Swellable activated carbon granules

Abstract

A swellable sorbent product for soil remediation that comprises comprising: micron- or nano-sized particulate sorbent material with a swellable material that swells upon introduction to a soil environment to disperse the sorbent within the soil environment. These swellable sorbent products are capable of efficiently reducing leaching of unwanted environmental damaging chemicals, such as PFAS, into surrounding ground or ground water.

Description

[0001] SWELLABLE ACTIVATED CARBON GRANULES

[0002] FIELD OF THE INVENTION

[0003] The present invention relates generally to swellable remediation agents in granular or pelletised form for soil remediation. More specifically, the present invention relations to the incorporation of in-situ soil remediation products in micron- or nano-sized particulate form, such as zeolites, clay minerals, oxyhydroxide powders, biochars, or activated carbon, and a swellable material to form a granulated product

[0004] BACKGROUND

[0005] Many particulate sorbent media are utilised for immobilising organic and inorganic contaminants in soil or removing them from water. The micron- or nano-sized absorbent is applied to a contaminated soil to chemically or physically interact with (and therefore immobilise) the contaminants contained within the soil and prevent them from leaching into ground or surface water.

[0006] Sorbents are used in treatment systems to detoxify industrial process water, in pump-and-treat systems for above-ground treatment of contaminated groundwater, as well as immobilize organic and inorganic contaminants in soil. Most sorbents are typically manufactured and used in granular or powder form whereby the particulate is loaded into fluid- or fixed-bed treatment systems or dispersed or distributed over the area subject to contamination.

[0007] While fine-grained powdered sorbents are known to have certain superior physical and chemical properties and high adsorption rate and capacity compared to granulated sorbents, for example powdered activated carbon (PAC) versus granular activated carbon (GAC) ; one of the drawbacks of powdered sorbents for soil remediation is the creation of substantial dust during routine handling, transport, and spreading on the field. The airborne dust produced is undesirable due to its health and safety risks for those exposed during their application on the field.

[0008] Granulation of fine materials is one of the methods to eliminate dust formation during fine materials transport and storage. However, the formation of granules involves the addition of a binder material and an increase in the particle size - this can result in the binder coating the pores of the sorbent material as well as reducing the active surface area of the sorbent, which results in a significant decrease in the efficacy of the sorbent material in adsorbing and immobilising contaminants in contaminated soil due to decreased surface area.

[0009] SUMMARY

[0010] Embodiments of the invention are directed towards a soil remediation granule containing a micron- or nano-sized particulate sorbent, which, when dispersed onto and / or into soil, can expand or swell when in contact with moisture in the soil to readily disperse the sorbent material within the soil matrix, to increase the area of activity of the sorbent, and increase the efficacy of the sorbent material.

[0011] In one embodiment there is a swellable sorbent product comprising: a co-granulated sorbent material with a swellable material, the swellable material being in an amount of about 1.0 - 20 % weight percent; wherein the granules are configured to swell upon introduction to a soil environment to disperse the sorbent material within the soil environment, and

[0012] In preference, the sorbent material is selected from the group of powdered activated carbon, granular activated carbon, carbon-based materials, clay mineral, and combinations thereof.

[0013] In preference, the clay mineral is selected from the group of clay minerals, activated clay minerals, oxy hydroxide minerals, zeolites, and combinations thereof.

[0014] In preference, the carbon-based material is selected from the group of biochar, coal, fly ash, graphite and graphene-based materials including graphene, graphene oxide and graphene or graphene oxide composites, carbon nanotubes, and combinations thereof.

[0015] In preference, the swellable sorbent product is comprised of a combination of activated carbon and minerals, carbon-based materials and minerals, activated carbon and plant nutrients and combinations thereof.

[0016] In preference, the swellable material is a hydrogel. In preference, the hydrogel is selected from the group of carboxymethyl cellulose (CMC), corn starch, guar gum, gum Arabic, sodium alginate, calcium alginate, rice starch, Inulin, sodium polyacrylate, carrageenan gum, psyllium husk, xanthan gum, chitosan, barley husk, bean gum, sodium bentonite or other water absorbing clays, and combinations thereof.

[0017] In preference, the swellable sorbent product includes one or more or more sources of nutrients selected from the group consisting of boron (B), zinc (Zn), manganese (Mn), molybdenum (Mo), nickel (Ni), copper (Cu), iron (Fe), chlorine (Cl), sulphur in its oxidized sulphate form (SO4), magnesium (Mg), calcium (Ca), and combinations thereof

[0018] In preference, the swellable sorbent product includes one or more fertilizer minerals selected from the group of phosphate, nitrogen, potassium.

[0019] A further embodiment resides in a method of capturing or immobilizing contaminants from soil comprising the steps of preparing a swellable sorbent product containing activated carbon, which, when dispersed onto and / or into soil, can expand or swell when in contact with moisture in the soil to readily disperse the activated carbon material within the soil matrix, to increase the area of activity of the activated carbon, and increase the efficacy of the activated carbon material, and applying it to an area of contaminated soil so that the swellable carbon product can be distributed and dispersed with the soil.

[0020] BRIEF DESCRIPTION

[0021] One embodiment of the invention with activated carbon is described below.

[0022] Figure la-d are microscopic images of swelling (expansion) of the compacted PAC-Corn starch and PAC-gum Arabic granules in contact with water;

[0023] Figure 2 shows microscopic images of swelling (expansion) of the compacted PAC-CMC-5% granule in contact with water

[0024] Figure 3 shows microscopic images of swelling (expansion) of the granulated PAC-CMC-5% granule in contact with water Figure 4 shows microscopic images of swelling (expansion) of the compacted PAC-guar gum-5% granule in contact with water.

[0025] Figure 5 shows microscopic images of swelling (expansion) of the compacted PAC-CMC- 2.5% granule in contact with water;

[0026] Figure 6 is a graph showing relative efficiencies of PF AS leaching tests for the present invention.

[0027] DETAILED DESCRIPTION

[0028] The term "PAC" as used herein refers to powdered activated carbon, being carbon that has been milled, usually less than 100 pm in diameter, and preferably sieved through a US Standard Mesh Size 80 sieve, to provide a very small particle size.

[0029] The term “GAC” as used herein refers to granular activated carbon of a larger particle size that PAC, for example sieved between US Standard Mesh Size 20 and US Standard Mesh Size 40.

[0030] Different methods / technologies can be applied to prepare remediation swellable materials in granular or pellet forms. The granules or pellets can be prepared using rotary drum granulator, spraying granulator, disk granulation, roller compaction and extruder.

[0031] A broad range of swellable materials can be applied that expand with force and which have the potential to expand within the confines of the soil, and can include gelatinous materials, gums, and / or polysaccharides and swellable clays. Swellable materials such as a hydrogel material can comprise any of a variety of liquid or dry hydrogel materials which expand with force and which have the potential to expand within the confines of the soil, and can include, for example, gelatinous materials, gums, and / or polysaccharides. Hydrogel materials can comprise, for example, a material that provides one or more of the polymeric network described in Table 1 below: Table 1

[0032] Hydrogel materials

[0033] Experimental 1

[0034] Different swelling materials (SM) including, carboxymethyl cellulose (CMC), com starch, guar gum, gum arabic, polyacrylamide (PAM), tragacanth, polyacrylate and bentonite to prepare activated carbon granules, the swellable sorbent product, were investigated. Powdered activated carbon (PAC) was mixed with 5% w / w of SM and compacted using a companion die under a pressure of 11-13 KgForce (KgF). One formulation was also granulated using a granulation drum (PAC-CMC-5%). Other formulations were between 2.5- 40% weight percent. The PAC had a particle size of 69.4 pm and surface areas (measured by Brunauer-Emmett-Teller (BET))of 665.9 m2 / g.

[0035] The mixture of PAC-CMC-5% was placed in a rotating pan and a small amount of ultrapure deionized water was sprayed onto the fertilizer using a 50 pL min-1nebulizer while the drum was rotating at 12-15 rpm at an angle of 39.2°. Another method to granulate the PAC is to add the SM solution to PAC in the granulator. PAC+SM can be pelletized using an extruder. The crushing strength of the 10-15 granules was also measured using the ring penetrometer and reported in Table 2. The crushing strength shows the greatest compressive stress that a brittle solid (granules) can sustain without fracture. Granules with greater crushing strength create less dust during handling and transport.

[0036] The expansion and swelling of the granules are tested by soaking the granules in a Petri dish containing water and taking microscopic images or photos in different time frames.

[0037] Table 2. Summary of different formulation, the weight of granules their size and crushing strength. All pellets had a cylindrical shape 4mm (D) 4 mm (H). Tested granules had diameter range of 2.4 to 2.8. Experiment 2

[0038] In another experiment, the impact of a binder mixture on pellet crushing strength, swelling, and disintegration is assessed. Due to the superior crushing strength and swelling properties of carboxymethyl cellulose (CMC), it is combined with various SMs and swelling agents, including corn starch, polyacrylamide, tragacanth, and bentonite. CMC is mixed with different SMs or swelling agents at a ratio of 50:50, such as corn starch, polyacrylamide (PAM), tragacanth, and bentonite, and compacted using a companion die under a pressure of 11-13 KgForce (KgF).

[0039] Additionally, the influence of powdered activated carbon (PAC) particle size on pellet crushing strength and swelling is investigated. Two PAC (PAC 1&2) samples with particle sizes of 17.5 pm and 58 pm, and surface areas (measured by Brunauer-Emmett-Teller (BET)) of 996.5 and 769.6 m2 / g, respectively, are used. The PAC is mixed with 5% w / w of sodium montmorillonite (SM) or a 50:50 mixture of SM and compacted using a companion die under a pressure of 11-13 KgForce (KgF).

[0040] Furthermore, a blend of PAC and granular activated carbon (GAC) is examined by creating an activated carbon (AC) product containing 25% GAC and 75% PAC. The GAC has a particle size ranging from 150 pm to 1.7 mm and a BET surface area of 250 m2 / g, while the PAC has a particle size of 58 pm and a surface area of 769 m2 / g.

[0041] The expansion and swelling of the granules are tested by soaking the granules in a Petri dish containing water and taking microscopic images or photos in different time frames.

[0042] Experiment 3

[0043] Column leaching experiments (modified LEAF 1314) were performed for pellets and powdered materials using a PF AS-contaminated. The soil was mixed with 5% of either pelletised or powder formulation and dry packed in the column. The column experiments was performed for a week collecting 12 pore volumes of leachate. Results

[0044] The PAC-gum Arabia and PAC-Com starch were two formulations that were observed to swell quickly as soon as placed in the water, see Figure 1 a-d), but both formulations had lower crushing strength compared to other compacted formulations (Table 2). Other formulations with low crushing strength such as PAC -bentonite and polyacrylate were also disintegrated quicker than other formulations but complete disintegration occurred in 5 min.

[0045] The granulated or compacted PAC-CMC-5%, PAC -Polydactyl amide-5% and PAC- Tragacanth-5% started swelling when they were in contact with water but the swelling rate was less compared to PAC-gum Arabic / com starch / bentonite / polyacrylate. Both formulations were expanded over time and at 24h were changed to powder, as shown in Figures 2 and 3.

[0046] PAC-guar gum compacted granules swelled slightly when in contact with water but did not explode and kept their shape after 5 days of soaking in water.

[0047] PAC-CMC 2.5% compacted granule also swelled slightly and did not explode after 5 days of soaking in water. This showed that the percentage of SMs had a crucial effect on the disintegration of pellets.

[0048] PAC-5% CMC granules prepared using laboratory-based granulators had crushing strength less than pellets (Table 2) due to their smaller size. Increasing the rate of CMC to more than 5% , enhanced the crushing strength of the granules in addition to their disintegration rates.

[0049] The selection of a binder has a substantial impact on both the crushing strength and swelling behaviour of the pellets. Pellets with lower crushing strength generally disintegrate more rapidly compared to those with higher strength.

[0050] Carboxymethyl cellulose showed the greatest the crushing strength than all formulations, exhibiting relatively similar swelling properties after 24 hour.

[0051] When using a mixture of SM, the crushing strength of pellets — comprising a blend of carboxymethyl cellulose (CMC) and other SMs such as com starch, polyacrylamide, tragacanth, and bentonite — decreased compared to pellets containing only carboxymethyl cellulose (Table 2), but their disintegration rate increased substantially compared to pellets with only CMC. Pellets still maintain a high crushing strength, enabling them to withstand the pressure during handling. Powdered activated carbon size was also affected the crushing strength of the final pellet. Pellets made with PAC-1 with smaller particle size (17.5 pm) and 5% CMC had greater crushing strength (10.7±0.9 KgF) than those made with PAC-2 with 58 pm (7.4±0.7KgF). However, other properties of activated carbon may affect the crushing strength of the final product as PAC (69. 4 pm) used in experiment 1 had a similar particle size as PAC-2 (58 pm) but twice more crushing strength.

[0052] The crushing strength of a mixture of PAC and GAC decreased compared to only PAC pellets when pelletised with 5%CMC. PAC-5% CMC had a crushing strength of (10.7±0.9 KgF), while the crushing strength of the same PAC (75%) +GAC (25%)-5% CMC decreased to (5.7±0.7). However, a mixture of PAC+GAC-CMC 5% disintegrated faster.

[0053] A contaminated soil with PF AS (was treated with PAC and granular PAC and the leaching test was performed to evaluate PF AS leaching behaviour. PF AS leaching significantly decreased from treated soil with pelletised PAC compared to untreated soil (Control). However, the efficiency of powdered PAC was slightly better than pelletised formulation likely due to better coverage of powdered PAC, as shown in Figure 6.

[0054] Control -

[0055] Pelletised Powdered no PAC PAC treatment

[0056] Pg / L

[0057] PFHpA - perfluoroheptanoic acid 3.526 0.948 85 PFHpS - perfluoroheptanesulfonate 5.71 8.704 1931.87 PFHxA - perfluorohexanoic acid 12 6.048 239.705 PFHxS - perfluorohexanesulfonate 45.364 18.282 1482.03 PFNA - perfluorononanoic acid 3.491 4.356 96.27 PFNS - perfluorononanesulfonic acid 17.46 4.896 394.51 PFOA - perfluorooctanoic acid 8.046 9.882 400.56 PFOS - perfluorooctanesulfonic acid 2223.698 140.432 62312.94

[0058] The present invention shows the making and use of granules of a powdered activated carbon, mixture of PAC and GAC, carbon-based materials (including biochar, coal, fly ash, graphite and graphene-based materials), a mixture of carbon-based materials and mineral, and is applicable to powdered solid materials (in nano or micron size) with swellable properties. While granulation of the sorbents increases and improve their mode of application in the field, the swelling properties assist their dispersion in the soil and improve contaminants’ immobilisation in soil.

[0059] The present invention provides an effective method for handling, transporting and application of fine particulate sorbent material, such as activated carbon or absorbent clay minerals, while the physical and chemical properties are maintained.

[0060] From the examples, a form of the present invention is swellable sorbent product comprising: micron- or nano-sized particulate sorbent material with a swellable material, the swellable material being in an amount of about 1.0 - 20 % weight percent; wherein the granules are configured to swell upon introduction to a soil environment to disperse the sorbent within the soil environment. The sorbent material is selected from the group of powdered activated carbon, granular activated carbon, carbon based materials, and combinations of these.

[0061] The sorbent material is selected from the group of clay minerals, activated clay minerals, oxyhydroxide minerals, zeolites, and combinations thereof. In certain forms of the ivnetion, the sorbent material is selected from the group of biochar, coal, fly ash, graphite and graphene-based materials (including graphene, graphene oxide, graphene or graphene oxide composites) carbon nanotubes, and combinations thereof.

[0062] Additionally, the sorbent materials is selected from the group of nano- and micron size materials of carbon-based materials, clay minerals or combination thereof. The swellable material is a hydrogel in certain forms.

[0063] If a hydrogel is selected, it may be a hydrogel selected from the group of carboxymethyl cellulose (CMC), com starch, guar gum, gum Arabic, sodium alginate, calcium alginate, rice starch, Inulin, sodium polyacrylate, carrageenan gum, psyllium husk, xanthan gum, chitosan, barley husk, bean gum, sodium bentonite or other water absorbing clays, and combinations thereof.

[0064] Additionally, the swellable sorbent product includes one or more or more sources of nutrients selected from the group consisting of boron (B), zinc (Zn), manganese (Mn), molybdenum (Mo), nickel (Ni), copper (Cu), iron (Fe), chlorine (Cl), sulphur in its oxidized sulphate form (SO4), magnesium (Mg), calcium (Ca), and combinations thereof. In other forms of the invention, the swellable product includes one or more fertilizer minerals selected from the group of phosphate, nitrogen, potassium.

[0065] The swellable sorbent product can have the swellable material in an amount of about 1.0 - 10 % weight percent, or swellable material is in an amount of about 2 - 6 % weight percent.

[0066] The swellable sorbent product of the present invention can then be used for soil remediation to address contamination by PF AS, for example.

[0067] A method of capturing or immobilizing contaminants from soil comprising the steps of preparing a swellable sorbent product of any one of the above claims and applying it to an area of contaminated soil so that the swellable sorbent product can be distributed and dispersed with the soil.

[0068] The invention may be embodied in other specific forms without departing from the essential attributes thereof; therefore, and the illustrated embodiments should be considered in all respects as illustrative and not restrictive.

Claims

CLAIMS1. A swellable sorbent product comprising: micron- or nano-sized particulate sorbent material with a swellable material, the swellable material being in an amount of about 1.0 - 20 % weight percent; wherein the granules swell upon introduction to a soil environment to disperse the sorbent within the soil environment.

2. The swellable sorbent product of claim 1, wherein the sorbent material is selected from the group of powdered activated carbon, granular activated carbon, carbon based materials, and combinations thereof.

3. The swellable sorbent product of claim 1, wherein the sorbent material is selected from the group of clay minerals, activated clay minerals, oxyhydroxide minerals, zeolites, and combinations thereof.

4. The swellable sorbent product of claim 1 or 2, wherein the sorbent material is selected from the group of biochar, coal, fly ash, graphite and graphene-based materials (including graphene, graphene oxide, graphene or graphene oxide composites) carbon nanotubes, and combinations thereof.

5. The swellable sorbent product of claim 1 and 2, wherein the sorbent materials is selected from the group of nano- and micron size materials of carbon-based materials, clay minerals or combination thereof.

6. The swellable sorbent product of claim 1, wherein the sorbent materials are combinations of any materials in claims 3 and 4.

7. The swellable sorbent product of any one of the above claims, wherein the swellable material is a hydrogel.

8. The swellable sorbent product of any one of the above claims, wherein the hydrogel is selected from the group of carboxymethyl cellulose (CMC), com starch, guar gum, gum Arabic, sodium alginate, calcium alginate, rice starch, Inulin, sodiumpolyacrylate, carrageenan gum, psyllium husk, xanthan gum, chitosan, barley husk, bean gum, sodium bentonite or other water absorbing clays, and combinations thereof.

9. The swellable sorbent product of any one of the above claims, wherein the swellable sorbent product includes one or more or more sources of nutrients selected from the group consisting of boron (B), zinc (Zn), manganese (Mn), molybdenum (Mo), nickel (Ni), copper (Cu), iron (Fe), chlorine (Cl), sulphur in its oxidized sulphate form (SO4), magnesium (Mg), calcium (Ca), and combinations thereof.

10. The swellable sorbent product of any one of the above claims, wherein the swellable product includes one or more fertilizer minerals selected from the group of phosphate, nitrogen, potassium.

11. The swellable sorbent product of any one of the above claims, wherein the swellable material is in an amount of about 1.0 - 10 % weight percent.

12. The swellable sorbent product of any one of the above claims, wherein the swellable material is in an amount of about 2 - 6 % weight percent.

13. The swellable sorbent product of any one of the above claims when used for soil remediation.

14. A method of capturing or immobilizing contaminants from soil comprising the steps of preparing a swellable sorbent product of any one of the above claims and applying it to an area of contaminated soil so that the swellable sorbent product can be distributed and dispersed with the soil.

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