Method for analyzing multi-component calcium compounds in desulfurization waste ash

Abstract

The invention discloses a method for analyzing multi-component calcium compounds in desulfurization waste ash, which belongs to the technical field of chemical analysis and comprises the following specific steps: (a) determining the total calcium content by adopting an EDTA (Ethylene Diamine Tetraacetic Acid) titration method; (b) measuring calcium hydroxide by hydrochloric acid titration according to the characteristic that sucrose and calcium hydroxide generate sucrose calcium; (c) oxidizing calcium sulfite based on an iodometric method, and calculating the content of calcium sulfite through back titration of residual iodine with sodium thiosulfate; (d) measuring the content of calcium sulfate and calcium sulfite by using hydrogen peroxide oxidation combined with a barium sulfate weight method, and calculating calcium sulfate through a difference value; and (e) converting the total calcium and the calcium content of each component into CaO, and calculating calcium carbonate through a subtraction method. According to the method, through step-by-step titration and oxidation-reduction reaction, by combining core advantages of a titration method and a gravimetric method, accurate determination of total calcium, calcium hydroxide, calcium sulfite and calcium sulfate is achieved, calcium carbonate is calculated through the difference value between the total calcium content and the calcium contribution of each component, complex separation steps are avoided, and efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical analysis, and more specifically, to a method for analyzing multi-component calcium compounds in desulfurized waste ash. Background Art

[0002] The components of desulfurized waste ash in the glass industry are complex and usually contain various calcium compounds such as CaCO3, Ca(OH)2, CaSO3, and CaSO4. Existing standards (such as GB / T5484-2012) are only applicable to the determination of single calcium compounds and cannot solve the problem of mutual interference when multiple calcium compounds coexist. In addition, the resource utilization of desulfurized ash (such as as building materials or chemical raw materials) urgently requires accurate component analysis data support, but there is currently a lack of targeted systematic analysis methods. By systematically analyzing the content of each calcium compound, data support can be provided for the classified utilization of desulfurized ash (such as building materials and chemical raw materials). Summary of the Invention

[0003] To solve the above problems in the prior art, the object of the present invention is to provide a method for analyzing multi-component calcium compounds in desulfurized waste ash, including the following steps:

[0004] (a) Determination of total calcium content: After the sample is dissolved in hydrochloric acid solution, the pH is adjusted to 12-13, magnesium oxide standard solution and triethanolamine solution are added, and with malachite green as the indicator, the total calcium content is determined by EDTA titration method;

[0005] (b) Determination of calcium hydroxide content: The sample is dispersed with water, sucrose solution is added to react with calcium hydroxide to form calcium saccharate, and with phenolphthalein as the indicator, the calcium hydroxide content is determined by titrating calcium saccharate with hydrochloric acid standard solution;

[0006] (c) Determination of calcium sulfite content: An excessive amount of iodine standard solution is added to the sample to oxidize calcium sulfite, and after acidification, the remaining iodine is back-titrated with sodium thiosulfate to calculate the calcium sulfite content;

[0007] (d) Determination of calcium sulfate content: The sample is oxidized by hydrogen peroxide, and the total amount of calcium sulfate and calcium sulfite is determined in an acidic solution. Combining with the calcium sulfite content measured by the iodometric method, the calcium sulfate content is calculated;

[0008] (e) Calculation of calcium carbonate content: After converting the contents of total calcium, calcium sulfate, calcium hydroxide, and calcium sulfite into CaO, the calcium carbonate content is calculated by the difference method.

[0009] In step (a), the sample dissolution condition is to add hydrochloric acid solution (1+1), heat to boiling for dissolution, and the volume-mass ratio of hydrochloric acid to the sample is 15-20:1.

[0010] In step (a), the concentration of the EDTA standard solution is 0.01 mol / L, the pH is adjusted using 20% potassium hydroxide solution, the concentration of the magnesium oxide standard solution is 0.5 mg / mL, and the triethanolamine solution is triethanolamine solution (1+1).

[0011] The total calcium content is calculated as calcium oxide, and the calculation formula is:

[0012]

[0013] where C1 is the concentration of the EDTA standard solution, in mol / L;

[0014] V1 is the volume of the EDTA standard solution consumed in titration, in ml;

[0015] m1 is the sample mass, in g;

[0016] 56.08 is the molar mass of calcium oxide, in g / mol;

[0017] 25 is the dilution ratio of the sample solution.

[0018] In step (b), the water is carbon dioxide-free water, the mass concentration of the sucrose solution is 30%, the solid-liquid ratio of the sample to the sucrose solution is 1:80 - 100, the reaction standing time is 15 minutes, and the concentration of the hydrochloric acid standard solution for titration is 0.5 mol / L.

[0019] The calculation formula for the calcium hydroxide content is:

[0020]

[0021] where C2 is the concentration of the standard hydrochloric acid solution for titration, in mol / L;

[0022] V2 is the volume of the standard hydrochloric acid solution consumed in sample titration, in ml;

[0023] V0 is the volume of the standard hydrochloric acid solution consumed in blank sample titration, in ml;

[0024] m2 is the sample mass, in g;

[0025] 74.10 is the molar mass of calcium hydroxide, in g / mol.

[0026] In step (c), the concentration of the iodine standard solution is 0.05 mol / L, and its addition amount is in a molar ratio of 2.5 - 3.0:1 to calcium sulfite; the acidification uses hydrochloric acid solution (1+1), and after addition, it needs to be stirred for 10 minutes and left to stand in the dark for 5 minutes; the concentration of the sodium thiosulfate standard solution is 0.1 mol / L.

[0027] The calculation formula for the mass fraction of the calcium sulfite hemihydrate is as follows:

[0028]

[0029] CaSO3·1 / 2H2O% = SO2% × 2.016

[0030] Where: C3 is the concentration of the iodine standard solution, with the unit of mol / L;

[0031] K is the volume ratio of the iodine standard solution to the sodium thiosulfate standard solution;

[0032] V3 is the volume of sodium thiosulfate consumed during titration, with the unit of ml;

[0033] m3 is the mass of the sample taken, with the unit of g;

[0034] 25 is the initial volume of the iodine standard solution added, with the unit of ml;

[0035] 64.06 is the molar mass of sulfur dioxide, g / mol;

[0036] 2.016 is the conversion coefficient of sulfur dioxide to calcium sulfite hemihydrate.

[0037] In step (d), the concentration of hydrogen peroxide is 30 wt%, and the volume-mass ratio of hydrogen peroxide to the sample is 150 - 250:1; the concentration of the barium chloride solution is 100 g / L, and the volume-mass ratio of barium chloride to the sample is 80 - 100:1; the calcium sulfate content is determined by the barium sulfate gravimetric method, and the calculation formula is as follows:

[0038]

[0039] CaSO4% = SO3% × 1.7003

[0040] Where: m4 is the mass of the sample, with the unit of g;

[0041] m5 is the mass of the barium sulfate precipitate, with the unit of g;

[0042] m0 is the mass of the precipitate in the blank test, with the unit of g;

[0043] 0.343 is the conversion coefficient of barium sulfate to sulfur trioxide;

[0044] 1.7003 is the conversion coefficient of sulfur trioxide to calcium sulfate.

[0045] Convert the total calcium content, calcium sulfate content, active calcium content, and calcium sulfite content obtained from the analysis into percentage contents calculated as CaO, and then calculate the percentage content of calcium carbonate.

[0046] The calculation formula for the calcium carbonate content is as follows:

[0047] W% = (W1% - W2% - W3% - W4%) × 1.785

[0048] Wherein, W1% is the total calcium content, calculated as CaO, and the unit is %;

[0049] W2% is the calcium content of calcium sulfate, calculated as CaO, and the unit is %;

[0050] W3% is the calcium content of calcium hydroxide, calculated as CaO, and the unit is %;

[0051] W4% is the calcium content of calcium sulfite, calculated as CaO, and the unit is %.

[0052] The analysis method of multi-component calcium compounds in the desulfurized waste ash of the present invention has the following advantages:

[0053] 1. Through stepwise titration and redox reactions (EDTA titration, iodometric method, barium sulfate gravimetric method), the accurate determination of total calcium, calcium hydroxide, calcium sulfite, and calcium sulfate is realized. The calcium carbonate is calculated by the difference between the total calcium content and the calcium contribution of each component, avoiding complex separation steps and improving efficiency;

[0054] 2. By using triethanolamine to mask heavy metals and magnesium oxide to eliminate the interference of calcium precipitation, the sharpness of the titration end point is increased, ensuring the accuracy of samples with complex components;

[0055] 3. The reaction time of each step is short (for example, the reaction of calcium sucrose only takes 15 minutes), and the operation conditions such as light avoidance and acidification are clear, reducing human error;

[0056] 4. This solution combines the core advantages of titration method and gravimetric method, uses conventional reagents such as sucrose, hydrochloric acid, and EDTA, does not require large-scale instruments (such as inductively coupled plasma emission spectrometer), and can complete the whole process detection depending on conventional titration devices, realizing the efficient, low-cost, and environmental-friendly analysis of multi-component calcium compounds in desulfurized waste ash. Specific Embodiments

[0057] The following further elaborates on the present invention with specific embodiments, but the present invention is not limited to these embodiments.

[0058] Example 1

[0059] 1. Determination of total calcium content

[0060] Accurately weigh about 0.3 g of the sample, accurate to 0.0001 g. Place it in a washed and dried beaker, add a small amount of water to disperse the sample, add 5 ml of hydrochloric acid solution (1+1), cover with a watch glass, and heat to boiling and dissolve on an electric furnace. After cooling, transfer the solution to a 250 ml volumetric flask, wash the beaker at least 6 - 8 times, transfer the washing liquid into the volumetric flask as well, and make up the volume to the mark and shake well.

[0061] Use a pipette to transfer 10 ml of the solution from the volumetric flask to a 250 ml conical flask, add a small amount of water, add 2 ml of magnesium oxide standard solution with a concentration of 0.5 mg / ml, add 3 - 4 ml of triethanolamine solution (1+1), add one drop of malachite green indicator, add 20% potassium hydroxide solution dropwise to adjust the pH value until the solution changes from blue-green to colorless, and then add 2 ml in excess. Add a small amount of calconcarboxylic acid indicator, and titrate with 0.01 mol / L EDTA standard solution (when titrating for the first time, the indicator can be added first. After getting familiar with the amount of EDTA used, it is more accurate to add the indicator when titrating close to the end point).

[0062] The total calcium content is calculated as calcium oxide, and the calculation formula is as follows:

[0063]

[0064] Among them, C1 is the concentration of the EDTA standard solution, in mol / L;

[0065] V1 is the volume of the EDTA standard solution consumed in titration, in ml;

[0066] m1 is the mass of the sample, in g;

[0067] 56.08 is the molar mass of calcium oxide, in g / mol;

[0068] 25 is the dilution ratio of the sample solution.

[0069] 2. Determination of calcium hydroxide content

[0070] Weigh about 0.5 g of the sample, accurate to 0.0001 g, and place it in a 250 ml conical flask with a ground glass stopper. Quickly add 50 ml of carbon dioxide-free water, shake the conical flask to disperse the sample, add 50 ml of sucrose solution, cover the bottle stopper, shake well, and let it stand for 15 min. During this period, shake it once every 5 min. Remove the bottle stopper and wash the bottle stopper and the bottle wall with carbon dioxide-free water. Add 4 - 5 drops of phenolphthalein indicator solution, and titrate with 0.5 mol / L hydrochloric acid standard solution. Near the end point, titrate at a rate of about 1 drop per second and keep shaking the conical flask until the pink color of the solution disappears. After adding the last drop of hydrochloric acid standard solution, the pink color does not reappear within 30 s.

[0071] The calculation formula for calcium hydroxide content is:

[0072]

[0073] Among them, C2 is the concentration of the standard hydrochloric acid solution for titration, with the unit of mol / L;

[0074] V2 is the volume of the standard hydrochloric acid solution consumed in the titration of the sample, with the unit of ml;

[0075] V0 is the volume of the standard hydrochloric acid solution consumed in the titration of the blank sample, with the unit of ml;

[0076] m2 is the mass of the sample, with the unit of g;

[0077] 74.10 is the molar mass of calcium hydroxide, with the unit of g / mol.

[0078] 3. Determination of calcium sulfite - iodometric method

[0079] Weigh about 0.2 g of the test sample, accurate to 0.0001 g, and place it in a 250 - ml washed and dried conical flask with a ground - glass stopper. Add 50 ml of water, shake to disperse the sample, transfer 25 ml of the iodine standard solution, shake well, add 20 ml of hydrochloric acid (1 + 1), put in a magnetic stirring bar, cover the flask stopper, place the conical flask on a magnetic stirrer, stir for 10 min, and place it in the dark for 5 min. Rinse the flask stopper and the inner wall of the flask with water, titrate with the sodium thiosulfate standard solution until it turns light yellow, add about 2 ml of soluble starch solution, and then continue titrating until the blue color disappears.

[0080] The calculation formula for the mass fraction of calcium sulfite hemihydrate is:

[0081]

[0082] CaSO3·1 / 2H2O% = SO2% × 2.016

[0083] Among them: C3 is the concentration of the iodine standard solution, with the unit of mol / L;

[0084] K is the volume ratio of the iodine standard solution to the sodium thiosulfate standard solution;

[0085] V3 is the volume of sodium thiosulfate consumed during titration, with the unit of ml;

[0086] m3 is the mass of the test sample weighed, with the unit of g;

[0087] 25 is the initial volume of the iodine standard solution added, with the unit of ml;

[0088] 64.06 is the molar mass of sulfur dioxide, g / mol;

[0089] 2.016 is the conversion coefficient of sulfur dioxide to calcium sulfite hemihydrate.

[0090] 4. Determination of Calcium Sulfate - Barium Sulfate Gravimetric Method

[0091] Weigh 0.2 g of the sample into a 250 ml beaker to disperse the sample. Add 40 ml of hydrogen peroxide and 15 ml of buffer solution with pH = 4.3, heat to boiling and simmer for 5 - 10 min. Remove from the heat and let it cool slightly. While stirring, add 10 ml of hydrochloric acid (1 + 1), heat the solution to boiling and simmer for 5 min. Filter with medium - speed quantitative filter paper and wash with hot water 10 - 12 times. Collect the filtrate and washing liquid in a 250 m beaker. Press a small piece of quantitative filter paper at the bottom of the glass rod, cover with a watch glass, heat to boiling, and slowly add 15 ml of hot BaCl₂ solution drop - by - drop from the cup mouth while simmering. Continue to simmer for several minutes until the precipitate forms well, then let it stand at room temperature for 24 hours. The volume of the solution should be kept at about 200 ml. Filter with slow - speed quantitative filter paper, wash with warm water, and wipe the beaker and glass rod with a small piece of quantitative filter paper. Transfer the precipitate and filter paper together into a platinum crucible that has been ignited to a constant weight. After complete ashing, place it in a high - temperature furnace at 900 °C and burn for 30 minutes. Take out the crucible, cool for 15 min and weigh it.

[0092] The calcium sulfate content is determined by the barium sulfate gravimetric method, and the calculation formula is:

[0093]

[0094] CaSO₄% = SO₃% × 1.7003

[0095] Where: m4 is the mass of the sample, in g;

[0096] m5 is the mass of the barium sulfate precipitate, in g;

[0097] m0 is the mass of the precipitate in the blank test, in g;

[0098] 0.343 is the conversion factor of barium sulfate to sulfur trioxide;

[0099] 1.7003 is the conversion factor of sulfur trioxide to calcium sulfate.

[0100] 5. Calculation of Calcium Carbonate Content

[0101] Convert the ① total calcium content, ② calcium sulfate content, ③ active calcium content, and ④ calcium sulfite content obtained from the analysis into percentage contents calculated as CaO respectively, and then calculate the percentage content of calcium carbonate.

[0102] Assume that the converted percentage contents are W1%, W2%, W3%, and W4% respectively. Then the percentage content of calcium carbonate is:

[0103] W% = (W1% - W2% - W3% - W4%) × 1.785

[0104] Among them, W1% is the total calcium content, calculated as CaO, with the unit of %.

[0105] W2% is the calcium content of calcium sulfate, calculated as CaO, with the unit of %.

[0106] W3% is the calcium content of calcium hydroxide, calculated as CaO, with the unit of %.

[0107] W4% is the calcium content of calcium sulfite, calculated as CaO, with the unit of %.

[0108] Calculation example of the result of Experimental Example 1

[0109] 1. Calculation of the total calcium content result

[0110] The total calcium content is calculated as calcium oxide. The concentration of the EDTA standard solution used, C1 = 0.00995 mol / L, the volume of the EDTA standard solution consumed in titration, V1 = 9.90 ml, and the mass of the sample taken, m1 = 0.3002 g. The calculation results are as follows:

[0111]

[0112] 2. Calculation of the calcium hydroxide content result

[0113] The concentration of the standard hydrochloric acid solution used in titration, C2 = 0.526 mol / L, the volume of the standard hydrochloric acid solution consumed, V2 = 2.75, V0 = 0, and the mass of the sample taken, m2 = 0.4988 g. The calculation results are as follows:

[0114]

[0115] Among them, it contains

[0116] 3. Calculation of the calcium sulfate hemihydrate content result

[0117] The concentration of the iodine standard solution, C3 = 0.04788 mol / L, the volume ratio of the iodine standard solution to the sodium thiosulfate standard solution, K = 1.13636, the volume of sodium thiosulfate consumed in titration, V3 = 14.08 ml, and the mass of the test sample taken, m3 = 0.2012 g. The mass fractions of sulfur dioxide and calcium sulfate hemihydrate are calculated as follows:

[0118]

[0119] CaSO3·1 / 2H2O% = SO2% × 2.016 = 27.66%

[0120] Among them, it contains

[0121] 4. Calculation of the calcium sulfate content result

[0122] The mass of the sample taken, \(m_4 = 0.2005\ g\), the mass of the barium sulfate precipitate after ignition, \(m_5 = 0.1946\ g\), and the mass of the precipitate after ignition in the blank test, \(m_0 = 0.0022\ g\). The calculation formula is as follows:

[0123]

[0124] \(CaSO_4\%=SO_3\%\times1.7003 = 26.80\%\)

[0125] Among them, it contains

[0126] 5. Calculation of the calcium carbonate content result

[0127] The \(CaO\%\) content in calcium carbonate = total \(CaO\%\) - \(CaO\%\) content in calcium hydroxide - \(CaO\%\) content in calcium bisulfite hemihydrate - \(CaO\%\) content in calcium sulfate = \(46.0\%\) - \(8.14\%\) - \(12.01\%\) - \(11.04\%\) = \(14.81\%\)

[0128] \(CaCO_3\%=14.81\times100.09 / 56.08 = 26.43\%\)

[0129] Weigh the solid sample 5 times respectively. According to the detection method in Example 1 and the calculation method in Experimental Example 1, analyze it 5 times, and the experimental results are as follows:

[0130] Sample number <![CDATA[CaSO4]]> <![CDATA[CaSO3·1 / 2H2O]]> <![CDATA[Ca(OH)2]]> <![CDATA[CaCO3]]> 1# 24.51 28.08 6.23 32.40 2# 24.62 27.90 6.24 32.16 3# 24.51 28.05 6.38 32.29 4# 24.59 27.72 6.16 32.14 5# 24.76 27.98 6.23 32.38 Average value 24.60 27.95 6.25 32.27 Relative standard error 0.42 0.52 1.29 0.37

[0131] The RSDs of both \(CaSO_4\) and \(CaCO_3\) are \(<0.5\%\), indicating that the detection method has extremely high precision for the determination of these two substances. The RSD of \(CaSO_3\cdot1 / 2H_2O\) is \(0.53\%\). The error mainly comes from the oxidation sensitivity of calcium sulfite, but it is still better than the industry standard (usually \(>1\%\)).

[0132] The RSD value of \(Ca(OH)_2\) is \(1.29\%\). The error sources mainly include three aspects: First, calcium hydroxide is easy to deliquesce, resulting in a mass deviation caused by moisture absorption during the weighing process, especially when the laboratory humidity is high, the influence is significant; second, when judging the titration end point, the phenolphthalein indicator is easily affected by \(CO_2\) in the air under neutral conditions, resulting in the color turning red, which interferes with the accurate reading of the titration volume; third, the percentage content of this component is relatively low (about \(6\%\)), and the smaller denominator makes the relative error calculation magnified. From the results of parallel samples, the 5 detection values are all concentrated between \(6.16\%\) and \(6.38\%\), and the range is only \(0.22\%\), indicating that despite the above interference factors, this method can still ensure the repeatability and stability of the detection results, and its error level is within a reasonable range among similar chemical analysis methods, and it can meet the quantitative analysis requirements of the calcium hydroxide content in desulfurized waste ash in the glass industry.

[0133] Finally, it should be noted that although the present invention has been described in detail with general descriptions and specific embodiments above, based on the present invention, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for analyzing multi-component calcium compounds in desulfurized waste ash, characterized in that, It includes the following steps: (a) Determination of total calcium content: After the sample is dissolved in hydrochloric acid solution, the pH is adjusted to 12 - 13, magnesium oxide standard solution and triethanolamine solution are added, and with malachite green as the indicator, the total calcium content is determined by EDTA titration method; (b) Determination of calcium hydroxide content: The sample is dispersed with water, sucrose solution is added to react with calcium hydroxide to form calcium saccharate, and with phenolphthalein as the indicator, the calcium hydroxide content is determined by titrating calcium saccharate with hydrochloric acid standard solution; (c) Determination of calcium sulfite content: An excessive amount of iodine standard solution is added to the sample to oxidize calcium sulfite, and after acidification, the remaining iodine is back - titrated with sodium thiosulfate to calculate the calcium sulfite content; (d) Determination of calcium sulfate content: The sample is oxidized by hydrogen peroxide, and the total amount of calcium sulfate and calcium sulfite is determined in an acidic solution. Combining with the calcium sulfite content measured by the iodometric method, the calcium sulfate content is calculated; (e) Calculation of calcium carbonate content: After converting the contents of total calcium, calcium sulfate, calcium hydroxide, and calcium sulfite into those calculated as CaO respectively, the calcium carbonate content is calculated by the difference method.

2. The method according to claim 1, wherein In step (a), the sample dissolution condition is to add hydrochloric acid solution (1 + 1), heat to boiling for dissolution, and the volume - mass ratio of hydrochloric acid to the sample is 15 - 20:

1.

3. The method according to claim 1, wherein In step (a), the concentration of the EDTA standard solution is 0.01 mol / L, the pH is adjusted using 20% potassium hydroxide solution, the concentration of the magnesium oxide standard solution is 0.5 mg / mL, and the triethanolamine solution is triethanolamine solution (1 + 1).

4. The method according to claim 1, wherein The total calcium content is calculated as calcium oxide, and the calculation formula is: Where, C1 is the concentration of the EDTA standard solution, in mol / L; V1 is the volume of the EDTA standard solution consumed in titration, in ml; m1 is the sample mass, in g; 56.08 is the molar mass of calcium oxide, in g / mol; 25 is the dilution ratio of the sample solution.

5. The method according to claim 1, characterized in that, In step (b), the water is carbon - dioxide - free water, the mass concentration of the sucrose solution is 30%, the solid - liquid ratio of the sample to the sucrose solution is 1:80 - 100, the reaction standing time is 15 minutes, and the concentration of the hydrochloric acid standard solution for titration is 0.5 mol / L.

6. The method according to claim 1, characterized in that, The calculation formula for the calcium hydroxide content is: Where, C2 is the concentration of the standard hydrochloric acid solution for titration, in mol / L; V2 is the volume of the standard hydrochloric acid solution consumed in titrating the sample, in ml; V0 is the volume of the standard hydrochloric acid solution consumed in titrating the blank sample, in ml; m2 is the sample mass, in g; 74.10 is the molar mass of calcium hydroxide, in g / mol.

7. The method according to claim 1, characterized in that, In step (c), the concentration of the iodine standard solution is 0.05 mol / L, and its addition amount is in a molar ratio of 2.5 - 3.0:1 to calcium sulfite; the acidification uses hydrochloric acid solution (1 + 1), and after adding, it needs to be stirred for 10 minutes and left standing in the dark for 5 minutes; the concentration of the sodium thiosulfate standard solution is 0.1 mol / L.

8. The method according to claim 1, characterized in that The calculation formula for the mass fraction of calcium sulfite hemihydrate is: CaSO3·1 / 2H2O% = SO2%×2.016 Where: C3 is the concentration of the iodine standard solution, in mol / L; K is the volume ratio of the iodine standard solution to the sodium thiosulfate standard solution; V3 is the volume of sodium thiosulfate consumed during titration, in ml; m3 is the mass of the sample taken, in g; 25 is the initial volume of the iodine standard solution added, in ml; 64.06 is the molar mass of sulfur dioxide, g / mol; 2.016 is the conversion coefficient of sulfur dioxide to calcium bisulfite hemihydrate.

9. The method according to claim 1, wherein In step (d), the concentration of hydrogen peroxide is 30 wt%, and the volume-mass ratio of hydrogen peroxide to the sample is 150 - 250:1; the concentration of the barium chloride solution is 100 g / L, and the volume-mass ratio of barium chloride to the sample is 80 - 100:1; the calcium sulfate content is determined by the barium sulfate gravimetric method, and the calculation formula is: CaSO4% = SO3% × 1.7003 where: m4 is the mass of the sample, in g; m5 is the mass of the barium sulfate precipitate, in g; m0 is the mass of the precipitate in the blank test, in g; 0.343 is the conversion coefficient of barium sulfate to sulfur trioxide; 1.7003 is the conversion coefficient of sulfur trioxide to calcium sulfate.

10. The method according to claim 1, wherein The calculation formula for the calcium carbonate content is: W% = (W1% - W2% - W3% - W4%) × 1.785 where, W1% is the total calcium content, calculated as CaO, in %; W2% is the calcium content of calcium sulfate, calculated as CaO, in %; W3% is the calcium content of calcium hydroxide, calculated as CaO, in %; W4% is the calcium content of calcium sulfite, calculated as CaO, in %.

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