining the contents of lithium, sodium, potassium, calcium and magnesium oxides in lithium ore based on inductively coupled plasma optical emission spectrometry according to claim 1, characterized in that In step 2, the detection wavelengths of lithium in the lithium ore are selected as 670.783nm and 610.365nm, the detection wavelengths of sodium are selected as 588.995nm and 589.592nm, the detection wavelength of potassium is selected as 766.491nm, the detection wavelength of calcium is selected as 315.887nm, and the detection wavelengths of magnesium are selected as 285.213nm and 279.553nm.

4. The method for simultaneously determining the contents of lithium, sodium, potassium, calcium and magnesium oxides in lithium ore based on inductively coupled plasma optical emission spectrometry according to claim 1, characterized in that In step 2, the parameters of the inductively coupled plasma emission spectrometer were set as follows: emission power of 1.2 kW, integration time of 5 s, plasma gas flow rate of 12 L / min, atomizing gas flow rate of 0.75 L / min, pump speed of 17 rpm, and observation height of 6 mm.

5. The method for simultaneously determining the contents of lithium, sodium, potassium, calcium and magnesium oxides in lithium ore based on inductively coupled plasma optical emission spectrometry according to claim 1, characterized in that In step 3, the standard curves of each element are as follows:

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