TITANATE SORBENTS FOR METAL IONS AND METHOD OF MAKING AND USING

Abstract: A method for removing metal ions from solution comprises the steps of providing titanate particles by spray-drying a solution or slurry comprising sorbent titanates having a particle size up to 20 micrometers, optionally in the presence of polymer free of cellulose functionality as binder, said sorbent being active towards heavy metals from Periodic Table (CAS version) Groups IA, IIA, IB, IIB, IIIB, and VIII, to provide monodisperse, substantially spherical particles in a yield of at least 70 percent of theoretical yield and having a particle size distribution in the range of 1 to 500 micrometers. The particles can be used free flowing in columns or beds, or entrapped in a nonwoven, fibrous web or matrix or a cast porous membrane, to selectively remove metal ions from aqueous or organic liquid.

Description: TITANATE SORBENTS FOR METAL IONS AND METHOD OF MAKING AND USING The invention was made with Government support under Contract AR21-96 C-33089 awarded by the Department of Energy. The Government has certain rights in the invention. Field of the Invention The present invention pertains to substantially spherical, monodisperse sorptive particles, a method therefor, and a method of using the particles in loose form, in a column, or enmeshed in a web or membrane for extraction of metal ions, particularly radioactive forms of these ions, from solution. The method and particles are particularly useful in the remediation of nuclear wastes. Background of the Invention The conventional method of preparing titanate particles suffers from two significant drawbacks. First, grinding the dried solids must be done carefully so as to minimize formation of unusable fines. Second, since a wide range of particle sizes results from grinding, the paniculate must be sized through sieves. These operations are time-consuming and inevitably cause loss of product. Sized titanates can then be loaded into columns in order to remove metals from radioactive waste solutions. Spray-drying of solid materials is a method known in the art for preparation of useful solids, including titanates, pigments, and food stuffs. See, for example, Kirk-Othmer Encyclopedia of Chemical Technology, 4th Ed., John Wiley & Sons, New York, 1993; Vol. 8, p. 475 - 519, particularly pp. 505-508; C. Stnimillo and T. Kudra, "Drying: Principles, Applications and Design", Gordon .and Breach, New York, 1986, pp. 352 - 359; and Masters, K., Spray Drying Handbook, 4 th Ed., John Wiley & Sons, New York, 1985; pp. 548-567, particularly pp. 549, 550 and 565. Crystalline sodium nonatitanate has been disclosed as an ion exchanger for strontium in WO 97/14652. Certain binders are stated to be useful for binding the sodium nonatitanate into larger particles. Spray-drying is not disclosed. In U.S. Pat. Nos. 4,138,336 and 5,128,291 spray-drying of porous titania in the presence of an inorganic binder is disclosed. Crystalline silicotitanates as ion exchangers have been disclosed in W094/19277 and in Pacific Northwest National Laboratories publication PNL-8847, UC-510 (October 1993). Summary of the Invention Briefly, the present invention provides a method of removing metal ions from solution comprising the steps of: proving titanate particles by spray-4dryιng a solution or slurry compnsing utanate particles, preferably having a particle size up to 20 micrometers, optionally in the presence of an organic binder free of cellulose functionality, to produce monodisperse, substantially spherical sorbent utanate particles in a yield of at least 70 percent of theoretical yield and having an average particle size in the range of 1 to 100 micrometers, said Utanate sorbents being acdve towards metals in Penodic Table (CAS version) Groups IA, IIA, IB, IIB, MB, and VIII, and introducing the spray-dned titanate particles into a metal ion containing solution wherein the metal ions are as mentioned above, preferably any of Sr, Cs, Am, Pu, and U, equilibrated with the solution, and then separated from the sorbed and/or exchanged metal ions The spray-dned particles can be in a loose form, or in agglomerated form, in a cartndge, or enmeshed in a porous membrane, matrix or web The particles preferably are any of crystalline sihcotitanate and sodium titanate particulates Preferably, the web or matnx is porous The sorbents preferably selected from polymers of olefins or acrylates, and more preferably are selected from the group consisting of silicotitanates and metal titanates, wherein the metal preferably is selected from Penodic Table (CAS version) Groups IA or IIA More preferably, the sorbents .are selected from the group consisting of cystalline sihcoUtanate (CST), and sodium utanate particles The liquid in the solution or slurry can be aqueous or organic liquid In a further aspect, there are disclosed substantially sphencal sorbent particles having an average particle size in the range of 1 to 100 micrometers, the particles being sorptive towards metals from Penodic Table (CAS version) Groups IA, IIA, IB, IIB, IIIB, and VIII Preferably, the sphencal particles can be crystalline sihcotitanate, and sodium nonatitanate The particles can be used in columns or beds to selectively remove heavy metal ions from Periodic Table Groups IA, IIA, IB, IIB, IIIB, and VIII, preferably any of Cs, Sr, Ag, Co, Cr, Au, Hg, U, Pu, Am, more preferably Sr, Cs, Am, Pu, and U, and other transuranic ions from aqueous solutions In a still further aspect, the sphencal sorptive particles that have been spray-dned, optionally in the presence of olefin or acrylate polymenc binder, can be enmeshed in a nonwoven, fibrous web, matrix, or membrane The webs or matrices or membranes, which preferably are porous, can be used in solid phase extraction (SPE) procedures to selectively remove metal ions from aqueous solutions by passing a solution of the metal ion through or by the particle loaded web, matnx, or membrane In yet another aspect, the invention provides an SPE device, such as a cartndge which in prefened embodiments can be pleated or spirally wound, compnsing a fibrous non-woven SPE web compnsing sphencal, monodisperse particles which, in prefened embodiments, can be crystalline sihcotitanate or sodium titanate paniculate In particular, the particulate can be enmeshed in the SPE web which preferably can compπse ρoly(m- or p-terephthalamide) fibers enclosed in the cartndge device Preferably, the web is porous In another embodiment, the invention provides a method of removing the specified metal ions from an aqueous solution comprising passing the aqueous solution through an SPE column comprising spherical, monodisperse sorptive particles made by the method of this invention, the particles preferably being crystalline sihcotitanate or sodium titanate paniculate. In this application: "crystalline sihcotitanate" can be designated CST; "drain time" means the time required to dewater a slurry of particles and fibers when making a sheet; "monodisperse" means a monomodal particle size distribution (i.e., particles of uniform size in a dispersed phase) about a mean in a range of 1 up to about 500 micrometers, preferably 1 to about 60 micrometers, as illustrated in FIG. 1; "particles" and "particulate" are used interchangeably; "size" means the diameter of a spherical particle or the largest dimension of an inegularly shaped particle; "sodium titanate" includes "sodium nonatitanate"; "sorptive" or "sorb" means by one or both of absorption and adsorption and includes ion exchange; "substantially spherical" means particles that are spherical, ovoid (having an elliptical cross-section), or toroidal, that are free of sharp corners; and "web", "matrix", and "membrane" are used interchangeably and each term includes the others. The overall process yield in making particles of the invention using a spray-dryer with a diameter of at least 1 m is at least 70 percent, preferably 80-90 percent or more, compared to a yield of about 60 percent or less when using prior art ground and sieved particles. Preferably, the resulting particles are free of submicron size particles, with not more than 15 percent of particles being <5 micrometers in size. The spray-drying process substantially eliminates product particles having submicron sizes. Additionally, free-flowing spherical particles or agglomerates thereof will pack with point contact in columns, resulting in less channeling and a lower pressure drop during extraction compared with, for example, inegularly shaped prior art particles having the same average size. Inegularly shaped prior art particles, particularly those less than 5 micrometers in size can pack tightly and lead to a high pressure drop in extraction applications. When irregularly shaped prior art particles are greater than 50 micrometers in size, channeling can result as liquids pass through, resulting in poor separations. It has been found that compacting the spray dried particles with low pressure (as by hand pressure) .and then heating to about 130 °C for 72 hours results in a sponge-like (porous) shaped article having excellent separating ability without building back-pressure. Further, the advantages of the particles of the invention in webs, matrices, or membranes include reduced dram time by a factor of at least three compared to non-sphencal, inegularly shaped, pnor art particles typically obtained from a gnnding process, when incorporated in a sheet article Further, sheet articles can be made using particles of this invention, whereas in many cases sheet articles cannot be made m a timely fashion from pnor art ground and sieved particles because of excessive dram time or inability to control the sheet forming process The sheet articles formed from spray-dned particles often have lower flow resistance than sheet articles made from ground and screened particles and are therefor more efficient in use Brief Description of the Drawing FIG 1 is a graph of a monodisperse particle size distnbution for typical spray-dned particles of the invention Detailed Description of Preferred Embodiments In prefened embodiments, sorptive particles useful in the present invention include substantially sphencal sorptive titanate particles of crystalline sihcotitanate (CST), (available from UOP, Tarrytown, NY) or sodium nonatitanate (available from Al edSignal, Inc , Mornstown, NJ These particles can be useful to sorb metal ions, preferably strontium (Sr), cesium (Cs), amencium (Am), plutomum (Pu), uranium (U), and other transuranic elements which may be in their radioactive forms The commercially available CST or sodium titanate, which compnse particles of megular shapes can be slurned with liquid, preferably water, and then spray-dned, optionally in the presence of an organic binder that is free of cellulose functionality and preferably is selected from olefin or acrylate polymers, preferably using a spinning disk atomizer, and then collecting the resulting substantially sphencal titanate particles having a size distnbution in the range of about 1 to 500 micrometers, preferably about 1 to 100 micrometers, more preferably 1 to 60 micrometers, and most preferably 5 to 20 micrometers Sphencal particles in the size range of about 100 to 500 micrometers can be useful in industnal separations In the process for providing a slurry of the sorptive particles of the invention, an organic binder, wherein more preferably the binder is selected from styrene butadiene copolymer, a vinyhdene halide emulsion, an acrylic (co)polymer of acrylates and/or methacrylates, and an acrylic colloidal dispersion The binder may facilitate production of the desired particles An organic binder such as styrene polybutadiene copolymer (e g , available under the trade designation "GOODRITE 1800 x 73 ", from B F Goodnch Company, BrecksviUe, OH) preferably can be used Organic binders can be present in the slurry in an amount in the range of 5-50 weight percent, preferably 15-25 weight percent of the particles present In some instances the slurry can be sonicated to reduce or maintain particles in a submicron size range It is prefened that the particles m the slurry not be dned pnor to subjecting them to the spray drying techmque In addition, particles in a slurry that contain a binder can also desirably be mechanically agitated and preferably also sonicated as the slurry is pumped into the spray drying unit Spray-drying of the slurry can be accomplished using well-known techniques which include the steps of 1) atomization, using a spinning disk, of the matenal introduced into the dryer, 2) removing of moisture as, for example, by contact of the material with hot gas, and 3) separation of dry product from the exhaust drying agent The slurry preferably has a solids content in the range of 3 to 15 percent by weight, more preferably 5 to 10 percent by weight, most preferably 5 to 7 5 percent by weight, to ensure smooth operation of the apparatus After spray-drying, the particles are free-flowing with most preferred average diameters in the range of 5-20 micrometers The particle can be evaluated for its Ion exchange capacity (see Brown, G N , Carson, K J , DesChane, J R , Elovich, R J , and P K Berry, September 1996 Chemical and Radiation Stability of a Proprietary Cesium Ion Exchange Matenal Manufactured from WWL Membrane and Superlig™ 644 PNNL-11328, Pacific Northwest National Laboratory, Richland, Waslungton ) by testing for the batch -distnbution coefficient or Kj which is descnbed as follows The batch distnbution coefficient, K d is an equihbnum measure of the overall ability of the solid phase ion exchange matenal to remove an ion from solution under the particular expenmental conditions that exist during the contact The batch I is an indicator of the selectivity, capacity, and affinity of an ion for the ion exchange matenal in the presence of a complex matnx of competing ions In most batch Kd tests, a known quantity of ion exchange matenal is placed in contact with a known volume of solution containing the particular ions of interest The matenal is allowed to contact the solution for a sufficient time to achieve equihbnum at a constant temperature, after which the solid ion exchange matenal and liquid supernate are separated and analyzed In this application, the batch K 4 values were determined m one procedure by contacting 0 10 g of the particle with 20 mL of TAN matnx, for 20 hours with shaking (see formulation below) TAN* Waste Simulant Composition * TAN means Test Area North, NEEL Department of Energy Installation, Idaho Falls. ID ** The concentration values for Sr and Ca in the Table above are for the determination of K_ values only For breakthrough curve data the concentrations for Sr, Ca, and Mg ions were changed to 3 42E-6, 1 36E-3, and 3 87E-4, respectively, see Example 27, below Concentrations for other ions remained constant in the solution In a second procedure, the batch Kj values were determined by contacting 0 02 g of particle with 20 mL of liqmd (Solution A) for 24 hours with shaking Solution A compnsed 0 1 M sodium hydroxide admixed with 5 M soώum nitrate containing 55 ppm Sr ion in deiomzed water The equation for determining the Kj can be simplified by deternumng the concentration of tlie analyte before and after contact and calculating the quantity of analyte on the ion exchanger by difference Where is the initial amount or activity of the ion of interest in the feed solution pnor to contact, C f is the amount or activity after contact, V is the solution volume, M is the exchanger mass, F is tlie mass of dry ion exchanger divided by the mass of wet ion exchanger (F-factor) Ka (normal units are mL/g) represents the theoretical volume of solution (mL) that can be processed per mass of exchanger (dry weight basis) under equihbnum conditions More preferably, the expenmental equipment that was required to complete the batch Kj determinations included an analytical balance, a constant temperature water bath, an oven for F- factor determinations, a vanable speed shaker table, 20-mL scintillation vials, 0 45 μm synnge filters, tlie appropnate ion exchanger, and simulant solutions The particles were all dned thoroughly pnor to testing Approximately (0 10 g) or (0 02 g) of each matenal, respectively, was contacted with 20 mL of the TAN matnx or Solution A (respectively) The sample bottles were placed into a 25°C constant temperature bath and shaken lightly for 20 hours or 24 hours, respectively. The samples were then filtered with a 0.45 micrometer syringe filter to separate the resin material from the solution and the resulting liquid was analyzed for strontium content by ICP (inductively coupled plasma). The particles of the invention can be enmeshed in vartous fibrous, nonwoven webs or matrices,which perferably are porous. Types of webs or matrices include fibrillated polytetrafluoroetliylene (PTFE), microfibrous webs, macrofibrous webs, and polymer pulps. 1. Fibrillated PTFE The PTFE composite sheet material of the invention is prepared by blending the paniculate or combination of particulates employed with a PTFE emulsion until a uniform dispersion is obtained and adding a volume of process lubricant up to approximately one half the volume of the blended particulate. Blending takes place along with sufficient process lubricant to exceed sorptive capacity of the particles in order to generate the desired porosity level of the resultant article. Preferred process lubricant amounts are in the range of 3 to 200 percent by weight in excess of that required to saturate the particulate, as is disclosed in U.S. Pat. No. 5,071,610. The aqueous PTFE dispersion is then blended with the particulate mixture to form a mass having a putty-like or dough-like consistency. The sorptive capacity of the solids of the mixture is noted to have been exceeded when small amounts of water can no longer be incorporated into the mass without separation. This condition should be maintained throughout the entire mixing operation. The putty-like mass is then subjected to intensive mixing at a temperature and for a time sufficient to cause initial fibrillation of the PTFE particles. Preferably, the temperature of intensive mixing is up to 90°C, preferably it is in the range of 0° to 90°C, more preferably 20° to 60°C. Minimizing the mixing at the specified temperature is essential in obtaining extraction media and chromatographic transport properties. Mixing times will typically vary from 0.2 to 2 minutes to obtain the necessary initial fibrillation of the PTFE particles. Initial mixing causes partial disoriented fibrillation of a substantial portion of the PTFE particles. Initial fibrillation generally will be noted to be at an optimum within 60 seconds after the point when all components have been fully incorporated into a putty-like (dough-like) consistency. Mixing beyond this point will produce a composite sheet of inferior extraction medium and chromatographic properties. Devices employed for obtaining the necessary intensive mixing are commercially available intensive mixing devices which are sometimes refened to as internal mixers, kneading mixers, double-blade batch mixers as well as intensive mixers and twin screw compounding mixers. The most popular mixer of this type is the sigma-blade or sigma-arm mixer. Some commercially available mixers of this type are those sold under the common designations Banbury mixer, Mogul mixer, C. W. Brabender Prep mixer and C. W. Brabender sigma blade mixer. Other suitable intensive mixing devices may also be used. The soft putty-like mass is then transferred to a calendertng device where the mass is calendered between gaps in calendering rolls preferably maintained at a temperature up to 125°C, preferably in the range of 0° to about 100°C, more preferably in the range of 20°C to 60°C, to cause additional fibrillation of the PTFE particles of the mass, and consolidation while maintaining the water level of the mass at least at a level of near the sorptive capacity of the solids, until sufficient fibrillation occurs to produce the desired extraction medium. Preferably the calendering rolls are made of a rigid material such as steel. A useful calendering device has a pair of rotatable opposed calendering rolls each of which may be heated and one of which may be adjusted toward the other to reduce the gap or nip between the two. Typically, the gap is adjusted to a setting of 10 millimeters for the initial pass of the mass and, as calendering operations progress, the gap is reduced until adequate consolidation occurs. At the end of the initial calendering operation, the resultant sheet is folded and then rotated 90° to obtain biaxial fibrillation of the PTFE particles. Smaller rotational angles (e.g., 20° to less than 90°) may be preferred in some extraction and chromatographic applications to reduce calender biasing, i.e., unidirectional fibrillation and orientation. Excessive calendering (generally more than two times) reduces the porosity which in turn reduces the solvent wicking in thin layer chromatography (TLC) and the flow-through rate in tlie filtration mode. During calendering, the lubricant level of the mass is maintained at least at a level of exceeding the absorptive capacity of the solids by at least 3 percent by weight, until sufficient fibrillation occurs and to produce porosity or void volume of at least 30 percent and preferably 40 to 70 percent of total volume. The prefened amount of lubricant is determined by measuring the pore size of the article using a Coulter Porometer as described in the Examples below. Increased lubricant results in increased pore size and increased total pore volume as is disclosed in U.S. Pat. No. 5,071,610. The calendered sheet is then dried under conditions which promote rapid drying yet will not cause damage to the composite sheet or any constituent therein. Preferably drying is carried out at a temperature below 200°C. The preferred means of drying is by use of a forced air oven. The preferred drying temperature range is from 20°C to about 70°C. The most convenient drying method involves suspending the composite sheet at room temperature for at least 24 hours. The time for drying may vary depending upon the particular composition, some particulate materials having a tendency to retain water more than others. The resultant composite sheet preferably has a tensile strength when measured by a suitable tensile testing device such as an Instron brand (Canton, MA) tensile testing device of at least 0.5 MPa. The resulting composite sheet has uniform porosity and a void volume of at least 30 percent of total volume. The PTFE aqueous dispersion employed in producing the PTFE composite sheet of the invention is a milky-wWte aqueous suspension of minute PTFE particles. Typically, the PTFE aqueous dispersion will contain about 30 percent to about 70 percent by weight solids, the major portion of such solids being PTFE particles having a particle size in the range of about 0.05 to about 0.5 micrometers. The commercially available PTFE aqueous dispersion may contain other ingredients, for example, surfactant materials and stabilizers which promote continued suspension of the PTFE particles. Such PTFE aqueous dispersions are presently commercially available from Dupont de Nemours Chemical Corp., for example, under the trade designations "TEFLON 30", "TEFLON 30B", or "TEFLON 42". The first two contain about 59 percent of about 61 percent solids by weight which are for the most part 0.05 to 0.5 micrometer PTFE particles and from about 5.5 percent to about 6.5 percent by weight (based on weight of PTFE resin) of non-ionic wetting agent, typically octylphenol polyoxyethylene or nonylphenol polyoxyethylene. Teflon™ 42 contains about 32 to 35 percent by weight solids and no wetting agent but has a surface layer of organic solvent to prevent evaporation. A prefened source of PTFE is available under the trade designation "FLUON" from ICI Amertcas, Inc. Wilmington, DE. It is generally desirable to remove, by organic solvent extraction, any residual surfactant or wetting agent after formation of the article. In other embodiments of the present invention, the fibrous membrane (web) can comprise non-woven, macro- or microfibers preferably selected from the group of fibers consisting of polyamide, polyolefin, polyester, polyurethane, glass fiber, polyvinylhalide, or a combination thereof. The fibers preferably are polymeric. (If a combination of polymers is used, a bicomponent fiber may be obtained.) If polyvinylhalide is used, it preferably comprises fluorine of at most 75 percent (by weight) and more preferably of at most 65 percent (by weight). Addition of a surfactant to such webs may be desirable to increase tlie wettability of the component fibers. 2. Macrofibers The web can comprise thermoplastic, melt-extruded, large-diameter fibers which have been mechanically-calendered, air-laid, or spunbonded. These fibers have average diameters in tlie general range of 50 μm to 1,000 μm. Such non-woven webs with large-diameter fibers can be prepared by a spunbond process which is well known in the art (see, e.g., U.S. Pat. Nos. 3,338,992, 3,509,009, and 3,528,129.) As described in these references, a post-fiber spinning web-consolidation step (i.e., calendering) is required to produce a self-supporting web. Spunbonded webs are commercially available from, for example, AMOCO, Inc. (Napierville, IL). Non-woven webs made from large-diameter staple fibers can also be formed on carding or air-laid machines (such as that available under the trade designation "RANDO- WEBBER", Model 12BS made by Curlator Corp., East Rochester, NY), as is well known in the art (see, e.g., U.S. Pat. Nos. 4,437,271, 4,893,439, 5,030,496, and 5,082,720). A binder is normally used to produce self-supporting webs prepared by the air-laying and carding processes and is optional where the spunbond process is used. Such binders can take the form of resin systems which are applied after web formation or of binder fibers which are incorporated into the web during the air laying process. Examples of common binder fibers include adhesive-only type fibers such as those available under the trade designation "KODEL 43UD" from Eastman Chemical Products, Kingsport, TN, and bicomponent fibers, which are available in either side-by-side form (e.g., available under the trade designation "CHISSO ES FIBERS" from Chisso Corp., Osaka, Japan) or sheath-core form (e.g., available under the trade designation "MELTY FTBER TYPE 4080" from Unitika Ltd., Osaka, Japan). Application of heat and/or radiation to the web "cures" either type of binder system and consolidates the web. Generally speaking, non-woven webs comprising macrofibers have relatively large voids. Therefore, such webs have low capture efficiency of small-diameter particulate (reactive supports) which is introduced into the web. Nevertheless, particulate can be incorporated into the non- woven webs by at least four means. First, where relatively large particulate is to be used, it can be added directly to the web, which is then calendered to actually enmesh the particulate in the web (much like the PTFE webs described previously). Second, particulate can be incorporated into the primary binder system (discussed above) which is applied to the non-woven web. Curing of this binder adhesively attaches the particulate to the web. Third, a secondary binder system can be introduced into the web. Once the particulate is added to the web, the secondary binder is cured (independent of the primary system) to adhesively incorporate the particulate into the web. Fourth, where a binder fiber has been introduced into tlie web during the air laying or carding process, such a fiber can be heated above its softening temperature. This adhesively captures particulate which is introduced into the web. Of these methods involving non-PTFE macrofibers, those using a binder system are generally the most effective in capturing particulate. Adhesive levels which will promote point contact adhesion are prefened. Once the particulate (reactive supports) has been added, the loaded webs are typically further consolidated by, for example, a calendering process. This further enmeshes the particulate within the web structure. Webs comprising larger diameter fibers (i.e., fibers which average diameters between 50 micrometers and 1,000 micrometers) have relatively high flow rates because they have a relatively large mean void size. Microfibers When the fibrous web comprtses non-woven microfibers, those microfibers provide thermoplastic, melt-blown polymeric materials having active particulate dispersed therein. Prefened polymeric materials include such polyolefins as polypropylene and polyethylene, preferably further comprising a surfactant, as described in, for example, U.S. Pat. No. 4,933,229. Alternatively, surfactant can be applied to a blown microfibrous (BMF) web subsequent to web formation. Polyamide can also be used. Particulate can be incorporated into BMF webs as described in U.S. Pat. No. 3,971,373. Microfibrous webs of the present invention have average fiber diameters up to 50 micrometers, preferably from 2 micrometers to 25 micrometers, and most preferably from 3 micrometers to 10 micrometers. Because the void sizes in such webs range from 0.1 micrometer to 10 micrometers, preferably from 0.5 micrometer to 5 micrometers, flow through these webs is not as great as is flow through the macrofibrous webs described above. 4. Cast Porous Membranes Solution-cast porous membranes can be provided by methods known in the art. Such polymeric porous membranes can be, for example, polyolefin including polypropylene, polyamide, polyester, polyvinyl chloride, and polyvinyl acetate fibers. 5. Fibrous Pulps The present invention also provides a solid phase extraction sheet comprising a porous fibrous pulp, preferably a polymeric pulp, comprising a plurality of fibers that mechanically entrap active particles, and preferably a polymeric hydrocarbon binder, tlie weight ratio of particles to binder being at least 13:1 and the ratio of average uncalendered sheet thickness to effective average particle diameter being at least 125:1. Generally, the fibers that make up the porous polymeric pulp of the SPE sheet of the present invention can be any pulpable fiber (i.e., any fiber that can be made into a porous pulp). Prefened fibers are those that are stable to radiation and/or to a variety of pHs, especially very high pHs (e.g., pH = 14) and very low pHs (e.g., pH = 1). Examples include polyamide fibers and those polyolefin fibers that can be formed into a pulp including, but not limited to, polyethylene and polypropylene. Particularly prefened fibers are aromatic polyamide fibers and aramid fibers because of their stability to both radiation and highly caustic fluids. Examples of useful aromatic polyamide fibers are those fibers of the nylon family. Polyacrylic nitrile, cellulose, and glass can also be used. Combinations of pulps can be used. Examples of useful aramid fibers are those fibers sold under the trade designation "KEVLAR" from DuPont, Wilmington, DE. Such fiber ("KEVLAR") pulps are commercially available in three gTades based on the length of the fibers that make up the pulp. Regardless of the type of fiber(s) chosen to make up the pulp, the relative amount of fiber in the resulting SPE sheet (when dried) ranges from about 12.5 percent to about 30 percent (by weight), preferably from about 15 percent to 25 percent (by weight). Useful binders in the SPE sheet of the present invention are those materials that are stable over a range of pHs (especially high pHs) and that exhibit little or no interaction (i.e., chemical reaction) with either the fibers of the pulp or the particles entrapped therein. Polymeric hydrocarbon materials, originally in the form of latexes, have been found to be especially useful. Common examples of useful binders include, but are not limited to, natural rubbers, neoprene, styrene-butadiene copolymer, acrylate resins, and polyvinyl acetate. Preferred binders include neoprene and styrene-butadiene copolymers. Regardless of the type of binder used, the relative amount of binder in the resulting SPE sheet (when dried) is about 3 percent to about 7 percent, preferably about 5 percent. The preferred amount has been found to provide sheets with nearly the same physical integrity .as sheets that include about 7 percent binder while allowing for as great a particle loading as possible. It may be desirable to add a surfactant to the fibrous pulp, preferably in small amounts up to about 0.25 weight percent of the composite. In some cases the binder present in or on the particles from the spray-drying process was sufficient and no additional binder was necessary to make the SPE sheet. Because the capacity and efficiency of the SPE sheet depends on the amount of particles included therein, high particle loading is desirable. The relative amount of particles in a given SPE sheet of the present invention is preferably at least about 65 percent (by weight), more preferably at least about 70 percent (by weight), and most preferably at least about 75 percent (by weight). Additionally, the weight percentage of particles in the resulting SPE sheet is at least 13 times greater than the weight percentage of binder, preferably at least 14 times greater than the weight percentage of binder, more preferably at least 15 times greater than tlie weight percentage of binder. Regardless of the type or amount of the particles used in the SPE sheet of the present invention, they are mechanically entrapped or entangled in the fibers of the porous pulp. In other words, the particles are not covalently bonded to the fibers. Objects and advantages of this invention are further illustrated by the following examples. The particular materials and amounts thereof, as well as other conditions and details, recited in these examples should not be used to unduly limit this invention. EXAMPLES Example 1. Crystalline sihcotitanate (CST) bound with a styrene butadiene emulsion (available under tlie trade designation "GOODRITE 1800x73") The material was prepared as follows: 0.80g nonionic surfactant (available under the trade designation "TERGITOL TMN-06" from Union Carbide Corp., Danbury, CT) was dispersed in 2743g deionized water with an air mixer. To this was then added 1282.8g of ground crystalline sihcotitanate (available under the trade designation "IONSIV IE 910" from UOP, Tarrytown, NJ; 150g, 11.7% solids) with agitation. Slowly to this was added 150.9 g of a styrene butadiene emulsion (available under the trade designation "GOODRITE 1800x73" from B.F. Goodrich, BrecksviUe, OH; 39% solids, 58.5g) with stirring. This mixture was mixed for 1 hour with an air mixer. This slurry was then sonicated using an ultrasonic generator (available under the trade designation "BRANSON SONTFIER E MODULE", Model EMW50-16, with sonication module, Model WF-316, from Branson Ultrasonics Corporation, Danbury, CT) with a flow through rate of 175 mL/min. The material was then fed into the spray drier (available under the trade designation "NJRO ATOMIZER", Serial number #2402, Model 68, Order No. 093-1413-00, Niro Atomizer, Inc., Columbia, MD) at 35 mL/min. Spray drying conditions were as follows: Inlet air temperature: 196 °C Outlet Temperature: 74.5°C Slurry feed rate: 35 mL/min, 2.1 L/hour Spinning disc air motor pressure: 400 KPa, (58 psig) Cyclone Magnahelic pressure: 0.47 in H 2 0 (1.19 x 10° kg/cm 2 ) After spray drying the particle was dried in a vacuum oven for 24 hours at 130°C and 709 Ton (28 inches Mercury vacuum) to remove all moisture. Recovered dried CST/Styrene butadiene emulsion ("GOODRITE 1800x73") was observed under a scanning electron microscope (Cambridge Model S240, LEO Electromicroscopy Inc., Thomwood, NY,) to be mostly spherical in shape with some large agglomerates formed. Measurement of the particles using a particle size analyzer (available under the trade designation "HORIBA", Model LA-900, from Horiba Instruments, Inc., Irvine, CA), showed the average particle size of approximately 29.78 micrometers with 0 percent of tlie particles less than 5 micrometers. The yield of bound CST was 72 percent. Example 2. CST bound with styrene butadiene emulsion ("GOODRITE 1800x73") The material was prepared by dispersing 0.80g nonionic surfactant ("TERGITOL TMN- 06") in 1481g deionized water with an air mixer. To this was then added 1159g of ground crystalline sihcotitanate (150g, 13.0 % solids; "IONSIV IE 910") with agitation. Slowly to this was added 150.1 g styrene butadiene emulsion ("GOODRITE 1800x73"; 39% solids, 58.5g) with stirring. This mixture was mixed for 1 hour with an air mixer. The slurry was spray dried using the spray drier ("NTRO ATOMIZER", Serial number #2402) at 35 mL/min. Spray drying conditions were as follows: Inlet air temperature: 197 °C Outlet Temperature: 81.1°C Slurry feed rate: 35 mL/min, 2.1 L hour Spinning disc air motor pressure: 400 KPa, (58 psig) Cyclone Magnahelic pressure: 0.47 in H 2 0 (1.19 x 10 ~3 kg/cm 2 ) After spray drying the particle was dried in a vacuum oven for 24hours at 130°C and 709 Ton to remove all moisture. Recovered dried CST/styrene butadiene emulsion ("GOODRITE 1800x73") was observed under a scanning electron microscope (Cambridge Model S240) to be spherical in shape with some large agglomerates formed. Measurement of the particles using the ("HORIBA", Model LA-900) particle size analyzer showed the average particle size of approximately 86.8 micrometers with 4.3 percent of the particles less than 5 micrometers. The yield of bound CST was 79 percent. Example 3. CST The material, 317g crystalline sihcotitanate powder ("IONSIV IE 910"), was ground with 600 mL deionized water in a ball mill using zirconia media for 4 hours it was then reduced to 5% solids with 5740 mL deionized water. This mixture was mixed for 1 hour with a air mixer. The slurry was spray dried using the spray drier ("NTRO ATOMIZER", Serial number #2402) at 35 mL/min. Spray drying conditions were as follows: Inlet air temperature: 200 °C Outlet Temperature: 67. PC Slurry feed rate: 35 mL/min, 2.1 L/hour Spinning disc air motor pressure: 400 KPa, (58 psig) Cyclone Magnahelic pressure: 0.47 in H 2 0 (1.19 x 10 "3 kg/cm 2 ) After spray drying the particle was dried in a vacuum oven for 24 hours at 130°C and 709 Ton to remove all moisture. Measurement of the particles using the particle size analyzer ("HORIBA", Model LA-900) showed the average particle size of approximately 15 micrometers with 5.5 percent of the particles less than 5 micrometers. The yield of CST was 93 percent. Example 4. CST (comparative). Crystalline sihcotitanate ("IONSIV IE 910") as received from the supplier had an average particle size (as determined using the particle size analyze ("HORIBA", LA-900) of 0.394 micrometer with 81% of the particle less than 5 micrometers. The particles as examined by scanning electron microscope (SEM) were predominately irregular in shape and consisted of particles and agglomerates. Example 5. Sodium titanate bound with styrene butadiene emulsion ("GOODRITE 1800x73") This particle was prepared by dispersing 0.80g nonionic surfactant ("TERGITOL TMN- 06") in 2743g deionized water with an air mixer. To this was then added 1468.9g of sodium nonatitanate (AlliedSignal, Morristown, NJ; 150g, 9.9% solids) with agitation. Slowly to this was added 150.1 g sytrene butadiene emulsion ("GOODRITE 1800x73"; 39% solids, 58.5g) with stirring. This mixture was mixed for 1 hour with a air mixer. This slurry was then sonicated using the sonifier ("BRANSON SONIFIER") with a flow through rate of 175 mL/min. The material was then fed into the spray drier ("NTRO ATOMIZER", Serial number #2402) at 40 mL/min. Spray drying conditions were as follows: Inlet air temperature: 196 °C Outlet Temperature: 68.5°C Slurry feed rate: 40 mL/min, 2.4 L/hour Spinning disc air motor pressure: 380 KPa, (55.1 psig) Cyclone Magnahelic pressure: 0.47 in H 2 0 (1.19 x 10 "3 kg/cm 2 ) After spray drying the particle was dried in a vacuum oven for 24 hours at 130°C and 709 Ton to remove all moisture. Recovered dried sodium titanate/styrene butadiene emulsion ("GOODRITE 1800x73") was observed under a scanning electron microscope (Cambridge Model S240) to be spherical in shape with some agglomerates formed. Measurement of the particles using a particle size analyzer ("HORIBA", Model LA-900) showed the average particle size of approximately 41.2 micrometers with 14 percent of the particles less than 5 micrometers. The yield of bound sodium titanate was 84 percent. Example 6. Sodium titanate A slurry of sodium nonatitanate purchased from AlliedSignal was mixed for 12 hour with a low shear air mixer. The material was then fed into the spray drier ("NTRO ATOMIZER", Serial number #2402) at 40 mL/min. Spray drying conditions were as follows: Inlet air temperature: 200 °C Outlet Temperature: 73.5°C Slurry feed rate: 40 mL/min, 2.4 L/hour Spinning disc air motor pressure: 400 KPa, (58 psig) Cyclone Magnahelic pressure: 0.47 in H 2 0 (1.19 x 10 "3 kg/cm 2 ) After spray drying the particle was dned in a vacuum oven for 24 hours at 130°C and 709 Ton to remove all moisture Recovered dned sodium nonatitanate was observed under a scanning electron microscope (Cambndge Model S240) to be sphencal in shape Measurement of the particles using the particle size analyzer ("HORIBA", Model LA-900), showed the average particle size of approximately 11 8 micrometers with 8 percent of the particles less than 5 micrometers The yield of sodium titanate was 91 percent Example 7. Sodium titanate (comparative) Sodium nonatitanate (AlliedSignal, Morristown, NJ) as received from the supplier had an average particle size (as determined using the particle size analyzer ("HORIBA", Model LA-900) of 3 0 micrometers with 70% of the particle less than 5 micrometers m largest diameter The particles as examined by scanning electron microscope were predominately megular in shape with particles and agglomerates Example 8. Sodium titanate bound with a heat reactive acrylic copolymer latex (available under the trade designation "HYCAR 26138") The particle was prepared by adding 1 21 g nomomc surfactant ("TERGITOL TMN-06") into 2985g sodium nonatitanate slurry ( 200g, 6 7% solution) with an air mixer Slowly to this was added 156g reactive acrylic copolymer latex (available under the trade designation "HYCAR 26138" from B F Goodnch, Cleveland, Ohio, 78g, 50% solids) with stirnng This mixture was mixed until it was spray dned The slurry was spray dried using the spray dner ("NTRO ATOMIZER", Senal number #2402) at 45 mL/min Spray drying conditions were as follows Inlet air temperature 200 °C Outlet Temperature 72 6°C Slurry feed rate 45 mL/min, 2 7 L/hour Spuming disc air motor pressure 380 KPa, (55 psig) Cyclone Magnahelic pressure 0 43 in H 2 0 (1 09 x 10 "3 kg/cm 2 ) After spray drying the particle was dned in a vacuum oven for 24 hours at 130°C and 709 Ton to remove all moisture Recovered dned sodium nonatitanate/reactive acrylic copolymer latex ("HYCAR 26138") was observed under a scanning electron microscope (Cambndge Model S240) to be textured spheres which are mostly agglomerated together and some bonding between the particles Measurement of the particles using the particles using the particle size analyzer ("HORIBA", Model LA-900), showed the average particle size of approximately 38 7 micrometers with 0 5 percent of the particles less than 5 micrometers The yield of bound sodium titanate was 72 percent Example 9. Sodium titanate bound with a vinylidene chloride emulsion (available under the trade designation "PERMAX 801") The particle was prepared by adding 1.4 g nonionic surfactant ("TERGITOL TMN-06") into 2985g sodium nonatitanate slurry ( 200g, 6.7% solution) with an air mixer. Slowly to this was added 135 g vinylidene chloride emulsion (available under the trade designation "PERMAX 801" from B.F. Goodrich, Cleveland, OH; 78g, 57.5% solids) with stirring. This mixture was mixed until it was spray dried. The slurry was spray dried using the spray ("NTRO ATOMIZER", Serial number #2402) at 45 mL/min. Spray drying conditions were as follows: Inlet air temperature: 200 °C Outlet Temperature: 72.2°C Spinning disc air motor pressure: 400 KPa, (58 psig) Cyclone Magnahelic pressure: 0.47 in H 2 0 (1.19 x 10 "3 kg/cm 2 ) After spray drying the particle was dried in a vacuum oven for 24 hours at 130°C and 709 Torr to remove all moisture. Recovered dried sodium titanate/vinylidene chloride emulsion ("PERMAX 801") was observed under a scanning electron microscope (Cambridge Model S240) to be agglomerates of smooth spheres with some particles bonded together. Measurement of the particles using the particle size analyzer ("HORIBA", Model LA-900) showed an average particle size of approximately 48.3 micrometers with 0 percent of the particles less than 5 micrometers. The yield of bound sodium titanate was 72 percent. Example 10. Sodium titanate bound with a waterborne acrylic resin ("MAINCOTE HG-54D") The particle was prepared by adding 1.2g nonionic surfactant ("TERGITOL TMN-06 into 3333g sodium nonatitanate slurry (223g, 6.7% solution) with an air mixer. Slowly to this was added 190.24g waterborne acrylic resin (available under the trade designation "MAINCOTE HG- 54D" from Rolun and Haas, Philadelphia, PA; 78g, 41% solids) with stirrtng. This mixture was mixed until it was spray dried. The slurry was spray dried using the spray drier ("NTRO ATOMIZER, Serial number #2402) at 45 mL/min. Spray drying conditions were as follows: Inlet air temperature: 200 °C Outlet Temperature: 71.5°C Slurry feed rate: 45 mL/min, 2.7 L/hour Spinning disc air motor pressure: 390 KPa, (57 psig) Cyclone Magnahelic pressure: 0.47 in H 2 0 (1.19 x 10 "3 kg/cm 2 ) After spray drying the particle was dried in a vacuum oven for 24 hours at 130°C and 709 Ton to remove all moisture. Recovered dried sodium nonatitanate/waterborne acrylic resin ("MAΓNCOTE HG-54D") was observed under a scanning electron microscope (Cambrtdge Model S240) to be textured spheres with some agglomeration with little bonding between the spheres. Measurement of the particles using the particle size analyzer ("HORTBA", Model LA-900) showed an average particle size of approximately 36.7 micrometers with 0 percent of the particles less than 5 micrometers. The yield of bound sodium titanate was 85 percent. Example 11. Sodium titanate bound with an acrylic emulsion ("RHOPLEX MULTILOBE 200") The particle was prepared by adding 1.2g nonionic surfactant ("TERGITOL TMN-06") into 3333g sodium nonatitanate slurry (224g, 6.7% solution) with an air mixer. Slowly to this was added 145.8g acrylic emulsion ("RHOPLEX MULTILOBE 200" from Rohm and Haas, Philadelphia, PA; 78g, 53.5% solids) with stirrtng. This mixture was mixed until it was spray dried. The slurry was spray dried using the spray drier ("NTRO ATOMIZER, Serial number #2402) at 45 mL/min. Spray drying conditions were as follows: Inlet air temperature: 200 °C Outlet Temperature: 75.1°C Slurry feed rate: 45 mL/min, 2.7 L/hour Spinning disc air motor pressure: 390 KPa, (57 psig) Cyclone Magnahelic pressure: 0.43 in H 2 0 (1.09 x 10 '3 kg/cm 2 ) After spray drying the particle was dried in a vacuum oven for 24 hours at 130°C and 709 Ton to remove all moisture. Recovered dried sodium titanate/acrylic emulstion ("RHOPLEX MULTILOBE 200") was observed under a scanning electron microscope (Cambridge Model S240) to be textured spheres that are mostly agglomerated together with bonding between the spheres. Measurement of the particles using the particle size analyzer ("HORIBA", Model LA-900) showed an average particle size of approximately 34.3 micrometers with 1 percent of the particles less than 5 micrometers. The yield of bound sodium titanate was 81 percent. Example 12. Sodium titanate bound with styrene butadiene emulsion ("GOODRITE 1800x73") The particle was prepared by adding 1.92g nonionic surfactant ("TERGITOL TMN-06") into 6312g sodium titanate slurry (278g, 4.4% solution) with an air mixer. Slowly to this was added 278.5g a styrene butadiene emulsion ("GOODRITE 1800x73 ";108.7g, 39% solids) with stirring. This mixture was mixed until it was spray dried. The slurry was spray dried using the spray drier ("NTRO ATOMIZER", Serial number #2402) at 45 mL/min. Spray drying conditions were as follows: Inlet air temperature: 200 °C Outlet Temperature: 71.0°C Slurry feed rate: 45 mL/min, 2.7 L hour Spinning disc air motor pressure: 390 KPa, (57 psig) Cyclone Magnahelic pressure: 0.47 in H 2 0 (1.19 x 10 "3 kg/cm 2 ) After spray drying the particle was dried in a vacuum oven for 24 hours at 130°C and 709 Ton to remove all moisture. Recovered dried sodium nonatitanate/styrene butadiene emulsion ("GOODRΠΈ 1800x73") was observed under a scanning electron microscope (Cambridge Model S240) to be spherical in shape with some agglomerates formed. Measurement of the particles using the particle size analyzer ("HORIBA", Model LA-900) showed the average particle size of approximately 27.3 micrometers with 1.3 percent of the particles less than 5 micrometers. The yield of bound sodium titanate was 90 percent. Example 13 (comparative). A particle filled porous web was prepared from the CST particles (unprocessed particles), as described in Example 4. Into a 4 L blender (available under the trade designation "WARING BLENDOR") was added 2000 ml of hot water, 0.25 g nonionic dispersant (available under the trade designation "TAMOL 850" from Rohm and Haas Co, Philadelphia, PA); this was mixed for 30 seconds on low speed. Into the blender was then added 14.35g aramid pulp (available under the trade designation "KEVLAR 1F306"; 83.5 % solids, 12g dry weight Dupont, Wilmington, DE) and again this was mixed for 30 seconds. To this mixture was then added 169.2g CST particles from Example 4 (26.6% solids, 45g dry weight) and again mixed for 30 seconds. Next, 7.69g styrene butadiene emulsion ("GOODRITE 1800x73") was added (39% solids, 3 g dry weight), and again mixed for 30 seconds. Then 20 g of 25% alum (aluminum sulfate in water) was added with mixing on low for an additional minute, to this was then added 1.2 g of an acrylamide modified cationic copolymer (1% solution of a material available under the trade designation "NALCO 7530" from Nalco Chemical Co., Chicago, IL) with mixing continuing for 4 seconds. The mixture was then poured into a sheet mold (Williams Apparatus Co., Watertown, NY) equipped with a 413 cm 2 porous screen having pores size 0.171 mm (80 mesh) at the bottom and allowed to drain, drain time was 135 seconds. The resulting wet sheet was pressed in a pneumatic press (Air Hydraulics Inc., Jackson, MI) at approximately 5 1 KPa for 5 minutes to remove additional water. Finally the porous web was dried on a handsheet dryer (Williams Apparatus Co.) for 90 minutes at 100°C. Tensile strength was determined using an electronic tensile tester (available under the trade designation "THWING ALBERT MODEL QCII-XS" from the Thwing Albert Instrument Company, Philadelphia, PA) equipped with a 227 Kg load cell at 10% load range. The tensile strength was determined to be 6130 KPa with 133% elongation without break. Example 14. A particle filled porous web was prepared as described in Example 13 using CST/styrene butadiene emulsion ("GOODRITE 1800x73") particles from Example 1. The drain time was 40 seconds. The tensile strength was determined with the electronic tensile tester ("THWING ALBERT MODEL QCII-XS") to be 797psig (5495 KPa) with 134% elongation without break. Example 15. A particle filled porous web was prepared as described in Example 13 using CST particles from Example 2. The drain time was 135 seconds. The tensile strength was determined with the electronic tensile tester ("THWING ALBERT MODEL QCII-XS") to be 697 psig (4805 KPa) with 95% elongation without break. Preferably, the CST particles are combined with a binder (see Example 14) to optimize the -drain time of the web. Example 16. A particle filled porous web was prepared from the CST/styrene butadiene emulsion particles ("GOODRTTE 1800x73") from Example 2. Into a 4 L blender ("WARING BLENDOR") was added 2000 ml of hot water and 0.25 g nonionic dispersant ("TAMOL 850") which was mixed for 30 seconds on low. Into the blender was then added 14.35g of aramid pulp ("KEVLAR 1F306"; 83.5 % solids, 12g dry weight) and again this was mixed for 30 seconds. To this mixture was then added 45g CST/styrene butadiene emulsion ("GOODRTTE 1800x73") particles from Example 2 (100% solids) and again mixed for 30 seconds. No additional binder, other than that in or on the particles, was used. The mixture was then poured into a sheet mold (Williams Apparatus Company) equipped with a 413 cm 2 porous screen having pores size 0.171 mm (80 mesh) at the bottom and allowed to drain, drain time was 25 seconds. The resulting wet sheet was pressed in an pneumatic press (Air Hydraulics) at approximately 551 KPa for 5 minutes to remove additional water. Finally the porous web was dried on a handsheet dryer (Williams Apparatus Company) for 90 minutes at 100°C. The strength tensile was determined with the electronic tensile tester ("THWING ALBERT MODEL QCII-XS") to be 129 psig (889 KPa). Example 17 (comparative). A particle filled porous web was prepared as described in Example 13 from the sodium titanate particles described in Example 7. The drain time was 720 seconds. The tensile strength was determined with the electronic tensile tester ("THWING ALBERT MODEL QCII-XS") to be 1283 psig (8845 KPa) with 159% elongation without break. Example 18. A particle filled porous web was prepared as described in Example 13 from the sodium titanate particles described in Example 6. The drain time was 20 seconds. The tensile strength was determined with the electronic tensile tester ("THWING ALBERT MODEL QCII-XS") to be 110 psig (758 KPa). Example 19. A particle filled porous web was prepared as described in Example 13 from the sodium titanate/styrene butadiene emulsion ("GOODRTTE 1800x73") particles described in Example 5. The drain time was 35 seconds. The tensile was determined with the electronic tensile tester ("THWING ALBERT MODEL QCII-XS") to be 910 psig (6247 KPa) with 136% elongation without break. Example 20. A particle filled porous web was prepared using the sodium titanate/styrene butadiene emulsion ("GOODRITE 1800x73") particles described in Example 5. Into a 4 L blender ("WARING BLENDOR") was added 2000 ml of hot water and 0.25 g nonionic dispersant ("TAMOL 850") which was mixed for 30 seconds on low. Into the blender was then added 14.35g of aramid pulp ("KEVLAR 1F306") (83.5 % solids, 12g dry weight) and again this was mixed for 30 seconds. To this mixture was then added 45 g sodium titanate/styrene butadiene emulsion ("GOODRITE 1800x73") particle (100% solids) and again mixed for 30 seconds. No additional binder, other than that in or on the particles, was used. The mixture was then poured into a sheet mold (Williams Apparatus Co.) equipped with a 413 cm 2 porous screen having pores size 0.171 mm (80 mesh) at the bottom and allowed to drain, drain time was 15seconds. The resulting wet sheet was pressed in an pneumatic press (Air Hydraulics) at approximately 551 KPa for 5 minutes to remove additional water. Finally the porous web was dried on a handsheet dryer mold (Williams Apparatus Co.) for 90 minutes at 100°C. The tensile strength was determined with the electronic tensile tester ("THWING ALBERT MODEL QCII-XS") to be 59 psig (406 KPa). Example 21. A particle filled porous web was prepared using the sodium titanate/styrene butadiene emulsion ("GOODRITE 1800x73") particles described in Example 5. Into a 4 L blender ("WARING BLENDOR") was added 2000 ml of hot water and 0.25 g nonionic dispersant ("TAMOL 850") which was mixed for 30 seconds on low. Into the blender was then added 14.35g of aramid pulp ("KEVLAR 1F306") (83.5 % solids, 12g dry weight) and again this was mixed for 30 seconds. To this mixture was then added 45g sodium titanate/styrene butadiene emulsion ("GOODRITE 1800x73") particle (100% solids) and again mixed for 60 seconds. No additional binder, other than that in or on the particles, was used. To this was then added 20 g of 25% alum (aluminum sulfate in water useful as a coelescing) and mixed for 30 seconds. The mixture was then poured into a sheet mold (Williams Apparatus Co.) equipped with a 413 cm 2 porous screen having pores size 0.171 mm (80 mesh) at the bottom and allowed to drain, drain time was 40 seconds. The resulting wet sheet was pressed in a pneumatic press (Air Hydraulics) at approximately 551 KPa for 5 minutes to remove additional water. Finally the porous web was dried on a handsheet dryer (Williams Apparatus Co.) for 90 minutes at 100°C. The tensile strength was determined with the electronic tensile tester ("THWING ALBERT MODEL QCII- XS") to be 220 psig (1516 KPa) with 153% elongation without break. Example 22. A particle filled porous web was prepared as described in Example 13 from the sodium titanate/reactive acrylic copolymer latex ("HYCAR 26138") particles described in Example 8. The drain time was 180 seconds. The tensile strength was determined with the electronic tensile tester ("THWING ALBERT MODEL QCII-XS") to be 592 psig (4081 KPa) with 98% elongation without break. Example 23. A particle filled porous web was prepared as described in Example 13 from the sodium titanate/vinylidene cliloride emulsion ("PERMAX 801") particles described in Example 9. The drain time was 40 seconds. The tensile strength was determined with the electronic tensile tester ("THWTNG ALBERT MODEL QCII-XS") to be 504 psig (3475 KPa) with 103% elongation without break. Example 24. A particle filled porous web was prepared as described in Example 13 from the sodium titanate/waterborne acrylic resin ("MAINCOTE HG-54D") particles described in Example 10. The drain time was 180 seconds. The tensile strength was determined with the electronic tensile tester ("THWING ALBERT MODEL QCII-XS") to be 797 psig (5500 KPa) with 83% elongation without break. Example 25. A particle filled porous web was prepared as described in Example 13 from the sodium titanate/acrylic emulsion ("RHOPLEX MULTILOBE 200") particles described in Example 11. The drain time was 90 seconds. The tensile strength was determined with tlie electronic tensile tester ("TH ING ALBERT MODEL QCII-XS") to be 890 psig (6136 KPa) with 99% elongation without break. Example 26. A particle filled porous web was prepared as described in Example 13 from the sodium titanate/styrene butadiene emulsion ("GOODRITE 1800x73") particles described in Example 12. The drain time was 35 seconds. Example 27. Into a 8.3 cm by 3.1 cm diameter tube capped at one end with a rubber stopper was placed approximately 50 g of sodium titanate/ styrene butadiene emulsion ("GOODRITE 1800x73") particles from Example 12, which had not been vacuum dried. The particle was compacted as much as possible using hand pressure and then placed in the vacuum oven and dried at 130°C and 709 Ton for 72 hours. When the matertal was cooled and removed from the oven, the material retained the cylindrical shape and did stick together to form a sponge-like mass. The tube was then used as a column with the cylindrical dried particle being used in the column for separation. The cylindrical dried particles were preconditioned with 0.1 M NaOH/5M NaN0 3 with a flow rate of 30 mL/min for 30 min. Deionized water was then passed through the column at 30 mL for 10 min. The TAN matrix was then passed through the column at 30 mL/min. for 4 hours. This column was very efficient in removing Ca, Mg, and Sr ions from the TAN matrix: pressure was about 7 KPa. There were no detectable Ca, Sr, or Mg ions in the effluent. It was unexpected that the small average particle size (27 micrometers) resulted in low back pressure without channeling and with excellent separation. Example 28 Capacity data was obtained by running I determination using two different solutions: 1) TAN matrix with 3 ppm Sr, 545 ppm Ca, and 195 ppm Mg; and 2) a solution of 55 ppm Sr in 0.1 molar sodium hydroxide and 5 molar sodium nitrate. Data are as follows: Table 1 Tan Matrtx (2.5 ppm Sr) Capacities determined using TAN Matrix as in Table 1 and Table 2 show that the capacity of the spray dried particles as evaluated by Ka determination did not deviate significantly from the starting material. Table 2 Capacity and Ka determination with TAN matrix (4 ppm Sr) Table 3 Capacity and Ka determination with 0.1 M NaOH/5 M NaN0 3 (54 ppm Sr) ♦ comparative sample as prepared in W097/14652, Example 21. Table 4 Capacity and K determination with 0.1 M NaOH/5 M NaN0 3 (57 ppm Sr) The data of Tables 3 and 4 show that sodium titanate particles with binders according to the present invention retained more sorptive capacity towards strontium than comparative sodium titanate after processing particles with cellulose acetate as binder as disclosed in W097/14652. (W097/14652 discloses a multi-step process to increase porosity and % retention from 1.8 to 9.5.) The data of Table 4 also show an increase in sorptive capacity for the spray dried material without binder (Example 6) compared with sodium titantate that has not been spray dried. Example 29. Tensile strengths were determined both wet and dry. The wet tensile was evaluated in two ways. The first evaluation involved soaking the sample for 7 days in deionized water, removing the sample from the water and blotting the surface dry prior to testing. The second wet tensile evaluation involved soaking the sample for 7 days in NCAW (neutralized cunent acid waste from Hanford, Washington, see formulation below). The sample was removed from the NCAW and rinsed with deionized water twice; the surface was then blotted dry prior to testing. The tensile strength was determined using the electronic tensile tester ("THWING ALBERT MODEL QCII-XS") equipped with a 227 Kg load cell at 10% load range. Table 5 Tensile Strengths Dry versus Wet The wet tensile strength, as expected, was lower than the dry tensile strength. The wet tensile strengths were very similar for both the deionized and NCAW samples. The most significant difference was for tlie sodium titanate comparative which had a difference of 64% between the two wet tensile strengths The difference for the sodium titanate/styrene butadiene emulsion ("GOODRITE 1800 x 73") samples were both 91% It is important to note that the retained strength even m NCAW, was sufficient for the matenal to perform as a usable SPE disk or cartndge NCAW Waste Simulant Composition NCAW (Neutralized cunent acid waste) simulant is considered to be representative of Hanford (Washington) tank wastes In actual tanks the concentration of Cs ranges from 1 OE-2 to 1 OE-5 M as Cesium nitrate Various modifications and alterations of this invention will become apparent to those skilled m the art without departing from the scope and intent of this invention, and it should be understood that this invention is not to be unduly limited to tlie illustrative embodiments set forth herein

Claims: We claim: 1. A method for removing metal ions from solution comprising the steps of: a) providing titanate particles by spray-drying a solution or slurry comprtsing titanate particles, optionally in the presence of an organic binder free of cellulose functionality, to produce monodisperse, substantially sphencal sorbent titanate particles in a yield of at least 70 percent of theoretical yield and having a particle size in the range of 1 to 500 micrometers, said titanate sorbents being active towards ions of metals in Periodic Table (CAS version) Groups IA, IIA, IB, IIB, IIIB, and VIII, and b) introducing the spray-dried titanate particles into a metal ion containing solution wherein the metal ions are as mentioned above, equilibrated with the solution, and then separated from the sorbed and/or exchange metal ions. 2. The method according to claim 1 wherein said titanate sorbents are selected from the class consisting of crystalline silicotitanates and alkali metal titanates. 3. The method according to claim 1 wherein said alkali metal titanate is sodium titanate. 4. The method according to claim 1 wherein said solution or slurry further comprises said binder. 5. The method according to claim 4 wherein said binder is an organic binder selected from the group consisting of olefin polymers and acrylate (co)polymers. 6. The method according to claim 5 wherein said binder is styrene butadiene copolymer. 7. The method according to claim 5 wherein said binder is selected from the group consisting of vinylidene halide emulsion, an acrylate copolymer, an acrylic colloidal dispersion, and a styrene acrylic solution. 8. The method according to claim 1 wherein said sorbent titanate particles are in a loose or agglomerated form. 9. The method according to claim 1 wherein said titanate particles are incorporated in a porous matrix, membrane or web. 10. The method according to claim 1 wherein said spray-drying comprises the steps of: a) atomizing said titanate, b) removing moisture from said atomized titanate, and c) separation of the dry titanate. 11. The method according to claim 1 wherein said solution or slurry comprises at least one of aqueous and organic liquids. 12. The method according to claim lwherein said spherical particles have a size average in the range of 1 to 100 micrometers. 13. The method according to claim 1 wherein said particles are in a column. 14. The method according to claim 1 wherein said spray-dried particles have been compressed into a porous, shaped article. 15. The method according to claim 1 wherein said yield of spray-dried titanates is at least 80 percent of theoretical yield. 16. The method according to claim 1 wherein said metals are selected from the group consisting of Sr, Cs, Am, Pu. and U. 17. A composite article comprising a non-woven web, matrix or membrane having incorported therein monodisperse, substantially spherical titanate particles having an average particle size in tlie range of 1 to 100 micrometers. 18. The composite article according to claim 17 wherein said particles have an average size in the range of 5 to 20 micrometers. 19. The composite article according to claim 17 wherein said particles have an average size in the range of 1 to 60 micrometers. 20. The composite article according to claim 17 wherein said particles further comprise a binder. 21. The composite article according to claim 17 wherein said web. matrix, or membrane is incorporated in an SPE cartridge. 22. The composite article according to claim 20 wherein said binder is a polymer of olefin or acrylate monomers. 23. The composite article according to claim 17 wherein said titanate particles are selected from the group consisting of crystalline sihcotitanate and alkali metal titanate. 24. The composite article according to claim 17 wherein said web, matrix, or membrane is a fibrous web, a fibrous pulp, a cast membrane, or fibrillated polytetrafluoroethylene. 25. The composite article according to claim 17 which is present in a metal ion containing solution wherein said metal ions are selected from Periodic Table Groups IA, IIA, IB, IIB, IIIB, and VIII.

Inventors: LUNDQUIST SUSAN H, WHITE LLOYD R, LUNDQUIST, SUSAN, H., WHITE, LLOYD, R.
Applicants: MINNESOTA MINING & MFG, MINNESOTA MINING AND MANUFACTURING COMPANY
Application year: 1998
Main classification: B01J20
IPC codes: B01D15, B01J20, D21H13, D21H17, D21H27, G21F9