ASTM D7126-15
Standard Test Method for On-Line Colorimetric Measurement of Silica

Standard No.

ASTM D7126-15

Release Date

2015

Published By

American Society for Testing and Materials (ASTM)

Status

Be replaced

Replace By

ASTM D7126-15(2023)

Latest

ASTM D7126-15(2023)

Scope

5.1 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.

5.2 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.

5.3 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.

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 SiO₂8201;(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.

ASTM D7126-15 Referenced Document

• ASTM D1066 Standard Practice for Sampling Steam
• ASTM D1129 Standard Terminology Relating to Water
• ASTM D1193 Standard Specification for Reagent Water
• ASTM D2777 Standard Practice for Determination of Precision and Bias of Applicable Methods of Committee D-19 on Water
• ASTM D3370 Standard Practices for Sampling Water from Closed Conduits
• ASTM D3864 Standard Guide for Continual On-Line Monitoring Systems for Water Analysis
• ASTM D5540 Standard Practice for Flow Control and Temperature Control for On-Line Water Sampling and Analysis
• ASTM D859 Standard Test Method for Silica in Water*， 2021-11-01 Update

ASTM D7126-15 history

• 2023 ASTM D7126-15(2023) Standard Test Method for On-Line Colorimetric Measurement of Silica
• 2015 ASTM D7126-15 Standard Test Method for On-Line Colorimetric Measurement of Silica
• 2010 ASTM D7126-10 Standard Test Method for On-Line Colorimetric Measurement of Silica
• 2006 ASTM D7126-06 Standard Test Method for On-Line Colorimetric Measurement of Silica