Testing and Performance Criteria for Stabilized/Solidified Waste Forms - Stabilization and Solidification of Hazardous, Radioactive, and Mixed Wastes - page 287

11.2.3.1 Serial Batch Tests

Serial batch tests are similar to agitated extraction tests, except that the leachant is
replaced after a specific time until the desired number of leaching periods have been
achieved. The temporal release of leachable constituents can be inferred by con-
structing an extraction profile using the data obtained. Typical tests are the multiple
extraction procedure (MEP) 20,21 and sequential batch extraction, 12,22-24 which give a
procedure for multiple extractions in addition to the single extraction method stated
earlier.

11.2.3.1.1 USEPA Multiple Extraction Procedure 20
The MEP test involves an initial extraction with acetic acid, which is intended to
simulate municipal solid waste leachate, and at least eight subsequent extractions
with an inorganic acid mixture (nitric and sulfuric acids) to simulate acid rain. The
MEP test starts with the EP-Tox test (see Section 11.2.2.1.2), which is run for 24
hours. After the 24-hour rotation period and filtration of the leachate, seven additional
extractions are performed on the solid phase of the sample captured on the filter.
The extraction fluid is a mixture of inorganic acids with pH 3.0 ± 0.2, which is
prepared in a similar manner as the SPLP leaching fluid (see Section 11.2.2.1.3).
During each subsequent extraction, the synthetic rain extraction fluid is added to the
waste at an L/S ratio of 20:1, and the mixture is rotated for 24 hours per extraction.
After each extraction, the final pH is measured, and the leachate is collected and
analyzed. If the concentration of any of the chemical constituents of concern
increases in the seventh and eighth extractions, the extraction must be repeated until
the concentration in the extract ceases to increase. This test is currently used for the
USEPA's delisting program.

11.2.3.1.2 ANSI/ANS-16.1-2003 21
The ANSI/ANS-16.1-2003 test uses a solid monolith of the waste form in a specific
geometric shape, typically a cylinder (but other shapes can be used). A sample
monolith with a known initial quantity of the contaminant is immersed quiescently
in deionized water, although repository groundwater or simulated groundwater is
encouraged, at a ratio of 10 for the leachant volume (cm 3 ) to monolith geometric
surface area (cm 2 ). The leachate is replaced with fresh leachant at specified times
(2 hours, 7 hours, 1 day, 2 days, 3 days, 4 days, 5 days, and optionally 19 days, 47
days, and 90 days) for the purpose of keeping the contaminant surface concentration
at or close to zero. This results in the maximum driving force into the leachant and
the maximum leach rate for a monolith in this quiescent leachant. The main purpose
is to approach the boundary conditions for the analytical solution of Fick's second
law for the special case of zero surface concentration with an initial condition of
even distribution in the monolith. This allows estimation of an effective diffusion
coefficient using Fick's second law. The negative logarithm of the average coefficient
is defined as the leachability index, a measure of performance for the leach resistance
of the waste form matrix. Using the negative logarithm minimizes the large error
bar for the effective diffusion coefficient usually found among samples of the same
matrix and gives a measure of performance, even if the data do not agree well with
the simple diffusion control behavior predicted by Fick's second law.