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IS 1917-3 (1992): Chemical analysis of quartzite and highsilica sand, Part 3: Determination of silica [MTD 13: Oresand Raw Materials]

IS 1917 ( Part 3 ) : 1992

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Indian Standard

CHEMICAL ANALYSIS OF QUARTZITE AND HIGH SILICA SAND

PART 3 DETERMINATION OF SILICA

( First Revision )

UDC 553.57 : 553 [ 546.28 ]

@ BIS 1992

BUREAU OF INDIAN STANDARDS MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG

NEW DELHI 110002

March 1992 Price Group 1

Methods of Chemical Analysis of Ores, Minerals and Allied Materials for Metallurgical Industry Sectional Committee, MTD 29

FOREWORD

This Indian Standard ( Part 3 ) ( First Revision ) was adopted by the Bureau of Indian Standards, after the draft finalized by the Methods of Chemical Analysis of Ores, Minerals and Allied Materials for Metallurgical Industry Sectional Committee had been approved by the Metallur- gical Engineering Division Council.

IS 1917 : 1962 <Methods of chemical analysis of quartzite and high silica sand’ covers the methods for the determination of silica and other constituents of quartzite and high silica sand. The committee decided to revise this standard into different parts and covering determination of each element in a separate part, which on publication would supersede the determination of that element given in IS 1917 : 1962. The determination of loss on ignition, silica, sodium, potassium, aluminium, iron, calcium, magnesium and titanium oxide in quartzite and high silica sand have been covered in this series.

This part covers the determination of silica. The other parts in this series are:

Part 1 Determination of loss on ignition Part 2 Determination of sodium and potassium Part 4 Determination of aluminium Part 5 Determination of iron Part 6 Determination of calcium and magnesium

Part 7 Determination of titania

In this revision the determination of total silica by gravimetric method has been replaced by determination of major silica by gravimetric method and residual silica by photometric method.

In reporting the result of a test or analysis made in accordance with this standard, if the final value, observed or calculated, is to be rounded off, it shall be done in accordance with IS 2 : 1960 ‘Rules for rounding off numerical values ( revised)‘.

Indian Standard

CHEMICAL ANALYSIS OF AND HIGH SILICA

PAfiT 3 DETERMINATION OF

Is I917 (Pqrt 3. ), : 1992

QUARTZITE SAND SILICA

( First Revision )

1 SCOPE

: Ti%is standard ( Part 3 ) covers the methods for determination of silica in the range above

.90 percent in quartzite and high silica sand.

2 REFERENCES

The following Indian Standards are necessary adjuncts to this

IS No.

1070 : 1977

1811 : 1984

2245 : 1962

3 SAMPLING

3.1 The sample

standard.

Title

Water for general laboratory use ( second revision )

Methods of sampling foundry sand ( jirst revision ) Methods of sampling quartzite

shall be drawn and prepared after quartering in accordance with IS 2245 : 1962 or IS 1811 : 1984, as the case may be.

3.2 Grind 3 to 5 g of the sample so that it passes through IS Test Sieve No. 15 ( 149 microns ). Dry the sample in a weighing bottle at 105” to 110°C for 2 h. Keep the weighing bottle stoppered in a desiccator and cool to room temperature. The sample is ready for chemical analysis.

4 QUALITY OF REAGENTS

Unless specified otherwise, analytical grade reagents and distilled water ( see IS 1070 : 1977 ) shall be employed for the test.

5 DETERMINATION OF MAJOR SILICA RY GRAVIMETRIC METHOD

5.1 Outline of the Method

The sample is fused with fusion mixture and the fused mass extracted with hydrochloric

1

acid. The silica is rendered insoluble through dehydration and baking. The maior sX:a thus obtained by filtration, is h3drofluorlsed and determined by d;&rence. The residual silica is determined yhoto:netri~:aily and added to the major silica to get ‘total silica.

5.2 Reagents

5.2.1 Fusion Mixture

Mix 6 g of sodium carbonate with 4 g of potassium carbonate.

5.2.2 Dilute Sulphuric Acid, 1 : 1 ( v/v )

5.2.3 Potassium Bisulphate, solid

5.2.4 Dilute Hydrochlo7z Acid, 1 : 2 ( v/v )

5.2.5 Hydrojuoric Acid, 48 percent

5.3 Procedure

5.3.1 Weigh accurately O-5 g of the finely ground test sample in a platinum crucible. Add 3 to 4 g of anhydrous fusion mixture and mix thoroughly with a platinum rod. Heat the crucible gently at first and finally at 950” to 1000°C for at least half an hour with occasional swriling of the melt with platinum tipped tongs to get a clear melt. Cool and observe that a transparent mass is obtained. Place the crucible and the lid into a platinum dish containing 75 to 100 ml of dilute hydrochloric acid ( 1 : 2 ) and 2 drops of dilute sulphuric acid ( 1 : 1 ). Cover the dish with the watch glass. When the reaction ceases, wash the crucible and the lid thoroughly with water. Evaporate the solution over a steam bath until the smell of hydrochloric acid is no longer detected. Finally cover the dish with the watch glass and bake the mass for an hour in an air oven at 105” to 110°C. Cool and digest the contents of platinum dish with about 50 ml of dilute hydrochloric acid ( 1 : 2 ). Filter through fine textured filter paper. Transfer quantitatively all the residue by hot water to the filter paper. Wash the residue five times

IS 1917 ( Part 3 ) : 1992

with hot dilute hydrochloric acid ( 1 ; 20 ) and then with hot water until free from chloride. Preserve the filtrate and washings ( Main filtrate A ) in a 500 ml beaker for the subsequent determination of residual silica by the photometric method.

5.3.2 Ignite the paper with the residue in a weighed platinum crucible raising the temper- ature gradually and finally at 950” to 1000°C for 30 minutes. Cool in a desiccator and weigh. Moisten the residue with a few ml of water, add 1 drop of dilute sulphuric acid and 10 ml of hydrofluoric acid. Keep the crucible covered at room temperature for 10 minutes. Then remove the lid and place the crucible on a sandbath for evaporation and continue up to copious fuming. Cool the crucible, add further 5 ml of hydrofluoric acid and repeat the process. Lastly, drive out all the acid to obtain a dry residue. Finally, ignite the residue at 1000°C for 30 minutes. Repeat heating, cooling and weighing until constant mass is obtained.

.5.4 Calculation -B

Major silica, percent by mass=‘7 X 100

where

A = mass in g, of impure silica, B = mass in g, of residue after hydrofluori-

sation, and

C = mass in g, of the sample taken.

6 DETERMINATION OF RESIDUAL SILICA BY PHOTOMETRIC METHOD

6.1 Outline of the Method

Soluble silica is converted into heteropolysili- comolybdate by the addition of ammonmm molybdate. The complex is reduced to molyb- denum blue and measured at 810 nm.

6.2 Reagents

6.2.1 Ammonium Molybdate Solution

Dissolve 10 g ammonium molybdate, in 100 ml of water, filter, if necessary.

6.2.2 Standard Silica Solution

6.2.2.1 Fuse 0.2 g of powdered ( 200 mesh ) and dried ( 105” to 110 C ) pure silica with 5 g of fusion mixture in a .platinum crucible. Cool and dissolve the melt in 300 ml of water containing polythene water bath flask-.

2 g of sodium hydroxide in a beaker. Warm the solution on a and dilute to 500 ml in a volumetric

6.2.2.2 Prepare a standard working solution containing O-04 mg/mI of silica solution immediateIy before use by diluting the above solution. Store in a high density poIythene bottle.

6.2.3 Ascorbic Acid Solufion, 10 percent ( mfv ).

Store in an amber bottle ( stable up to 5 days ).

6.2.4 Oxalic Acid Solution, 10 percent ( m/v ).

6.2.5 EDTA Solution ( @OS M )

Dissolve 18.6 g of disodium saIt of EDTA in water and dilute to 1 btre.

6.3 Procedure

6.3.1 Fuse the residue as obtained under 5.3.2 with 1 g of potassium bisulphate. Dissolve the melt in water containing few drops of hydro- chloric acid. Add the solution to the main filtrate obtained as under 5.3.1. Cool and dilute to 500 ml in a volumetric flask. Take an aliquot of 10 ml into a 100 ml volumetric flask. Add 5 ml of EDTA solution, a drop of phenolphthalein solution and then ammonia solution dropwise until the colour changes to red. Add 10 ml of ammonium molybdate solution and allow to stand f;,r 10 minutes. Now add 5 ml of oxalic acid followed by 5 ml of ascorbic acid and dilute to 100 ml. Allow the soIution to stand for half an hour for development of full colour. Measure the absorbance at 810 nm in 10 mm cell against a test blank soIution prepared in the same way, but without the sample. Compute the silica content from the calibration curve.

6.4 Calibration

6.4.1 Establish a calibration curve by taking 0, 1, 2, 3, 4 and 5 ml of standard silica solution in 100 ml calibrated flasks. Carry out the entire stage of procedure as given in 6.3 without the main solution. Measure the absorbance of the above aliquots against the reagents blank. Draw a calibration curve by plotting absor- bance against amount of silica in mg. Compare and convert the absorbance of the test solution to the amount of silica with the help of the calibration curve.

6.5 Calculation

Residual silica, =fiZ, x 100 percent by mass M

where A~1 - mass in mg, of the residual sibca pre-

sent in 10 ml aliquot of the main filtrate A ( 5.3.1 ), and

M = mass in mg, of the sample represented by the aliquot.

2

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