Method for measuring content of magnesium oxide in solid waste

Abstract

The invention discloses a method for determining the content of magnesium oxide in solid waste, and belongs to the field of analysis and detection. The method for determining the magnesium oxide content in the solid waste comprises the following steps: performing alkali melting on a sample by using a flux, and then cooling; adding the cooled material into a hydrochloric acid solution to obtain a dissolved solution; adding strongly basic anion exchange resin into the dissolved solution, stirring and filtering; adding a hydrochloric acid aqueous solution, nitric acid and an ethanol aqueous solution into the filtrate and heating; after cooling, metering the volume of the solution, recording as a solution A, adding an ammonium chloride solution into the solution A, and heating; dropwise adding ammonia water until a precipitate is generated, and recording the solution as a solution B; adding ammonium persulfate into the solution B, heating, filtering and precipitating, and recording the filtrate as a solution C after the volume of the filtrate is constant; adding the solution C into an alkaline buffer solution, adding a calcium-magnesium indicator, and titrating with an EDTA standard titration solution until the color is changed; adding a calcium indicator into the solution C, adding a potassium hydroxide solution, and titrating with an EDTA (Ethylene Diamine Tetraacetic Acid) standard titration solution until color changes; and calculating the content of magnesium oxide in the solid waste. Interference ions are removed through a specific sequence, so that the accuracy of a test result is ensured.

Description

Technical Field

[0001] This invention relates to the field of analytical testing, and in particular to a method for determining the magnesium oxide content in solid waste. Background Technology

[0002] With the rapid development of my country's industrialization, the amount of solid waste generated by industries such as metallurgy, chemicals, energy, and steelmaking has increased dramatically. Its safe disposal and resource utilization have become urgent needs for sustainable development. Magnesium oxide content in solid waste is one of its key physicochemical indicators, and accurate detection is crucial for environmental risk assessment and resource utilization decisions. On the one hand, magnesium oxide reacts with water to form alkaline substances, and its content directly affects the leaching toxicity and environmental risk level of solid waste, serving as an important basis for determining whether it is hazardous waste. On the other hand, in the field of resource utilization, such as as building materials, excessively high magnesium oxide content can lead to cracking risks in building materials due to poor volume stability, severely restricting its safe and high-value utilization. While large-scale instrumental analysis methods (such as AAS and ICP-OES / MS) offer high precision, they are expensive, have high operating costs, require highly skilled operators, and face complex sample pretreatment and matrix effect correction challenges, making them difficult to rapidly popularize and apply in grassroots testing institutions and waste-generating enterprises.

[0003] Traditional methods have drawbacks such as high cost and long processing time, and are easily affected by interference from other impurity ions, resulting in low accuracy in magnesium oxide content detection. Therefore, it is necessary to develop a simple, interference-resistant, accurate, and low-cost method for determining magnesium oxide content in solid waste to meet the growing dual demands of environmental regulation and the development of a circular economy. Summary of the Invention

[0004] This invention provides a method for determining the magnesium oxide content in solid waste, which solves the problems of large interference, cumbersome operation and poor accuracy in the existing technology for determining the magnesium oxide content in solid waste.

[0005] The technical solution of the present invention is as follows:

[0006] Solid waste contains magnesium, calcium, chromium, iron, aluminum, and manganese. The method for determining the magnesium oxide content in solid waste includes the following steps:

[0007] S1. Weigh the sample, melt the sample with a mixed flux of anhydrous sodium carbonate and boric acid, and then cool it; add the cooled material to hydrochloric acid solution to dissolve it, and obtain the solution after completion;

[0008] S2. Remove interfering ions from the dissolved solid waste in the order of chromium ions → iron ions, aluminum ions → manganese ions; specifically:

[0009] Add a strong base anion exchange resin to the solution, stir, filter, and collect the filtrate; add hydrochloric acid aqueous solution, nitric acid and ethanol aqueous solution to the filtrate and heat; after cooling, dilute the solution to a volumetric flask and record the volume as solution A. Solution A is the solution for removing chromium ions, and the volume of solution A is recorded as V1.

[0010] Take a volume of solution A of V2, add 10 mL of ammonium chloride solution with a concentration of 200 g / L, heat the solution to a gentle boil; add ammonia water dropwise (1+1) until a precipitate forms; then add another 6~8 mL of ammonia water dropwise (1+1), and denote this as solution B. Solution B is the solution for removing chromium ions, iron ions and aluminum ions.

[0011] Add ammonium persulfate to solution B, heat to boiling for 3-5 minutes to remove manganese ions, let stand and filter to remove the precipitate, collect the filtrate into a volumetric flask, and dilute to volume. This solution is called solution C. Solution C is a solution that removes chromium ions, iron ions, aluminum ions and manganese ions; the volume of solution C is V3.

[0012] S3. Take a volume of solution C of V4, add a buffer solution with a pH of 9-10, add 0.5-2g of acid chrome blue K-naphthol green B mixed indicator, and titrate with EDTA standard titration solution until the solution color changes from dark green to blue-green as the endpoint. Record the volume of EDTA solution used as V5; the concentration of EDTA standard titration solution is 0.010mol / L.

[0013] S4. Take solution C with a volume of V4, add 0.5~2g of calcein-methylthymol blue-phenolphthalein mixed indicator, add 15mL of potassium hydroxide solution with a concentration of 200g / L, and titrate with EDTA standard titration solution until the green fluorescence disappears and turns pure purple-red as the endpoint. The concentration of EDTA standard titration solution is 0.010mol / L; record the volume of EDTA solution used as V6.

[0014] S5. Calculate the magnesium oxide content in solid waste using the following formula.

[0015]

[0016] In the formula, w is the mass percentage of magnesium oxide in the solid waste; m is the weight of the sample.

[0017] According to the aforementioned method for determining the magnesium oxide content in solid waste, in S1, 0.2g of air-dried 100-mesh sample is weighed, and the mixed flux is 5g; the mass ratio of anhydrous sodium carbonate to boric acid in the mixed flux is 1:0.7.

[0018] Further, 1.0g of mixed flux was weighed into a platinum crucible, 3.0g of mixed flux was weighed and mixed with 0.20g of solid waste sample and placed in the platinum crucible; then 1.0g of mixed flux was weighed and covered on the solid waste sample.

[0019] According to the aforementioned method for determining the magnesium oxide content in solid waste, in S1, the hydrochloric acid solution is prepared by mixing hydrochloric acid and water at a volume ratio of 1:4.

[0020] According to the aforementioned method for determining the magnesium oxide content in solid waste, hydrochloric acid aqueous solution, nitric acid and ethanol aqueous solution are added to the filtrate and heated until the sample is completely dissolved. The hydrochloric acid aqueous solution is prepared by mixing hydrochloric acid and water at a volume ratio of 1:1; the density of nitric acid is 1.39 g / mL; and the ethanol aqueous solution is prepared by mixing ethanol and water at a volume ratio of 5:95.

[0021] According to the aforementioned method for determining the magnesium oxide content in solid waste, the buffer solution in S3 is prepared as follows: 67.5g of ammonium chloride is dissolved in water, 570mL of ammonia water is added, and the solution is diluted with water to 1L.

[0022] According to the aforementioned method for determining the magnesium oxide content in solid waste, the preparation method of the acid chrome blue K-naphthol green B mixed indicator in S3 is as follows: weigh 1.000g of acid chrome blue K, 2.5g of naphthol green B and 50g of dried potassium nitrate, and mix and grind them in a mortar.

[0023] According to the aforementioned method for determining the magnesium oxide content in solid waste, the preparation method of the calcein-methyl thymol blue-phenolphthalein mixed indicator in S4 is as follows: weigh 1.0g calcein, 1.0g methyl thymol blue, 0.2g phenolphthalein and 50g dried potassium nitrate, mix and grind them finely.

[0024] The method for determining the magnesium oxide content in solid waste provided by this invention has at least the following advantages compared with the prior art:

[0025] (1) The determination method of the present invention integrates the multi-step impurity removal into a modular process through the continuous operation of "resin chromium removal → ammonia precipitation of iron and aluminum → ammonium persulfate oxidation to remove manganese", reducing the number of operation steps and reagent consumption. At the same time, it avoids the drawbacks of traditional precipitation method such as impurity residue and reduction method such as harmful gas. It takes into account the treatment efficiency, environmental protection and operation safety, and ensures that the titration reaction is specifically for calcium and magnesium ions, which significantly improves the measurement accuracy and repeatability of titration results. It fundamentally guarantees the accuracy of magnesium oxide determination results in solid waste. The data is reliable and can be used in rigorous scenarios such as environmental monitoring and solid waste resource utilization assessment.

[0026] (2) The sample melting process of the test method of the present invention adopts a sandwich structure of "flux-sample-flux" to ensure that the sample is fully wrapped, effectively preventing the loss of volatile components at high temperature and the corrosion of the crucible by the sample, thereby improving the accuracy and reproducibility of the results. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] All reagents used in the embodiments of this invention are commercially available.

[0029] Weigh 1.0 g of mixed solvent (1 part anhydrous sodium carbonate and 0.7 parts boric acid finely ground and mixed) into a platinum crucible; weigh 3.0 g of mixed solvent and 0.20 g of solid waste sample (air-dried to 100 mesh), accurate to 0.0001 g, mix well, and place in the platinum crucible; then weigh another 1.0 g of mixed solvent to cover it. This "flux-sample-flux" sandwich structure ensures the sample is fully encapsulated, effectively preventing the loss of volatile components at high temperatures and the corrosion of the crucible by the sample, thus improving the accuracy and reproducibility of the results.

[0030] Cover the crucible with a slight gap, and perform alkaline melting of the sample using a mixed flux of anhydrous sodium carbonate and boric acid. Melt in an 850°C high-temperature oven for 1 hour. Remove the crucible and, while it is still molten, gently and steadily rotate it in a circular motion to allow the melt to solidify evenly on the inner wall of the crucible. Ensure the shaking speed and force are appropriate to prevent spillage and sample loss. This step of shaking while hot ensures that the melt adheres evenly to the inner wall of the crucible, forming a thin layer with a larger specific surface area. This greatly facilitates the subsequent acid leaching step, shortens the dissolution time, and avoids clumping and incomplete dissolution caused by uneven cooling.

[0031] Rinse the outer wall of the crucible thoroughly with deionized water to ensure it is free of impurities. Immerse it in a 250mL glass beaker containing hydrochloric acid solution (prepared by mixing hydrochloric acid and water in a 1:4 volume ratio). Heat on a hot plate until the solid is completely dissolved in the hydrochloric acid. The resulting solution is a liquid. If any solids that are difficult to dissolve in hydrochloric acid remain, they can be crushed and stirred with a polytetrafluoroethylene rod to aid in their dissolution.

[0032] After cooling the solution, add 15g of a strong basic anion exchange resin (IRA-900), stir for 5 minutes, and filter. Collect the filtrate in a 250mL beaker, wash the beaker three times with hot water, and wash the resin ten times. Add 20mL of hydrochloric acid (1+1), 8 drops of nitric acid (density 1.39 g / mL), and 20mL of anhydrous ethanol (5+95), and heat until the sample is completely dissolved. After cooling to room temperature, transfer to a 250mL volumetric flask. Wash the beaker and polytetrafluoroethylene rod at least three times with deionized water, and transfer the washing solution to the 250mL volumetric flask as well. Finally, make up to volume, shake well, and record this as solution A. The volume V1 of solution A is 250mL. The quaternary ammonium groups of the strong basic anion exchange resin selectively adsorb CrO4²⁻ / Cr2O7²⁻. Since Fe³⁺, Al³⁺, and Mn²⁺ are all cations, they will not be adsorbed by anion exchange resins. Therefore, chromium must be removed before these cations are precipitated.

[0033] Take 100 mL of solution A (V2 = 100 mL) into a 250 mL beaker, add 10 mL of ammonium chloride solution (concentration 200 g / L), and heat on a hot plate, keeping it at a gentle boil without splashing. Add ammonia water (1+1) dropwise until precipitates form (at this point, iron and aluminum precipitates), then add an excess of 8 mL of ammonia water (1+1) to obtain solution B. The ammonium chloride-ammonia water buffer system (pH≈9) aims to allow Fe³⁺ and Al³⁺ to form insoluble hydroxide precipitates (Fe(OH)₃, Al(OH)₃), while Mn²⁺ will not precipitate at this pH. Therefore, iron, aluminum, and manganese can be separated by filtration.

[0034] Add 0.45g of ammonium persulfate to solution B and heat to boiling. This step removes manganese ions. Let stand until the precipitate settles, then filter while hot using rapid qualitative filter paper. Wash the precipitate and filter paper several times with hot water until clean. Collect the filtrate and washings in a 250mL volumetric flask, dilute to volume, and record as solution C. The volume of solution C is V3 (V3 = 250mL).

[0035] Pipette 50 mL of solution C into a 250 mL Erlenmeyer beaker (V4 = 50 mL), add 50 mL of water, 20 mL of pH buffer solution, and 1 g of Acid Chrome Blue K-Naphthol Green B mixed indicator. Titrate with 0.010 mol / L EDTA standard titration solution until the solution color changes from dark green to blue-green. Record the volume of EDTA solution used at this point as V5. In this method, EDTA (ethylenediaminetetraacetic acid) can form stable complexes with calcium and magnesium ions in alkaline buffer solutions.

[0036] The buffer solution is prepared by dissolving 67.5g of ammonium chloride in water, adding 570mL of ammonia water, and diluting with water to 1L. The mixed indicator of acid chrome blue K and naphthol green B is prepared by weighing 1.000g of acid chrome blue K, 2.5g of naphthol green B, and 50g of dried potassium nitrate, and mixing and grinding them finely in a mortar.

[0037] Pipette 50 mL of solution C into a 250 mL Erlenmeyer beaker (V4 = 50 mL), dilute to 200 mL, add a small amount of calcein-methyl thymol blue-phenolphthalein mixed indicator, add 15 mL of potassium hydroxide solution (200 g / L), and titrate with 0.010 mol / L EDTA standard titration solution until the green fluorescence disappears and a pure purple-red color appears. Record the volume of EDTA solution used at this point as V6.

[0038] The preparation method of the calcein-methyl thymol blue-phenolphthalein mixed indicator is as follows: 1.0g calcein, 1.0g methyl thymol blue, 0.2g phenolphthalein, and 50g dried potassium nitrate are mixed and ground finely. The magnesium oxide content in solid waste is calculated using a formula.

[0039] The determination method of this invention integrates multiple impurity removal steps into a modular process through continuous operation of "resin chromium removal → ammonia precipitation of iron and aluminum → ammonium persulfate oxidation to remove manganese," reducing the number of operation steps and reagent consumption. It also avoids the drawbacks of traditional precipitation methods such as impurity residues and reduction methods such as harmful gases, balancing processing efficiency, environmental friendliness, and operational safety. It ensures that the titration reaction is specifically targeted at calcium and magnesium ions, significantly improving the metrological accuracy and repeatability of the titration results. This fundamentally guarantees the accuracy and reliability of magnesium oxide determination results in solid waste, making it suitable for rigorous scenarios such as environmental monitoring and solid waste resource utilization assessment.

[0040] In this embodiment of the invention, five different groups of samples (denoted as Sample 1, Sample 2, Sample 3, Sample 4, and Sample 5) were taken. Each group of samples was tested four times using the testing method described above. The average value was then compared with the true value of the sample. The test results are shown in Table 1.

[0041] Table 1

[0042]

[0043] The data shows that the sample detection data has high precision and accuracy, indicating that the detection method is generally reliable. The detection results of Sample 1 and Sample 5 fluctuated slightly, but the deviation between the average value and the true value is still within an acceptable range (relative error <3%).

[0044] Finally, it should be noted that the above-described embodiments are merely specific implementations of the present invention, used to illustrate the technical solutions of the present invention, and not to limit them. The scope of protection of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments within the scope of the technology disclosed in the present invention, or make equivalent substitutions for some of the technical features; and these modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be covered within the scope of protection of the present invention.

Claims

1. A method for determining the magnesium oxide content of a solid waste, characterized by, The solid waste contains magnesium element, calcium element, chromium element, iron element, aluminum element and manganese element; the method for measuring the content of magnesium oxide in the solid waste comprises the following steps: S1, a sample is weighed, the sample is subjected to alkali fusion with a mixed flux of anhydrous sodium carbonate and boric acid, and then cooled; the cooled sample is added to a hydrochloric acid solution for dissolution, and a dissolved solution is obtained after completion; S2, interference ions in the dissolved solution of the solid waste are removed in the order of chromium ions→iron ions, aluminum ions→manganese ions; specifically: A strong basic anion exchange resin is added to the dissolved solution, stirred and filtered; hydrochloric acid aqueous solution, nitric acid and ethanol aqueous solution are added to the filtrate and heated; after cooling, the solution is diluted to a volumetric flask, and after dilution, it is recorded as solution A, and the volume of solution A is recorded as V1; V2 of solution A is taken, 10 mL of 200 g / L ammonium chloride solution is added, and the solution is heated to a micro-boiling state; ammonia water (1+1) is added dropwise until the precipitate is generated; 6-8 mL of ammonia water (1+1) is added dropwise, and it is recorded as solution B; Ammonium persulfate is added to solution B, heated and boiled for 3-5 min, and the precipitate is filtered and collected, and the filtrate is collected in a volumetric flask, and after dilution, it is recorded as solution C, and the volume of solution C is V3; S3, V4 of solution C is taken, a buffer solution with a pH value of 9-10 is added, 0.5-2 g of an acid chrome blue K-naphthol green B mixed indicator is added, and EDTA standard titration solution is added dropwise until the solution color changes from dark green to blue-green as the end point, and the volume of EDTA solution used is recorded as V5; the concentration of the EDTA standard titration solution is 0.010 mol / L; S4, V4 of solution C is taken, 0.5-2 g of a calcein-methyl thymol blue-phenolphthalein mixed indicator is added, 15 mL of 200 g / L potassium hydroxide solution is added, and EDTA standard titration solution is added dropwise until the green fluorescence disappears and a pure purple red color appears as the end point, and the volume of EDTA solution used is recorded as V6; the concentration of the EDTA standard titration solution is 0.010 mol / L; S5, the content of magnesium oxide in the solid waste is calculated by the following formula, In the formula, w is the mass proportion of magnesium oxide in the solid waste; m is the weight of the sample.

2. The method for determining the magnesium oxide content in solid waste according to claim 1, characterized by, In S1, 0.2 g of air-dried 100 mesh sample is weighed, and the mixed flux is 5 g; the mass ratio of anhydrous sodium carbonate to boric acid in the mixed flux is 1:0.

7.

3. The method for determining the magnesium oxide content in solid waste according to claim 2, characterized by, 1.0 g of the mixed flux is weighed in a platinum crucible, 3.0 g of the mixed flux is mixed with 0.20 g of the solid waste sample, and then placed in a platinum crucible; 1.0 g of the mixed flux is weighed and placed on the solid waste sample.

4. The method for determining the magnesium oxide content in solid waste according to claim 1, characterized by, In S1, the hydrochloric acid solution is prepared by mixing hydrochloric acid and water in a volume ratio of 1:

4.

5. The method of claim 1, wherein To the filtrate, hydrochloric acid aqueous solution, nitric acid and ethanol aqueous solution are added and heated to completely dissolve the sample; the hydrochloric acid aqueous solution is prepared by mixing hydrochloric acid and water in a volume ratio of 1:1; the density of nitric acid is 1.39 g / mL; the ethanol aqueous solution is prepared by mixing ethanol and water in a volume ratio of 5:

95.

6. The method of determining the magnesium oxide content in solid waste according to claim 1, characterized by, In S3, the buffer solution is prepared by dissolving 67.5 g of ammonium chloride in water, adding 570 mL of ammonia water, and diluting with water to 1 L.

7. The method of claim 1, wherein the solid waste is a waste containing magnesium oxide. In S3, the preparation method of the acid chrome blue K-naphthol green B mixed indicator is as follows: 1.000 g of acid chrome blue K, 2.5 g of naphthol green B and 50 g of dried potassium nitrate are weighed and mixed and finely ground in a mortar.

8. The method of claim 1, wherein In S4, the preparation method of the calcein-methyl thymol blue-phenolphthalein mixed indicator is as follows: 1.0 g of calcein, 1.0 g of methyl thymol blue, 0.2 g of phenolphthalein and 50 g of dried potassium nitrate are weighed and mixed and finely ground.

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