Leaching Processes and Evaluation Tests for Inorganic Constituent Release from Cement-Based Matrices - Stabilization and Solidification of Hazardous, Radioactive, and Mixed Wastes - page 230

10.4.1 Leaching Test Applications.............................................................. 244
10.4.2 Leaching Test Classification by Application ................................... 245
10.4.2.1 Screening Tests ................................................................. 245
10.4.2.2 Field Mimicking or Simulation Tests............................... 246
10.4.2.3 Intrinsic Property Tests ..................................................... 247
10.4.3 Leaching Tests by Procedural Groups............................................. 248
10.4.3.1 Equilibrium Tests .............................................................. 248
10.4.3.2 Mass-Transport Rate Tests ............................................... 255
10.4.4 Variables Affecting Leaching Test Results...................................... 258
10.4.4.1 Leachant Composition ...................................................... 259
10.4.4.2 pH Control ........................................................................ 259
10.4.4.3 Particle-Size/Contact Time ............................................... 259
10.4.4.4 Liquid-to-Solid Ratio........................................................ 260
10.4.4.5 Open/Closed Systems ....................................................... 261
10.5 Leaching Data Presentation and Interpretation ........................................... 261
10.5.1 Equilibrium-Based Tests .................................................................. 261
10.5.2 Mass-Transport Tests ....................................................................... 262
10.5.2.1 Diffusivity in Reactive Media .......................................... 263
10.5.2.2 Regression of Diffusivity from Leaching Data................ 264
10.5.2.3 Changes in Mass-Transport Behavior .............................. 265
10.6 Leaching Test Selection ............................................................................... 266
10.6.1 Leachate-Controlled Monofill Example .......................................... 266
10.6.2 Uncontrolled Near-Surface Placement ............................................ 267
References.............................................................................................................. 268

10.1 INTRODUCTION

The earliest waste treatment techniques similar to current stabilization/solidification
(S/S) processes were descended from industrial practices and aimed at improving
the handling of industrial and radioactive process waste sludge through dewatering
and encapsulating the waste in a cementitious matrix. 1,2 Leaching performance and
environmental impact were rarely considered until the advent of environmental
regulations in the early 1970s.
Specific to S/S wastes, the primary goal of leaching characterization is to esti-
mate environmental impact under assumed release conditions. Secondary goals may
be to develop more effective treatment recipes, evaluate the efficacy of a selected
treatment process, or meet waste acceptance criteria for disposal. At some phase of
the treatment development and disposal or utilization process, S/S waste forms are
typically subjected to one or more leaching tests in order to predict environmental
impact of trace contaminants (e.g., heavy metals, organics, pesticides, radionuclides).
However, the development of S/S treatment recipes durable enough for long-term
waste containment demands that additional attention be paid to major matrix com-
ponents (e.g., calcium, hydroxide, aluminum), as well as infiltration of environmental
components affecting the durability of the waste material (e.g., acids, carbon dioxide,
sulfate or chloride ions, chelating agents).