Hazardous waste stabilization

Albino V and others (1996) Potential application of Ettringite generating systems for hazardous waste stabilization. J Hazard Mater 51 241-252... 

Chapter 16 Applications of CBPCs to Hazardous Waste Stabilization... 

W. Pietsch, Size enlargement by agglomeration for solid waste treatment or minimization and for hazardous waste stabilization. Preprints 4th Pollution Prevention Topical Conference, Seattle, WA, USA, AIChE, New York, NY, USA (1993), 202-208. 

Size enlargement by agglomeration for solid waste treatment or minimization and for hazardous waste stabilization. 

Electrokinetics. Electrokinetics is a tested technology that has been used for over half a century to dewater and stabilize soils, and has recently been investigated for in situ use at hazardous waste sites (23). Primarily used for metals removal, the technology utilizes an electrical field to generate a flow and concentration gradient in porous and semiporous soils. 

Solidification/Stabilization technologies are techniques designed to be used as final waste treatment. A major role of these processes is posttreatment of residuals produced by other processes such as incineration or chemical treatment. In some cases, solidification/ stabilization processes can serve as the principal treatment of hazardous wastes for which other detoxification techniques are not appropriate. High volume, low toxicity wastes (such as contaminated soils) are an example of this application. 

Applicability Most hazardous waste slurried in water can be mixed directly with cement, and the suspended solids will be incorporated into the rigid matrices of the hardened concrete. This process is especially effective for waste with high levels of toxic metals since at the pH of the cement mixture, most multivalent cations are converted into insoluble hydroxides or carbonates. Metal ions also may be incorporated into the crystalline structure of the cement minerals that form. Materials in the waste (such as sulfides, asbestos, latex and solid plastic wastes) may actually increase the strength and stability of the waste concrete. It is also effective for high-volume, low-toxic, radioactive wastes. 

U.S. Environmental Protection Agency, "Handbook for Stabilization/ Solidification of Hazardous Wastes", EPA/540/2-86/001. 

Spent pickle liquor is considered a hazardous waste (K062) because it contains considerable residual acidity and high concentrations of dissolved iron salts. For example, spent pickle liquor and waste acid from the production of stainless steel is considered hazardous. The hazardous constituents in K062 are lead, nickel, and hexavalent chromium. Waste pickle liquor sludge generated by lime stabilization of spent pickle liquor is not considered hazardous unless it exhibits one or more of the characteristics of hazardous waste. An estimated 6 million tons of spent pickle liquor are generated annually in the U.S.1... 

Removal actions are short-term cleanup actions that usually address problems only at the surface of a site. They are conducted in response to an emergency situation (e.g., to avert an explosion, to clean up a hazardous waste spill, or to stabilize a site until a permanent remedy can be found). Removal actions are limited to 12 months duration or 2 million in expenditures, although in certain cases these limits may be extended. Removals may occur at any point in time after the PA has been conducted. 

Revegetation is a cost-effective method to stabilize the surface of hazardous waste disposal sites, especially when preceded by capping and grading. Revegetation decreases erosion by wind and water and contributes to the development of a naturally fertile and stable surface environment. It may be part of a long-term site reclamation project, or it may be used on a temporary or seasonal basis to stabilize intermediate cover surfaces at waste disposal sites. 

An example of the effects of waste settlement can be illustrated by a recent incident at a hazardous waste landfill facility in California.5 At this facility, waste settlement led to sliding of the waste, causing the standpipes (used to monitor secondary leachate collection sumps) to move 60-90 ft downslope in 1 day. Because there was a very low coefficient of friction between the primary liner and the geonet, the waste (which was deposited in a canyon) slid down the canyon. There was also a failure zone between the secondary liner and the clay. A two-dimensional slope stability analysis at the site indicated a factor of safety (FS) greater than 1. A three-dimensional slope stability analysis, however, showed that the safety factor had dropped below one. Three-dimensional slope stability analyses should therefore be considered with canyon and trench landfills. 

M.J. Cullinane, L.W. Jones and P. G. Malone, Handbook for Stabilization/Solidification of Hazardous Waste, EPA/540/2-86-001, USEPA, Risk Reduction Engineering Laboratory, Cincinati, OH, 1986. 

The liquid effluent, which consists of water from the evaporator/crystallizer used to produce the solid filter cake produced by the brine-recovery operation, should not pose a significant hazard to human health or to the environment. While the evaporator/crystallizer system has not been tested yet, the composition of the water and solid filter cake can be readily determined from an analysis of the SCWO liquid effluent. As shown in Table 5-10, the liquid effluent is essentially free of organics. The source of the chromium and nickel that were found in some of the effluents is generally believed to be corrosion products from the SCWO reactor components. These elevated levels of metals indicate that the solid filter cake will need to be treated (e.g., by stabilization) prior to disposal in a hazardous waste landfill. 7... 

Leo Weitzman received his Ph.D. in chemical engineering from Purdue University. He is a consultant with 30 years of experience in the development, design, permitting, and operation of equipment and facilities for treating hazardous wastes and remediation debris. Dr. Weitzman has extensive experience in the disposal of hazardous waste and contaminated materials by thermal treatment, chemical reaction, solvent extraction, biological treatment, and stabilization. He has published over 40 technical papers... 

Some of the most common stabilizing agents used in hazardous waste disposal are Portland cement, lime, fly ash, and cement kiln dust. Small quantities of hazardous wastes are disposed of by incineration, energy conversion, manufacture of fuels, or other practical applications. 

TABLE 1 Asphaltic Metals Stabilization (AMS) vs. Hazardous Waste Landfill Disposal (HWLD) Cost Comparison... 

Table 1 gives a cost comparison of asphaltic metals stabilization (AMS) versus hazardous waste landfill disposal (HWLD). The AMS eliminated 173.00/ton in state and county taxes. 

Ceramicrete is an ex situ stabilization technology that uses chemically bonded phosphate ceramics to stabilize low-level radioactive waste and hazardous waste containing radionuclides and heavy metals. The technology mixes phosphates with acidic solution, causing an exothermic reaction similar to that used in forming concrete. But while concrete is based on relatively weak hydrogen and van der Waals bonding, Ceramicrete uses a combination of ionic, covalenf and van der Waals bonds to stabilize contaminants. 

OTD estimated that cement stabilization would produce 2,080,600 yd of stabilized wastes that could not be delisted and would have to be stored as mixed waste. The Duratek vitrification system would generate 417,000 yd of waste that may meet criteria for delisting as hazardous wastes and could be stored as only radioactive wastes (D114432, Appendix A). 

Polymer-based stabilization/solidification (S/S) is a technology for the ex situ treatment of radioactive, mixed, and hazardous wastes. It is a process in which polymers are created within the waste matrix to solidify and physically immobilize the hazardous constituents of contaminated materials. The goal is to prevent the migration of contaminants into the environment by forming a solid mass. 

Stabilization/solidification is a proven technology for the in situ or ex situ treatment of certain hazardous wastes. It uses additives or processes to physically and/or chemically immobilize... 

Table 1 shows the vendor s cost comparison between the molecular bonding system technology and hazardous waste land filling. The data compares stabilization costs with transportation and disposal costs (D15306A, p. 3). 

The Stablex process is an ex situ hazardous waste fixation and solidification technology. This technology uses laboratory analyses to select appropriate physical and chemical treatment steps, followed by stabilization and solidification to produce an environmentally secure, nonleachable material. The final Stablex material is placed in landfill cells as a slurry so that it forms a monolith within the cell. 

Waste brine is considered a hazardous waste and requires off-site stabilization and disposal at an approved disposal facility. 

---