Methods for chemical analysis of nickel matte - Determination of sulfur content - Combustion-neutralization titrimetric method
1 Scope
This part specifies the methods for determining the sulfur content in nickel matte.
This part is applicable to the determination of sulfur content in nickel matte, with a determination range of 15%–25%.
2 Principle
The test portion is combusted in a stream of air at 1,250 °C–1,300 °C using copper wire as the flux to transform sulfur into sulfur dioxide, which is absorbed by hydrogen peroxide and oxidized to sulphuric acid. The solution is titrated with a standard titration solution of sodium hydroxide using methyl red- hypo-methyl blue solution as a mixed indicator until the solution changes from purplish red to bright green.
3 Reagents
3.1 Copper wire (the mass fraction of copper ≥ 99.95%, with a diameter of 0.25 mm–0.5 mm).
3.2 Acid absorption solution (potassium dichromate-sulphuric acid solution): Dissolve 5 g of potassium dichromate with a small amount of water by heating, cool it and add 100 mL of sulphuric acid.
3.3 Desiccant: Anhydrous calcium chloride.
3.4 Alkali absorption solution: Sodium hydroxide (50 g/L).
3.5 Phenolphthalein indicator (10 g/L), ethanol solution.
3.6 Methyl red-methylene blue solution mixed indicator: Weigh 0.3 g of methyl red and 0.25 g of methylene blue and dissolve them in 500 mL of absolute ethanol.
3.7 Hydrogen peroxide absorbent solution (prepared immediately before use): Take 50 mL of hydrogen peroxide, dilute it to 1 L with water, add 10 mL of the mixed indicator (3.6) and titrate to bright green with sodium hydroxide solution (3.8).
3.8 Sodium hydroxide standard volumetric solution: [c(NaOH) ≈ 0.065 mol/L]:
3.8.1 Preparation: Prepare a saturated sodium hydroxide solution and leave it in a plastic bottle until the solution is clear. Take 32 mL of supernate, dilute it to 10 L with water free of carbon dioxide and shake well.
3.8.2 Calibration: Weigh four portions of 0.300 g (to the nearest of 0.000 1 g) of potassium hydrogen phthalate (standard reagent) pre-dried at 100 °C–105 °C for 2 h, place them in 300-mL conical flasks, dissolve them with 60 mL of hot water free of carbon dioxide, cool and add 2 drops of phenolphthalein indicator (3.5) and titrate them with sodium hydroxide standard volumetric solution until light red.
Carry out blank test along with the calibration.
The titration coefficient of the sodium hydroxide standard volumetric solution to sulfur shall be calculated using Formula (1):
(1)
where,
FS——the titration coefficient, the mass of sulfur equivalent to 1.00 mL of sodium hydroxide standard volumetric solution, mg/mL;
m1——the mass of potassium hydrogen phthalate, g;
V1——the volume of sodium hydroxide standard volumetric solution consumed during titrating the potassium hydrogen phthalate solution, mL;
V0——the volume of sodium hydroxide standard volumetric solution consumed during titrating the blank test solution, mL;
204.2——the molar mass of potassium hydrogen phthalate [M(C8H5KO4)], g/mol
16.03——the molar mass of sulfur [M(1/2S)], g/mol.
The average of four test results is taken as the result. The range of the four calibration results shall not be greater than 0.006 0 mg/mL, otherwise, measure again.
4 Apparatus
Foreword i
1 Scope
2 Principle
3 Reagents
4 Apparatus
5 Analytical procedures
6 Calculation and expression of analysis results
7 Precision
8 Quality assurance and control
