L/O/G/O
STABILIZATION AND SOLIDIFICATION
For Asso. Prof. Dr. Kajornsak Sopajaree
By
Miss Natthawadee Chantrawichaikun 550631031 Miss Ritthipond Laitun 550631042
253747 HAZARD WASTE MAN
INTRODUCTION
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Stabilization and solidification have been widely applied in the management of hazardous wastes.
the remediation of hazardous wastes sites
1
The technologies are being applied to
2
the treatment of contaminated land where large quantities of soil containing contaminants are encountered
3
the treatment of residue from other treatment process
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STABILIZATION
In general terms, stabilization is a process where additives are mixed with waste to minimize the rate of contaminant migration from the waste and to reduce the toxicity of the waste
SOLIDIFICATION
A process employing additives by which the physical nature of the waste (as measured by the engineering properties of strength, compressibility, and/or permeability) is altered during the process.
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OBJECTIVES
STABILI ZATION
SOLIDIFI CATION
Encompass both the reduction in waste toxicity and mobility as well as an improvement in the engineering properties of the stabilized material
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DEFINITIONS
STABILIZATION
To minimize the rate of contaminant migration into environment To reduce the level of toxicity
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DEFINITIONS
FIXATION
Improve the handling and physical characteristics of the waste Decrease the surface area across which transfer or loss of contaminants can occur Limit the solubility of any pollutants contained in the waste Reduce the toxicity of the contaminants
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DEFINITIONS
SOLIDIFICATION
Increase the strength Decrease the compressibility Text in here Decrease the permeability of the waste
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DEFINITIONS
The potential for contaminant loss from a stabilized mass is usually determined by leaching tests. Leaching is the process by which contaminants are transferred from a stabilized matrix to a liquid medium such as water.
During stabilization, certain contaminants may be destroyed such as by the dechlorination of chlorinate hydrocarbons. Other organics may disappear as a result of volatilization. However, the stabilization of inorganic contaminants that are already in their atomic form such as cadmium, lead, and other metals should mimic nature.
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DEFINITIONS
Stabilization must be considered as a waste treatment process that reduces, to an acceptable or geologically slow rate, the movement of contaminants into environment.
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REGULATIONS
It has been recognized that the disposal of liquid wastes in landfills is an environmentally unsound practice. Liquids migrate downward through the landfill, assist in the generation of leachate, and potentially migrate through defects in the liner system. As a consequence of the high mobility of liquid hazardous wastes, their disposal in landfills had been prohibited in the US. This ban has resulted in the increased use of stabilization in order to preclude disposal of liquid wastes. In this application, the stabilization agents must chemically bond the hazardous chemical in liquid wastes. The agents cannot act simply as absorbents (physically containing the liquids much the same way in which a sponge holds water).
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Land disposal
Solidification of industrial wastes
Site remediation
APPLICATIONS
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LAND DISPOSAL
The land disposal of liquid waste increases the likelihood of contaminant migration (and is currently banned under U.S. regulations.). Liquid waste, along with wet sludges, must be stabilized prior to landfilling. To effectively stabilized liquids, the stabilization agents cannot be absorbents (such as sawdust). The liquids absorbed by agents could be easily released (desorbed) in the landfill when compressed under additional loads. That is, as more material is landfilled, the weight of the overlying material would squeeze the liquids out of the underlying material. Therefore, the liquids must be chemically and physically bound by the stabilization reagents so that they are not expelled by the consolidation stress or leached out by the downward percolation of precipitation.
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SITE REMEDIATION
The remediation of contaminated sites having organic wastes, inorganic wastes, and/or contaminated soils may be accomplished employing stabilization technology. For site remediation, stabilization is used to 1. improve the handling and physical characteristics of the wastes, 2. decrease the rate of contaminant migration by decreasing the surface area across which the transfer of pollutants can occur and by limiting the solubility of pollutants, and 3. reduce the toxicity of certain contaminants.
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SITE REMEDIATION
Stabilization is particularly well suited for sites where the hazard involves large quantities of soils contaminated at low levels. In many instances it may not be environmentally sound nor cost-effective to excavate, transport, and landfill or incinerate soils contaminated with low levels of pollutants because of 1. the additional air pollution caused by excavation equipment, trucks, and the exposure of buried contaminated soils to the air, which enhances the volatilization of organics; and 2. the increased risks as a result of traffic accidents.
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SOLIDIFICATION OF INDUSTRIAL WASTE
Solidification (affecting of physical properties such as strength and compressibility) improves the engineering properties and may reduce the rate at which contaminants migrate into the environment. Although many of the hazardous waste materials may not endanger the public health or the environment, the materials are frequently structurally unstable, aesthetically unsuitable, and their condition precludes other uses of the sites area. Thus, the primary goal of solidification is the improvement of the structural integrity of the material.
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MECHANISMS
MACROENCAPSULATION MICROENCAPSULATION
ABSORPTION ADSORPTION
PRECIPITATION DETOXIFICATION
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MECHANISMS
MACROENCAPSULATION
Macroencapsulation is the mechanism by which hazardous waste constituents are physically entrapped in a larger structural matrix, that is, the hazardous waste constituents are held in discontinuous pores within the stabilizing materials. Upon physical degradation (breakdown) of the stabilized material, even to relatively large particle sizes, the entrapped materials are free to migrate. The stabilized mass may breakdown over time (as measured on a geologic time scale) due to imposed environmental stress. These stresses include such thing as repeated cycles of wetting and drying or freezing or thawing, introduction of percolating fluids, and physical loading stresses.
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MICROENCAPSULATION
In microencapsulation, hazardous waste constituents are entrapped within the crystalline structure of the solidified matrix at a microscopic level. As a result, even if the stabilized materials degrade into relatively small particle sizes, most of the stabilized hazardous wastes remains entrapped. However, as with macroencapsulation, because the waste is not chemically altered or bound, the rates of contaminant release from the stabilized mass may increase as the particle size decreases and more surface area is exposed.
MACROENCAP SULATION
This gives rise to a greater degree of macroencapsulation in the laboratory (a greater number of particles to be encapsulated) than in the field (fewer, but larger, particles to be encapsulated)
MICROENCAP SULATION
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ABSORPTION
Absorption is the process by which contaminants are taken into the sorbent in very much the same way a sponge takes on water. As applied in stabilization, absorption requires the addition of solid material (sorbent) to soak up or absorb the free liquids in the waste. The process is primarily employed to remove free liquid to improve the waste-handling characteristics, that is, to solidify the waste. The liquids are free to squeeze out of the material should the mass be subjected to consolidating stresses.
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THE MOST COMMON ABSORBENT
Soil Fly ash Cement Kiln dust Lime Kiln dust Clay minerals including bentonite, kaolinite, vermiculite, and zeolite Sawdust Hay and straw
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ADSORPTION
In addition to the physical entrapment within the stabilized and solidified mass described above, electrochemical interactions may occur. Adsorption is the phenomena by which contaminants are electrochemically boned to stabilizing agents within the matrix. These are typically considered surface phenomena and the nature of the bonding may be through van der Waals or hydrogen bonding. Contaminants that are chemically adsorbed (fixed) within the stabilized matrix are less likely to be release into the environment than those that are not fixed. Unlike microencapsulation and macroencapsulation, where simple particle breakdown may enhance the rate of contaminant migration, additional physicochemical stress is necessary to desorb the material from their adsorbing surfaces.
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ADSORPTION
The stabilization of organic wastes using organically modified clays illustrates how adsorption can be used in waste stabilization. Organically modified clays are clays which have been altered by replacing exchangeable inorganic cations adsorbed on the clay surfaces with long- chain organic cations, rendering the clays organophilic. Organophilic clays have an affinity for organic molecules. Without modification, naturally occurring clays are generally organophobic.
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ADSORPTION
Organic waste molecules are than adsorbed to the clay as show in Fig. 1. The adsorption bond strength must then be overcome if the organic waste molecules were to be released to migrate into the environment.
FIGURE 1 Organic waste adsorbed to an organophilic clay
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PRECIPITATION
Certain stabilization processes will precipitate contaminants from the waste resulting in a more stable form of the constituents within the waste. Precipitates such as hydroxides, sulfides, silicates, carbonates, and phosphates are than contained within the stabilized mass as part of the material structure. This phenomenon is applicable to the stabilization of inorganic wastes such as metal hydroxide sludges. For example, metal carbonates are typically less soluble than metal hydroxides. At high pH, the reaction to form a metal carbonate from a metal hydroxides sludge, is as follow: Me(OH)2 + H2CO3
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MeCO3(s) + 2H2O
Where Me represents a metallic cation
DETOXIFICATION
Certain chemical reactions taking place during the stabilization process may result in a waste with reduced toxicity. Detoxification is any mechanism that changes a chemical constituent into another constituent (or form of the same constituent) that is either less or non-toxic.
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TECHNOLOGY
Compartmentalized by types of additive
Binder >> to strength gain with stabilization Sorbent >> to retaining contaminants in the stabilized matrix
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TECHNOLOGY
Application of Table 11-2 depends on
Concentration of contaminant Quantity of reagent Synergistic effects of multiple contaminants and reagents
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CEMENT
Principal reagent portland cement
Portland cement made by
Firing a mixture of limestone and clay (or other silicate) in kiln at high Temp.
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CEMENT
Cement-based stabilization
Wastes materials + cement
Mixed
Adding water
Hydrat ion
crystalline structure consist of calcium alumino silicate
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CEMENT
Cement-based stabilization is best suited for inorganic waste especially for heavy metals High pH of cement, metals are retained in insolubility hydroxide / carbonate salt Hg is predominantly held by Physical Microencapsulation
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CEMENT
Organic contaminants interfere with the hydration process >> reduce strength,not easily to stabilized To reduce organic contaminants interfere with the hydration and enhance stabilization
Natural clays Vermiculite Soluble sodium silicate
Stabilization with cement utilization for fixing inorganic waste
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CEMENT
Advantages
1
2 Technology of cement is well known Materials costs are relatively low
3 Equipment and personnel readily available 4 Extensive dewatering of wet sludge
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CEMENT
Advantages
5
6 Process with sufficient water
Alkalinity of cement can neutralize acid waste
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CEMENT
Disadvantages
Sensitive of cement to the presence of certain contaminants that could retard or prohibit proper hydration and the resulting setting and hardening of the material
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POZZOLAND
Pozzoland can be react with lime and water to produce a cementitious material
Pozzolanic concrete Fly ash
ground Furnance slag
Cement kiln dust
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POZZOLAND
Stabilized materials
Soil like consistency Slow leaching Unburned carbon in fly ash may adsorb organic from waste
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POZZOLAND
Application
For organic and inorganic materials Heavy metals
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LIME
Calcium hydroxide Ca(OH)2 Added to raise the pH of acidity sludges with other reagents to provide the main stabilization reaction
Fly ash stabilization
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SOLUBLE SILICATE
Metals stabilization
Silica reagents are acidified to form a Monosilic Acid solution to which metal-bearing wastes are added Combination of liquid soluble silicate and cement
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ORGANICALLY MODIFIED CLAYS
Accomplished through the replacement of inorganic cation within clay crystalline mineralogical structure with organic cation (Quaternary Ammonium ions) Additional agents are added to provide shear strength and solidify
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MODIFIED LIME
For stabilization of organic waste Convert toxic organic wastes to an inert mass The process employs a calcium oxide-based reagent modified with stearic acid Heat and water-as-steam are giving off during reaction Wastes is converted to a dry water repellent quite strong, relatively impermeable to water
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Thermosetting Organic Polymer
Stabilized through an organic polymer
process that involves mixing of a monomer such as UF acts as a catalyst to form polymer materials a sponge-like trapping solid particles of HZW within the matrix Final waste product often dried and container prior to ultimate disposal
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Thermosetting Organic Polymer Advantages
General result are low density Small quantities of additives are required to solidify waste
Most application in
solidification of liquid Non-volatile Organic HZW
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Thermoplastic materials
Blending molten thermoplastic materials with waste at high Temp. When cooled typically containerized for ultimate disposal Attention for mixed waste
Waste that is both hazardous and radioactive
The waste stabilized is no longer considered hazardous
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Thermoplastic materials
Limitation
The presence of organic chemicals that act as solvent to the stabilizing thermoplastic materials
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VITRIFICATION
Melting and fusion of materials at 1600C Rapid cooling >>> non- crystalline, amorphous form Both an in situ technique and an in plant technique Waste more structurally stable with a reduced potential for contaminant migration into environmental
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In Situ Vitrification
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