Leaching Processes and Evaluation Tests for Inorganic Constituent Release from Cement-Based Matrices - Stabilization and Solidification of Hazardous, Radioactive, and Mixed Wastes - page 261

tests (e.g., flow-through column tests and L/S ratio batch tests) to infer pore water
composition. Several researchers have used high pressures applied to cementitious
materials to extract pore solution at L/S ratios much below practical laboratory batch
extractions. 178,217-221
In order to relax solubility constraints (e.g., to measure availability of sparingly
soluble constituents), a higher L/S ratio or a shift in solution pH is required. Thus,
leaching tests used to measure release flux (e.g., ANSI/ANS-16.1, MT001.1) utilize
large L/S ratios, often specified on the basis of liquid-to-surface area ratios.

10.4.4.5 Open/Closed Systems

When tests are conducted in open containers, exchange between the atmosphere and
the test system (i.e., solid and liquid) may lead to ambiguous results. For example,
tank leaching in vessels that are not air-tight may lead to neutralization of the leachate
and precipitation on the solid specimen via carbonation. During equilibrium-based
testing, addition of acid aliquots to open vessels may alter the resultant equilibrium
by allowing the escape of evolved gases from acid-reactive solids (e.g., carbonated
S/S materials). Therefore, control and definition of the testing conditions are essential
to accurate interpretation of leach testing results.

10.5 LEACHING DATA PRESENTATION AND

INTERPRETATION

Data obtained from leaching tests must be presented and interpreted in the context
of the goal of each test and the applied testing conditions. Consistency should be
checked between (i) different equilibrium tests and (ii) concentrations in mass-
transport rate tests and pH-driven solubility limitations.

10.5.1 E QUILIBRIUM -B ASED T ESTS

Equilibrium-based data may be presented in terms of leachate concentration (mg/L)
(Figure 10.5a) or in terms of the amount of constituent released from the solid phase
(mg/kg) (Figure 10.5b). Release is calculated by multiplying the concentration by
the L/S ratio of the leaching test. Schematic test data for the following three extrac-
tion tests are compared:

1. Solubility/release data as a function of pH (solid line) as might result from

the SR003.1 or prEN 14429 protocols

2. Solubility/release data as a function of L/S ratio as determined from

sequential extractions for L/S 2 mL/g ( ) as might

result from EN 12457-3 protocol at natural pH (data shown for solubility-
limited release using open symbols and availability-limited release using
closed symbols)

, ● ) and L/S 8 ml/g ( ▫ ,

3. Available content, or potential leachable amount, determined at pH 4 (Δ)

as might be provided by AV001.1 or NEN 7341.