Controlling mechanisms of metals release form cement-based waste form in acetic acid solution

Thesis/Dissertation · Tue Jan 01 04:00:00 EST 1991

OSTI ID:5121071

Cheng, Kuang Ye

The purpose of this dissertation is to identify the individual leaching mechanisms of metals by knowing the pH profile within the leached specimen and the physical and chemical properties of the leached material. Leaching of cement-based waste form in acetic acid solutions with different acidic strengths has been investigated in this work. The pH profile along the acid penetration route in the cement-based waste form was identified by various pH color indicators. The pH in the surface altered layer varies from 5.0 to 6.0, which is very close to the pH in the bulk leachate. A reacting zone, where the pH abruptly changes from 6 to 12, sharply divides the altered surface layer from the remaining unleached waste form or kernel. Leaching of metals is controlled by the acidity available in the leachant. Dissolution of alkaline materials leaves a silica-rich layer on the surface of the cement-based waste form. This surface layer exhibits different properties than those of the unleached material. The surface layer has a higher water content, is lighter weight, and is soft and friable. Furthermore, the abundant silicate content on the solid surface detains portion of the leached metals, while they are moving through the leached layer into bulk solution. The leaching of metals is a consequence of acid penetration. The distance from the solid/solution interface to the front of the leaching boundary can be regarded as the depth of leaching zone, where the metals dissolve and diffuse out of the waste form. The metal ions diffuse through the leached layer may be retarded on the solid surface by the pH-dependent adsorption reactions. It is found that the leaching process through the leached layer is diffusion-controlled for calcium and cadmium, whereas diffusion and adsorption occur simultaneously in the leached layer for lead and arsenic.

• Research Organization: Cincinnati Univ., OH (United States)
• OSTI ID: 5121071
• Country of Publication: United States
• Language: English

Related Subjects

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12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
54 ENVIRONMENTAL SCIENCES
540220* -- Environment
Terrestrial-- Chemicals Monitoring & Transport-- (1990-)
ACETIC ACID
ADSORPTION
ARSENIC
BUILDING MATERIALS
CARBOXYLIC ACIDS
CEMENTS
CHEMICAL PROPERTIES
DISPERSIONS
DISSOLUTION
ELEMENTS
LEACHATES
LEACHING
LEAD
MANAGEMENT
MATERIALS
METALS
MIXTURES
MONOCARBOXYLIC ACIDS
ORGANIC ACIDS
ORGANIC COMPOUNDS
PH VALUE
PHYSICAL PROPERTIES
SEMIMETALS
SEPARATION PROCESSES
SOLUTIONS
SORPTION
WASTE DISPOSAL
WASTE FORMS
WASTE MANAGEMENT