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| Standard ID | GB/T 7143-2025 (GB/T7143-2025) | | Description (Translated English) | Methods for chemical analysis of silica sand for foundry | | Sector / Industry | National Standard (Recommended) | | Classification of Chinese Standard | J31 | | Classification of International Standard | 25.120.20 | | Word Count Estimation | 26,286 | | Date of Issue | 2025-02-28 | | Date of Implementation | 2025-09-01 | | Issuing agency(ies) | State Administration for Market Regulation, National Standardization Administration |
GB/T 7143-2025.Chemical analysis methods for silica sand for foundry
GB/T 7143-2025 English version. Methods for chemical analysis of silica sand for foundry
ICS 25.120.20
CCSJ31
National Standard of the People's Republic of China
Replace GB/T 7143-2010
Chemical analysis method of silica sand for foundry
Released on 2025-02-28
2025-09-01 Implementation
State Administration for Market Regulation
The National Standardization Administration issued
Table of Contents
Preface III
1 Range 1
2 Normative references 1
3 Terms and Definitions 1
4 Sample preparation 1
5 Test methods 1
Table 1 Permissible error of aluminum oxide content determined by EDTA complexometric titration
Table 2 Amount of sample removed for determination of alumina content 8
Table 3 Permissible error of the determination of aluminum oxide content by chrome azuro blue S photometry 8
Table 4 Permissible error of sulfosalicylic acid spectrophotometric determination of iron oxide content 10
Table 5 Amount of sample removed for determination of iron oxide content 10
Table 6 Permissible error of iron oxide content determined by o-phenanthroline photometric method 11
Table 7 Amount of sample removed for determination of titanium oxide content 12
Table 8 Permissible error in determination of titanium oxide content by diantipyryl methane photometry 12
Table 9 Permissible error of calcium oxide content determined by EDTA complexometric titration 14
Table 10 Allowable error of magnesium oxide content determined by EDTA complexometric titration 16
Table 11 Preparation of sodium chloride and potassium chloride mixed standard solution series 16
Table 12 Testing conditions for sodium oxide and potassium oxide content 17
Table 13 Permissible deviation of potassium oxide and sodium oxide content determined by flame photometry 17
Table 14 Preparation of mixed standard series solution 18
Table 15 Measurement wavelength of each element 19
Table 16 Permissible deviation of chemical composition of silica sand determined by fluorescence spectroscopy 21
Preface
This document is in accordance with the provisions of GB/T 1.1-2020 "Guidelines for standardization work Part 1.Structure and drafting rules for standardization documents"
Drafting.
This document replaces GB/T 7143-2010 "Chemical analysis methods for silica sand for foundry". Compared with GB/T 7143-2010, except for the structural adjustment
In addition to the integration and editorial changes, the main technical changes are as follows.
a) The scope of application of the standard has been changed (see Chapter 1, Chapter 1 of the.2010 edition);
b) The requirements for sample preparation have been changed (see 4.2, 3.2 and 3.3 of the.2010 edition);
c) The analytical procedure for determining the silicon dioxide content by the hydrochloric acid primary dehydration mass-molybdenum blue spectrophotometric method has been changed (see 5.2.1.4,
4.1.2.4 of the.2010 edition);
d) The test method overview has been changed (see 5.1.2, Chapter 4 of the.2010 edition);
e) The indicator for calcium oxide determination has been changed (see 5.4.2.1, 4.3.1.1 of the.2010 edition);
f) The calcium oxide determination procedure has been changed (see 5.4.2.4, 4.3.1.4 of the.2010 edition);
g) The tolerance for the determination of magnesium oxide content by EDTA complexometric titration has been changed (see 5.4.3.6, 4.3.2.6 of the.2010 edition);
h) Added fluorescence spectrometry for the determination of silicon dioxide, aluminum oxide, iron oxide, titanium oxide, calcium oxide, magnesium oxide, potassium oxide and sodium oxide
Content (see 5.6);
i) Delete the determination of acid consumption value (see 4.5 of the.2010 edition).
Please note that some of the contents in this document may involve patents. The issuing organization of this document does not assume the responsibility for identifying patents.
This document is proposed and coordinated by the National Casting Standardization Technical Committee (SAC/TC54).
This document was drafted by. Jinan Shengquan Group Co., Ltd., China Machinery Engineering Institute Group Shenyang Foundry Research Institute Co., Ltd.,
Shandong Heavy Equipment Testing Technology Co., Ltd., Chongqing Changjiang Modeling Materials (Group) Co., Ltd., Guangxi Lanke Resources Recycling Co., Ltd.
Zhejiang Mechanical and Electrical Vocational and Technical University, Huazhong University of Science and Technology, Ludong University, Qingdao University of Technology, Shenyang University of Technology, Wuhan University of Technology,
Chengde Dongwei New Material Technology Co., Ltd., Wuxi Sanfeng Instrument Equipment Co., Ltd., Guangdong Zhuli Casting Technology Co., Ltd., Clariant
Chemical Technology (Shanghai) Co., Ltd., Meike (Guangzhou) New Materials Co., Ltd., Shandong Institute of Standardization, Shenzhen Information Vocational and Technical College,
Jinan Shengquan Casting Materials Co., Ltd., Dongfeng Forging Co., Ltd., Yantai Binglun Intelligent Machinery Technology Co., Ltd., Hubei Gucheng County Donghua Machinery
Machinery Co., Ltd., Jiangsu Xihua Casting Co., Ltd., Henan Weiye New Materials Co., Ltd., Jiangyin Tianrun Modeling Materials Technology Co., Ltd.,
Taiyuan Sangao Energy Development Co., Ltd., Jiangsu Jinyang Machinery Co., Ltd., Chiping Xinfa Aluminum Products Co., Ltd., Changsha Deka Technology Co., Ltd.
Company, Zhejiang Aoli New Materials Technology Co., Ltd., Xi'an Aerospace Engine Co., Ltd., CRRC Qishuyan Locomotive and Rolling Stock Technology Research Institute Co., Ltd.
Co., Ltd. and AECC Harbin Dongan Engine Co., Ltd.
The main drafters of this document are. Li Donghua, Gao Hui, Zhao Zhenyu, Li Yuancai, Wang Yu, Liu Jingmei, Liu Ye, He Zefen, Wang Lifeng, Liu Guomei,
Liu Chunjing, Yu Benli, Zhang Yancheng, Wang Xiaodong, Xue Jiang, Yu Ruilong, Liu Chunxia, Sun Pu, Li Dongyu, Yin Bing, Chen Xiulin, Liu Weihua, Chen Kaimin,
Wan Peng, Gao Xin, Zhang Zhifeng, Lü Chenming, Ma Tao, Cui Lanfang, Wang Xiaolei, Zhang Shiwei, Li Wenao, Liu Qinshuang, Liu Jun, Lü Jiyang, Sha Jinyang,
Zhang Chenggen.
This document was first issued in 1986, revised for the first time in.2010, and this is the second revision.
Chemical analysis method of silica sand for foundry
1 Scope
This document describes the sample preparation and test methods for the chemical composition analysis of silica sand for foundry use.
This document applies to silicon dioxide, aluminum oxide, iron oxide, titanium oxide, oxygen and other minerals in natural silica sand, selected quartz sand and artificial quartz sand for foundry use.
Determination of chemical components such as calcium oxide, magnesium oxide, potassium oxide, sodium oxide content, etc.
Note. The determination methods listed in this document should be selected according to specific circumstances.
2 Normative references
The contents of the following documents constitute essential clauses of this document through normative references in this document.
For referenced documents without a date, only the version corresponding to that date applies to this document; for referenced documents without a date, the latest version (including all amendments) applies to
This document.
GB/T 601 Preparation of standard titration solutions for chemical reagents
GB/T 603 Preparation of preparations and products used in chemical reagent test methods
GB/T 2684 Test methods for foundry sand and mixtures
GB/T 5611 Casting Terminology
GB/T 6682 Specifications and test methods for water used in analytical laboratories
GB/T 8170 Rules for rounding off values and expression and determination of limit values
GB/T 21114-2019 X-ray fluorescence spectrochemical analysis of refractory materials - Fused glass disc method
3 Terms and definitions
The terms and definitions defined in GB/T 5611 apply to this document.
4.Sample preparation
4.1 The sample should be representative and uniform, without any foreign impurities.
4.2 The test sample is divided into four parts (if the particle size is too large, it should be crushed to less than 0.8 mm and magnets should be used to remove the particles that may be introduced during the crushing process).
After the iron is added, it is further reduced), and finally about 20g of sample is obtained, which is ground until all of it passes through a 75μm sieve (i.e., No..200 sieve).
Weigh the bottle, dry it at 105℃~110℃ for 2h, then put it in a desiccator and cool it for later use.
5 Test methods
5.1 Overview
5.1.1 Unless otherwise specified, the standard solutions, preparations and products used in the analysis shall be prepared in accordance with the provisions of GB/T 601 and GB/T 603.
Use analytically pure reagents and grade 3 water in accordance with GB/T 6682.
All are factory original concentrations.
5.1.2 All test methods shall be measured twice in parallel, and the average value shall be taken as the final test result; the test result shall be determined according to GB/T 8170.
......
GB/T 7143-2010
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 71.040.99
J 31
Replacing GB/T 7143-1986
Methods for chemical analysis of silica sand for foundry
ISSUED ON: SEPTEMBER 26, 2010
IMPLEMENTED ON: FEBRUARY 01, 2011
Issued by: General Administration of Quality Supervision, Inspection and
Quarantine of PRC;
National Standardization Administration.
Table of Contents
Foreword ... 3
1 Scope ... 4
2 Normative references ... 4
3 Preparation of specimens ... 4
4 Test method ... 5
4.1 Determination of silicon dioxide content ... 5
4.2 Determination of aluminum oxide, iron oxide, titanium oxide content ... 10
4.3 Determination of calcium oxide, magnesium oxide, potassium oxide, sodium oxide
content ... 21
4.4 Determination of iron oxide, calcium oxide, magnesium oxide, potassium oxide,
sodium oxide content by atomic absorption spectrophotometry ... 28
4.5 Determination of acid consumption value ... 31
Methods for chemical analysis of silica sand for foundry
1 Scope
This standard specifies the preparation and test methods of chemical analysis specimens
of silica sand for foundry.
This standard applies to the analysis of silicon dioxide, aluminum oxide, iron oxide,
titanium oxide, calcium oxide, magnesium oxide, potassium oxide, sodium oxide
content, acid consumption value of natural silica sand, selected quartz sand, artificial
quartz sand for foundry.
The parallel determination methods in this standard can be selected according to
specific circumstances.
2 Normative references
The provisions in following documents become the provisions of this Standard through
reference in this Standard. For the dated references, the subsequent amendments
(excluding corrections) or revisions do not apply to this Standard; however, parties who
reach an agreement based on this Standard are encouraged to study if the latest versions
of these documents are applicable. For undated references, the latest edition of the
referenced document applies.
GB/T 601 Chemical reagent - Preparations of reference titration solutions
GB/T 603 Chemical reagent - Preparations of reagent solutions for use in test
methods
GB/T 2684 Test methods for foundry sands and molding mixtures
GB/T 6682 Water for analytical laboratory use - Specification and test methods
GB/T 8170 Rules of rounding off for numerical values and expression and
judgement of limiting values
3 Preparation of specimens
3.1 The specimens must be representative and uniform, without any foreign impurities.
3.2 The specimens for acid consumption value determination are selected from the
specimens and carried out in accordance with the provisions of GB/T 2684.
3.3 The specimens for determination of other indicators are reduced by quartering (if
the particle size is too large, it shall be crushed to less than 0.8 mm first; the iron
introduced during the crushing process shall be removed by a magnet before being
reduced). Finally, about 20 g of specimen is obtained, which is ground until all of them
pass through a 75 µm sieve (i.e., a 200-mesh sieve). Place the above specimen in a
weighing bottle; dry at 105 °C ~ 110 °C for 2 h; then put it in a dryer; cool it and set it
aside.
4 Test method
Unless otherwise specified, the standard solutions, preparations, products used in the
analysis are prepared in accordance with GB/T 601 and GB/T 603. Use reagents
confirmed to be analytically pure and grade 3 water in accordance with GB/T 6682. The
reagents used in the test, if the concentration is not specified, are the original
concentration at the time of exit-factory.
The test results are determined according to the rounded value comparison method in
GB/T 8170.
4.1 Determination of silicon dioxide content
4.1.1 Determination of silicon dioxide content by hydrochloric acid primary
dehydration weight-molybdenum blue absorptiometry
4.1.1.1 Principle
The specimen is melted and decomposed with sodium carbonate; the sinter is dissolved
with hydrochloric acid; the silicic acid is evaporated to dryness to dehydrate;
hydrochloric acid is added to dissolve soluble salts, filtered and burned into silicon
dioxide, then treated with hydrofluoric acid to make silicon escape in the form of silicon
tetrafluoride. The difference in mass before and after hydrofluoric acid treatment is the
amount of silicon dioxide in the precipitate; the amount of residual silicon dioxide in
the filtrate is determined by molybdenum blue absorptiometry. The sum of the two is
the content of silicon dioxide in the specimen.
4.1.1.2 Reagents and materials
a) Anhydrous sodium carbonate;
b) Hydrochloric acid;
c) Hydrofluoric acid;
d) Ethanol: 95%;
4.1.1.4 Analysis steps
a) Preparation of test solution:
Weigh 0.5 g of specimen (accurate to 0.0001 g); place in a platinum crucible; add
1.5 g of anhydrous sodium carbonate; mix with the specimen; add 0.5 g of
anhydrous sodium carbonate to cover the surface; place in a high-temperature
box-type resistance furnace; gradually heat from low temperature to 1000 °C ~
1050 °C; keep at this temperature for 15 min ~ 20 min; clamp the platinum
crucible with crucible tongs with platinum heads; rotate carefully to make the
molten material evenly adhere to the inner wall of the platinum crucible; cool it;
cover with a watch glass; add 20 mL of hydrochloric acid [4.1.1.2e)] to dissolve
the molten block; place the platinum crucible in a water bath; heat until the
carbonate is completely decomposed and no more bubbles are emitted; remove it;
wash the watch glass with hot water; remove the watch glass; then place the
platinum crucible in a water bath to evaporate to dryness; place in an electric oven
and dry at 130 °C for 1 h.
Cool it; add 5 mL of hydrochloric acid [4.1.1.2b)]; let it stand for 5 min; add about
20 mL of hot water; stir to dissolve the salts; add appropriate amount of filter
paper pulp and stir; filter with medium-speed quantitative filter paper; collect the
filtrate and washing liquid in a 250 mL volumetric flask; wash the platinum
crucible wall and precipitate with hot hydrochloric acid [4.1.1.2 g)], until there is
no iron ion (check with potassium thiocyanate solution); continue to wash with
hot water, until there is no chloride ion (check with silver nitrate solution).
Move the precipitate and filter paper into the platinum crucible together; add 2
drops of sulfuric acid to the precipitate; dry it at low temperature on an electric
furnace; then move it into a high-temperature furnace; gradually increase the
temperature to fully ash the filter paper; finally burn it at 1150 °C ~ 1200 °C for
1 h; cool to room temperature in a dryer; weigh it; burn repeatedly until constant
weight (the difference between two burning weighing is ≤ 0.0002 g, which is
constant weight).
Wet the precipitate with water; add 3 drops of sulfuric acid and 5 mL ~ 7 mL of
hydrofluoric acid; evaporate to dryness in a low-temperature furnace; repeat the
process once; continue heating until all the sulfur trioxide smoke is gone; burn the
crucible at 1150 °C ~ 1200 °C for 15 min; cool to room temperature in a desiccator;
weigh it; burn repeatedly until constant weight (the difference between two
burning weighing is ≤ 0.0002 g, which is constant weight).
b) Determination of the specimen:
Dilute the above filtrate with water to the mark; shake well; pipette 25 mL into a
100 mL plastic cup; add 5 mL of potassium fluoride solution; shake well; let it
stand for 10 min; add 5 mL of boric acid solution; add 1 drop of p-nitrophenol
For quartz sand specimens with a silicon dioxide content of more than 95%, after
burning to constant weight, treat with nitric acid and hydrofluoric acid to make silicon
escape in the form of silicon tetrafluoride; then burn to constant weight. The weight
loss is the silicon dioxide content.
4.1.2.2 Reagents and materials
a) Nitric acid;
b) Hydrofluoric acid.
4.1.2.3 Instruments
a) Analytical balance: Accuracy 0.0001 g;
b) Platinum crucible: 30 mL ~ 100 mL;
c) High temperature box resistance furnace.
4.1.2.4 Analysis steps
Weigh about 1 g of specimen, accurate to 0.0001 g; place in a platinum crucible with
constant weight (the difference between two burning weighing is ≤ 0.0002 g); put in a
high-temperature furnace; gradually heat from low temperature to 950 °C ~ 1000 °C;
keep warm for 1 h; take out and cool slightly; immediately put in a desiccator; cool to
room temperature; weigh it. Repeat burning (15 min each time); weigh until constant
weight (the difference between two burning weighing is ≤ 0.0002 g, which is constant
weight).
Moisten the specimen after burning with a few drops of water; add 5 mL of nitric acid
and 5 mL ~ 8 mL of hydrofluoric acid; cover the crucible with a small gap; heat for 30
minutes without boiling on a low-temperature electric furnace (the test solution shall be
clear at this time); wash the crucible cover with a small amount of water; continue
heating and evaporating to dryness; remove it; cool it; add 5 mL of nitric acid and 5 mL
of hydrofluoric acid; evaporate it again to dryness; then add 5 mL of nitric acid along
the crucible wall; evaporate it again to dryness; treat it with nitric acid twice; finally
raise the temperature until no nitrogen oxide is released. Move the platinum crucible
into a high-temperature box-type resistance furnace; first at low temperature; then burn
it at 1000 °C ~ 1050 °C for 30 minutes; take it out and place it in a desiccator; cool it
to room temperature; weigh it; repeat the burning (burning for 15 minutes each time)
until constant weight. Perform a blank test at the same time.
4.1.2.5 Result calculation
Silicon dioxide content is expressed as mass fraction X2, the value is expressed in %,
which is calculated according to formula (2):
c) Chloroform;
d) Potassium pyrosulfate;
e) Hydrochloric acid: 1 + 1;
f) Sulfuric acid: 1 + 1;
g) Ammonia water: 1 + 1;
h) Copper iron reagent solution: 10%, prepare it when needed, filter it before use;
i) Acetic acid-ammonium acetate buffer solution (pH = 6.1): Take 300 g of
ammonium acetate; dissolve it in 500 mL water; add 15 mL of glacial acetic acid;
dilute it with water to 1000 mL; shake it well;
j) Disodium ethylenediaminetetraacetic acid (EDTA) solution: 0.025 mol/L, weigh
9.3060 g of standard EDTA; dissolve it in 500 mL warm water; cool it; transfer it
into a 1000 mL volumetric flask; dilute it with water to the mark; shake it well;
k) Zinc standard solution: c(Zn) = 0.01000 mol/L, weigh 0.6538 g of metallic zinc
(99.95% or more); add 10 mL of hydrochloric acid to a 250 mL beaker; heat to
dissolve; cool it; transfer to a 1000 mL volumetric flask; add 2 ~ 3 drops of methyl
orange indicator; slowly neutralize with ammonia until the solution just turns
yellow; then adjust the solution from yellow to red with hydrochloric acid; add 5
~ 6 drops in excess; dilute with water to the mark; shake well;
l) Methyl orange indicator: 1 g/L;
m) Xylenol orange indicator: 8 g/L.
4.2.1.1.3 Instruments
a) Analytical balance: Accuracy 0.0001 g;
b) Platinum crucible: 30 mL ~ 100 mL;
c) High temperature box-type resistance furnace;
d) Volumetric flask: 250 mL, Class A;
e) Single-line pipette: 5 mL, 10 mL, 15 mL, 50 mL, Class A;
f) Separatory funnel: 125mL, Class A;
g) Burette: 50 mL, graduation value 0.1 mL, Class A.
4.2.1.1.4 Analysis steps
g) Alumina standard solution: Weigh 0.1058 g of aluminum (content not less than
99.95%) into a plastic beaker; add 50 mL of sodium hydroxide solution (20%);
heat and dissolve in a water bath; cool and add hydrochloric acid (1 + 1) dropwise,
until it becomes acidic; add 20 mL in excess; heat in a water bath until the solution
is clear; cool it; transfer to a 1000 mL volumetric flask; dilute to the mark with
water; shake well; this solution is equivalent to 0.2 mg of aluminum oxide per
milliliter. Transfer 25.00 mL of the above solution into a 1000 mL volumetric
flask; add 20 mL of hydrochloric acid (1 + 1); dilute to the mark with water; shake
well; this solution is equivalent to 0.005 mg of aluminum oxide per milliliter;
h) Methyl orange indicator: 1 g/L;
i) Chrome azure S solution: 0.5 g/L, prepared with ethanol (1 + 1).
4.2.1.2.3 Instruments
a) Spectrophotometer;
b) Single-marked pipettes: 5 mL, 10 mL, 20 mL, 25 mL, 50 mL, Class A;
c) Volumetric flasks: 50 mL, 200 mL, 250 mL, 1000 mL, Class A.
4.2.1.2.4 Analysis steps
a) Pipette 50 mL of test solution (A) into a 200 mL volumetric flask; dilute to the
mark with water; shake well.
b) According to the content of aluminum oxide in the specimen, pipette the above
test solution into two 50 mL volumetric flasks as specified in Table 2, one as the
color developing solution and the other as the reference solution.
c) Color solution: Add 6 drops of hydrogen peroxide and 5 mL of zinc-EDTA
solution; let it stand for 5 minutes; add 1 drop of methyl orange indicator;
neutralize part of the acid with ammonia; carefully add ammonia until the solution
just turns yellow; immediately add nitric acid until it turns red; add 5 mL in excess;
shake well; let stand for a while; add 3 mL of chrome azurol blue S solution and
5 mL of hexamethylenetetramine solution; dilute to the mark with water; shake
well; let stand for 20 minutes.
d) Reference solution: Operate at the same time as the color solution, but before
adding the chrome azurol blue S solution, add 5 drops of ammonium fluoride
solution.
e) Select an appropriate colorimetric dish according to the provisions of Table 2;
measure the absorbance at a wavelength of 545 nm; find the corresponding
amount of aluminum oxide from the working curve.
method
4.2.2.1.1 Principle
For specimens with an iron oxide content of 0.050% ~ 3.00%, in an ammonia medium,
trivalent iron and sulfosalicylic acid form an orange-yellow complex; the absorbance is
measured at a wavelength of 430 nm.
4.2.2.1.2 Reagents and materials
a) Ammonia water: 1 + 1;
b) Sulfosalicylic acid solution: 30%;
c) Standard iron oxide solution: Accurately weigh 0.1000 g of standard iron oxide
that has been pre-burned at 400 °C for 30 min and cooled to room temperature in
a desiccator into a beaker; add 10 mL of hydrochloric acid (1 + 1); heat to dissolve;
transfer to a 1000 mL volumetric flask after cooling; shake well. Each milliliter
of this solution is equivalent to 0.1 mg of iron oxide.
4.2.2.1.3 Instruments
a) Spectrophotometer;
b) Single-line pipette: 10 mL, 20 mL, Class A;
c) Volumetric flask: 100 mL, 1000 mL, Class A.
4.2.2.1.4 Analysis steps
a) Determination of specimen: Pipette 10 mL of test solution (A) into a 100 mL
volumetric flask; add 10 mL of sulfosalicylic acid solution; add 3 ~ 5 drops of
ammonia water until it turns stable yellow; dilute with water to the mark; shake
well; use the reagent blank as reference; select a 1 cm cuvette; measure the
absorbance of the solution at 430 nm; find the amount of iron oxide from the
working curve.
b) Drawing of working curve: Pipette 0.00 mL, 1.00 mL, 2.00 mL, 4.00 mL, 6.00
mL, 8.00 mL, 10.00 mL, 12.00 mL of iron oxide standard solution into eight 100
mL volumetric flasks respectively; perform the following operations according to
analysis step 4.2.2.1.4a); measure the absorbance; draw the working curve.
4.2.2.1.5 Result calculation
The iron oxide content is expressed as mass fraction X5, the value is expressed in %,
which is calculated according to formula (5):
4.3 Determination of calcium oxide, magnesium oxide, potassium
oxide, sodium oxide content
The specimen is decomposed with hydrofluoric acid-perchloric acid to remove silicon,
evaporated with perchloric acid to remove fluoride; the residue is leached with dilute
hydrochloric acid and diluted to a certain volume; the calcium oxide, magnesium oxide,
potassium oxide and sodium oxide are determined by liquid separation.
4.3.1 Determination of calcium oxide content by EDTA complexometric titration
4.3.1.1 Principle
For specimens with calcium oxide content above 0.10%, triethanolamine is used to
mask interfering elements such as iron and aluminum. In a strong alkaline medium,
calcein-thymolphthalein-acridine is used as a mixed indicator, calcium is directly
titrated with EDTA standard solution.
4.3.1.2 Reagents and materials
a) Hydrofluoric acid;
b) Perchloric acid: 1 + 1;
c) Hydrochloric acid: 1 + 11;
d) Triethanolamine: 1 + 2;
e) Potassium hydroxide solution: 30%, stored in a plastic bottle;
f) Disodium ethylenediaminetetraacetic acid (EDTA) standard solution: c(EDTA) =
0.005 mol/L; weigh 1.86 g of EDTA in a 500 mL beaker; add about 200 mL of
water; heat to dissolve; dilute to 1000 mL with water.
g) Calcium oxide standard solution: 1 mg/mL, weigh 1.7848 g of high-purity
calcium carbonate that has been dried at 105 °C ~ 110 °C for 2 h and cooled to
room temperature in a desiccator; put it in a 300 mL beaker; add about 150 mL of
water; add 10 mL of hydrochloric acid (1 + 1) to dissolve it; heat and boil for
several minutes to drive away carbon dioxide; cool it; dilute it with water to 1000
mL; shake it well; this solution is equivalent to 1 mg calcium oxide per milliliter;
h) Calcein-thymolphthalein-acridine mixed indicator: Weigh 0.2 g of calcein, 0.1 g
of thymolphthalein, 0.4 g of acridine, 20 g of dried potassium sulfate; mix and
grind well.
4.3.1.3 Instruments
4.3.2 Determination of magnesium oxide content by EDTA complexometric
titration
4.3.2.1 Principle
For specimens with magnesium oxide content above 0.10%, triethanolamine is used to
mask interfering elements such as iron and aluminum. In an ammonia buffer medium,
acid chrome blue K-naphthol green B is used as a mixed indicator. The total amount of
calcium and magnesium is directly titrated with EDTA standard solution. The
magnesium content is obtained by the difference between the total amount of calcium
and magnesium and the calcium content.
4.3.2.2 Reagents and materials
a) Ammonia: 1 + 1;
b) Triethanolamine: 1 + 2;
c) Ammonia-ammonium chloride buffer solution (pH = 10): Weigh 67.5 g of
ammonium chloride; dissolve in 200 mL of water; add 570 mL of ammonia; dilute
to 1000 mL with water; shake well;
d) Disodium ethylenediaminetetraacetic acid (EDTA) standard solution: c(EDTA) =
0.005 mol/L; weigh 1.86 g of EDTA in a 500 mL beaker; add about 200 mL of
water; heat to dissolve; dilute to 1000 mL with water;
e) Acid chrome blue K-naphthol green B mixed indicator: 1 + 2; grind the mixed
indicator and potassium nitrate in an agate mortar at a ratio of 1 + 50; store in a
brown wide-mouth bottle.
4.3.2.3 Instruments
a) Single-line pipette: 5 mL, 10 mL, 100 mL, Class A;
b) Volumetric flask: 1000 mL, Class A;
c) Conical flask: 300 mL;
d) Burette: 50 mL, graduation value 0.1 mL, Class A.
4.3.2.4 Analysis steps
Pipette 100 mL of specimen (B) (50 mL for specimens containing more than 1%
magnesium oxide) into a 300 mL conical flask; add 5 mL of triethanolamine; dilute to
150 mL with water; add ammonia water to adjust the solution pH to about 10 (check
with precision test paper); then add 10 mL of ammonia water-ammonium chloride
buffer solution and appropriate amount of acid chrome blue K-naphthol green B mixed
indicator; add EDTA standard solution until the test solution changes from purple-red
equivalent to 1 mg of calcium oxide per milliliter;
g) Magnesium oxide standard solution: 1 mg/mL; accurately weigh 1.0000 g of
magnesium oxide that has been burned at 900 °C for 2 h and cooled to room
temperature in a desiccator; place it in a 100 mL beaker; add 20 mL of
hydrochloric acid; heat it to dissolve; cool it to room temperature; transfer it to a
1000 mL volumetric flask; dilute it to the mark with water; shake it well; store it
in a dry plastic bottle. This solution is equivalent to 1 mg of magnesium oxide per
milliliter;
h) Iron oxide standard solution: 1 mg/mL; accurately weigh 1.0000 g of iron oxide
that has been burned at 400 °C for 30 min and cooled to room temperature in a
desiccator; place it in a 200 mL beaker; add 50 mL of hydrochloric acid; heat to
dissolve; cool to room temperature; transfer to a 1000 mL volumetric flask; dilute
to the mark with water; shake well; store in a dry plastic bottle. This solution is
equivalent to 1 mg of iron oxide per milliliter;
i) Potassium oxide standard solution: 1 mg/mL; accurately weigh 1.5830 g of
potassium chloride that has been dried at 110 °C for 2 h and cooled to room
temperature in a desiccator; place it in a 150 mL beaker; add water to dissolve;
transfer to a 1000 mL volumetric flask; add 10 mL of hydrochloric acid; dilute to
the mark with water; shake well; store in a dry plastic bottle. This solution is
equivalent to 1 mg of potassium oxide per milliliter;
j) Sodium oxide standard solution: 1 mg/mL; accurately weigh 110 °C dried for 2 h
and cooled to room temperature in a desiccator; place it in a 150 mL beaker; add
water to dissolve; transfer to a 1000 mL volumetric flask; add 10 mL of
hydrochloric acid; dilute to the mark with water; shake well; store in a dry plastic
bottle. This solution is equivalent to 1 mg of potassium oxide per milliliter; dry
for 2 h; then cool to room temperature in a dryer. Place 1.8859 g of sodium
chloride in a 150 mL beaker; dissolve it in water; transfer it to a 1000 mL
volumetric flask; add 10 mL of hydrochloric acid; dilute with water to the mark;
shake well; store in a dry plastic bottle. Each milliliter of this solution is
equivalent to 1 mg of sodium oxide;
k) Mixed standard solution: Pipette 50 mL of each of the above five standard
solutions in a 1000 mL volumetric flask; add 10 mL of hydrochloric acid; dilute
with water to the mark; shake well; set aside. The concentrations of iron oxide,
calcium oxide, magnesium oxide, potassium oxide, sodium oxide in this mixed
standard solution are all 50 μg/mL. Preparation of mixed standard series solutions:
Use twelve 500 mL volumetric flasks to prepare a series of standard solutions
according to the proportions in Table 14.
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