Method for measuring chromium content in laterite nickel ore

Abstract

A method for measuring chromium content in a laterite nickel ore, comprising the following steps: S1, adding in sequence nitric acid, phosphoric acid, perchloric acid, and sulfuric acid to a laterite nickel ore sample to be measured, and mixing evenly to obtain a mixed solution A; S2, when the amount of nitric acid is not 0, heating the mixed solution A to remove water and nitric acid, and then raising the temperature to remove perchloric acid, to obtain a mixed solution C; when the amount of nitric acid is 0, heating the mixed solution A directly to remove water and perchloric acid, to obtain a mixed solution C; S3, cooling the mixed solution C, adding water to dilute, boiling again to dissolve salts, cooling, filtering, and diluting for use, and recording as a mixed solution D; and S4, testing the mixed solution D by ICP to calculate the chromium content in the laterite nickel ore. By using nitric acid, phosphoric acid, perchloric acid, and sulfuric acid to perform redox reaction and combining the same with ICP to perform testing, the problems of few process sample testing and analysis methods, long detection time, and complicated procedures in the hydrometallurgy of laterite nickel ore are solved.

Description

Detection method of chromium content in laterite nickel ore Technical Field

[0001] The present invention relates to the field of chromium content detection, and in particular to a method for detecting chromium content in laterite nickel ore. Background Art

[0002] With global economic development in the 1990s, nickel demand grew by an average of over 4% annually over the first five years. For the next five to ten years, the growth rate is projected to be 3.5% to 4%, with Asia projected to see a 7% increase. However, the world's sulfide nickel resources available for near-term development are limited. To date, approximately 70 million tons of nickel metal have been discovered globally. Among these, laterite nickel resources are abundant, with a global total of 41 million tons, offering low exploration costs. As technology matures and demand increases, research on the detection of various target elements in laterite nickel ore has steadily advanced in recent years, leading to the initial development of a series of national and industry standards.

[0003] The main sample pretreatment methods for analyzing various elements in laterite nickel ore include acid dissolution and alkaline fusion, and detection methods include inductively coupled plasma emission spectrometry (ICP-AES), atomic absorption spectrometry (AAS), inductively coupled plasma mass spectrometry (ICP-MS), and titration. Chromium, a naturally occurring compound, is very stable and difficult to reduce, so its detection methods are relatively simple, primarily relying on traditional manual titration analysis. This requires high professional expertise and is also time-consuming and material-consumable, hindering subsequent sustainable development.

[0004] Summary of the Invention

[0005] The purpose of the present invention is to overcome the above technical deficiencies and provide a method for detecting the chromium content in laterite nickel ore, so as to solve the technical problems of the prior art in that the detection time of chromium content in laterite nickel ore is long and the steps are complicated.

[0006] In order to achieve the above technical objectives, the technical solution provided by the present invention is:

[0007] In a first aspect, the present invention provides a method for detecting the chromium content in laterite nickel ore, comprising the following steps: S1, adding 0-5 mL of nitric acid, 1-10 mL of phosphoric acid, 1-10 mL of perchloric acid and 1-10 mL of sulfuric acid to a laterite nickel ore sample to be tested in sequence, and mixing them evenly to obtain a mixed solution A; S2, when the amount of nitric acid is not 0, heating the mixed solution A to remove water and nitric acid to obtain a mixed solution B; heating the mixed solution B again to remove perchloric acid to obtain a mixed solution C; or when the amount of nitric acid is 0, directly heating the mixed solution A to remove water and perchloric acid to obtain a mixed solution C; S3, after cooling the mixed solution C, diluting it with water, boiling it again to dissolve salts, filtering and diluting it after cooling, and setting it aside, recorded as a mixed solution D; S4, measuring the mixed solution D by ICP to calculate the chromium content in the laterite nickel ore.

[0008] Compared with the prior art, the present invention has the following beneficial effects:

[0009] The present invention selects a suitable detection method for research and optimization, conducts redox reaction using nitric acid, phosphoric acid, perchloric acid and sulfuric acid, and combines it with ICP for determination, thus solving the problems of few process sample testing and analysis methods, long detection time and complicated procedures in laterite nickel ore hydrometallurgy. DETAILED DESCRIPTION

[0010] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0011] For the following references with dates, only the versions with dates are applicable to the present invention; for the following references with no dates, their updated versions (including all amendments) are applicable to the method of the present invention.

[0012] Unless otherwise specified, analytical grade reagents and distilled water, deionized water or water of equivalent purity were used in all analyses and tests.

[0013] Existing detection methods involved in the present invention:

[0014] (1) According to the Chemical Analysis Methods for Laterite Nickel Ore Part 21: Determination of Chromium Content by Ammonium Ferrous Sulfate Titration, the determination range is 0.3% to 3.5%. The absolute difference between the two test results obtained under repeatability conditions within the average value range shall not exceed the repeatability limit r, and the case of exceeding the repeatability limit r shall not exceed 5%;

[0015] (2) The permissible error stipulated in the "Determination of Chromium Content by Ferrous Ammonium Sulfate Titration" is that when the chromium content (mass fraction) is ≥97%, the difference between two analytical results (two results obtained by weighing two samples and performing the same operation on the same sample) should be ≤0.4%;

[0016] (3) "Soil Testing Part 12: Determination of Total Chromium in Soil" stipulates that the relative difference between repeated test results is allowed to be ≤8%.

[0017] The method for detecting the content of chromium in laterite nickel ore of the present invention comprises the following steps:

[0018] S1, digestion of the laterite nickel ore sample: add 0-5 mL of nitric acid, 1-10 mL of phosphoric acid, 1-10 mL of perchloric acid, and 1-10 mL of sulfuric acid to every 0.1 g of the laterite nickel ore sample, shake well, and obtain a mixed solution A;

[0019] S2, when the amount of nitric acid is not 0, the mixed solution A is placed on a hot plate and heated to remove water and nitric acid, thereby obtaining a mixed solution B; the mixed solution B is further heated to remove perchloric acid, and the temperature is maintained until the perchloric acid smoke is completely eliminated, thereby obtaining a mixed solution C;

[0020] When the amount of nitric acid is 0, the mixed solution A is placed on a hot plate and heated directly to remove water and perchloric acid to obtain mixed solution C;

[0021] S3, remove mixed solution C from the hot plate and cool to room temperature, add a small amount of water and boil again to dissolve the salts, cool to room temperature, filter and dilute to volume in a volumetric flask, dilute for later use, and record as mixed solution D;

[0022] S4, the mixed solution D is determined by ICP (selecting standard curve points according to the content), and then the chromium content in the laterite nickel ore is calculated.

[0023] Preferably, the laterite nickel ore sample to be tested has a particle size of less than 160 μm, is dried in an oven at 105° C. to 110° C. for 2 h, and is placed in a desiccator to cool to room temperature for later use.

[0024] The laterite nickel ore samples to be tested include low chromium content samples (0.0007% ≤ M Cr <4%), medium chromium content samples (4%≤M Cr <25%) and high chromium content samples (25%≤M Cr ≤50%); in step S1:

[0025] When the laterite nickel ore sample to be tested is a low-chromium sample, add 0 mL of nitric acid, 2-10 mL of phosphoric acid, 1-3 mL of perchloric acid, and 2-10 mL of sulfuric acid to every 0.1 g of the sample to be tested;

[0026] When the laterite nickel ore sample to be tested has a medium chromium content, add 1-5 mL of nitric acid, 5-10 mL of phosphoric acid, 4-8 mL of perchloric acid, and 5-10 mL of sulfuric acid to every 0.1 g of the sample to be tested;

[0027] When the laterite nickel ore sample to be tested is a sample with a high chromium content, 1-5 mL of nitric acid, 5-10 mL of phosphoric acid, 5-10 mL of perchloric acid, and 5-10 mL of sulfuric acid are added to every 0.1 g of the sample to be tested.

[0028] Preferably, the concentration of perchloric acid is 12.44 mol / L; the concentration of nitric acid is 13 mol / L; the concentration of phosphoric acid is 14.63 mol / L; and the concentration of sulfuric acid is 18 mol / L.

[0029] Preferably, in step S2, when the amount of nitric acid is not 0, the mixed solution A is heated to 200-250° C. and kept warm for 5-30 minutes; the mixed solution B is heated to 300-350° C. and kept warm for 15-90 minutes.

[0030] Preferably, in step S2, when the amount of nitric acid used is 0, the mixed solution A is heated to 300-350° C. and kept warm for 15-40 minutes until the perchloric acid smoke is completely eliminated.

[0031] If the heating and holding time is too short, the reaction will be incomplete; if the time is too long, pyrophosphate will be generated, which will reduce the accuracy.

[0032] Preferably, in step S3, the ratio of the added water to the laterite nickel ore sample to be tested in step S1 is 20-40 mL: 0.1 g; and the boiling time is 1-2 min.

[0033] Preferably, in step S3, the mass concentration of the mixed solution D is 0.0007%-50%. Further preferably, if the concentration in the mixed solution D is relatively high, for example, exceeding 50%, the mixed solution D needs to be diluted to ensure that it can be detected by the instrument; the dilution specifically includes taking a portion from the mixed solution D and then adjusting the volume to obtain a mixed solution E, for example: taking 5 ml of the mixed solution D and adjusting the volume to a 100 ml volumetric flask, with a dilution factor of 20 times; ensuring that the concentration of the mixed solution E (the final test solution) is between 0.0007% and 50%.

[0034] Preferably, the ICP parameters are set as shown in Table 1 below.

[0035] Table 1 ICP parameter settings

[0036] Note: The standard curve is based on 2% 1:1 sulfur-phosphorus acid mixture.

[0037] Because mixed liquid D contains a large amount of sulfate and phosphate, it is easy to clog and cause the equipment to stall. Therefore, it is necessary to reduce atomization (carrier gas), increase detection power, and increase cooling gas protection equipment. All conditions must be coordinated and work together to complete the detection.

[0038] Preferably, step S4 specifically includes: under given conditions, obtaining a chromium standard curve (linearity greater than 0.999) by testing a chromium standard solution, obtaining a concentration value of the mixed solution D by testing the mixed solution D under the same test conditions, and finally obtaining a sample content value by calculation.

[0039] Among them, the standard curve is to input the numerical values ​​of each point of the known chromium standard solution, measure the intensity value of each point in sequence through ICP, and then draw a standard curve through all the points with the horizontal axis as concentration and the vertical axis as intensity; and when the sample to be tested (mixed solution D) is measured, there will be a corresponding intensity value, and the instrument will automatically calculate the concentration value through the standard curve.

[0040] The calculation formula of chromium content in laterite nickel ore is: Cr (%) = C*D*V / (10000*m);

[0041] C: Measured concentration of mixed solution D in mg / L,

[0042] D: dilution factor (the dilution factor when testing mixed solution D is 1),

[0043] V: constant volume mL,

[0044] m: Sample mass in g.

[0045] The main mechanism of action of the present invention:

[0046] The present invention utilizes nitric acid, phosphoric acid, sulfuric acid, and perchloric acid to carry out redox reactions; no hydrochloric acid or hydrofluoric acid needs to be added to the formula of the present invention, thereby avoiding the adverse phenomenon of digestion of the sample to be tested caused by the reducing properties of hydrochloric acid or hydrofluoric acid; and simultaneously, the present invention uses a strong oxidant for oxidation determination in processing high-content chromium samples, because the chromium sample has a stable structure and is difficult to reduce, thereby saving time.

[0047] The present invention is further described in detail below through specific examples and comparative examples.

[0048] Experimental samples:

[0049] (1) Laterite nickel ore: purchased from Zhejiang Tsingshan Iron and Steel Co., Ltd.

[0050] (2) National first-class standard material, chromite composition analysis standard material GBW(E)070135, purchased from Wuhan Ruichen Standard Material Technology Co., Ltd.;

[0051] (3) National first-class standard material, nickel ore and nickel concentrate composition analysis standard material GBW(E)070116, purchased from Jinan Zhongbiao Technology Co., Ltd.

[0052] The sample particle size should be less than 160 μm. Dry it in an oven at 105°C to 110°C for 2 hours, place it in a desiccator and cool it to room temperature before use.

[0053] Example 1

[0054] Weigh 0.1000g (±0.0001g) of sample into a 250mL hard conical flask, clean the wall of the flask with a small amount of water, add 5mL of phosphoric acid, 2mL of nitric acid, 5mL of perchloric acid, and 5mL of sulfuric acid in sequence, shake well, heat the mixture to 250℃ on a hot plate to remove water and nitric acid, then heat the mixture to 350℃ to remove perchloric acid until the perchloric acid smoke is clear, remove and cool to room temperature, add a small amount of water (about 30mL) and boil again for 1min to dissolve the salts, cool and dilute to a 250mL volumetric flask for use, and perform ICP or atomic absorption determination. The sample content value is calculated.

[0055] Detection limit, accuracy and repeatability:

[0056] According to the method of the present invention, the blank was measured 12 times continuously, and the detection limit was calculated by 3 times the standard deviation. The detection limit of each element is shown in Table 2 (the blank result is the lowest value that can be detected);

[0057] The accuracy (ΔlgC) and repeatability were calculated by measuring the national standard material GBW(E)070135 (which has a standard value and can be used to calculate accuracy and repeatability) 12 times in a row, and the repeatability was calculated by measuring the experimental sample (which has no standard value and can only be used to measure repeatability) 12 times in a row. The results are shown in Table 2.

[0058] Titration test: The national standard material GBW(E)070135 was titrated using the "Chemical Analysis Methods for Laterite Nickel Ores Part 21: Determination of Chromium Content - Ammonium Ferrous Sulfate Titration Method". The results are shown in Table 2 below.

[0059] Table 2 Detection limit, accuracy and reproducibility data

[0060] As can be seen from Table 2, relative to the titration test, the results of the special treatment process of the present invention combined with the ICP test are slightly lower. This is mainly because the results of human intervention are relatively more stable than those of instrumental testing. However, the accuracy and repeatability of the results of the determination using the method of the present invention are within the indicators of the method specification.

[0061] Specification requirements

[0062] Referring to GB / T 223.11-2008, "Steel and Alloys—Determination of Chromium Content by Visual Titration or Potentiometric Titration," a standard solution with known chromium content was tested. The results are shown in Table 3 below. As can be seen from Tables 2 and 3, the repeatability of the present method is superior to that of the reference standard. Therefore, this method can meet production needs.

[0063] Table 3 Repeatability and reproducibility requirements

[0064] Example 2

[0065] The only difference from Example 1 is that the amount of acid and the reaction time are adjusted. The other step conditions are the same as those in Example 1. The specific parameter conditions and test results are shown in Table 4 below.

[0066] Table 4 Specific parameter conditions and test results of Example 2

[0067] The method of the present invention can judge the content of chromium according to the color (green) of chromium in the digestion process. The more green the solution, the more perchloric acid is needed. Perchloric acid (1-10 mL) can also be added according to the sample properties. As shown in Table 4, for samples with low chromium content of laterite nickel ore, only 1-3 mL perchloric acid is needed, and nitric acid can be omitted. For high-content samples of chrome concentrate (a kind of laterite nickel ore), more perchloric acid (4-10 mL) needs to be added. In all digestion processes, every 0.1 g of sample to be tested only needs 13-22 mL of acid. The operation process is simple, short in time (1 h to 1.5 h), and has few interferences. As can be seen from Table 2, the accuracy and repeatability of the measurement results are within the method specification and can meet production requirements.

[0068] As shown in Table 4 above, a too-short reaction time can lead to incomplete reaction in high-content samples (GBW(E)070135), resulting in inaccurate test results. Similarly, to allow sufficient reaction time for the nitric acid, the temperature should be raised to 250°C and held for 15-30 minutes before being raised to 350°C.

[0069] Comparative Example 1

[0070] Testing was performed using existing methods, specifically those described in "Methods for Chemical Analysis of Laterite Nickel Ore Part 21: Determination of Chromium Content - Ferrous Ammonium Sulfate Titration." The sample was placed in a 30mL corundum crucible containing 4g of sodium peroxide and stirred thoroughly. The crucible was then covered with 1g to 2g of sodium oxide and calcined on a hot plate. The crucible was then melted in a furnace at 750°C to 800°C and held for 5 minutes, shaking once. The crucible was removed and allowed to cool. The crucible was then placed in a 500mL beaker and 100mL to 150mL of hot water was added. After the violent reaction subsided, sulfuric acid was added with stirring until the hydroxide precipitate dissolved. A 20mL excess of sulfuric acid was added, followed by 5mL of phosphoric acid. The crucible was rinsed with water and heated to decompose the hydrogen peroxide. The crucible was removed and allowed to cool slightly, and water was added to a volume of approximately 200mL. 5mL of silver nitrate solution, 0.5mL of manganese sulfate solution, and 20mL of ammonium persulfate solution were added and shaken thoroughly. Heat and boil until the solution develops a stable purple-red color, then continue boiling for 5 minutes. Add 10 mL of hydrochloric acid and continue boiling for 5-10 minutes. Cool to room temperature with running water. Titrate with standard ammonium ferrous sulfate solution until the solution turns pale yellow. Add 3 drops of N-phenylanthranilic acid solution and continue titrating until the solution changes from rose-red to bright green. This process is cumbersome, time-consuming (2.5 hours), and requires high-quality personnel.

[0071] Comparative Example 2

[0072] Testing was performed using existing testing methods, specifically as described in "Soil Testing Part 12: Determination of Total Chromium in Soil." Weigh 0.5g (accurate to 0.0001g) of an air-dried sample that has passed a 0.149mm sieve into a 100mL tall beaker (or Erlenmeyer flask). Add a few drops of water to moisten the sample. Add 1.5mL of concentrated sulfuric acid and shake carefully. Add 1.5mL of concentrated phosphoric acid and 3mL of nitric acid and shake carefully. Cover with a watch glass and heat on a hot plate (maintaining the surface temperature below 220°C) until a large amount of white smoke is emitted. If the soil sample does not turn white, remove the beaker and allow it to cool slightly. Add 1mL of nitric acid and continue heating until thick white smoke is emitted. Remove the beaker and allow it to cool slightly. Rinse the watch glass and beaker walls with water. Transfer the contents of the beaker intact to a 50mL volumetric flask, fill with water to the mark, shake well, and dry filter, set aside to clarify, or centrifuge. Perform a blank test simultaneously. Accurately pipette 5.00 mL of clear test solution into a 25 mL colorimetric tube. Add 1-2 drops of potassium permanganate solution until the solution turns purple-red. Boil in a boiling water bath for 15 minutes. If the purple-red color fades, add another drop of potassium permanganate solution until the purple color persists. Shake well. While hot, add sodium azide solution dropwise and quickly shake thoroughly until the purple-red color just disappears. Place the colorimetric tube in cold water and quickly cool. Add 1 mL of phosphoric acid solution, shake well, and add water to the mark. Add 2 mL of diphenylcarbonyl solution and shake well. After 5 minutes, use a 3 cm cuvette to adjust the instrument's zero point colorimetric reading at a wavelength of 540 nm, using the zero concentration of the standard series solution as a reference. This process is also cumbersome, time-consuming (3.5 hours), and prone to interference.

[0073] Comparative Example 3

[0074] The test was performed using an existing method, specifically the "Determination of Chromium Content by Ferrous Ammonium Sulfate Titration Method." The sample is placed in a 500mL Erlenmeyer flask, and 70mL of water, 12mL of sulfuric acid, and 5mL of phosphoric acid are added. Heat at low temperature until the sample is completely dissolved, remove the sample, and dilute to approximately 200mL with water. Add 1mL to 2mL of manganese sulfate solution, followed by 10mL of silver nitrate solution and 40mL of ammonium persulfate solution. Boil until the chromium is oxidized to dichromic acid, which gives rise to the reddish color of permanganate. Continue boiling for 5 minutes, bubbling vigorously, to decompose the excess ammonium persulfate. Add 10mL of sodium chloride solution and boil until the permanganate is completely decomposed. Continue boiling for 2-3 minutes, cool to room temperature, and add water to a volume of approximately 200mL. Titrate with standard ammonium sulfate titrant until the solution changes from orange to yellow-green. Add 8 drops of N-phenylanthranilic acid indicator solution and continue titrating until the solution changes from purple-red to green. This is the endpoint. The process is cumbersome, time-consuming (3 hours) and requires high personnel quality.

[0075] Compared with the above comparative examples 1-3, the detection method of the present invention is easy to master, fast and simple, saves more than 1 hour compared with other methods, and the process is refined, energy-saving and cost-reducing; the introduction of high-end equipment replaces traditional processes, and the measurement range is wide (0.0007% to 50%); at the same time, it provides the industry with more detection means and realizes diversified detection.

[0076] Comparative Example 4

[0077] Hydrochloric acid was used instead of phosphoric acid, and the other steps and conditions were the same as in Example 1.

[0078] As a result, it was found that hydrochloric acid is a reducing agent and cannot play the role of phosphoric acid in decomposing the sample in the present invention.

[0079] Compared with the existing technology, the present invention utilizes acid dissolution instead of alkali fusion acid extraction, and introduces high-end equipment (inductively coupled plasma emission spectroscopy) to replace traditional manual analysis, resulting in a wide measurement range (0.0007-50%). In a sulfuric acid medium, the sample is decomposed with phosphoric acid, and the element to be measured is oxidized to a high-valent state using nitric acid and perchloric acid. The sample is diluted to a constant volume and then measured by ICP. After adding 5mL of sulfuric acid, 5mL of phosphoric acid, 2mL of nitric acid, and 10mL of perchloric acid, the detection limit is 0.0007%, and the repeatability is less than or equal to 0.242%. This overcomes the shortcomings of existing hydrometallurgical analysis and testing technologies for laterite nickel ore and provides a diversified detection method.

[0080] The specific embodiments of the present invention described above do not limit the scope of protection of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the scope of protection of the claims of the present invention.

Claims

1. A method for detecting the content of chromium in laterite nickel ore, characterized in that: The following steps are involved: S1, adding 0-5 mL of nitric acid, 1-10 mL of phosphoric acid, 1-10 mL of perchloric acid and 1-10 mL of sulfuric acid to the laterite nickel ore sample to be tested, and mixing them uniformly to obtain a mixed solution A; S2, when the amount of nitric acid is not 0, the mixed solution A is heated to remove water and nitric acid to obtain a mixed solution B; the mixed solution B is heated again to remove perchloric acid to obtain a mixed solution C; Or when the amount of nitric acid is 0, the mixed solution A is directly heated to remove water and perchloric acid to obtain mixed solution C; S3, after the mixture C is cooled, water is added to dilute it, and it is boiled again to dissolve the salts. After cooling, it is filtered and diluted for use, which is recorded as the mixture D; S4, the mixed solution D is measured by ICP to calculate the chromium content in the laterite nickel ore.

2. The method for detecting the content of chromium in laterite nickel ore according to claim 1, characterized in that: The chromium content in the laterite nickel ore sample to be tested is recorded as M Cr , including 0.0007% ≤ M Cr Samples with low chromium content of <4%, 4%≤M Cr <25% of the medium chromium content samples and 25% ≤ M Cr For samples with a high chromium content of ≤50%, 0 nitric acid is added to the samples with a low chromium content; 1 to 5 mL of nitric acid is added to every 0.1 g of the samples with a medium chromium content and a high chromium content.

3. The method for detecting the content of chromium in laterite nickel ore according to claim 2, characterized in that: For every 0.1 g of low chromium content sample, add 0 mL of nitric acid, 2-10 mL of phosphoric acid, 1-3 mL of perchloric acid, and 2-10 mL of sulfuric acid.

4. The method for detecting the content of chromium in laterite nickel ore according to claim 2, characterized in that: For every 0.1 g of medium chromium content sample, add 1-5 mL of nitric acid, 5-10 mL of phosphoric acid, 4-8 mL of perchloric acid, and 5-10 mL of sulfuric acid.

5. The method for detecting the content of chromium in laterite nickel ore according to claim 2, characterized in that: To every 0.1 g of high chromium content sample, add 1-5 mL of nitric acid, 5-10 mL of phosphoric acid, 5-10 mL of perchloric acid, and 5-10 mL of sulfuric acid.

6. The method for detecting the content of chromium in laterite nickel ore according to any one of claims 1 to 5, characterized in that: The concentration of perchloric acid is 12.44 mol / L; the concentration of nitric acid is 13 mol / L; the concentration of phosphoric acid is 14.63 mol / L; and the concentration of sulfuric acid is 18 mol / L.

7. The method for detecting the content of chromium in laterite nickel ore according to claim 1, characterized in that: In step S2, when the amount of nitric acid is not 0, the mixed solution A is heated to 200-250° C. and kept warm for 5-30 min; the mixed solution B is heated to 300-350° C. and kept warm for 15-90 min.

8. The method for detecting the content of chromium in laterite nickel ore according to claim 1, characterized in that: In step S2, when the amount of nitric acid is 0, the mixed solution A is heated to 300-350° C. and kept warm for 15-40 min until the perchloric acid smoke is completely eliminated.

9. The method for detecting the content of chromium in laterite nickel ore according to claim 1, characterized in that: In step S3, the ratio of the added water to the laterite nickel ore sample to be tested in step S1 is (20-40) mL: 0.1 g; and the boiling time is 1-2 min.

10. The method for detecting the content of chromium in laterite nickel ore according to claim 1, characterized in that: In step S3, the mass concentration of the mixed solution D is 0.0007% to 50%.

11. The method for detecting the content of chromium in laterite nickel ore according to claim 1, characterized in that: In step S4, the parameters of ICP measurement are set as follows: cooling gas flow rate 13 L / min, carrier gas flow rate 0.75 L / min, auxiliary gas flow rate 0.8 L / min, plasma power 1350-1400 W, detection wavelength 267.716 nm, and pump speed 30 Rpm.

12. The method for detecting the content of chromium in laterite nickel ore according to claim 1, characterized in that: In step S4, the chromium standard solution is tested by ICP to obtain a standard curve of chromium; then under the same test conditions, the mixed solution D is measured by ICP, the measurement result is substituted into the standard curve to obtain the concentration value of the mixed solution D, and the chromium content in the laterite nickel ore is calculated.

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