Patent Application
20210039993
The invention is directed to muscovite-enriched compositions with high affinity for heavy metal atoms. The muscovite-enriched compositions are useful for the sequestration of heavy metals.
Aqueous solutions of radioactive waste have been found percolating through soils adjacent to sites where radioactive materials have been produced, for instance, in nuclear reactors. A large constituent of this aqueous radioactive waste is radiocesium, in which 137Cs is the predominant isotope. Concern for the fate of 137Cs stems fourfold from its high fission yield and moderately long half-life (30.17 years) and the high mobility and high biological availability of Cs in certain regolith environments.
Radiocesium has been introduced into the environment as a direct result of nuclear accidents, nuclear weapons testing, and other nuclear development activities. For example, at the Savannah River Site (Aiken, S.C., USA), approximately 1900 curies of 137Cs were released into the environment, as reported in 1991. Another locality of high radiocesium contamination is the area around the Fukushima Dai-ichi reactors (Fukushima Prefecture, Japan). Radiocesium and radioactive iodine were accidentally released from the Fukushima Dai-ichi reactors in 2011 in one of the largest accidental releases of radionuclides. Short-lived radioactive iodine decayed away within a matter of months, and 134Cs has mostly decayed away; 137Cs is by far the most abundant remaining radionuclide found in soils of Fukushima Prefecture and surrounding areas of Japan.
There remains a need for methods of eliminating heaving metals from contaminated area, including soils and drinking waters. There remains a need for eliminating lead contamination from drinking water sources. There remains a need for methods of eliminating 137Cs from contaminated areas. There remains a need for methods of safely sequestering 137Cs over the lifetime of its radioactivity. The remains a need for limiting the spread of inadvertently released 137Cs. There remains a need for building materials capable of sequestering radiocesium unintentionally released from a reactor source.
Disclosed herein are compositions and methods of sequestering heavy metals, including 137Cs. In some instances, the compositions can be contacted with a contaminated area in order to remove the heavy metals, including 137Cs. For instance, the composition can be admixed with contaminated soils and bodies of water. Contaminated waters can be passed through a sorption bed containing the composition enriched in potassium-depleted muscovite. Also disclosed here are concretes and other building materials that include a potassium-depleted muscovite. The building materials may be advantageously deployed in the construction of structures intended to house nuclear reactors and other sources of radiocesium and radioactive heavy metals.
The details of one or more embodiments are set forth in the descriptions below. Other features, objects, and advantages will be apparent from the description and from the claims.
Before the present methods and systems are disclosed and described, it is to be understood that the methods and systems are not limited to specific synthetic methods, specific components, or to particular compositions. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting.
As used in the specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from “about” one particular value, and/or to “about” another particular value. When such a range is expressed, another embodiment includes¬ from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another embodiment. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint.
“Optional” or “optionally” means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where said event or circumstance occurs and instances where it does not.
Throughout the description and claims of this specification, the word “comprise” and variations of the word, such as “comprising” and “comprises,” means “including but not limited to,” and is not intended to exclude, for example, other additives, components, integers, or steps. “Exemplary” means “an example of” and is not intended to convey an indication of a preferred or ideal embodiment. “Such as” is not used in a restrictive sense, but for explanatory purposes.
Disclosed are components that can be used to perform the disclosed methods and systems. These and other components are disclosed herein, and it is understood that when combinations, subsets, interactions, groups, etc. of these components are disclosed that while specific reference of each various individual and collective combinations and permutations of these may not be explicitly disclosed, each is specifically contemplated and described herein, for all methods and systems. This applies to all aspects of this application including, but not limited to, steps in disclosed methods. Thus, if there are a variety of additional steps that can be performed it is understood that each of these additional steps can be performed with any specific embodiment or combination of embodiments of the disclosed methods.
Disclosed herein are compositions and methods for sequestering heavy metals, for instance Cs, Rb, Ba, Sr, and Pb. In some cases, the Cs is 137Cs. In some embodiments, a composition including a muscovite-enriched mineral composition is contacted with an area contaminated with one or more heavy metals, including 137 Cs. In some embodiments, a muscovite-enriched mineral composition is included in a building material, for instance a concrete mix. The muscovite can be potassium-depleted muscovite, for instance potassium-depleted muscovite can contain no more than 10%, no more than 9%, no more than 8%, no more than 7%, no more than 6%, no more than 5%, or no more than 4% by mass of potassium relative to the total mass of the muscovite. Potassium content can be determined and reported as mass fraction K2O using conventional elemental analysis.
Although the mineral composition may contain other phyllosilicates and other minerals, it is preferred the mineral composition contains muscovite in an amount that is at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% by mass relative to the total mass of the mineral composition. Muscovite content may be assessed using X-ray diffraction and PANalytical's HighScore Semi-Quantitative Analysis. Other components that may be present in the composition include kaolin minerals and quartz.
The mineral compositions useful for the sequestration of radiocesium may be characterized by the particle sizes of the minerals. For instance, the mineral composition can have an overall particle size distribution in which Dio (the value of particle size exceeded by 90% of the composition, by mass) will be at least 5 μm, at least 10 μm, at least 15 μm, at least 20 μm, at least 25 μm, at least 30 μm, at least 40 μm, at least 50 μm, at least 75 μm, or at least 100 μm. In some instances, the mineral composition can have a particle size distribution in which D10 (the value of particle size exceeded by 90% of the muscovite, by mass) will be at least 5 μm, at least 10 μm, at least 15 μm, at least 20 μm, at least 25 μm, at least 30 μm, at least 40 μm, at least 50 μm, at least 75 μm, or at least 100 μm.
In some embodiments, the mineral composition can have an overall particle size distribution in which D90 (the value of particle size exceeded by 10% of the composition, by mass) will be no more than 2,000 μm, no more than 1,500 μm, no more than 1,250 μm, no more than 1,000 μm, no more than 900 μm, no more than 800 μm, no more than 700 μm, no more than 600 μm, or no more than 500 μm. In some embodiments, the muscovite can have a particle size distribution in which D90 (the value of particle size exceeded by 10% of the muscovite, by mass) will be no more than 2,000 μm, no more than 1,500 μm, no more than 1,250 μm, no more than 1,000 μm, no more than 900 μm, no more than 800 μm, no more than 700 μm, no more than 600 μm, or no more than 500 μm.
The compositions disclosed herein have high affinity for cesium atoms (as monovalent cations). The affinity may be assessed by Kd ([Cs]solid/[Cs]aqueous), as measured at a total electrolyte content of 1 mmol/L, that is greater than 1,000 L/kg, greater than 1,200 L/kg, greater than 1,400 L/kg, greater than 1,600 L/kg, greater than 1,800 L/kg, or greater than 2,000 L/kg. High affinities for other heavy metals, including Pb, Ba, Sr, and Rb, can also be observed.
The compositions disclosed herein may be used to sequester and remove cesium from areas contaminated with high concentrations of 137 Cs. For instance, the compositions can remove cesium from a contaminated area that can include 137 Cs in an amount of at least 500 kBq/m2, at least 750 kBq/m2, at least 1000 kBq/m2, at least 1,250 kBq/m2, at least 1,500 kBq/m2, at least 2,000 kBq/m2, at least 2,500 kBq/m2, or at least 3,000 kBq/m2.
Heavy metals, including radiocesium can be sequestered within or removed from contaminated soils and water bodies. In some embodiments, the compositions can simply be blended into the contaminated soil. Over time, the heavy metals will aggregate in the potassium-depleted muscovite, thereby effectively immobilizing it. In other embodiments, the compositions can be contacted with contaminated soils and waters for a time sufficient to sequester the heavy metal, for instance radiocesium, after which time the compositions can be removed and safely stored. The compositions can be placed within a permeable container and then buried in contaminated soils or submerged in contaminated waters. In other embodiments, a fixed bed device can be employed, in which contaminated water is passed through a tube containing the potassium-depleted muscovite. The water can be pumped or be fed through the tube under the force of gravity.
Also disclosed herein are building materials including a muscovite-enriched mineral composition, as described above. Exemplary building compositions include concretes including a muscovite-enriched mineral composition. For instance, the muscovite-enriched mineral composition is present in a dry concrete mix in an amount from 0.1-20% by weight, from 0.5-20% by weight, from 1-20% by weight, from 2.5-20% by weight, from 5-20% by weight, from 7.5-20% by weight, from 10-20% by weight, from 15-20% by weight, from 10-15% by weight, from 5-10% by weight, from 0.5-5% by weight, from 0.5-2.5% by weight, or from 1-5% by weight. In some instances, the muscovite-enriched mineral composition is present in an amount no more than 20% by weight, no more than 15% by weight, no more than 12.5% by weight, no more than 10% by weight, no more than 7.5% by weight, no more than 5% by weight, no more than 2.5% by weight, or no more than 1% by weight.
In some aspects of the invention, the muscovite-enriched mineral composition is combined with a cement, sand, and aggregate to give a concrete mix. A preferred cement is Portland cement. Exemplary weight ratio combinations are presented in the following table:
The following examples are for the purpose of illustration of the invention only and are not intended to limit the scope of the present invention in any manner whatsoever.
A sample of a potassium-depleted muscovite-enriched mineral composition was obtained from the Georgia kaolin deposits, separated from mined kaolin by Southeast Performance Minerals. The bulk sample had the following particle size distribution:
A small fraction (8% by mass) of the bulk sample consists of particles that have diameters between 0.25 mm and 0.84 mm. Most (79% by mass) of the bulk sample consists of particles between 0.044 mm and 0.25 mm in diameter, and 13% (by mass) of the bulk sample consists of particles smaller than 0.044 mm in diameter.
The X-ray diffraction pattern for a randomly oriented powdered portion of the bulk sample is shown in
Each value of interlayer spacing (d-value) in
Diffraction patterns of parts of a very finely powdered portion of the bulk sample, prepared as oriented mounts on glass petrographic slides, are shown in
With respect to experimentally determined d-values, the HighScore software indicated that the mineral dickite is a better match than kaolinite; however, based on the sample's original locality, the sample deductively contains kaolinite. The most intense diffraction peaks corresponding exclusively to nacrite (2.41 Å) and dickite (2.32 Å) were not observed. Kaolinite is the prevalent kaolin group mineral in the sample. Since the d-values remained unchanged in the ethylene glycol-solvated mount, the sample is unlikely to contain a significant fraction of smectite. This solvation demonstrated also that kaolinite-smectite interstratified minerals were not present in this sample. An evident asymmetric peak on the high d-value side of the 001 peak for kaolinite was not observed. Kaolinite is not interstratified with other phyllosilicate minerals (muscovite) in the sample.
The mass fractions of major element oxides in the muscovite-enriched mineral composition (as received and split) are shown in the central column of Table 5 (below) as percent by mass of corresponding oxides. The sum of the major element oxides including loss on ignition (LOI) is 99.22%. The chemical composition of the muscovite alone was calculated by correction for the 21% of kaolinite and the 3% of quartz in the sample, as determined by X-ray diffraction. The K2O content of the muscovite (9.98%) is less than that of pure muscovite (11.81 wt. %), which demonstrates that the muscovite is potassium-depleted.
The sorption of radioactive cesium (137Cs) from aqueous solution onto the muscovite-enriched mineral composition was observed in 20 test suspensions (each a 0.1 g test portion of the sample in 10 mL of liquid) containing variable amounts of added stable cesium (133Cs). The activity of radioactive cesium remaining in the liquid phase after 18 hours, 60 days, and 130 days of tumbling was determined by liquid scintillation counting (LSC). The liquid phase 137Cs activity concentration was obtained directly from LSC measurement. Solid phase 137Cs activity was calculated from the difference between the quantity of added 137Cs and that of 137Cs remaining in the aqueous phase.
Tables 6a, 6b, and 6c (below) present the aqueous and solid phase concentrations of Cs as calculated from the LSC data for the three sampling events (18 hours, 60 days, and 130 days, respectively). Tables 6a, 6b, and 6c also include the Ka values for each batch sorption test suspension at 18 hours, 60 days, and 130 days and the concentration of total Cs in each batch sorption test suspension. No data are shown for two additional test suspensions, which were blanks to which no 137Cs and no 133Cs were added.
Following 130 days of batch sorption experimentation, desorption test suspensions were created by centrifuging each suspension, decanting the supernatant liquid, and replacing the supernatant liquid with a solution of NaCl (10 mM NaCl for 1a-10a; 1 mM NaCl for 1b-10b) to introduce Na+ as a counterion. These desorption test suspensions were tumbled for 60 days, then centrifuged and sampled to yield the following data.
Tables 7a and 7b present data collected after 60 days of desorption for test suspensions containing 10 mM NaCl and 1 mM NaCl, respectively. The activity concentrations of 137Cs in the aqueous phase were measured directly by LSC. The activity of 137Cs in the solid phase was calculated as the difference between the activity of 137Cs on the solid at the start of the desorption period and the measured activity of aqueous 137Cs. The fraction of 137Cs desorbed from the mica, a measure of the reversibility of the sorption reaction, was found by subtracting from unity the ratio of 137Cs activity on the solid at the sampling time (t) to the 137Cs activity on the solid at the start of the desorption process.
The compositions and methods of the appended claims are not limited in scope by the specific compositions and methods described herein, which are intended as illustrations of a few aspects of the claims and any compositions and methods that are functionally equivalent are intended to fall within the scope of the claims. Various modifications of the compositions and methods in addition to those shown and described herein are intended to fall within the scope of the appended claims. Further, while only certain representative compositions and method steps disclosed herein are specifically described, other combinations of the compositions and method steps also are intended to fall within the scope of the appended claims, even if not specifically recited. Thus, a combination of steps, elements, components, or constituents may be explicitly mentioned herein or less, however, other combinations of steps, elements, components, and constituents are included, even though not explicitly stated. The term “comprising” and variations thereof as used herein is used synonymously with the term “including” and variations thereof and are open, non-limiting terms. Although the terms “comprising” and “including” have been used herein to describe various embodiments, the terms “consisting essentially of” and “consisting of” can be used in place of “comprising” and “including” to provide for more specific embodiments of the invention and are also disclosed. Other than in the examples, or where otherwise noted, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood at the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, to be construed in light of the number of significant digits and ordinary rounding approaches.
This application claims the benefit of U.S. Provisional Application 62/620,710, filed Jan. 23, 2018, the contents of which are hereby incorporated in its entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2019/014742 | 1/23/2019 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62620710 | Jan 2018 | US |
