WO2017015318A1

WO2017015318A1 - Mesoporous titanosilicates and uses thereof

Info

Publication number: WO2017015318A1
Application number: PCT/US2016/043046
Authority: WO
Inventors: Xiaolin Yang; Alfonse Maglio; Doan Lieu
Original assignee: Basf Corporation
Priority date: 2015-07-20
Filing date: 2016-07-20
Publication date: 2017-01-26

Abstract

Disclosed in certain embodiments are amorphous titanosilicates for the removal of heavy metals and radionuclides from aqueous solutions.

Description

MESOPOROUS TITANOSILICATES AND USES THEREOF

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority of U.S. Provisional Patent Application Serial No. 62/194,672, filed July 20, 2015, which is hereby incorporated by reference herein in its entirety.

BACKGROUND

[0002] Strontium-90 (⁹⁰Sr) is a radioactive isotope of strontium produced by nuclear fission of

235

U. The element is detectable in 99% of the drinking water in the US, and it is present at levels of concern in 7% of public water systems. At elevated levels, strontium can replace calcium in bones, adversely affecting skeletal health. Thus, developing effective strontium removal sorbents has immediate need in removing Strontium-90 from radioactive waste water generated by nuclear facilities and power plants, and is of long-term importance for reducing strontium in drinking water.

[0003] It is desirable for an effective strontium sorbent to have high adsorbent capacity and selectivity for Sr⁺² amidst the presence of other cations, such as Na⁺¹ and Ca⁺², in nuclear wastewater and drinking water that are typically present in concentrations several orders of magnitude greater than the concentration of Sr⁺². Inorganic ion exchanging sorbents are advantageous over organic exchangers (such as organic resins) for such purposes, since the former are more selective, cost effective, resistant to severe chemical, thermal, and radiation degradation in a nuclear plant environment, and are suitable for vitrification of the radioactive materials for long- term storage.

[0004] Crystalline silicotitanates (CSTs) are commercially available sorbents that have been considered highly effective for strontium removal from high salinity radioactive wastewaters.

Despite their high strontium removal efficiencies, CSTs are difficult to produce under high temperature and pressure with a long crystallization time, and require very expensive

organometallic precursors, such as alkoxides of silicon, titanium, and niobium. Moreover, the toxic raw materials used in CST manufacture are hazardous for sorbent production and waste effluent treatment. Thus, there exists a need in the art to find cost-effective and safer alternatives to current sorbents used for radionuclide removal. OBJECTS AND SUMMARY OF THE DISCLOSURE

[0005] It is an object of certain embodiments to provide systems and methods for removing heaving metals and/or radionuclides from aqueous solutions, such as seawater and ground water.

[0006] It is an object of certain embodiments to provide a sorbent material with high selectivity for strontium cations and/or cesium cations.

[0007] It is an object of certain embodiments to provide a method of producing sorbents that are free of toxic materials and are less expensive to produce than CSTs.

[0008] The above objects and others may be met by the present disclosure, in which certain embodiments are directed to a titanosilicate for removing strontium, cesium, and/or other heavy cations from aqueous solutions.

[0009] In certain embodiments, the titanosilicate is an amorphous titanosilicate.

[0010] In certain embodiments, the titanosilicate has a first distribution of pores having a first average pore diameter from about 20 A to about 50 A, and a second distribution of pores having a second average pore diameter from about 50 A to about 400 A.

[0011] In certain embodiments, the second plurality of pores accounts for at least about 70% of a total pore volume of the titanosilicate.

[0012] In certain embodiments, the titanosilicate has a first atomic ratio of Ti to Si from 0.5 to 2.0, and a second atomic ratio of Na to Si from 0.2 to 1.5.

[0013] Certain embodiments are also directed to a method of producing an amorphous titanosilicate.

[0014] Certain embodiments are also directed to a method of removing radionuclides from an aqueous solution. The method includes contacting the aqueous solution with an amorphous titanosilicate. In some embodiments, the radionuclides include strontium cations, with the strontium cations being present at an initial concentration in the aqueous solution prior to contacting the aqueous solution with the amorphous titanosilicate, and the strontium cations being present at a final concentration in the aqueous solution after contacting the aqueous solution with the amorphous titanosilicate. In one embodiment, strontium cation removal efficiency is greater than 80%, greater than 85%, or greater than 90%.

[0015] Certain embodiments are also directed to a titanosilicate having a first distribution of pores having a first average pore diameter from about 20 A to about 50 A, a second distribution of pores having a second average pore diameter from about 50 A to about 400 A, and strontium cations or cesium cations adsorbed therein. [0016] The term "cations adsorbed therein", as used herein (e.g., with respect to strontium or cesium cations), is intended to encompass various mechanisms of ion adsorption including, but not limited to, ion exchange, chemical bonding, and physical adsorption.

[0017] The term "bimodal", as used herein, refers to a statistical distribution having two distinct maxima.

[0018] The term "bimodal pore distribution", as used herein, refers to a material having two distinct distributions of nanoscale pores (e.g., as observable via N2 adsorption), with each distribution (if modeled as Gaussian distributions) being centered at particular pore radius or diameter, which may be referred to as an "average pore radius" or "average pore diameter", respectively for the distribution. Although a sorbent may include additional distributions of pores (e.g., macropores), the term "bimodal pore distribution" is intended to refer to only those pore distributions having average pore radii that are less than 5000 A.

[0019] The term "aqueous solution", as used herein, refers to any water containing volume, including simulated seawater, actual seawater, ground water, tap water, water streams, etc.

[0020] The term "sorbent", as used herein, refers to a material that can adhere gas molecules, cations, or other species within its structure. Specific materials include, but are not limited to, titanosilicates, metal organic framework, activated alumina, silica gel, activated carbon, molecular sieve carbon, zeolites, mixed metal oxides, polymers, resins and clays. Certain adsorbent materials may preferentially or selectively adhere particular species.

[0021] The term "particles", as used herein, refers to a collection of discrete portions of a material each having a largest dimension ranging from 0.1 μιη to 50 mm. The morphology of particles may be crystalline, semi-crystalline, or amorphous. The term "particle" may also encompass powders down to 1 nm in radius. The size ranges disclosed herein can be mean or median size. It is noted also that particles need not be spherical, but may be in a form of cubes, cylinders, discs, or any other suitable shape as would be appreciated by one of ordinary skill in the art.

[0022] The term "monolith", as used herein, refers to a single block of a material. The single block can be in the form of, for example, a brick, a disk, or a rod and can contain channels for increased fluid flow/distribution. In certain embodiments, multiple monoliths can be arranged together to form a desired shape. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present disclosure is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings in which like references indicate similar elements, in which:

[0024] Figure 1 is a block diagram illustrating a method for preparing a titanosilicate in accordance with embodiments of the present disclosure;

[0025] Figure 2 is a plot of strontium content versus time for dynamic strontium ion-exchange testing of different sorbent samples;

[0026] Figure 3 is a plot of strontium content versus time for static strontium ion-exchange testing of different sorbent samples;

[0027] Figure 4 is a plot of X-ray diffraction spectra of different sorbent samples;

[0028] Figure 5 is a plot of pore size distribution of different sorbent samples;

[0029] Figure 6A is an electron micrograph of a comparative example sorbent; and

[0030] Figure 6B is an electron micrograph of a titanosilicate prepared in accordance with an embodiment.

DETAILED DESCRIPTION

[0031] The present disclosure has been described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader scope of the embodiments of the disclosure as set for in the appended claims. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.

[0032] Embodiments of the present disclosure relate to titanosilicates, and, more specifically, to amorphous, mesoporous titanosilicates used as sorbents for adsorption of radionuclides, such as strontium, from aqueous solutions (e.g., water streams and static bodies of water). Moreover, the disclosed titanosilicates are adapted for the removal of radionuclide cations from aqueous solutions that contain substantial amounts of competing cations. In some embodiments, the titanosilicates have a pore distribution centered near 80 A in diameter (referred to herein as "mesopores") as well a smaller pore distribution centered near 15 A to 20 A that is typically present in other types of amorphous titanosilicates.

[0033] A comparative example adsorbent (hereinafter referred to as "CEA") is now described, which was used for evaluating the performance of the embodiments of the present disclosure. CEA was produced in accordance with Example 1 disclosed in United States Patent Application

Publication No. 2014/019082. [0034] While the disclosed mesoporous titanosilicates utilize similar inexpensive inorganic raw materials as other titanosilicates (e.g., CEA) under ambient conditions, other reaction conditions differ. For example, the mesoporous titanosilicates described herein are produced by dropwise addition of a titanium-containing acid into a silicon-containing base instead of the opposite order. Without being bound by theory, it is believed that precipitation in a basic local environment allows silicon anions to be in a less bonded state with other silicon species and more mobile before reacting with titanium species, leading to the formation of more ion-exchangeable sites in a more open structure.

[0035] The disclosed titanosilicates demonstrate different properties and improved strontium removal performance over other silicates, such as CEA. For example, in certain embodiments, the disclosed titanosilicates have a total pore volume (e.g., as determined by N2 adsorption) of about 50% higher than that of CEA, and a Na/Si atomic ratio (i.e., ion exchangeable site) of about 30% higher than that of CEA. The strontium removal efficiency was greater than 90% in some embodiments (compared to less than 60% for CEA), and the strontium distribution coefficient was more than tripled as compared to CEA. It is believed the mesopore structure of the disclosed titanosilicates results in more exchangeable sites accessible by Sr⁺² cations, leading to superior strontium removal.

[0036] Certain aspects of the present disclosure are directed toward a titanosilicate (e.g., an amorphous titanosilicate). In one embodiment, the titanosilicate includes a bimodal pore distribution. In one embodiment, a first plurality of pores of the bimodal pore distribution has a first average pore diameter from about 20 A to about 50 A, and a second plurality of pores of the bimodal pore distribution has a second average pore diameter from about 50 A to about 400 A. In other embodiments, the titanosilicate may have multiple pore distributions (e.g., a first, a second, a third, etc., distribution) each having different average pore diameters. Thus, embodiments of the present disclosure are not limited to bimodal pore distributions as defined herein.

[0037] In one embodiment, the second plurality of pores accounts for at least about 70% of a total pore volume of the titanosilicate. In one embodiment, the titanosilicate includes a first atomic ratio of Ti to Si from 0.5 to 2.0. In one embodiment, the titanosilicate includes a second atomic ratio of Na to Si from 0.2 to 1.5.

[0038] In one embodiment, an average surface area of the amorphous titanosilicate is less than 250 m²/g, less than 240 m²/g, less than 230 m²/g, less than 220 m²/g, less than 210 m²/g, less than 200 m²/g, less than 190 m²/g, less than 180 m²/g, less than 170 m²/g, less than 160 m²/g, or less than 150 m²/g. The surface area may be determined, for example, by the Brunauer-Emmett- Teller (BET) method according to DIN ISO 9277:2003-05 (which is a revised version of DIN 66131), using a multipoint BET measurement in the relative pressure range from 0.05-0.30 p/po- [0039] In one embodiment, wherein an average pore volume of the bimodal pore distribution is greater than 0.25 cc/g, greater than 0.30 cc/g, greater than 0.35 cc/g, greater than 0.40 cc/g, greater than 0.45 cc/g, or greater than 0.50 cc/g.

[0040] In one embodiment, the titanosilicate is adapted for removal of one or more of alkaline cations, alkaline earth cations, and heavy metal cations from an aqueous solution. In one embodiment, the titanosilicate is adapted for selective removal of strontium cations and/or cesium cations, as well as radionuclides thereof, from an aqueous solution. In one embodiment, the titanosilicate is adapted for the removal of Sr⁺² radionuclides.

[0041] In one embodiment, the titanosilicate further includes exchangeable cations that, when the titanosilicate is contacted with an aqueous solution, are exchangeable for K⁺¹, Cs⁺¹, Mg⁺², Ca⁺², Sr⁺², Ba⁺², Pb⁺², Cd⁺², Hg⁺², or combinations thereof present in the aqueous solution.

[0042] In one embodiment, the titanosilicate is in a form of a powder, pellets, granules, beads, extrudates, a monolith, a membrane, or coating on a substrate. Titanosilicate particles can be of any suitable size, for example, from 0.0001 mm to 10 mm, from 0.001 mm to 5 mm, from 0.01 mm to 3 mm, from 0.1 mm to 1 mm, or any other suitable range.

[0043] In one embodiment, a strontium removal efficiency of the titanosilicate is greater than 80% when a powdered form of the titanosilicate is mixed with an aqueous sample solution at a 1 :500 weight ratio, the aqueous sample solution having an initial strontium content from 3 ppm to 10 ppm. In one embodiment, the aqueous sample solution is simulated seawater. In one embodiment, the aqueous sample solution is ground water.

[0044] Another aspect of the present disclosure is directed toward a method of removing radionuclides from an aqueous solution. In one embodiment, the method includes contacting the aqueous solution with a titanosilicate according to any of the embodiments described herein. The radionuclides may include strontium cations. The strontium cations may be present at an initial concentration (Co) in the aqueous solution prior to contacting the aqueous solution with the titanosilicate. The strontium cations may present at a final concentration (Q) in the aqueous solution after contacting the aqueous solution with the titanosilicate. The strontium cation removal efficiency (R) may be greater than 70% in some embodiments, greater than 80% in some embodiments, and greater than 90% in some embodiments, with strontium cation removal efficiency being defined as follows:

R=(Co-Q)/C₀ (%) (Eq. 1) [0045] In one embodiment, the initial concentration ranges from 3 ppm to 10 ppm. In one embodiment, the final concentration is less than 1 ppm. In one embodiment, the final concentration is less than 1 ppm 20 hours after the aqueous solution was contacted with the amorphous titanosilicate.

[0046] Figure 1 is a block diagram illustrating a method 100 for preparing a titanosilicate in accordance with embodiments of the present disclosure. At block 110, a first aqueous solution is prepared, with the first aqueous solution containing a silicon compound. In one embodiment, the first aqueous solution contains Na₂Si0₃- 5H₂0. The Na₂Si0₃-5H₂0 may be added to deionized water (DI-H₂O), for example, in an amount from 2 wt% to 30 wt%, from 3 wt% to 20 wt%, or from 5 wt% to 10 wt% expressed in Na₂SiC>3. In one embodiment, a basic solution, such as NaOH solution, may be added to the first aqueous solution.

[0047] At block 120, a second aqueous solution is prepared, with the second aqueous solution containing a titanium compound. In one embodiment, the second aqueous solution may contain TiOCl₂-HCl, for example, in an amount from 20 wt% to 30 wt% expressed in TiOCl₂.

[0048] At block 130, a combined solution is produced by adding the second solution to the first solution in a drop-wise manner while stirring the first solution. In one embodiment, the second solution may be added such that a weight ratio of the second solution to the first solution ranges from 0.1:1 to 0.75:1, or from 0.1:0.2 to 0.1:0.5.

[0049] At block 140, the slurry is maintained at a pH above 9. In one embodiment, NaOH or HC1 is added to the slurry to adjust the pH of the final precipitation slurry to range from 9.5 to 10.5 (e.g., 10). In one embodiment, after completion of the precipitation, the slurry is aged for a period of time from 30 minutes to 24 hours (e.g., 1 hour). In one embodiment, the slurry is stirred during this time.

[0050] At block 150, after the time duration, the slurry is filtered and dried to obtain the amorphous titanosilicate. In one embodiment, the filtered slurry is washed with DI-H₂O (e.g., washed 1 to 5 times). In one embodiment, after washing, the filtered slurry is dried at a temperature from 70°C to 150°C for 8 to 24 hours. Dried portions of the amorphous titanosilicate are placed back in DI-H₂O to be fractured into smaller pieces naturally (e.g., without using additional force). The fractured amorphous titanosilicate is dried again and sieved to the particle size as desired.

ILLUSTRATIVE EXAMPLES

[0051] The following illustrative examples provide experimental conditions for producing amorphous, mesoporous titanosilicates for the removal of strontium cations from aqueous solutions, in accordance with some of the embodiments described herein. The examples set forth to assist in understanding the embodiments of the present disclosure and should not, of course, be construed as specifically limiting the embodiments described and claimed herein. Such variations of the disclosed embodiments, including the substitution of all equivalents now known or later developed, which would be within the purview of those skilled in the art, and changes in formulation or minor changes in experimental design, are to be considered to fall within the scope of the embodiments described herein.

EXAMPLE 1: TITANOSILICATE PREPARATION

[0052] A first solution was prepared by dissolving 44.2 g of Na₂S0₃.5H₂0 in 50 g of DI-H₂0, after which 93.0 g of 6M NaOH was added. The solution is then diluted with 500 g of DI-H₂0. A second solution of TiOCl₂- HCL solution (25 wt%TiC10₂) was added to the first solution in a dropwise manner while vigorously stirring the first solution to form a combined precipitation slurry. The amount of the second solution that was used was dependent on a desired Ti/Si atomic ratio. The slurry was maintained to have a pH above 9 during the precipitation, while a final pH of 9.5- 10.5 was achieved by adjusting with dilute NaOH or HC1 solution. The slurry was aged for 1 hour while stirring. After aging the slurry, the slurry was filtered, washed three times with DI-H₂0, and dried overnight at 110°C, fractured in DI-H₂0 naturally for about 1 hour, filtered, and dried again at 110°C overnight.

EXAMPLE 2: STRONTIUM ION-EXCHANGE TESTING

[0053] Strontium ion-exchange testing was conducted by two different methods (dynamic and static) using simulated seawater solution. The ionic components of simulated seawater solution (30%) is shown in Table 1.

Table 1: Salt compositions of simulated seawater (30%)

[0054] For the dynamic testing, sorbent particle size was between 20 and 30 mesh. 10 g of the sieved sample was placed in a column. Simulated seawater solution was passed through the column at a speed of 1 mL/min. The effluent was collected at various times and analyzed using inductively coupled plasma mass spectrometry (ICP-MS) as a function of solution passing time.

[0055] For the static testing, the fractured sorbent was ground into a powder and passed through 325 mesh sieve. 0.20 g of powdered sorbent sample was added to 100 g of simulated seawater and stirred for a period of time as desired. The resulting slurry was filtered, and the filtrate was collected for strontium concentration analysis using ICP-MS analysis. The pH of the filtrate was measured and the filtered solid was collected for mass balance analysis.

[0056] Strontium removal performance is measured by strontium removal efficiency (R), as defined above according to Eq. 1, and strontium distribution coefficient (Kj). K is defined as:

K_d = (i_.C_o-C C {%) (Eq. 2)

where W is the weight of sorbent in gram and V is the volume of the solution in mL.

[0057] For comparative purposes, the samples used in both the static and dynamic tests were the mesoporous titanosilicate (MTS), described above in Example 1, and CEA. Figure 2 plots the strontium concentration versus time in the dynamic effluent of the simulated seawater during treatment by the sorbents, indicating that MTS was significantly more effective for strontium removal than CEA. For example, after a treatment of 24 hours, the strontium concentration in the MTS-treated effluent was 380 ppb, which corresponds to a strontium removal efficiency of 92%. On the other hand, the strontium concentration in the CEA-treated effluent was 2090 ppb, which corresponds to a strontium removal efficiency of 55%.

[0058] Figure 3 plots the static strontium concentration versus time in the simulated seawater during treatment by the sorbents. Once again, treatment with MTS demonstrated significantly higher strontium removal efficiency than treatment with CEA. After 20 hours, the strontium removal efficiency for MTS is about 84% versus 59% for CEA. The strontium distribution coefficient at 20 hours is 2696 mL/g for MTS versus 776 mL/g for CEA.

EXAMPLE 3: X-RAY DIFFRACTION ANALYSIS

[0059] Sorbent samples MTS and CEA, as described above in Example 2, were analyzed using X-ray diffraction (XRD). XRD was performed using a PANalytical MPD X'Pert Pro diffraction system with CuKa radiation generator settings of 45 kV and 40 mA. The optical path was defined by a 1/4° divergence slit, 0.04 radian soller slits, 15 mm mask, 1/2° anti-scatter slits, the sample, 0.04 radian soller slits, a Ni filter, and a PIXCEL position sensitive detector. Samples were first prepared by grinding in a mortar and pestle and then backpacking (about 2 grams) into a round mount. The data collection from the round mount covered a range from 10° to 90° 2Θ using a step scan with a step size of 0.026° 2Θ and a count time of 600 seconds per step. Peak fitting of the XRD powder patterns was conducted using Jade Plus 9 analytical XRD software. Phases present in each sample were identified by search/match of the PDF-4/Full File database from the International Center for Diffraction Data (ICDD).

[0060] Figure 4 shows XRD powder patterns revealing that both MTS and CEA samples are amorphous. The XRD powder patterns of CEA showed a broad peak centered at 2Θ = 28° due to the diffraction of very small pores. However, the XRD powder pattern for MTS revealed a bimodal pore structure having, in addition to the peak at 28°, a broad peak centered at about 6° indicating a much larger pore size (large <i-spacing).

EXAMPLE 4: N₂ POROSITY

[0061] N2 porosity data was obtained on a Micromeritics TriStar 3000 porosity analyzer. A 0.3- 0.5 gram sample was first degassed at 120°C for 6 hours and then equilibrated in liquid nitrogen. The degas temperature was selected to be 120°C since higher temperatures will damage the sorbent pore structure while lower temperatures are insufficient for removing moisture. The total surface area was calculated based on the BET method as described herein. The pore volume (PV) was calculated using the single-point total pore volume for pores between 10 A and 300 A radius. The average pore width (PW) was calculated using the method of 4V/A by BET.

[0062] Figure 5 shows the pore size distribution for MTS and CEA. Consistent with the XRD results, the N2 the adsorption pore size distribution of MTS also showed two peaks (a bimodal distribution), while that of CEA only had one peak. The single-pore structure of CEA is located at about 20 A in radius. For MTS, in addition to the small pore structure, a much larger and more dominant mesopore structure was formed centered at about 50 A. Because of the formation of the larger mesopores, MTS has a higher pore volume than CEA, namely 0.32 cc/g versus 0.22 cc/g in spite of its lower BET surface area, namely 197 m²/g for MTS versus 384 m²/g for CEA.

EXAMPLE 5: ELEMENTAL ANALYSIS

[0063] ICP-MS was conducted first by digesting solid powder using the fusion method followed by quantitative analysis of the diluted solution.

[0064] Besides the differences in physical properties, MTS is different in its chemical composition from CEA. Table 2 compares the atomic Ti/Si and Na/Si ratio of MTS versus CEA, revealing that, although the Ti/Si ratios of the two sorbents are similar, MTS has a Na/Si ratio that is about 50% higher than that of CEA. Without being bound by theory, it is believed that the higher strontium removal performance of MTS is at least partially due to its larger number of intrinsic ion- exchangeable sites.

Table 2: Chemical compositions of sorbent samples

EXAMPLE 6: ELECTRON MICROSCOPY

[0065] Scanning electron microscope (SEM) data was collected using a JEOL JEM2011 200KeV LaB6 source microscope with a Bruker Ge EDS system using Spirit software. Digital images were captured with a bottom mount Gatan 2K CCD camera and Digital Micrograph collection software. All samples were powdered samples prepared and analyzed as dry dispersions on 200 mesh lacey carbon coated Cu grids.

[0066] Figures 6A and 6B are micrographs of CEA and MTS, respectively, at 50,000X magnification, revealing a tight, rock- like morphology for CEA while MTS has a much looser and flower-like morphology.

[0067] In the foregoing description, numerous specific details are set forth, such as specific materials, dimensions, processes parameters, etc., to provide a thorough understanding of the embodiments of the present disclosure. The particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments. The words "example" or "exemplary" are used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as "example" or "exemplary" is not necessarily to be construed as preferred or advantageous over other aspects or designs. Rather, use of the words "example" or "exemplary" is intended to present concepts in a concrete fashion. As used in this application, the term "or" is intended to mean an inclusive "or" rather than an exclusive "or". That is, unless specified otherwise, or clear from context, "X includes A or B" is intended to mean any of the natural inclusive permutations. That is, if X includes A; X includes B; or X includes both A and B, then "X includes A or B" is satisfied under any of the foregoing instances. In addition, the articles "a" and "an" as used in this application and the appended claims should generally be construed to mean "one or more" unless specified otherwise or clear from context to be directed to a singular form.

[0068] Reference throughout this specification to "an embodiment", "certain embodiments", or "one embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrase "an embodiment", "certain embodiments", or "one embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment, and such references mean "at least one".

Claims

What is claimed is:

1. An amorphous titanosilicate comprising:

a bimodal pore distribution, wherein a first plurality of pores of the bimodal pore distribution has a first average pore diameter from about 20 A to about 50 A, wherein a second plurality of pores of the bimodal pore distribution has a second average pore diameter from about 50 A to about 400 A, and wherein the second plurality of pores accounts for at least about 70% of a total pore volume of the amorphous titanosilicate.

2. The amorphous titanosilicate of claim 1, further comprising a first atomic ratio of Ti to Si from 0.5 to 2.0.

3. The amorphous titanosilicate of either claim 1 or claim 2, further comprising a second atomic ratio of Na to Si from 0.2 to 1.5.

4. The amorphous titanosilicate of any of claims 1-3, wherein an average Brunauer-Emmett- Teller (BET) surface area of the amorphous titanosilicate is less than 250 m²/g.

5. The amorphous titanosilicate of any of claims 1-4, wherein an average pore volume of the bimodal pore distribution is greater than 0.3 cc/g.

6. The amorphous titanosilicate of any of claims 1-5, wherein the amorphous titanosilicate is adapted for removal of one or more of alkaline cations, alkaline earth cations, and heavy metal cations from an aqueous solution.

7. The amorphous titanosilicate of any of claims 1-6, wherein the amorphous titanosilicate is adapted for selective removal of one or more of strontium cations or cesium cations from an aqueous solution.

8. The amorphous titanosilicate of any of claims 1-7, further comprising exchangeable cations including H⁺¹, Na⁺¹, K⁺¹, NH₄ ⁺¹, Mg⁺², Ca⁺², or combinations thereof.

9. The amorphous titanosilicate of any of claims 1-8, wherein the amorphous titanosilicate is in a form of a powder, pellets, granules, beads, extrudates, a monolith, a membrane, or coating on a substrate.

10. The amorphous titanosilicate of any of claims 1-9, wherein a strontium removal efficiency of the amorphous titanosilicate is greater than 80% when a powdered form of the amorphous titanosilicate is mixed with an aqueous sample solution at a 1:500 weight ratio, the aqueous sample solution having an initial strontium content from 3 ppm to 10 ppm.

11. The amorphous titanosilicate of claim 10, wherein the aqueous sample solution comprises simulated seawater.

12. The amorphous titanosilicate of claim 10, wherein the aqueous sample solution comprises ground water.

13. An amorphous titanosilicate comprising:

a bimodal pore distribution, wherein a first plurality of pores of the bimodal pore distribution has a first average pore diameter from about 20 A to about 50 A, and wherein a second plurality of pores of the bimodal pore distribution has a second average pore diameter from about 50 A to about 400 A;

a first atomic ratio of Ti to Si from 0.5 to 2.0; and

a second atomic ratio of Na to Si from 0.2 to 1.5.

14. The amorphous titanosilicate of claim 13, wherein the second plurality of pores accounts for at least about 70% of a total pore volume of the amorphous titanosilicate.

15. The amorphous titanosilicate of either claim 13 or claim 14, wherein an average BET surface area of the amorphous titanosilicate is less than 250 m²/g.

16. The amorphous titanosilicate of any of claims 13-15, wherein an average pore volume of the bimodal pore distribution is greater than 0.3 cc/g.

17. The amorphous titanosilicate of any of claims 13-16, wherein the amorphous titanosilicate is adapted for removal of one or more of alkaline cations, alkaline earth cations, and heavy metal cations from an aqueous solution, the heavy metal cations comprising one or more of Pb⁺², Cd⁺², or

18. The amorphous titanosilicate of any of claims 13-17, wherein the amorphous titanosilicate is adapted for selective removal of one or more of strontium cations or cesium cations from an aqueous solution.

19. The amorphous titanosilicate of any of claims 13-18, further comprising exchangeable cations comprising H⁺¹, Na⁺¹, K⁺¹, NH₄ ⁺¹, Mg⁺², Ca⁺², or combinations thereof.

20. The amorphous titanosilicate of any of claims 13-19, wherein the amorphous titanosilicate is in a form of a powder, pellets, granules, beads, extrudates, a monolith, a membrane, or coating on a substrate.

21. The amorphous titanosilicate of any of claims 13-20, wherein a strontium removal efficiency of the amorphous titanosilicate is greater than 80% when a powdered form of the amorphous titanosilicate is mixed with an aqueous sample solution at a 1:500 weight ratio, the aqueous sample solution having an initial strontium content from 3 ppm to 10 ppm.

22. The amorphous titanosilicate of claim 21, wherein the aqueous sample comprises simulated seawater.

23. The amorphous titanosilicate of claim 21, wherein the aqueous sample comprises ground water.

24. A titanosilicate for removing one or more of strontium, cesium, or other heavy cations from aqueous solutions containing seawater, the titanosilicate comprising:

a first distribution of pores having a first average pore diameter from about 20 A to about

50 A;

a second distribution of pores having a second average pore diameter from about 50 A to about 400 A, wherein the second plurality of pores accounts for at least about 70% of a total pore volume of the titanosilicate;

a first atomic ratio of Ti to Si from 0.5 to 2.0; and

a second atomic ratio of Na to Si from 0.2 to 1.5.

25. The titanosilicate of claim 24, wherein the titanosilicate is amorphous.

26. The titanosilicate of either claim 24 or 25, wherein the first and second distributions of pores collectively define a bimodal pore distribution.

27. The titanosilicate of any of claims 24-26, wherein an average BET surface area of the titanosilicate is less than 250 m²/g.

28. The titanosilicate of any of claims 24-27, wherein an average pore volume of the first and second distributions of pores is greater than 0.3 cc/g.

29. The titanosilicate of any of claims 24-28, wherein the titanosilicate is adapted for removal of one or more of alkaline cations, alkaline earth cations, and heavy metal cations from an aqueous solution.

30. The titanosilicate of any of claims 24-29, wherein the titanosilicate is adapted for selective removal of one or more of strontium cations or cesium cations from an aqueous solution.

31. The titanosilicate of any of claims 24-30, further comprising exchangeable cations comprising H⁺¹, Na⁺¹, K⁺¹, NH₄ ⁺¹, Mg⁺², Ca⁺², or combinations thereof.

32. The titanosilicate of any of claims 24-31, wherein the titanosilicate is in a form of a powder, pellets, granules, beads, extrudates, a monolith, a membrane, or coating on a substrate.

33. The titanosilicate of any of claims 24-32, wherein a strontium removal efficiency of the titanosilicate is greater than 80% when a powdered form of the titanosilicate is mixed with an aqueous sample solution at a 1:500 weight ratio, the aqueous sample solution having an initial strontium content from 3 ppm to 10 ppm.

34. The titanosilicate of claim 33, wherein the aqueous sample comprises simulated sea water.

35. The titanosilicate of claim 33, wherein the aqueous sample comprises ground water.

36. An amorphous titanosilicate having a strontium removal efficiency of greater than 80% when a powdered form of the amorphous titanosilicate is mixed with an aqueous sample solution at a 1:500 weight ratio, the aqueous sample solution having an initial strontium content from 3 ppm to 10 ppm.

37. The amorphous titanosilicate of claim 36, wherein the strontium removal efficiency is greater than 90%.

38. The amorphous titanosilicate of either claim 36 or claim 37, wherein the aqueous sample solution comprises simulated seawater.

39. The amorphous titanosilicate of any of claims 36-38, comprising:

a bimodal pore distribution, wherein a first plurality of pores of the bimodal pore distribution has a first average pore diameter from about 20 A to about 50 A, wherein a second plurality of pores of the bimodal pore distribution has a second average pore diameter from about 50 A to about 400 A.

40. A method of removing radionuclides from an aqueous solution, the method comprising: contacting the aqueous solution with an amorphous titanosilicate, wherein the radionuclides comprise strontium cations, wherein the strontium cations are present at an initial concentration in the aqueous solution prior to contacting the aqueous solution with the amorphous titanosilicate, wherein the strontium cations are present at a final concentration in the aqueous solution after contacting the aqueous solution with the amorphous titanosilicate, and wherein strontium cation removal efficiency is greater than 80%.

41. The method of claim 40, wherein the initial concentration is from 3 ppm to 10 ppm, and wherein the final concentration is less than 1 ppm.

42. The method of either claim 40 or claim 41, wherein the final concentration is less than 1 ppm 20 hours after the aqueous solution was contacted with the amorphous titanosilicate.

43. The method of any of claims 40-42, wherein the amorphous titanosilicate comprises a bimodal pore distribution, wherein a first plurality of pores of the bimodal pore distribution has a first average pore diameter from about 20 A to about 50 A, and wherein a second plurality of pores of the bimodal pore distribution has a second average pore diameter from about 50 A to about 400 A.

44. The method of any of claims 40-43, wherein the second plurality of pores accounts for at least about 70% of a total pore volume of the amorphous titanosilicate.

45. The method of any of claims 40-44, wherein the amorphous titanosilicate comprises an atomic ratio of Ti to Si from 0.5 to 2.0.

46. The method of any of claims 40-45, wherein the amorphous titanosilicate comprises an atomic ratio of Na to Si from 0.2 to 1.5 after contacting the aqueous solution with an amorphous titanosilicate.

47. The method of any of claims 40-46, wherein the titanosilicate is in a form of a powder, pellets, granules, beads, extrudates, a monolith, a membrane, or coating on a substrate.

48. The method of any of claims 40-47, wherein the aqueous solution comprises simulated seawater or ground water.

49. A titanosilicate comprising:

50 A;

a second distribution of pores having a second average pore diameter from about 50 A to about 400 A; and

strontium cations or cesium cations adsorbed therein.

50. A titanosilicate of claim 49, further comprising strontium cations adsorbed therein, the strontium cations being present in an amount of greater than 0.001 wt% with respect to a total weight of the titanosilicate.