GB/T 3654.10-2024Ferroniobium - Determination of aluminum content - EDTA titrimetric method (English PDF)

0 Warning

Persons using this document should have practical experience of work in a regular laboratory. The document does not point out all the possible safety problems. It is the responsibility of the user to adopt suitable safety and health measures and to ensure compliance with the conditions laid down in the relevant national regulations.

1 Scope

The document specifies a method for determining the aluminum content of ferroniobium by EDTA titration.

It applies to the determination of aluminum in ferroniobium over a mass fraction range of 1.00 % to 9.00 %.

2 Normative references

The content of the following documents constitutes indispensable provisions of this document through normative reference in the text. For dated references, only the version corresponding to that date applies; for undated references, the latest version, including all amendments, applies.

GB/T 4010 Ferroalloys—Sampling and preparation of samples for chemical analysis; GB/T 6379.1 Accuracy (trueness and precision) of measurement methods and results—Part 1: General principles and definitions; GB/T 6379.2 Accuracy (trueness and precision) of measurement methods and results—Part 2: Basic method for the determination of repeatability and reproducibility of a standard measurement method; GB/T 6682 Water for analytical laboratory use—Specification and test methods; GB/T 8170 Rules of rounding off for numerical values and expression and judgement of limiting values; GB/T 12806 Laboratory glassware—One-mark volumetric flasks; GB/T 12808 Laboratory glassware—One-mark pipettes.

3 Terms and definitions

The document lists no terms and definitions that require defining.

4 Principle

The test portion is fused with sodium peroxide and sodium hydroxide, leached with sodium chloride solution and manganese is reduced with ethanol; the bulk of the niobium, iron, titanium and the manganese are separated by dry filtration. Part of the filtrate is acidified, hydrogen peroxide is added to test solutions containing tungsten, the acidity of the solution is adjusted to pH 3 to 3.5 and aluminum is precipitated with ammonium benzoate. After separation, an excess of EDTA solution is added to the aluminum in acid solution. At pH 5.5 to 6.2, in the presence of xylenol orange indicator, the excess EDTA is titrated with zinc standard solution; the EDTA complexed with aluminum is then displaced with sodium fluoride and titrated again with zinc standard solution.

5 Reagents

Unless otherwise stated, only approved analytical grade reagents are used in the analysis, and the water used is distilled water of grade three or better as specified in GB/T 6682, or water of equivalent purity.

The list comprises: sodium peroxide, solid; sodium hydroxide, solid; sodium fluoride, solid; hydrochloric acid of density 1.19 g/mL; hydrochloric acid 1+1; nitric acid of density 1.42 g/mL; perchloric acid of density 1.67 g/mL; hydrogen peroxide 30 %; anhydrous ethanol; ammonia solution of density 1.15 g/mL; ammonia solution 1+1; sodium chloride solution 200 g/L; ammonium acetate solution 200 g/L; ammonium benzoate solution 100 g/L; wash solution, prepared by adding 1 mL of the ammonium benzoate solution to 88 mL of water; 4-nitrophenol solution 1 g/L; acetic acid and sodium acetate buffer solution, prepared by dissolving 20 g of sodium acetate trihydrate in water, adding 0.9 mL of glacial acetic acid, transferring to a 100 mL volumetric flask, diluting to the mark with water and mixing; xylenol orange solution 2 g/L; methyl orange solution 1 g/L.

EDTA standard solution, c(EDTA) = 0.01000 mol/L: 3.7226 g of disodium ethylenediaminetetraacetate dihydrate, primary reference reagent, is dissolved in water, transferred to a 1000 mL volumetric flask, diluted to the mark with water and mixed.

Aluminum standard solution, 0.5 mg/mL: 0.5000 g of high purity aluminum is placed in a plastic beaker, 20 mL of 10 % sodium hydroxide solution is added and the beaker is heated in a hot water bath until dissolution is complete. After cooling, the solution is acidified by pouring in 30 mL of the hydrochloric acid of density 1.19 g/mL in one operation, mixed, cooled to room temperature, transferred to a 1000 mL volumetric flask, diluted to the mark with water and mixed; 1 mL of this solution contains 0.50 mg of aluminum.

Zinc standard solution, c(Zn) = 0.01 mol/L: it is prepared either by dissolving 0.6538 g of zinc of purity above 99.9 % in a small volume of hydrochloric acid 1+1, diluting with water to about 200 mL, adjusting with the two ammonia solutions until Congo red paper turns purplish grey, transferring to a 1000 mL volumetric flask, diluting to the mark and mixing; or by weighing 0.8138 g of zinc oxide, primary reference reagent, previously ignited to constant mass at 800 °C, wetting it with water in a beaker, adding 20 mL of hydrochloric acid 1+1, dissolving with heating, evaporating to 3 mL to 5 mL, transferring to a 1000 mL volumetric flask, adding 2 to 3 drops of methyl orange solution, neutralising with the ammonia solution 1+1 until the colour is yellow, then adding hydrochloric acid 1+1 until the colour turns red plus an excess of 5 to 6 drops, diluting to the mark with water and mixing.

Standardisation of the zinc standard solution: a volume of aluminum standard solution corresponding to the aluminum content of the test portion is transferred to a pure iron crucible and evaporated to dryness, 0.20 g of niobium metal is added, and the procedure of 8.4 is followed, omitting 8.4.3; a blank test is carried out by the same procedure, with no aluminum standard solution added to the iron crucible. The titre of the zinc standard solution for aluminum is obtained from equation (1). The equation as printed could not be reconstructed from the digitised text and is therefore not reproduced; its symbols are T, titre of the zinc standard solution for aluminum, in mg/mL; V, volume of aluminum standard solution taken for the standardisation, in mL; C, concentration of the aluminum standard solution, in mg/mL; K, aliquot ratio of the test solution, equal to 0.25; V1, volume of zinc standard solution consumed in the standardisation, in mL; V0, volume of zinc standard solution consumed by the reagent blank in the standardisation, in mL.

6 Instruments and equipment

Ordinary laboratory instruments and equipment are used; unless otherwise specified, volumetric flasks and pipettes conform to GB/T 12806 and GB/T 12808 respectively.

Analytical balance with a readability of 0.1 mg.

7 Sampling and sample preparation

Sampling and sample preparation are carried out as specified in GB/T 4010; the test sample passes a 0.125 mm sieve.

8 Analytical procedure

Test portion: 0.25 g of sample is weighed to the nearest 0.0001 g.

Number of determinations: at least two independent determinations are carried out on the same sample.

Blank test: a blank test is carried out along with the sample.

Determination, first step: the test portion is placed in a pure iron crucible with 5 g of sodium peroxide and 5 g of sodium hydroxide, stirred and covered, and fused for 10 min to 15 min in a furnace at 700 °C; it is then removed, cooled to room temperature and placed in a 250 mL polytetrafluoroethylene beaker containing 50 mL of sodium chloride solution, and the melt is leached with heating at low temperature, 100 mL of hot water being added for the leaching. The cover and the crucible are removed and washed, 5 mL of anhydrous ethanol is added and the solution is mixed; heating is continued to boiling, gentle boiling is maintained for 5 min and the solution is cooled to room temperature under running water.

Determination, second step: the solution is transferred to a 200 mL volumetric flask, diluted to the mark with water and mixed, then poured quickly into a dry plastic beaker and left to stand for a moment; it is dry filtered through two rapid quantitative filter papers in a plastic funnel into a plastic beaker and the precipitate is discarded. Ferroniobium containing tungsten is treated by the third step, ferroniobium free from tungsten by the fourth step.

Determination, third step, for material containing tungsten: 50.00 mL of the filtrate is transferred to a 250 mL beaker, 15 mL of hydrochloric acid of density 1.19 g/mL and 5 mL of hydrogen peroxide are added quickly and the solution is mixed. It is heated to boiling until large bubbles form, the hydrogen peroxide being completely decomposed. After removal and slight cooling, 10 mL of ammonium acetate solution is added, the solution is adjusted to pH 3 to 3.5 with the two ammonia solutions and heated to near boiling, and 10 mL of ammonium benzoate solution is added dropwise, followed by mixing. The solution is held for 30 min, filtered hot through a medium speed filter paper, and the beaker and the precipitate are washed 2 to 3 times with warm wash solution. The precipitate and the filter paper are transferred to the original beaker, 5 mL of nitric acid and 5 mL of perchloric acid are added, the filter paper is destroyed on a high temperature hot plate and the solution is fumed with perchloric acid to near dryness; it is then removed, cooled to room temperature, 50 mL of water is added and the salts are dissolved with slight heating, after which the fifth step is followed.

Determination, fourth step, for material free from tungsten: 50.00 mL of the filtrate is taken from the plastic beaker, transferred to a 250 mL beaker, and 15 mL of hydrochloric acid of density 1.19 g/mL is added quickly, followed by mixing.

Determination, fifth step: the test solution from the third or fourth step is diluted with water to about 80 mL, 20 mL of EDTA standard solution is added, at the rate of 4 mL of EDTA standard solution for each 1 mg of aluminum in the aliquot, and the solution is heated on a hot plate and boiled for 2 min to 3 min. It is removed, 1 to 2 drops of 4-nitrophenol solution are added, the solution is adjusted with the two ammonia solutions until it just turns yellow, then with hydrochloric acid 1+1 until the yellow colour disappears, plus an excess of 1 to 2 drops; boiling is continued for 2 min, 10 mL of the acetic acid and sodium acetate buffer solution is added and boiling is continued for 30 s. The solution is removed, cooled to room temperature under running water, 2 drops of xylenol orange solution are added and it is titrated with zinc standard solution until the colour changes from brownish yellow to purplish red, the volume not being recorded.

Determination, sixth step: 1 g of sodium fluoride is added, the solution is boiled for 1 min to 2 min and cooled to room temperature under running water; if it is purplish red, hydrochloric acid 1+1 may be added dropwise until the purplish red colour just disappears. The solution is then titrated again with zinc standard solution until it turns purplish red, which is the end point, and the volume is recorded.

9 Calculation and expression of results

The aluminum content of the sample, expressed as a mass fraction in %, is calculated from equation (2). The equation as printed could not be reconstructed from the digitised text and is therefore not reproduced; its symbols are T, titre of the zinc standard solution for aluminum, in mg/mL; V3, volume of zinc standard solution consumed by the EDTA released during the determination, in mL; V2, volume of zinc standard solution consumed by the blank run with the sample, in mL; m1, mass of the test portion, in g; K, aliquot ratio of the test solution, equal to 0.25.

If the absolute value of the difference between two independent analytical results on the same sample is not greater than the repeatability limit r, the arithmetic mean is taken as the analytical result. If that absolute difference is greater than the repeatability limit r, further determinations are made and the result is established as specified in Annex A. Rounding is carried out in accordance with GB/T 8170 and the result is retained to two decimal places.

10 Precision

The precision trial was carried out by 5 laboratories on 10 different levels of aluminum content, each laboratory testing each level three times independently; the precision established by the statistical methods of GB/T 6379.1 and GB/T 6379.2 is given in Table 1, and the raw data of the trial in Annex B.

Table 1 has three columns, the determination range as a mass fraction in %, the repeatability limit r in % and the reproducibility R in %, and a single row covering the range 1.00 % to 9.00 %; in that row the repeatability limit is given as r = 0.0083m + 0.0957 and the reproducibility as R = 0.1199 + 0.0114m, where m is the content of the element determined, as a mass fraction in %.

Under repeatability conditions, the absolute difference between two independent test results is not greater than the repeatability limit r, and the cases in which it is greater than r do not exceed 5 %. Under reproducibility conditions, the absolute difference between two independent test results is not greater than the reproducibility R, and the cases in which it is greater than the reproducibility limit R do not exceed 5 %.

11 Test report

The test report includes the name and address of the laboratory; the date of issue of the test report; the number of this document; the details needed to identify the test sample; the analytical results; the number of the result; and any abnormal phenomena observed during the determination, together with any operation not specified in this document that may have affected the results obtained on the sample or on the certified reference material.

A Annex A (normative) Flow chart of the acceptance procedure for sample analysis results

The flow chart of the acceptance procedure for sample analysis results is given as Figure A.1, with a note stating that r is the repeatability limit. The content of the flow chart itself is graphical and is not reproduced in this description.

B Annex B (informative) Raw data of the precision trial

Table B.1 records the raw data of the precision trial for aluminum: the individual results reported by the five laboratories, three per laboratory, for the ten aluminum content levels. In the digitised text the laboratory numbers run into the first value of each block and rows and columns cannot be matched reliably, so the individual values are not reproduced here.

C Relationship to previous standards

The document replaces GB/T 3654.10-1983, Methods for chemical analysis of ferroniobium—Determination of aluminum content by EDTA volumetric method. Besides structural and editorial changes, the foreword lists the following technical changes: the determination range was changed to 1.00 % to 9.00 %; ammonium hydroxide was changed to ammonia solution; instruments and equipment were added as a clause; sampling and sample preparation were added as a clause; the test portion mass was changed; the number of determinations was added; the expression of analytical results was added; the repeatability limit and the reproducibility limit replaced the permissible difference; and the content of the test report was added.

The document was first published in 1983 and this is the first revision. It is Part 10 of GB/T 3654, a series of analytical methods for ferroniobium planned in 9 parts, of which the foreword and the introduction list Parts 1 to 6 and Parts 8 to 10.