Stabilization of Wastes

Forrester Environmental Services, Inc., has developed a group of technologies for the stabilization of wastes containing heavy metals, such as lead, cadmium, arsenic, mercury, copper, zinc, and antimony. These technologies have been used in both industrial pollution prevention and remediation applications. One version of the technology involves the use of water-soluble phosphates and various complexing agents to produce a less soluble lead waste. This process results in a leach-resistant lead product. 

The radiation stability of waste forms is determined by changes in their structure, chemical,... 

Perret, D., Crovisier, J.-L. et al. 2003. Thermodynamic stability of waste glasses compared to leaching behaviour. Applied Geochemistry, 18, 1165-1184. 

Chemical stabilization of waste materials offers the potential to reduce the leachability of contaminants present in the waste. As shown in Fig. 1, it involves the conversion of the available fraction (or soluble species) of an element in a waste to an unavailable fraction (insoluble... 

Levine, H.S., "Conversion of Fuel Hulls to Zirconate Ion Exchanger for Stabilization of Wastes from the Thorium Fuel Cycle," Symposium on Waste Management and Fuel Cycles "78," Edited by R.G. Post and M.E. Wacks, Tucson, AZ, March (I978). 

Ashes and residues. These are the materials remaining from the burning of wood, coal, coke, and other combustible wastes. Residues from power plants normally are composed of fine powdery materials, cinders, clinkers, and small amounts of burned and partially burned materials. Fly ash from coal boilers and CKD (cement kiln dust) are frequently sold for stabilization of waste, waste bulking operations, and incorporation into building products such as gypsum from sulfur dioxide scrubbing. 

The variance in process conditions, rainfall contributions, and related considerations make equalization facilities for stabilization of waste flow and strength essential. 

The effectiveness of landfills aeration has been tested in various countries around the world both in Europe (Germany, Austria, Italy, the Netherlands, Switzerland), North America (USA) and Asia (Japan, Malaysia) for more than 20 years. Different technical solutions, which vary primarily in the method of oxygen supply to the landfill, have been used. The selection of a relevant solution depends mainly on the final intention of its application, landfill construction, available financial resources, and legislation. In Europe, aeration is usually applied as a method for an acceleration of old landfill stabilization, commenced when the landfill gas production becomes insufficient for profitable energy recovery. Such an activity shortens the period of the residual gas production. This gas is usually released to the atmosphere because of problems with its combustion. The accelerated stabilization of waste, by a few-week aeration, is also used as the initial phase preeeding of landfill mining. It allows to obtain an evident improvement in sanitary eonditions before the workers will enter. 

Sulfur polymer cement shows promise as an encapsulation and stabilization agent for use with low level radioactive and mixed wastes. Use of SPC allows accommodation of larger percentages of waste than PCC. As of this writing (1997), SPC-treated waste forms have met requirements of both the Nuclear Regulatory Commission (NRC) and the Environmental Protection Agency (EPA). 

The importance of the final settling, or humus, tank can be seen by an examination of what occurs in the trickling filter itself. A new filter is broken in by applying settled sewage as in the normal operation. After a period of time the microbial, or zoogleal, mass forms on the filter medium and stabilizes the waste. Waste material is first adsorbed, and then assimilated by the microorganisms. 

The complexers maybe tartrate, ethylenediaminetetraacetic acid (EDTA), tetrakis(2-hydroxypropyl)ethylenediamine, nittilotriacetic acid (NTA), or some other strong chelate. Numerous proprietary stabilizers, eg, sulfur compounds, nitrogen heterocycles, and cyanides (qv) are used (2,44). These formulated baths differ ia deposition rate, ease of waste treatment, stabiHty, bath life, copper color and ductiHty, operating temperature, and component concentration. Most have been developed for specific processes all deposit nearly pure copper metal. 

Copper etchants do not directly influence the electroless plating process, but are used merely to remove unwanted copper, and should not affect the deposit properties. The costs of waste treatment and disposal have led to disuse of throw-away systems such as chromic—sulfuric acid, ferric chloride, and ammonium persulfate. Newer types of regenerable etchants include cupric chloride, stabilized peroxide, and proprietary ammoniacal etchant baths. 

METALWORKING FLUID Fluid applied to a tool and workpieee to eool, lubrieate, earry away partieles of waste and provide eoiTosion proteetion. Generally eomprising neat mineral oils, or water-based materials, or a mixture of the two. Fluids may also eontain emulsifiers, stabilizers, bioeides, eoiTosion inhibitors, fragranees and extreme pressure additives. 

As a first step in the selection process, the applicability of the various solidification/ stabilization processes for specific contaminants can be determined using Table 12. Since these waste treatment systems vary widely in their applicability, cost, and pretreatment requirements, many are limited as to the types of waste that can be economically processed. Waste characteristics such as organic content, inorganic content, viscosity and... 

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. 

Tittlebaum, Marty E., Roger Seals, Frank Cartledge, Stephanie Engels, Louisiana State University. State of the Art on Stabilization of Hazardous Organic Liquid Wastes and Sludges. Critical Reviews in Environmental Control, Volume 15, Issue 2,1985. 

Comminution Shredding. A mechanical treatment process which cuts large pieces of waste into smaller pieces so that they won t plug pipes or damage equipment. Contact stabilization Contact stabilization is a modification of the conventional activated sludge process. In contact stabilization, two aeration tanks are used. One tank is for separate reaeration of the return sludge for at least four hours before it is permitted to flow into the other aeration tank to be mixed with the primary effluent requiring treatment. 

Waste management is a field that involves tlie reduction, stabilization, and ultimate disposal of waste. Waste reduction is tlie practice of minimizing file amount of material tliat requires disposal. Some of the common ways in which waste reduction is accomplished are incineration, compaction, and dewatering. The object of waste disposal is to isolate tlie material from tlie biosphere, and in the case of radioactive wtiste, allow it time to decay to sufficiently safe levels. 

Despite all the advantages of this process, one main limitation is the continuous catalyst carry-over by the products, with the need to deactivate it and to dispose of wastes. One way to optimize catalyst consumption and waste disposal was to operate the reaction in a biphasic system. The first difficulty was to choose a good solvent. N,N -Dialkylimidazolium chloroaluminate ionic liquids proved to be the best candidates. These can easily be prepared on an industrial scale, are liquid at the reaction temperature, and are very poorly miscible with the products. They play the roles both of the catalyst solvent and of the co-catalyst, and their Lewis acidities can be adjusted to obtain the best performances. The solubility of butene in these solvents is high enough to stabilize the active nickel species (Table 5.3-3), the nickel... 

As mentioned several times Lewis acids are highly valuable catalysts but the most commonly used ones such as aluminium chloride and boron trifluoride are highly water sensitive and are not usually recovered at the end of a reaction, leading to a significant source of waste. In recent years there has been much research interest in lanthanide triflates (trifluoro-methanesulfonates) as water stable, recyclable Lewis acid catalysts. This unusual water stability opens up the possibility for either carrying out reactions in water or using water to extract and recover the catalyst from the reaction medium. 

Reduction in VOC emissions Reduced user exposure to harmful materials Reduced hazardous production waste Possibly less expensive Stability of formulation at low temperatures Acceptability of drying rate Energy costs for drying Adequacy of corrosion resistance Wear properties High gloss properties Storage stability Water resistance... 

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