Testing and Performance Criteria for Stabilized/Solidified Waste Forms - Stabilization and Solidification of Hazardous, Radioactive, and Mixed Wastes - page 286

TABLE 11.1
Operating Parameters for BS EN 12457

Part 1 2 3 4

Particle size (mm) < 4 < 4 < 4 < 10

L/S ratio (l/kg) 2 10 2 + 8 10

Contact time (h) 24 24 6 + 18 24

11.2.2.1.8 Acid Neutralization Capacity (ANC)
The ANC test 3 is a measure of the ability of a material to neutralize acid. This is a
key variable for long-term material behavior, because it affects precipitation of
metals and maintenance of matrix physical integrity. 2 The test involves mixing
subsamples of a material with increasing quantities of mineral acid for 48 hours,
prior to measurement of leachate pH to obtain a titration plot. 2,3,15 Analysis of
contaminants in the leachate can be used to assess their availability at pH values of
interest. This approach is similar to that used in other availability tests, such as NEN
7341 16 and prEN 14429. 17
These availability tests are themselves agitated extraction tests. Although not
yet in common use, prEN 14429 has been developed from the ANC and NEN 7341
to investigate contaminant availability as a variable distinct from total contaminant
concentration. The test involves a 24-hour extraction of granular material at con-
trolled pH.
Modification of the ANC to use acetic acid, as a way of optimizing binder
addition to pass the TCLP, was proposed by Isenburg and Moore, 18 but is less useful
for understanding leaching behavior, in part due to the development of a buffer
system that alters the titration curve.

11.2.2.2 Sequential Chemical Extraction Tests

Increasingly aggressive leachants may be used to obtain information on the mech-
anisms of contaminant binding in a material. Most sequential chemical extraction
tests for metals are based on a method developed by Tessier et al., 19 which divides
the contaminants into five fractions: 1) ion-exchangeable, 2) bound to surface oxides
and carbonates, 3) bound to iron and manganese oxides, 4) bound to organics, and
5) residual. The test was originally proposed to examine respeciation of contaminants
due to treatment, but has fallen into disuse except as a research tool because of
concerns with the definition of speciation and reproducibility. 2

11.2.3 D YNAMIC T ESTS

Dynamic tests are not as commonly used as extraction tests. They can also be divided
into several categories. 6 The serial batch test, which is the most common type, and
flow-around and flow-through tests are briefly summarized below: