Calcium silicate particles for phosphate reduction

Abstract

The invention relates to calcium silicate particles comprising Tobermorite and characterized with a Ca / Si molar ratio of less than 0.7, a BET surface area greater than 50 m2 / g, and CaO content of between 10 and 50 wt%. The invention further relates to the production thereof, and the use of calcium silicate particles for the removal of phosphate.

Description

[0001] CALCIUM SILICATE PARTICLES FOR PHOSPHATE REDUCTION

[0002] TECHNICAL FIELD

[0003] The present disclosure relates generally to calcium silicate particles, production thereof, and the use of calcium silicate particles for the removal of phosphate.

[0004] BACKGROUND OF THE INVENTION

[0005] Excess phosphate in both fresh and salt water is the leading cause of eutrophication. Eutrophication is the nutrient-induced increase in phytoplankton in water that leads to algae blooms, toxic blooms (red tide), tainted drinking water, and hypoxia. Hypoxia occurs when dense algal blooms eventually die and microbial decomposition severely depletes dissolved oxygen, creating a hypoxic or anoxic ‘dead zone' lacking sufficient oxygen to support most organisms. The leading cause of excess phosphate in water is run- off from farming due to fertilizer usage and livestock waste. Other sources include phosphate mining and human waste. The typical level of phosphorus in an algae bloom is between 100 and 500 ppb. Greater than 100 ppb may trigger periodic blooms and long-term eutrophication will usually be prevented if total phosphorus levels are below 100 ppb. Thus, an effective treatment that could reduce phosphate / phosphorous levels in water would be beneficial.

[0006] In humans, excess phosphate in the body is the result of chronic kidney disease / renal failure and can lead to hypocalcemia. Treatment of hyperphosphatemia (excess phosphate in the body) includes reduction in dietary intake of phosphate, inhibition of intestinal phosphate by absorption with phosphate binders, and removal of phosphate with dialysis. The reduction of dietary phosphate has low patient adherence as phosphate rich foods including meats, beans, whole grains, soy, nuts, and cola beverages are difficult for patients to remove from the diet. One goal in treating people with end stage renal disease (ESRD) is to prevent phosphorus in the foods they eat from being absorbed into their bloodstream. To help with this, doctors prescribe medicines called phosphorus / phosphate binders, which are taken with meals and snacks. Binders act as sponges that soak up phosphorus typically as phosphate. So instead of going into the bloodstream, the phosphorus stays in the stomach and then passes through the gastrointestinal system. Key to the performance is rapid phosphate binding. Common medicines used for this purpose include polyamine polymers such as Regegel / Sevelamer, heavy metal complexes such as lanthanum chloride, lanthanum carbonate, and calcium carbonate, and calcium acetate. A phosphate binder with faster binding, higher efficacy, lower dosing, and less side effects would be beneficial.

[0007] Calcium silicates for phosphate binding have been reported in the literature. In Ceramics International 39(2013) 1385-1391 , the use of porous calcium silicates with surface areas between 11.91 - 121 .03 m2 / g and Ca / Si molar ratios equal to or greater than 0.60 were reported to be effective in removing phosphate. These calcium silicates were reported to have structures made up of Jennite CagSi6Oi8(OH)6.8H2O (Ca / Si molar ratio of 1 .5) and Xonotlite CaeSi6Oi7(OH2) (Ca / Si ratio of 1) and free silica and Ca(OH)2. In this reference, tobermorite Ca5SieOi6(OH)2.4 H2O (Ca / Si ratio of 0.83) with a surface area of 49.85 m2 / g was also found to remove phosphates from water. In US patent 10,246,346, a calcium silicate containing a Ca / Si molar ratio of between 1 and 3 and a crystalline structure containing Portlandite, Halite, Calcite, Larnite and Calcio-olivine was found to be effective in removing phosphate.

[0008] In Water Research 47 (2013) 2251-2259, a calcium silicate with a Ca / Si molar ratio of greater than 0.8 is utilized to remove phosphate from water.

[0009] Nevertheless, there remains the need for improving the efficiency and selectivity of calcium silicate particles for the removal of phosphates from aqueous solutions, in particular water (both fresh and salt) and water-based solutions. Although calcium silicates have been reported in the literature to be capable of removing phosphates from water, the key performance parameters have not been identified and targeted.

[0010] SUMMARY OF THE INVENTION

[0011] The present invention relates to calcium silicate particles comprising Tobermorite and having i) a Ca / Si molar ratio of less than 0.7, ii) BET surface area greater than 50 m2 / g, and iii) CaO content of between 10 and 50 wt%.

[0012] The BET surface area is preferably greater than 75 m2 / g, more preferably greater than 100 m2 / g, most preferably greater than 150 m2 / g.

[0013] The BET surface area is determined according to ISO 9277 using the BET nitrogen adsorption method of Brunaur et al., J. Am. Chem. Soc., 60, 309 (1938).

[0014] The BJH pore volume is preferably greater than 0.5 cc / g, more preferably greater than 0.8 cc / g, and most preferably greater than 1.0 cc / g.

[0015] The BJH pore volume is determined according to ISO 15901-2 as BJH Desorption cumulative volume of pores between 17 angstrom and 3,000 angstrom diameter , Halsey, G. D., J. Chem. Phys. (1948), 16, pp. 931.

[0016] The CaO content may be between 15 and 40 wt% or between 20 and 35 wt%.

[0017] The particles advantageously have a size of from 1 to 100 microns. The calcium silicate particles may also have been granulated to a size of from 100 and 5000 microns.

[0018] Preferably the calcium silicate particles have a performance factor of greater than 1200, more preferably greater than 2000, even more preferably greater than 3000. The present invention also related to a composition comprising the calcium silicate particles. For certain application the composition may be a pharmaceutical composition.

[0019] According to the present invention, the calcium silicate particles or any composition thereof can be used to remove phosphate from an aqueous solution stream.

[0020] Preferably the aqueous solution is selected from fresh water sources, brine and salt water sources, golf course ponds, manufacturing effluents, waste streams, agricultural run-off, retention ponds, animal farm run-off, animal park run-off, streams, lakes, canals, reservoirs, residential and commercial storm-water run-off, wastewater treatment plant discharge, food processing discharge, industrial wastewater discharge, residential wastewater discharge, meat processing residuals, toilet water, and aquarium water.

[0021] The calcium silicate particles or any composition thereof can be used to remove phosphate from an aqueous waste stream, preferably an aqueous waste stream generated from the precipitation of sodium silicate derived from rice husk ash or another silica containing biogenic material. Phosphate is often found as an impurity in silicate derived from biogenic sources.

[0022] The present invention also relates to calcium silicate particles or any composition thereof for use in removing phosphate from a human or animal patient.

[0023] The patient may suffer from hyperphosphatemia.

[0024] According to the present invention, calcium silicate particles or any composition thereof can be used as food supplement.

[0025] The present invention further relates to a process for the preparation of calcium silicate particles by reacting precipitated silica or silica gel with lime (CaO / CaOH) in an aqueous solution. Preferably the reaction is performed in an agitated vessel capable of maintaining the temperature between 30 and 100 °C, preferably at a temperature of 30°C -100°C, more preferably 60-95 °C.

[0026] The present invention further relates to a method for reducing phosphate from an aqueous solution, the method comprising contacting the calcium silicate particles or any composition thereof with an aqueous solution containing phosphate in a batch or column flow through system.

[0027] BRIEF DESCRIPTION OF THE FIGURES

[0028] FIG. 1 : XRD of amorphous silica used in reaction with calcium hydroxide to form calcium silicate particles.

[0029] FIG. 2: XRD of the material produced in Example 1 (primarily Tobermorite).

[0030] FIG. 3: XRD of the material produced in Example 4 (primarily Tobermorite).

[0031] FIG. 4: XRD of the material produced in Comparative Example 1 (Wollastonite).

[0032] FIG. 5: XRD of the material produced in Comparative Example 3 (low level of Tobermorite and amorphous silica). FIG. 6: XRD of the material produced in Comparative Example 2 (low level of Tobermorite and amorphous silica).

[0033] FIG. 7: XRD of the material produced in Comparative Example 4.

[0034] FIG. 8: SEM image of Example 4.

[0035] FIG. 9: Phosphate Removal as function of sodium sulfate concentration with the material produced in Example 4.

[0036] FIG. 10: Phosphate removal from 4 wt% waste sodium sulfate stream using the granulated material according to Example 4 granule in a column at various flow rates.

[0037] DEFINITIONS

[0038] Unless otherwise indicated, the following definitions are applicable to this disclosure. If a term is used in this disclosure but is not specifically defined herein, the definition from the IUPAC Compendium of Chemical Terminology, 2nd Ed (1997), can be applied, as long as that definition does not conflict with any other disclosure or definition applied herein, or render indefinite or non-enabled any claim to which that definition is applied. To the extent that any definition or usage provided by any document incorporated herein by reference conflicts with the definition or usage provided herein, the definition or usage provided herein prevails.

[0039] An amorphous material is a type of substance that lacks a definite crystalline structure. A non-crystalline or amorphous material is one where the measured X-ray powder diffraction (XRPD) pattern is essentially continuous in appearance. A disordered structure is a crystalline material that lacks long range order and appears broadened in XRD patterns. An essentially crystalline structure can also have amorphous, and disordered and crystalline patterns in the XRD.

[0040] Tobermorite is a calcium silicate hydrate mineral with chemical formula: Ca5Si6O16(OH)2-4H2O or Ca5Si6(O, OH)18-5H2O.

[0041] All publications and patents mentioned herein are incorporated herein by reference for the purpose of describing and disclosing, for example, the constructs and methodologies that are described in the publications, which might be used in connection with the presently described invention.

[0042] DETAILED DESCRIPTION OF THE INVENTION

[0043] Calcium Silicate Particles

[0044] Calcium silicate particles with improved phosphate removal comprise Tobermorite and have the following characteristics: i) a molar ratio Ca / Si of less than 0.7, ii) a BET surface area of greater than 50 m2 / g, iii) a wt% CaO of between 10 and 50wt%.

[0045] The BET surface area of the calcium silicate particles of the present invention is preferably greater than 75 m2 / g, more preferably greater than 100 m2 / g, most preferably greater than 150 m2 / g. The BET surface area of the calcium silicate of the present invention is preferably lower than 400 m2 / g, more preferably lower than 300 m2 / g, most preferably lower than 260 m2 / g.

[0046] According to an aspect of the invention, the BET surface area is between 100 and 300 m2 / g or between 150 and 260 m2 / g.

[0047] The BJH pore volume of the present invention is preferably greater than 0.5 cc / g, more preferably greater than 0.8 cc / g, and most preferably greater than 1.0 cc / g.

[0048] The CaO content of the calcium silicate particles of the present invention is preferably between 15 and 40wt%, more preferably between 20 and 35wt%.

[0049] The calcium silicate particles have a molar ratio Ca / Si lower than about 0.7. For example, the calcium silicate particles may be about 0.65 or lower, about 0.6 or lower.

[0050] In some aspects of the present invention, the calcium silicate particles have a molar ratio Ca / Si between 0.1 and 0.7. In other cases, the calcium silicate particles have a molar ratio Ca / Si between 0.3 and 0.7.

[0051] In some aspects of the present invention, the calcium silicate particles, comprising Tobermorite and having a molar ratio Ca / Si of less than 0.7 and both high surface area and high calcium oxide content. The performance factor such calcium silicate particles can be represented by multiplying the surface area (BET) by the percent calcium oxide (% CaO x Surface Area).

[0052] The calcium silicate preferably has a pH between 8.0 and 12.0, preferably between 8.5 and 11.0, more preferably between 9.0 and 10.5.

[0053] The calcium silicate particles may be crystalline, can be amorphous, can be synthetic, or a combination thereof. Moreover, the inventive calcium silicate can comprise precipitated calcium silicate.

[0054] The calcium silicate particles may have a size from 1 to 100 microns.

[0055] The calcium silicate particles of any of the preceding aspects / embodiments, wherein the particles have been granulated to a size ranging from 100 and 5000 microns.

[0056] The calcium silicate particles may also be granulated via know processes to make particles between 100 and 5000 microns preferably between 200 and 2000 microns, more preferably between 300 and 1500 microns.

[0057] In some aspects of the present invention, the calcium silicate particles have phosphate binding initial rate (moles / liter-sec) preferably greater than 0.005, preferably greater than 0.0070 or greater than 0.0080.

[0058] In some aspects of the present invention, the calcium silicate particles preferably have a performance factor for removing phosphate at an efficient rate of greater than 1200, more preferably greater than 2000, even more preferably greater than 3000. Preferably the calcium silicate particle has a selectivity coefficient of phosphate over sulfate of greater than 700 or 800.

[0059] Processes For Producing Calcium Silicate

[0060] In one aspect of the present invention, the calcium silicate particles are prepared by the reaction of a precipitated silica with lime (CaO / CaOH) in an aqueous solution. The precipitated silica can be used either in the dry form or used wet after a washing step in a typical manufacturing process. The reaction could be done in an agitated vessel capable of maintaining the desired temperature between 30 and 100 °C. The calcium hydroxide could be a slurry with 5 to 20 % solid content of calcium hydroxide, more preferably 10-18%. The calcium hydroxide could be a slurry in water.

[0061] The precipitated silica has preferably a surface area ranges from 1 to 1000 m2 / g, a particle size ranging from 1 to 500 microns and a pore volume ranging from 0.5 to 2.0 cc / g.

[0062] The stirring in process step could be done at a temperature between 30°C -100°C (reacting step) more preferably 60-95 °C.

[0063] The drying of the calcium silicate could be done in a spray dryer or flash dryer at temperatures sufficient to evaporate the water from the solids.

[0064] Calcium silicate particle size control can be achieved by either using a milled precipitated silica or by milling the final calcium silicate material. Typical particle size ranges useful in the invention are 1 to 100 microns, The resulting calcium silicate particles can also be granulated via know processes to make particles between 100 and 5000 microns.

[0065] Phosphate Removal

[0066] The calcium silicate particles of the invention can be used for phosphate removal from aqueous solutions.

[0067] Aqueous solutions include but are not limited to fresh water sources, brine and salt water sources, golf course ponds, manufacturing effluents including waste streams from phosphate mining ponds and the precipitation of sodium silicate derived from rice husk ash. Other aqueous solutions contemplated for applications of the invention include agricultural run-off, retention ponds, animal farm run-off, animal park run-off, streams, lakes, canals, reservoirs, residential and commercial storm-water run-off, wastewater treatment plant discharge, food processing discharge, industrial wastewater discharge, residential wastewater discharge, meat processing residuals, toilet water, and aquarium water.

[0068] The calcium silicate particles of the present invention react with phosphates to form insoluble calcium silicate phosphate complexes. This effectively removes the phosphate from the soluble solution phase into a solid phase where it is no longer available to be used as a nutrient to promote eutrophication. In some cases, the calcium silicate phosphate product can be recovered and utilized as a slow-release fertilizer to supply calcium, phosphate and silica to plants to promote growth. The ability to remove phosphate selectively with a background of other anions such as sulfate and chloride is also a key ability of the inventive calcium silicates.

[0069] The calcium silicate particles and any of the compositions disclosed herein can be used in methods of treatment for reducing phosphate from an aqueous fluid. The method may comprise contacting any of the calcium silicate particles (or any of the formulations / compositions) disclosed herein with an aqueous fluid containing phosphate. The process can involve contacting phosphate containing streams with the calcium silicate in a batch or column flow through system. Any suitable amount of the calcium silicate particles (or compositions) can be used, and for any appropriate period of time.

[0070] Removal of phosphorus can occur in different ways. For example, a calcium silicate of the present invention is contacted with an aqueous solution containing phosphates in a reaction chamber that is designed to speed the rate of contact using centrifugal force, for example a Taylor vortex system operated under laminar flow conditions.

[0071] In a different embodiment, the calcium silicate is contacted with an aqueous solution containing phosphates as a dry feed or slurry mix into the final DAF or process stream. In another embodiment, contact occurs by way of an AdEdge™ Filtration System, e.g. in case of high concentration removal.

[0072] Increasingly important in wastewater treatment plants is the phosphate recovery from wastewater and sludge, since phosphorus is an important and finite raw material. Accordingly, after removal of phosphorus, the calcium silicates containing removed phosphate of the present invention can be recovered and used as source of phosphorus, e.g. recycled as fertilizers.

[0073] The herein disclosed calcium silicate particles can also be used for phosphate removal from the human or animal body.

[0074] The method can comprise contacting any of the calcium silicate particles (or any of the compositions) disclosed herein with an aqueous fluid containing phosphate in the human or animal stomach. Any suitable amount of the calcium silicate particles (or compositions) can be used, and for any appropriate period of time. Preferably the daily dosage is greater than 500 mg, more preferably greater than 1000 mg and most preferably greater than 1500 mg.

[0075] If used for the treatment of hyperphosphatemia, the calcium silicate particles of the present invention can be used as phosphate binders. A typical phosphate level for adults is between 2.8 and 4.5 mg / dL, whereas a typical phosphate level for children is between 4.0 to 7.0 mg / dL. In case of hyperphosphatemia different phosphate binders can be prescribed by healthcare providers. When used as phosphate binders, the calcium silicate particles hereby disclosed can be administered via the oral route as chewable compositions or as powder compositions to be dissolved / diluted in water or added to food before use.

[0076] Pharmaceutical Compositions

[0077] This invention relates further to pharmaceutical compositions comprising the calcium silicate particles of the invention. The composition may be chewable tablets, tablets, mini-tablets (micro-tablets) formed with and without prior processing like wet granulation or dry granulation (e.g roller compaction), granulate and tablets especially formed by direct compression of the calcium silicate particles.

[0078] The compositions may include stabilization agents, or any pharmaceutical excipient known in the art.

[0079] The invention further relates to a process for preparing the pharmaceutical administration form, e.g. by blending the active ingredient and specific excipients into the new compositions and then compressing or directly compressing the compositions into the final form (e.g. direct compressed tablets) or the filling and use in e.g. dispensers or sachets.

[0080] METHOD OF MEASUREMENTS

[0081] The BET surface areas disclosed herein were determined according to ISO 9277 on a Micromeritics TriStar II 3020 V1 .03 using, respectively, the BET nitrogen adsorption method of Brunaur et al., J. Am. Chem. Soc., 60, 309 (1938). The BJH pore volume was determined according to ISO 15901-2 as BJH Desorption cumulative volume of pores between 17 angstrom and 3,000 angstrom diameter, Halsey, G. D., J. Chem. Phys. (1948), 16, pp. 931 , and such techniques are well known to those skilled in the art.

[0082] The pH values disclosed herein (5% pH) were determined in an aqueous system containing 5 wt. % solids in deionized water using a pH meter.

[0083] Scanning electron microscopy images were taken on a Zeiss Sigma instrument equipped with a field emission detector. Samples were dispersed in methanol and then the methanol slurry was dried on an aluminum sample holder. The dry samples were sputter coated with platinum to minimize charging before images were taken.

[0084] The d50 median particle size refers to the particle size for which 50% of the sample has a smaller size and 50% of the sample has a larger size. Median particle size (d50), mean particle size (average), and d95 were determined via the laser diffraction method using a Horiba LA 300 instrument. Dry particles were submitted to the instrument for analysis.

[0085] XRD was conducted on a Brucker ASX D2 Phaser with a start at 15 deg 2 theta and a stop at 70 deg 2 theta using a 0.03 deg step. Time of step was 0.3 sec and rotation of 15 rpm. DIFFRAC.EVA software was used to identify different crystal structures present.

[0086] The %CaO (calcium concentrations) were determined by the following method. Between 0.4000g - 1 .0000g of silica was wet with a few drops of deionized water in a 50 mL beaker. 10 ml of perchloric acid (72 %) was added and the beaker was slowly heated on a hot plate in a fume hood. As the beaker was heated, dense white fumes evolved. A watch glass was put to cover the beaker and left on the hot plate with occasional swirling for 2 hours. After cooling, the contents of the beaker was gravimetrically filtered to a 2500 ml volumetric flask. The beaker was then policed with hot deionized water and the washings were also added to the filter setup. Filter paper was washed with approximately 200 ml of hot deionized water and was added to the volumetric flask. After cooling, 5.00 ml of a 100 ppm scandium internal standard solution was added and the volumetric flask was filled to the mark with deionized water. The concentrations of the metals in the solution were then determined by ICP-OES. CaO wt% is reported as based on a dry basis after subtracting loss of ignition (LOI). For example, a calcium silicate was determined to be composed of 29 wt% CaO, 54wt % SiO2 and a loss on ignition (LOI) of 16 wt%. After adjusting for LOI, the calcium silicate is reported to be 34.5 wt% CaO and 64.5 wt% SiO2. All examples are reported after adjusting for LOI.

[0087] Sulfate concentrations were measured on a LECO SC832 series combustion analyzer from LECO, St. Joseph, Michigan, USA. The samples were placed in a combustion boat and heated to approximately 1350 °C under an oxygen rich environment. Carbon and sulfur are released as their respective oxides and are measured by IR spectroscopy. The concentration of sulfur or carbon is determined by comparison with known standards.

[0088] Phosphorus concentrations were determined by two separate preparations. For filtrate samples approximately 15.0 grams was weighed into a 50 mL ICP-MS tube. The solution was diluted with water to approximately 35 mL, then 0.50 mL of 100 ppm scandium internal standard was added to the ICP-MS tube. 1 .0 mL of nitric acid was added to the tube and diluted to 50 mL.

[0089] The solution was then run on the Perkin Elmer Optima 8300 with a 10, 200 ppm phosphorus calibration curve. For precipitated silica or calcium silicate products; 1.00g of the sample was weighed into a 50 mL platinum crucible. Sample was wet with a small amount of deionized water, and then 10 mL of perchloric acid, followed by roughly 20 mL of hydrofluoric acid was added to the dish. The sample was heated on a hotplate until dense white fumes evolved. After the evolution of the fumes, approximately 4 mL of deionized water is added to the dish and heated until dense fumes evolve. Sample was then removed from the hotplate and cooled. The cooled sample was transferred to a 100 mL digitube, with rinsing of 5 mL hydrochloric acid and deionized water. 1 .0 mL of 100 ppm scandium internal standard is then added to the digitube. Then digitube is then brought to volume and the solution run on the ICP-OES using the same calibration curve as the filtrate samples. Results are reported in ppm phosphorus.

[0090] The selectivity Coefficient K for PO4 / SO4 was calculated by measuring the concentrations of the various components using the equation below where CS stands for Calcium silicate bound anions PO4 or SO4.

[0091] Amorphous precipitated silicas and silica gels are prepared by the reaction of aqueous sodium silicate with a mineral acid such as sulfuric acid and is well known in the art.

[0092] EXAMPLES

[0093] Calcium Silicate Synthesis

[0094] Example 1

[0095] To a 1 gallon (3.78541 L) reactor containing 1500 g of deionized water was added 200 g of a precipitated silica with a surface area of 178 m2 / g, pore volume of 0.89 cc / g and an average particle size of 14 microns. While stirring at 300 - 350 RPM and 60 °C, 933 grams of a lime slurry of 18% CaO was added and the mixture digest for 60 minutes while maintaining 60 °C, 750 RPM after lime addition. Measure the pH in the beginning and the end of the reaction.

[0096] After reaction, wash and dewater the batch and dry the cake overnight at 120°C. Key properties are presented in table 1 .

[0097] Example 2

[0098] To a 2 gallon reactor containing 4000 g of deionized water was added 524 grams of a precipitated silica with a surface area of 529 m2 / g, pore volume of 1 .3 cc / g and average particle size of 40 microns. While stirring at 400 -600 RPM and 60 °C, 1416 grams of a lime slurry of 15.6 wt% CaO was added and the mixture digest for 180 minutes while maintaining 60°C, 600 RPM after lime addition. Measure the pH in the beginning and the end of the reaction. After reaction, wash and dewater the batch and dry the cake overnight at 105°C. Key properties are presented in table 1.

[0099] Example 3

[0100] To a 1 gallon (3.78541 L) reactor containing 1500 g of deionized water was added 200 g of a precipitated silica with a surface area of 212 m2 / g, pore volume of 1 .3 cc / g and average particle size of 25 microns. While stirring at 300 - 350 RPM and 60 °C, 933 grams of a lime slurry of 18 wt% CaO was added and the mixture digest for 60 minutes while maintaining 60 °C, 750 RPM after lime addition. Measure the pH in the beginning and the end of the reaction.

[0101] After reaction, wash and dewater the batch and dry the cake overnight at 120°C. Key properties are presented in table 1 .

[0102] Example 4

[0103] To a 1 gallon (3.78541 L) reactor containing 1400 g of deionized water was added 1034 g of a precipitated silica with a surface area of 167 m2 / g, pore volume of 0.50 cc / g and average particle size of 12 microns. While stirring at 450 RPM, 553 grams of a lime slurry of 17wt% CaO and 11 .5 grams of a 38% solids sodium aluminate was added and the mixture digested for 120 minutes while maintaining 96 °C. Measure the pH in the beginning and the end of the reaction. After reaction, wash and dewater the batch and dry the cake overnight at 120°C. Key properties are presented in table 1 .

[0104] Example 4 Granule

[0105] The calcium silicate of the inventive example 4 are granulated via an Eirich EL-1 high intensity mixer into spheres of approximately 400 microns.

[0106] Example 5

[0107] To a 2 gallon reactor containing 3000 g of deionized water was added 397 grams of a precipitated silica with a surface area of 529 m2 / g, pore volume of 1 .3 cc / g and average particle size of 40 microns. While stirring at 400-600 RPM and 60 °C, 1478 grams of a lime slurry of 18 wt% CaO was added and the mixture digest for 180 minutes while maintaining 60 °C, 600 RPM after lime addition. Measure the pH in the beginning and the end of the reaction. After reaction, wash and dewater the batch and dry the cake overnight at 105°C. Key properties are presented in table 1.

[0108] Comparative Example 1

[0109] A commercial calcium silicate product called RXCIPIENTS® FM-1000 available from Evonik Industries AG. Key properties are presented in table 1.

[0110] Comparative Example 2

[0111] A commercial calcium silicate product called ZEOFREE® 5133 available from Evonik Industries AG. Key properties are presented in table 1 .

[0112] Comparative Example 3

[0113] To a 1 gallon (3.78541 L) reactor containing 1887g of deionized water was added 1296 g of a precipitated silica with a surface area of 92 m2 / g, pore volume of 0.33 cc / g and average particle size of 11 microns.

[0114] While stirring at 450 RPM, 345g grams of a lime slurry of 18% CaO was added and the mixture digest for 120 minutes while maintaining a temperature of 96C. Measure the pH in the beginning and the end of the reaction.

[0115] After reaction, wash and dewater the batch and dry the cake overnight at 120°C. Key properties are presented in table 1 .

[0116] Comparative Example 4

[0117] This material was prepared as described in US patent 10,246,346 B2. Key properties are presented in table 1 .

[0118] Phosphate Removal Testing

[0119] To 300 grams of an aqueous 0.3% solution of sodium hydrogen phosphate was added 1 gram of a calcium silicate with rapid stirring. After 5 minutes a 30 ml sample was removed and filtered with a 0.45 micron filter. The level of P was analysed against the initial solution and the percent removal was measured. This was converted to an initial rate of reaction in moles / liter-sec and reported in table 1 .

[0120] Phosphate Removal from sodium sulfate solution (batch)

[0121] 0.5 grams of the calcium silicate prepared according to Example 4 were added to a 30 gram solution containing 165 ppm PO4 (55 ppm P) and varying amounts of sodium sulfate. The solution was mixed for 1 hour and the remaining concentration of phosphate and sulfate measured and reported in Figure 9. Selectivity Coefficient PO4 / SO4 for Example 4 was calculated at different concentrations and determined to be on average K = 900.

[0122] Phosphate Removal from sodium sulfate solution (column)

[0123] 45 ml of a granular calcium silicate prepared according to Example 4 Granule were added in a 250 ml, 4 cm diameter, fritted column equipped with a stopcock to control flow rate. A waste solution, containing 4wt% sodium sulfate and sodium phosphate (111 ppm of P) obtained from the precipitation of sodium silicate derived from rice husk ash silica with sulfuric acid, was flowed through the column at various flow rates and the effluent sampled and phosphate concentration (P) measure as shown in Figure 10.

[0124] Table 1 From the results presented in Table 1 , it can be seen that the calcium silicate particles of the invention achieve the highest performance factor and the highest initial phosphate binding rate.

[0125] Figure 8 shows SEM image of Example 4.

[0126] Figure 9 shows phosphate removal percentage using example 4 as a function of sodium sulfate concentration between the range of 0 and 4.75% sodium sulfate. Selectivity can be calculated from this information using the formula provided.

[0127] Figure 10 shows phosphate removal from 4 wt% waste sodium sulfate stream, generated from the reaction of rice husk ash silicate with sulfuric acid, using the granulated material according to Example 4 granule in a column at various flow rates.

[0128] Phosphate Removal from Artificial Gastric Juice

[0129] In this testing, the calcium silicates of the present invention were tested and compared against the commercial pharmaceutical phosphate binder lanthanum carbonate (Sigma Aldrich in the removal of phosphate from artificial gastric juices ( Carolina Biologies, pH =1 , 99.2% water, 0.50%, 0.22% HCI, thymol 0.10%) at various pH values. The pH was modified via addition of sodium bicarbonate to be within the typical stomach biological pH range of 1 to 3.5. To a 40 ml sample of the artificial gastric juice containing various levels of sodium phosphate (monosodium hydrogen phosphate) was added 0.3 grams of example 4 and compared against 0.3 grams of lanthanum carbonate. After 1 hour of stirring the phosphate concentration was measured as phosphorous and the results shown in Table 2.

[0130] Table 2

[0131] From the results presented in Table 2, it can be seen that the inventive calcium silicate such as Example 4 outperforms the established lanthanum carbonate phosphate binder at stomach acid pH of greater than 2.

Claims

CLAIMS1. Calcium silicate particles comprising Tobermorite and having, i) a Ca / Si molar ratio of less than 0.7, ii) BET surface area greater than 50 m2 / g, and iii) CaO content of between 10 and 50 wt%.

2. The calcium silicate particles of claim 1 , wherein the BET surface area is greater than 75 m2 / g, preferably greater than 100 m2 / g, most preferably greater than 150 m2 / g.

3. The calcium silicate particles of claim 1 , wherein the BJH pore volume is greater than 0.5 cc / g, preferably greater than 0.8 cc / g, most preferably greater than 1.0 cc / g.

4. The calcium silicate particles of any of the preceding claims, wherein the CaO content is between 15 and 40 wt%, preferably between 20 and 35 wt%.

5. The calcium silicate particles of any of the preceding claims, wherein the particles have a size of from 1 to 100 microns.

6. The calcium silicate particles of any of the preceding claims, wherein the particles have been granulated to a size ranging of from 100 and 5000 microns.

7. The calcium silicate particles of any of the preceding claims, having a performance factor for removing phosphate at an efficient rate of greater than 1200, preferably greater than 2000, more preferably greater than 3000.

8. A composition comprising the calcium silicate particles of any of the preceding claims.

9. Calcium silicate particles according to any of claims 1 to 7 or of a composition according to claim 8 for use in removing phosphate from a human or an animal patient.

10. The calcium silicate particles or the composition for use according to claim 9, wherein the patient suffers from hyperphosphatemia.

11. Use of the calcium silicate particles according to claim 1 to 7 or of the composition according to claim 8 to remove phosphate from an aqueous solution, preferably selected from fresh water sources, brine and salt water sources, golf course ponds, manufacturing effluents, waste streams, agricultural run-off, retention ponds, animal farm run-off, animal park run-off, streams, lakes, canals, reservoirs, residential and commercial storm-water run-off, wastewater treatment plant discharge, food processing discharge, industrial wastewater discharge, residential wastewater discharge, meat processing residuals, toilet water, and aquarium water.

12. Use of the calcium silicate particles or composition thereof according to claim 11 to remove phosphate from an aqueous stream, preferably an aqueous waste stream generated from the precipitation of sodium silicate derived from rice husk ash with sulfuric acid.

13. Use of calcium silicate particles according to any of claims 1 to 7 or of a composition according to claim 8 as food supplement.

14. Process for the preparation of calcium silicate particles according to any of claims 1 to 7 by reacting precipitated silica or silica gel with lime (CaO / CaOH) in an aqueous solution, at a temperature between 30 and 100 °C, preferably at a temperature of 30°C -100°C, more preferably 60-95 °C.

15. A method for reducing phosphate from an aqueous solution, the method comprising contacting calcium silicate particles according to any of claims 1 to 7 or of a composition according to claim 8 with an aqueous solution containing phosphate in a batch or column flow through system.

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