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Aluminum and Silicon content testing in coal combustion residue by Persee A3F atomic absorbance spectrophotometer

Equipment and Reagent
Equipment:
1. Persee atomic absorption spectrophotometer A3F/AFG, equipped with nitrous oxide/acetylene gas supply, with Persee Al, Si hollow cathode lamps.
2. Burning furnace: capable of burning at 1000C with adequate air circulation
3. Platinum or silicon burning disks: capable of burning at 1000C
4. Stirring hotplate and magnetic bars, capable of heating at 200C

Reagent:
1. Aluminum Stock Solution 1000-ppm:
2. Silicon Stock Solution 200-ppm
3. Lithium Tetraborate (Li2B4O7)
4. HCl solution: add 50mL of HCl and constant volume to 1000mL with pure water
5. Blank solution: prepare a solution of 2g/L Li2B4O7 in HCl solution

Standard solutions:
1. Al Standard Solution (Al content 5, 10, 15, 20, 30mg/L): transfer 0.50, 1.0, 1.5, 2.0, 3.0mL of Al Stock Solution 1000-ppm into 100mL volumetric flask, dilute to 100mL with Blank Solution and mix well.
2. Si Standard Solution (Si content 10, 15, 20, 25, 30mg/L): transfer 5, 7.5, 10, 12.5, 15mL of Silicon Stock Solution 200-ppm into 100mL volumetric flask, dilute to 100mL with Blank Solution.

Equipment Condition
Instrument Working Parameters:

Table 1. Instrument Working Parameters.

Coal Sample Preparation:
Pulverize sample, take homogeneous parts and pass 250 μm sieve

Determine moisture content (heat at 107±2 C until mass constant, divided by original mass) if required

[Combustion]Put sieved sample (a thin layer) onto a roasting dish and put it in burning furnace. Heat to 500C
for 1 hr, then rise temp to 750C for 3 hr. Set until room temperature.

Grind sample until all of sample pass through 75 μm sieve

Heat at 500C for another 1hr

Take 0. 1g sample to a silicon or platinum dish, add 0.5g Li2B4O7 and mix well.

Add another 0.5g Li2B4O7 cover the mixture.

[Fusion and dissolve] heat mixture 1000C for 1hr

Set until room temp. Rinse the outside of the dish carefully. Then, take it to a beaker and add around
150mL HCl solution with a stirring bar. Heat and stir just below boiling for 30min. Make sure there’s no visible precipitate in the beaker.

Set until room temp. Then, take the liquid to a 200mL volumetric flask. Rinse the bar, dish and beaker with HCl solution and transfer the washing liquid into the flask as well. Constant the volume with HCl solution to 200mL.

Take 20mL of the above solution and constant volume to 50mL as testing solution.

Experiment Procedure
Note: change the concentration of standards and dilute the testing accordingly if it’s not appropriate.

Standard Curve: Al
Apply the Al lamp. Preheat for 30min. Adjust the energy well. Apply instrument parameters as in the figure above.
Test the Abs for: Blank solution, Al Standard Solutions (Al concentration of 5, 10, 15, 20, 30mg/L) and testing solution. Use Persee AAS software AAWIN to make standard curve and calculate automatically.

Standard Curve: Si
Apply the Si lamp. Preheat for 30min. Adjust the energy well. Apply instrument parameters as in the figure above.
Test the Abs for: Blank solution, Si Standard Solutions (Si concentration of 10, 15, 20, 25, 30mg/L) and testing solution. Use Persee AAS software AAWIN to make standard curve and calculate automatically.

Results
To ensure a reliable result, try to achieve a linear ratio of over 0.995. The sensitivity of the experiment is high.
The detection limits of Al and Si are 1.5mg/L and 0.002mg/L. The RSD value of the mixed standard solution is 0.78%.

 

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