(Solidification and Stabilization)
TECHNOLOGY DESCRIPTION:
In this solidification and stabilization process, pozzolanic materials react with polyvalent metal ions and other waste components to produce a chemically and physically stable solid material. Optional binders and reagents may include soluble silicates, carbonates, phosphates, and borates. The end product may be similar to a clay-like soil, depending on the characteristics of the raw waste and the properties desired in the end product.
The figure below illustrates the Chemfix Technologies, Inc. (Chemfix), process. Typically, the waste is first blended in a reaction vessel with pozzolanic materials that contain calcium hydroxide. This blend is then dispersed throughout an aqueous phase. The reagents react with one another and with toxic metal ions, forming both anionic and cationic metal complexes. Pozzolanics that accelerate and other reagents that precipitate metals can be added before or after the dry binder is initially mixed with the waste.
When a water soluble silicate reacts with the waste and the pozzolanic binder system, colloidal silicate gel strengths are increased within the binder-waste matrix, helping to bind polyvalent metal cations. A large percentage of the heavy metals become part of the calcium silicate and aluminate colloidal structures formed by the pozzolans and calcium hydroxide. Some of the metals, such as lead, adsorb to the surface of the pozzolanic structures. The entire pozzolanic matrix, when physically cured, decreases toxic metal mobility by reducing the incursion of leaching liquids into and out of the stabilized matrices.
WASTE APPLICABILITY:
This process is suitable for contaminated soils, sludges, ashes, and other solid wastes. The process is particularly applicable to electroplating sludges, electric arc furnace dust, heavy metal contaminated soils, oil field drilling muds and cuttings, municipal sewage sludges, and residuals from other treatment processes. This process effectively treats heavy metals, such as antimony, arsenic, lead, cadmium, hexavalent chromium, mercury, copper, and zinc. In addition, when combined with specialized binders and additives, this process can stabilize low-level nuclear wastes. With modifications, the system may be applied to wastes containing between 10 to 100 percent solids.
STATUS:
The solidification and stabilization process was accepted into the SITE Demonstration Program in 1988. The process was demonstrated in March 1989 at the Portable Equipment Salvage Company site in Clackamas, Oregon. The Technology Evaluation Report (EPA/540/5-89/011a) and the Applications Analysis Report (EPA/540/A5-89/011) are available from EPA.
In addition, several full-scale remediation projects have been completed since 1977, including a 1991 high solids CHEMSET® reagent protocol designed by Chemfix to treat 30,000 cubic yards of hexavalent chromium-contaminated, high solids waste. The average chromium level after treatment was less than 0.15 milligram per liter and met toxicity characteristic leaching procedure (TCLP) criteria. The final product permeability was less than 1 × 10-6 centimeters per second (cm/sec).
DEMONSTRATION RESULTS:
The demonstration yielded the following results:
The technology effectively reduced copper and lead concentrations in the wastes. The concentrations in the TCLP extracts from the treated wastes were 94 to 99 percent less than those from the untreated wastes. Total lead concentrations in the untreated waste approached 14 percent.
The volume of excavated waste material increased between 20 and 50 percent after treatment.
During the durability tests, the treated wastes showed little or no weight loss after 12 cycles of wetting and drying or freezing and thawing.
The unconfined compressive strength of the wastes varied between 27 and 307 pounds per square inch after 28 days. Hydraulic conductivity of the treated material ranged between 1 × 10-6 cm/sec and 6.4 × 10-7 cm/sec.
Air monitoring data suggest there was no significant volatilization of polychlorinated biphenyls during the treatment process.
Treatment costs were approximately $73 per ton, including mobilization, labor, reagents, and demobilization, but not disposal.
FOR FURTHER INFORMATION:
EPA PROJECT MANAGER:
Edwin Barth
U.S. EPA
National Risk Management Research Laboratory
26 West Martin Luther King Drive
Cincinnati, OH 45268
513-569-7669
Fax: 513-569-7585
TECHNOLOGY DEVELOPER CONTACT:
David Donaldson
Chemfix Technologies, Inc.
3500 North Causeway Boulevard
Suite 720
Metairie, LA 70002
504-831-3600
Fax: 504-833-4615