ASTM D6385-99 Test for Determining Acid-Extractable Content in Activated Carbon by Ashing

Scope:

ASTM D6385-99 test method is used to quantitatively determine extractable acid content, used in evaluating activated carbon samples containing soluble acid impurities. These soluble acid impurities can affect applications of activated carbon. Hydrochloric acid is used in this test method as the extracting acid. All elements or compounds present in the activated carbon sample, which can be acid extracted, are assumed to form water-soluble chloride salts. Hydrochloric acid may not solubilize all impurities of activated carbon.

Test Procedure:

The percent acid extractable content of an activated carbon sample is determined by the difference between the percent mass of total ash of a sample and the percent mass of total ash of a sample that has been acid extracted. A representative sample is ground or milled so that 95 % or more of the sampled mass passes through a No. 325 U.S. mesh screen.  The total ash content of the screened sample is determined. Sufficient dried activated carbon is weighed so that the estimated amount of ash will be at least 0.1 g.

Quantitatively the sample is transferred to a 250 ml beaker. Reagents are added to the carbon in the beaker in the following order: 100 ml of water, then 25 ml of concentrated hydrochloric acid is slowly added. The beaker is stirred to wet the sample thoroughly. The beaker and contents are boiled on a hot plate for at least 5 min. A watch glass covers the beaker while the carbon acid-water mixture is boiling. After boiling, the beaker is allowed to cool.

The mixture is vacuum filtered through the 7 cm filter funnel with hardened filter paper in place. The carbon retained on the filter paper is washed with several portions of water to thoroughly remove all acid residue. The Filtrate is discarded unless analysis of acid-soluble components in this extract is desired. The filter, filter paper, and carbon are transferred into an oven and dried for 30 min at 150°C. This allows easy separation of the paper and carbon from the Buchner filter. Quantitatively the paper and carbon are transferred to a tared crucible. The ash content of the dried, acid extracted carbon is determined using the mass of the carbon sample. The carbon and paper are ashed thoroughly using a suitable muffle furnace at 650°C.

Specimen Size: 

The samples should be dried to a constant weight before the test. If the sample cannot be dried, the percent moisture should be determined, and the appropriate correction to the sample weight should be made. 

Data: 
The extractable acid content is reported