IRON-COMPRISING COMPOSITION FOR IN SITU PREPARATION OF A REMEDIATION SOLUTION

TECHNICAL FIELD

The present disclosure relates generally to the field of groundwater and soil remediation. More particularly, the disclosure relates to a stable iron-comprising suspension for preparation of a groundwater remediation solution.

BACKGROUND

In situ groundwater remediation is often performed by injection of treatment chemicals into contaminated aquifers (groundwater-saturated soil) . E.g. , soluble treatment chemicals, such as sodium permanganate, can be dissolved completely into water and easily pumped into a contaminated site, here for oxidative soil decontamination.

In the art, compositions and methods have been developed over the years for the purpose of eliminating toxic contaminants, such as chlorinated hydrocarbons from groundwater. Some methods involve zero valent metals (ZVM) , often zero valent iron (ZVI) , and methods of adding the compositions into the contaminated groundwater. Herein, the metals serve as a transportable, respective pumpable, solid electrochemical reductant suitable for e.g. , reacting with and converting trichloroethylene and similar compounds into ethene and other innocuous substances. The in-ground chemical reactions are advantageous in being rapid on a time scale relevant for contamination removal, and when the metals react with trichloroethylene and/or chlorinated ethenes the degradation pathway is known to bypass the formation of partially dechlorinated and toxic intermediaries such as vinyl chloride, leaving instead innocuous metal chlorides.

However, while such solid-phase treatment chemicals, e.g. , zero valent iron, (ZVI' s) , are useful for in-situ treatment, they are difficult to apply by in-situ injection in-ground due to their water-insoluble, particulate nature.

It is therefore useful to develop improvements to the injection transport of ZVI particles for in-situ remediation. Improving transport results in better contact with dispersed contaminants, lower application costs (fewer injection points) , and overall better results for on-site clean-up.

In the art, e.g. , from US 2016/0289106, compositions and methods are known for in-situ remediation of contaminated ground water and soil, comprising an oil phase, a water- miscible non-aqueous liquid phase, in combination with a solid metal particulate phase, mixed to form a 3-phase oilin-oil emulsion, which can be diluted with water on-site for in-ground use without sedimentation of the solid metal particles .

A problem of the prior art compositions is their formulation as emulsions, which require complex formulation for preventing metal sedimentation as the formed emulsions are diluted with water on-site, and while the original emulsions undergo phase transformation from oil-in-oil emulsions to oil-in-water diluted micellar compositions.

The present invention avoids this complex problem of emulsion formation by forming stable slurries of zero valent iron in a water-miscible organic carrier in the presence of some amounts of water and slurry-forming additives. Thereby the dilution problem reduces from a complex phase-inversion process to the formation of compositions which are dilutable with water at all concentrations without phase-inversions taking place simultaneously.

Further, the present invention is additional advantageous by providing improvements to the distribution (transport) of small iron particles through groundwater and soil upon injection for in-situ groundwater remediation.

SUMMARY OF THE INVENTION

In a first aspect and embodiment of the present invention there is herein detailed a concentrated slurry composition for remediation of groundwater, said concentrated slurry composition consisting based on total weight of the composition of: 30 wt% to 50 wt% iron powder, 1 wt% to 15 wt% of water, 0.1 wt% to 1.5 wt% of a surfactant, and at least 40 wt% of an organic water-miscible liquid carrier as balance, and, optionally, up to 10 wt% of an organic electron donor solution and/or a remediation chemical. The concentrated slurry composition is for dilution with water prior to on-site and in-ground use.

In an embodiment thereof, there is herein detailed a concentrated slurry composition for remediation of groundwater, wherein iron powder is present at a concentration from 35 wt% to 45 wt% in the concentrated slurry composition, preferably is present at 40 wt% in the concentrated slurry composition.

In an embodiment thereof, there is herein detailed a concentrated slurry composition for remediation of groundwater, wherein water is present from 8 to 12 wt% in the concentrated slurry composition.

In an embodiment thereof, there is herein detailed a concentrated slurry composition for remediation of groundwater, wherein the organic water-miscible liquid carrier is present from 45 wt% to 55 wt% in the concentrated slurry composition.

In an embodiment thereof, there is herein detailed a concentrated slurry composition for remediation of groundwater, wherein the organic water-miscible liquid carrier is selected from at least one of glycerol, propylene glycol, a liquid polyethylene glycol, or a PEG-n type polyethylene glycol, wherein n is 10 or smaller.

In an embodiment thereof, there is herein detailed a concentrated slurry composition for remediation of groundwater, wherein the organic water-miscible liquid carrier is one or both of glycerol or propylene glycol.

In an embodiment thereof, there is herein detailed a concentrated slurry composition for remediation of groundwater, wherein the surfactant is one or both of an anionic surfactant or a non-ionic surfactant.

In an embodiment thereof, there is herein detailed a concentrated slurry composition for remediation of groundwater, wherein an anionic surfactant is an alkali metal salt or a sulfonic acid surfactant of a long-chain (C12-C20) carboxyl chain.

In an embodiment thereof, there is herein detailed a concentrated slurry composition for remediation of groundwater, wherein the non-ionic surfactant is selected from a sorbitan ethoxylate or a Tween-type surfactant.

In an embodiment thereof, there is herein detailed a concentrated slurry composition for remediation of groundwater, wherein a sorbitan ethoxylate surfactant is either Polysorbate 20 or Polysorbate 80, and a Tween-type surfactant is a Tween ethoxylated derivative of sorbitan esters, preferably Tween-20.

In an embodiment thereof, there is herein detailed a concentrated slurry composition for remediation of groundwater, wherein the concentrated slurry composition has an apparent viscosity from 2000 to 5000 cp as measured at 6 RPM with a Brookfield DV1 viscometer (spindle #2) at a temperature of 20°C.

In an embodiment thereof, there is herein detailed a concentrated slurry composition for remediation of groundwater, wherein the concentrated slurry composition has an apparent viscosity from 2500 to 4500 cp, preferably from 3000 to 4000 cp, and more preferably about 3500 cp, as measured at 6 RPM with a Brookfield DV1 viscometer (spindle #2) at a temperature of 20°C.

In an embodiment thereof, there is herein detailed a concentrated slurry composition for remediation of groundwater, wherein the specific gravity is from 1.75 to 1.85 g/mL as determined by using a 83.2 ml BYK-Gardner PV- 9654 specific gravity cup with 0.5 % tolerance.

In an embodiment thereof, there is herein detailed a concentrated slurry composition for remediation of groundwater, wherein the specific gravity is from 1.76 to 1.84 g/mL, from 1.77 to 1.83 g/mL, from 1.78 to 1.82 g/mL, from 1.79 to 1.81 g/mL or more preferably is 1.80 g/mL as determined by using a 83.2 mL BYK-Gardner PV-9654 specific gravity cup with 0.5 % tolerance.

In an embodiment thereof, there is herein detailed a concentrated slurry composition for remediation of groundwater, wherein the iron particles in the slurry have average diameter between 1 and 25 microns as measured by as measured by a laser light scattering method following ISO 22312:2017 and ASTM C136.

In an embodiment thereof, there is herein detailed a concentrated slurry composition for remediation of groundwater, wherein the iron particles in the slurry have average diameter between 1 and 10 microns as measured by as measured by a laser light scattering method following ISO 22312:2017 and ASTM 0136.

In a second aspect there is herein detailed a method for the preparation of a ready-to use solution for injecting into groundwater for groundwater remediation, the method comprising: providing a concentrated slurry composition in accordance with any of embodiments of the aforementioned first aspect, diluting with water to form a diluted solution, wherein the final concentration of iron in the diluted solution is from 0.1 wt% to 5 wt%, such as from 1 wt% to 2 wt% based on total weight of the final diluted solution. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1. Maximum injection pressure of each column (Column

1, Column 2 and Column 3) as disclosed below.

Figure 2. Iron distribution by magnetic susceptibility measurement. Comparison of the control (black bars) with the invention (dotted bars) .

It is to be understood, that the embodiments shown in the figures are for illustration of the present invention and cannot be construed as being limiting on the present invention. Unless otherwise indicated, the drawings are intended to be read (e.g. , cross-hatching, arrangement of parts, proportion, degree, etc. ) together with the specification, and are to be considered a portion of the entire written description of this disclosure.

DETAILED DESCRIPTION

It is disclosed herein a concentrated slurry composition for remediation of groundwater, said concentrated slurry composition consisting based on total weight of the composition of 30 to 50 wt% iron powder, 1 to 15 wt% of water, 0.1 to 1.5 wt% of a surfactant, and at least 40 wt% of an organic water-miscible liquid carrier as balance. Optionally, up to 10 wt% of an organic electron donor solution and/or a remediation chemical may be further added to the concentrated slurry composition.

The concentrated slurry composition for remediation of groundwater is suitable for its purpose on-site and in-ground after dilution with water, and accordingly, there is also herein detailed a concentrated slurry composition for remediation of groundwater after dilution with water, said concentrated slurry composition consisting based on total weight of the composition of: 30 wt% to 50 wt% iron powder, 1 wt% to 15 wt% of water, 0.1 wt% to 1.5 wt% of a surfactant, and at least 40 wt% of an organic water-miscible liquid carrier as balance, and, optionally, up to 10 wt% of an organic electron donor solution and/or a remediation chemical .

The concentrated slurry composition according to the invention is a slurry of a zero valent iron in a liquid water-organic carrier solution. The composition can be easily transported and diluted on-site to the desired iron concentration without phase-inversion and particle sedimentation. The composition is for remediation of groundwater and is useful in destroying toxic contaminants in groundwater and soil by injection into aquifers.

The present slurries of the invention have been found to be stable for transport as concentrated slurries over the stated ranges of concentration and have been found to be dilutable with water to obtain a desired end-concentration of slurrified powder iron in water without powder sedimentation at the requisite time scales for in-ground use.

The powder iron (a zero valent iron) is present in the composition in the amount of from 30 wt% to 50 wt%, from 35 wt% to 45 wt%, more preferably from 38 wt% to 43 wt%. In a preferable embodiment the amount of powder zero valent iron is about 40 wt%.

A minor amount of water is added to the composition. The water added is in an amount from 1 to 15 wt% of water, preferably from 3 to 14 wt%, from 5 to 13 wt%, and more preferably from 8 to 12 wt% based on the total weight of the composition. If the water amount exceeds 20 wt% it has been found that an instable slurry is formed wherein the powder iron sediments out.

In accordance with the present disclosure the concentrated slurry composition further contains 0.1 to 1.5 % of a surfactant. In preferred embodiments, the surfactant is selected from non-ionic and anionic surfactants.

In accordance with the disclosure the concentrated slurry composition further contains an organic water-miscible liquid carrier. The organic water-miscible liquid carrier may be selected from glycerol, propylene glycol, and liquid polyethylene glycols, such as PEG-n type polyethylene glycols wherein n is 10 or smaller. These water-miscible liquids are considered generally safe to use, also for water-remediation and are therefore recommended in the context of the present invention .

The organic water-miscible liquid carrier is added such that it comprises at least 40 wt% of the total weight of the slurry composition. In the compositions of the inventions, it does not exceed about 70 wt% of the concentrated slurry composition. However, it is preferable, that the organic water-miscible liquid carrier is from 45 wt% to 55 wt% of the concentrated slurry composition by weight and that the further components are adjusted to allow for this concentration interval. Thereby an optimal effect of stability during later on-site dilution has been observed by the present inventor.

Optionally, an organic electron donor solution and/or a remediation chemical, can be added to the compositions of the invention, such that the organic electron donor solution and/or the remediation chemical does not exceed 10 wt% of the concentrated slurry composition.

An organic electron donor in the sense of the present invention is an organic compound designed to biodegrade naturally and stimulate anaerobic biodegradation of halogenated contaminants. Examples of suitable electron donors include ethyl lactate and vegetable oils such as soybean oil. Irrespective of the choice of the electron donor, the amount of the chemical has to be adapted to the amounts of the other components, such that the electron donor stays solvated in the organic water-miscible liquid carrier, rather than forming a 3 ^rd phase in the concentrated slurry compositions of the present invention. Thereby the abovementioned problems of phase-inversion are avoided by retaining a powder in liquid slurry instead of a complex multiphase emulsion.

In contrast to existing prior art iron powder slurries in water, or simple iron powder concentrates in glycerol, the concentrated slurry composition in accordance with the invention is easily transported and has superior properties when diluted to a ready-to-use solution. A benefit of the present invention is that when mixed and diluted with water at the point of use, the injected iron particulates transport further through groundwater and soil than simple iron slurries. Further, improved transport of ZVI particles upon injection results in easier application, better contact with contaminants, and reduced time and cost for the injection process .

In accordance with the present invention, the compositions of the present invention comprise a surfactant in an amount from 0.1 wt% to 1.5 wt% based on the total weight of the composition. The surfactant can be one or more of an anionic and/or a non-ionic surfactant. The benefits of such surfactants are to improve dispersion of the solid iron particles, preventing them from agglomerating and minimizing their interactions with soil particles in use.

Preferably, in the context of the present invention, an anionic surfactant is an alkali metal salt of a long-chain carboxyl (C12-C20) or a sulfonic acid surfactant of the same (C12-C20) length.

Preferably, the non-ionic surfactant is a sorbitan ethoxylate, such as Polysorbate 20 or Polysorbate 80, but also various Tween surfactants, such as Tween ethoxylated derivative of sorbitan esters of smaller size, preferably Tween-20 have proven useful.

In accordance with an embodiment of the present invention, the concentrated slurry composition preferably has an apparent viscosity from 2000 to 5000 cp as measured at 6 RPM with a Brookfield DV1 viscometer (spindle #2) at a temperature of 20 °C. Preferably, the apparent viscosity is from 2500 cp to 4500 cp, from 3000 cp to 4000 cp, and more preferably around 3500 cp .

The method employed by the present inventor for measuring apparent viscosity was filling a pint container 500 ml of a sample of the concentrated slurry composition according to the invention. The spindle was then lowered into the sample to the immersion groove of the spindle in accordance with the instructions of the manufacturer. The viscometer was turned on and the value was recorded after the dial reading settled. The reading was then multiplied by the factor for #2 spindle at 6 RPM, which is 50 to yield the determined value for the apparent viscosity. When the instructions of the manufacturer of the equipment is followed carefully, the determined apparent viscosity using the spindle method is in good correlation with other methods of determining viscosity.

In accordance with a preferred embodiment of the invention, the concentrated slurry composition has a specific gravity of from 1.75 g/mL to 1.85 g/mL, preferably 1.8 g/mL, as determined by using a 83.2 ml BYK-Gardner PV-9654 specific gravity cup with 0.5% tolerance at 20°C and standard pressure. In an embodiment thereof, there is herein detailed a concentrated slurry composition for remediation of groundwater, wherein the specific gravity is from 1.76 to 1.84 g/mL, from 1.77 to 1.83 g/mL, from 1.78 to 1.82 g/mL, from 1.79 to 1.81 g/mL or more preferably is 1.80 g/mL as determined by using a 83.2 mL BYK-Gardner PV-9654 specific gravity cup with 0.5% tolerance at 20°C and standard pressure .

The specific gravity is measured as follows. The cup was placed on the scale and the scale was fared. Then the sample was filled to the brim of the cup. The lid was placed on the cup and the excess material that was pressed out of the cup was wiped away. The full weight of the cup was recorded and the specific gravity determined by dividing the full weight of the sample by the total volume of the gravity cup.

In order for the iron powder contained in the present compositions to function in accordance with the intended use, it is preferable that less than 10 wt% based on the iron particles shall have a particle size above 50 microns. When the powder size becomes too large, sedimentation and conglomeration by size exclusion sedimentation and conglomeration during pumping was observed to become apparent in the concentrated slurry compositions of the invention.

Preferably, the average diameter of the iron particles of the present powder are between 1 micron and 25 microns, from between 1 micron and 20 microns, between 2 microns and 15 microns, between 3 microns and 14 microns, more preferably the iron particles in the dispersion have average diameter between 1 and 10 microns as measured by a laser light scattering method following ISO 22312:2017 and ASTM C136. Measurements presented herein were performed using dynamic light scattering using a Microtrac S3500 equipment. it is preferable that less than 10 wt% based on the iron powder shall have a powder size below 0.5 micron. In general, when the fraction of iron powder below 1 micron increases, in-ground reactivity has been observed to decrease and hence it is preferably to keep the fraction of iron particles below 1 micron at a minimum.

In accordance with another aspect, there is disclosed a method for the preparation of a ready-to use solution for injecting into groundwater for groundwater remediation, said method comprising: providing a concentrated slurry composition as described herein above, diluting with water to form a diluted solution wherein the final concentration of iron in the diluted solution is from 0.1 wt% to 5 wt%, such as from 1 wt% to 2 wt% based on total weight of the final diluted solution.

It shall be understood that all aspects relating to the composition are applicable in the method for preparation of a ready-to-use solution for injecting into the groundwater EXAMPLES

SAMPLE COLUMNS

(1) Column 1: iron powder in water, - Comparative Sample 1

(2) Column 2: Invention, - Sample 2 According to the invention

(3) Column 3: iron powder in glycerol and water, Comparative Sample 3

Example 1.

Three plastic columns (4' long by 2" inner diameter) were loaded with water-saturated sand, taking precaution to avoid entrainment of air. Using a peristaltic pump, water was then flowed through each column at a flowrate of 260 mL/min, maintaining approximately 5 psi of pressure. For each test condition, the feed was then switched from water to the test sample while keeping the pumping rate constant. The test sample for Column 1 (Control) was a simple iron slurry consisting of 0.87% w/w iron powder in water. In Column 2, the present invention was tested at the same iron loading. In Column 3, a mixture of glycerol (1.3 wt%) , water (97.83 wt%) , and iron powder (0.87 wt%) was tested as a control for the presence of glycerol. The iron powder in all cases was Hbganas CleanER™-5 from Hbganas Environment Solutions, LLC. 3000 Weston Parkway Cary, NC 27513, USA.

Pumping was continued for each sample for 10 minutes. While the injection pressure in Column 2 was consistent at approximately 5 psi, the pressure in the control column rose to near 35 psi, shown in Figure 1, indicating some clogging by the simple iron slurry. Each feed was then switched back to water, and pumping continued for another 10 minutes. The columns were then sealed for further analysis. The collected eluents from the control Columns 1 and 3 were clear with no apparent presence of iron. Eluent from Column 2 was a darkcolored suspension, indicating the elution of iron particles, and showing the improved penetration of the solution according to the present invention, wherein the comparative compositions are stuck in the upper regions of the columns and do not reach the bottom.

Magnetic susceptibility measurements were made along the length of each column to determine the relative concentration of iron metal particles in the saturated sand. The magnetic susceptibility was measured using a Barrington MS2/MSC magnetic susceptibility meter. The measurements were taken at 1-inch intervals along the entire length of the column. The data, summarized in Figure 2, indicate that the control sample deposited more iron in the first two feet of the column, while the invention transported significantly more iron particles to the 2 - 4-foot section of the column.

Further analysis of the magnetic susceptibility data was performed to evaluate the relative amount of iron distributed beyond two feet for each test sample. The results, normalized to the amount of iron distributed by the control sample, are shown in Table 1.

Table 1. Relative amount of iron distributed further than 2 feet, normalized to control.

CLOSING COMMENTS

Although the present invention has been described in detail for purpose of illustration, it is understood that such detail is solely for that purpose, and variations can be made therein by those skilled in the art in practicing the claimed subject matter, from a study of the drawings, the disclosure, and the appended claims.

The term "comprising" as used in the claims does not exclude other elements or steps. The indefinite article "a" or "an" as used in the claims does not exclude a plurality. A reference sign used in a claim shall not be construed as limiting the scope.