Determination of Total Aluminum in Aluminum Ash by Ethylenediaminetetraacetic Acid Titration with Alkali High-Temperature Melting

In order to strengthen the recycling and utilization of aluminum resources in aluminum ash, the method was proposed to determine the total aluminum in aluminum ash by ethylenediaminetetraacetic acid (EDTA) titration with alkali high-temperature melting. In response to the complexity of the aluminum ash matrix and the high content of calcium, magnesium, and fluorine, the pre-treatment and titration conditions were optimized. After drying and wetting with ethanol, 0.1 g of the sample was taken, 3 g of sodium hydroxide and 2 g of sodium phosphate were added (forming precipitates with calcium and magnesium and separating them out, to prevent calcium and magnesium hydroxides from adsorbing Al³⁺), and the mixture was pre-melted at 400 ℃ for 20 min. Then 1g of sodium peroxide was added, and the mixture was melted at 750 ℃ for 15 min. Boiling water was added to dissolve all the frits by boiling, and 3 mL of 6 mol·L^-1 hydrochloric acid solution was added. The mixed solution was boiled to remove hydrogen peroxide. After diluting to 100 mL by water and filtering, 25 mL of the filtrate was taken, mixed with 10 mL of 6 mol·L^-1 hydrochloric acid solution and 5 mL of perchloric acid, and the mixed solution was heated to near dryness to eliminate the complexation interference of F^- with high content in the sample on Al³⁺. The residue was dissolved by 10 mL of 6 mol·L^-1 hydrochloric acid solution, and 10 mL of water, 8 mL of 40 g·L^-1 EDTA solution, and xylene orange indicator were added. The solution obtained was adjusted to bright yellow color by 6 mol·L^-1 hydrochloric acid solution, and boiled for 5 min, allowing EDTA to fully chelate Al³⁺. Then 15 mL of acetic acid-sodium acetate buffer solution (pH 5.8) and xylenol orange indicator were added, and 1 000 mg·L^-1 zinc standard solution was added for titration until the solution turned orange red. Then 5 mL of potassium fluoride solution (100 g·L^-1) was added, and the mixed solution was boiled for 5 min, to completely replace the Al³⁺ from EDTA complex. After adding 10 mL of acetic acid-sodium acetate buffer solution (pH 5.8) and xylenol orange indicator, titration was conducted with 1 000 mg·L^-1 zinc standard solution until the solution turned orange red, and the volume of titrant consumed was recorded. Total aluminum was calculate by titration. It was shown that the total aluminum recoveries were found in the range of 96.8%-103%, and RSDs (n=6) of the determined values was less than 1.0%. The proposed method was suitable for the determination of total aluminum in aluminum ash from mining smelting in laboratories with limited experimental conditions.