PRIORITY DOCUMENT

[0001] The present application claims priority from Australian Provisional Patent Application No 2022902237 titled “Sorbent Application Test Method” filed on 9 August 2022, the content of which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

[0002] The present disclosure relates to the remediation of contaminated materials. In a particular form, the present disclosure relates to a method that supports remediation processes which involve the use of sorbents.

BACKGROUND

[0003] Soil and other materials at former industrial sites are often contaminated with a number of different organic and inorganic substances, including per- and polyfluoroalkyl substances (PFASs), which are of concern from a health and environmental perspective. Before such a site can be redeveloped for residential or other use, the materials must be remediated to remove or minimise the risk that such contaminants may otherwise pose. The remediation can be done on-site, or, in some cases, such as in infrastructure projects where contaminated material is excavated and transported to other sites for reuse or disposal, materials that have been removed from a site may also need to be treated to minimise the risk of PFASs leaching off-site.

[0004] A common method of remediating such materials involves the use of sorbents which absorb or adsorb the contaminants. The sorbents are applied to, for example, the soil and blended with the soil, resulting in the conversion of one or more contaminants to a less soluble, mobile and/or toxic form, and leading to a reduction in the hazard potential of the material. Where this stabilisation results in a less soluble or mobile contaminant, this leads to a reduced level of leachability of that contaminant from the material. In turn, this results in a reduced risk that the material could cause groundwater contamination and/or toxicity to humans or animals contacting the material.

[0005] Typically, sorbents are blended into contaminated materials at a known percentage (% w/w) to immobilize contaminants. However, there is presently no method that allows one to check whether the desired dosing has been achieved, and/or how evenly (or otherwise) the sorbent is distributed throughout the treated material. In order to achieve a successful remediation of a site, it would be preferable if one or both of these factors could be assessed. Current approaches typically measure efficiency (effective immobilisation) of sorbent in respect of contaminant leachability reduction. The method used for this is the Australian Standard Leaching Procedure (ASLP). The contaminant concentration is compared pre- and post-treatment, and only informs contaminant leachability reductions based on sorbent efficiency, but does not provide any details regarding sorbent dose accuracy or variation through a material. Dye methods have also been used to characterise sorbents and assess their capacity (via dye proxy measure) to sorb target contaminants (see, for example, Sorengard, M. et al. (2020) J Env Chem Eng vol. 8(3), p 103744). This approach also does not assess the dosing of sorbents to a material, or the variability thereof.

[0006] There is thus a need to provide a method that allows the dose of sorbent applied to a contaminated material to be determined. There is also a need to provide a method that allows the uniformity of the application of a sorbent to a contaminated material to be determined.

SUMMARY

[0007] According to a first aspect, there is provided a method of determining the dose of a sorbent in contaminated material, the method comprising: a) providing representative samples of contaminated material to which a sorbent has been applied; b) mixing each of the samples obtained in step a) with a dye that binds to the sorbent; c) measuring the UV-Vis absorbance of each of the dyed samples produced in step b); and d) determining the dose of the sorbent in the contaminated material by comparing the UV-Vis absorbance of each sample measured in c) to a standard calibration curve prepared by measuring the UV-Vis absorbance of samples comprising: the material of the same type as used in step a) but to which the sorbent has not been applied; the sorbent, and the dye.

[0008] The method may include an additional step of determining the dose and uniformity of distribution of the sorbent in the material using the dose of the sorbent determined in step d) and the Relative Standard Deviation (RSD) derived therefrom. Therefore, there is also provided a method of determining the dose and uniformity of distribution of a sorbent in contaminated material, the method comprising: a) providing representative samples of contaminated material to which a sorbent has been applied; b) mixing each of the samples obtained in step a) with a dye that binds to the sorbent; c) measuring the UV-Vis absorbance of each of the dyed samples produced in step b); d) determining the dose of the sorbent in the material by comparing the UV-Vis absorbance of each sample measured in c) to a standard calibration curve prepared by measuring the UV- Vis absorbance of samples comprising: material of the same type as used in step a) but to which the sorbent has not been applied; the sorbent, and the dye; and e) determining the uniformity of distribution of the sorbent in the material using the dose of the sorbent determined in step d) and the Relative Standard Deviation (RSD) derived therefrom.

[0009] In one form, step b) may further comprise centrifuging the mixed samples. The centrifugation may be carried out in the presence of a solvent that increases the specific gravity of the sample.

[0010] The sorbent may be an alum-based sorbent, a carbon-based sorbent, a mineral-based sorbent, a resin-based sorbent, or a combination thereof. The sorbent may be an alum-based sorbent or a carbonbased sorbent, or a mixture thereof.

[0011] The dye preferably has a low affinity for adsorption or absorption to the contaminated material. The dye may be an azo dye, such as Methyl red. The dye may be a thiazine dye, such as Methylene blue. The dye may be a xanthene dye, such as Rose Bengal.

BRIEF DESCRIPTION OF DRAWINGS

[0012] Embodiments of the present disclosure will be discussed with reference to the accompanying drawings wherein:

[0013] Figure 1 is a flow chart depicting one embodiment of the method of the present invention;

[0014] Figure 2 is a calibration curve prepared as described in Example 1 and on the basis of the data in Table 1; and

[0015] Figure 3 is a calibration curve prepared as described in Example 1 and on the basis of mean dose and mean absorbance as given in Table 2.

DESCRIPTION OF EMBODIMENTS

[0016] The present inventors have surprisingly found that the dose of sorbent present in a material that has been subjected to a remediation treatment with the sorbent can be simply determined using known dyes and analytical methods.

[0017] There is therefore provided a method of determining the dose of a sorbent in contaminated material, the method comprising: a) providing a representative set of samples of contaminated material to which a sorbent has been applied; b) mixing each of the samples obtained in step a) with a dye that binds to the sorbent; c) measuring the UV-Vis absorbance of each of the dyed samples produced in step b); and d) determining the dose of the sorbent in the contaminated material by comparing the UV-Vis absorbance of each sample measured in c) to a standard calibration curve prepared by measuring the UV-Vis absorbance of samples comprising: material of the same type as used in step a) but to which the sorbent has not been applied; the sorbent, and the dye.

[0018] The present inventors have also surprisingly found that the uniformity of the distribution of the sorbent through a material can also be easily determined using the same dyes and analytical methods, and further including a statistical analysis of the data generated using the analytical methods.

[0019] The method may include an additional step of determining the dose and uniformity of distribution of the sorbent in the material using the dose of the sorbent determined in step d) and the Relative Standard Deviation (RSD) derived therefrom. Therefore, the method also comprises: a) providing representative samples of contaminated material to which a sorbent has been applied; b) mixing each of the samples obtained in step a) with a dye that binds to the sorbent; c) measuring the UV-Vis absorbance of each of the dyed samples produced in step b); d) determining the dose of the sorbent in the material by comparing the UV-Vis absorbance of each sample measured in c) to a standard calibration curve prepared by measuring the UV- Vis absorbance of samples comprising: material of the same type as used in step a) but to which the sorbent has not been applied; the sorbent, and the dye; and e) determining the uniformity of distribution of the sorbent in the material using the dose of the sorbent determined in step d) and the Relative Standard Deviation (RSD) derived therefrom.

[0020] The method can be applied to any site or material requiring remediation. The method may be applied to any contaminated material type, however the method is particularly suitable for application to materials such as soils, mining tailings and by-products, sludge wastes (e.g. effluent treatment sludges), industrial wastes, tunnelling and excavation spoils, rock and asphalt, or mixtures thereof. Preferably, the material is soil. The method may be used in land management (i.e. where soil is treated with sorbent and reused on the same site), and may also be applied to contaminated material that has been taken from a site, such as stockpiled material, transient soil, and in treatment facilities.

[0021] The contaminants that may be present in the material include inorganic contaminants such as metals, metalloids, halogens and nutrients (particularly, one or more of antimony, arsenic, boron, cadmium, chromium, cobalt, copper, cyanide, fluoride, lead, manganese, mercury, molybdenum, nickel, phosphate, selenium, uranium, and zinc) and organic contaminants including, for example, polycyclic aromatic hydrocarbons (PAHs), total petroleum hydrocarbons (TPH), "benzene, toluene, ethylbenzene and xylenes" (BTEX), benzo[a]pyrene (B(a)P), volatile organic compounds (VOCs), organic pesticides and herbicides, polychlorinated biphenyls (PCBs), per- and poly-fluorinated hydrocarbons (PFASs) such as perfluorooctanylsulfonate (PFOS), dioxins and specific organic compounds such as naphthalene, carbon tetrachloride and trichloroethylene.

[0022] The sorbent may be any sorbent that is typically used for the stabilisation of inorganic contaminants, organic contaminants or the simultaneous stabilisation of inorganic and organic contaminants. The sorbent may be an alum-based sorbent, a carbon-based sorbent, a mineral-based sorbent, a resin-based sorbent, or a combination thereof. Examples of carbon-based sorbents are activated charcoal, and Biochar, which is a product of the slow pyrolysis of biomass. An example of a mineralbased sorbent is Fluoro-Sorb®, which is composed of bentonite and long-chain quaternary ammonium salts. An example of an alum-based sorbent is an alum sludge composition. A suitable alum sludge composition is described in WO 2011/038459. The sorbent may be an alum-based sorbent or a carbonbased sorbent, or a combination thereof. A combination of an alum-based sorbent and a carbon-based sorbent is also described in WO 2011/038459 and is sold under the trade name RemBind®.

[0023] By “representative set of samples” it is meant that the samples of material are obtained from the material that has been treated with the sorbent in such a way that the set of samples reflects the characteristics of the whole site or material treated with the sorbent. There are standards that set out how many samples need to be taken and how they are to be taken in order to obtain a representative set of samples, and a person skilled in the art will be aware of such standards and how to apply them. Examples of suitable standards are the Victorian Guidelines IWRG 702 and AS 4482.1. These standards dictate the number of samples that are required to be taken to ensure that the samples are representative based on material volume. The samples are collected from a spread or grid-like pattern to remove bias. Collected samples are subjected to a splitter prior to analysis to ensure that they are well-mixed.

[0024] The method comprises mixing each of the samples obtained in step a) with a dye that binds to the sorbent. The dye will typically be in the form of a solution, and the mixing can be performed using any suitable method (e.g., vortexing) that facilitates the binding of the dye to the sorbent. By “binding” it is meant that the dye adsorbs onto or absorbs into the sorbent in such a way that it is retained on or by the sorbent, thus allowing an absorption spectrum of the dyed sorbent to be obtained.

[0025] Any dye that binds to the sorbent, and that will allow an absorption spectrum of the dyed sorbent to be obtained, will be suitable for use in the present invention. The dye preferably has a low affinity for adsorption or absorption to the material being analysed. For example, some soils, such as claybased soils and soils that contain large amounts of organic matter, may adsorb or absorb the dye to a significant extent. For example, the present inventors have found that clay-based soils and sandy soils adsorb Methylene blue dye to a significant extent. In one embodiment of the methods of the present invention, the dye is not Methylene blue when the contaminated material is a clay-based soil or a sandy soil. It is therefore important to use a material that is composed of the same, or a very similar, matrix in the calibration method. This is an important feature of the present invention. The dye may be an azo dye, such as Methyl red. The present inventors have found that Methyl red is an effective dye across a variety of different soil types. The dye may be a thiazine dye, such as Methylene blue. The dye may be a xanthene dye, such as Bengal Red. The dye to be used will also depend on the type of sorbent that is being analysed.

[0026] Where a solution of a dye is to be used, the concentration of the dye in the solution will depend on the type of dye being used, and may also depend on the type of sorbent, the type of spectrophotometer, as well as the type of material that is being analysed. A suitable dye concentration may be about 90 mg/L to about 5000 mg/L. For some sorbent and contaminated material combinations, the present inventors have found that the dye concentration may need to be as high as from about 1000 mg/L to about 5000 mg/L. When Methyl red is used as the dye, a suitable concentration has been found to be about 90 mg/L to about 110 mg/L, about 95 mg/L to about 105 mg/L or about 100 mg/L across a variety of contaminated material types, but for some soil and sorbent combinations, a concentration of about 200 mg/L, about 300 mg/L, about 400 mg/L, about 500 mg/L, about 600 mg/L, about 700 mg/L, about 800 mg/L, about 900 mg/L, about 1000 mg/L, and up to about 2000 mg/L may be used. The solution will typically be an aqueous solution.

[0027] In some embodiments, step b) may further comprise centrifuging the mixed samples. When certain materials (particularly certain soils) are used, colloids form in the samples following the addition of a dye and subsequent mixing. Colloids disperse light, affecting the absorbance of the light passing through the samples, and leading to inaccurate absorbance readings and erroneous results. The present inventors have found that centrifuging the dyed samples mitigates this problem. The present inventors have also found that adding particular solvents to the samples prior to centrifugation further retards the formation of colloids. It is postulated that this may be due to an increase in the specific gravity of the samples upon the addition of such solvents. Therefore, step b) may further comprise centrifuging the mixed samples in the presence of a solvent that increases the specific gravity of the sample. Examples of suitable solvents that may be used include, but are not limited to, chlorinated solvents and solvents bearing hydroxyl groups, such as alcohols (e.g., methanol). The solvent may be used in an amount of about 5% v/v to about 25% v/v. For example, using solvent in an amount of no more than about 10% v/v has been found to work well when using methanol as the solvent.

[0028] Following mixing (and optionally centrifugation), the samples may be filtered (e.g., using a suitable filter paper or a syringe filter) to remove any solids, and the UV-Vis absorbance of each of the dyed samples produced in step b) is measured. Any UV-Vis spectrophotometer can be used for the measurement. An example of a suitable spectrophotometer is the Shimadzu UV-1900 spectrophotometer. It may also be possible to carry out the method of the present invention on-site, in which case a portable unit, such as the DR6000™ UV VIS Spectrophotometer from Hach may be used. The absorbance may be measured at any wavelength that is suitable for the particular dye being used. An example of a suitable wavelength in respect of Methyl red is 435 nm or 518 nm.

[0029] To determine the dose of sorbent that has been applied to the material to be remediated, the measured absorbance values need to be correlated to a dose of sorbent using an appropriate calibration curve. Therefore, the method of the present invention also comprises the step of determining the dose of the sorbent in the material by comparing the UV-Vis absorbance of each sample measured in step c) to a standard calibration curve prepared by measuring the UV-Vis absorbance of samples comprising: material of the same type as used in step a) but to which the sorbent has not been applied; the sorbent, and the dye.

[0030] A person skilled in the art will be aware of how to prepare a suitable calibration curve. For example, sorbent can be added to samples of the contaminated material (material that has not already been treated with the sorbent should be used) in increasing concentrations to achieve dosing of, for example, 1 % w/w, 1.5 % w/w, 2 % w/w, 2.5 % w/w, 3 % w/w and 5% w/w of sorbent. Typically, the concentration of sorbent will be about 1 % w/w to about 5 % w/w. The samples of untreated material should also be representative, in that the samples of material should be obtained in such a way that the set of samples reflects the characteristics of the whole material. As discussed above, a person skilled in the art will be aware of such standards and how to apply them. Examples of suitable standards are the Victorian Guidelines IWRG 702 and AS 4482.1.

[0031] The following steps will typically be performed in the same way as steps b) and c). The samples may be mixed, and the dye is added. Preferably, the concentration of the dye used will be the same as that used in step b). The dyed samples may also be mixed, followed by an optional centrifugation step (which may also include the use of methanol), as discussed above in relation to step b). The dyed samples may then be filtered, and the UV-Vis absorbance of each of the dyed samples produced in step b) will be measured and plotted to give a calibration curve. Examples of methods of the present invention are given in Examples 1 and 2 and Figure 1, and example calibration curves are given in Figures 2 and 3.

[0032] The calibration curve can be used to determine the dose of sorbent in a sample of a contaminated material to which a sorbent has been applied. This is done by simply dying the sample (as described herein), measuring the UV-Vis absorbance of the sample and, using the calibration curve, finding the sorbent dose value that corresponds to the measured absorbance.

[0033] The present inventors have also surprisingly found that the uniformity of the distribution of the sorbent through the material can also be easily determined by further conducting a statistical analysis of the measured UV-Vis absorbance data. Specifically, by determining the mean dose of sorbent and the standard deviation of the sorbent doses, the relative standard deviation (RSD) can be determined. It is the RSD that provides the degree of homogeneity (“uniformity”) of the sorbent in the material, thus determining the uniformity of distribution of the sorbent in the material. A person skilled in the art will be aware of how to calculate the RSD using the sorbent dose data obtained from steps a) to d). For example, the following calculation method can be used:

1. calculate the mean of the doses;

2. subtract the mean from each dose in the data to determine the deviation for each dose;

3. square the deviations for each dose;

4. add together the squared deviations;

5. divide the sum of the squared deviations by the total number of values used to get the variance;

6. find the square root of the variance to get the standard deviation of the data;

7. multiply the standard deviation by 100 and then divide this number by the mean.

[0034] Reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that such prior art forms part of the common general knowledge.

[0035] It will be understood that the terms “comprise” and “include” and any of their derivatives (e.g., comprises, comprising, includes, including) as used in this specification, and the claims that follow, is to be taken to be inclusive of features to which the term refers, and is not meant to exclude the presence of any additional features.

[0036] The invention is hereinafter described with reference to the following, non-limiting examples.

EXAMPLES

[0037] Example 1

[0038] The flow chart in Figure 1 summarises the following method. A 100 mg/L Methyl red solution was prepared. Sorbent (RemBind®) was added to 20 g of soil matrix to achieve dosing of 0 % w/w, 1 % w/w, 1.5 % w/w, 2 % w/w, 2.5 % w/w, 3 % w/w and 5 % w/w and vortexed for 1 minute to mix well.

After vortexing, 50 mL of 100 mg/L Methyl red solution was added to each sample and the dyed samples were vortexed again for 1 minute. The samples were left to settle for 30 minutes before being centrifuged at 3000 rpm for 20 minutes. The samples were then filtered through Whatman’s #1 filter paper before adding 1 drop of 32% HC1 to each sample. The Methyl red spectra were then measured using a UV-Vis (Shimadzu UV-1900) at 435 nm to develop matrix-corrected calibration curves for use in the remainder of the method (Tables 1 and 2, and Figures 2 and 3). [0039] A sufficient number of field samples from a field remediated with RemBind® were collected in accordance with Victorian Guidelines IWRG 702 and AS 4482.1. Each field sample consisted of 20 g of soil, to which 50 mL Methyl red was added. The dyed samples were vortexed, centrifuged (at 3000 rpm for 20 min), and filtered through Whatman’s #1 filter paper, before having 1 drop of 32% HC1 added to each sample. The Methyl red absorbance spectra were then measured using a UV-Vis spectrophotometer (Shimadzu UV-1900) at 435 nm, and the dose % w/w of RemBind® added to each sample was determined using the Methyl red absorbance spectra and the calibration curve obtained as detailed above in paragraph [0038]. The results are shown in Table 3. Values derived for these samples were then assessed statistically for mean value, upper and lower confidence interval values, deviation, and relative standard deviation (RSD) (see Table 4).

TABLE 1

Calibration sample preparation. TABLE 2

Calibration sample preparation including mean values.

TABLE 3

Field sample results.

TABLE 4

Statistical output.

[0040] Example 2

[0041] Calibration curves were prepared using a 100 mg/L Methyl red stock solution which was used to prepare six calibration standards for the instrument (0, 1, 2.5, 5, 7.5 and 10 mg/L). In addition, a set of matrix matched calibration standards were prepared from the same soil by adding 50 mL of the 100 mg/L Methyl red stock solution and ~20 g of soil to a sufficient number of centrifuge tubes to achieve duplicate matrix matched calibration standards where a range of sorbent applications (0 % w/w, 0.5 % w/w, 1 % w/w, 1.5 % w/w, 2 % w/w, 2.5 % w/w and 3 % w/w) were achieved by adding 0 g, 0.1 g, 0.2 g, 0.3 g, 0.4 g, 0.5 g, or 0.6 g of sorbent to each tube, respectively.

[0042] For testing and analysing samples of different sorbents and matrices, two different sorbents (either an alum and carbon blend i.e., a mixed mineral product “MM”, or a high-performance lignite- derived activated carbon that has undergone an acid and/or steam activation process "PAC”) were added to 20 g of three different soil matrices (clay, sand or compost) to achieve dosing of 2.5 % w/w and vortexed for 30 seconds to mix well. After vortexing, 50 mL of 100 mg/L Methyl red solution was added to each sample and the dyed samples were vortexed again for 1 minute. The samples were left to settle for 30 minutes before being centrifuged at 3000 rpm for 20 minutes. The samples were then filtered through Whatman’s #1 filter paper before adding 1 drop of 32% HC1 to each sample. The Methyl red spectra were then measured using a UV-Vis (Shimadzu UV-1900) at 518 nm, and the dose (% w/w) of sorbent added to each sample was determined using the Methyl red absorbance spectra and calibration curves obtained as detailed above in paragraph [0041]. The results are shown in Table 5.

[0043] It will be appreciated by those skilled in the art that the disclosure is not restricted in its use to the particular application or applications described. Neither is the present disclosure restricted in its preferred embodiment with regard to the particular elements and/or features described or depicted herein. It will be appreciated that the disclosure is not limited to the embodiment or embodiments disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the scope as set forth and defined by the following claims.