YS/T 273.4-2020 English PDF (YST273.4-2020)

This Part specifies the method for determination of aluminum content in cryolite. This section applies to the determination of aluminum content in cryolite. Measurement range: 9.00% ~ 20.00%. 2 Method summary The sample is melted with acidic potassium sulfate or potassium pyrosulfate, to remove fluorine; the frit is dissolved with hydrochloric acid. Take a portion of the test solution. Add excess Na2EDTA, to form a complex between the aluminum element and EDTA. Under weakly acidic conditions, use xylenol orange as an indicator. Use zinc nitrate standard titration solution, to titrate the excess Na2EDTA. Add sodium fluoride. Heat to displace EDTA. Then use zinc nitrate standard solution, to titrate the released EDTA. Calculate the aluminum content by using the millimeters of zinc nitrate standard titration solution, which is consumed in the titration. 3 Reagents Unless otherwise stated, only reagents and deionized water determined to be of analytical grade are used in the analysis. 3.1 Acid potassium sulfate or potassium pyrosulfate. 3.2 Sodium fluoride. 3.3 Hydrochloric acid (1 + 1). 3.4 Hydrochloric acid (1 + 3). 3.5 Sodium hydroxide solution (100 g/L). 3.6 Buffer solution (pH value 5.6): Weigh 333 g sodium acetate trihydrate. Dissolve in water. Add 15 mL of glacial acetic acid. Use water to dilute it to 1000 mL. Mix well. YS/T 273.4-2020 www.ChineseStandard.net ? Buy True-PDF ? Auto-delivery. Page 6 of 9 3.7 Na2EDTA solution (0.05 mol/L): Weigh 9.3 g of disodium ethylenediaminetetraacetate (Na2EDTA) into a 250 mL beaker. Add 100 mL of water. Heat to dissolve. Cool slightly. Use water to dilute to 500 mL. Mix well. 3.8 Zinc nitrate standard titration solution (approximately 0.01853 mol/L): - Pretreatment: Place about 10 g of zinc particles (wZn ¡Ý 99.99%) in a 250 mL beaker. Add about 100 mL of water. Add a small amount of nitric acid (1 + 1). Stir to dissolve the oxides on the surface of the zinc particles. When the zinc particle is bright silvery white. pour off ...