SUMMARY OF THE INVENTION

[0019] The present invention concerns a method for removing inorganic contaminants in particulate form from contaminated soil wherein the inorganic contaminants have a degree of liberation of at least 60%. The present method may decontaminate soil from a contaminated land so that the soil reaches satisfactory inorganic contaminants levels. In particular, MENVIQ environmental norms for soils applicable in the province of Quebec may be reached with the methods of the present invention.

[0020] In a specific embodiment, organic contaminants are also removed from the soil so contaminated. In a more specific embodiment, metallurgical characterisation of the soil is performed prior to decontamination in order to reduce the volume of soil subjected to treatment.

[0021] According to an embodiment of the present invention, there is provided a method for decontaminating soil containing inorganic contaminants having a degree of liberation of at least 60%, comprising the steps of removing from a coarse fraction at least a portion of inorganic contaminants in particulate form contained therein with a jig to produce a treated coarse fraction, removing from an intermediate fraction at least a portion of inorganic contaminants in particulate form contained therein with a separator selected from the group consisting of a spiral and a classifier to produce a treated intermediate fraction; removing from a fine fraction at least a portion of inorganic contaminants in particulate form contained therein with a separator selected from the group consisting of a flotation cell and a multi-gravity separator to produce a treated fine fraction, whereby the combined treated coarse, intermediate and fine fractions are impoverished in inorganic contaminants. In a specific embodiment, the method may further comprise a step of removing a non-contaminated portion of the coarse fraction. According to other specific embodiments, the coarse fraction consists essentially in particles having a size within the range 1.7 mm and 6.4 mm, inclusively; the intermediate fraction consists essentially in particles having a size within the range of 106 μm to 1.7 mm, inclusively; and the fine fraction consists essentially in particles having a size equal to or smaller than 106 μm.

[0022] According to an other aspect of the present invention, there is provided a method comprising not only inorganic contaminants removal steps as described above but also a step of removing from an organically contaminated portion of the soil at least a portion of the organic contaminants contained therein with an attrition cell. This method is applied when excessive organic contaminants levels are identified in the contaminated soil as defined by the application that is intended for the soil or by applicable environmental norms. In a particular embodiments the steps of removing inorganic contaminants comprise the substeps of identifying the at least one organically contaminated grain-size fraction; b) isolating the at least one contaminated fraction identified in step a); c) washing the at least one contaminated fraction isolated in step b) in an attrition cell, whereby at least a portion of organic contaminants contained therein are solubilised in a liquid phase; d) separating from a solid phase, the liquid phase of step c) containing solubilised organic contaminants; e) flocculating at least a portion of the solubilised organic contaminants to produce a flocculated phase, whereby the solid phase of step d) is soil impoverished in organic contaminants.

[0023] According to a further aspect of the present invention, there is provided a method for decontaminating soil containing inorganic contaminants having a degree of liberation of at least 60%, comprising the steps of a) screening the soil to remove a non-contaminated fraction of the soil, wherein said non-contaminated fraction consists essentially in particles larger than those of the coarse fraction; b) screening the undersize from step a) to obtain a coarse fraction, and a coarse fraction undersize; c) removing at least a portion of the inorganic contaminants from the coarse fraction, with a jig; d) screening the coarse fraction undersize from step b) to obtain an intermediate fraction, and an intermediate fraction undersize; e) removing at least a portion of the inorganic contaminants from the intermediate fraction, with a separator selected from the group consisting of a spiral and a fluidised bed classifier;f) screening the intermediate fraction undersize from step d) to obtain a fine fraction; and g) removing at least a portion of the inorganic contaminants from the fine fraction, with a separator selected from the group consisting of an enhanced gravity concentrator and a flotation cell. According to other specific embodiments, the coarse fraction consists essentially in particles having a size within the range 1.7 mm and 6.4 mm, inclusively; the intermediate fraction consists essentially in particles having a size within the range of 106 μm to 1.7 mm, inclusively; and the fine fraction consists essentially in particles having a size equal to or smaller than 106 μm. In a particular embodiment, the method further comprises a step of removing from an organically contaminated portion of the soil at least a portion of the organic contaminants contained therein with an attrition cell. In a more specific embodiment, the removal of organic contaminants is performed by a) identifying the at least one organically contaminated grain-size fraction; b) isolating the at least one contaminated fraction identified in step a); c) washing the at least one contaminated fraction isolated in step b) in an attrition cell, whereby at least a portion of organic contaminants contained therein are solubilised in a liquid phase; d) separating from a solid phase the liquid phase of step c) containing solubilised organic contaminants; e) flocculating at least a portion of the solubilised organic contaminants to produce a flocculated phase, whereby the solid phase of step d) is soil impoverished in organic contaminants.

[0024] As used herein, the term “inorganic contaminants” includes both radioactive and non-radioactive metals, and is otherwise intended to encompass the full breadth of metal contaminants known to those skilled in the art; in particular for example as used herein, the terminology “inorganic contaminants” is meant to include or refer to Pb, Cu and Zn.

[0025] As used herein, the terminology “organic contaminants” is intended to refer to all organic compounds which tend to adhere to soil, and which may present environmental hazards when permitted to remain in the soil; in particular for example as used herein, the terminology “organic contaminants” is meant to include or refer to C10-C50 petroleum hydrocarbons (i.e. hydrocarbon materials containing from 10 to 50 carbon atoms).

[0026] As used herein the terminology “degree of liberation” is meant to refer to the percentage of minerals occurring as free particles in the soil in relation to the total content of minerals. The “degree of liberation” may be determined (e.g. visually counted) for example in accordance with the teachings of Wills, B. A., 1998, “Mineral processing technology”, fourth edition, Pergamon Press, pg 855 (the entire contents of this document and in particular pages 25 to 29 from Willis is/are incorporated herein by reference).

[0027] As used herein, the terminology “particulate form” is meant to define the state of inorganic contaminants that are not adsorbed on soil particles or dissolved in the soil.

[0028] As used herein, the terminology or word “aggregate” and any similar word (whether as noun, adjective, etc.) shall be understood as referring to or as characterizing (or emphasising) a “soil”, “sediment”, “material”, etc. or any portion thereof as a mass of individual particles or components of the same or varied size (e.g. the size of the components may be not uniform and may range from microscopic granules to 10 cm and larger); it is also to be understood that the particle size distribution of any particular soil mass, etc. may be different from that of another soil mass, etc.

[0029] As, used herein, the terminology or word “soil” and the like (whether as noun, adjective, etc.) shall be understood as referring to superficial earth crust, whether natural or man made (i.e. unconsolidated mantle), namely aggregate material including but not limited to

[0030] aggregate material disposed on dry land masses (e.g. soil aggregate material);

[0031] sedimentary aggregate including any bottom sediments of fresh or marine water systems;

[0032] aggregate material which has an organic matter portion derived for example from plant or animal sources; organic material such as plant material would usually form part of the courser aggregate material as described hereinafter and would include, for example, tree stumps, ligneous particles, etc.;

[0033] aggregate material derived from human activities, such as, for example, mineral aggregate materials, fill aggregate materials as well as sediments arising in water-ways;

[0034] mineral aggregate residues from mining operations, such as those present in a tailings pond;

[0035] etc.

[0036] Thus as used herein, the terminology “soil” includes all forms of particulate matter, such as, for example, clay, fines, sand, rock, humus, etc. and in particular for example, soil particles and embankment material particles.

[0037] As used herein, the terminology “inorganic contaminants” refers to metals (e.g. Pb, Cu and Zn) individually or collectively. The terminology “at least a portion of inorganic contaminants” is meant to refer to at least a portion of any one metal (e.g. any one of Pb, Cu and Zn) or of a combination thereof.

[0038] As used herein, the terminology “impoverished” is used herein to refer to the reduced content of contaminants in a sample of soil after being subjected to the method of the present invention (“treated soil”) as compared to its content prior to being so subjected. In particular, it may refer to the reduced content in any one metal or a combination thereof (e.g. of Zn, Pb and/or Cu).

[0039] As used herein, the terminology “consists essentially in” is meant to reflect the fact that the means according to specific embodiments used for isolating a specific soil fraction are by nature imprecise so that the fraction may contain particles larger than the specified threshold.

[0040] As used herein, the terminology “large debris” is meant to refer to material in the soil to be decontaminated that has a size equal or larger than 6 cm. It includes material such as rocks and large pieces of metals.

[0041] As used herein, the terminology “coarse fraction” is meant to refer to the fraction of the soil from which large debris have been removed and constituted of particles of a size within the functional range of the separator used to decontaminate the coarse fraction, namely a jig. Jigs are recognised as being functional with particles larger than 170 μm.

[0042] As used herein, the terminology “intermediate fraction” is meant to refer to a fraction of the soil and having a particulate size that is smaller than that of the coarse fraction and that is within the functional range of the separator used to decontaminate the intermediate fraction, namely a separator selected from the group consisting of spiral and fluidised bed classifier. Hence, the spiral and the fluidised bed classifier are recognised as being functional with particles within the size range 60 μm and 2000 μm.

[0043] As used herein, the terminology “fine fraction” is meant to refer to a fraction of the soil having a particulate size that is smaller than that of the intermediate fraction and that is within the functional range of the separator used to decontaminate the fine fraction, namely a separator selected from the group consisting of a multi-gravity separator (“MGS”) and a flotation cell. Hence, the MGS and the flotation cells are recognised as being functional with particles within the size range 1 μm to 300 μm, and 10 μm to 300 μm, respectively.

[0044] As used herein,, the terminology “classify”, “classification” and the like shall, be understood as referring to the dividing of an aggregate material into size groupings or portions and as including separation of constituent components in accordance with size, (e.g. size separation by screening, gravity separation, etc.).

[0045] It is to be understood herein, that if a “class”, “range”, “group of substances”, etc. is mentioned with respect to a particular characteristic (e.g., temperature, concentration, size, time etc.) of the present invention, the present invention relates to and explicitly incorporates herein each and every specific member and combination of sub-class, sub-ranges or sub-groups therein whatsoever. Thus, any specified class, range or group is to be understood as a shorthand way of referring to each and every member of a class, range or group individually as well as each and every possible sub-class, sub-range or sub-group encompassed therein; and similarly with respect to any sub-class, sub-range or sub-group therein. Thus, for example,

[0046] with respect to the number of carbon atoms, the mention of the range of 1 to 6 carbon atoms is to be understood herein as incorporating each and every individual number of carbon atoms as well as sub-ranges such as, for example, 1 carbon atoms, 3 carbon atoms, 4 to 6 carbon atoms, etc.;

[0047] with respect time, a time of 1 minute or more is to be understood as specifically incorporating herein each and every individual time, as well as sub-range, above 1 minute, such as for example 1 minute, 3 to 15 minutes, 1 minute to 20 hours, 1 to 3 hours, 16 hours, 3 hours to 20 hours etc.;

[0048] and similarly with respect to any other parameters whatsoever, such as percentage(s), particle size, particle size disribution, volume, pore size,, temperature, pressure, concentrations, elements, (carbon) atoms, etc.

[0049] It is in particular to be understood herein that for any class, group or range, no matter how defined, a reference thereto is a shorthand way of mentioning and including herein each and every individual member described thereby as well as each and every possible class or sub-group or sub-class of members whether such class or sub-class is defined as positively including particular members, as excluding particular members or a combination thereof; for example an exclusionary definition for a formula may read as follows: “provided that when one of A and B is —X and the other is Y, —X may not be Z”.

DESCRIPTION OF SPECIFIC EMBODIMENTS

[0050] FIGS. 2 and 3 illustrate various steps included in a specific embodiment of the present invention. The present invention describes a method for the removal of contaminants from soil. A specific embodiment of the method comprises two general steps. The first step consists in the removal of inorganic contaminants from the soil. In the second step, organic contaminants are removed from soil impoverished in inorganic contaminants. If required, for recycling purpose, organic contaminants can also be isolated from the inorganic concentrates. In a further specific embodiment, the method includes complete dehydration of the decontaminated material, yielding final products ready for disposal. This is advantageous for the following reasons:

[0051] a) versatility: the method can thus be used in cases where the soil carries only either one of inorganic or organic contaminants;

[0052] b) reduction of volume treated: only the most contaminated grain-size fraction(s) of the material is subjected to organic contaminants removal;

[0053] c) to facilitate the treatment, the operator can choose to use the dehydrated form of the contaminated material. This can be of interest when surfactant agents are added to the solid for removal of organic contaminants.

[0054] The inorganic and organic concentrates obtained from the process can be used as feedstock to other industries.

Inorganic Contaminants Removal

[0055] Referring to FIG. 2 , the contaminated soil 101 , is first pre-treated on a triple decks vibrating screen, EQ-01, where the non-contaminated fraction and large debris are separated out and routed on a belt conveyor to the impoverished soil pile. Water is also added in order to produce a pulp for the subsequent operations and to facilitate the screening of the material. In a specific embodiment where the soil used had the contaminants distribution illustrated at FIG. 1 , the apertures of the three screens were set to 18 mm, 6.4 mm and 1.7 mm respectively. In this non-limiting example, the fraction +6.4 mm was directed to the decontaminated material pile because globally, the resulting material (+6.4 mm and decontaminated material) satisfied the province of Quebec C norms for Pb, Zn and Cu. The apertures of the screens is therefore adjusted to the required grain-size depending of the grain-size distribution of the contaminants in the targeted material and the environmental norms of the contaminated soil's jurisdiction.

[0056] The contaminated fraction −6.4 mm+1.7 mm, namely here the coarse fraction, 102 , obtained from the previous screening procedures was transported by a belt conveyor to the jigs section. Water was added to the pulp to obtain a pulp % weight ratio solid/pulp of 11%. The contaminated pulp was fed to two jigs set in line. The action of the first jig produced a concentrate of heavy minerals and materials containing mainly the inorganic contaminants and a lighter material impoverished in contaminants. The lighter material was fed to a second jig for a supplementary gravimetric separation. This second separation was conducted to reach Quebec inorganic contaminants regulation limits for soil decontamination and may therefore not be desirable for decontaminating soils in other jurisdictions. The jigs' highly contaminated concentrates, 103 , were combined and dehydrated using a vibrating screen of 106 μm aperture. Likewise, the partly decontaminated soil, 104 , was dehydrated by a similar procedure. These screens were employed solely for dehydration purpose. The resulting water was free of solid and therefore returned to the water process reservoir. Screw conveyors transported the concentrates to a container and the partly decontaminated material to the stocking pile.

[0057] The undersize, 105 , −1.7 mm was fed to two vibrating screens with cut off apertures of 106 μm, EQ-02. The resulting grain-size fraction −1.7 mm+106 μm, namely the intermediate fraction, 106 , was diluted with wash water to a weight ratio of 30% and then directed to spirals (Reichert MG-4). The products obtained from the spirals, a dense fraction rich in inorganic contaminants, 107 , and light fraction partly decontaminated, 108 , were sent to dehydration vibrating screens, aperture 106 μm. The water was pumped to the water process reservoir. Screw conveyors directed the contaminated concentrate to containers and the partly decontaminated phase to the stocking pile.

[0058] The undersize, 109 , −106 μm, namely the fine fraction was pumped to a clarifier. The overflow was returned to the water process reservoir. The underflow, 110 , adjusted to a weight ratio of 30%, with dilution water, was directed to a MegaSep MGS Mozley™ unit, EQ-03. The centrifugal force combined to the vibrating action of this equipment permitted a gravimetric separation of the fines based on volumetric mass differences. Two flows were obtained from the MegaSep, a dense one and a light one. The dense fraction rich in inorganic contaminants, 111 , was pumped to a thickener. The underflow was returned to the water process reservoir while the underflow was pumped to the containers receiving the highly contaminated concentrates. The light fraction, 112 , was submitted to a similar set of operations with the underflow water returning to the water process reservoir and the underflow to the partly decontaminated pile.

[0059] The water surplus exiting the water process reservoir was clarified before being rejected in the municipal water collecting system.

Organic Contaminants Removal

[0060] Although the specific embodiment described hereafter is applicable to material where only the −106 μm fraction is contaminated by organic products, the organic process disclosed generally herein is applicable to any grain-size fraction. Also, in this particular embodiment, the material used was not contaminated by inorganic contaminants so that the material was subjected to the organic decontamination step only. However, had it been contaminated also by inorganics, the inorganic removal step would have first been performed, and then, the fraction(s) of the partially decontaminated material containing the contaminants would have been subjected to the organics removal step.

[0061] In some cases, other equipment adapted to the grain-size fraction of the material can replace the centrifuges for the dehydration steps. Referring to FIG. 3 , after the screening procedures, the −106 μm flow was directed to a thickener to increase its weight ratio to 45%. The thickener underflow, 201 , was pumped to two in line attrition cells. Before the attrition step, the surfactant agent Hostapur™ SAS 60 was added to the pulp, 202 . This surfactant solubilizes hydrophobic organic contaminants during attrition. The solid was then separated from the pulp by centrifugation, centrifuge-01. The solid, 70% weight ratio, centrifuge underflow, substantially free from the organic contaminants, 203 , was accumulated in a reservoir. The centrifuge overflow, 204 , mainly water containing the dissolved organic contaminants, was pumped to a reservoir. The reservoir exit flow was routed to a water treatment process in order to flocculate/coagulate the organic contaminants. The exit flow was pumped to a second centrifuge, centrifuge-02. At the entry of the centrifuge, a coagulating agent, 205 , (Alum™, Al2(SO4)3) and a flocculating agent, 206 , (Percol™, 338) were added to the flow. The organic concentrate 207 , obtained from the centrifuge underflow was disposed in a reservoir. The centrifuge overflow, 208 was directed to a clarifier where fines sunk at the bottom. The clarifier underflow, 209 , was combined with the organic contaminants concentrate. The clarifier underflow was pumped to the water process reservoir. Water surplus, 210 , could be returned if necessary to the municipal sewer.

[0062] For all samples studied, the water rejected from the processes illustrated at FIGS. 2 and 3 showed no sign of contamination either by organic or inorganic contaminants.

[0063] Any means for routing and transferring the soil, material or pulp is within the scope of these inventions.

[0064] The following inventions are described in further details by the following non-limiting examples.

[0065] The implementation and results of Examples 2 to 6 provided herein are summarised in Tables 1 and 37 to 43.

[0066] Optimisation results are presented in Tables 3 to 36 below. 1

[0067] The chemical analyses for the inorganic contaminants were performed by inductively coupled plasma atomic emission spectroscopy (“ICP-AES”). The organic contaminants were determined by an extraction in hexane with a finish by either a gravimetric method or gas chromatography. The samples were also submitted to a complete mineralogical and grain-size analysis.

EXAMPLE 1

Optimization Assays and Results

[0068] Assays were performed to determine the inorganic contaminants removal efficiency of various separators on samples of contaminated soil of the Montreal region. Each separator was tested with various granulometric fractions of soil. The efficiency of the present method was analysed in terms of environmental norms applicable in Montreal, namely the MENVIQ norms (Table 2). Tables 3 to 10 below provide the optimisation parameters and results for the jig. Tables 13 to 22 below provide the optimisation parameters of the spiral. Tables 23 to 24 below provide the optimisation parameters of the fluidised bed classifier. Tables 25 to 34 below provide the optimisation parameters of the multi-gravity separator. Tables 35 to 36 below provide the optimisation parameters of the flotation cells. The results presented in these tables that all the separators used were able to generate soil impoverished in inorganic contaminants. The operation parameters presented in these tables are those that varied during the assays. The feed contents were calculated along with light and heavy fraction contents of inorganic contaminants. Most cleaning coefficients were calculated with the following formula (1-(output concentration/feed concentration)*100 because the output is normally constituted of the light fraction and the concentrate of the heavy fraction. The MGS cleaning coefficients were calculated with the following formula: (1-(output heavy fraction concentration/feed concentration)*100 because in the optimisation trials, the contaminants were concentrated in the light fraction for an unknown reason. In the pilot/long-term trials, no such aberration occurred: the contaminants were concentrated in the heavy fraction.

EXAMPLE 2

Inorganics Removal in Soil Divided in Four Fractions Comprising the use of Spirals

[0069] Assays were performed to determine the consistency in inorganic contaminants removal efficiency of a method of decontamination according to a specific embodiment of the method of the present invention, namely one using jigs, spirals and MGS. Samples of the most contaminated zone of a contaminated land of the region of Montreal. More than 50% of the mass was localised in the grain-size fraction superior to 106 μm. The +106 μm fraction contained about 75% of the inorganic contaminants. This soil is typical of the Montreal contaminated areas. This method permitted the removal of 70% of the inorganic contaminants. For this Example, samples were taken from the most contaminated zone of a Montreal contaminated soil, Table 37 below provides operation parameters and cleaning coefficients for each of Pb, Cu and Zn separately. Because the organic contaminants concentrations were below the targeted decontamination values, they were not treated.

EXAMPLE 3

Inorganics Removal in Soil Divided in 2 Fractions

[0070] For the fraction −106 μm, a froth flotation cell replaced the MGS Mozley gravimetric separator. Results indicated a slight decrease in the removal of the inorganic contaminants, for this specific grain-size fraction, from 70% to 55%. This reduction in the removal of contaminants was not detrimental to the overall targeted decontamination values.

EXAMPLE 4

Inorganics Removal in Soil Divided in 4 Fractions Comprising the use of Fluidised Bed Classifier

[0071] In this example, the spirals were replaced by a fluidised bed classifier for the decontamination of the grain-size fraction −1.7 mm+106 μm. Removal of the inorganic contaminants dropped from 65% to 45%.

EXEMPLE 5

Organics Removal in −45 μm Fraction of Harbour Comprising Hostapur SAS60™

[0072] The starting material consisted in a highly contaminated sediment obtained form the Montreal Harbour. Sixty per cent of this material showed a grain-size distribution below 45 μm and contained 30 000 ppm of C10-C50 petroleum hydrocarbons. The surfactant used Hostapur™SAS 60, at the concentration of 5 000 ppm, is manufactured by Hoechst Inc. After the attrition steps, the C10-C50 concentration in the sediment dropped by 90%.

EXAMPLE 6

Organics Removal in −45 μm Fraction of Harbour Comprising Aerosol OT™

[0073] The surfactant used was Aerosol OT™ also at the 5 000 ppm level. Decontamination results achieved were similar to those reached with Hostapur™. 2

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