ASTM D7126-06
(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 (g/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 D 859.
1.5 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.
General Information
Relations
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation:D7126–06
Standard Test Method for
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 D3370 Practices for Sampling Water from Closed Conduits
D3864 Guide for Continual On-Line Monitoring Systems
1.1 This test method covers the on-line determination of
for Water Analysis
soluble silica in water by colorimetric analysis using the
D5540 Practice for Flow Control and Temperature Control
molybdenum blue method, also known as the heteropoly blue
for On-Line Water Sampling and Analysis
method.
1.2 This test method is applicable for silica determination in
3. Terminology
water with silica concentrations within 0.5 - 5000 ppb (µg/L).
3.1 Definitions—For definitions of terms used in this test
1.3 This test method covers the determination of soluble
method, refer to Terminology D1129 and Practice D3864.
silica SiO (silicon dioxide) or silicates in water. Soluble silica
3.2 Definitions of Terms Specific to This Standard:
compounds are considered molybdate reactive silica. This test
3.2.1 heteropoly compound—a compound in which groups
method does not cover the determination of colloidal or
of different elements are joined together by metal-metal bonds.
polymeric silica, which is considered non-molybdate reactive
3.2.2 metalloid—an element which has properties that are
silica.
intermediate between those of a metal and a nonmetal.
1.4 This test method does not cover the laboratory or grab
3.2.3 photodetector—a device for detecting and measuring
sample measurement of silica in water. Refer to Test Method
the intensity of radiant energy.
D859.
1.5 This standard does not purport to address all of the
4. Summary of Test Method
safety concerns, if any, associated with its use. It is the
4.1 This test method describes the analysis of soluble silica
responsibility of the user of this standard to establish appro-
by analyzing a sample from a continuous stream. This test
priate safety and health practices and determine the applica-
method is based on the colorimetric determination of soluble
bility of regulatory limitations prior to use.
silica by the formation and reduction of molybdosilicic acid.
Reduced molybdosilicic acid forms a molybdenum blue com-
2. Referenced Documents
2 plex. The optical absorbance of this complex is typically
2.1 ASTM Standards:
measured at 815 6 10 nm. The absorbance is directly propor-
D859 Test Method for Silica in Water
tional to the concentration of silica in the sample.
D1066 Practice for Sampling Steam
4.2 This on-line test method requires reagents which are
D1129 Terminology Relating to Water
added sequentially with separate reaction periods. Each reac-
D1192 Guide for Equipment for SamplingWater and Steam
3 tion must be allowed to go to completion before the next
in Closed Conduits
reagent is added.
D1193 Specification for Reagent Water
D2777 Practice for Determination of Precision and Bias of
5. Significance and Use
Applicable Test Methods of Committee D19 on Water
5.1 Silicon (Si), a metalloid, is the second most abundant
element in the earth’s crust. Various forms of silica (silicon
This test method is under the jurisdiction of ASTM Committee D19 on Water
dioxide SiO ) are found in quartz, sand and rocks. The
and is the direct responsibility of Subcommittee D19.03 on Sampling of Water and
degradation of these rocks results in silica found in natural
Water-Formed Deposits, Analysis of Water for Power Generation and Process Use,
waters. Silica in natural waters can be found as ionic silica,
On-Line Water Analysis, and Surveillance of Water.
Current edition approved March 1, 2006. Published March 2006. DOI: 10.1520/ silicates, colloidal or suspended particles.
D7126-06.
5.2 Elevated temperatures and pressure can cause silica in
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
water to vaporize and form deposits or scale. Scale deposits of
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
silica will coat boilers and turbine blades used in power plants.
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
The presence of silica scale affects the ability of metals to
Withdrawn. The last approved version of this historical standard is referenced
on www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D7126–06
transfer heat. Silica needs to be removed when deionized water 8.2 Silica Solution, Standard—To prepare a silica standard
is used as a rinse for manufacturing wafers in the semiconduc- solution, dissolve ACS reagent grade or better sodium meta-
tor industry. silicate (Na SiO •9H O) and dilute with deionized water to
2 3 2
5.3 Silica is commonly removed by demineralization using volume, or use commercially prepared standards. Refer to the
anion exchange resins, distillation, reverse osmosis or precipi- instrument manufacturers manual for the correct standard
tation in a lime softening process. The on-line measurement of concentration to use. Standards and samples should not be
silica is the preferred method to laboratory analyses for frozen, which can result in lower soluble silica values. (1)
industries trying to obtain and monitor ultra-pure water. Since Standards should be prepared at room temperature and stored
silica is one of the first species to breakthrough anion exchange at 4°C to maintain maximum stability.
resins,on-linesilicamonitoringisfrequentlyusedtodetermine 8.3 Silica Reagents—The colorimetric analysis described in
the need for regeneration of an anion or mixed resin bed. this method requires at least 3 reagents for the on-line
determination of silica. The reagents necessary for this method
6. Interferences
are specific for the on-line instrument, colorimeter or spectro-
6.1 Colored and turbid samples and reagents may interfere
photometer used. Refer to the instrument manufacturers rec-
inthecolorimetricdetectionofsilica.Atlowlevels(ppbrange)
ommended reagents. It is essential that the reagents used are
samples can be filtered to eliminate particles and suspended matched to the analyzer. Either use reagents provided or
solids in solutions, however filtration is not recommended,
prescribed by the manufacturer or validate the results obtained
because of the potential to introduce silica contamination. A from any other reagent formulation. This validation must
blank (zero) absorption can be performed prior to the final
include validation of the calibration data.
absorption measurement to reduce interferences from turbidity
NOTE 1—All reagents and calibration standards used in this test method
and color.
should be stored in polyethylene, plastic or other non-silica containing
6.2 Phosphate interferes in the colorimetric detection of
bottles.
silica by reacting with the molybdate compound used in the
NOTE 2—The first reagent used is an acidified molybdate reagent which
first reagent to form molybdophosphoric acid. Molybdophos- reacts with silica in the sample to form molybdosilicic acid. If phosphate
is present in the sample, molybdophosphoric acid is also
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.