FCLYSAl0071 Determination of aluminum content in aluminum and aluminum alloys – EDTA titration method (1)

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Aluminum and aluminum alloys — Determination of aluminum content — EDTA titration method (1) 1 Scope This method is applicable to the determination of aluminum content in silicon-barium aluminum alloys. 2 Principle: The sample is dissolved in nitric acid, hydrofluoric acid, and perchloric acid. Other elements are separated by precipitation with sodium hydroxide. At pH 4.5, an excess of EDTA is added and the mixture is boiled for 2 minutes to ensure complete complexation of aluminum with EDTA. Using PAN as an indicator, the excess EDTA is back-titrated with copper standard solution while the mixture is still hot. The aluminum content is calculated based on the volume of copper standard solution consumed and the volume of EDTA standard solution added. 3 Reagents 3.1 Sodium hydroxide. 3.2 Nitric acid, approximately 1.42 g/mL. 3.3 Hydrochloric acid, 1+1. 3.4 Nitric acid, 1+1. 3.5 Hydrofluoric acid, approximately 1.15 g/mL. 3.6 Perchloric acid, approximately 1.68 g/mL. 3.7 Ammonia water, 1+1. 3.8 Phenolphthalein ethanol solution, 1 g/L. 3.9 1-(2-Pyridylazo)-2-naphthol (PAN) ethanol solution, 1 g/L. 3.10 Acetic acid-sodium acetate buffer, pH≈4.5: Weigh 64 g of sodium acetate trihydrate and dissolve it in water; add 68 mL of acetic acid, then dilute to 1000 mL with water. 3.11 Sodium hydroxide-sodium chloride mixed wash: Weigh 1 g of sodium hydroxide and 4 g of sodium chloride, and dissolve them in 100 mL of water. 3.12 EDTA standard solution, c(EDTA)≈0.02 mol/L. 3.12.1 Preparation: Weigh 7.446 g of disodium ethylenediaminetetraacetate, dissolve it in water, transfer the solution to a 1000 mL volumetric flask, dilute to the mark with water, and mix well. 3.12.2 Calibration: Transfer 3 portions of 20.00 mL EDTA standard solution into 250 mL conical flasks, add 5 drops of PAN ethanol solution, and titrate with copper standard solution until a purplish-red color is reached as the endpoint. Take the average of the three calibration results; the range between the three results should not be greater than 0.05 mL. Calculate the concentration of the EDTA standard solution using the following formula: Where: c1 —— concentration of the EDTA standard solution, in mol/L ； c2 —— concentration of the copper standard titration solution, mol/L ； V1 —— Volume of EDTA standard solution taken, mL ； V2 — the volume, in mL, of copper standard titrant required to titrate the EDTA standard solution. 3.13 Copper standard titration solution, c(Cu2+)=0.02 mol/L: Weigh 1.2709 g of metallic copper (with a purity of ≥99.99%) into a 250 mL beaker, add 20 mL of nitric acid (1+1), heat to dissolve the material and evaporate the solution to 2–3 mL. Transfer the remaining solution to a 1000 mL volumetric flask, neutralize it with ammonia water (1+1) until the methyl orange indicator turns yellow; then adjust the pH with hydrochloric acid (1+1) until the indicator turns red, adding 5 drops more of the acid than necessary. Finally, dilute the solution to the mark with water and mix well. 4 Test samples: The test samples are drill cuttings smaller than 5 mm. 5 Analysis steps 5.1 Sample weighing Weigh approximately 0.10 g of the sample, with an accuracy of 0.0001 g. 5.2 Preparation of the test solution: Place the sample in a 250 mL polytetrafluoroethylene beaker, add a small amount of water to moisten it, then add 5 mL of nitric acid. Hydrofluoric acid is added drop by drop, and the mixture is shaken until the sample dissolves; a few extra drops of hydrofluoric acid are added thereafter. 10 mL of perchloric acid is added, and the mixture is heated until smoking occurs, after which it is evaporated until the volume is about 5 mL. 5.3 Precipitation separation: Transfer the sample solution to a 250 mL beaker, add water until the volume reaches around 100 mL, heat to 50°C, and slowly add 10 g of sodium hydroxide while stirring. Boil for 3–5 minutes, then cool the mixture. Filter it into a 250 mL volumetric flask, wash it 3–5 times with a sodium hydroxide-sodium chloride mixture, dilute to the mark, and mix well. 5.3 Determination: Transfer 25.00 mL of the sample solution into a 250 mL conical flask, add 10 mL of EDTA standard solution, add 1 drop of phenolphthalein ethanol solution (1 g/L), neutralize with hydrochloric acid (1+1) until colorless, add 20 mL of acetic acid-sodium acetate buffer solution, bring to a boil at low temperature for 2 minutes, add 5 drops of PAN ethanol solution (1 g/L), and titrate with copper standard solution until a purplish-red color appears as the endpoint; record the volume of titrant used. 6 Result Calculation The aluminum content is calculated using the following formula, expressed as a mass fraction: Where: WAl/% —— the mass fraction of aluminum, % ； c1——Concentration of the EDTA standard solution, mol/L ； c2 —— concentration of the copper standard titration solution, mol/L ； V3 —— Volume of EDTA standard solution added, mL ； V4 —— the volume of copper standard titrant consumed to titrate the excess EDTA standard solution, in mL ； V5 — Total volume of the test solution, mL ； V — Volume of the sample solution taken, mL ； m — mass of the sample, in g.