ASTM D7126-10
(Test Method)Standard Test Method for On-Line Colorimetric Measurement of Silica
Standard Test Method for On-Line Colorimetric Measurement of Silica
SIGNIFICANCE AND USE
Silicon (Si), a metalloid, is the second most abundant element in the earth’s crust. Various forms of silica (silicon dioxide SiO2) are found in quartz, sand and rocks. The degradation of these rocks results in silica found in natural waters. Silica in natural waters can be found as ionic silica, silicates, colloidal or suspended particles.
Elevated temperatures and pressure can cause silica in water to vaporize and form deposits or scale. Scale deposits of silica will coat boilers and turbine blades used in power plants. The presence of silica scale affects the ability of metals to transfer heat. Silica needs to be removed when deionized water is used as a rinse for manufacturing wafers in the semiconductor industry.
Silica is commonly removed by demineralization using anion exchange resins, distillation, reverse osmosis or precipitation in a lime softening process. The on-line measurement of silica is the preferred method to laboratory analyses for industries trying to obtain and monitor ultra-pure water. Since silica is one of the first species to breakthrough anion exchange resins, on-line silica monitoring is frequently used to determine the need for regeneration of an anion or mixed resin bed.
SCOPE
1.1 This test method covers the on-line determination of soluble silica in water by colorimetric analysis using the molybdenum blue method, also known as the heteropoly blue method.
1.2 This test method is applicable for silica determination in water with silica concentrations within 0.5 - 5000 ppb (μg/L).
1.3 This test method covers the determination of soluble silica SiO2 (silicon dioxide) or silicates in water. Soluble silica compounds are considered molybdate reactive silica. This test method does not cover the determination of colloidal or polymeric silica, which is considered non-molybdate reactive silica.
1.4 This test method does not cover the laboratory or grab sample measurement of silica in water. Refer to Test Method D859.
1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: D7126 − 10
StandardTest Method for
1
On-Line Colorimetric Measurement of Silica
This standard is issued under the fixed designation D7126; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope D2777 Practice for Determination of Precision and Bias of
Applicable Test Methods of Committee D19 on Water
1.1 This test method covers the on-line determination of
D3370 Practices for Sampling Water from Closed Conduits
soluble silica in water by colorimetric analysis using the
D3864 Guide for On-Line Monitoring Systems for Water
molybdenum blue method, also known as the heteropoly blue
Analysis
method.
D5540 Practice for Flow Control and Temperature Control
1.2 This test method is applicable for silica determination in
for On-Line Water Sampling and Analysis
water with silica concentrations within 0.5 - 5000 ppb (µg/L).
3. Terminology
1.3 This test method covers the determination of soluble
silica SiO (silicon dioxide) or silicates in water. Soluble silica 3.1 Definitions—For definitions of terms used in this test
2
compounds are considered molybdate reactive silica. This test method, refer to Terminology D1129 and Practice D3864.
method does not cover the determination of colloidal or 3.2 Definitions of Terms Specific to This Standard:
polymeric silica, which is considered non-molybdate reactive 3.2.1 heteropoly compound, n—a compound in which
silica. groups of different elements are joined together by metal-metal
bonds.
1.4 This test method does not cover the laboratory or grab
3.2.2 metalloid, n—an element which has properties that are
sample measurement of silica in water. Refer to Test Method
intermediate between those of a metal and a nonmetal.
D859.
3.2.3 photodetector, n—a device for detecting and measur-
1.5 The values stated in SI units are to be regarded as
ing the intensity of radiant energy.
standard. No other units of measurement are included in this
standard.
4. Summary of Test Method
1.6 This standard does not purport to address all of the
4.1 This test method describes the analysis of soluble silica
safety concerns, if any, associated with its use. It is the
by analyzing a sample from a continuous stream. This test
responsibility of the user of this standard to establish appro-
method is based on the colorimetric determination of soluble
priate safety and health practices and determine the applica-
silica by the formation and reduction of molybdosilicic acid.
bility of regulatory limitations prior to use.
Reduced molybdosilicic acid forms a molybdenum blue com-
plex. The optical absorbance of this complex is typically
2. Referenced Documents
measured at 815 6 10 nm. The absorbance is directly propor-
2
2.1 ASTM Standards:
tional to the concentration of silica in the sample.
D859 Test Method for Silica in Water
4.2 This on-line test method requires reagents which are
D1066 Practice for Sampling Steam
added sequentially with separate reaction periods. Each reac-
D1129 Terminology Relating to Water
tion must be allowed to go to completion before the next
D1193 Specification for Reagent Water
reagent is added.
5. Significance and Use
1
This test method is under the jurisdiction of ASTM Committee D19 on Water
5.1 Silicon (Si), a metalloid, is the second most abundant
and is the direct responsibility of Subcommittee D19.03 on Sampling Water and
element in the earth’s crust. Various forms of silica (silicon
Water-Formed Deposits, Analysis of Water for Power Generation and Process Use,
On-Line Water Analysis, and Surveillance of Water
dioxide SiO ) are found in quartz, sand and rocks. The
2
Current edition approved Dec. 1, 2010. Published March 2011. Originally
degradation of these rocks results in silica found in natural
approved in 2006. Last previous edition approved in 2006 as D7126 – 06. DOI:
waters. Silica in natural waters can be found as ionic silica,
10.1520/D7126-10.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or silicates, colloidal or suspended particles.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
5.2 Elevated temperatures and pressure can cause silica in
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. water to vaporize and form deposits or scale. Scale deposits of
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
1
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D7126 − 10
silica will coat boilers and turbine blades used in power plants. 8. Reagents
The presence of silica scale affects the abili
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation:D7126–06 Designation: D7126 – 10
Standard Test Method for
1
On-Line Colorimetric Measurement of Silica
This standard is issued under the fixed designation D7126; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This test method covers the on-line determination of soluble silica in water by colorimetric analysis using the molybdenum
blue method, also known as the heteropoly blue method.
1.2 This test method is applicable for silica determination in water with silica concentrations within 0.5 - 5000 ppb (µg/L).
1.3 This test method covers the determination of soluble silica SiO (silicon dioxide) or silicates in water. Soluble silica
2
compounds are considered molybdate reactive silica. This test method does not cover the determination of colloidal or polymeric
silica, which is considered non-molybdate reactive silica.
1.4 This test method does not cover the laboratory or grab sample measurement of silica in water. Refer to Test Method D859.
1.5
1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to use.
2. Referenced Documents
2
2.1 ASTM Standards:
D859 Test Method for Silica in Water
D1066 Practice for Sampling Steam
D1129 Terminology Relating to Water D1192Guide for Equipment for Sampling Water and Steam in Closed Conduits
D1193 Specification for Reagent Water
D2777 Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D19 on Water
D3370 Practices for Sampling Water from Closed Conduits
D3864 Guide for Continual On-Line Monitoring Systems for Water Analysis
D5540 Practice for Flow Control and Temperature Control for On-Line Water Sampling and Analysis
3. Terminology
3.1 Definitions —For definitions of terms used in this test method, refer to Terminology D1129 and Practice D3864.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 heteropoly compoundheteropoly compound, n—a compound in which groups of different elements are joined together by
metal-metal bonds.
3.2.2 metalloidmetalloid, n—an element which has properties that are intermediate between those of a metal and a nonmetal.
3.2.3 photodetectorphotodetector, n—a device for detecting and measuring the intensity of radiant energy.
4. Summary of Test Method
4.1 This test method describes the analysis of soluble silica by analyzing a sample from a continuous stream. This test method
is based on the colorimetric determination of soluble silica by the formation and reduction of molybdosilicic acid. Reduced
molybdosilicic acid forms a molybdenum blue complex. The optical absorbance of this complex is typically measured at 815 6
10 nm. The absorbance is directly proportional to the concentration of silica in the sample.
4.2 This on-line test method requires reagents which are added sequentially with separate reaction periods. Each reaction must
be allowed to go to completion before the next reagent is added.
1
This test method is under the jurisdiction of ASTM Committee D19 on Water and is the direct responsibility of Subcommittee D19.03 on Sampling of Water and
Water-Formed Deposits, Analysis of Water for Power Generation and Process Use, On-Line Water Analysis, and Surveillance of Water.Water
Current edition approved MarchDec. 1, 2006.2010. Published March 2011. Originally approved in 2006 as D7126–06. DOI: 10.1520/D7126-106.
2
For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
1
---------------------- Page: 1 ----------------------
D7126 – 10
5. Significance and Use
5.1 Silicon (Si), a metalloid, is the second most abundant element in the earth’s crust. Various forms of silica (silicon dioxide
SiO ) are found in quartz, sand and rocks. The degradation of these rock
...
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