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Waste materials in Geon environmental applications


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Waste materials in Geon environmental applications

  1. 1. National Conference on Recent Advances in Ground Improvement Techniques February 24-25, 2011, CBRI Roorkee, India Waste Materials in Geoenvironmental Applications Naveen, B.P.a, Anil Kumar Sharmaa, Sivapullaiah, P. Vb. and Sitharam, T. G.b a Research Scholar, Department of Civil Engg., IISc, Bangalore-560012, India. b Professor, Department of Civil Engg., IISc, Bangalore-560012, India. ABSTRACT Large quantities of waste materials are generated in the industrial world. Land and ground water contamination is a serious issue associated with the disposal of various waste materials. Further the disposal of most of the huge quantities of waste materials requires considerable land space. Use of these materials not only overcomes their disposal problems but also achieves economy. Some of the prominent industrial waste materials are fly ash, blast furnace slag, red mud, organically modified clays etc. The present paper describes the various approaches to use these materials for ground improvement. The mechanical improvement in the soil properties is described in this paper. To overcome the environmental concerns various methods to tests the stabilized materials by appropriate leaching tests have to be performed. Keywords: Solidification/Stabilization, Waste materials, Fly ash, Physical tests, leaching tests 1. INTRODUCTION 1.1 General Although there has been concern about land pollution since the onset of industrialization, this has been restricted to a relatively limited number of people. Consequently, until recently, land has not been seen as deserving protection to the same extent as air or water, but now it is recognized that land pollution cannot continue unabated. The recognition has risen because of incidents of contamination, the scarcity of usable land and increased general concern about the effect of industrial activity on the environment. Many technologies being considered for treating hazardous waste may produce residues still requiring management. In many cases, land disposal will be the only option available for these residues, which may be concentrated with toxic contaminants. In addition, waste banned from land disposal must be manageable by an alternative technology. If not, land disposal may still be the only option available. Pretreatment of banned waste may also help make it more acceptable for land disposal. Use of the waste materials is big option in finding solution to this problem. 1.2 Ground Improvement Methods Solidification/stabilization (S/S) is being considered as a technology available for treating selected waste prior to landfill. It is also being considered for treating residues from other treatment technologies. S/S technology has been used for approximately 20 years to manage industrial waste. S/S employs selected materials (e.g., Portland cement, fly ash, lime, etc.) to alter the physical and chemical characteristics of the waste stream prior to disposal in the 155
  2. 2. land. The goal of the S/S process is to limit the spread, via leaching, of contaminated material. The end product resulting from the solidification process is a monolithic block of waste with high structural integrity. Types of solidifying/stabilizing agents include the following: Portland; gypsum; modified sulfur cement, consisting of elemental sulfur and hydrocarbon polymers; and grout, consisting of cement and other dry materials, such as acceptable fly ash or blast furnace slag. Processes utilizing modified sulfur cement are typically performed ex situ. 2. STABILIZATION TECHNOLOGIES USING WASTE MATERIALS 2.1 Fly ash The disposal of fly ash is becoming more expensive each year due to large land needs for its disposal .The best way to solve the disposal problem fly ash is to decrease the quantity for disposal with the utilization of fly ash in the industry. Fly ash has been increasingly utilized in construction application, such as fills, concrete, pavements, wastewater treatment, landfill barrier material, grouts and others. Protecting the environment from hazardous pollutants associated with waste generation and disposal is a major concern in today’s heavily industrialized world. Thus far, various technologies have been developed which transform hazardous wastes to nontoxic, or reduce the potential release of toxic species into the environment. One such promising technology is stabilization/solidification (S/S) of solid wastes by means of adding cementitious binders, like lime and cement (Conner, 1990). During S/S applications, the toxic constituents present in the waste form are physically as well as chemically ‘‘fixed’’, that is, their mobility is significantly reduced so as to minimize the threat to the environment and also ensure compliance with existing regulatory standards. Moreover, the stabilized wastes may attain adequate stress-strain properties to enable their utilization in construction applications, such as engineering fill, road or pavement sub grade, backfill, and base material. Fly ash can be added to wastes (coarse-grained) in order to increase the available pozzolanic surface area, and hence improve one or all of the following properties of the waste mixture (1) Strength (2) Workability (3) Buffering capacity (capacity to resist pH changes) (4) Heavy metal leachability. 156
  3. 3. The addition of fly ash during the quicklime– sulfate S/S treatment results in a high strength, swell-resistant monolithic solid, attaining levels of strength similar to those of concrete products. With respect to heavy metal release, the addition of fly ash was directly responsible for the effective immobilization of both lead and hexavalent chromium, whereas it further enhances trivalent chromium immobilization. 2.2 Ground granulated blast-furnace slag (GGBS) Blast-furnace slag is produced as a by-product of the iron and steel production industries. Its earthy constituents come from iron ore processing, and it consists of the same oxides as Portland cement, but in different proportions. Immediately after its production, slag is usually quenched for rapid cooling in a process known as granulation. The granulation results in a reactive amorphous glass and avoids any crystallization. Like Portland cement, blast-furnace slag also reacts with water (i.e. is hydrated) to form specific hydrated calcium silicates known as tobermorite gels. However, unlike basic Portland cement, it forms this critical cementing agent (tobermorite gel) by consuming the slaked lime, Ca(OH)2 provided by the hydration of the Portland cement. Removal of some of the slaked lime is advantageous, since less of it in the waste form will lead to less dissolution of the lime over time, and thus consequently less long-term waste from degradation. In addition, there will be less slaked lime available to potentially react with salts, and thus produce undesired expansive and destructive minerals in the future. 2.3 Red mud Red mud is a solid waste product of the Bayer process, the principal industrial means of refining bauxite in order to provide alumina as raw material for the electrolysis of aluminium by the Hall–Héroult process. A typical plant produces one to two times as much red mud as alumina. This ratio is dependent on the type of bauxite used in the refining process. Red mud is composed of a mixture of solid and metallic oxide-bearing impurities, and presents one of the aluminium industry's most important disposal problems. The red colour is caused by the oxidized iron present, which can make up to 60% of the mass of the red mud. In addition to iron, the other dominant particles include silica, unleached residual aluminium, and oxide. This waste material has a reddish-brown color and a superfine particle size distribution. Alkalis, iron oxides and hydroxides, aluminum hydroxides, calcium carbonate, titanium, and silica form its chemical composition. The addition of Red Mud (RM) and Cement-Red Mud (CRM) increases the unconfined compressive strengths of composite samples. Both RM and 157
  4. 4. CRM additives plays (Kalkan, 2006) an important role at the Atterberg limits. The addition of these additives changed the soil groups from high-plasticity soil group (CH) to lowplasticity soil group (MH).In the same compaction effort, the γd max and wopt values of composite samples increases by adding RM and CRM. Also, the addition of RM and CRM decreased the void ratio values of composite samples due to increasing the γd,max of composite samples. 2.4 Organically modified clays Organically modified clays have been recently employed in conjunction with other stabilization reagents in order to entrap the organic portion of the waste to be stabilized. Organically modified clays are produced when natural clays are organically modified to become organophilic. This characteristic is in contrast to their organophobic nature. The modification process is accomplished through the replacement of inorganic cations within the clay crystalline mineralogical structure with organic cations, typically Quaternary ammonium ions. After this replacement process, organic molecules are adsorbed within the crystalline structure of the clay, which then swells in the presence of organic contaminants. In the production of organically modified clay, the exchangeable inorganic cations in the intercrystalline region are replaced with organic cations. The result is a nearly identical clay structure where organic cations occupy the inter-crystalline region. Organophilic clays typically are added to the waste first and allowed to interact with the organic components. Additional agents are added to provide shear strength and solidify the material into a monolithic mass. Several materials have been investigated for use as organic sorbents for s/s systems. These include metal oxides, clays, natural materials (peat moss, natural zeolites, vermiculite, etc.), synthetic materials (zeolites, fly ash, organic polymers, etc.), and activated carbon. Most current research has focused on organophilic clays. These are typically bentonite or montmorillonite clays in which tetra-alkyl ammonium compounds are substituted between the clay layers to increase the inter-lamellar spacing and enhance the adsorption of organic molecules. Initial results indicate that these modified clays may be useful for immobilization of certain organic compounds, but not for others. The organophilic bentonites are prepared by replacing the exchangeable inorganic cations present in bentonite particles with a quaternary ammonium salt. Various clay-to-soil ratios were applied to determine the efficiency of the modified bentonite in enhancing the cement-based s/s of BTEX contaminated soils. The findings of this study by Gitipour et al. (1997) reveal that organophilic bentonite can act as a successful adsorbent for removing the aromatic organics 158
  5. 5. from contaminated soils. Thus, this material is viable for enhancing the performance of cement-based s/s processes, as an adsorbent for petroleum spills, and for landfill liners and slurry walls. Organophilic clays have been shown to play a significant role in removing contaminants from liquid wastes (Boyd et al. 1988b; Smith et al. 1990) concluded from their study that modified clays are recommended for use as stabilizing agents at sites contaminated with aromatic wastes. 2.5 Asphalt emulsions Asphalt emulsions are very fine droplets of asphalt dispersed in water that are stabilized by chemical emulsifying agents like detergents. The emulsions are available as either cationic or anionic emulsions. The emulsified asphalt process involves adding emulsified asphalts having the appropriate charge to hydrophilic liquid or semi-liquid wastes at ambient temperature. After mixing, the emulsion breaks, the water in the waste is released, and the organic phase forms a continuous matrix of hydrophobic asphalt around the waste solids. In some cases, additional neutralizing agents, such as lime or gypsum, may be required. After sufficient time to set and cure, the waste is uniformly distributed throughout the resulting solid asphalt, which is impermeable to water. 3. PROMINENT USES AFTER SOLIDIFICATION/STABILIZING S/S-treated soil, sediment, and sludge are often reused. Most frequently this occurs on a property that is being cleaned up. Reusing treated material on-site, rather than hauling it away and bringing in new material, protects the surrounding community from the hazards posed by increased truck traffic, truck noise, air pollution, and damage to roadways. Some of the most prominent uses are: 1.Provides an excellent base for pavement placed over the entire site. 2.Used as structural fill. 3.Port redevelopment. 4.Reuse of treated material saved developers significant cost while providing for site Re-development that is protective of human health and the environment. Some the examples of the S/S technology are as follows: 1.Former Wood Treating Facility, Port Newark, New Jersey 159
  6. 6. 2.Re-Use of New York Harbor Sediments. 3.Hercules 009 Landfill Superfund Site, Brunswick, Ga. 3.1 Alternate to stabilize soil Stabilization converts hazardous elements into less soluble, mobile or toxic forms. Mixing the right combination of binding reagents into contaminated soils allows them to be either excavated and disposed of in a landfill, or re-used on site to support redevelopment. The solidification treatment has the further benefit of improving the structural properties of the site as well. The improved compressive strength of this type of soil treatment versus other treatment methods, can serve to improve the site conditions for development in addition to treating the contamination. 3.2 Efficiency of solidification and arrest of contaminant Solidification/stabilization (S/S) treatment does not generally result in a reduction of the total concentration of hazardous constituents (contaminants) in a treated material. S/S protects human health and the environment by immobilizing hazardous constituents within the treated material. Protection is achieved by preventing migration of hazardous constituent to human and environmental receptors. Contrast that with "dig and dump" remedies that merely move the hazardous constituents to another place. S/S fits into a risk-based remedy decision. Further, an in-situ remedy lowers risks to surrounding communities since less excavation is involved. S/S can treat a very broad group of hazardous constituents, both inorganic and organic. Most other remediation treatment technologies cannot. This lowers cost of the remediation of properties. Protective remedies at a lower cost conserve resources that can be applied to other sites. More sites remediated means greater overall protection of human health and the environment. 4.PHYSICAL AND CHEMICAL TESTS Most S/S projects require treatability studies and final performance testing of the treated contaminated material. These tests can be placed into two groups: physical and chemical. Physical tests are conducted to characterize and contrast waste before and after solidification/stabilization. It provides basic information on the treatability of the waste material and allows some estimate to be made of the cost of waste treatment and handling. Physical property characterization of unstabilised/unsolidified wastes focuses on treatability, excavation, transport, storage and mixing 160 considerations. Physical testing of
  7. 7. stabilized/solidified wastes helps to demonstrate the relative success or failure of a stabilization/solidification process. 4.1 Physical Tests The commonly specified physical tests in project performance standards include: 1. The Paint Filter Test (pass/fail), (USEPA Method 9095-SW846) -5 2. Hydraulic conductivity (<1X10 cm/sec),(EPA Method 9100-SW846) 3. Unconfined compressive strength (0.34 MPa (>50 psi)).ASTM D2166-85) 4. Atterberg Limit test(ASTM D4318-84) 5. Suspended Solids(USEPA Method 208C) 4.1.1 Paint Filter Test), (USEPA Method 9095-SW846) This method is used to determine the presence of free liquids in a representative sample of waste. A predetermined amount of material is placed in a paint filter. If any portion of the material passes through and drops from the filter within the 5-min test period, the material is deemed to contain free liquids. 4.1.2 Hydraulic conductivity,(EPA Method 9100-SW846) Hydraulic conductivity is one of the hydraulic properties of the soil; the other involves the soil's fluid retention characteristics. These properties determine the behavior of the soil fluid within the soil system under specified conditions. More specifically, the hydraulic conductivity determines the ability of the soil fluid to flow through the soil matrix system under a specified hydraulic gradient; the soil fluid retention characteristics determine the ability of the soil system to retain the soil fluid under a specified pressure condition. The -5 Hydraulic conductivity should be (<1X10 cm/sec) 4.1.3 Unconfined compressive strength , (ASTM D2166-85) This test method covers the determination of the unconfined compressive strength of cohesive soil in the intact, remolded, or reconstituted condition, using strain-controlled application of the axial load. This test method provides an approximate value of the strength of cohesive soils in terms of total stresses. This test method is applicable only to cohesive materials which will not expel or bleed water (water expelled from the soil due to deformation or compaction) during the loading portion of the test and which will retain intrinsic strength after removal of confining pressures, such as clays or cemented soils. Dry and crumbly soils, fissured or varved materials, silts, peats, and sands cannot be tested with 161
  8. 8. this method to obtain valid unconfined compression strength values. The UC strength value should be 0.34 MPa (>50 psi). 4.1.4 Atterberg Limit test, (ASTM D4318-84) These test methods are used as an integral part of several engineering classification systems to characterize the fine-grained fractions of soils and to specify the fine-grained fraction of construction materials .The liquid limit, plastic limit, and plasticity index of soils are also used extensively, either individually or together, with other soil properties to correlate with engineering behavior such as compressibility, hydraulic conductivity (permeability), compactibility, shrink-swell, and shear strength. 4.1.5 Suspended Solids(USEPA Method 208C) A well-mixed sample is filtered through a weighed standard glass-fiber filter and the residue retained on the filter is dried to a constant weight at 103 to 105°C. The increase in weight of the filter represents the total suspended solids. If the suspended material clogs the filter and prolongs filtration, it may be necessary to increase the diameter of the filter or decrease the sample volume. To obtain an estimate of total suspended solids, calculate the difference between total dissolved solids and total solids. One must know the suspended solid of the supernatants. 4.2 Chemical Tests (Leaching tests) Chemical tests are more devoted to leaching tests which are used to compare the effectiveness of various stabilization/solidification processes. A simple definition of leaching is the transfer of a substance or compound from a solid to a liquid phase when the two are in contact. It is a complex phenomenon and occurs in nature as a result of physical and chemical weathering processes involving the interaction between a soil or rock and water. Chemical tests are more often used to evaluate the performance of Solidification/Stabilization as a treatment process for hazardous waste. 1. The TCLP: Toxicity Characteristic Leaching Procedure 2. Extraction procedure(EP) Toxicity test Method 3. Equilibrium leach test 4. Acid Neutralization capacity 4.2.1 Toxicity Characteristic Leaching Procedure(The TCLP)(Federal Register 1986) 162
  9. 9. The TCLP, or Toxicity Characteristic Leaching (not Leachate) Procedure is designed to determine the mobility of both organic and inorganic analytes present in liquid, solid, and multiphasic wastes. This is usually used to determine if a waste may meet the definition of EP Toxicity, that is, carrying a hazardous waste code under RCRA (40 CFR Part 261) of D004 through D052. As it is the generator's responsibility to make this determination, but generators often contract outside labs to perform the TCLP test, these questions and answers may be helpful to generators. For this reason and sometimes in cleanup actions, businesses are often asked to perform an analysis on their waste using the TCLP. 4.2.2 Extraction procedure Toxicity (EP Tox) test Method(USEPA 1986) This method is used to determine whether a waste exhibits the characteristic of Extraction Procedure Toxicity. The procedure may also be used to simulate the leaching which a waste may undergo if disposed of in a sanitary landfill. Method 1310 is applicable to liquid, solid, and multiphase samples. 4.2.3 Equilibrium leach test (Environment Canada and Alberta Environmental Centre (1986) This leach test involves static leaching of hazardous constituents in distilled water.The particle size of the crushed sample is much smaller than that of TCLP and EP Tox to allow greater contact surface area and to reduce the time needed to achieve equilibrium conditions. 4.2.4 Acid Neutralization capacity (Environment Canada and Alberta Environmental Centre (1986) Acid-neutralizing capacity or ANC in short is a measure for the overall buffering capacity against acidification for a solution, e.g. surface water or soil water.ANC is defined as the difference between cations of strong bases and anions of strong acids (see below), or dynamically as the amount of acid needed to change the pH value from the sample's value to a chosen different value. [1] The concepts alkalinity are nowadays often used as a synonym to positive ANC and similarly acidity is often used to mean negative ANC. Alkalinity and acidity however also have definitions based on an experimental setup (titration). 5. CONCLUSIONS The paper describes various types of materials to improve the geotechnical behavior of soils. Apart from greatly enhancing the properties of soils, the use of waste materials can greatly reduce the disposal problems and consequent land and ground water contamination problems. 163
  10. 10. The mechanical and leaching concerns can be checked with appropriate physical and chemical test. REFERENCES 1. American Society of Testing for Materials (2001). “Standard Test Method for Determining the Resistance of Solid Wastes to Freezing and Thawing”,. American Society of Testing for Materials ASTM D4842-90. 2. Boyd, S.A., Lee, J.F. and Mortland, M.M. (1988a) Attenuating organic contaminant mobility by soil modification. Nature, 333, 345–347 3. Carlton C. Wiles. “A review of solidification/stabilization technology”, Journal of Hazardous Materials, 14 (1987) 5-2, Elsevier Science Publishers B.V., Amsterdam. 4. Carlton C. Wiles. “a review of solidification/stabilization technology”, Journal of Hazardous Materials, 14 (1987) 5-2 Elsevier Science Publishers B.V., Amsterdam. 5. Conner, J.R. and Hoeffner, S.L. (1998). “Critical review of stabilisation/solidification technology”. Crit. Rev. Environ.Sci. Technol., 28 (4), 397–462. 6. Dimitris Dermatas, Xiaoguang Meng, “Utilization of fly ash for stabilization/solidification of heavy metal contaminated soils”, Engineering Geology 70 (2003) 377–394. 7. Ekrem Kalkan, “Utilization of red mud as a stabilization material for the preparation of clay liners”, Engineering Geology 87 (2006) 220–229. 8. Environment Agency, “Review of scientific literature on the use of stabilization/solidification for the treatment of contaminated soil, solid waste and sludges (2004) Science Report SC980003/SR2. 9. Gitipour, S., Bowers, M.T. and Bodocsi, A. (1997). “The Use of Modified Bentonite for Removal of Aromatic Organics from Contaminated Soil”,. Journal of Colloid and Interface Science 196, pp. 191-198. 10. Kamon Masashi, Jan Hartlén and Takeshi Katsumi, “Reuse of waste and its environmental Impact”, Council of European Professional Informatics Societies. 11. P.G. Malone and R.J. Larson, “Scientific basis of hazardous waste immobilization”, In Hazardous and Industrial Solid Waste Testing: Second Symposium, ASTM STP 805, ASTM, 1916 Race Street, Philadelphia, PA 19103, 1983. 12. Smith, A., Jaffe, P.R. and Chiou, C.T. (1990) Effect of ten Quaternary ammonium cations on tetrachloromethane sorption to clay from water. Environ. Sci. Technol., 24 (8), 1167–1172. 13. U.S. Environmental Protection Agency, “Stabilization/Solidification of CERCLA and RCRA Wastes: Physical Tests, Chemical Testing Procedures, Technology Screening, and Field Activities” 1989. 164