WO2013086641A1

WO2013086641A1 - Process for decontamination of soils polluted with metals, pentachlorophenol, dioxins and furans and contaminants removal from leachates

Info

Publication number: WO2013086641A1
Application number: PCT/CA2012/050904
Authority: WO
Inventors: Jean-François BLAIS; Nicolas REYNIER; Guy Mercier
Original assignee: Institut National De La Recherche Scientifique (Inrs)
Priority date: 2011-12-16
Filing date: 2012-12-17
Publication date: 2013-06-20
Also published as: CA2857703A1; CA2762060A1

Abstract

A process for decontamination of soil contaminated with a preservative comprising contaminants including at least one leaching step wherein the soil is contacted with water and an inorganic base at a concentration between about 0.1 M and about 2 M at a temperature lower than about 100°C, to form an alka line mixture and solubilise at least a portion of the contaminants present in the soil. The process may include at least one attrition step, prior to the at least one leaching step, to produce an aqueous mixture of soil including fine soil particles. The process further includes separating a contaminant- poor soil from a contaminant-rich leachate, and recovering at least one of the contaminants. The process may also include a crushing and/or screening step before the at least one attrition step or the at least one leaching step. The contaminants include metals and/or organic compounds, such as pentachlorophenol, dioxins and furans.

Description

PROCESS FOR DECONTAMINATION OF SOILS POLLUTED WITH METALS, PENTACHLOROPHENOL, DIOXINS AND FURANS AND CONTAMINANTS

REMOVAL FROM LEACH ATES

FIELD OF THE INVENTION

The present invention generally relates to wood treating sites and more particularly to a method of decontamination. More specifically, this invention relates to a process for decontaminating soil polluted by metals, pentachlorophenol, dioxins and furans and extracting contaminants from contaminated solutions.

BACKGROUND OF THE INVENTION

To increase wood lifetime, chemical treatments are often applied to particularly protect wood against insects and fungi. Main chemical preservatives are Chromated Copper Arsenate (CCA), Pentachlorophenol (PCP) and polychlorined dibenzodioxins and dibenzofurans (PCDDF). Many of the chemical preservatives may be toxic to organisms and consequently harmful if released into the environment.

The number of wood treating sites in Canada has remained around 65 for many years (Morris P. I., Wang J. (2006), Wood preservation in Canada, Technical Report, China Wood Protection, 15 p.), but the number of sites where poles are stored is much higher. In the United-States, more than 60 sites were ranked on the list of national priority intervention (US Congress (1995). Cleaning up contaminated wood-treating sites. OTA- BP-ENV-164, Office of Technology Assessment, U.S. Government Printing Office, September, Washington, DC, 45 p.). In Scandinavian countries, more than 500 wood treating sites are contaminated by metals or pentachlorophenol or dioxins and furans, with direct impacts on the environment (Ottosen, L. M., Ribeiro, A.B. & Melcher, E. (2002). Polluted wood preservation sites. Federal Research Centre for Forestry and Forest Products, Institute of Wood Biology and Wood Protection, Hamburg, Germany, 10 p.).

Due to the lack of appropriate technologies for soil remediation, selected approaches were chemical stabilization and solidification or excavation and disposal of contaminated soils. There is currently and will continue to be a need for techniques for remediating wood treating sites. There are some known techniques for dealing with soil that has been contaminated with one or more preservatives such as CCA or PCP or PCDDF. Such techniques fall under the general categories of incineration, dechlorination, thermal desorption, solvent extraction, bioremediation and soil washing.

Destructive methods such as incineration, dechlorination, thermal desorption and separation methods such as extraction with organic solvents are effective to remove organic contaminants such as pentachlorophenol and dioxins and furans, but do not allow a decontamination of metal from soils (Sahle-Demessie, E., Grosse, D. W. & Bates, E. R. (2000). Solvent extraction and soil washing treatment of contaminated soils from wood preserving sites: Bench-scale studies. United States Environmental Protection Agency, Cincinnati, Ohio, 25 p.).

Bioremediation techniques were used for pentachlorophenol and polycyclic aromatic hydrocarbons removal from soil but are less effective for removing metals, dioxins and furans from soils (Biotrol^® Patent, USEPA (1992). BioTrol soil washing system for treatment of a wood preserving site, applications analysis report. EPA/540/A5-91/003 Report, United States Environmental Protection Agency, Cincinnati, Ohio, 76 p.).

Soil washing is the best technique for decontamination of soils polluted with metals, pentachlorophenol and dioxins and furans, but the known techniques are often ineffective or have process costs that make them non-applicable on an industrial scale. In this regard, Riveiro-Huguet and Marshall (Riveiro-Huguet, M. & Marshall, W. D. (2011). Scaling up a treatment to simultaneously remove persistent organic pollutants and heavy metals from contaminated soils. Chemosphere, 83, 668-673.) describe a process including an ultrasonic leaching step with surfactants and chelatants which cost approach US$137,000 per ton of treated soil.

There is a variety of disadvantages and challenges related to the known techniques for decontaminating soil from wood treating sites. Main disadvantages are process efficiency for organic compounds or metals and cost-effectiveness.

There is indeed a need for a technology that overcomes at least one of the disadvantages of what is known in the field. SUMMARY OF THE INVENTION

The present invention responds to the above need by providing a process for the decontamination of soil containing wood- preservative contaminants.

Accordingly, there is provided a process for decontamination of soil contaminated with a preservative including contaminants.

In one aspect, the process includes contacting the soil with water and an inorganic base at a concentration between about 0.1 M and about 2 M at a temperature lower than about Ι ΟΟ , to form an alkaline mixture and solubi lise at least a portion of the contaminants present in the soil, thereby producing a contaminant-rich leachate and a contaminant-poor soil. The process further includes separating the contaminant-poor soil from the contaminant-rich leachate.

In another aspect, the step of contacting the soil may also include contacting with a leaching surfactant, such that the alkaline mixture includes the leaching surfactant. Optionally, the alkaline mixture has a leaching surfactant concentration between about 0.05% and about 5% by weight.

In another aspect, the process may include adjusting a soil content of the alkaline mixture between about 50 g/L and about 500 g/L of the mixture.

In another aspect, the contaminants may include metals, organic compounds or a combination thereof. Optionally, the contaminants may include metals, pentachlorophenol, dioxins and furans, derivatives thereof, analogues thereof, isomers of such contaminants, or a combination thereof.

Further optionally, the contaminants may include pentachlorophenol (PCP), polychlorined dibenzodioxins and polychlorined dibenzofurans (PCDDFs), derivatives thereof, isomeric analogues thereof or a combination thereof.

In another aspect, the contaminants may come from preservatives including chromated copper arsenate (CCA), PCP, PCDDFs, or a combination thereof.

In another aspect, the inorganic base may include sodium hydroxide. Optionally, the inorganic base may include a sodium, potassium or calcium base, a used base, a recycled base, or a combination thereof. In another aspect, the surfactant may include a cationic head, an anionic head, both anionic and cationic heads, a neutral head, or a combination thereof. Optionally, the surfactant may be synthetic or a biosurfactant, or a combination thereof.

In another aspect, the surfactant may include an amphoteric biosurfactant. Optionally, the surfactant may be an amphoteric biosurfactant. The surfactant may include cocamidopropylbetaine. Optionally, the surfactant may be cocamidopropylbetaine.

In another aspect, the process may include mixing the alkaline mixture for a leaching period sufficient to adequately solubilise the contaminants present in the soil. Optionally, the leaching period of the mixing of the alkaline mixture may be between about 0.5 and about 24 h.

In another aspect, the alkaline mixture may have a temperature between about 20Ό and about 80Ό.

In another aspect, the step of contacting producing the contaminant-rich leachate and the contaminant-poor soil may be performed in a single leaching step. Alternately, the step of contacting producing the contaminant-rich leachate and the contaminant-poor soil may be performed in multiple leaching steps.

In another aspect, the multiple leaching steps may be performed sequentially. Optionally, the sequential leaching steps may utilize the same or different inorganic bases. The sequential leaching steps may utilize the same or different concentrations of the inorganic base(s). Additionally, the sequential leaching steps may utilize the same or different surfactants, and may utilize the same or different concentrations of the surfactant(s).

In another aspect, the leaching steps may be operated in batch, semi-continuous or continuous mode in tank reactors.

In another aspect, after the leaching step or steps, the contaminant-poor soil may be separated from the contaminant-rich leachate by decantation, filtration, centrifugation, or another technique of solid-liquid separation, or a combination thereof.

In another aspect, the process may include washing the separated contaminant-poor soil to remove residual solubilised contaminants. Optionally, the washing may be done by rinsing the solids resulting from a previous filtration step or by mixing the solids re- suspended in the washing solution, followed by a step of solid-liquid separation. In another aspect, the washing may be done in one or more steps with water, a dilute alkaline solution, or an acid solution. The different washing steps may be performed with the same or different washing solutions.

In another aspect, the contaminant-rich leachate and spent washing liquids may be combined to obtain a solution containing the totality of the target contaminants, referred to as the contaminant solution.

In another aspect, some or all of spent washing waters may be directly used as process water for the operation of the initial leaching steps for a subsequent batch or quantity of contaminated soil.

In another aspect, the contaminant-rich leachate and the spent washing liquids may be referred to as alkaline leachate, which may include at least a portion of the contaminant- rich leachate or the spent washing liquids or a combination thereof, and wherein the process may include treating at least a portion of the alkaline leachate to recover at least one of the contaminants therefrom.

In another aspect, the recovered contaminant may include a metal. Optionally, at least a portion of the recovered metal may include copper arsenic, chromium, copper, or a combination thereof. Alternatively, at least a portion of the recovered metal may be recovered in the form of mixed metalloid compounds and/or as pure metal. The metal contaminant may be recovered by means of chemical precipitation, ion exchange, solvent extraction, adsorption or a combination thereof.

In another aspect, after the alkaline leachate has been treated to remove the at least one of the contaminants, a resulting treated solution may be used as process water for the contacting step forming the alkaline mixture.

In another aspect, at least two of pentachlorophenol, dioxins and furans, copper, chromium and arsenic may be simultaneously removed from the alkaline leachate. Optionally, all of pentachlorophenol, dioxins and furans, copper, chromium and arsenic may be simultaneously removed from the alkaline leachate.

In another aspect, the removal may be performed by a total precipitation technique using an iron salt. The iron salt may include ferric chloride or sulfate. The total precipitation technique may also use a strong acid. The strong acid may include sulfuric acid. In another aspect, the alkaline leachate may be treated to remove at least one organic compound. The at least one organic compound may include pentachlorophenol, dioxins and furans or a combination thereof. Optionally, the at least one organic compound may be removed by means of chemical precipitation, ion exchange, solvent extraction or adsorption or a combination thereof. Further optionally, the organic compound may be removed from the alkaline leachate by means of ion exchange resins, or activated carbons, or a combination thereof.

In another aspect, the decontaminated soil and/or the contaminants extracted from the soil and/or alkaline leachate may be disposed of or recycled.

In another aspect, the process may include, prior to contacting the soil with the water and the inorganic base to form the alkaline mixture, the steps of:

mixing the soil with an initial amount of water so as to form an aqueous mixture of soil;

subjecting the aqueous mixture of soil to attrition during an attrition period to solubilise at least a portion of the contaminants present in the soil; and subjecting the aqueous mixture of soil to separation to produce a contaminant-rich liquid, a contaminant-depleted soil and a contaminated sludge.

In another aspect, the step of mixing the soil with the initial amount of water also includes mixing with an attrition surfactant such that the aqueous mixture includes the attrition surfactant. Optionally, the aqueous mixture of soil may have an attrition surfactant concentration between about 0.05% and about 5% by weight.

In another aspect, the attrition surfactant may have a cationic head, an anionic head, both cationic and anionic heads, a neutral head or a combination thereof. Optionally, the attrition surfactant may include a biosurfactant. Optionally, the attrition surfactant may include cocamidopropylbetaine.

In another aspect, the process may include providing a soil content of the aqueous mixture of soil to obtain a soil concentration between about 50 g/L and about 500 g/L of mixture.

In another aspect, the attrition period may be between about 0.01 h and about 1 h. In another aspect, the attrition step may be repeated until a pre-determined minimum concentration of the contaminants in the contaminant-rich liquid is reached.

In another aspect, the separation of the aqueous mixture of soil may include decantation, filtration, centrifugation, or a combination thereof.

In another aspect, the process may include crushing and/or screening the soil so as to obtain fine soil particles. The crushing and/or screening step may be performed prior to contacting the soil with water and an inorganic base. Optionally, the crushing and/or screening step may be performed prior to mixing the soil with the initial amount of water to form the aqueous mixture of soil. The screening of the soil may include screening according to four solid fractions >4 mm, 4-1 mm, 1-0.125 mm and <0.125 mm. Alternatively, the soil may be crushed and/or screened so as to have particle size inferior to about 1 cm. Optionally, the soil may be crushed and/or screened so as to have particle size inferior to about 0.6 mm.

In another aspect, there is provided a process for contaminant extraction from a contaminated solution. The process may include:

contacting the contaminated solution with a coagulant at a pH favoring precipitation of pentachlorophenol, copper, chromium and arsenic; and/or contacting the contaminated solution with an activated carbon or an ion exchange resin favoring pentachlorophenol, dioxins and furans extraction.

In another aspect, the process may include at least one step or feature as defined in the present description and/or figures for treating the contaminated soil, the contaminated solution, the contaminants and/or any of resulting streams or fractions of the process.

In another aspect, there is provided a process for decontamination of soil contaminated with a preservative including contaminants. The contaminants may include metals and/or organic compounds, wherein:

the metals include arsenic, chromium, copper, and/or other metal species; and the organic compounds include pentachlorophenol and derivatives thereof, dioxins and furans and/or other organic species;

The process may further include the steps of:

contacting the soil with water, an inorganic base, and with or without a leaching surfactant, at a temperature lower than about 100Ό , the concentrations of the inorganic base and the leaching surfactant being sufficient to enable solubilisation of a substantial amount of the contaminants present in the soil, thereby producing a contaminant-rich leachate and contaminant-poor soil; and separating the contaminant-poor soil from the contaminant-rich leachate.

In another aspect, the process may include at least one step or feature as defined in the present description and/or figures.

the metals include arsenic, chromium, copper, and/or other metal species; and the organic compounds include pentachlorophenol and derivatives thereof, dioxins and furans, and/or other organic species.

The process may further include the steps of:

mixing the soil with water and with or without an attrition surfactant so as to form an aqueous mixture of soil;

subjecting the soil to attrition by agitating the aqueous mixture of soil to solubilise at least a portion of the contaminants; and

subjecting the aqueous mixture of soil to separation to produce a contaminant- rich liquid, a contaminant-depleted soil and a contaminated sludge;

contacting the contaminated sludge with water and a base, at a temperature lower than about 100Ό, to enable solubilisation of a substantial amount of the contaminants present in the contaminated sludge, thereby producing a contaminant-rich leachate and contaminant-poor soil; and

separating the the contaminant-poor soil from the contaminant-rich leachate.

In another aspect, the dioxins and furans may include PCDDFs and isomeric analogues thereof. Optionally, the metals and organic compounds may be from preservatives. Optionally, the preservatives may include chromated copper arsenate, PCP and/or PCDDFs.

In another aspect, the base may be an inorganic base and the contacting step may further include adding a leaching surfactant, concentrations of the inorganic base and the leaching surfactant being sufficient to enable solubilisation of the substantial amount of the contaminants present in the contaminated sludge.

Additional embodiments, aspects and features of the present invention will be described and defined herein.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig 1 is a flowchart of the process according to an embodiment of the present invention.

Fig 2 is a graph of As, Cr, Cu and PCP solubilisation from wood treating site soil after leaching by several chemical reagents.

Figs 3A and 3B are graphs of As, Cr, Cu and PCP solubilisation from wood treating site soil after sodium hydroxide leaching at various base concentration and pulp density.

Figs 4A and 4B are graphs of As, Cr, Cu and PCP solubilisation from wood treating site soil after sodium hydroxide leaching at various temperature and reaction time.

Fig 5 is a graph of PCDDFs solubilisation from wood treating site soil after sodium hydroxide leaching with several surfactants according to optimized parameters.

Fig 6 is a graph of As, Cr, Cu and PCP removal yields after precipitation step with various volume of coagulant.

Fig 7A and 7B are a graph of As, Cr, Cu and PCP removal yields after contacting soil leachates with several adsorbents or ion exchange resins.

Fig 8 is a graph of As, Cr, Cu, PCP and PCDDFs removal yields after contacting soil leachates with best adsorbents, ion exchange resins or after optimised precipitation step.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Process embodiments of the present invention provide an effective and economical technique to remove contaminants from soil and to treat the resulting leachate solutions. In one optional aspect of the process embodiments of the present invention, they are used in relation to soil containing arsenic, chromium, copper, pentachlorophenol, dioxins and furans.

Definitions

"About", when qualifying the value of a variable or property - such as concentration, temperature, pH, particle size and so on - means that such variable or property can vary within a certain range depending on the margin of error of the method or apparatus used to evaluate such variable or property. For instance, the margin of error for temperature may range between ± 1 ^*C and ± 5 .

"Contaminated soil" means a soil that may be in any state, granular or powder form and so on, which has at some time been in contact with a wood preservative to thereby become "contaminated". It should be understood that the contaminated soil may be mixed with uncontaminated soil at various point in the process in order to form an overall soil quantity to meet certain governmental or environmental standards.

"Preservative" means a compound for treating wood in order to increase its useful lifetime or compound which come from decomposition of initial compound. Preservatives may include a fungicide component and an insecticide component to combat those two factors that so often lead to the deterioration of wood. There are many different types of preservatives that have been used to treat wood.

"Inorganic base" means a base lacking a carbon atom and may be a hydroxide or a carbonate of sodium, potassium or calcium or a combination of such bases. It should also be understood that the inorganic base may be a used or recycled base.

"Surfactant" means a compound that lowers the surface tension of a liquid or that between a liquid and a solid. Surfactants may act as detergents, wetting agents, emulsifiers, foaming agents, and dispersants. Surfactants can have a cationic, anionic, both anionic and cationic or neutral head and can be synthetic or a biosurfactant. An attrition surfactant is a surfactant as defined above that may be used during the attrition step according to the presently described processes. A leaching surfactant is a surfactant as defined above that may be used during the leaching step of the presently described processes.

"Contacting", when pertaining to the contaminated soil and the inorganic base and water, means that those elements contact each other so as to enable diffusion of the contaminants from the soil phase into the alkaline solution phase. The "contacting" will often be referred to as leaching herein and may include techniques such as soaking, batch mixing, trickling, spraying, continuous flow-by, or various combination of such contacting techniques.

"Attrition", when pertaining to the contaminated soil and water, means subjecting a mixture of contaminated soil and water to agitation to induce physical wear of the soil and separation into smaller soil particles. Attrition may also aid in desorbing fine soil particles from larger soil particles. The attrition may help enable diffusion of the contaminants from the soil particles into the aqueous solution. The attrition may include techniques such as mixing, blending, milling or any similar agitation techniques available. An attrition step may be performed in conjunction with other actions, such as contacting the soil with water, and the contacting step may include soaking, batch mixing, trickling, spraying, continuous flow-by, or various combinations of such contacting techniques.

"Separating", when pertaining to the contaminant-rich solution and the contaminant-poor soil, means any suitable solid-liquid separation technique.

"Arsenic" (As), "chromium" (Cr), "copper" (Cu), unless specified otherwise, each means a compound containing the given element and may include solubilised ions, complexes, derivatives, isomers, as the case may be. For instance, the term "chromium" may include chromium III and chromium VI; "arsenic" may include arsenate in association with CCA or solubilised in an aqueous medium; while "copper" may include the element in association with CCA, solubilised, or in its pure metallic form upon recovery. Thus, these elements should be read with a mind to their relationship with the process steps, process conditions and other interacting compounds.

"Pentachlorophenol" (PCP), "dioxins and furans" (PCDDFs), unless specified otherwise, each means a compound containing the given compounds and may include solubilised ions, complexes, derivatives, isomers, as the case may be. For instance, the term "pentachlorophenol" may include all chlorophenols such as dichlorophenol, trichlorophenol and tetrachlorophenol; "dioxins and furans" may include all 210 isomers of polychlorined dibenzodioxins and polychlorined dibenzofurans. Thus, these compounds should be read with a mind to their relationship with the process steps, process conditions and other interacting compounds.

"Contaminant-rich solution" means a solution containing the contaminants removed from the contaminated soil during a leaching step. It should also be understood that for subsequent treatment of the solution to remove or recover contaminants, the contaminant-rich solution from the initial step may be combined with solutions from other leaching or washing steps to form an overall contaminant-rich solution. Thus, the contaminant-rich solution may be combined with other streams, or be subjected to various other steps before it is treated to recover one or more of the contaminants. Embodiments of the processes

Fig 1 shows a flow diagram of the various stages of one embodiment of the process.

In one aspect, the process includes at least one leaching step of the contaminated soil to solubilise arsenic, chromium, copper, PCP and PCDDF, also referred to as contaminants, from the contaminated soil. The at least one leaching step is performed with water and an inorganic base, and may be performed with an additional leaching surfactant. A decontaminated soil and alkaline leachates are formed with the leaching step.

In another aspect, the process further includes at least one treatment step for the recovery of metals and organic compounds from the alkaline leachates. Smaller yield of removal for PCDDF can be obtained if the inorganic base only is used. The decontaminated soil and the contaminants extracted from the soil may be safely disposed.

In another aspect, the process may include, before the at least one leaching step, at least one attrition step where the contaminated soil is subjected to attrition so as to facilitate further solubilisation of arsenic, chromium, copper, PCP and/or PCDDF from the contaminated soil into a liquid phase. The at least one attrition step may be performed with an attrition surfactant to enhance solubilisation of the contaminants

According to one embodiment of the process, the attrition step may be performed without adding any liquid to the contaminated soil during attrition, by milling, for example, so as to produce fine soil particles. This step may be referred to as dry attrition. The fine soil particles may further be subjected to the at least one leaching step.

According to another embodiment of the process, the attrition step may include mixing the contaminated soil with water and with or without an attrition surfactant at a concentration between about 0.05% and about 5% so as to form an aqueous mixture of soil. The attrition step further includes agitating the aqueous mixture of soil for a period sufficient to adequately solubilise contaminants present in large soil fractions and form an aqueous suspension of soil including soil fractions and fine soil particles. Optionally, the agitation duration may be between about 0.01 h and about 1 h. The attrition step may therefore be performed so as to solubilise in water at least a portion of contaminants present in the initial contaminated soil. Optionally, the attrition surfactant may be added such that the aqueous mixture of soil has an attrition surfactant concentration between about 0.05% and about 5% by weight. The attrition surfactant may have cationic, anionic, both anionic and cationic or neutral head and can be synthetic or a biosurfactant, or a combination thereof. More particularly, the attrition surfactant may be an amphoteric biosurfactant, such as cocamidopropylbetaine.

Optionally, the amount of water and/or the amount of contaminated soil that are mixed together during the attrition step may be adjusted so as to obtain an aqueous mixture of soil having a soil concentration between about 50 g/L and about 500 g/L of solution.

According to another embodiment of the process, the at least one attrition step may be a single attrition step or include several sequential attrition steps that employ the same or different attrition surfactants and concentrations of attrition surfactants. Optionally, the attrition step(s) may be operated in batch, semi-continuous or continuous mode in tank reactors.

In another aspect, subsequent to the at least one attrition step and before the at least one leaching step, the process may include a first separation step to separate the aqueous suspension of soil into a contaminant-rich solution, a contaminated sludge (also referred to as attrition sludge) and a contaminant-depleted soil. Optionally, the separation step may include decantation, filtration, centrifugation, or another standard technique of solid-liquid separation.

In another aspect, the at least one leaching step of the process includes basification of soil by a mixture of an inorganic base and water so as to produce an alkaline solution. More particularly, the at least one leaching step includes contacting the soil with a mixture of water and an inorganic base at a concentration between about 0.1 M and about 2 M, to solubilise in the mixture at least a portion of contaminants present in the soil. The at least one leaching step may also include adding a leaching surfactant. This contacting step may also be called a primary alkaline leaching step.

It should be understood that the soil which is subjected to the leaching step may be a contaminated soil as defined above, the contaminant-depleted soil as defined above if the process includes an attrition step prior to the leaching step, or a combination thereof. In another aspect, the at least one leaching step may further include mixing the alkaline solution for a period sufficient to adequately solubilise contaminants present in the soil. Optionally, the duration may be between about 0.5 h and about 24 h.

It should be understood that the expression "adequately solubilise" refers herein to a solubilisation of the contaminants respecting the governmental decontamination norms, such as MDDEFP norms in the province of Quebec.

According to one embodiment of the process, the soil content of the alkaline solution for the at least one leaching step may be adjusted to be between about 50 and about 500 g/L of solution.

According to another embodiment of the process, the inorganic base may be added so as to obtain an alkaline solution having a base concentration between about 0.1 M and about 2 M. The inorganic base used as a leaching agent may be sodium, potassium or calcium base, used base, recycled base or a combination thereof. Optionally, the inorganic base may be sodium hydroxide.

According to another embodiment of the process, the leaching surfactant may be added so as to obtain an alkaline solution having a leaching surfactant concentration between about 0.05% and about 5% by weight. The leaching surfactant may have cationic, anionic, both anionic and cationic or neutral head and can be synthetic or a biosurfactant, or a combination thereof. The leaching surfactant may be an amphoteric biosurfactant, such as cocamidopropylbetaine.

According to another embodiment of the process, the alkaline solution may be maintained at a temperature below about 100Ό. Opti onally, the temperature may be between about 20Ό and about 80Ό.

According to another embodiment of the process, the at least one leaching step may be a single leaching step or may include several sequential leaching steps that employ the same or different bases and leaching surfactants and concentrations of the bases and surfactants. Optionally, the leaching step(s) may be operated in batch, semi-continuous or continuous mode in tank reactors.

According to another embodiment of the process, the attrition surfactant and the leaching surfactant may be the same or different and have same or different concentrations in solution. In another aspect, the process may include a crushing and/or screening step so as to obtain for instance soil having a size inferior to about 1 cm, preferably inferior to about 0.6 mm. More particularly, the process may include crushing and/or screening the contaminated soil so as to obtain for instance several soil fractions having the following sizes: >4 mm, 4-1 mm, 1-0.125 mm and <0.125 mm. This step may be performed before the at least one attrition step, or between the at least one attrition step and the at least one leaching step.

In another aspect, subsequent to the at least one leaching step, the process may include a separation step wherein the soil is separated from the alkaline solution, thereby obtaining a contaminant-poor soil and a contaminant-rich alkaline leachate. Optionally, the separation step may include decantation, filtration, centrifugation, or another standard technique of solid-liquid separation.

In another aspect, the process may further include a washing step to remove residual solubilised contaminants from the soil with a washing solution. The washing of the soil may be done by rinsing the solids resulting from a previous filtration step with the washing solution. Alternately, the washing of the soil may be done by mixing the solids re-suspended in the washing solution, followed by a step of solid-liquid separation. The washing of the soil may be done in one or more steps with water, a dilute alkaline solution, or an acid solution. Optionally, the different washing steps may be performed with the same or different washing solutions.

In another aspect, the process may further include combining the contaminant-rich solution from the attrition step, the contaminant-rich alkaline leachate from the leaching step and the spent washing liquids to obtain a solution containing the totality of the targeted contaminants. Optionally, some or all of the washing liquids may also be directly used as process water for the operation of the initial leaching step for a subsequent batch or quantity of contaminated soil.

In another aspect, the process may also include treating the contaminant-rich solution, the contaminant-rich alkaline leachate, the spent washing liquids or a combination thereof, to recover at least one of the contaminants. The combination of the contaminant-rich solution, the contaminant-rich alkaline leachate and the spent washing liquids will be generally referred to herein as the "contaminant solution", which contains the solubilised contaminants. It should be understood, however, that the solution treated to recover solubilised contaminants may be the contaminant-rich solution or the alkaline leachate or the spent washing liquid only. Optionally, the treating step may include one or a combination of the following techniques: chemical precipitation, ion exchange, solvent extraction and adsorption. After the contaminant solution has been treated to remove the contaminants, it may for example be used as process water for the operation of the leaching step.

In another embodiment of the process, pentachlorophenol, copper, chromium and arsenic may be simultaneously removed from the contaminant solution by a total precipitation technique using an iron salt (e.g. ferric chloride or sulfate) with a strong acid (e.g. sulfuric acid). Organic compounds such as PCP and PCDDF can be removed from the solution by using ion exchange resins or activated carbons.

Optionally, the decontaminated soil and the contaminants extracted from the soil can be safely disposed of or recycled.

Embodiments of the present invention provide a number of advantages. Advantages will be understood as per the above and the examples and experimental data obtained through the extensive studies presented below.

For instance, the use of inorganic base and surfactant, such as sodium hydroxide and cocamidopropylbetaine respectively, allows good metal, pentachlorophenol, dioxins and furans solubilisation yields from soil at a low chemical cost. The relatively low temperature (< 100°C) used during the leaching step can be reached at low energy cost. Furthermore, the addition of at least one washing step after the leaching step is useful to remove the dissolved contaminants still present in the soil.

EXAMPLES, EXPERIMENTATION & ADDITIONAL INFORMATION

The embodiments of the present invention will be further comprehended and elaborated in light of the following examples and results, which are to be understood as exemplary and non-limiting to what has actually been invented.

General Methodology

The following describes the general methodology of examples of an embodiment of the process of the present invention.

So/7 characterisation

Experiments were conducted on four polluted soils F1 , S1 , S2 and S3. The measured contaminants concentrations for the four soils were between 50 and 250 mg kg^"1 for As, 35 and 220 mg kg^"1 for Cr, 80 and 350 mg kg^"1 for Cu, and 2.5 and 30 mg kg^"1 for PCP. S2 and S3 soils were the most heavily contaminated by metals and PCP. PCDDF concentrations reached 1 390 mg kg^"1, 1 380 mg kg^"1, 3 730 mg kg^"1, and 6 290 mg kg^"1 for F1 , S1 , S2, and S3 soils respectively.

So/7 attrition

An attrition step was performed on the four F1 , S1 , S2 and S3 soils to determine efficient and economical design and operation for removing, for example, As, Cu, Cr, CCA, PCP and PCDDF. Soil samples were passed through several sieves to separate soil in four fractions as followed: >4 mm, 4-1 mm, 1-0.125 mm and <0.125 mm. Attrition was conducted on the three first. Experiments were carried out on 2 kg of soil for a 40% (w v^'1) pulp density (PD) at room temperature (T = 22 ± 2°C). During attrition, after 20 minutes of agitating at 1000 revolutions per minute (rpm) (attrition cell), contaminant- depleted soil, attrition sludge and washing solutions were separated. The contaminant- depleted soil was then dried at 60°C and analyzed. Non-ionic surfactant (TW80) and amphoteric surfactant (BW) at a concentration of 0.5% were evaluated for contaminants removal.

So/7 decontamination

A series of leaching experiments were performed in Erlenmeyer flasks (250 ml_) in triplicate with 10 g of the F1 soil fraction < 1 mm. The volume was set at 100 ml_ for a PD of 10% (w v^"1). Experiments were conducted at room temperature (T = 22 ± 2 ) for 60 minutes using a rotary incubator (Lab-Line Environ-Shaker, Model 3528) set at 200 rotations per minute (rpm). Mineral acids (H₂S0₄, HCI, and HN0₃), bases (NaOH, KOH, and Ca(OH)₂), organic acid (lactic acid) and ethanol were evaluated for their ability to solubilise PCP and CCA. The concentrations of mineral acids and bases were set at 1 N. The lactic acid and ethanol concentrations were adjusted to 25% and 50% (v v^"1 in water), respectively. The leaching solution and soil were separated by vacuum filtration (500 hPa) on a Whatman 934-AH filter (pore size = 1.5 μηι). The soil was then dried at room temperature to avoid volatilization of organics before analysis. Experiments were also conducted under different conditions (temperature, time, PD, concentration of leaching solution) to investigate the influence of these conditions on the removal of pollutants. Another series of sequential leaching experiments were performed in a 2 L beaker on dry soil with fractions of 0-2 mm or 0-6 mm. Soils were screened using a sieve with a 2- or 6-mm-square diagonal aperture and allowed to dry overnight at room temperature. Leaching steps were performed by mixing 100 g of S1 or S2 soil with 1 L of alkaline solution (1 M NaOH), carried out over 2 h at 80 u sing a hot plate and in the presence of a surfactant (Brij 35, CAS, BW, Igepal CA-720, SDS, Tween 80, or Triton X-100) at a concentration of 1 or 2% (v w^"1). Agitation was performed using an immersed axial impeller or by magnetic stirring at between 300 and 750 rpm. After each leaching step, the mixture was allowed to settle for at least 2 h, and the leachate was recovered. After three leaching steps, the soil was mixed with 1 L of water at room temperature, and the mixture was stirred vigorously at 1 150 rpm. The solution was then allowed to settle overnight before being filtered with Whatman No. 4 cellulose paper (porosity = 20- 25 μηι). The soil and filter were then dried overnight at room temperature. The concentrations of PCP, PCDDF, and metals in the dry soil were then measured.

Chemical precipitation and coagulation

Coagulation experiments occurred in 250 ml_ beaker with magnetic stirring at 250 rpm using a Teflon-covered bar. Leachate pH was initially stabilized to the appropriate pH by adding sulfuric acid solution. Then, ferric sulfate solution Fe₂(S0₄)₃ was added into the 100 or 200 mL leachates. The pH was re-adjusted after ferric sulfate addition. Solutions were mixed together at 250 rpm for 30 min, and then settled down for 24 h. The supernatant was collected and filtrated on Whatman 934AH membranes for further soluble metals and pentachlorophenol analysis. Industrial ferric sulfate solution from Environnement EagleBrook Canada Ltee (Varennes, Canada) containing 160 g Fe/L was used.

Ion exchange resin and adsorbent

Experiments regarding ion exchange resin and adsorbent assessed the potential of ion exchange and adsorption for selective recovery of contaminants. Experiments were conducted in batch mode. Five grams of resin or adsorbent were mixed with 250 mL soil leachate in 500 mL Erlenmeyer flasks and agitated at 200 revolutions per minute (rpm) (Orbital shaker, Lab-line Environ-Shaker, model 3528) for 24 h to ensure that chemical equilibrium was attained. Thereafter, liquid to solid separation was made by filtration onto Whatman 934AH filter. Ion exchange resins studied are anionic (Lewatit MP500, Lewatit SR7, Amberlite IRA900), cationic (Lewatit TP207), adsorption (Lewatit F036, Lewatit VPOC, Lewatit AF5). Adsorbent studied are granular, medium or fine anthracite (anthra G, anthra M and anthra F), Norit, Aquamerik and Darco granular activated carbon (CAG N, CAG A, and CAG D), powdered activated carbon (CAP), alumina and silica.

Analytical techniques

Metal and metalloid analyses were performed by inductive coupled plasma with atomic emission spectroscopy (ICP-AES) (Varian, model Vista-AX simultaneous ICP-AES) according to the CEAEQ method. Soils were digested with aqua regia (1/4 nitric acid and 3/4 hydrochloric acid) at 80 for 8 h. Analysis wa s controlled using reference certified solutions obtained from SCP Science, and yttrium was used as the internal standard.

PCP analysis was performed by gas chromatography with mass spectroscopy (GC-MS) (Perkin Elmer, model Clarus 500, column type DB-5, 30 mm x 0.25 mm x 0.25 μηι) according to the CEAEQ method. Samples were extracted with Soxhlet in methylene chloride over a period of 12 h, followed by extraction in sodium hydroxide, then derivatized (chemically transformed) with anhydrous acetate, and finally extracted in methylene chloride. Tribromophenol was used as the recovery standard, and phenanthren d10 was used as the internal standard.

Analysis of the 17 major polychlorinated dibenzo-p-dioxins and dibenzofurans was performed using the CEAEQ method by GC-MS with an RTX-Dioxin column of 60 mm x 0.25 mm x 0.25 μηι. To analyze the PCDDF content in the soils, between 15 and 20 g of soil (based on the expected contamination) were precisely weighed. The Soxhlet extraction was done with toluene, and then the samples were purified and concentrated using a multilayer silica column eluted with hexane and an alumina column eluted in three fractions with mixtures of hexane and of dichloromethane. The eluate was concentrated in a brown microwave vial and evaporated to dryness under nitrogen stream. A volume of 50 of internal standard was then added, and the sample was analyzed by GC-MS. Quantification was performed with 13C-labeled analogs purchased from Wellington laboratories.

Economic aspect

The chemical costs associated to the decontamination of wood treating sites soils were calculated on the basis of the following unitary prices. The sodium hydroxide (99.9% pure powder) was estimated at a cost of US$500/t and the cocamidopropylbetaine (solution at 35% w/w) was calculated at a cost of US$1000/t. The sulfuric acid (solution at 93% w/w) was evaluated at a cost of US$80/t and the ferric sulfate solution (160 g Fe/L) at a cost of US$500/t.

Example 1 : Selection of the leaching reagent

Assays were conducted to determine the effectiveness of several leaching reagents (inorganic and organic acids, ethanol and bases) in solubilising metals (mainly As, Cu and Cr) and PCP. The inorganic acids and bases had a concentration of 1 N, and the ethanol and lactic acid had concentrations of 50% (v v^"1) and 25% (v v^"1), respectively. These concentrations correspond to the optimum values identified in Subramanian (Subramanian, B. (2007). Exploring neoteric solvent extractants: Applications in the removal of sorbates from solid surfaces and regeneration of automotive catalytic converters. Division of Research and Advanced Studies, University of Cincinnati, Cincinnati, Ohio, 82 p.) and Khodadoust et al. (Khodadoust, A. P., Reddy, K. R. & Maturi, K. (2005). Effect of different extraction agents on metal and organic contaminant removal from a field soil. J. Hazard. Mater., 117(1), 15-24.). A mass of 10 g of F1 soil was stirred with 100 mL of solution (for a PD of 10%) at room temperature for 1 h. The removal yields obtained during these leaching assays are presented in Figure 2.

Referring to Figure 2, H₂S0₄, HN0₃ and lactic acid show good potential for the solubilisation of the three metals As, Cu and Cr, while HCI does not dissolve As and Cr. Contrary to the observations of Subramanian (2007), lactic acid and mineral acids did not solubilise PCP. Ethanol, used by Khodadoust et al. (2005) to solubilise metal, does not allow good dissolution of CCA, but solubilises 50% of PCP. NaOH and KOH solutions yield the best solubilisation of PCP (85-90%). This result confirms the observation made by Banerji S. K., Wei, S. M. & Bajpai, R. K. in Pentachlorophenol interactions with soil, Water Air Soil Pollut., 69 (1-2), 149-163, 1993 (Banerji et al. (1993)), that increasing the pH of the washing solution promotes the solubilisation of PCP because its interactions with soil are lower. On the other hand, this result invalidates the interpretation of DiVincenzo and Sparks (DiVincenzo, J. P. & Sparks, D. L. (2001). Sorption of the neutral and charged forms of pentachlorophenol on soil: Evidence for different mechanisms. Arch. Environ. Contam. Toxicol., 40, 445-450.) that PCP sorption in an alkaline medium seems irreversible. Sodium and potassium hydroxide also solubilise 50% of As and 30 to 40% of Cu. Sodium hydroxide was selected for further assays to develop a treatment for soil contaminated with PCP and CCA in an alkaline medium. Sodium hydroxide was chosen rather than potassium hydroxide because of its lower cost and slightly higher efficiency.

Example 2: Effect of operating parameters

Different leaching conditions were studied to determine their influence on contaminant solubilisation and obtain operating condition ranges for the experimental design. Figures 3A, 3B, 4A and 4B show the removal of CCA and PCP in an alkaline medium as a function of the base concentration (3A), PD (3B), temperature (4A) and leaching time (4B). Assays were conducted in triplicate on 10 g of the 0-2 mm fraction of F1 soil and 100 ml_ of alkaline solution.

Referring to Figure 3A, solubilisation of metals increases up to 40% and 60% for Cu and As, respectively, for a solution of 2 N NaOH. For PCP, maximum solubilisation (90%) is reached at a concentration of 1 N NaOH. This concentration was chosen to obtain sufficient solubilisation of contaminants while limiting the increase in the operating costs for chemical reagents.

Referring to Figure 3B, an increase in the PD from 5% to 20% slightly decreased the removal of metal and significantly reduced the solubilisation of PCP, from 99% to 62%. A PD of 10% may be a good compromise between obtaining good efficiency and using a smaller leaching reactor.

Referring to Figure 4A, temperature strongly influences the solubilisation of PCP and CCA. The temperature may be set around 80 to enha nce the solubilisation of PCP and As. This result is consistent with observations by Tse et al. (Tse, K. K. C. & Lo, S. L. (2002). Desorption kinetics of PCP-contaminated soil: effect of temperature. Water Res., 36, 284-290.) on the influence of temperature, noting that optimal PCP solubilisation from soil occurred at 75 .

Referring to Figure 4B, reaction time has less influence on contaminant solubilisation according to the relative error of the triplicate tests. Solubilisation yields increase slightly during the process. A reaction time of 2 h was set for the solubilisation of contaminants because previous results indicate that this amount of time is optimal. Example 3: Evaluation of surfactant for PCDDF solubilisation

Assays were conducted on S1 soil with an anionic (sodium dodecyl succinate), two amphoteric (cocamidopropyl hydroxysultaine CAS and betaine BW) and four non-ionic (Brij-35, lgepal-CA720, Tween-80, Triton-X100) surfactants. Experimental parameters determined previously were used. Figure 5 presents PCDDF solubilisation at surfactant concentration of 10 g kg^"1 (1 %). SDS, Tween 80 and Triton X100 allow the best PCDDF removal which approaches 60% with only one leaching step.

In other experiments, it was shown that some surfactants reduce or enhance PCP and CCA solubilisation. With 3 leaching steps, best results were obtained with the amphoteric surfactant BW which increases PCP and CCA solubilisation. Otherwise, it shows acceptable removal yields for PCDDF and has advantages to be non-toxic and biodegradable.

Example 4: Leaching process characteristics and cost

Since alkaline soil washing with surfactant seems to be a promising method to treat soils contaminated with both organic and inorganic pollutants, process was tested on the four contaminated soils. For the purpose of an optional embodiment of the process, the parameters for leaching of wood treating site soil were selected as follows:

1. Soil content: 100 g/L;

2. Base type and concentration: 0.75 M NaOH;

3. Temperature: 80°C;

4. Reaction time: 2 h;

5. Leaching / rinsing step: 3 / 1 ; and

6. Surfactant type and concentration: 3% BW.

Table 1 gives the removal yields of PCP, CCA and PCDDF evaluated on pollutant concentrations in the soil before and after treatment. Table 1 : Removal yields of PCP, CCA and PCDDF for the four soils after 3 alkaline leaching steps and 1 rinsing step with surfactant BW at concentration of 30 g kg^"1, t = 120 min, T = 80°C, NaOH = 0,75M, PD = 10% (w v¹)

As Cr Cu PCP PCDDF

F1 soil

(mg/kg) (mg/kg) (mg/kg) (mg/kg) (ng/kg)

Before treatment 52.0 60.6 81 .5 2.12 1 ,394

After treatment 20.7 55.6 49.6 0.49 270

Solubilisation 59% 8% 41% 77% 81%

As Cr Cu PCP PCDDF

S1 soil

(mg/kg) (mg/kg) (mg/kg) (mg/kg) (ng/kg)

Before treatment 90.6 67.2 143 8.06 1 ,375

After treatment 6.63 22.6 19.9 1 .35 147

Solubilisation 92% 66% 91% 83% 89%

As Cr Cu PCP PCDDF

S2 soil

(mg/kg) (mg/kg) (mg/kg) (mg/kg) (ng/kg)

Before treatment 262 199 346 7.01 3,730

After treatment 62.1 152.0 185.4 0.61 874

Solubilisation 74% 21% 48% 91% 77%

As Cr Cu PCP PCDDF

S3 soil

(mg/kg) (mg/kg) (mg/kg) (mg/kg) (ng/kg)

Before treatment 91 .1 83.0 148 47.2 6,289

After treatment 13.5 54.2 66.7 0.92 603

Solubilisation 84% 34% 58% 98% 90%

This chemical leaching allows good metals solubilisation with average removal yields of 77% for As, 32% for Cr and 60% for Cu. Moreover, it allows very good organic pollutants solubilisation with average removal yields of 87% for PCP and 84% for PCDDF. Cost associated to chemical leaching depends on sodium hydroxide concentration. For F1 and S1 soils, base concentration of 0.5 M allows sufficient soil decontamination according to Quebec regulation on contaminated soil. For S2 soil, a base concentration of 1 M is needed and for S3 soil, a base concentration of 0.75 M. In those cases, cost associated to chemical leaching for the treatment of 1 t of dry soil is between US$145 and US$265. This estimate does not take into account the possibility of recycling the final alkaline leachate after contaminant removal. This alkaline leaching has good potential for industrial application. A closed loop system may also further lower operational costs.

Example 5: Attrition process characteristics

Attrition process was first tested on the highly contaminated S2 soil. S2 soil was screened into four fractions using sieves as follows: >4 mm, 4-1 mm, 1-0.125 mm and <0.125 mm. Attrition was conducted on the three first fractions.

For the purpose of an optional embodiment of the process, the parameters for the attrition of wood treating site soil were selected as follows:

1. Soil content: 400 g/L;

2. Temperature: 20°C;

3. Reaction time: 20 min;

4. Attrition step: 3; and

5. Without surfactant.

Table 2 gives the concentration of PCP, CCA and PCDDF in each soil fractions before and after treatment.

Table 2: Concentration of PCP, CCA and PCDDF for the S2 soil before and after 3 attrition step without surfactant, t = 20 min, T = 20°C, PD = 40% (w v¹)

S2 soil As Cr Cu PCP PCDDF

Treatment

fraction (mg/kg) (mg/kg) (mg/kg) (mg/kg) (ng/kg)

> 4 mm 52 24 98 0.2 1 089

Before

1 -4 mm 71 75 134 1 .0 1 857 treatment

0.125-1 mm 84 153 158 1 .3 1 267

> 4 mm 37 12 49 0.3 144

1 -4 mm 3 attrition 30 129 67 0.9 198

0.125-1 mm 46 212 108 3.7 328

These attrition steps allow very good metals and organic pollutants solubilisation as final concentration of all fractions are above Quebec soil regulation criteria for industrial reuse. Example 6: Combination of attrition and leaching process

Attrition process was then tested on two contaminated F1 and S3 soils. F1 and S3 soils were screened into four fractions using sieves as followed: >4 mm, 4-1 mm, 1-0.125 mm and <0.125 mm. Attrition was conducted on the three first fractions whereas leaching was conducted on the last fraction.

1. Soil content: 400 g/L;

2. Temperature: 20°C;

3. Reaction time: 20 min;

4. Attrition step: 3; and

5. Surfactant type and concentration: 0.5% BW.

According to an optional embodiment of the process, the parameters for leaching of wood treating site soil were selected as follows:

1. Soil content: 100 g/L;

2. Base type and concentration: 0.75 M NaOH;

3. Temperature: 80°C;

4. Reaction time: 2 h;

5. Leaching / rinsing step: 3 / 1 ; and

6. Surfactant type and concentration: 3% BW.

Table 3 gives the concentration of PCP, CCA and PCDDF in each soil fractions before and after treatment.

Table 3: Concentration of PCP, CCA and PCDDF for the F1 soil before and after 3 attrition step with surfactant BW at concentration of 5 g kg^"1 (t = 20 min, T = 20 , PD = 40% (w V^"1) or 3 leaching and 1 rinsing step with surfactant BW at concentration of 30 g kg ¹, t = 120 min, T = 80°C, NaOH = 0,75M, PD = 10% (w v¹). F1 soil As Cr Cu PCP PCDDF

1 reaimeni

fraction (mg/kg) (mg/kg) (mg/kg) (mg/kg) (ng/kg)

> 4 mm 17 56 5 0.1 59

1 -4 mm Before 51 420 271 0.6 90

0.125-1 mm treatment 84 247 271 0.7 1 340

< 0.125 mm 400 564 1 034 4.2 4 295

> 4 mm 36 107 50 0.1 41

1 -4 mm 3 attrition 12 186 58 0.1 1 17

0.125-1 mm 32 95 89 0.1 197

< 0.125 mm 3 leaching 86 653 876 1 .1 432

Table 4: Concentration of PCP, CCA and PCDDF for the S3 soil before and after 3 attrition step with surfactant BW at concentration of 5 g kg^"1 (t = 20 min, T = 20°C, PD = 40% (w V^"1) or 3 leaching and 1 rinsing step with surfactant BW at concentration of 30 g kg ¹, t = 120 min, T = 80°C, NaOH = 0,75M, PD = 10% (w v¹).

S3 soil As Cr Cu PCP PCDDF

1 reaimeni

fraction (mg/kg) (mg/kg) (mg/kg) (mg/kg) (ng/kg)

> 4 mm 13 7 13 3.0 2,059

1 -4 mm Before 27 134 49 24.1 2,795

0.125-1 mm treatment 33 128 59 17.4 4,235

< 0.125 mm 124 108 202 144 1 1 ,026

> 4 mm 36 1 1 43 1 .4 363

1 -4 mm 3 attrition 18 303 39 3.8 448

0.125-1 mm 24 177 54 2.2 373

< 0.125 mm 3 leaching 97 222 239 52 3,680

Attrition steps allow very good metals and organic pollutants solubilisation as final concentration of all fractions of the two soils are above Quebec soil regulation criteria for industrial reuse. The chemical leaching allows very good metals and organic pollutants solubilisation too. As the finest fraction is highly contaminated, an increase of the number of leaching steps or of the surfactant and/or base concentration must be considered to reach soil regulation criteria of the province of Quebec. Example 7: Coagulation and precipitation of soil leachate using sulfuric acid and ferric sulfate

Contaminants concentration in mixture of leachate from the four soil are 4.53 mg/L of As, 0.79 mg/L of Cr, 3.95 mg/L of Cu, 1.83 mg/L of PCP and 127 ng/L of PCDDF-TEQ. Precipitation was studied to recover PCP and CCA from leachates. Figure 6 presents removal yields during precipitation step with various volume of ferric sulfate solution containing 160 g Fe/L. The addition of 2 mL of ferric solution to 100 mL of soil leachate with pH adjustment using sulfuric acid removed 98% of As, 92% of Cu and 85% of PCP. Pentachlorophenol precipitation depends of pH which control equilibrium between pentachlorophenate anion and the protonate form and so its solubility (Lee, L. S., Suresh, P., Rao, C, Nkedi-Kizza, P. & Delfino, J. J. (1990). Influence of solvent and sorbent characteristics on distribution of pentachlorophenol in octanol-water and soil- water systems. Environ. Sci. Technol., 24(5), 654-661). Decreases of pH reduce solubility of pentachlorophenol due to its pKa = 4.75 (for acidic pH solubility is less than 20 mg/L whereas for alkaline pH solubility is up to 200 g/L). Arsenic coagulation is due to both the precipitation of iron arsenate (FeAs0₄.2H₂0) and the adsorption of arsenic onto hydrous ferric oxides. In the aqueous phase, soluble chromium is able to precipitate as Cr(OH)₃. Copper is able to precipitate as hydroxides Cu(OH)₂ and co-precipitate with ferric hydroxides (Janin, A., Blais, J. F., Drogui, P., Zaviska, F. & Mercier, G. (2009a). Selective recovery of metals in leachate from chromated copper arsenate wastes using electrochemical technology and chemical precipitation. Hydromet., 96, 318-326., and Janin, A., Blais, J. F., Mercier, G. & Drogui, P. (2009b). Selective recovery of metals in leachate from chromated copper arsenate treated wood using ion exchange resins and chemical precipitation. J. Hazard. Mater., 169, 1099-1 105.). The presence of the three metals in solution influences individual precipitation behaviour of arsenic, chromium and copper. This could be explained by metal-metal interactions as arsenic, chromium and copper are able to form mixed compounds like Cu₃(As04)2.2H₂0 and CuCr0₄ (Blais, J. F., Djedidi, Z., Ben Cheikh, R., Tyagi R. D. & Mercier, G. (2008). Metals precipitation from effluents. A review. Pract. Period. Hazard. Toxic Radioactive Waste Manag., 12 (3), 135-149).

Pentachlorophenol, copper, chromium and arsenic may be simultaneously removed from the solution by a total precipitation technique using an iron salt (e.g. ferric sulfate) with a strong acid (e.g. sulfuric acid). Due to low cost of sulfuric acid, process cost for treatment of leachate produced during decontamination of 1 t of soil is less than US$30.

Example 8: Contaminant removal by ion exchange and adsorption with batch mode experiments

Figures 7 A and 7B show As, Cr, Cu and PCP removal yields after contacting soil leachates with several adsorbents or ion exchange resins.

100 mL of soil leachate was used and a mass of resin and adsorbent of 5 g was added. According to Figure 7A, adsorbents studied (anthracite, granular activated carbon, powdered activated carbon, alumina and silica) allow to remove PCP and some copper but are all enable to remove arsenic and chromium. Activated carbon powder and Norit granular activated carbon give the best removal yield (98%) for PCP. Ion exchange resins studied in Figure 7B are anionic, cationic or adsorption resin. All resins allow removal of pentachlorophenol. Anionic resins show the best removal yields for metal removal. Removal yields for Cu, Cr and PCP with Lewatit SR7 approach 83%, 41 % and 99% respectively.

Ion exchange and adsorption on activated carbon are usually selective separation technologies and could be highly specific. Selective separation technologies are useful for contaminants extraction. Activated carbons are often used for organic pollutants removal whereas resins are mainly used for ionic compounds extraction. Anionic resins were chosen due to ionic form of metals and PCP in soil leachate. In such alkaline conditions, pentachlorophenol, arsenic, copper and chromium are mainly in anionic form. Pentachlorophenol form is PCP^" due to pH, speciation of arsenic was analysed and shows that 98% is in pentavalent oxidation state (As0₄ ^3"), Norkus et al. (Norkus, E., Vaskelis, A. & Zakaite, I. (1996). Influence of ionic strength and OH- ion concentration on the Cu(ll) complex formation with EDTA in alkaline solutions. Talanta, 43, 465-470.) have demonstrated that copper and chromium form an anionic complex with hydroxide: Cu(OH)₄ ^2" and Cr(OH)₄ ^" respectively.

Best adsorbent and ion exchange resin were compared to precipitation for contaminants removal from soil leachate including dioxins and furans extraction. As, Cr, Cu, PCP and PCDDF removal yields after contacting soil leachates with Lewatit SR7, Lewatit VPOC, Norit activated carbon, powder activated carbon or after optimised precipitation step are presented in Figure 8. 100 mL of soil leaching and 5 g of resin or adsorbent or 2 mL of ferric sulfate (160 g Fe/L) were used. Lewatit SR 7, Lewatit VPOC and Norit granular activated carbon allow the best extractions of PCDDF with removal yields of 97%, 93% and 91 % respectively, whereas precipitation step removes less than 20% of PCDDF.

According to the present invention, extraction of all contaminants present in soil leachate could be achieved by contacting the contaminated solution with a coagulant at a pH favoring precipitation of pentachlorophenol, copper, chromium and arsenic and contacting the contaminated solution with an activated carbon or an ion exchange resin favoring pentachlorophenol, dioxins and furans extraction.

Claims

A process for decontamination of soil contaminated with a preservative comprising contaminants, comprising:

contacting the soil with water and an inorganic base at a concentration between about 0.1 M and about 2 M at a temperature lower than about lOCTC, to form an alkaline mixture and solubilise a t least a portion of the contaminants present in the soil, thereby producing a contaminant-rich leachate and contaminant-poor soil; and

separating the contaminant-poor soil from the contaminant-rich leachate.

The process of claim 1 , wherein the step of contacting the soil includes also contacting with a leaching surfactant, such that the alkaline mixture comprises the leaching surfactant and has a leaching surfactant concentration between about 0.05% and about 5% by weight.

The process of claim 1 or 2, wherein the contaminants comprise metals, organic compounds or a combination thereof.

The process of claim 3, wherein the contaminants comprise:

metals;

pentachlorophenol;

dioxins and furans;

derivatives thereof;

analogues thereof;

isomers of such contaminants; or

a combination thereof.

The process of claim 4, wherein the contaminants comprise:

pentachlorophenol;

polychlorined dibenzodioxins;

polychlorined dibenzofurans;

derivatives thereof; isomeric analogues thereof; or

a combination thereof.

6. The process of any one of claims 1 to 5, wherein the contaminants come from preservatives comprising chromated copper arsenate, pentachlorophenol, polychlorined dibenzodioxins, polychlorined dibenzofurans or a combination thereof.

7. The process of any one of claims 1 to 6, comprising adjusting a soil content of the alkaline mixture between about 50 g/L and about 500 g/L of the mixture.

8. The process of any one of claims 1 to 7, wherein the inorganic base comprises sodium hydroxide.

9. The process of any one of claims 1 to 8, wherein the inorganic base comprises a sodium, potassium or calcium base, a used base, a recycled base or a combination thereof.

10. The process of any one of claims 1 to 9, wherein the surfactant comprises an amphoteric biosurfactant.

11. The process of any one of claims 1 to 10, wherein the surfactant is an amphoteric biosurfactant.

12. The process of any one of claims 1 to 11 , wherein the surfactant comprises cocamidopropylbetaine.

13. The process of any one of claims 1 to 12, wherein the surfactant is cocamidopropylbetaine.

14. The process of any one of claims 1 to 13, wherein the surfactant comprises a cationic head, an anionic head, both anionic and cationic heads, a neutral head, or a combination thereof.

15. The process of any one of claims 1 to 14, wherein the surfactant is synthetic or a biosurfactant, or a combination thereof.

16. The process of any one of claims 1 to 15, comprising mixing the alkaline mixture for a leaching period sufficient to adequately solubilise the contaminants present in the soil.

17. The process of claim 16, wherein the leaching period of the mixing of the alkaline mixture is between about 0.5 and about 24 h.

18. The process of any one of claims 1 to 17, wherein the temperature of the alkaline mixture is between about 20°C and about 80°C.

19. The process of any one of claims 1 to 18, wherein the step of contacting producing the contaminant-rich leachate and the contaminant-poor soil, is performed in a single leaching step.

20. The process of any one of claims 1 to 18, wherein the step of contacting producing the contaminant-rich leachate and the contaminant-poor soil, is performed in multiple leaching steps.

21. The process of claim 20, wherein the multiple leaching steps are performed sequentially.

22. The process of claim 21 , wherein the sequential leaching steps utilize the same or different inorganic bases.

23. The process of claim 22, wherein the sequential leaching steps utilize the same or different concentrations of the inorganic base(s).

24. The process of any one of claims 21 to 23, wherein the sequential leaching steps utilize the same or different surfactants.

25. The process of claim 24, wherein the sequential leaching steps utilize the same or different concentrations of the surfactant(s).

26. The process of any one of claims 20 to 25, wherein the leaching steps are operated in batch, semi-continuous or continuous mode in tank reactors.

27. The process of any one of claims 1 to 26, wherein, after the leaching step or steps, the contaminant-poor soil is separated from the contaminant-rich leachate by decantation, filtration, centrifugation, or another technique of solid-liquid separation, or a combination thereof.

28. The process of any one of claims 1 to 27, comprising washing the separated contaminant-poor soil to remove residual solubilised contaminants.

29. The process of claim 28, wherein the washing is done by rinsing solids resulting from a previous filtration step or by mixing the solids re-suspended in the washing solution, followed by a step of solid-liquid separation.

30. The process of claim 28, wherein the washing is done in one or more steps with water, a dilute alkaline solution, or an acid solution.

31. The process of claim 28, wherein different washing steps are performed with the same or different washing solutions.

32. The process of claim 28, wherein the contaminant-rich leachate and spent washing liquids are combined to obtain a solution containing the totality of the target contaminants.

33. The process of claim 28, wherein some or all of spent washing waters are directly used as process water for the operation of the initial leaching steps for a subsequent batch or quantity of contaminated soil.

34. The process of any one of claims 1 to 33, wherein the contaminant-rich leachate and the spent washing liquids are referred to as alkaline leachate, which comprises at least a portion of the contaminant-rich leachate or the spent washing liquids or a combination thereof, and wherein the process comprises treating at least a portion of the alkaline leachate to recover at least one of the contaminants therefrom.

35. The process of claim 34, wherein the recovered contaminant comprises a metal.

36. The process of claim 35, wherein at least a portion of the recovered metal comprises copper arsenic, chromium, copper or a combination thereof.

37. The process of claim 35, wherein at least a portion of the recovered metal is recovered in the form of mixed metalloid compounds and/or as pure metal.

38. The process of any one of claims 35 to 37, wherein the metal contaminant is recovered by means of chemical precipitation, ion exchange, solvent extraction or adsorption or a combination thereof.

39. The process of any one of claims 34 to 38, wherein, after the alkaline leachate has been treated to remove the at least one of the contaminants, the resulting treated solution is used as process water for the contacting step forming the alkaline mixture.

40. The process of any one of claims 1 to 39, wherein at least two of pentachlorophenol, dioxins and furans, copper, chromium and arsenic are simultaneously removed from the alkaline leachate.

41. The process of any one of claims 1 to 40, wherein all of pentachlorophenol, dioxins and furans, copper, chromium and arsenic are simultaneously removed from the alkaline leachate.

42. The process of claim 40 or 41 , wherein the removal is performed by a total precipitation technique using an iron salt.

43. The process of claim 42, wherein the iron salt comprises ferric chloride or sulfate.

44. The process of claim 42 or 43, wherein the total precipitation technique also uses a strong acid.

45. The process of claim 44, wherein the strong acid comprises sulfuric acid.

46. The process of claim 34, wherein the alkaline leachate is treated to remove at least one organic compound.

47. The process of claim 40, wherein the organic compound comprises pentachlorophenol, dioxins and furans or a combination thereof.

48. The process of claim 46 or 47, wherein the organic compound is removed by means of chemical precipitation, ion exchange, solvent extraction or adsorption or a combination thereof.

49. The process of claim 46 or 47, wherein the organic compound is removed from the alkaline leachate by means of ion exchange resins or activated carbons or a combination thereof.

50. The process of any one of claims 1 to 49, wherein the decontaminated soil and/or the contaminants extracted from the soil and/or alkaline leachate are disposed of or recycled.

51. The process of any one of claims 1 to 50, further comprising, prior to contacting the soil with water and the inorganic base to form the alkaline mixture, the steps of:

mixing the soil with an initial amount of water so as to form an aqueous mixture of soil; subjecting the aqueous mixture of soil to attrition during an attrition period to solubilise at least a portion of the contaminants present in the soil; and subjecting the aqueous mixture of soil to separation to produce a contaminant-rich liquid, a contaminant-depleted soil and a contaminated sludge.

52. The process of claim 51 , wherein the step of mixing the soil with water also includes mixing with an attrition surfactant such that the aqueous mixture comprises the attrition surfactant,

53. The process of claim 52, wherein the aqueous mixture of soil has an attrition surfactant concentration between about 0.05% and about 5% by weight.

54. The process of claim 52 or 53, wherein the attrition surfactant has a cationic head, an anionic head, both cationic and anionic heads, a neutral head or a combination thereof.

55. The process of any one of claims 52 to54, wherein the attrition surfactant comprises a biosurfactant.

56. The process of claim 55, wherein the attrition surfactant comprises cocamidopropylbetaine.

57. The process of any one of claims 51 to 56, comprising providing a soil content of the aqueous mixture of soil to obtain a soil concentration between about 50 g/L and about 500 g/L of mixture.

58. The process of any one of claims 51 to 57, wherein the attrition period is between about 0.01 h and about 1 h.

59. The process of any one of claims 51 to 58, wherein the attrition step is repeated until a pre-determined minimum concentration of the contaminants in the contaminant-rich liquid is reached.

60. The process of any one of claims 51 to 59, wherein the separation of the aqueous mixture of soil comprises decantation, filtration, centrifugation, or a combination thereof.

61. The process of any one of claims 1 to 60, further comprising crushing and/or screening the soil so as to obtain fine soil particles.

62. The process of any one of claims 51 to 60, further comprising crushing and/or screening the soil so as to obtain fine soil particles.

63. The process of claim 61 or 62, wherein the crushing and/or screening step is performed prior to contacting the soil with water and an inorganic base.

64. The process of claim 62, wherein the crushing and/or screening step is performed prior to mixing the soil with the initial amount of water to form the aqueous mixture of soil.

65. The process of any one of claims 61 to 64, wherein the screening of the soil comprises screening according to four solid fractions >4 mm, 4-1 mm, 1-0.125 mm and <0.125 mm.

66. The process of any one of claims 61 to 64, wherein the soil is crushed and/or screened so as to have particle size inferior to about 1 cm.

67. The process of claim 66, wherein the soil is crushed and/or screened so as to have particle size inferior to about 0.6 mm.

68. A process for contaminant extraction from a contaminated solution, comprising:

69. The process of claim 68, comprising at least one step or feature as defined in any one of claims 1 to 67 for producing the contaminated solution and/or treating any of resulting streams or fractions of the process.

70. A process as defined in any one of claims 1 to 69, comprising at least one step or feature as defined in the present description and/or figures for treating the contaminated soil, the contaminated solution, the contaminants and/or any of resulting streams or fractions of the process.

71. A process for decontamination of soil contaminated with a preservative comprising contaminants, the contaminants comprising metals and/or organic compounds, wherein: the metals comprise arsenic, chromium, copper, and/or other metal species; and

the organic compounds comprise pentachlorophenol and derivatives thereof, dioxins and furans and/or other organic species;

wherein the process comprises the steps of:

contacting the soil with water, an inorganic base, and with or without a leaching surfactant, at a temperature lower than about 100 , the concentrations of the inorganic base and the leaching surfactant being sufficient to enable solubilisation of a substantial amount of the contaminants present in the soil, thereby producing a contaminant-rich solution and contaminant-poor soil; and

separating the contaminant-rich solution from the contaminant-poor soil.

72. The process of claim 71 , comprising at least one step or feature as defined in any one of the claims 1 to 70 and/or the present description and/or figures.

73. A process for decontamination of soil contaminated with a preservative comprising contaminants, the contaminants comprising metals and/or organic compounds, wherein:

the metals comprise arsenic, chromium, copper, and/or other metal species; and

the organic compounds comprise pentachlorophenol and derivatives thereof, dioxins and furans, and/or other organic species;

wherein the process comprises the steps of:

subjecting the aqueous mixture of soil to separation to produce a contaminant-rich liquid, a contaminant-depleted soil and a contaminated sludge; contacting the contaminated sludge with water and a base, at a temperature lower than about Ι ΟΟ , to enable solub ilisation of a substantial amount of the contaminants present in the contaminated sludge, thereby producing a contaminant-rich leachate and contaminant- poor soil; and

separating the contaminant-poor soil from the contaminant-rich leachate.

74. The process of any one of claims 71 to 73, wherein the dioxins and furans comprise polychlorined dibenzodioxins, dibenzofurans and isomeric analogues thereof.

75. The process of any one of claims 71 to 74, wherein the metals and organic compounds are from preservatives.

76. The process of claim 75, wherein the preservatives comprise chromated copper arsenate, pentachlorophenol and/or polychlorined dibenzodioxins and dibenzofurans.

77. The process of claim 73, wherein the base is an inorganic base and the contacting step further comprises adding a leaching surfactant, concentrations of the inorganic base and the leaching surfactant being sufficient to enable solubilisation of the substantial amount of the contaminants present in the contaminated sludge.