Standard Guide for Use of Coal Combustion Products for Solidification/Stabilization of Inorganic Wastes

Importancia y uso:

4.1 General—CCPs can have chemical and mineralogical compositions that are conducive to use in the chemical stabilization of trace elements in wastes and wastewater. These elements include, but are not limited to, arsenic, barium, boron, cadmium, chromium, cobalt, lead, molybdenum, nickel, selenium, vanadium, and zinc. Chemical stabilization may be accompanied by solidification of the waste treated. Solidification is not a requirement for the stabilization of many trace elements, but does offer advantages in waste handling and in reduced permeability of the stabilized waste. This guide addresses the use of CCPs as a stabilizing agent with or without addition of other materials.

Note 1: In the United States, S/S is considered the BDAT for the disposal of some wastes that contain metals since they cannot be destroyed by other means (2).

4.1.1 Advantages of Using CCPs—Advantages of using CCPs for waste stabilization include their availability in high volumes, and generally good product consistency from a single source. In addition, in some instances certain CCPs can partly or entirely replace other expensive stabilization materials such as Portland cement. CCPs vary depending on the combustion or emission control process and the coal or sorbents used, or both, and CCPs contain trace elements, although usually at very low concentrations. CCPs are generally an environmentally suitable materials option for waste stabilization, but the compatibility of a specific CCP must be evaluated with individual wastes or wastewater through laboratory-scale tests followed by full-scale demonstration and verification. CCPs suitable for the chemical stabilization have the ability to incorporate large amounts of free water via hydration reactions. These same hydration reactions frequently result in the formation of mineral phases that stabilize or chemically immobilize the trace elements of concern. CCPs that exhibit high pHs (>11.5) offer advantages in stabilizing trace elements that exist as oxyanions in nature (such as arsenic, boron, chromium, molybdenum, selenium, and vanadium) and trace elements that form oxyhydroxides, carbonates or other low-solubility precipitates at high pH (such as cadmium, barium, nickel, and zinc).

4.2 Chemical/Mineralogical Composition—Since many CCPs are generated at higher temperature, reactions with water during contact with aqueous solutions can be expected. Mineral formation may contribute to the chemical stabilization and/or solidification achieved in the waste treatment process. One example of this type of chemical stabilization is achieved by ettringite formation. Reduced leachability of several trace elements has been correlated with ettringite formation in hydrated high-calcium CCPs typically from U.S. lignite and subbituminous coal, and dry FGD materials. These materials worthy candidates for use in this chemical stabilization process. Lower-calcium CCPs in presence of sulfate sources, may also be effective with the addition of a calcium source that maintains the pH above 11.5. Ettringite forms as a result of hydration of many high-calcium CCPs in presence of sulfate sources, so adequate water must be available for the reaction to occur. The mineral and amorphous phases of CCPs contribute soluble elements required for ettringite formation, and the ettringite formation rate can vary based on the mineral and amorphous phase compositions.

4.3 Regulatory Framework: 

4.3.1 Waste Management Framework—Waste stabilization activities most often occur within a regulatory waste management framework. This regulatory framework will generally establish minimum waste sampling and characterization requirements as well as establish documentation, qualification, and performance criteria for waste management activities. The framework may also prescribe or prohibit certain waste management practices. The applicable requirements of the regulatory framework may be formalized in a permit. This guide is intended to be applied within the context of a regulatory waste management framework.

Note 2: The U. S. regulatory framework is briefly described in Stabilization/Solidification of CERCLA and RCRA Wastes: Physical Tests, Chemical Testing Procedures, Technology Screening, and Field Activities (2).

4.3.2 Beneficial Use Framework—Beneficial use activities often occur within a regulatory framework. In some locations, new beneficial uses require prior regulatory approval as part of a beneficial use determination. Beneficial use determinations may require specific characterization of the material and the beneficial use. Jurisdictions that require approval of beneficial use may also maintain exemptions or predeterminations for certain materials or beneficial uses.

Subcomité:

E50.03

Referida por:

E3355-23

Volúmen:

11.06

Número ICS:

13.030.40 (Installations and equipment for waste disposal and treatment)

Palabras clave:

coal combustion products; inorganic waste; solidification; stabilization;