AU2022221463A1 - In-situ Per- and PolyFluoroAlkyl Substance Immobilisation using Powdered Activated Carbon and High-Shear Mixing with an Enclosed Integrated Spreader System - Google Patents

Abstract

The present invention relates to a method of remediating an in situ horizon of Per- or PolyFluoroAlkyl Substance (PFAS)-contaminated soil through the use of a Powdered Activated Carbon (PAC) reagent and a soil stabilizer, whereby a horizon of contaminated soil is mixed with the PAC so as to provide a means for immobilisation of at least a portion of the corresponding PFAS contamination. ...... .... rnl 4pJ 000

Description

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IN-SITU PER- AND POLYFLUOROALKYL SUBSTANCE IMMOBILISATION USING POWDERED ACTIVATED CARBON AND HIGH-SHEAR MIXING WITH AN ENCLOSED INTEGRATED SPREADER SYSTEM PRIORITY DETAILS

The present application claims priority from Application No. 2021902705, filed in Australia on 24 August 2021, the entirety of which is incorporated herein by reference.

TECHNICAL FIELD

[0001] The present invention relates generally to the field of the contamination of land with Per- or PolyFluoroAlkyl Substances and more particularly methods of remediation through the use of Powdered Activated Carbon.

BACKGROUND

[0002] PFAS (Per- and PolyFluoroAlkyl Substances) are a class of synthetic chemicals used in a range of industries globally. The class in particular includes PerFluoroOctanoic Acid (PFOA) and PerFluoroOctaneSulfonic acid (PFOS) which have been widely used as surfactants because they lower the surface tension of water more than hydrocarbon-based surfactants.

[0003] One application favouring the use of PFAS, and PFOA/PFOS in particular, includes the manufacture of firefighting foams for liquid fuel fires. Even though fires only arise occasionally, the foams are frequently deployed as part of commissioning, testing, and training. The PFAS component of such foams can remain in the upper soil horizons, be transported downgradient via surface drainage, or be transported vertically toward the groundwater horizon with each consecutive rain event. Once mobilised in the groundwater, PFAS is difficult to remove and can be transported great distances, to resurface in river systems and groundwater bores in particular, such as the drinking water bores used by remote communities.

[0004] PFAS compounds do not break down in the environment and can accumulate over time. With a growing body of literature evidencing adverse health and environmental effects upon exposure to PFAS, this class of chemicals is gradually being phased out particularly in first world countries. Nevertheless, PFAS chemicals continue to have a range of industrial applications, continue to by synthesised abroad, and persist at existing contamination sites.

[0005] The remediation of contaminated land is an important step in mitigating PFAS exposure. A conventional approach to the treatment of PFAS-contaminated soil involves immobilising the leachable PFAS compounds with a sequestration reagent such as Powdered Activated Carbon (PAC). The immobilised PFAS compounds remain in the soil, however their activity is significantly reduced whereby they are less prone to leaching into, for example, water ways. In an alternative, the contaminated material can be stored onsite in lined repositories, but not without significant cost.

[0006] Treatment of PFAS soil contamination using PAC has conventionally been performed ex-situ by excavating the contaminated soil and transporting it to a treatment facility where the PAC is applied, and then transporting the treated soil back to the excavation site for reinstatement (so-called ex situ treatment). More particularly, the conventional approach requires excavation, loading, transport, stockpiling, treatment, re-stockpiling, re-loading, re transporting, spreading and compaction of the contaminated soil volumes.

[0007] These activities are associated with significant machinery requirements, project cost, time, and the risk of dispersing contaminated soils to other areas, including by airborne dust and from water run-off. The latter can be particularly problematic as a water treatment plant may be required onsite to meet the prevailing standards. The conventional approach is also one of batching and is not adapted for continuous processing.

[0008] Furthermore, many PFAS-contaminated sites are characterised by the PFAS being concentrated within the upper soil horizons and spread over large areas. The material handling involved with conventional ex-situ treatment is not particularly well adapted to such sites.

[0009] Impermeable capping layers are often used in combination with ex situ treatment. In particular, a physical cap can be emplaced over PFAS contaminated soils to limit erosion (whether by traffic or natural processes) and to limit transportation of PFAS by wind or water. Conventional caps include asphalt, concrete, compacted clay, and geomembranes, which all suffer the drawback of cost as well as the need for engineered drainage in particular due to their impermeability and the corresponding increase in natural ground level.

[0010] In situ approaches to treatment are favorable because they minimize equipment requirements and capital cost, avoid rehandle, and minimize associated problems including dust generation.

[0011] Prior art methods and equipment that are proposed for the in situ treatment of hazardous materials in soils are known from US5348422 and CN209680795U. In US5348422 there is disclosed a method of forming an in-situ process reactor using trenching machinery to install a network of reagent feed conduits and contaminant removal conduits. The reagents are fed through the network to solubilise the hazardous materials which are then removed from site. In CN209680795U there is disclosed equipment that is proposed to be used for the in-situ remediation of heavy metals in farmland soil. The equipment consists of tractor-driven rotary hoe attachments that are configured with drip nozzles. In both prior art documents, the methods and equipment are purposed merely for loosening soil and for delivering soluble agents.

[0012] The present invention originates out of a desire to ameliorate some of the deficiencies in the prior art, and in particular to provide a means of in situ PFAS treatment that is adapted to high volume projects.

DISCLOSUREOFTHE INVENTION

[0013] In a first aspect, the present invention relates to a method of remediating an in situ horizon of Per- or PolyFluoroAlkyl Substance (PFAS) contaminated soil through the use of a Powdered Activated Carbon (PAC) reagent and a soil stabilizer; the horizon of soil having a lineal extent and a depth; the soil stabilizer being provided with a means of propulsion in a forward direction along the lineal extent of the horizon and consisting of: a drum or rotor for mixing the PFAS-contaminated soil with the PAC, the drum or rotor having a rotational axis and a plurality of elements for ripping the PFAS-contaminated soil disposed about the drum or rotor at predetermined radii from the rotational axis, a container or chute for holding a predetermined quantity of the PAC, and a means of releasing the PAC from the container or chute and spreading the PAC substantially uniformly onto the horizon substantially forward of the drum or rotor; the method consisting of the steps of: lowering the drum or rotor into at least an upper portion of the horizon, and while releasing and spreading the PAC onto the horizon, and with the drum or rotor rotating, propelling the soil stabilizer in the forward direction, whereby the at least upper portion of the horizon is mixed with the PAC so as to provide a means for immobilisation of at least a portion of the corresponding PFAS contamination.

In a second aspect, the present invention relates to a method of treating PFAS contaminated soil with a PAC reagent using a soil recycler machinery; said soil recycler machinery having a soil hopper, a soil mixer fed from the soil hopper, and a conveyor extending from the soil mixer to a discharge point; said method consisting of the steps of: forming a slurry from dry PAC combined with a liquid, excavating a predetermined volume of the PFAS-contaminated soil and releasing said volume of soil into the soil hopper, releasing a predetermined volume of the PAC slurry into the soil mixer, mixing the volume of soil and the volume of PAC slurry within the soil mixer, and then discharging the PAC-treated PFAS contaminated soil from the conveyor.

DESCRIPTION OF FIGURES

[0014] Embodiments of the present invention will now be described in relation to figures, wherein

Figure 1 is a cutaway drawing of the soil stabilizer of one preferred embodiment whilst in operation.

Figure 2 is an illustration of the slurry tanker of a second preferred embodiment whilst in operation.

DETAILED DESCRIPTIONOF PREFERRED EMBODIMENTS

[0015] With reference to Figure 1, according to a preferred embodiment of the invention there is provided a method of remediating an in situ horizon of Per- or PolyFluoroAlkyl Substance (PFAS)-contaminated soil 1 through the use of a Powdered Activated Carbon (PAC) reagent 2 and a soil or pavement stabilizer 3. The horizon of soil 1 has a lineal extent and a depth.

[0016] The soil stabilizer 3 is provided with a means of propulsion in a forward direction along the lineal extent of the horizon 1, and consists of: a drum or rotor 4 for mixing the PFAS-contaminated soil 1 with the PAC 2, the drum or rotor 4 having a rotational axis and a plurality of elements 5 for ripping the PFAS-contaminated soil 1 disposed about the drum or rotor 4 at predetermined radii from the rotational axis, a container or chute 6 for holding a predetermined quantity of the PAC 2, and a means 7 of releasing the PAC 2 from the container or chute 6 and spreading the PAC 2 substantially uniformly onto the horizon 1 substantially forward of the drum or rotor 4.

[0017] The method consists of the steps of: lowering the drum or rotor 4 into at least an upper portion of the horizon 1, and while releasing and spreading the PAC 2 onto the horizon 1, and with the drum or rotor 4 rotating, propelling the soil stabilizer 3 in the forward direction, whereby the at least upper portion of the horizon 1 is mixed with the PAC 2 so as to provide a means for immobilisation of at least a portion of the corresponding PFAS contamination.

[0018] In the preferred embodiment, the elements 5 for ripping the PFAS contaminated soil consist of picks, chisels, or blades that are adapted and configured on the drum or rotor 4 to excavate a soil or bituminous or cementitious material consisting of a substantially continuous solid phase.

[0019] Thereby advantageously, the soil stabilizer 3 is provided as re-purposed in-situ pavement stabilisation machinery which can provide the high shear rates desirable under the present invention, and can perform well in the moist to wet clays, sandy soils, and clay-sand blends that are desirable in applications of the present invention.

[0020] The soil stabilizer 3 is capable of high shear mixing. Such high shear mixing is understood in the art as the mechanical mixing of two particulate components to a degree sufficient for the two particulate components to be substantially homogenous. The term 'substantially' will be understood here as a functional reference to an effective plateauing in the relevant activity of an active portion of the particulate components when measured against the degree of mixing.

[0021] The degree of high shear mixing can be measured with reference to the cross-sectional area of the elements or tools 5 (whether picks, chisels, blades, or otherwise) swept through the horizon 1 per unit time and per unit length of the drum or rotor 4. For this purpose the following metricized equation is adopted:

[0022] Equation 1:

rotationrate x tool length x tool width x tool count drum length

[0023] Where rotation rate is expressed in revolutions per minute of the drum 4, tool length is expressed in metres of the tool 5 radially extending above the surface of the drum 4, tool width is expressed as the average width of the tool 5

(measured parallel to the axis of the drum 4) as extending above the surface of the drum 4, tool count is the number of the tools 5 installed on the drum 4 during use, and drum length corresponds to the effective working width of the soil stabilizer 3.

[0024] Preferably, the metric has a value of between 30 and 750. More preferably, the metric has a value of between 50 and 450. Most preferably, the metric has a value of between 80 and 300.

[0025] Preferably, the PAC 2 is mixed with the PFAS-contaminated soil 1 in a ratio of 2t of PAC 2 for every 100t of PFAS-contaminated soil 1. It will be appreciated that the person skilled in the art can vary the ratio of PAC 2 according to the extent of PFAS contamination and other characteristics such as the activity of the PAC 2. Preferably, the PAC 2 has an iodine number of 900 according to ASTM D4607.

[0026] In the preferred embodiment, the soil stabilizer machinery 3 is provided with a conveying unit 8 to continuously release the PAC 2 from the container or chute 6, and an auger unit 9 to continuously spread the PAC 2 substantially uniformly along an axis parallel to the rotational axis of the drum or rotor 4.

[0027] In the preferred embodiment, the soil stabilizer machinery 3 is provided with a means to continuously feed the PAC 2 into the container or chute 6 while the soil stabilizer machinery 3 is being propelled in the forward direction.

[0028] Preferably, the PAC 2 is delivered directly to the soil stabilizer machinery 3 from the supplier in a pneumatic tanker to allow pneumatic delivery into the container or chute 6 to avoid rehandling and associated dust issues. In an alternative embodiment, the PAC 2 is stored in onsite bulk storage such as a silo and then delivered to the soil stabilizer machinery 3 in the pneumatic tanker. Where haulage distances from the supplier are too great, conventional bulka-bag transport/stowage is provided. The bulka-bags are unloaded into the onsite bulk storage with the addition of moisture for dust suppression.

[0029] In the preferred embodiment the means of propulsion consists of a tractor, however in other embodiments the means of propulsion is integrated with the soil stabilizer machinery.

[0030] In another embodiment, the method is further provided with the step of releasing and spreading a powdered bentonite along with the PAC 2 onto the horizon 1. Accordingly the at least upper portion of the horizon 1 when mixed with the PAC 2 and bentonite is provided with a reduced permeability arising from an occupation of soil pore space by the bentonite and/or from intermingled lens of contiguous bentonite.

[0031] Preferably, the powdered bentonite is mixed with the PAC 2 before feeding the mixture into the container or chute 6. Preferably, the bentonite is added in a proportion of 2-6% by weight of soil and more preferably about 4%.

[0032] The reduced permeability effectively provides an in situ capping layer whereby a leaching potential of the corresponding PFAS is reduced. This process is particularly advantageous where the need for a separate capping layer as provided through a separate process is otherwise too costly, and allows the surface levels to remain substantially the same.

[0033] A covering layer of low permeability soil will in some circumstances be advantageous for protecting the underlying soil from erosion, traffic, and the effects of seasonal drying and wetting. The latter in particular may induce cracking, forming a pathway for water migration.

[0034] In another embodiment, the method is further provided with the step of releasing and spreading a cementitious binder along with the PAC 2 onto the horizon 1. Accordingly, the at least upper portion of the horizon when mixed with the PAC 2 and the cementitious binder is provided with an increased soil strength upon cure for resisting erosion and dust generation. It will be appreciated that the use of cementitious binder also reduces the permeability.

[0035] Preferably, the cementitious binder consists of lime (having both quick lime and hydrated lime components) and/or cement, optionally with the addition of pozzolan. More preferably, the cementitious binder consists of lime or cement in a proportion of 3-5% by weight of soil and most preferably about 4%. Preferably, the strength gains of the selected cementitious binder are controlled to substantially occur over 4 to 48 hours following application to allow time for soil compaction processes.

[0036] Accordingly there is provided a means of in situ treatment of PFAS contaminated soil 1 with PAC 2 to immobilise the PFAS, and/or with bentonite to reduce a permeability hence leachability of the PFAS contaminated soil, and/or with a cementitious binder to increase the durability of the soil. The PFAS can accordingly be both chemically and physically contained.

[0037] In preferred applications the depth of the horizon of soil 1 is less than 500mm, corresponding to the preferred radius of the drum or rotor 4 of about 500mm. It will be appreciated that the radius of the drum or rotor 4 can be adapted to suit the prevailing digging conditions of a particular site.

[0038] In an alternative embodiment of the present invention, where the depth of the horizon of soil 1 is substantially greater than 500mm or substantially greater than the radius of the drum or rotor 4, there is provided a first modified method wherein the method of remediating the horizon of PFAS contaminated soil is repeated in multiple passes along the lineal extent of soil however with intermediate windrow re-handle.

[0039] In a first step of the first modified method, a predetermined depth of the horizon 1 is windrowed to at least one side of a predetermined path of the soil stabilizer machinery 3, with a remainder of the horizon 1 being left in situ along the path. In a second step, the method of remediating the horizon of PFAS contaminated soil is then performed along the remainder of the horizon 1. In a third step, a predetermined volume of the windrow(s) is returned to the path of the soil stabilizer machinery 3. In a fourth step, the method of remediating the horizon of PFAS contaminated soil is performed along the returned soil.

[0040] The third and fourth steps are repeated as many times as is necessary to exhaust the windrow(s). For example, given a 1.2m deep horizon 1, 0.8m of depth can be windrowed and the remaining in situ 0.4m remediated, then 0.4m of depth returned from the windrow and remediated, then the final 0.4m of depth returned from the windrow and remediated.

[0041] The first modified method may also be adapted to the treatment of stockpiles. In lieu of a windrowing approach, the stockpiled material is re handled onto the path with each pass of the soil stabilizer machinery 3. Preferably the stockpile is shaped with a broad profile having multiple predetermined paths of the soil stabilizer machinery 3 across its width.

[0042] In another modified method, a first predetermined depth of the horizon 1 is remediated according to the method of remediating the horizon of PFAS contaminated soil, the resultant remediated soil is then windrowed to at least one side of a predetermined path of the soil stabilizer machinery 3, then a second predetermined depth of the horizon 1 is remediated according to the method of remediating the horizon of PFAS contaminated soil, and then the windrowing and the remediation repeated as many times as necessary to reach the desired depth, whereafter the windrowed remediated soil is returned to the excavation. Preferably the remediated soil is thereafter compacted for geotechnical performance.

[0043] With further reference to Figure 2, according to a second preferred embodiment of the invention there is provided a second modification to the method of remediating an in situ horizon of PFAS-contaminated soil 1 as described in the first preferred embodiment.

[0044] According to the modified method of the second preferred embodiment, there is provided a further and preceding step wherein the PAC reagent 2 is mixed with a liquid to form a PAC slurry 21. Preferably the liquid consists of water. Preferably the mixing is performed mechanically, for example in a vessel having mixing rotors.

[0045] Preferably a predetermined quantity of the PAC slurry 21 is transferred to and contained in a slurry tanker 22 for use during the method. Preferably the slurry tanker 22 is provided with a pneumatic mixer for maintaining the PAC slurry 21 in a state of suspension. The pneumatic mixer consists of at least one set of apertures in a flowtube of compressed air that delivers a spread of air bubbles through said apertures and into the PAC slurry 21 within the slurry tanker 22. Preferably the slurry tanker 22 has a capacity of between 4,000 and ,000 Litres.

[0046] Preferably the slurry tanker 22 is provided on a self-propelled vehicle. In other embodiments and as illustrated in Figure 2, the slurry tanker 22 is propelled by a tractor 23 and coupled thereto for power.

[0047] According to said second modified method there is further provided a means 24 of releasing the PAC slurry 21 from the slurry tanker 22 and spreading the PAC slurry 21 substantially uniformly onto the horizon 1 forward of the drum or rotor 4. Preferably the means 24 consists of a pump in connection with spray or spreading nozzles 25. Preferably the spreading nozzles 25 are disposed along a boom and are configured to spread the PAC slurry 25 across a lateral extent of the horizon 1, said lateral extent substantially corresponding to the width of the drum or rotor 4. In other embodiments the spreading nozzles 25 are configured to release the PAC slurry 21 across the lateral extent by purely spraying or kinematic means and without being disposed along a boom.

[0048] It will be appreciated that the liquid content of the PAC slurry 21 must be varied to be suitable for the selection of equipment and the chosen PAC parameters such as particle size. For example, a water content of between 35 % may be preferred for hydraulically driven equipment, whereas a water content of between 55-70% may be preferred for pneumatically driven equipment. Preferably, the ratio of water to dry PAC used for forming the PAC slurry 21 is about 2:1 to about 1:1. It will also be appreciated that the water content may be determined according to the prevailing compaction or geotechnical requirements, including the hydration of lime.

[0049] Accordingly the modified method of the second preferred embodiment consists of the steps of: mixing the PAC reagent 2 with the liquid to form the PAC slurry 21, releasing and spreading the PAC slurry 21 onto the horizon 1, lowering the drum or rotor 4 into at least an upper portion of the horizon 1, and with the drum or rotor 4 rotating, propelling the soil stabilizer 3 in the forward direction, whereby the at least upper portion of the horizon 1 is mixed with the PAC slurry 21 so as to provide a means for immobilisation of at least a portion of the corresponding PFAS contamination.

[0050] Preferably, the modified method of the second preferred embodiment further consists of the step of spreading a lime or cement onto the horizon 1, said step being performed after the step of releasing and spreading the PAC slurry 21 onto the horizon 1.

[0051] Preferably, the step of the modified method of the second preferred embodiment involves releasing and spreading the PAC slurry 21 onto the horizon 1, is performed in advance of the soil stabilliser 3 and in the forward direction whereby the soil stabiliser 3 and the slurry tanker 22 are operated in a substantially continuous manner. It will be understood that substantial continuity of operation refers to the soil stabiliser 3 and the slurry tanker 22 advancing along a strip of the horizon 1 at substantially the same average speed (averaging out downtime).

[0052] Preferably, the soil stabiliser 3 is advanced in the forward direction over a portion of the PAC slurry 21 whilst the pore space of the portion of PAC slurry 21 is at least partly occupied with the liquid. It will be appreciated that when the PAC slurry 21 is applied to a relatively dry soil, the liquid will be adsorbed from the PAC slurry 21 into the dry soil and will also tend to evaporate depending upon the prevailing atmospheric humidity. There may therefore exist an optimum timeframe during which all of the steps of the modified method of the second preferred embodiment must be performed on the PAC slurry 21. Substantial continuity of operation may be used to address such a loss of the liquid over time.

[0053] Accordingly the modified method of the second preferred embodiment provides a means for temporarily binding the particles of the PAC reagent 2 to one another by means of intermediary pore water, before the step of in situ high shear mixing is performed. The generation of PAC dust is thereby averted or at least minimised and without detracting from the continuous nature of the process, because the slurry tanker 22 can be propelled in front of the soil stabiliser 3.

[0054] Other powdered reagents can be mixed in with the PAC slurry 21 or applied separately for example via the container or chute. As described in the first preferred embodiment, such reagents can be selected from a cementitious binder, and a bentonite. When using a cementitious binder such as Portland cement, the binder will start curing upon exposure to moisture. Accordingly it may be necessary to use a binder of slow-setting chemistry and/or to minimise the time delay between the slurry tanker 22 spreading the PAC slurry 21 and the soil stabiliser 3 performing the in situ shear mixing.

[0055] Accordingly there are provided methods that significantly reduce project costs and treatment time when compared with the prior art, with reference to ex situ treatment methods in particular. Furthermore, the present invention minimises the risk of dispersing contaminated soil to other areas. The method is amenable to significantly greater volumetric rates of material processed, and is particularly amenable to wet and clayey soils which would otherwise require pre treatment or drying. Machinery requirements are minimised.

[0056] According to another aspect of the invention there is provided a method of treating PFAS-contaminated soil with a PAC reagent using a soil recycler machinery. The soil recycler machinery has a soil hopper, a soil mixer fed from the soil hopper, and a conveyor extending from the soil mixer to a discharge point. Preferably the soil mixer consists of a pug mill. In another embodiment the soil mixer consists of a paddle mixer.

[0057] The method consists of the steps of: forming a slurry from dry PAC combined with a liquid, excavating a predetermined volume of the PFAS contaminated soil and releasing said volume of soil into the soil hopper, releasing a predetermined volume of the PAC slurry into the soil mixer, mixing the volume of soil and the volume of PAC slurry within the soil mixer, and then discharging the PAC-treated PFAS-contaminated soil from the conveyor.

[0058] Preferably the step of releasing the volume of soil into the soil hopper, is performed before the step of releasing the volume of the PAC slurry into the soil mixer, whereby the volume of soil is fed from the soil hopper into the soil mixer concurrently with the volume of the PAC slurry being released into the soil mixer.

[0059] Preferably the soil recycler machinery further has an additive hopper and a screw feeder in connection with the additive hopper, and the soil mixer is fed from the additive hopper via the screw feeder. Preferably the volume of the PAC slurry is released into the soil mixer from the additive hopper via the screw feeder.

[0060] In another embodiment the PAC slurry is fed to the soil mixer via spray or drip lines that are positioned above the soil hopper or between the soil hopper and the soil mixer. Preferably the feed rate of the PAC slurry into the soil mixer is controlled by a programmable logic controller provided with the soil recycler machinery.

[0061] Preferably the soil recycler machinery further has a swing gate for controlling the feed rate of soil transferred from the soil hopper to the soil mixer, and the soil mixer is fed from the soil hopper via the swing gate.

[0062] Preferably the liquid consists of water and the PAC slurry is formed in a ratio of between 1:1 and 3:1 of the water to the dry PAC. More preferably the ratio is about 2:1. Preferably the PAC slurry is formed in at least one mixing tank and then transferred to a holding tank that has an agitator for maintaining the PAC slurry in a state of suspension. Preferably the agitator consists of an impeller or a pneumatic agitator.

[0063] Preferably the soil recycler machinery is positioned in a predetermined location and the untreated soil is excavated and handled into the soil recycler machinery, whereat the soil is treated, and whereafter the treated soil can be stockpiled or handled to a desired location.

[0064] In another embodiment there is provided a strip of PFAS-contaminated soil, and the method is performed on a first portion of said strip in advance of the soil recycler machinery, said first portion once treated being released from the discharge point behind the soil recycler machinery, whereafter the soil recycler machinery is advanced along the strip, and the method is then performed on a second portion of said strip.

[0065] Accordingly there is provided a high shear means for mixing the dry PAC into the PFAS-contaminated soil without releasing airborne PAC dust and causing associated environmental and compliance problems.

[0066] While the invention has been described with reference to preferred embodiments above, it will be appreciated by those skilled in the art that it is not limited to those embodiments, but may be embodied in many other forms, variations and modifications other than those specifically described. The invention includes all such variation and modifications. The invention also includes all of the steps, features, components and/or devices referred to or indicated in the specification, individually or collectively and any and all combinations or any two or more of the steps or features.

[0067] In this specification, unless the context clearly indicates otherwise, the word "comprising" is not intended to have the exclusive meaning of the word such as "consisting only of", but rather has the non-exclusive meaning, in the sense of "including at least". The same applies, with corresponding grammatical changes, to other forms of the word such as "comprise", etc.

[0068] Other definitions for selected terms used herein may be found within the detailed description of the invention and apply throughout. Unless otherwise defined, all other scientific and technical terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which the invention belongs.

[0069] Any promises made in the present document should be understood to relate to some embodiments of the invention, and are not intended to be promises made about the invention in all embodiments. Where there are promises that are deemed to apply to all embodiments of the invention, the applicant/patentee reserves the right to later delete them from the description and they do not rely on these promises for the acceptance or subsequent grant of a patent in any country.

Claims (30)

CLAIMS:

1. A method of remediating an in situ horizon of Per- or PolyFluoroAlkyl Substance (PFAS)-contaminated soil through the use of a Powdered Activated Carbon (PAC) reagent and a soil stabilizer machinery; the horizon of soil having a lineal extent and a depth; the soil stabilizer machinery being provided with a means of propulsion in a forward direction along the lineal extent of the horizon and consisting of: a drum or rotor for mixing the PFAS-contaminated soil with the PAC, the drum or rotor having a rotational axis and a plurality of elements for ripping the PFAS-contaminated soil disposed about the drum or rotor at predetermined radii from the rotational axis, the method consisting of the steps of: releasing and spreading the PAC onto the horizon, and with the drum or rotor lowered into at least an upper portion of the horizon, and with the drum or rotor rotating, propelling the soil stabilizer machinery in the forward direction, whereby the at least upper portion of the horizon is mixed with the PAC so as to provide a means for immobilisation of at least a portion of the corresponding PFAS contamination.

2. A method according to Claim 1 wherein the steps of the releasing and spreading of the PAC, and the propelling of the soil stabilizer machinery, are performed simultaneously.

3. A method according to Claim 1 or 2 wherein the PAC is in powdered form during the releasing or spreading.

4. A method according to Claim 1 or 2 wherein the PAC is in slurry form during the releasing or spreading.

5. A method according to Claim 3 wherein the soil stabilizer machinery further consists of: a container or chute for holding a predetermined quantity of the PAC, and a means of releasing the PAC from the container or chute and spreading the PAC substantially uniformly onto the horizon substantially forward of the drum or rotor.

6. A method according to Claim 4 further involving the use of a slurry tanker for holding a predetermined quantity of a PAC slurry formed by mixing the PAC with a liquid, the slurry tanker being provided with a means of releasing the PAC slurry and spreading the PAC slurry containing the PAC substantially uniformly onto the horizon substantially forward of the soil stabilizer machinery.

7. A method according to any one of the preceding claims wherein the elements for ripping the PFAS-contaminated soil consist of picks, chisels, or blades that are adapted and configured on the drum or rotor to excavate a soil or bituminous or cementitious material consisting of a substantially continuous solid phase.

8. A method according to any one of the preceding claims wherein the soil stabilizer machinery is provided as re-purposed in-situ pavement stabilisation machinery.

9. A method according to Claim 5 or any one of the preceding claims when dependent upon Claim 5 wherein the soil stabilizer machinery is provided with a conveying unit to continuously release the PAC from the container or chute, and an auger unit to continuously spread the PAC substantially uniformly along an axis parallel to the rotational axis of the drum.

10.A method according to Claim 5 or any one of the preceding claims when dependent upon Claim 5 wherein the soil stabilizer machinery is provided with a means to continuously feed the PAC into the container or chute while the soil stabilizer machinery is being propelled in the forward direction.

11.A method according to Claim 6 or any one of the preceding claims when dependent upon Claim 6 wherein the slurry tanker is provided with spreading nozzles to continuously release the PAC slurry from the slurry tanker.

12.A method according to Claim 6 or any one of the preceding claims when dependent upon Claim 6 wherein the slurry tanker is provided with a pneumatic mixer to maintain the PAC slurry in a state of suspension.

13.A method according to any one of the preceding claims wherein there is further provided the step of releasing and spreading a powdered bentonite along with the PAC, or releasing and spreading a slurried mixture of bentonite and the PAC, onto the horizon whereby the at least upper portion of the horizon when mixed with the PAC and the bentonite is provided with a reduced permeability.

14.A method according to any one of the preceding claims wherein there is further provided the step of releasing and spreading a cementitious binder along with the PAC, or releasing and spreading a slurried mixture of the cementitious binder and the PAC, onto the horizon whereby the at least upper portion of the horizon when mixed with the PAC and the cementitious binder is provided with an increased soil strength after curing.

15.A method according to any one of the preceding claims wherein the depth of the horizon of soil is less than 500mm.

16.A method according to Claim 2 wherein the soil stabilizer machinery and the slurry tanker are operated in a substantially continuous manner.

17.A modified method of remediating an in situ horizon of Per- or PolyFluoroAlkyl Substance (PFAS)-contaminated soil through the use of a

Powdered Activated Carbon (PAC) reagent and a soil stabilizer machinery, consisting of the steps of: a first step wherein the method of remediating the horizon of PFAS contaminated soil according to any of the preceding claims is performed along a first predetermined depth of the horizon,

a second step wherein the remediated first predetermined depth of the horizon is windrowed to at least one side of a predetermined path of the soil stabilizer machinery, with a second predetermined depth of the horizon being left in situ along the path,

a third step wherein the method of remediating the horizon of PFAS contaminated soil according to any of the preceding claims is performed along the second predetermined depth of the horizon, and

a later step wherein a predetermined volume of the windrow(s) is returned to the path of the soil stabilizer machinery.

18.A method according to Claim 1 wherein the soil stabilizer machinery is adjusted of high-shear mixing.

19.A method according to Claim 18 wherein the soil stabilizer machinery is in accordance with Equation 1

rotationrate X tool lengthx toolwidth x tool count drum I length

Equation 1

whereby, in use, the metric value is between 30 and 750, and where the rotation rate is expressed in revolutions per minute of the drum, the tool length is expressed as an average in metres of the radial extension of the elements above the surface of the drum, the tool width is expressed as the average width of the elements as measured parallel to the axis of the drum and above the surface of the drum, the tool count is the number of the tools installed on the drum during said use, and the drum length corresponds to the working width of the soil stabilizer when in use

20.A method according to Claim 19 wherein the metric has a value between 50 and 450.

21.A method of treating PFAS-contaminated soil with a PAC reagent using a soil recycler machinery; said soil recycler machinery having a soil hopper, a soil mixer fed from the soil hopper, and a conveyor extending from the soil mixer to a discharge point;

said method consisting of the steps of:

forming a slurry from dry PAC combined with a liquid,

excavating a predetermined volume of the PFAS-contaminated soil and releasing said volume of soil into the soil hopper,

releasing a predetermined volume of the PAC slurry into the soil mixer,

mixing the volume of soil and the volume of PAC slurry within the soil mixer,

and then discharging the PAC-treated PFAS-contaminated soil from the conveyor.

22.The method according to claim 1 wherein the soil mixer consists of a pug mill.

23.The method according to any one of the preceding claims wherein the step of releasing the volume of soil into the soil hopper, is performed before the step of releasing the volume of the PAC slurry into the soil mixer, whereby the volume of soil is fed from the soil hopper into the soil mixer concurrently with the volume of the PAC slurry being released into the soil mixer.

24.The method according to any one claims 21-23 wherein the soil recycler machinery further has an additive hopper and a screw feeder in connection with the additive hopper, and the soil mixer is fed from the additive hopper via the screw feeder, and the volume of the PAC slurry is released into the soil mixer from the additive hopper via the screw feeder.

25.The method according to any one claims 21-23 wherein the PAC slurry is fed to the soil mixer via spray or drip lines that are positioned above the soil hopper or between the soil hopper and the soil mixer.

26.The method according to any one of the preceding claims wherein the feed rate of the PAC slurry into the soil mixer is controlled by a programmable logic controller provided with the soil recycler machinery.

27.The method according to any one of the preceding claims wherein the soil recycler machinery further has a swing gate for controlling the feed rate of soil transferred from the soil hopper to the soil mixer, and the soil mixer is fed from the soil hopper via the swing gate.

28.The method according to any one of the preceding claims wherein the liquid consists of water and the PAC slurry is formed in a ratio of between 1:1 and 3:1 of the water to the dry PAC.

29.The method according to claim 28 wherein the ratio is about 2:1.

30.The method according to any one of the preceding claims wherein the PAC slurry is formed in at least one mixing tank and then transferred to a holding tank that has an agitator for maintaining the PAC slurry in a state of suspension.