1 Scope
This standard specifies the test method for the iodine adsorption capacity of wood-based activated carbon.
This standard applies to the determination of the iodine adsorption capacity of wood-based activated carbon.
2 Normative references
The following documents are essential for the application of this document. For cited documents that have a date, only the edition dated accordingly shall apply to this document. For cited documents that have no date, the latest edition (including all amendments) shall apply to this document.
GB/T 6682 — Specifications and test methods for water used in analytical laboratories
3. Methodology Summary
A specified amount of sample is shaken with an iodine solution for adsorption, then filtered; the filtrate is collected, and the residual iodine in the filtrate is titrated using a sodium thiosulfate solution. The iodine value is determined as the amount of iodine adsorbed per gram of carbon (expressed in mg), under conditions where the concentration of residual iodine is 0.02 mol/L (1/2 I₂).
4 Instruments and Reagents
The water used in this standard shall comply with the Grade 3 water specification of GB/T 6682; unless otherwise specified, all reagents mentioned herein refer to analytical reagents.
4.1 Balance, with an accuracy of 0.0001 g.
4.2 Electric constant-temperature drying oven.
4.3 Oscillator, frequency: 240–275 Hz.
4.4 Sealed sample grinding mill.
4.5 Second timer.
4.6 Drier.
4.7 Stoppered conical flask, 250 mL.
4.8 Acid burette, 10 mL, accuracy 0.05 mL; Base burette, 50 mL, accuracy 0.1 mL.
4.9 Wide-mouth conical flask, 250 mL.
4.10 Graduated cylinders: 100 mL and 1000 mL.
4.11 Volumetric flasks, in clear and brown.
4.12 Beaker.
4.13 Funnel, with an inner diameter of 100 mm at the top opening.
4.14 Reagent bottles: colorless and brown.
4.15 Qualitative filter paper, GB/T 1914, medium speed (102), φ12.5 cm.
4.16 Pipettes: 10 mL and 50 mL.
4.17 Concentrated hydrochloric acid (GB/T 622).
4.18 Iodine (GB/T 675).
GB/T 12496.8—2015
4.19 Potassium iodide (GB/T 1272).
4.20 Sodium thiosulfate [Na₂S₂O₃·5H₂O] (GB/T 637). 637)。
4.21 Soluble starch (HG/T 2759).
4.22 Potassium iodate (GB 1258).
4.23 Anhydrous sodium carbonate (GB/T 639).
4.24 Color-changing silica gel (HG/T 2765.4).
5 Solutions
5.1 Standard iodine (1/2 I₂) solution (0.1000 mol/L)
Weigh out 19.100 g of potassium iodide and dissolve it completely in a beaker containing approximately 30 mL of water. Under stirring, add 12.700 g of iodine until it is fully dissolved in the potassium iodide solution. Cover the beaker with a lid, seal it, and keep it in the dark for at least 4 hours, stirring intermittently to ensure complete dissolution of all solids. Finally, transfer the solution to a 1 L brown volumetric flask, dilute it with water to the mark, shake thoroughly, and allow it to stand for 2 days. After standardization, store the solution in a brown reagent bottle. Ensure that the weight ratio of potassium iodide to iodine in the standard iodine solution is 1.5:1.
Calibration: Transfer 25 mL of iodine solution into a 250 mL wide-mouth conical flask using a pipette, and titrate it with the calibrated sodium thiosulfate standard solution. When the solution turns pale yellow, add 2 mL of starch indicator solution, and titrate dropwise until the solution becomes colorless; this point constitutes the endpoint.
The concentration of the iodine solution is calculated using Equation (1):
…………………………………
(1)
Where:
C1-concentration of the iodine (1/2 I₂) standard solution, expressed in moles per liter (mol/L);
C2 — concentration of the sodium thiosulfate standard solution, expressed in moles per liter (mol/L);
V₂-the volume of the standard sodium thiosulfate solution consumed during the titration, expressed in milliliters (mL);
V₁ — Volume of iodine solution used during calibration, expressed in milliliters (mL).
5.2 Starch Indicator Solution
Weigh 1.0 g of soluble starch, add 1 0 mL of water, then under stirring, add 190 mL of boiling water; bring to a gentle boil for 4–5 min, cool to room temperature, and collect the upper clear supernatant for use. This solution shall be prepared immediately before use and stored in a refrigerator.
5.3 Potassium iodate solution (0.1000 mol/L)
Dry at least 4 g of potassium iodate for 2 h at 110 °C ± 5 °C, then cool in a desiccator to room temperature. Dissolve 3.5667 g ± 0.0001 g of the dried potassium iodate in approximately 100 mL of distilled water, transfer the solution to a 1 L volumetric flask, dilute to the mark, mix thoroughly, and then transfer the solution to a wide-mouth reagent bottle for later use.
5.4 Hydrochloric acid solution (5 wt%)
First, use a 1000 mL graduated cylinder to measure 550 mL of distilled water and transfer it into a 1 L reaction flask. Then, in a fume hood or ventilation cabinet, use a 100 mL graduated cylinder to measure 70 mL of concentrated hydrochloric acid, immediately transfer it into the aforementioned reaction flask, cap the flask, shake it, and mix thoroughly before setting it aside for further use.
5.5 Sodium thiosulfate standard solution (0.1000 mol/L)
Weigh 24.820 g of sodium thiosulfate and dissolve it in 75 mL ± 25 mL of freshly boiled distilled water; then add 0.1 g ± 0.01 g of sodium carbonate to prevent changes in the concentration of the sodium thiosulfate solution due to bacterial decomposition. Subsequently, transfer the above solution to a 1 L volumetric flask and dilute it with water.
After reaching the target volume, transfer the solution to a brown glass bottle, protect it from light, and allow it to stand for 4 days before calibration.
Calibration: Using a pipette, transfer 25 mL of the prepared potassium iodate solution into a 250 mL wide-mouth conical flask. Then add 2.00 g ± 0.01 g of potassium iodide, and shake the conical flask until all potassium iodide crystals have completely dissolved. Next, using a pipette, transfer 5.0 mL of concentrated hydrochloric acid into the conical flask (perform this operation under a fume hood), then titrate the free iodine with sodium thiosulfate solution until a pale yellow color appears in the conical flask. Add 2 mL of starch indicator, continue titration until the solution becomes colorless, record the data, and calculate the concentration of sodium thiosulfate using Equation (2):
Where:
C3-Concentration of the sodium thiosulfate standard solution, expressed in moles per liter (mol/L);
C4-concentration of the potassium iodate solution, expressed in moles per liter (mol/L);
V₄-Volume of potassium iodate solution used in the standardization, in milliliters (mL);
V₃-Volume of the sodium thiosulfate solution consumed, in milliliters (mL).
6. Operational Steps
6.1 Take several samples and place them in a sealed sample preparation grinder for crushing; then, transfer the samples that have passed through a 200-mesh sieve (71 μm) into an oven and dry them at 150 °C until they reach constant weight. Weigh 0.5000 g of the sample (accurate to 0.0001 g), place it in a dry, 250 mL stoppered conical flask with ground-mouth, accurately add 10.0 mL of 5 wt% hydrochloric acid to thoroughly moisten the sample, heat the mixture on a electric stove until it boils, maintain slight boiling for (30 ± 2) s, allow it to cool to room temperature, then add 50.0 mL of the calibrated iodine standard solution. Immediately stopper the flask, shake it on a shaker for 15 min, and quickly filter the mixture into a dry beaker.
6.2 Pipette 10 mL of the filtrate into a 250 mL wide-mouth conical flask containing 100 mL of distilled water. Titrate the mixture with a calibrated sodium thiosulfate standard solution. When the solution turns pale yellow, add 2 mL of starch indicator solution, continue titration until the solution becomes colorless, and record the volume of sodium thiosulfate used. For each sample, perform duplicate experiments and calculate the average value.
7. Result Calculation
The iodine adsorption value A is calculated according to Equation (3):
In equations (3), (4), and (5):
A-iodine adsorption value of the sample, expressed in mg/g; A-iodine adsorption value of the sample, expressed in mg/g;
-amount of iodine adsorbed per gram of activated carbon, expressed i
n mg/g; D — correction factor (determined from the concentration c of the residual filtrate using Table 1);
C₁ — concentration of the iodine (½I) standard solution, in units of mol/L; C₂ — concentration of the sodium thiosulfate standard solution, in units of mol/L; V₂ — volume of sodium thiosulfate standard solution consumed, in units of mL;
m-mass of the specimen, in grams (g);
