Contaminated Land Remediation Technologies

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Contaminated Land Remediation Technologies : 

Contaminated Land Remediation Technologies Ali Anwar

Introduction : 

Introduction The contamination of subsurface soil all over the world is a serious and challenging problem (Rivas 2009). Some of the main contaminates found in soil include: Arsenic Cadmium Mercury Lead Polycyclic Aromatic Hydrocarbons (POP) Polycyclic Chlorinated Biphenyls (PCB) Polycyclic Aromatic Hydrocarbons (PAH)

Introduction : 

Introduction Soils can be contaminated with heavy metals from numerous sources including (Adriano 1986): Abandoned mining wastes Incomplete collection of used batteries Leakage of landfill leachate Improper treatment of industrial wastes Military activities All of the contaminants mentioned are toxic to people.

Introduction : 

Introduction These contaminants are known for their carcinogenic, mutagenic and teratogenic properties. A study by Perera et al., 2009 has found that high prenatal exposure to PAH is associated with lower IQ (Perera, 2009). It is vital for human health and longevity to develop techniques which can remove such toxins from land safely, permanently and inexpensively.

Remediation Technologies : 

Remediation Technologies Contaminated soil remediation technologies can be divided into 3 groups: Thermal Remediation Biological Remediation Chemical Remediation Each of these groups has its advantages and its disadvantages.

Thermal Remediation Technologies : 

Thermal Remediation Technologies Thermal disposal technologies use high temperatures (over 1,100˚C) to catalyse the oxidation, reduction and pyrolysis processes used in order to break down any toxins within a soil sample.

Biological Remediation Technologies : 

Biological Remediation Technologies Biological disposal technologies use biotic material to accelerate the detoxification of contaminated soils. Biological remediation can be divided into 2 groups: Phytoremediation – using green plants to remediate toxic soil Bioremediation – using microorganism, enzymes and fungi to remediate toxic soil

Chemical Remediation Technologies : 

Chemical Remediation Technologies The chemical remediation process employs strong oxidizing and reducing agents to react with toxins, rendering them harmless. These reactions are usually liquid or solid based, but also gas based.

Selected Remediation Technologies : 

Selected Remediation Technologies Each the three groups of remediation technologies has a vast variety of methods and target-specific techniques. For this presentation, I will cover the following methods: Sorptive & Complexing Technologies Mechanochemical Technologies Electrokinetic Technologies

Sorptive and Complexing Remediation Technologies : 

Sorptive and Complexing Remediation Technologies Sorption refers to a process where absorption and adsorption occur simultaneously. In adsorption, atoms or molecules accumulate on surfaces of materials. This process creates a film of the adsorbate on the adsorbent's surface.

Adsorption Model : 

Adsorption Model Adsorption is a random distribution of molecules on the material surface

Sorptive and Complexing Remediation Technologies : 

Sorptive and Complexing Remediation Technologies Absorption is a chemical and/or physical process where atoms, ions or molecule enter a solid, liquid or gas matrix and becomes a part of it. Therefore, sorption is the effect of gases or liquids being incorporated into a material of a different physical state which then adhere to the surface of another molecule.

Sorptive and Complexing Remediation Technologies : 

Sorptive and Complexing Remediation Technologies Minamisawa et al., 2002 studied the adsorbtive capacity of roasted coffee beans. Cheaper alternative to other typical adsorbents e.g. silica gels, zeolites and activated carbon (Minamisawa, 2002). Adsorption percentage of the heavy metal ions were above 90% for all coffee beans tested.

Adsorption of Cu(II) Ions on Indonesia Robusta Coffee : 

Adsorption of Cu(II) Ions on Indonesia Robusta Coffee ●: Washed & dried coffee ▲: Dried coffee ◯ : Washed coffee △: Untreated coffee Minamisawa, 2002

Adsorption of Cd(II) Ions on Coffee & Activated Carbon : 

Adsorption of Cd(II) Ions on Coffee & Activated Carbon ● : Coffee ▲: Activated Carbon Minamisawa, 2002

Time-course of Cd(II) adsorption at pH 6.7 on various biomaterials : 

Time-course of Cd(II) adsorption at pH 6.7 on various biomaterials ▲ Coarse Tea △ Aloe * Yuzu Green Tea Chitosan Tea Coffee Zeolite Activated Carbon Minamisawa, 2004

Time-course of Pb(II) adsorption at pH 4 on various biomaterials : 

Time-course of Pb(II) adsorption at pH 4 on various biomaterials ▲ Coarse Tea △ Aloe * Yuzu Green Tea Chitosan Tea Coffee Zeolite Activated Carbon ▲ Coarse Tea △ Aloe * Yuzu Green Tea Chitosan Tea Coffee Zeolite Activated Carbon Minamisawa, 2004

Sorptive and Complexing Remediation Technologies : 

Sorptive and Complexing Remediation Technologies Davis, 1984 and Xu et al., 1989 studied the effect of pH and organic compounds on heavy metal sorption. They concluded that some organic compounds did enhance and inhibit metal soprtion, while high pH levels inhibited surface-ligand-metal complexes. Holm et al., 1994 studied the sorption of Cd(II), Pb(II) and Cu(II) to kaolinite from landfill leachate-contaminated growndwater. They concluded that pH affected the ions’ ability to form complexes.

Sorptive and Complexing Remediation Technologies : 

Sorptive and Complexing Remediation Technologies Davis, 1984 and Xu et al., 1989 studied the effect of pH and organic compounds on heavy metal sorption. They concluded that some organic compounds did enhance and inhibit metal soprtion, while high pH levels inhibited surface-ligand-metal complexes. Holm et al., 1994 studied the sorption of Cd(II), Pb(II) and Cu(II) to kaolinite from landfill leachate-contaminated growndwater. They concluded that pH affected the ions’ ability to form complexes.

Sorptive and Complexing Remediation Technologies : 

Sorptive and Complexing Remediation Technologies Sorptive remediation technologies can lead to incorporation of metals into insoluble mineral phases therefore reducing the bioavailability of toxic contaminants.

Mechanochemical Remediation Technologies : 

Mechanochemical Remediation Technologies Chemical reactions are activated by energy. Many forms of energy can initiate these reactions; the most common form is thermal energy. Mechanochemistry is the study of chemical reactions which are initiated by mechanical/kinetic energy (Heineke, 1984).

Mechanochemical Remediation Technologies : 

Mechanochemical Remediation Technologies Mechanochemistry has been exploited since the Stone Age when flint was used to start fires, but it was only defined at the beginning of the 20th century by W. Ostwald(Heineke, 1984). Mechanochemical reactions were thought to be solely triggered by the heat generated upon impact. This has been dispelled as more studies into the mechanisms and kinetics of mechanochemical processes have been done (Urakaev, 2000 and Tkacova, 1990).

Mechanochemical Remediation Technologies : 

Mechanochemical Remediation Technologies Urakaev et al., 2000 developed a “hot spot” model. “Hot spot” temperatures reach over 1000K from impact friction. Phonons are another mechanochemical trigger (Tkacova, 1990) Phonons are altered vibration frequencies of crystal lattices which can disrupt chemical bonds (Tkacova, 1990).

Mechanochemical Remediation Technologies : 

Mechanochemical Remediation Technologies The processes of mechanochemical reactions can be divided into three categories (Bellingham, 2005):  Mechanical Milling Reaction Milling Mechanical alloying Process of interest for contaminated land remediation is the reaction milling process (RM).

Mechanochemical Remediation Technologies : 

Mechanochemical Remediation Technologies RM uses kinetic energy imparted by ball bearings to break the bonds of targeted contaminants. The bonds are broken to allow organic and inorganic reactions to occur (Steinike, 2000 and Kaupp, 2005): Complex Formation REDOX Reactions Ion Exchange

Mechanochemical Remediation Technologies : 

Mechanochemical Remediation Technologies RM is achieved by placing contaminated soil into a rotating mill with ball bearings. The mill rotates at high speeds so the ball can crash into the contaminants and break their bonds. Ions and radicals bind to the reactive fractured surfaces and are fractured againe. The final products are small molecules (Robertson, 2008): Ethane, methane, CO2, H2, H2O & C

Contaminated soil is fed into the mill where the motor rotates the axel and flingers which in turn rotates the balls and crash into the contaminated soil : 

Contaminated soil is fed into the mill where the motor rotates the axel and flingers which in turn rotates the balls and crash into the contaminated soil Robertson, 2008

Mechanochemical Remediation Technologies : 

Mechanochemical Remediation Technologies It is important to note that once the matrix is spinning in the mill, the majority of the mechanochemical reaction will occur in the aerosolized soil i.e. powder Powder behaviour under the mechanical action of an impacting ball (Delogu, 2003) Intensity of the impact can be calculated by two equations: Impact Energy = 1/2Nmv2, where N is the collision frequency and m and v are the mass and velocity of the ball (Delogu, 2003). Total Energy = Impact Energy x t, where t is the milling time (Delogu, 2003).

Mechanochemical Remediation Technologies : 

Mechanochemical Remediation Technologies Stepwise summary of Reactive Milling (Robertson, 2008): Ball strikes and fractures a target mineral particle. Each fracture causes a huge number of chemical bonds to break. The broken bonds e.g. Si-O yield extremely reactive radicals. Molecules settle on the surface of the “broken” particles. Electron transfer occurs which form energetic ions. The energetic ions fragment to form neutral species Some of these species include C, H2O, CO2, H2, Cl2 and CH4 Si-O bonds breaking (Robertson, 2008)

Electrokinetic Remediation Technologies : 

Electrokinetic Remediation Technologies Electrokinetic remediation is a developing in situ remedial technique that has great potential of treating soils contaminated with heavy metals (Al-Hamdan, 2008). Electrokinetic remediation utilizes direct current or low potential gradients applied to electrodes inserted in heavy metal-contaminated land (Probstein, 1993).

Electrokinetic Remediation Technologies : 

Electrokinetic Remediation Technologies Heavy metals intrinsically carry either a negative or positive charge. Therefore, according to the charge of the heavy metal, it would travel through the soil towards the anode or cathode (Al-Hamdan, 2008). Once these heavy metals reach the electrodes, they can then be extracted by a number of methods: Precipitation - Adsorption Complexation - Electroplating (Probstein, 1993; Mattson, 2000; Alshawabkeh, 2005)

Electrokinetic Remediation Technologies : 

Electrokinetic Remediation Technologies The movement of the charged heavy metals through the soil matrix is known as electrokinesis. Electrokinesis is the particle or fluid transport produced by an electric field acting on a fluid having a net mobile charge (Patterson, 1981). The force acting on the fluid, is given by the equation: F = Id/K ‘F’ is the resulting force, measured in Newtons ‘I’ is the current flow, measured in amperes ‘d’ is the distance between electrodes, measured in metres ‘K‘is the ion mobility coefficient of the fluid, measured in m2/Volt sec (Patterson, 1981).

Electrokinetic Remediation Technologies : 

Electrokinetic Remediation Technologies Another way heavy metals can be transported through the soil matrix to the electrodes is by a phenomenon called electroosmosis. Electroosmosis is the movement of water (and whatever is contained in the water) through a porous media by applying a direct current (DC) field. In this case, the porous media is soil (Athmer 2006).

Electrokinetic Remediation Technologies : 

Electrokinetic Remediation Technologies Soil typically has a negative surface charge. To balance this charge, a row of cations line up along the soil particle surfaces (Ho, 1997). DC fields create the rows of cations on the soil particle surfaces which start sliding along towards the cathode due to electrical attraction (Ho, 1999a).

Electrokinetic Remediation Technologies : 

Electrokinetic Remediation Technologies The movement of this layer of cations drags the bulk soil water along with it and individual cations and anions also move towards either the cathode or anode. These ionic migrations cancel each other out and have no real effect on the bulk water transport. This electromigration must be taken into consideration when treating soils contaminated with metals and other inorganic compounds (Ho, 1997).

Electroosmosis : 

Electroosmosis Athmer, 2006

Electrokinetic Remediation Technologies : 

Electrokinetic Remediation Technologies Electromigration has been used in a limited role of late for the remediation of metal contaminated soils at industrial sites, but the results were not always great. The main problem with electromigration of metals is the pH control required at the cathodes. Water is oxidized at the anode and releases oxygen and creating H+ which result in an acid front moving towards the cathode. H2 is evolved at the cathode and a base front of OH- is generated and moves towards the anode (Athmer, 2006).

Electrokinetic Remediation Technologies : 

Electrokinetic Remediation Technologies Precipitation of the metal ions to metal hydroxides will occur when they reach the base front. When this occurs, the ions will not reach the cathode therefore, cannot be extracted from the soil (Athmer, 2006). The use of electroosmosis to remediate soils contaminated with organic contaminants is simpler. Organic compounds are not affected by pH. The only requirement for the process to be successful is that the electrodes must be hydraulically and electrically conductive.

Electrokinetic Remediation Technologies : 

Electrokinetic Remediation Technologies Electrokinetic technology has a beneficial side effect; the electricity applied to the soil directly results in heating of the soil. The soil warming not only increases the mobilization of volatile organics but also increases the electroosmotic permeability by lowering the viscosity of the pore water

Double effect of pore flushing by moving water and increased temperatures to mobilize VOCs : 

Double effect of pore flushing by moving water and increased temperatures to mobilize VOCs Athmer, 2006

THANK YOU FOR YOUR ATTENTION : 

THANK YOU FOR YOUR ATTENTION THE END Questions??

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