GB/T 8151.1-2012Methods for chemical analysis of zinc concentrates -- Part 1: Determination of zinc content -- Precipitate separation-Na2EDTA titrimetric method and extractive separation -- Na2EDTA titrimetric method (English PDF)

2.1 Method summary

The testing material was dissolved by hydrochloric acid, nitric acid and sulfuric acid, and precipitated and separated coexisting elements such as iron, manganese and lead.

A masking agent is added to the filtrate to mask small amounts of interfering elements.

In the acetic acid-sodium acetate buffer solution with pH 5~6, using xylenol orange as an indicator, titrate with Na2EDTA standard titration solution. The measured result is the total content of zinc and cadmium; and the content of cadmium is deducted, which remains the content of zinc.

2.2 Reagents

Unless otherwise specified, only use reagents and distilled water or deionized water or equivalent purity water confirmed to be analytically pure in the analysis.

2.2.1 Metal zinc (wZn >= 99.99%) has no oxidation on the surface before use. Zinc is washed by hydrochloric acid (1+9) for 1 min; then rinsed by water and acetone; and dried in an oven at 50°C.

2.2.2 Ammonium chloride.

2.4.3 Blank test

Do the blank test with the testing material.

2.4.4 Determination

2.4.4.1 Place the testing material (2.4.1) in a 400mL beaker; add a small amount of water for wetting (if the sample contains a high content of silica, 1g of ammonium fluoride shall be added); add 10mL of hydrochloric acid (2.2.5); cover the watch glass, dissolve at a low temperature to expel the hydrogen sulfide for 5min ~ 10min. Add 5mL of nitric acid (2.2.6) to complete decomposition of the testing material; take off the watch glass.

2.4.4.2 When the lead content is less than 4%, add 5 mL of sulfuric acid (2.2.12); and continue to heat until it is wet and salty [if the testing material contains high content of carbon, it may be taken off when it is steamed to emit white smoke and left to cool.

Add 1mL~2mL of perchloric acid (2.2.8) and continue heating until it is wet and salty], take off and let cool. Add 20mL of sulfuric acid (2.2.13); cover the watch glass; heat to dissolve the salt; cool slightly; rinse the watch glass and the wall of the beaker with water; and dilute the volume to about 60 mL [if the iron content in the solution is low, add iron sulfate stock solution (2.2.21) makes the solution contain about 20mg of iron].

2.4.4.3 When the lead content is greater than 4%, add 5mL of sulfuric acid (2.2.7) to heat it up to thick white smoke appears; and steam to a volume of about 2mL; take off it, and cool. Rinse the watch glass and the wall of the beaker with water; and dilute the volume to about 50mL; heat it to boil for 10min; cool to room temperature; and stand for 1h. Filter with slow quantitative filter paper; take the filtrate with a beaker; wash the beaker and precipitate for 5 times by sulfuric acid (2.2.14), respectively; wash the beaker and precipitate for 1 time by water, respectively; retain the filtrate.

2.4.4.4 Add 3g~5g of ammonium chloride (2.2.2) and 5mL of ammonium persulfate

solution (2.2.17) to 2.4.4.2 or 2.4.4.3; neutralize with ammonia water (2.2.9) until precipitation is complete, and then excess 10mL. Heat to boil slightly for 1min~2min;

filter with fast qualitative filter paper while it is hot; wash the beaker and the precipitate with hot washing liquid for 2 ~ 3 times, respectively; and retain the filtrate.

2.4.4.5 Wash the precipitate by hot washing solution into the beaker of the original precipitate; add hydrochloric acid (2.2.11) to dissolve the precipitate; add 5 mL of ammonium persulfate solution (2.2.17); and neutralize it with ammonia (2.2.9) till the precipitate is complete; and then excess 10 mL. Heat to boil slightly for 1min~2min;

take off; filter through the original filter paper in the beaker of the retentate; wash the beaker and the precipitate with hot washing liquid for 3 ~ 4 times, respectively.

2.4.4.6 Boil the filtrate (2.4.4.5) and concentrate to a volume of about 100mL; and completely destroy the excessive ammonium persulfate; take off it and let it cool.

use iodide ion to mask cadmium; and titrate zinc with Na2EDTA solution at pH 5.5.

3.2 Reagents

During the analysis, use the analytical reagents and Class-II water specified in GB/T

6682.

3.2.1 Metal zinc (wZn>=99.99%) has no oxidation on the surface before use. Zinc is cleaned by hydrochloric acid (3.2.2) (1+9) for 1 min; then rinsed by water and acetone;

and dried in an oven at 50°C.

3.2.2 Hydrochloric acid (rho201.16g/mL~1.19g/mL).

3.2.3 Liquid bromine.

3.2.4 Nitric acid (rho201.42g/mL).

3.2.5 Hydrofluoric acid (rho201.13g/mL~1.15g/mL).

3.2.6 Hydrochloric acid (1+4).

3.2.7 Sulfuric acid (1+1).

3.2.8 Ammonia (rho200.89g/mL).

3.2.9 Methyl isobutyl ketone (4-methyl-2-pentanone).

3.2.10 Anhydrous ethanol.

3.2.11 Masking agent: dissolve 60g of thiourea, 100g of diammonium hydrogen citrate,

200g of ammonium thiocyanate in water and dilute to 1L; and filter if necessary.

3.2.12 Sodium fluoride solution (20g/L).

3.2.13 Thiourea solution (100g/L).

3.2.14 Potassium iodide solution (1000g/L), prepared on the same day.

3.2.15 Buffer solution: dissolve 250g of hexamethylenetetramine (methenamine) in

water; add 60mL of acetic acid (rho201.05g/mL); and then dilute to 1L.

3.2.16 Iron stock solution (45g/L): dissolve 45g of iron nitrate [Fe(NO3)3·9H2O] in water

and dilute to 1L.

3.2.17 Xylenol orange: evenly mix 1g of xylenol orange and 99g of potassium nitrate crystals, and grind it in a ceramic vessel with a pestle. When the color is consistent, it is considered that the mixture is uniform.

3.2.18 Disodium ethylenediaminetetraacetic acid (Na2EDTA) standard titration solution

Take 2.50g of specimen, accurate to 0.0001g.

3.4.2 The number of determinations

Perform 2 determinations independently and take the average value.

3.4.3 Blank test

Do a blank test with the testing material (add 5mL of iron stock solution to help turbidity analysis).

3.4.4 Determination

3.4.4.1 Put the testing material (3.4.1) into a 300mL conical beaker; moisten it with

20mL of water. Add 2mL~3mL of liquid bromine (3.2.3); react at room temperature for

15min and shake occasionally. Add 15mL nitric acid (3.2.4); stand for 15min; put the conical flask on the electric stove to heat; boil to expel the bromine vapor; add 100mL of water after cooling; heat to boil, and cool.

3.4.4.2 If the testing material is completely dissolved, transfer the test solution into a

500mL volumetric flask and dilute to the mark with water; otherwise, filter the solution into a 500mL volumetric flask by medium-speed filter paper; wash the insoluble residue on the filter paper by water; and put the filtered insoluble residue and filter paper in a

25mL platinum crucible; put into a muffle furnace at 800°C for ashing; add 2mL of sulfuric acid (3.2.7), 2mL of nitric acid (3.2.4) and 2mL of hydrofluoric acid (3.2.5); and evaporate the solution to nearly dry and cool. Add a small amount of water to dissolve the soluble salt; filter the solution by medium-speed filter paper; combine the filtrate and the cleaning solution into the same volumetric flask mentioned above; and dilute to the mark with water.

If the testing material contains lead, the platinum crucible may be damaged. In this case, the insoluble residue should be treated as follows:

Rinse the insoluble residue into a large polytetrafluoroethylene beaker with thin running water. Then put the filter paper in a ceramic crucible; put it in a muffle furnace at 600°C ~ 700°C for ashing; and cool the crucible to room temperature.

Use a small amount of water to clean the material in the crucible to the large beaker of polytetrafluoroethylene used above; and then add 2mL of sulfuric acid (3.2.7), 2mL of nitric acid (3.2.4), and 2mL of hydrofluoric acid (3.2.5); then evaporate the solution to near dryness; take off it and cool. Add a small amount of water to dissolve the soluble salt; filter the solution with medium-speed filter paper; combine the filtrate and the cleaning solution into the same volumetric flask mentioned above; and dilute to the mark with water.

If it is determined that the filter paper does not contain zinc, the ashing process can be omitted.

Appendix A (Informative)

Influence of Potential Interference Elements

A.1 Cadmium

While extracting zinc, cadmium is extracted in large quantities. Before the final titration, cadmium must be masked with potassium iodide.

A.2 Cobalt

When the organic phase turns blue, it indicates that most of the cobalt in the specimen is extracted along with the zinc. If the cobalt content is no more than 0.05%, its influence may be ignored. Otherwise, it shall be determined by atomic absorption spectrometry after EDTA titration; and then subtract the content of cobalt from the zinc value obtained from the analysis.

A.3 Lead

When the lead content is greater than 7%, there shall be interference. In the dissolution stage, it shall precipitate in the form of lead sulfate, which may be separated by filtration.

A.4 Manganese

When the manganese content is greater than 2%, there shall be interference, which reduces the analysis result. However, zinc concentrates in international trade rarely have this content of manganese.

A.5 Magnesium

When the magnesium content is greater than 5%, there shall be interference, which reduces the analysis results. However, the maximum magnesium content of zinc concentrate reported in international trade is 0.8%.

A.6 Titanium and vanadium

When the titanium and vanadium content is greater than 0.2%, there shall be interference. However, there is no such content in zinc concentrates in international trade.

A.7 Other elements

Other elements no more than the following content do not interfere with Method-2:

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