GB/T 31924-2015Nickel pig iron—Determination of nickel content—The dimethylglyoxime gravimetric method (English PDF)

7.3.1 Weighing of empty crucible

Place a mixture of 20 mL of hot hydrochloric acid (see 4.4), 10 mL of nitric acid (see 4.3) and 30 mL of water into the filter crucible (see 6.1) for filtration, then, use warm water to wash the acidic substances on the crucible. Place the crucible in an oven at 145 °C to dry for 2 h. In a desiccator, cool it down to room temperature, then, quickly weigh it.

7.3.2 Dissolution of specimen

7.3.2.1 Place the specimen in a 400 mL beaker; add 10 mL of water; add 0.5 g ~ 1 g of ammonium fluoride (see 4.2). Let it stand for 2 min. Then, add 5 mL of hydrochloric acid (see 4.4) and let it stand for 1 min. Add 20 mL of nitric acid (see 4.3); maintain the volume and heat it up at a low temperature, until the sample no longer dissolves [if the sample is insoluble, add another 0.5 g ~ 1 g of ammonium fluoride (see 4.2)]; add 10 mL of perchloric acid (see 4.5); continue to heat it up, until it emits perchloric acid smoke and the volume reaches 2 mL ~ 3 mL; add 40 mL of water to boil and dissolve the salts. If the specimen is completely dissolved, proceed in accordance with 7.3.3; if the sample has a small amount of residue, proceed in accordance with 7.3.2.2.

7.3.2.2 If there is a small amount of residue, filter it; collect the filtrate in a 500 mL beaker; use hot water to wash it, until it is acid-free; this is the mother solution. Place the residue and filter paper in a platinum crucible for low-temperature ashing. After ashing, add 2 g ~ 3 g of the mixed solvent (see 4.1); send it into a 900 °C high-temperature furnace to melt for 10 min, until it is limpid, then, take it out, shake it and cool down to room temperature. Use a small amount of water to leach it in the original beaker; use water to wash the platinum crucible; add 10 mL of hydrochloric acid (see 4.7) to acidify it and combine it with the mother solution.

7.3.3 Treatment of test solution

Add 10 mL of tartaric acid solution (see 4.9) to the test solution (see 7.3.2); dilute the solution to 250 mL. Under constant stirring, use ammonia water (see 4.6) to adjust to pH 4.5; use hot water at 60 °C ~ 80 °C to dilute to 300 mL.

7.3.4 Precipitated nickel

While stirring, add dimethylglyoxime (see 4.10) to the test solution (see 7.3.3). For every 1 mg of nickel, 0.4 mL of dimethylglyoxime (see 4.10) needs to be added, and an excess of 20 mL (the volume shall not exceed 1/3 of the volume of the test solution, so as not to dissolve part of the precipitate in ethanol). Then, while stirring, use ammonia water (see 4.6) to slowly adjust the solution to pH 8 ~ 9. After thoroughly stirring it, let it stand for 30 min to coagulate the precipitate.

7.3.5 Filtration, drying and weighing

Transfer the precipitate (see 7.3.4) to a dry filter crucible that has reached a constant […]