Environmental Engineering Reference
In-Depth Information
11.2.2
E XTRACTION T ESTS
Extraction tests are the most common tests and they have been subdivided by
Wastewater Technology Centre (WTC) 6 into several categories, of which agitated
and sequential chemical extraction tests are the most relevant for S/S materials.
11.2.2.1
Agitated Extraction Tests
An extraction test can be agitated to maintain a homogeneous mixture and promote
contact between the solid and the leachant, thereby accelerating attainment of steady
state conditions. To decrease physical barriers to mass transport, granular or crushed
samples are used with the leachant at a specified liquid-to-solid ratio (L/S). They
measure the chemical properties of the system and not the rate-limiting mechanisms.
The common agitated extraction tests include:
11.2.2.1.1 Toxicity Characteristic Leaching Procedure (TCLP) 8
The TCLP is a commonly used, standard, single-batch leaching test, which was devel-
oped by the United States Environmental Protection Agency (USEPA) as a rapid reg-
ulatory compliance test for determining whether or not a waste is suitable for disposal
in a landfill with municipal waste. Because of the presence of organic acids in this
scenario, the test uses acetic acid buffered to pH 4.93 (or 2.88) with sodium acetate, to
a maximum buffering capacity of 2 meq/g of wet waste, at an L/S of 20:1, for 18 hours.
The test has been criticized because it does not take into account the characteristics of
an S/S material, or management scenarios other than municipal waste landfill disposal.
The test is conducted on granular material and therefore does not give credit for
reduction in leachability due to production of a monolithic material. More importantly,
since the maximum buffering capacity is often exceeded by a cement-based solidified
material, the test conditions can result in an arbitrary final leachate pH. Since the final
leachate pH is critical for solubility of contaminants, a combination of tests that measure
contaminant solubility at different pHs is more informative.
11.2.2.1.2 Extraction Procedure Toxicity Test (EP-tox) 9
The EP-Tox was a USEPA regulatory compliance test, which was commonly used
until superseded by the TCLP. It is also a standard single-batch leaching test, which
uses 0.5N acetic acid to maintain the leachate at pH 5, with a maximum acid addition
of 2 meq/g of wet waste, at an L/S of 20:1 for 24 hours. The test makes provision
for testing of monolithic samples, but it also has the drawback that the final leachate
pH is arbitrary.
11.2.2.1.3 Synthetic Precipitation Leaching Procedure (SPLP) 10
The SPLP is a standard single-batch compliance test, which was developed as an
alternative to the TCLP for situations where disposal is outside municipal waste
landfills. It uses an acid mix containing sulfuric/nitric acid (60/40 w/w) for an initial
leachant pH of 4.2 or 5 at an L/S of 20:1, for 18 hours. In practice, applied to S/S
material, this initial leachant pH makes little difference to the final leachate pH,
which reflects that of the alkaline S/S material.
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