ASTM D859-16

Standard Test Method for Silica in Water

SIGNIFICANCE AND USE
5.1 Silicon comprises about 28 % of the lithosphere and is, next to oxygen, the most abundant element. It is found as the oxide in crystalline forms, as in quartz; combined with other oxides and metals in a variety of silicates; and in amorphous forms. Silicon is the most abundant element in igneous rocks and is the characteristic element of all important rocks except the carbonates. It is the skeletal material of diatoms but is not known to play a significant role in the structure of processes of higher life forms.  
5.2 Silica is only slightly soluble in water. The presence of most silica in natural waters comes from the gradual degradation of silica-containing minerals. The type and composition of the silica-containing minerals in contact with the water and the pH of the water are the primary factors controlling both the solubility and the form of silica in the resulting solution. Silica may exist in suspended particles, as a colloid, or in solution. It may be monomeric or polymeric. In solution it can exist as silicic acid or silicate ion, depending upon pH. The silica content of natural waters is commonly in the 5 to 25 mg/L range, although concentrations over 100 mg/L occur in some areas.  
5.3 Silica concentration is an important consideration in some industrial installations such as steam generation and cooling water systems. Under certain conditions, silica forms troublesome silica and silicate scales, particularly on high-pressure steam turbine blades. In cooling water systems, silica forms deposits when solubility limits are exceeded. In contrast, silica may be added as a treatment chemical in some systems, for example, in corrosion control. Silica removal is commonly accomplished by ion exchange, distillation, reverse osmosis, or by precipitation, usually with magnesium compounds in a hot or cold lime softening process.
SCOPE
1.1 This test method covers the determination of silica in water and waste water; however, the analyst should recognize that the precision and accuracy statements for reagent water solutions may not apply to waters of different matrices.  
1.2 This test method is a colorimetric method that determines molybdate-reactive silica. It is applicable to most waters, but some waters may require filtration and dilution to remove interferences from color and turbidity. This test method is useful for concentrations as low as 20 μg/L.  
1.3 This test method covers the photometric determination of molybdate-reactive silica in water. Due to the complexity of silica chemistry, the form of silica measured is defined by the analytical method as molybdate-reactive silica. Those forms of silica that are molybdate-reactive include dissolved simple silicates, monomeric silica and silicic acid, and an undetermined fraction of polymeric silica.  
1.4 The useful range of this test method is from 20 to 1000 μg/L at the higher wavelength (815 nm) and 0.1 to 5 mg/L at the lower wavelength (640 nm). It is particularly applicable to treated industrial waters. It may be applied to natural waters and wastewaters following filtration or dilution, or both. For seawater or brines, this test method is applicable only if matched matrix standards or standard addition techniques are employed.  
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.
Note 1: For many natural waters, a measurement of molybdate-reactive silica by this test method provides a close approximation of total silica, and, in practice, the colorimetric method is frequently substituted for other more time-consuming techniques. This is acceptable when, as frequent...

General Information

• Status: Historical
• Publication Date: 14-Jun-2016
• ICS: 13.060.50 - Examination of water for chemical substances
• Technical Committee: D19 - Water
• Drafting Committee: D19.05 - Inorganic Constituents in Water

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: D859 − 16
Standard Test Method for
1
Silica in Water
This standard is issued under the fixed designation D859; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
reactive silica by this test method provides a close approximation of total
1. Scope*
silica, and, in practice, the colorimetric method is frequently substituted
1.1 This test method covers the determination of silica in
for other more time-consuming techniques. This is acceptable when, as
water and waste water; however, the analyst should recognize frequently occurs, the molybdate-reactive silica is in the milligram per
litreconcentrationrangewhilethenonmolybdate-reactivesilica,ifpresent
that the precision and accuracy statements for reagent water
at all, is in the microgram per litre concentration range.
solutions may not apply to waters of different matrices.
1.7 Former Test Method A (Gravimetric—Total Silica) was
1.2 This test method is a colorimetric method that deter-
discontinued. Refer to Appendix X1 for historical information.
minesmolybdate-reactivesilica.Itisapplicabletomostwaters,
but some waters may require filtration and dilution to remove
2. Referenced Documents
interferences from color and turbidity. This test method is
2
useful for concentrations as low as 20 µg/L. 2.1 ASTM Standards:
D1066 Practice for Sampling Steam
1.3 This test method covers the photometric determination
D1129 Terminology Relating to Water
of molybdate-reactive silica in water. Due to the complexity of
D1193 Specification for Reagent Water
silica chemistry, the form of silica measured is defined by the
D2777 Practice for Determination of Precision and Bias of
analytical method as molybdate-reactive silica.Those forms of
Applicable Test Methods of Committee D19 on Water
silica that are molybdate-reactive include dissolved simple
D3370 Practices for Sampling Water from Closed Conduits
silicates, monomeric silica and silicic acid, and an undeter-
D4841 Practice for Estimation of Holding Time for Water
mined fraction of polymeric silica.
Samples Containing Organic and Inorganic Constituents
1.4 The useful range of this test method is from 20 to 1000
D5810 Guide for Spiking into Aqueous Samples
µg/L at the higher wavelength (815 nm) and 0.1 to 5 mg/L at
D5847 Practice for Writing Quality Control Specifications
the lower wavelength (640 nm). It is particularly applicable to
for Standard Test Methods for Water Analysis
treated industrial waters. It may be applied to natural waters
E60 Practice for Analysis of Metals, Ores, and Related
and wastewaters following filtration or dilution, or both. For
Materials by Spectrophotometry
seawater or brines, this test method is applicable only if
E275 Practice for Describing and Measuring Performance of
matched matrix standards or standard addition techniques are
Ultraviolet and Visible Spectrophotometers
employed.
3. Terminology
1.5 The values stated in SI units are to be regarded as
standard. No other units of measurement are included in this
3.1 Definitions:
standard.
3.1.1 For definitions of terms used in this standard, refer to
1.6 This standard does not purport to address all of the Terminology D1129.
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro- 4. Summary of Test Method
priate safety and health practices and determine the applica-
4.1 This test method is based on the reaction of the soluble
bility of regulatory limitations prior to use.
silica with molybdate ion to form a greenish-yellow complex,
which in turn is converted to a blue complex by reduction with
NOTE 1—For many natural waters, a measurement of molybdate-
1-amino-2-naphthol-1-sulfonic acid.
1
This test method is under the jurisdiction of ASTM Committee D19 on Water
and is the direct responsibility of Subcommittee D19.05 on Inorganic Constituents
2
in Water. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved June 15, 2016. Published June 2016. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 1945. Last previous edition approved in 2010 as D859 – 10. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/D0859-16. the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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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: D859 − 10 D859 − 16
Standard Test Method for
1
Silica in Water
This standard is issued under the fixed designation D859; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope*
1.1 This test method covers the determination of silica in water and waste water; however, the analyst should recognize that the
precision and accuracy statements for reagent water solutions may not apply to waters of different matrices.
1.2 This test method is a colorimetric method that determines molybdate-reactive silica. It is applicable to most waters, but some
waters may require filtration and dilution to remove interferences from color and turbidity. This test method is useful for
concentrations as low as 20 μg/L.
1.3 This test method covers the photometric determination of molybdate-reactive silica in water. Due to the complexity of silica
chemistry, the form of silica measured is defined by the analytical method as molybdate-reactive silica. Those forms of silica that
are molybdate-reactive include dissolved simple silicates, monomeric silica and silicic acid, and an undetermined fraction of
polymeric silica.
1.4 The useful range of this test method is from 20 to 1000 μg/L at the higher wavelength (815 nm) and 0.1 to 5 mg/L at the
lower wavelength (640 nm). It is particularly applicable to treated industrial waters. It may be applied to natural waters and
wastewaters following filtration or dilution, or both. For seawater or brines, this test method is applicable only if matched matrix
standards or standard addition techniques are employed.
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.
NOTE 1—For many natural waters, a measurement of molybdate-reactive silica by this test method provides a close approximation of total silica, and,
in practice, the colorimetric method is frequently substituted for other more time-consuming techniques. This is acceptable when, as frequently occurs,
the molybdate-reactive silica is in the milligram per litre concentration range while the nonmolybdate-reactive silica, if present at all, is in the microgram
per litre concentration range.
1.7 Former Test Method A (Gravimetric—Total Silica) was discontinued. Refer to Appendix X1 for historical information.
2. Referenced Documents
2
2.1 ASTM Standards:
D1066 Practice for Sampling Steam
D1129 Terminology Relating to Water
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
D4841 Practice for Estimation of Holding Time for Water Samples Containing Organic and Inorganic Constituents
D5810 Guide for Spiking into Aqueous Samples
D5847 Practice for Writing Quality Control Specifications for Standard Test Methods for Water Analysis
E60 Practice for Analysis of Metals, Ores, and Related Materials by Spectrophotometry
E275 Practice for Describing and Measuring Performance of Ultraviolet and Visible Spectrophotometers
1
This test method is under the jurisdiction of ASTM Committee D19 on Water and is the direct responsibility of Subcommittee D19.05 on Inorganic Constituents in Water.
Current edition approved June 15, 2010June 15, 2016. Published July 2010June 2016. Originally approved in 1945. Last previous edition approved in 20052010 as
D859 – 05.D859 – 10. DOI: 10.1520/D0859-10.10.1520/D0859-16.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
1

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