GB/T 6730.28-2021Iron ores—Determination of fluorine content—Ion-selective electrode method (English PDF)

1 Scope

This document specifies a method for the determination of fluorine content using ion-selective electrode method.

This document applies to the determination of fluorine content in natural iron ores, iron concentrates, and lump ores, including sintered products. The determination range (mass fraction): 0.005 % ~ 1.00 %.

2 Normative references

The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

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 6730.1 Iron ores - Preparation of predried test samples for chemical analysis

GB/T 8170 Rules of rounding off for numerical values & expression and judgement of limiting values

GB/T 10322.1 Iron ores - Sampling and sample preparation procedures

GB/T 12806 Laboratory glassware - One-mark volumetric flasks

GB/T 12807 Laboratory glassware - Graduated pipettes

GB/T 12808 Laboratory glassware - One-mark pipettes

3 Terms and definitions

There are no terms or definitions to be defined in this document.

4 Principle

The sample is melted with sodium hydroxide and dissolved in water and hydrochloric acid. After dry filtration, in the presence of sodium citrate buffer solution, adjust the pH value of the test solution to 5.0 ± 0.1, and directly conduct potentiometric determination with a fluoride ion-selective electrode.

5 Reagents and materials

Unless otherwise stated, only approved analytical reagents and secondary water complying with GB/T 6682 or water equivalent to its purity shall be used in the analysis.

5.1 Sodium hydroxide, granular, dry.

5.2 Sodium hydroxide solution, 300 g/L.

DISSOLVE 75 g of sodium hydroxide in 250 mL of water.

5.3 Sodium hydroxide solution, 20 g/L.

DISSOLVE 5 g of sodium hydroxide in 250 mL of water.

5.4 Hydrochloric acid, rho ~ 1.19 g/mL.

5.5 Hydrochloric acid, 1 + 2.

5.6 Hydrochloric acid, 1 + 9.

5.7 Sodium citrate buffer solution, c(Na3C6H5O7 · 2H2O) = 1 mol/L.

In a 1 L beaker, WEIGH 294.1 g of sodium citrate and DISSOLVE it in 800 mL of water, USE hydrochloric acid (see 5.5) to adjust the pH to 5.0 ± 0.1. TRANSFER to a 1 L volumetric flask, DILUTE with water to the mark, and MIX well.

5.8 Fluorine standard solution A, stored in plastic bottles.

DRY an appropriate amount of sodium fluoride (purity greater than 99.7 %) at 105 °C.

WEIGH 1.108 g of dried sodium fluoride, DISSOLVE it in water, TRANSFER it to a 1 L volumetric flask, DILUTE it with water to the mark, and MIX well. 1 mL of this solution contains 500 µg of fluorine.

5.9 Fluorine standard solution B, stored in plastic bottles.

USE a pipette to transfer 100.00 mL of fluorine standard solution A (see 5.8), PUT it into a 500 mL volumetric flask, DILUTE it with water to the mark, and MIX well. 1 mL of this solution contains 100 µg of fluorine.

5.10 Fluorine standard solution C, stored in plastic bottles.

USE a pipette to transfer 50.00 mL of fluorine standard solution B (see 5.9), PUT it into a 500 mL volumetric flask, DILUTE it with water to the mark, and MIX well. This solution shall be prepared fresh before use. 1 mL of this solution contains 10 µg of fluorine.

5.11 Fluorine standard solution D, stored in plastic bottles.

USE a pipette to transfer 50.00 mL of fluorine standard solution C (see 5.10), PUT it into a 500 mL volumetric flask, DILUTE it with water to the mark, and MIX well. This solution shall be prepared fresh before use. 1 mL of this solution contains 1 µg of fluorine.

6 Instruments and equipment

Unless otherwise stated during analysis, use ordinary experimental instruments. One-mark volumetric flasks, graduated pipettes, and one-mark pipettes shall comply with the requirements of GB/T 12806, GB/T 12807, and GB/T 12808, respectively.

6.1 Balance: the scale value is 0.1 mg.

6.2 Ion meter (or pH meter): the scale value is 0.1 mV.

6.3 Magnetic stirrer: with a 2.5 cm × 0.4cm stirring rod covered with polyethylene.

6.4 Fluoride ion-selective electrode.

6.5 Calomel reference electrode.

6.6 pH glass electrode.

6.7 Silver crucible or nickel crucible: the generally used capacity is 25 mL ~ 30 mL, but 100 mL can also be used.

6.8 Muffle furnace: temperature control of 650 °C ~ 700 °C.

6.9 Plastic beaker: 100 mL and 200 mL.

8 Analysis steps

9 Result calculation and representation

10 Test report

The test report shall include the following information:

a) laboratory name and address; […]