WO2007096891A1

WO2007096891A1 - Simultaneous separation of heavy metals and organic materials from soil, sludge or sediments

Info

Publication number: WO2007096891A1
Application number: PCT/IL2007/000254
Authority: WO
Inventors: Zvi Ludmer; Amos Ullman; Neima Brauner; Tal Golan
Original assignee: Zvi Ludmer; Amos Ullman; Neima Brauner; Tal Golan
Priority date: 2006-02-27
Filing date: 2007-02-27
Publication date: 2007-08-30

Abstract

A process for simultaneous extraction of organic pollutants, organic materials and heavy metals, such as polyaromatic hydrocarbons, pesticides and other hazardous chemicals, from contaminated media is defined. The process steps comprise adding a partially miscible solvent mixture to the contaminated media, heating the mixture to a temperature at which one single liquid phase is formed, cooling the mixture to induce phase separation and separating the two liquid phase. Either the heavy metals, organic pollutants and organic materials will remain mainly in the organic phase or the organic pollutants and the organic materials are mainly to be found in the organic phase and the heavy metals complexed with the at least one chelator mainly in the aqueous phase. The invention relates to the use of benign solvents, which are partially miscible with water and possess a critical point of miscibility, with or without added chelating agents.

Description

PROCESS FOR SIMULTANEOUS SEPARATING HEAVY METALS, AND ORGANIC MATERIALS FROM A SOIL, SLUDGE OR SEDIMENTS

FIELD OF THE INVENTION

The invention relates in general to the field of soil pollution and to methods of remediation of soil, sediments, and other systems contaminated with heavy metals and/or organic pollutants.

BACKGROUND OF THE INVENTION

Hazardous organics materials and toxic heavy metal are common pollutants of soil and subsequent potential pollution of groundwater is a common problem at many hazardous waste sites. These include, for example, industrial or commercial sites on which production residues were improperly stored or buried. In other instances, the contamination may have occurred by leaks or mishandling in transportation of different hazardous materials. In addition to contributing to the pollution of groundwater, soil contamination often results in restricted utilization of the site and, in some cases, a complete prohibition on cultivation or other potential use of the area.

Major soil contaminant categories commonly reported at National Priority List NPL (of USA) sites are volatile organics, hydrophilic and hydrophobic organics, heavy metals, and radioactive material. The most frequently found heavy metal contaminants include lead, mercury, arsenic, chromium, cadmium and copper (Yarlagadda et al., 1995). The EPA estimates that in the US over 20 million cubic yards of soil at current NPL sites are contaminated with metals (Griffiths, 1995). Contaminated river sediments present the same problem and similar treatment methods can be applied. The treatment of dredged river sediments is one of the more costly operations related to the management of water systems. Pollutants from various sources (industrial, mining, municipal sewage, agricultural and other activities) have entered water ways over time. The sediments sink and become a source of toxic components due to their re- suspension, and can thus be one of the largest potential sources of risk to water quality. In the US for example, approximately 300 million m³ of sediments are dredged to deepen harbors and shipping lanes and of which 3-12 million m³ are highly contaminated (Abumaizar and Smith, 1999; Mulligan et al, 2001). Approximately 10% of the sediments in underlying water in the US are contaminated. This has implications on human health, the ecosystem, the economy and politics.

A similar and acute problem exists in the Kishon River located in northern Israel.

Municipal and industrial wastewater, as well as surface runoff and erosion, are the major sources of pollution of the river. As the river approaches its outlet into the

Mediterranean Sea, its flow slows down and there is an increase in sedimentation at its bottom. This bottom sludge has to be dredged out every 5 to 8 years along much of the riverbed to prevent flooding. The dredged sludge is contaminated with organic pollutants and heavy metals, which prohibit direct utilization of some of the sludge for land filling, agriculture, and a number of other uses.

The proper and efficient treatment and disposal of polluted soil, sludge and dredged river sediments, and the environmental risks associated with this waste material, are the problems that the present invention addresses.

Current decontamination methods There are numerous treatment technologies for sediments and soils contaminated with hazardous substances. Many of these technologies have been developed for treating contaminated soils at hazardous waste sites and are then tested also for sediments. However, the properties of sediments and soils can differ significantly and therefore, technologies that work for soils may not be as efficient for sediments. The higher percentage of clay, silt and organic matter of sediments are the most notable. Moreover, sediments frequently contain a wider spectrum of pollutants.

Contaminated sediments and soils may be treated by using one or more physical, chemical, or biological treatment technologies. Treatment technologies reduce contaminant concentrations, contaminant mobility, and/or toxicity of the sediments by one or more of following means: i. Volume reduction by separating the cleaner particles (frequently the coarse particles) from particles with greater affinity for contaminants; ii. Destruction or conversion of the contaminants to less toxic forms by thermal or chemical technologies; iii. Physical and/or chemical stabilization of the contaminants in the sediments to prevent losses by leaching, erosion, volatilization, or other environmental pathways; iv. Soil washing or solvent extraction to remove inorganic and organic contaminants. v. Bioremediation by bacteria and phyto-remediation by plants to mineralize organic compounds and to absorb inorganic contaminants.

A comprehensive review of a broad range of technologies for remediation of contaminated sediments is given by the US EPA (1994, 1997a, and 1997b). Methods for heavy metals cleanup were reviewed by Mulligan (2001). The effectiveness, feasibility and cost of numerous of the above remediation treatment technologies have been tested over wide ranges of contaminated soil/sediments conditions, in the laboratory and in the field. Several of those technologies were found to be technically feasible although they varied in their effectiveness depending on the contaminants present, water content, organic compounds concentration, particle size distribution, etc. The relevant remediation methods are described herein:

Soil Washing and solvent extraction -The term soil washing is generally used to describe extraction processes that use a water-based fluid as the solvent (USEPA 1994). Soil washing is considered as one of the most suitable techniques for removing trace metals. Many soil washing processes rely on particle-size separation to reduce the volume of contaminated material. Soil washing is performed on excavated soils and involve some or all of the following: 1. Mechanical scanning for the removal of oversized materials; 2. Size fractionation; 3. Separation of the fine fraction for volume reduction of the hazardous material (e.g. centrifuge, screening, hydocyclones, sedimentation, see Kuhlman, and Greenfield, 1999); 4. Removal of the heavy metals by dissolving or suspending the contaminants in a water-based fluid. It is well known that water alone is not a suitable extraction fluid. Acidic or chelating agents are used to dislodge and dissolve trace metals from solids into solution. Citric acid, Nitrilotriacetic acid (NTA), and Ethylenediaminetetraacetic acid (EDTA) and its chemically modified alternatives such as [S,S]-ethylenediaminedisuccinic acid (EDDS), are the most common alternatives suggested for cleaning polluted soils (Elliott and Brown, 1989, Elliott et al, 1989, Davis and Singh, 1995 and Wasay et al., 2001). Chelation is the process of stable complex formation (a chelate) between a metal cation and a ligand (chelating agent). Binding of the metal cation in a stable complex renders it unavailable for further reaction processes. The stability of a complex generally increases as the number of bonds increases between the ligand and the metal cation. Efficiency varies with the chelating agent and dosage used, and other factors as pH, temperature, presence of competing species, etc. A comprehensive review on different types of chelating agents for removal of heavy metals is given by Peters (1999).

EDTA is often chosen because it is most effective in removing a wide range of trace metals. Experimental results have shown that an EDTA solution is far superior for soil washing than either water or an anionic surfactant solution (Davis and Singh, 1995). The ability of EDTA to extract the metals without inducing a strong acidification of the medium is a very desirable characteristic. However, there are some problems with using EDTA as a metal chelating agent: (1) It may complex strongly with a wide variety of metal ions in soils including alkaline-earth cations such as Al, Ca, Fe, and Mg in addition to the targeted trace metals, and this may have a detrimental effect on the structure and physical properties of the soil matrix (Zeng et al, 2004); (2) EDTA may bind to the soil solid phase and no longer be available for the removal of contaminants (Papassiopi et al., 1999); There are additional problems associated with soil washing. In particular, soil washing for clays and silts is only marginally applicable (US EPA, 1997a). Soils that contain organics, natural or synthetic, are very difficult to treat and are particularly not good candidates for soil washing, as the organics will foul screens, interfere with separations and can form emulsion with the washing liquid. In any case, soil washing can not remove non-polar organic contaminants. Their presence in the soil requires additional, different treatments.

Solvent Extraction is an ex situ separation and concentration process in which nonaqueous liquids are used to separate organic contaminants from soils, sediments or sludge. The end products of the process include: particulate solids, water, and concentrated organic compounds. The primary application of solvent extraction is to remove organic contaminants such as polychlorinated biphenyls (PCBs), polynuclear aromatic hydrocarbons (PAHs), volatile organic compounds, halogenated solvents and petroleum hydrocarbons (USEPA, 1998). Most extraction processes do not destroy or detoxify the contaminants, but they reduce the volume of the contaminated material that must be subsequently treated or disposed. Volume reductions of 20-fold or more are possible, depending on the initial concentration of the contaminants in the sediments, the distribution coefficient and the extraction process efficiency (US EPA, 1994). Another advantage of the process is that most of the contaminants are transferred from the solid phase to a liquid phase, which is more easily managed in subsequent treatments or disposal processes. While liquid-liquid extraction is a well established unit operation in chemical, food and pharmaceutical industries (Lo et al., 1983), its application to soil remediation is complicated by the variety of influential factors introduced by the soil/sediment/sludge characteristics. Extraction processes can operate in a batch mode or continuous mode. Sediments slurry, after pre-treatment of oversized debris removal, and solvents are mixed together in an extractor. The solvents and the extracted organic contaminants are then transferred to a separator, where the solvent and organic compounds are separated from the water and the contaminants are subsequently removed from the solvent. Usually several extraction cycles are required to reduce contaminant concentrations in the sediments to target levels (US EPA, 1998).

The treated solids contain traces of solvent. Therefore, solvents selected for the extraction processes should be harmless and/or biodegradable. Some processes include an additional separation step designed to further remove, by distillation striping or other means, most of the solvent from the product solids. The separation of the solvents from the water and the contaminants for reuse is an important part of the extraction process, as the solvents represent a significant cost. This solvent separation can be accomplished by a combination of one or more of the following processes: gravity settlers, distillation and stripping. It is important to note that an intensive mixing of the organic solvents with the wetted soil in the present of impurities in the extractor can cause a formation of emulsion. The emulsion can not be separated in gravity settlers, and other means with higher energy consumption, such as centrifuges or distillation units should be used.

A number of process options for extraction are commercially available. An example is the Carver-Greenfield process (US EPA, 1992 and Trowbridege and Holcomb, 1996). This process was applied to remove PCBs and other organic compounds from waste material using food-grade oil.

One of the main problems in applying solvent extraction for soil/sediments remediation is encountered when non-aqueous poorly polar or non-polar solvents are used to remove the organic pollutants. This type of solvents is required when the pollutants are non-polar or slightly polar. Examples of such widespread pollutants include aliphatic hydrocarbons, PAHs and PCBs. To achieve an effective extraction, it is necessary to accomplish a good contact between the soil and the extracting agent. This is a difficult task when the solvents are non-polar and the soil is wet (Nardella et al

1999). The problem becomes more severe with clay and silt, where the hydrophobic solvents can not penetrate into the tiny pores between the fine particles. In order to overcome this problem, the soils are dehydrated as a part of the pre-treatment of the extraction, or following the first stage (in multi-stage extraction, Carver-Greenfield process, Trowbridege and Holcomb, 1996). Another solution is to use water soluble or partially soluble solvents. Nardella et al (1999) used a mixture of ethyl-acetate and acetone in such composition that is completely miscible with the water of the wet soil. Using this solvent system, soil coming from industrial sites, contaminated with PCB and PNA, were treated and high efficiency was reported. However, difficulties were encountered at the soil/solvent separation stage. A similar process (B.E.S.T) was previously reported by the US EPA (1993 and 1998). Triethylamine, which is partially soluble with water to remove PCB and PAH, and 96-99% removal of these contaminants was reported. A complete miscibility of the triethylamine with water system can be achieved by cooling (below about 15⁰C). Both cold extraction (complete miscibility) and hot extraction (partial miscibility) were tested. The hot extraction was found to be more effective in removing the organic contaminants. Also, solvent/water separation by gravity (in decanter) was abandoned at that process, possibly due to emulsion formation, and the separation was carried out by evaporation.

In general, the solvent extraction is applied only for removal of organic contaminants. The presence of heavy metals in the soil requires additional, different treatments.

Currently there is no single technology which is generally agreed as the preferable remediation one. For instance, thermal technologies are generally the most effective options for destroying organic contaminants, but are also the most expensive (Mulligan et al, 2001) but in addition they may be a source of hazardous gases such as dioxines. On the other hand, solidification/stabilization processes are considered an economic method to reduce the mobility of the heavy metal contaminants. However, immobilization of organic compounds in sediments is generally thought to be less effective. Its applicability is restricted to moisture contents < 50% and organic contents < 10%. The volume increase can reach by as much as 30% and leaching of the contaminants from the solidified sediments must be carefully monitored over time (Mulligan et al. 2001). There is therefore an unmet need for an efficient and cost-effective method for simultaneous removal of both organic pollutants and hazardous heavy metals from contaminated soil, sediment, and other material.

SUMMARY OF THE INVENTION

The present invention provides a process suitable for removal of both organic pollutants and hazardous heavy metals from solid or semisolid media, such as soil and sediment, within one or more cycles of heating and cooling. The novel process is herein defined as Phase Transition Extraction (PTE). Advantageously, the methods of the present invention may be used to provide simultaneous removal of both organic pollutants and hazardous heavy metals from contaminated media.

The PTE technology is based on the use of partially miscible solvent mixtures possessing a critical temperature of miscibility. Such solvent mixtures are also known as critical solution mixtures. According to the methods of the present invention the contaminated media is exposed to mixtures of organic solvents with or without added water, wherein these mixtures at low temperatures constitute separate phases, whereas at elevated temperatures they form a single phase that is capable of extracting the contaminants, thereby providing decontaminated treated media, also referred to herein as treated media. In cases where the contaminated media intended to be treated are semisolid, such as for example water containing sediment, the volume of water may be proportionately reduced to preserve the phase transition characteristics of the solvent mixtures used.

According to some embodiments of the present invention, mixtures of at least one organic solvent and water were used. Upon heating, the solvents form a single phase, thus enabling a contact on almost a molecular level between the organic solvents of the mixture and the target molecules contained within the contaminated media. On slight cooling, the system separates back into two phases; the extraction step was achieved whereby the organic pollutants concentrated mainly in the organic phase. Preferably, heavy metals can be removed simultaneously by chelators present in the solvent mixtures.

The contact of the organic solvent mixture in conjunction with one or more chelator with the heavy metals and the organic contaminants in the contaminated medium to be treated enables simultaneous and efficient removal of both types of contaminants.

According to one aspect of the invention a solvent mixture, optionally comprising at least one chelating moiety, is used to extract organic material and heavy metals from contaminated material.

The invention therefore provides a novel process for separating organic pollutants, organic materials and heavy metals, from contaminated media comprising the steps of: i. adding partially miscible solvent mixture to contaminated media; optionally together with at least one type of chelator; ii. heating the solvent-media mixture to a temperature which forms one single liquid phase; iii. cooling the mixture to induce phase separation; iv. separating the two liquid phases and the solids whereby the heavy metals, organic pollutants and organic materials are mainly in the organic phase, or whereby the organic pollutants and organic materials are mainly in the organic phase and the heavy metals are complexed with the at least one chelator mainly in the aqueous phase; thereby producing decontaminated media.

The decontamination process may be performed iteratively until the desired degree of decontamination is achieved. According to specific embodiments of the invention the process further comprises at least one of the following: v. filtering the treated media from the liquids; vi. removing the heavy metals complexed with the chelators and the organic materials from the liquids; and optionally vii. recycling at least one of the solvents, chelators, organic material and heavy metals for further use. According to the present invention benign solvent mixtures, which are known to be partially miscible with water, are used for extraction of pollutants. According to one embodiment the solvent mixture comprises ate leas one solvent acceptable for use in food industry. According to another embodiment the solvent mixture comprises at least one solvent selected from the group consisting of: ethyl acetate, ethyl alcohol, acetone, acetic acid According to specific embodiments the organic solvent mixture is selected from the group consisting of: ethyl acetate-ethyl alcohol, ethyl acetate-acetone, or ethyl acetate-acetic acid.

A chelating molecule or a mixture of chelating molecules, which are capable of forming chemical bonds with some metal ions known to be hazardous are also applied in the process. According to one embodiment the chelator or chelators are dissolved in the solvent mixture. According to yet another embodiment the chelating molecule or molecules are dissolved in water and added to the organic solvent mixture before, together with, or after adding the contaminated media. According to the present invention, the solvent system which includes the solvents mixture and optionally at least one chelating moiety, is mixed with contaminated media. The mixing is carried out during heating/cooling cycles across the miscibility curve. Alternatively a simple isothermal mixing at a certain given temperature can be used. The mixing, followed by separation of the liquid phases consists a single extraction stage.

According to one embodiment the treatment can be completed in a single step. According to another embodiment the treatment is performed in a series of stages or cycles.

According to one embodiment, the organic solvents can be regenerated for further use and the hazardous components are isolated for disposal or other use.

According to another embodiment the separation method involved inducing complete miscibility of the solvents with a mild temperature variation across the miscibility curve. According to yet another embodiment the temperature of the phase transition of the solvents is adjusted by changing the ratio of the solvents. The contaminated media according to the invention include, but are not limited to, wet or dry soil, sediment of any kind, sludge, and industrial sewage.

According to one embodiment, the organic material to be separated comprises at least one pollutant selected from the group consisting of: chloro-organic compound, volatile organic compound, aromatic molecule, aliphatic molecule, halogenated solvent and phenyl molecule. According to another embodiment the organic pollutant is selected from the group consisting of: polychlorinated biphenyl (PCB), polynuclear aromatic hydrocarbon (PAH), naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, benzo(e)pyrene, perylene, benzo(a)pyrene, benz(g,h,i)perylene, indeno(l,2,3-cd)pyrene, aliphatic hydrocarbon, chlorophyll, phthalate, antioxidant, petroleum hydrocarbon, aromatic fatty acid and aliphatic fatty acid. According to yet another embodiment the organic pollutants comprise at least one not-fully identified organic material.

According to one embodiment heating and cooling is achieved by the use of an external heating and cooling sources while according to another embodiment solar heaters and environment temperature are used. Yet, according to a further embodiment the temperature changes between day and night is used for cooling and/or heating.

According to a specific embodiment the temperature applied for formation of one phase is between 20 degrees Celsius to 65 degrees Celsius. According to one embodiment of the present invention the process of separating hazardous heavy metals, organic pollutants and other not-fully identified organic materials from a non separated soil or sediments containing water, comprises the steps of:

(a) creating a solvent mixture of water and at least one organic solvent and optionally at least one chelator;

(b) bringing contaminated media into contact with said solvent mixture to create a solvent/media mixture;

(c) optionally adding at least one chelator to the solvent/media mixture; (d) heating the solvent/media mixture to a temperature that the liquids can form a single liquid phase;

(e) cooling said solvent/media mixture to induce a phase separation of the liquids;

(f) filtering the media from the liquids; (g) separating the mainly organic phase from the mainly aqueous phase;

(h) recycling the solvents;

(i) separating the heavy metals and recycling the chelators; (J) removing of residue of organic solvents from the treated media; (k) optionally further treating the residual organic pollutants and solvents.

According to a specific embodiment the mainly organic phase comprises metal complexes, organic pollutants and optionally other not-fully identified organic materials, and the mainly aqueous phase consists of heavy metals. According to another embodiment the mainly organic phase comprises heavy metals, organic pollutants, and optionally other not-folly identified organic materials.

According to a specific embodiment the recycling of the organic solvents (step h) is performed by distillation, vacuum evaporation or striping and concentration of pollutants. According to another specific embodiment the further treatment of the residual organic pollutants and solvents involved bacteria.

According to one embodiment the at least one chelating agent is added to the solvent mixture prior to contacting with the contaminated media while according to another embodiment the chelating agent is added together or after contacting the solvent mixture with the contaminated media.

Further embodiments and the full scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. Other uses of the critical solution mixtures were previously published by Eliyahu,et al., Ludmer et al., and Ullmann et al.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 is a schematic presentation of the Phase Transition Extraction (PTE) process.

Figure 2 show HPLC analysis of the dissolved organic matter (DOM) content in organic-reach phase following a single PTE cycle. Figure 3 represents HPLC analysis of the DOM content in organic-reach phase following the second PTE cycle.

Figure 4 describes Kinetics of cadmium (Cd2+) removal with ammonium pyrrolidinedithiocarbamate (ADDC)/Cd2+ ratio of 200 using the PTE process.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides an extraction process which is fast, easy-to-use and cost-effective. The PTE technology is based on the use of partially miscible solvent mixtures possessing a critical temperature of miscibility. Such solvent mixtures are known as Critical Solution Mixtures. According to one example of the present invention, solvents used were a mixture of organic solvents and water. Upon heating, the solvents form a single phase, thus enabling a contact on almost a molecular level between the organic solvents of the mixture and the target molecules contained within the contaminated media. On slight cooling, the system separates back into two phases; the extraction step was achieved whereby the organic pollutants concentrated in the mainly organic phase. Simultaneously, heavy metals were removed by chelators present in the solvents/media mixture. One or more chelator which dissolves in the organic phase may be used resulting in a situation where all pollutants are concentrated in the mainly organic phase. Alternatively, the chelating agent may be dissolved in the aqueous phase and therefore the heavy metals are concentrated mainly in the aqueous phase while the organic pollutants are concentrated in the mainly organic phase. The process can be operated either by heating and cooling or by quasi isothermal mixing. The high penetration of the solvent system mixture into wetted porous media, possible hindrance of emulsion formation, with the simultaneous removal of metal and organic pollutants, lead to substantial improvements of the remediation process.

The hazardous heavy metal according to the invention may be selected from the group consisting Silver (Ag), Arsenic (As), Boron (B), Barium (Ba), Cadmium (Cd), Cobalt (Co), Chromium (Cr), Copper (Cu), Mercury (Hg), Lithium (Li), Manganese (Mn), Molybdenum (Mo), Lead (Pb), Scandium (Sc), Tin (Sn), Strontium (Sr), Titanium (Ti), Vanadium (V), Zinc (Zn) and radio-labeled metal such as from nuclear waist. The main importance of the process of the present invention is in its ability to remove hazardous organics and metal ions, simultaneously and efficiently, from contaminated systems, using benign solvents and chelating agents. This can reduce the cost of cleanup of some contaminated systems. Expected advantages of the novel process include: a. Good penetration of the solvents and chelating agents into even tiny pores: In particular, in case of pores containing water (wetted soil/sediments), where the penetration of immiscible solvents is problematic. b. Almost molecular level contact between the extracting solvent mixture and the target species with high mass transfer rates. c. Two remediation processes- soil washing for the removal of heavy metals, and solvent extraction for removal of organic pollutants are combined into a single process. d. Fast phase separation of the extracting solvents mixtures even of contaminated emulsion-forming system can be achieved. e. Simple gravity-driven separation of the three-phase mixture, namely soil, mainly water phase and the lighter mainly organic phase. f. The heavy metals complexes can be directed into the mainly aqueous phase or the mainly organic phase depending on the choice of chelators or chelator mixtures. g. The organic pollutants are directed in all alternatives into the mainly organic solvent mixture phase. h. The organic pollutants can be isolated from the mainly organic phase by conventional procedures such as distillation, vacuum evaporation and/ or stripping, i. Solvents from both liquid phases and solids can be recovered for reuse by conventional procedures such as distillation, vacuum evaporation and/ or stripping. j . The chelating agents from both phases can be partially or fully recovered for reuse, k. The simultaneous removal of both metal and organic pollutants increases the yield of the process. 1. At certain global locations the process can be easily adjusted to consume minimal amounts of energy originating from fossil sources, by operating the mixing and separation cycle based on the temperature differences between day and night or the use of solar energy. m. Traces of the organic solvents or pollutants in either of the liquid phases or solids can be treated with appropriate bacteria.

The present invention relates to a process for separating hazardous heavy metals, organic pollutants and other not-fully identified organic materials, together with heavy metals from a contaminated media, according to the following steps:

(a) bringing a soil/sediment composition into contact with an extracting solvent mixture, blended with each other and heated to a temperature that the liquids can form a single liquid phase. Into the liquids a chelator or a mixture of chelators has been dissolved prior or during contacting the liquids with the solids; (b) cooling said solvent mixture soil/sediment system to induce the phase separation of the liquids;

(c) filtration of the soil/sediment from the liquids;

(d) separating the mainly organic phase, which consists of metal complexes and of organic pollutants and other not-fully identified organic materials from the mainly aqueous phase which consists of hazardous heavy metals;

(e) or alternatively depending on the chelator or chelators used, separating the mainly organic phase, which consists of organic pollutants and other not-fully identified organic materials from the mainly aqueous phase with the heavy metals complexes; (f) recycling the organic solvents by distillation or vacuum evaporation or striping and concentration of pollutants;

(g) separating the heavy metals and recycling the chelators or chelator mixture from liquid phases for recycling;

(h) removing of residue of organic solvents from the treated soil/sediment; and optionally

(e) treating the residual organic pollutants and solvents using bacteria.

A good penetration of the solvents with the chelating agents into the soil pores is facilitated by the low surface tension of the selected partially miscible solvent system. If required, further improvement of the solvent penetration can be obtained by inducing complete miscibility of the solvents with a mild temperature variation across the miscibility curve. If the contaminated medium contains emulsion forming substances, the non-isothermal mixing (by heating and cooling) can hinder emulsion formation. This is probably due to the hindrance of stable and defined interfaces in the single phase (mixing) step and during the phase separation. The temperature of the phase transition of the solvents can be adjusted according to specific condition by changing the ratio of the solvents. Heating and cooling can be achieved either by the use of an external heating and cooling sources or the use of solar heaters and environment temperature, or by taking advantages of the temperature changes between day and night temperatures.

EXAMPLES

Example 1 - Remediation of Kishon River sediment. The Kishon River sediments are extremely polluted with different organic pollutants, such as Polycyclic Aromatic Hydrocarbons (PAHs), Polychlorinated Biphenyls (PCBs) and phthalates. These organic pollutants are hydrophobic and have great affinity for organic solvents.

The Phase Transition Extraction (PTE) process disclosed in the present invention was applied to sediments from the Kishon River.

The successfully removal of dissolved organic matter (DOM) from polluted river sediments by the process of the present invention is demonstrated in Figures 2 and 3. The content of the extracted DOM in the organic phase was tested by the HPLC technique. The HPLC analysis of samples obtained after the first extraction cycle are shown in Figure 2. In the single (first) cycle identified and not fully identified together with non-identified organic substances were extracted these include: PCBs, phenyls, fatty acids, pigments, phthalates, antioxidants, aromatic and eliphatic molecules, and the following PAHs: Anthracene, Phenanthrene, Naphthalene, Fluorene, Acenaphthalene, Acenaphthene, Fluoranthene, Benzo(e)pyrene, Perylene, Benzo(a)pyrene, Benz(g,h,i)perylene and Indeno(l,2,3-cd) pyrene.

A second extraction cycle was conducted in order to examine whether any DOM was left in the sediments, and the corresponding HPLC results are shown in Figure 3. As shown, essentially all the DOM were removed by a single extraction cycle. By means of the PTE process, a clean-up of the contaminated sediments from organic pollutants was achieved in a single extraction cycle. This novel extraction process appears to be much faster (about 20 minutes) and easier-to-use than the current standard methods.

Example 2 - removal of cadmium as an example of removal of heavy metals

The feasibility and performance of the process for heavy metal removal from polluted river sediments was demonstrated by the removal of cadmium using an organic soluble chelating agent. Those experiments were conducted with solvent to sediments mass ratio of 28,6 and with ammonium diethyldithiocarbamate (ADDC) or sodium diethyldithiocarbamate at concentration of 2.5 mM. Initial Cd2+ concentration in the sediments was 40 ppm. The mixture was heated to a about, of 55⁰C and the isothermal operation temperature was around 20⁰C.

Results of kinetic studies are shown in Figure 4. The process enables the removal of about 85% of cadmium from the sediments after only 20 minutes. Practically all of the cadmium was concentrated in the mainly organic phase of the solvent system, with a distribution coefficient being always higher than 20. The results for the kinetics of the extraction under isothermal conditions at room temperature of about 20⁰C (without phase transition) are also shown in Figure 4. The comparison indicates a clear advantage of the PTE process over the isothermal extraction. As shown, the removal of cadmium under isothermal conditions is limited to about 40%.

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Zeng, Q. R.; Sauve, S.; Allen, H. E.; Hendershot, W. H. Recycling EDTA solutions used to remediate metal-polluted soils. Environ Poll. 133(2):225-231; 2004. While the present invention has been particularly described, persons skilled in the art will appreciate that many variations and modifications can be made. Therefore, the invention is not to be construed as restricted to the particularly described embodiments, and the scope and concept of the invention will be more readily understood by reference to the claims, which follow.

Claims

1. A process for separating organic pollutants, organic materials and heavy metals from contaminated media comprising the steps of: i. adding partially miscible solvent mixture to contaminated media; optionally together with at least one type of chelator; ii. heating the solvent-media mixture to a temperature which forms one single liquid phase; iii. cooling the mixture to induce phase separation; iv. separating the two liquid phases whereby the heavy metals, organic pollutants and organic materials are mainly in the organic phase, or whereby the organic pollutants and organic materials are mainly in the organic phase and the heavy metals complexed with the at least one chelator mainly in the aqueous phase; thereby producing decontaminated media.

2. The process of claim 1 further comprising the step of: v. filtering the treated media from the liquids; vi. removing the heavy metals complexed with the chelators and the organic materials from the liquids; and optionally vii. recycling at least one of the solvents, chelators, organic material and heavy metals for further use.

3. The process of claim 1 wherein the solvent mixture comprises at least one solvent selected from the group consisting of: ethyl acetate, ethyl alcohol, acetone, and acetic acid.

4. The process of claim 1 wherein the solvent mixture comprises solvents acceptable for use in food industry.

5. The process of claim 3 wherein the solvent mixture is selected from the group consisting of: ethyl acetate-ethyl alcohol, ethyl acetate-acetone, or ethyl acetate-acetic acid.

6. The process of claim 5 wherein the solvent mixture further comprises water.

7. The process of claim 6 wherein the solvent mixture/water weight ratio is 0.8 to 1.2.

8. The process of claim 7 wherein weight ratio is 1:1.

9. The process of claim 1 wherein the solvent mixture comprises water.

10. The process of claim 1 wherein the at least one chelator is pre-dissolved in the solvent mixture.

11. The process of claim 10 wherein the at least one chelator is ammonium or sodium pyrrolidinedithiocarbamate (ADDC or SDDC).

12. The process of claim 1 wherein the at least one type of chelator is pre- dissolved in water.

13. The process of claim 12 wherein the chelator is selected form the group consisting of: EDTA, chemically modified EDTA compound, SDDC, citric acid, azelaic acid, acetylacetic acid, malic acid, phenylacetic acid, salicylic acid and phthalic acid.

14. The process of claim 1 wherein the contaminated media is selected from the group consisting of: wet soil, dry soil, sediment, sludge, and industrial sewage.

15. The process of claim 1, wherein said organic pollutants are polynuclear aromatic molecules.

16. The process of claim 1 wherein the organic pollutants comprises at least one compound selected from the group consisting of: polychlorinated biphenyl (PCB), polynuclear aromatic hydrocarbon (PAH), naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, benzo(e)pyrene, perylene, benzo(a)pyrene, benz(g,h,i)perylene, indeno(l,2,3-cd)pyrene, aliphatic hydrocarbon, chlorophyll, phthalate, antioxidant, petroleum hydrocarbon, aromatic fatty acid and aliphatic fatty acid.

17. The process of claim 1 wherein at least one organic pollutant is not well defined.

18. The process of claim 1 which involved a single extraction cycle.

19. The process of claim 1 comprising the steps: a. creating a solvent mixture of water and at least one organic solvent and optionally at least one chelator; b. bringing contaminated media into contact with said solvent mixture to create a solvent/media mixture; c. optionally adding at least one chelator to the solvent/media mixture; d. heating the solvent/media mixture to a temperature that the liquids can form a single liquid phase; e. cooling said solvent/media mixture to induce a phase separation of the liquids; f. filtering the media from the liquids; g. separating the mainly organic phase from the mainly aqueous phase; h. recycling the organic solvents; i. separating the heavy metals and recycling the chelators; j. removing of residue of organic solvents from the treated media; and k. optionally further treating the residual organic pollutants and solvents.

20. The process of claim 19 wherein the mainly organic phase comprises metal complexes, organic pollutants and optionally other not-fully identified organic materials, and the mainly aqueous phase comprises heavy metals.

21. The process of claim 19 wherein the mainly organic phase comprises heavy metals, organic pollutants, and optionally other not-fully identified organic materials.

22. The process of claim 20 wherein the recycling of the organic solvents (step h) is performed by distillation, vacuum evaporation or striping and concentration of pollutants.

23. The process of claim 19 wherein the further treatment of the residual organic pollutants and solvents involved bacteria.

24. The process of claim 1, wherein said heavy metals are selected from the group consisting Silver (Ag), Arsenic (As), Boron (B), Barium (Ba), Cadmium (Cd), Cobalt (Co), Chromium (Cr), Copper (Cu), Mercury

(Hg), Lithium (Li), Manganese (Mn), Molybdenum (Mo), Lead (Pb), Scandium (Sc), Tin (Sn), Strontium (Sr), Titanium (Ti), Vanadium (V), Zinc (Zn) and radio-labeled metal.

25. The process of claim 1, wherein temperature for one phase formation is between 20 degrees Celsius to 65 degrees Celsius.