A method for determining the chemical composition of carbide slag

Abstract

This invention discloses a method for determining the chemical composition of calcium carbide slag. The method first removes the moisture by ashing the calcium carbide slag, then digests it with concentrated nitric acid and hydrofluoric acid, followed by digestion with saturated boric acid. Finally, based on a standard solution, the concentration of each component is obtained by comparing the test solution and the blank solution, and then converted into the content of oxides. The experimental results show that the recovery rate of calcium oxide is over 96%, and the accuracy and precision meet the standard requirements.

Description

Technical Field

[0001] This invention belongs to the field of measurement technology, specifically relating to a method for determining the chemical composition of carbide slag, and more specifically to a method for determining the chemical composition of carbide slag by atomic emission spectroscopy using microwave digestion pretreatment. Background Technology

[0002] Limestone, as a desulfurizing agent in the desulfurization system of thermal power plants, is consumed in large quantities and is expensive. It also increases corrosion of equipment and pipelines, resulting in high slurry density in the absorption tower and increased power consumption in the slurry equipment system and gypsum dewatering system. Currently, this represents a huge investment for power plants. Calcium carbide slag, classified as Class II general industrial solid waste, is mainly composed of Ca(OH)2, which is slightly soluble in water and has strong water retention. Its calcium oxide content is generally ≥60%, and the purity of Ca(OH)2 is generally 80%-90%. Long-term accumulation not only occupies a large amount of land but also has a serious erosive effect on the soil. From the perspective of alleviating operational and environmental pressures, using calcium carbide slag as a desulfurizing agent is more effective. Its reaction rate and surface activity are higher than conventional limestone. Therefore, replacing limestone with calcium carbide slag significantly improves desulfurization efficiency and reduces desulfurization costs, achieving the goal of comprehensive waste utilization.

[0003] Ca(OH)2 in calcium carbide slag is a major component in desulfurization, and its content directly determines the desulfurization efficiency and effectiveness. However, there is no specific chemical composition measurement method for calcium carbide slag. Most methods follow the GB / T3286.1-2012 method for chemical analysis of limestone and dolomite, which involves cumbersome sample preparation, long testing cycles, and low measurement accuracy. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for determining the chemical composition of carbide slag by microwave digestion and atomic emission spectroscopy, thereby solving the problem of the lack of a method for measuring calcium oxide in carbide slag in the prior art.

[0005] To achieve the above objectives, the present invention employs the following technical solution:

[0006] A method for determining the chemical composition of carbide slag includes the following steps:

[0007] Step 1: Place the calcium carbide slag sample in a muffle furnace. With a gap left in the furnace door, heat the sample to a set temperature 1 and maintain the temperature for a set time 1. Then, heat the sample to a set temperature 2. After closing the furnace door, burn the sample at the set temperature 2 for a set time 2. Remove the sample and cool it to room temperature to obtain the process product. Crush the process product and place it in the muffle furnace to continue burning at the set temperature 2 until the mass change of the burned material does not exceed one-thousandth of the mass of the burned material itself. This will yield the ashed calcium carbide slag sample.

[0008] Step 2: Place the calcium carbide slag sample in a mixture of concentrated nitric acid and hydrofluoric acid, and perform the first digestion in a microwave digester. After complete digestion, add saturated boric acid solution to the first digestion solution and perform the second digestion in the digester. After the second digestion, the solution to be tested is obtained.

[0009] Step 3: Plot a standard working curve using standard solutions. Place both the test solution and the blank solution in an inductively coupled plasma atomic emission spectrometer to obtain the concentration of each analyte in the test solution.

[0010] Step 4: Determine the content of each component in the carbide slag by measuring the concentration of each substance to be tested. The components are expressed as oxides.

[0011] A further improvement of the present invention is that:

[0012] Preferably, in step 1, the temperature is set to 500℃ and the time is set to 30 minutes.

[0013] Preferably, in step 1, the second temperature is set to 805~825℃ and the second time is set to 30min.

[0014] Preferably, in step 2, during the first digestion, the volume ratio of concentrated nitric acid to hydrofluoric acid is 9:1, and the concentration of carbide slag in the mixture of concentrated nitric acid and hydrofluoric acid is 0.01 g / mL.

[0015] Preferably, the heating for the first digestion is divided into three stages: holding at 120°C for 1 minute, holding at 160°C for 5 minutes, and holding at 180°C for 15 minutes.

[0016] Preferably, the mass concentration of the saturated boric acid solution used in the second digestion is 4%, the second digestion temperature is 100℃, and the second digestion time is 15 min.

[0017] Preferably, in step 3, the blank solution is a test solution that does not contain carbide slag sample.

[0018] Preferably, the process of plotting the standard working curve is as follows: prepare a standard solution, place the standard solution in an inductively coupled plasma atomic emission spectrometer, and obtain the standard working curve.

[0019] Preferably, in step 2, if the carbide slag is not completely digested in the first digestion, concentrated nitric acid is added to continue the digestion.

[0020] Preferably, the formula for calculating the content of each component in the carbide slag is as follows:

[0021]

[0022] In the formula:

[0023] —Content of the analyte, %

[0024] C1—Concentration of the element to be measured in the sample solution, µg / mL;

[0025] C0—Concentration of the element to be tested in the blank solution, µg / mL;

[0026] D—Dilution factor of the sample solution to be tested;

[0027] V—Volume of the sample solution, mL;

[0028] G – The coefficient for converting the measured element into its oxide form.

[0029] m — sample mass.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] This invention discloses a method for determining the chemical composition of calcium carbide slag. The method first removes the moisture by ashing the calcium carbide slag, then digests it with concentrated nitric acid and hydrofluoric acid, followed by digestion with saturated boric acid. Finally, based on a standard solution, the concentration of each component is obtained by comparing the test solution and the blank solution, and then converted into the content of oxides. The experimental results show that the recovery rate of calcium oxide is over 96%, and the accuracy and precision meet the standard requirements. Attached Figure Description

[0032] Figure 1 This is a flowchart of the method of the present invention. Detailed Implementation

[0033] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0034] This invention discloses a method for determining the chemical composition of carbide slag, see [link to relevant documentation]. Figure 1 The method includes the following steps:

[0035] Step 1, High-temperature ashing

[0036] A certain amount of air-dried calcium carbide slag sample was weighed into an ash dish, spread evenly, ensuring that each square centimeter did not exceed 0.15 g. The dish was then placed in a muffle furnace at a temperature not exceeding 100℃. Under natural ventilation and with a 15 mm gap left in the furnace door, the temperature was slowly raised to 500℃ over 30 minutes. This temperature was maintained for 30 minutes to allow the organic sulfur and iron sulfide in the slowly ashing calcium carbide slag to be fully oxidized and discharged. The temperature was then raised to 815±10℃, and the furnace door was closed. The sample was then calcined at this temperature for 2 hours. After cooling, the calcium carbide slag sample was ground to 0.1 mm using an agate mortar. It was then placed back into the ash dish and calcined again at 815±10℃ for 30 minutes until the mass change did not exceed one-thousandth of the ash sample mass, which was considered constant weight. The purpose was to ensure that the moisture (including water of crystallization) or easily volatile and decomposable substances in the calcium carbide slag were completely volatilized and decomposed, thus reducing experimental error. To improve the precision of the test results, the sample should be taken out and placed in a desiccator. Before weighing, it should be burned at 815±10℃ for 30 minutes. After high-temperature ashing, the carbide slag sample loses all moisture and combustibles and is transformed into inorganic residue.

[0037] The muffle furnace used in this process is equipped with a temperature control device that can raise the temperature to 1200℃ and maintain it at a constant temperature of 815±10℃. The furnace chamber should have a corresponding constant temperature zone.

[0038] Step 2, Digestion process

[0039] The process involves digestion in a microwave digestion vessel made of PFA (soluble polytetrafluoroethylene), TFM (modified polytetrafluoroethylene), or quartz, with a volume of not less than 50 mL.

[0040] Step 2.1, First digestion

[0041] Accurately weigh (0.1±0.01) g of general analytical test calcium carbide slag sample (accurate to 0.0002 g) into a digestion vessel, slowly add 9 mL of concentrated nitric acid and 1 mL of hydrofluoric acid, cover and tighten the lid, and place it in the microwave digester according to the method specified in the microwave digester's operating instructions. It is recommended to set the parameters according to the microwave digestion program specified in Table 1 and perform heating digestion in sequence.

[0042] Table 1. Parameter settings for the first microwave digestion procedure.

[0043]

[0044] After the first digestion, cool the digestion vessel to room temperature, remove it, and slowly open the lid to check if the sample has been completely digested. If not completely digested, add 5 mL of concentrated nitric acid, cap and tighten the lid, place it in a microwave digester, and repeat the first digestion as specified in Table 1. The purpose of adding concentrated nitric acid is that nitric acid is a strong oxidizing agent that can oxidize metals into soluble nitrates, dissolving most sulfides; it is usually used in conjunction with hydrofluoric acid. This ensures complete digestion, guaranteeing that the silica in the carbide slag is released in gaseous form as silicon tetrafluoride, until digestion is complete, but the final solution volume must not exceed the instrument's specified safe volume.

[0045] Step 1.2,

[0046] After digestion is complete and the temperature inside the digestion vessel has cooled to room temperature, remove the digestion vessel, slowly open the lid, add 10 mL of 4% saturated boric acid solution. The purpose is to use it as a co-solvent to ensure that the chemical components (acidic oxides + basic oxides) in the carbide slag can be completely dissolved. Cover and tighten the lid, place it in the microwave digestion apparatus, set the microwave digestion program parameters as specified in Table 2, and perform the second digestion.

[0047] Table 2. Parameter settings for the second microwave digestion procedure.

[0048]

[0049] After the second digestion is completed and the temperature inside the digestion vessel has cooled to room temperature, remove the digestion vessel, open the lid, rinse the lid and inner wall of the digestion vessel with water, transfer the digestion solution into a 100mL plastic volumetric flask, and dilute to volume with water to obtain the solution to be tested.

[0050] Step 3: Compare with the blank solution and perform measurements.

[0051] The blank solution is prepared by repeating the same steps as the sample melting method (steps 1.1-1.2) without adding the sample.

[0052] This measurement procedure should be performed in accordance with the instruction manual for the atomic emission spectrometer. The optimal operating parameters of the instrument (including high-frequency power, nebulization pressure, carrier gas flow rate, injection rate, and integration time) should be determined in advance.

[0053] Before conducting a test on a sample solution, a fixed test method should be established, including setting the predicted elements, the corresponding reliable spectral lines, and the concentration of the standard series solutions used for calibration.

[0054] Step 3.1, Plotting the standard working curve

[0055] Select the determination method, and sequentially introduce the standard series solutions into the plasma through the nebulizer pipette in order of increasing standard solution concentration. The instrument automatically analyzes the results and plots a standard working curve using the internal standard method based on the experimental results. The horizontal axis represents the concentration of the elemental standard solution, and the vertical axis represents the absorbance of the corresponding element. The secondary standard curve should be a straight line passing through the origin, and the slope of the standard curve should reach more than 98%. Save the curve after confirming its reliability; otherwise, find the cause, correct it, and recalibrate.

[0056] Method for using standard working solutions:

[0057] (1) Determine the standard stock solutions: (existing conventional method DL / T1037-2018) including stock solutions of elements potassium, sodium, manganese, iron, calcium, magnesium, aluminum, and titanium, wherein the concentration of potassium, sodium, manganese, iron, calcium, magnesium, aluminum, and titanium solutions is 1000 mg / L. The standard stock solutions should be prepared using pure metals or salts with a purity of 99.999% or higher. Alternatively, commercially available certified standard solutions can be used instead or prepared.

[0058] Internal standard solution: a standard stock solution of yttrium (or other elements such as scandium and indium) with a concentration of 500 mg / L.

[0059] (5+95) Nitric acid (GB / T626) solution: Take 50 mL of concentrated nitric acid and dilute to 1000 mL.

[0060] (2) Mixed standard series solutions:

[0061] Prepare a mixed standard working solution of aluminum, iron, titanium, and sodium with the following specific requirements: aluminum ion concentration of 125 mg / L, iron ion concentration of 250 mg / L, titanium ion concentration of 10 mg / L, and sodium ion concentration of 50 mg / L.

[0062] The preparation process is as follows: accurately pipette 12.5 mL of aluminum standard stock solution, 25 mL of iron standard stock solution, 1 mL of titanium standard stock solution, and 5 mL of sodium standard stock solution into a 100 mL volumetric flask, dilute with water to the mark, and shake well.

[0063] Prepare a mixed standard working solution of calcium, magnesium, potassium, and manganese. (Calcium ion concentration: 250 mg / L; magnesium ion concentration: 50 mg / L; potassium ion concentration: 50 mg / L; manganese ion concentration: 50 mg / L)

[0064] Accurately pipette 25 mL of calcium standard stock solution, 5 mL of magnesium standard stock solution, 5 mL of potassium standard stock solution, and 5 mL of manganese standard stock solution into a 100 mL volumetric flask, dilute with water to the mark, and shake well. Transfer to a plastic bottle. (3) Mix the series of standard working solutions

[0065] Prepare two sets of mixed standard working solutions for instrument calibration according to Tables 3 and 4, including mixed standard working solutions of aluminum, iron, titanium, and sodium, and mixed standard working solutions of calcium, magnesium, potassium, and manganese. Add 1 mL of internal standard solution during preparation, and finally dilute to 50 mL with lithium tetraborate solution and store in plastic bottles.

[0066] Table 3. Group 1 Mixed Series Standard Working Solutions (Aluminum, Iron, Titanium, Sodium)

[0067]

[0068] Table 4, Group 2, Mixed Series Standard Working Solutions (Calcium, Magnesium, Potassium, Manganese)

[0069]

[0070] Step 2, Determination of the sample to be tested

[0071] Select the calibrated element working curve, and sequentially introduce the test solution and blank solution into the inductively coupled plasma atomic emission spectrometer (ICP) through the nebulizer pipette. The instrument automatically analyzes the samples and retrieves the internal standard curve based on the measurement results to obtain the concentration of the analyte element in the test sample solution.

[0072] 3.1 Calculation

[0073] Calculate the content of each component (as oxides) in the carbide slag using the following formula:

[0074]

[0075] In the formula:

[0076] —Content of the analyte, %

[0077] C1—Concentration of the element to be measured in the sample solution, µg / mL;

[0078] C0—Concentration of the element to be tested in the blank solution, µg / mL;

[0079] D—Dilution factor of the sample solution to be tested;

[0080] V—Volume of the sample solution, mL;

[0081] G – The coefficient for converting the measured element into oxides, see Table 5;

[0082] m—sample mass, g;

[0083] Table 5. Conversion coefficients G for the tested elements to oxides

[0084]

[0085] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method of determining the chemical composition of carbide slag, characterized by, It comprises the following steps: Step 1, place the carbide slag sample in a muffle furnace, and heat to a set temperature one with a gap left in the furnace door, and keep for a set time one, then heat to a set temperature two; after closing the furnace door, continue to burn at the set temperature two for a set time two, take out and cool to room temperature to obtain a process product, crush the process product, and continue to burn at the set temperature two in the muffle furnace until the mass change of the burning product is less than 0.1% of the mass of the burning product itself, to obtain the ashed carbide slag sample; In step 1, the set temperature one is 500℃, and the set time one is 30min; the set temperature two is 805~825℃, and the set time two is 30min; Step 2, place the carbide slag sample in a mixture of concentrated nitric acid and hydrofluoric acid, and perform the first digestion in a microwave digestion instrument, after complete digestion, add saturated boric acid solution to the first digestion solution, and perform the second digestion in the digestion instrument, after the second digestion, obtain the test solution; The heating of the first digestion is divided into three stages, in turn: keep at 120℃ for 1min, keep at 160℃ for 5min, and keep at 180℃ for 15min; The mass concentration of the saturated boric acid solution for the second digestion is 4%, the second digestion temperature is 100℃, and the second digestion time is 15min; In step 2, during the first digestion, the volume ratio of concentrated nitric acid to hydrofluoric acid is 9:1, and the concentration of the carbide slag in the mixture of concentrated nitric acid and hydrofluoric acid is 0.01g / mL; In step 2, if the carbide slag is not completely digested during the first digestion, add concentrated nitric acid for further digestion; Step 3, draw a standard working curve by a standard solution, place the test solution and the blank solution in an inductively coupled plasma atomic emission spectrometer to obtain the concentration of each measured substance in the test solution; Step 4, determine the content of each component in the carbide slag by the concentration of each measured substance, wherein the component is calculated as an oxide.

2. A method of determining the chemical composition of carbide slag according to claim 1, characterized in that, In step 3, the blank solution is a test solution without the carbide slag sample.

3. A method of determining the chemical composition of carbide slag according to claim 1, characterized in that, The drawing process of the standard working curve is: configure a standard solution, place the standard solution in an inductively coupled plasma atomic emission spectrometer to obtain a standard working curve.

4. A method of determining the chemical composition of carbide slag according to any one of claims 1 to 3, characterized in that, The content calculation formula of each component in the carbide slag is: In the formula: - content of the component under test, % C1——the concentration of the measured element in the test sample solution, µg / mL; C0——the concentration of the measured element in the test blank solution, µg / mL; D——the dilution multiple of the test sample solution; V——the volume of the sample solution, mL; G——the coefficient of the measured element converted into an oxide; m——the sample mass.

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