Methods for chemical analysis of nickel matte - Determination of copper content - Sodium thiosulphate titrimetric method
1 Scope
This standard specifies a method for determining the copper content in nickel matte.
This standard is applicable to the determination of copper content in nickel matte, with a determination range of 6%–55%.
2 Principle
The test portion is decomposed by hydrochloric acid and nitric acid-potassium chlorate saturated solution, in which the iron is masked by ammonium bifluoride, with the pH of the solution controlled within the range of 3.5–4. Potassium iodide is added to react with copper to produce cuprous iodide precipitate, with equal amount of iodine separated out. The copper content is indirectly determined by sodium thiosulphate standard volumetric solution by using starch solution as indicator.
3 Reagents
3.1 Ammonium bifluoride.
3.2 Potassium iodide.
3.3 Aqueous ammonia (ρ 0.90 g/mL).
3.4 Hydrochloric acid (ρ 1.19 g/mL).
3.5 Nitric acid (ρ 1.42 g/mL).
3.6 Nitric acid (1+1).
3.7 Sulphuric acid (1+1).
3.8 Urea saturated solution.
3.9 Potassium thiocyanate solution (100 g/L).
3.10 Nitric acid-potassium chlorate saturated solution: Dissolve potassium chlorate in nitric acid (3.5) until saturation.
3.11 Starch solution (5 g/L).
3.12 Copper standard solution: Accurately weigh 1.000 0 g of metallic copper (mass fraction of copper ≥ 99.95%), put it in a 400-mL beaker, add 20 mL of nitric acid (3.6) to dissolve it at low temperature, then evaporate the solution to viscous shape, and leave it to cool. Add 5 mL of sulphuric acid (3.7), heat the mixture until a large amount of white smoke appears and leave the solution to cool slightly. The add water and boil the solution to dissolve the salts, and leave it to cool to room temperature. Transfer the solution to a 1,000-mL volumetric flask and dilute it to the scale with water. The copper content of the solution is 1.0 mg/mL.
3.13 Sodium thiosulphate standard volumetric solution [c(Na2S2O3) ≈ 0.01 mol/L]
3.13.1 Preparation: Weigh 2.5 g of sodium thiosulphate (Na2S2O3·5H2O) and dissolve it in newly boiled water cooled to room temperature. Add 0.1 g of anhydrous sodium carbonate, dissolve it in the solution and transfer the solution into a 1,000-mL brown bottle, then dilute it to the scale with water. Calibrate the solution after leaving it for one week.
3.13.2 Calibration: Pipette 25.00 mL of copper standard solution (3.12) and put it into a 300-mL conical beaker, add aqueous ammonia (3.3) dropwise until the solution turns dark blue, and then follow the procedure in 4.3.3 below.
Calculate the titrimetric factor of sodium thiosulphate standard titration solution for copper using Formula (1):
(1)
where,
FCu——the titrimetric factor, i.e. the mass of copper corresponding to per unit volume of sodium thiosulphate standard volumetric solution, mg/mL;
ρ——the mass concentration of copper standard solution, mg/mL.
V1——the volume of copper standard solution pipetted, mL;
V2—— the volume of sodium thiosulphate standard volumetric solution consumed for titration of copper standard solution, mL.
Foreword i
1 Scope
2 Principle
3 Reagents
4 Analytical procedures
5 Calculation of analytical result
6 Precision
7 Quality assurance and control
