16. 481 Solidification-stabilization

Ex-situ Process - Pozzolan/Portland Cement
The process consists primarily of silicates from pozzolanic-based materials like fly ash, kiln dust, pumice, or blast furnace slag and cement-based materials like Portland cement.
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System Design
No well established design protocol Select appropriate formulation Waste removal, transportation, storage Mixing Setting and curing Waste transportation
Ex-situ Process
Factors limit process: Environmental conditions Applicability may affect the long-term The target immobilization. contaminant group is Some increase the volume. inorganics, including Certain wastes are radionuclides. incompatible with different Limited effectiveness processes. against organics and Organics are generally not pesticides, except immobilized. vitrification which Long-term effectiveness destroys most has not been organic contaminants. demonstrated for many.
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Factors Affecting S/S Process
Particle size and shape Solid content (too watery?) Specific gravity (phase separation?) Wetting (add surfactant?) Mixing (over-mixing affects gel formation?) Temperature (release of steam, and break up the solid mass) Chemical (some can retard or accelerate setting and curing)
Pozzolanic and cement-based binding agents are typically appropriate for inorganic contaminants.
The effectiveness of this binding agent with organic contaminants varies.
These materials chemically react with water to form a solid cementious matrix. They also raise the pH of the water which may help precipitate and immobilize some heavy metal contaminants.
CE 481 - Solidification/Stabilization
Jeff Kuo, Ph.D., P.E jkuo@
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Introduction
Solidification/stabilization (S/S) reduces the mobility of hazardous contaminants through both physical and chemical means. S/S seeks to trap or immobilize contaminants within their "host" medium. Leachability testing is typically performed to measure the immobilization of contaminants. S/S techniques can be used alone or combined with other treatment methods to yield a product or material suitable for land disposal or, in other cases, that can be applied to beneficial use.
Immobilization Mechanisms
Chemical reactions

Precipitation Redox
Organic waste encapsulated in binder matrix.

Complexation
Adsorption Encapsulation

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Ex-situ Process
Bituminization The process combines heated bitumen and a concentrate of the waste material, usually in slurry form, in a heated extruder containing screws that mix the bitumen and waste. Water is evaporated from the mixture to about 0.5% moisture. Emulsified Asphalt Asphalt emulsions are very fine droplets of asphalt dispersed in water that are stabilized by chemical emulsifying agents. The process adds emulsified asphalts having the appropriate charge (cationic or anionic) to hydrophilic liquid or semi-liquid wastes at ambient temperature.
micro macro
Organic waste adsorbed 4 to an organophilic clay
Common S/S Systems
Organic system bitumen polymers organophilic clay Inorganic System cement-based pozzolanic lime sodium silicates
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Ex-situ Process
Modified Sulfur Cement A thermoplastic material, easily melted (127 to 149 °C) and then mixed with the waste. The relatively low T used limit emissions of sulfur dioxide and hydrogen sulfide t. Polyethylene Extrusion The process mixes PE binders and dry waste using a heated cylinder containing a screw. The process has been tested on nitrate salt wastes at plant-scale, establishing its viability, and on various other wastes at the bench and pilot scale. 9
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Introduction Objectives
Pocket penetrometer evaluating a stabilized waste.
Production of solid for liquid or semi-liquid Reduction of contaminant solubility (and toxicity) Decrease in the exposed area across which transfer may occur Solidification: Increase strength Decrease compressibility Decrease K Stabilization Convert the contaminants to their less toxic or least soluble form 3 Metal fixation
Cost Ex situ S/S processes are among the most mature remediation technologies.
Data from more than a dozen vendors indicate an approximate cost of under $110 per metric ton ($100 per ton), including excavation.
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Vitrification/Molten Glass Ex-situ Process The processes employ heat up to 1,200° C to convert Soluble Phosphates waste materials into glassy The process adds products. phosphate and alkali for The high T destroys any control of pH to complex organic constituents with metal molecules of lowvery few byproducts. Heavy solubility. metals and radionuclides, It does not convert the are incorporated into the waste into a hardened, glass structure which is, monolithic mass. One generally, a relatively strong, application is in durable material that is stabilizing fly ash by resistant to leaching. immobilizing the lead and cadmium in the ash. 11