Stabilizing the Various Types of Contaminated Soils Using Different ...

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©PEARL publication, 2015. CJBAS Vol. ..... The stabilization process involves mixing a soil or waste with binders such as Portland cement, lime, fly ash .... Incorporation of RHA in the binder system was justified as leachability of lead from the ...
Canadian Journal of Basic and Applied Sciences ©PEARL publication, 2015

ISSN 2292-3381 CJBAS Vol. 03(12), 308-321, December 2015

Stabilizing the Various Types of Contaminated Soils Using Different Additives A review Mohammad Nikookara, Arefeh Jafarpour Lashkamib a b

M.S of Geotechnical Engineering, Guilan University, Rasht, Iran B.S of Civil Engineering, Guilan University, Rasht, Iran

Keywords:

Abstract

Stabilization, Additives, Contaminated Soils, Soil Characteristics.

Stabilization of problematic soils including contaminated soils, peat, silt, and the like through adding materials such as; cement, lime, bitumen, and etc. is one of effective methods for improving the geotechnical properties of soils which has been applied for many years now. There are a great number of techniques for stabilizing that can be used for various purposes by enhancing some aspects of soil behavior and improving the characteristics of soil. Most available remediation technologies for treatment of contaminated soils are very expensive and result in residues requiring further treatment. This study aims to overview of data published on stabilizing the various types of contaminated soils such as heavy and toxic metals (As, Cr, Cu, Pb and Zn) using different additives like ordinary portland cement (OPC), rice husk ash (RHA), lime, synthesized zeolite, and etc. The consequences of these findings for the stabilization of contaminated soils by the presence of heavy-toxic metals have been also throughly discussed.

1. Introduction Due to the presence of heavy and toxic metals the contamination of soils can result in serious negative consequences, such as, the loss of ecosystems and, of agricultural productivity, the deterioration of food chain, tainted water resources, economic damage, and human and animal serious health problems etc. In several parts of the world the soil contamination represents the most severe environmental problems [1]. Background knowledge of the sources, chemistry, and potential risks of toxic heavy metals in contaminated soils is a necessity to select the appropriate remedial options. The fact of the matter is that remediation of soil contaminated by heavy metals is necessary in order to reduce the associated risks, make the land resource available for agricultural production, enhance food security, and scale down land tenure problems as well. To clean up heavy metal contaminated soils In addition 

Corresponding Author : E-mail, [email protected] – Tel, (+98) 9111847131

Nikookar and Jafarpour Lashkami- Comput. Res Prog. Appl. Sci. Eng. Vol. 03(11), 308-321, December 2015

immobilization, soil washing, and phytoremediation are frequently listed among the best available technologies. Needless to say it could have been mostly demonstrated in developed countries. These technologies are recommended for field applicability and commercialization in developing countries also where agriculture, urbanization, and industrialization are leaving a legacy of environmental degradation. Excavation of contaminated soil was once the solution for soil remediation. Due to the high cost of excavation, final disposal of landfills, and lack of available landfill sites, these disposal methods are becoming increasingly less popular [2]. To decrease costs, various technologies are being developed and implemented for remediation of soils and sediments. In situ treatment of soil is preferable since they are more cost-effective and less disruptive than ex situ processes. However, there are very many difficulties with in-situ processes since they are more difficult to be controlled [3]. Chemical stabilization of problematic soils using chemical admixture is one of the various methods of stabilization which have been used to improve the soil performance. Stabilization with chemical additive involves treatment of the soil with some kind of chemical compound, which when added to the soil, would result in chemical reaction. The chemical reaction modifies or enhances the physical and engineering aspects of a soil, such as, volume stability and strength of a soil [4]. Of more recent interest is the stabi¬lization of contaminated soils and sewage sludges for use in bulk fill operations for highway earthworks [5]. Stabilization must then be considered as having both a physical aspect involving changes to the mechanical properties of the material, and a chemical aspect involving changes to the form and mobility of the contaminants present. Stabilization must therefore be considered as having both a physical aspect involving changes to the mechanical properties of the material, and a chemical aspect involving changes to the form and mobility of the contaminants present [6]. Stabilization reduces the mobility of hazardous substances and contaminants in the environment through both physical and chemical means. It physically binds or encloses contaminants within a stabilized mass and chemically reduces the hazard potential of a waste by converting the contaminants into less soluble, mobile, or toxic forms. Currently, several technologies can be employed to clean up the soils and the mining wastes contaminated by toxic metals, including thermal, biological, and physical/chemical procedures, or their appropriate combinations. These techniques usually require the removal of contaminated soil, its subsequent treatment and either replacing it on-site, or disposed in specific landfills, located in 309

Nikookar and Jafarpour Lashkami- Comput. Res Prog. Appl. Sci. Eng. Vol. 03(11), 308-321, December 2015

most cases rather away from the polluted areas; therefore, creating a secondary disposal problem, due to the presence of lead and of other toxic metals. Such treatment/removal technologies are generally costly to practice and destructive to the application sites, from which the wastes are removed. In addition, these removal technologies are often partially effective for the total removal (efficient clean up) of toxic metals, or for the sufficient reduction of their mobility and bioavailability to the environment [7]. The purpose of this paper is to summarize the major findings of data published on stabilization of various types of contaminated soils such as heavy and toxic metals (As, Cr, Cu, Pb and Zn) using different additives like ordinary portland cement (OPC), rice husk ash (RHA), lime, synthesized zeolite and etc. 2. Soil Contaminating Materials ‘Heavy metals’ is a widely-used term for elements with metallic properties - it is not, in fact, a scientifically accurate description, since the definition of ‘heavy’ is not fixed, and some so-called heavy metals, such as arsenic and antimony, are semi-metals or metalloids. The group ‘heavy metals’ for the purpose of discussing health risks or impacts generally includes: Arsenic (As), Lead (Pb), Cadmium (Cd), Chromium (Cr) (although only the form Cr(VI) is toxic), Copper (Cu), Mercury (Hg), Nickel (Ni) and Zinc (Zn). Several of these elements are necessary for human health, and are beneficial when taken in to the body in foods or as supplements at appropriate, low levels [8]. This study is an overview of data published on the stabilization and immobilization of five materials contaminating soils including one metalloid, As, and four heavy metals, Cr, Cu, Pb and Zn, in soils. 2.1. Arsenic Arsenic is one of the most toxic elements. Arsenic is classified as a metalloid (having some properties of a metal) and, like lead, occurs everywhere in the environment. Arsenic also has many beneficial uses but can cause human health problems if exposure is sufficient. Environmental contamination with arsenic because of human activities is less widespread than contamination from lead but can be of regional and local importance [9]. 2.2. Chromium

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Chromium is an important industrial metal used in diverse products and processes [10]. At many industrial and waste disposal locations, chromium has been released to the environment via leakage and poor storage during manufacturing or improper disposal practices [11]. 2.3. Copper Copper is the third most used metal in the world [12]. Copper is an essential micronutrient required in the growth of both plants and animals. In humans, it helps in the production of blood haemoglobin. In plants, Cu is especially important in seed production, disease resistance, and regulation of water. Copper is indeed essential, but in high doses it can cause anaemia, liver and kidney damage, and stomach and intestinal irritation. Copper normally occurs in drinking water from Cu pipes, as well as from additives designed to control algal growth. 2.4. Lead Lead (Pb) is one of the most common contaminants found in soils contaminated as a result of agricultural activities, urban activities and industrial activities such as mining and smelting. It is toxic both to humans and animals, especially to young children and hence presents a serious environmental and health hazard [13]. Lead is a heavy, soft, malleable metal. Due to its physical and chemical properties, industry has found countless uses for lead in our daily lives. While certain uses of lead are banned, lead is still found in a myriad of products such as, lead in paint, lead in occupational settings (often brought home on clothes or skin), Lead from industrial emissions, Lead in drinking water and etc. 2.5. Zinc Zinc is a transition metal. Most Zn is added during industrial activities, such as mining, coal, and waste combustion and steel processing. Zinc provides the most cost-effective and environmentally efficient method of protecting steel from corrosion. Zinc is also an essential element which is indispensable for human health and for all living organisms. This essentiality makes the interaction between zinc and the environment complex. Despite, in the vicinity of some old industrial sites, levels of zinc in the soil, usually in combination with other metals, can be elevated due to high emissions in the past (historical contamination). Such sites need specific attention and appropriate risk management to limit exposure of the local ecosystem and prevent contamination from spreading to surrounding areas. Promising results have recently been obtained with metal immobilising compounds that, when mixed with contaminated soils, fix zinc and other metals to the soil complex, rendering them less available for uptake by organisms [14]. 3. Stabilization / Immobilization Results 311

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Stabilization involves the addition of reagents to the contaminated soil to produce more chemically stable constituents. The general approach for stabilization treatment processes involves mixing or injecting treatment agents to the contaminated soils. Inorganic binders (Table 1), such as clay (bentonite and kaolinite), cement, fly ash, blast furnace slag, calcium carbonate, Fe/Mn oxides, charcoal, zeolite [15, 16], and organic stabilizers (Table 2) such as bitumen, composts, and manures [17], or a combination of organic-inorganic amendments may be used. Table 1. Organic amendments for heavy metal immobilization [18]. Material Heavy metal immobilized Bark saw dust (from timber industry ) Cd, Pb, Hg, Cu Xylogen ( from paper mill waste water ) Zn, Pb, Hg Chitosan ( from crab meat canning industry ) Cd, Cr, Hg Bagasse ( from sugar cane ) Pb Poultry manure ( from poultry farm ) Cu, Pb, Zn, Cd Cattle manure (from cattle farm ) Cd Rice hulls ( from rice processing ) Cd, Cr, Pb Sewage sludge Cd Leaves Cr, Cd Straw Cd, Cr, Pb

Table 2. Inorganic amendments for heavy metal immobilization [18]. Material

Heavy metal immobilized

Lime ( from lime factory )

Cd, Cu, Ni, Pb, Zn

Phosphate salt ( from fertilizer plant )

Pb, Zn, Cu, cd

Hydroxyapatite (from phosphorite )

Zn, Pb, Cu, Cd

Fly ash ( from thermal power plant )

Cd, Pb, Cu, Zn, Cr

Slag (from thermal power plant )

Cd, Pb, Zn, Cr

Ca – montmorillonite ( mineral )

Zn, Pb

Portland cement ( from cement plant )

Cr, Cu, Zn, Pb

Bentonite

Pb

Many of the additives are not effective in immobilizing organic contaminants. Modified clays, however, are currently being studied for application in the stabilization/immobilization of organic contaminants. Recent tests with some silicate binders and some organic binders have shown success in immobilizing and perhaps treating some semivolatile and heavier organic contaminants [19]. The consequences of findings for the stabilization/immobilization of contaminated soils by the presence of heavy-toxic metals in this study have been discussed. 3.1. Arsenic

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The mobility of As in soil is mainly controlled by adsorption/desorption processes and coprecipitation with metal oxides. Therefore the most extensively studied amendments for As immobilization are oxides of Fe and, to a lesser extent, Al and Mn. Iron salts are commonly used for As stabilization purposes. Ferrous, Fe(II), sulfate was demonstrated to effectively reduce As mobility. Precipitation of Fe oxides, followed by the Fe sulfate application, causes acid (H2SO4) release. Co-mixing of lime is usually used to avoid soil acidification. Application rates based on As/Fe molar ratio can be more informative seeing as different soils have different contamination levels requiring different amounts of reactive Fe [20]. Moreover, pH and the type of organic matter might play a role in its varying effect on As mobility. Grafe et al. in 2002 [21] studied adsorption of As on synthetic ferrihydrite under the influence of three types of OM: peat humic acid (HA), Suwannee River fulvic acid (FA) and citric acid (CA). According to their results, FA and CA adsorption to ferrihydrite outcompeted As(III) adsorption at low pH, while only CA was able to reduce As(V) adsorption on ferrihydrite. HA and As sorption were not interfering and was suggested to be independent of each other. The authors also observed that goethite had a higher affinity for dissolved organic carbon (DOC) with a higher surface coverage and stronger bonds than ferrihydrite. Organic matter can change As speciation by reducing As(V) to more toxic and mobile As(III). Studies on nine artificially CCA-contaminated soils revealed that in mineral soils on average 92% of total As was As(V), while in highly organic soils the proportion of As(III) significantly increased to one third of the total soil As [22]. Stabilization is an established treatment technology often used to reduce the mobility of arsenic in soil and waste. The most frequently used binders for stabilization of arsenic are pozzolanic materials such as cement and lime. Stabilization can generally produce a stabilized product that meets the regulatory threshold of 5 mg/L leachable arsenic as measured by the TCLP. However, leachability tests may not always be accurate indicators of arsenic leachability for some wastes under certain disposal conditions. The stabilization process involves mixing a soil or waste with binders such as Portland cement, lime, fly ash, cement kiln dust, or polymers to create a slurry, paste, or other semi-liquid state, which is allowed time to cure into a solid form. When free liquids are present the S/S process may involve a pretreatment step (solidification) in which the waste is encapsulated or absorbed, forming a solid material. Pozzolanic binders such as cement and fly ash are used most frequently for the stabilization of arsenic.

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Figure1. Model of a Solidification/Stabilization System

Besides other stabilization techniques, acid-washing process used for arsenic contaminated soils. Results obtained from Tokunaga and Hakuta in 2002 [23], laboratory investigation on acid washing and stabilization of an artificial arsenic-contaminated soil indicated that: Acid-washing and stabilization processes have been developed for the remediation of arsenic(V)-contami¬nated soil. Kuroboku soil, a model soil, sorbed arsenic ions in the pH range 2~7 with the maximum sorption capacity of 3150 mg/kg. The arsenic desorption from the modelcontaminated soil (2830 mg As/kg soil) became appreciable in the pH range of