ASTM D6851-20

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Designation: D6851 − 02 (Reapproved 2011) D6851 − 20
Standard Test Method for
Determination of Contact pH with Activated Carbon
This standard is issued under the fixed designation D6851; 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 method is to be used in the determination of the pH of water on initial contact with activated carbon. This test method
is not meant as a replacement for Test Method D3838 and may give a different value.
1.2 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 to determine the applicability of regulatory
limitations prior to use.
1.2 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, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
1.3 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D1193 Specification for Reagent Water
D1293 Test Methods for pH of Water
D3838 Test Method for pH of Activated Carbon
E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods
E300 Practice for Sampling Industrial Chemicals
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
3. Summary of Test Method
3.1 A sample of carbon is stirred with water and the pH of the suspension is measured.
4. Significance and Use
4.1 The determination of contact pH can be used as a simple and fast measurement that can allow activated carbon producers
and users to have a standard method for assessing the effect various carbons will have on the initial pH of the water in contact with
the carbon. It has been determined that there is a bias between this method and Test Method D3838; they are not equivalent.
5. Interferences
5.1 pH electrodes used to measure this quantity can eventually become clogged over time with carbon fines. Suitable electrodes
can be found which have a detachable junction allowing the user, when necessary, to discard a fouled pH membrane.
5.2 Distilled water can become acidic on standing. Make sure that the water used meets the minimum requirements for ASTM
Type II water. Determine the pH as indicated in Test MethodMethods D1293.
This specification test method is under the jurisdiction of ASTM Committee D28 on Activated Carbon and is the direct responsibility of Subcommittee D28.02 on Liquid
Phase Evaluation.
Current edition approved Sept. 1, 2011Jan. 15, 2020. Published November 2011February 2020. Originally approved in 2002. Last previous edition approved in 20072011
as D6851 – 02 (2011). (2007). DOI: 10.1520/D6851-02R11.10.1520/D6851-20.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM 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.
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D6851 − 20
6. Apparatus
6.1 A pH meter (ambient temperature of 25 °C is assumed; if otherwise, temperature compensation is required for accurate pH
measurement.measurement).
6.2 A combination pH electrode, or glass-calomel electrodes used together.
6.3 A100 mLA 100-mL (TD) graduated cylindercylinder.
6.4 A250 mLA 250-mL glass beaker (for each sample)sample).
6.5 A polymer-coated magnetic stir bar (for each sample)sample).
6.6 Magnetic stir plateplate.
6.7 A balance capable of accurately measuring to 0.1 gg.
7. Reagents and Materials
7.1 Distilled or de-ionized water that meets the ASTM Type II requirementsrequirements.
7.2 Buffers to calibrate the pH meter; typically pH 4.0, pH 7.0, and/or pH 10.0pH 10.0, or combinations thereof.
8. Hazards
8.1 The water in contact with the carbon may have either a low or high pH. Take precautions accordingly and wear necessary
protective equipment to prevent injuries from spills and splashes.
9. Sampling, Test Specimens, and Test Units
9.1 Follow Practice E300 in the collection and preparation of samples.
10. Preparation of Apparatus
10.1 Use the procedure of Test Methods D1293 to standardize the pH meter before measurement.
11. Calibration and Standardization
11.1 See above section.
12. Conditioning
12.1 The sample should be tested as received.
13. Procedure
13.1 A representative sample should be taken from the quantity to be tested and prepared for testing (as received).
13.2 Ten (10) grams of sample (as received) will be used for the test. Place 10 g of a representative sample into a 250 mL
250-mL beaker.
13.3 The pH of the water to be used should be determined and recorded before use.
13.4 Using a graduated cylinder, measure and add 100 mL of water to the ten gram 10-g sample in the beaker.
13.5 Add one stir bar and stir for ten minutes10 min with sufficient turbulence to fluidize the sample in the beaker.
(Warning—Too vigorous stirr
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