CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to and the benefit of U.S. Provisional Patent Application Serial No. 63/288,535 filed on December 11, 2021, which is incorporated by reference.

BACKGROUND OF THE INVENTION

1. FIELD OF THE INVENTION

[0002] This present invention pertains to refining crude phosphoric acid and more particularly to a system, apparatus and a process for refining and purifying a solution of crude phosphoric acid.

2. DESCRIPTION OF THE RELATED ART

[0003] A wet process for the manufacture of phosphoric acid typically adds ground phosphate rock to a reaction system containing a slurry of weak phosphoric acid and calcium sulfate crystals. The phosphate rock is partially dissolved by the weak phosphoric acid, and strong sulfuric acid is added to the system to react with the phosphate to form phosphoric acid and calcium sulfate. The calcium sulfate crystallizes out as gypsum, and the crystals are separated via gravity sedimentation, hydrocyclones, centrifugation and conventional filtration methods including filter presses and pressure leaf filters.

[0004] A book titled "‘Phosphoric Acid - Purification, Uses, Technology and Economics” written by Rodney Gilmour and published by CRC Press provides a thorough review of various processes used for producing phosphoric acid. U.S. Patent No. 4,164,550, issued to Hill, states that in the wet process for making phosphoric acid, a finely ground phosphate rock is reacted with dilute phosphoric acid and sulfuric acid to make a crude aqueous phosphoric acid solution that contains a substantial quantity of solid impurities, which is filtered to separate undissolved gypsum and other solid impurities to yield a crude aqueous product that is often referred to as a number one filtrate. Number one filtrate generally includes calcium, potassium, sodium, aluminum, iron, strontium, titanium, silicon, uranium, vanadium, fluorine, magnesium and organic impurities, some of which settle out as a sludge during transportation and storage if not removed from the filtrate. [0005] U.S. Patent No. 4,233,278, issued to Korchnak, describes an aqueous or wet process for making phosphoric acid in which a slurry of the acid is contacted with steam to remove volatile organic material, and extractants are used to remove humics and to recover heavy metals from the acid. U.S. Patent No. 4,762,692, issued to Beltz et al., describes a process for the precipitation and separation of cadmium sulfide from raffmates using hydrogen sulfide. U.S. Patent No. 4,800,071, issued to Kaesler et al., describes a process for separating gypsum in a phosphoric acid liquor using a sulfonated acrylamide polymer as a filter aid.

[0006] It is difficult and expensive to separate and remove the impurities that are in a crude phosphoric acid solution. Typical liquid-solid separation techniques include flotation, gravity sedimentation and thickening, hydrocyclones, centrifuges, filter presses, pressure leaf filters, pan filters, vacuum filters and belt filters. These methods of separation are typically limited to removal of particulates that are greater than one micron in size. The crude phosphoric acid solution contains a considerable number of particulates that are less than one micron in size, and there is a need for an economical means for removing sub-micron particulates.

SUMMARY OF THE INVENTION

|0007] The present invention pertains to a means for removing impurities from crude phosphoric acid. The present invention provides for a method and a system to remove impurities from crude phosphoric acid, where the method and system comprise a combination of an electrochemical treatment and a filtration system. A filtration process and apparatus have been found to be effective for removing precipitated material from a crude phosphoric acid solution at a substantially lower cost and to yield a product that has a higher purity than is obtained using conventional separation methods. Electrolytic oxidation - reduction systems are used for reducing and precipitating certain multi-valent metals that may be dissolved in the crude phosphoric acid solution and to mitigate fouling of the filtration membranes during the filtration process. Additional electrolytic oxidation - reduction systems are included for the further removal of organics and color from the permeate stream post filtration. The electrolytic reactors provide complete or partial oxidation, reduction, adsorption and/or precipitation of dissolved metals and other contaminates from the crude phosphoric acid. The subsequent removal of the precipitated particulates and colloidal material is achieved by continuous filtration. The system may be used with or without chemical reagents, and the two components may be applied individually for use in multiple locations within many refining and mineral extraction processes. Individual components may also be applied for treatment during storage and transportation of aqueous products on land or sea. The present invention provides a means for chemical, non-chemical and/or electrically assisted precipitation and subsequent removal of both dissolved and suspended contaminates from crude phosphoric acid and other fluids to produce a purer grade of phosphoric acid product or fluid in a safer environment, at lower costs and with less waste for final disposition.

[0008] The present invention provides in one embodiment a system for removing impurities from crude phosphoric acid comprising: a tank or vessel for receiving crude phosphoric acid, wherein the crude phosphoric acid contains dissolved and suspended contaminates; an electrochemical reactor for electrochemical treatment of the crude phosphoric acid; a filtration system comprising an porous ceramic membrane; piping for collecting a permeate stream from the filtration system; and piping for collecting a retentate stream. The ceramic porous membrane preferably comprises silicon carbide or zirconium oxide and preferably both. The ceramic porous membrane can be a microfiltration membrane, but is preferably an ultrafiltration membrane. The electrochemical reactor preferably comprises one or more electrolytic units configured to provide an electromotive force and/or an electric field across the porous membrane surface and/or to the crude phosphoric acid. The system preferably further comprises a recirculation loop for adding the retentate stream to the crude phosphoric acid before the crude phosphoric acid is fed to the filtration system.

|0009] The present invention provides in another embodiment a method for removing impurities from crude phosphoric acid comprising the steps of: providing an amount of crude phosphoric acid, wherein the crude phosphoric acid contains dissolved and/or suspended contaminates; treating the crude phosphoric acid to remove an amount of the dissolved and/or suspended contaminates; wherein the treatment comprises a combination of an electrochemical treatment and a filtration system, wherein the filtration system comprises a porous ceramic membrane; and collecting a permeate stream from the filtration system. The method preferably comprises treating the crude phosphoric acid with an electrochemical treatment step before the filtration system step. The method optionally comprises combining the electrochemical treatment step with the filtration system step within a single reactor. The method preferably comprises treating the permeate stream with at least one electrochemical treatment and preferably collecting a retentate stream from the filtration system, where the retentate stream is preferably treated with an electrochemical treatment. BRIEF DESCRIPTION OF THE DRAWINGS

|0010] A better understanding of the invention can be obtained when the detailed description of exemplary embodiments set forth below is considered in conjunction with the attached drawings in which:

[0011] Fig. 1 is a process flow diagram of a process for making phosphoric acid, according to the present invention;

[0012] Fig. 2 is a process flow diagram of a process for making phosphoric acid, according to the present invention; and

[0013] Fig. 3 is a process flow diagram of a process for making phosphoric acid incorporating several electrolytic redox components within the system, according to the present invention.

DEFINITIONS

[0014] The term “electrophoresis” or “electromigration” as used herein refers to the motion of ions or charged particles in a liquid media, which is driven by the EMF applied between the electrodes.

|0015] The term “adsorption” as used herein refers to the process by which a solid holds atoms, ions, or molecules of a gas, liquid, or solute as a thin film. These are surfaceactive phenomena related to the interaction of charges and surface tension.

|0016| The term “electro-sorption” (also abbreviated as ES) is used herein to refer to the migration of ions into the electrical double layer (EDL) that is formed along the pore surfaces of the electrode / liquid interface and is dependent on the electrode potential and physical properties (e.g., specific surface area) of the membrane.

[0017] The terms “electrochemical oxidation” (also abbreviated EO, or EOx) and “electrochemical reduction” (also abbreviated ER) are used herein to refer to complimentary reduction-oxidation or redox processes involving the transfer of electrons between the electrodes and the liquid medium. Oxidation is defined as a loss of electrons, and reduction is defined as a gain of electrons. These transfers may be direct electrochemical redox processes where a species (contaminate) is first adsorbed on the electrode surfaces and then removed by direct electron transfer from the electrodes. Indirect electrochemical redox processes first generate an intermediate reactant such as a hydroxyl radical, which subsequently reacts with a targeted species (contaminate). The primary action of ER is the transfer of an electron resulting in cleavage of a C - X bond.

|0018] The term “electro-osmosis” (also abbreviated EOs) as used herein refers to the motion of a liquid induced by the motion of net mobile electric charge within the liquid. As cations are moving toward the cathode, hydrated cations in solution are also carried toward the cathode, dragging the liquid along and forming an electro-osmotic flow (EOF).

[0019] The term “electrochemical treatment” as used herein refers to the use of an electric field or an electromotive force (EMF) to treat an aqueous mixture in order to produce electrokinetic and/or electorchemical effects in the aqueous mixture and its components. Electrokinetic or electrochemical effects include, but are not limited to: electrophoresis, adsorption, electro-sorption, electrochemical oxidation, electrochemical reduction, electroosmosis and precipitation or any combination thereof.

[0020] The terms “electrolytic reactor” and “electrocoagulation reactor” as used herein refer to systems able to create an electromotive force (EMF) and/or and electric field to an aqueous mixture and promoting electrokinetic or electrochemical effects including, but not limited to: electrophoresis, adsorption, electro-sorption, electrochemical oxidation, electrochemical reduction, electro-osmosis and precipitation or any combination thereof.

|0021] The term “fouling” as used herein is defined as a process resulting in loss of performance of a membrane due to the deposition of suspended or dissolved substances on its external surfaces, at its pore openings, or within its pores. Fouling may be subdivided into the following categories: biofouling caused by microbial growth (biofilm); particulate or colloidal caused by deposition of solids or colloidal materials; organic caused by sorption of dissolved organic matter; and inorganic caused by mineral precipitation (scaling).

|0022] As used herein “filtration” refers to a technique used to separate particles from a liquid for the purpose of purifying the liquid. Filtration can be achieved by passing the liquid through a membrane having pores of a defined size. The term microfiltration is used herein to refer to filtration through pores having a size greater than 100 nm. The term ultrafiltration is used herein to refer to filtration through pores having a size in the range of 10 to 100 nm. DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0023] The wet process for manufacturing phosphoric acid involves the addition of ground phosphate rock to a reaction system to generate a slurry of the ground rock with the addition of dilute phosphoric acid and sulfuric acid. The sulfuric acid helps dissolve the phosphate rock to form phosphoric acid and calcium sulfate (gypsum) crystals. The calcium sulfate crystals are separated by filtration and water washed to remove any remaining acid. A portion of the wash water is returned to the system as dilute phosphoric acid to aid in the further dissolution of the phosphate rock. Further refining is desirable to produce a contaminate- free product because phosphate ore contains a variety of organic species and heavy metal bearing minerals.

[0024] Crude merchant grade acid (MGA) is an intermediate phosphoric acid product that is used to produce fertilizers, animal feeds, and a variety of industrial products that include cleaning solutions, food and beverage additives and pharmaceuticals. Crude MGA is typically produced near mining locations and is shipped to other facilities for further refining. During shipment, contaminates continue to precipitate out as metal-bearing potassium salts and collect in the vessels in which they are shipped, which generates solids that must be filtered or otherwise removed during further refining processes. Additionally, tankers and vessels used for transport must have these solids removed periodically at a considerable cost. Typical MGA is received at a concentration of approximately 40% - 54% acid and generally contains suspended material that results from the post-precipitation of metal-bearing potassium salts as well as dissolved metal species. The dissolved heavy metal species remaining in solution with the MGA should be precipitated and removed. Contaminates remaining in solution include aluminum, arsenic, iron, strontium, uranium, titanium, vanadium, silicon, calcium, magnesium and fluorine among others. These contaminates are reduced and precipitated by the addition of sulfur-bearing species including, but not limited to, various sulfides and sulfites, which generate hydrogen sulfide gas in an acid environment, thereby creating extremely corrosive and hazardous conditions.

[0025] Typical MGA refining processes require the addition of reducing chemical compounds for the precipitation of dissolved metal species. Reducing chemicals used for this purpose are sulfur-bearing compounds that supply a quantity of electrons for transfer during reactions to reduce and precipitate dissolved metal species. Chemicals used for this purpose include sulfides, sulfites, and hydrogen sulfide gas. This process is sometimes referred to as sulfiding or dearsenication as in the removal of arsenic. The precipitated mass must then be separated from the acid solution by filtration because the high viscosity of the MGA is detrimental to typical gravity separation methods. Centrifugation is also difficult due to the nature of the fine, low gravity solids present in the precipitate. Sulfide precipitates are very fine and notorious for retarding conventional filtration rates due to coating and blinding of filter cloth media. Typical filtration is therefore accomplished using large pan filters, pressure leaf filters, rotary drum filters and filter presses, table filters and belt filters, all of which require pre-coating and body feed with a disposable media such as diatomaceous earth, perlite, zeolite, pumice, ash or other disposable filtration media. These filter systems also operate under a vacuum to assist filtration rates. The filters are taken offline periodically to dispose of and replace the spent media resulting in downtime and lost production. The disposable media bulks up the total volume and weight of residuals that must be transported and disposed of as hazardous waste in appropriate landfills, which increases costs and associated liabilities considerably. Conventional methods of filtration can remove suspended particulates in the range of 3.0 to 5.0 pm. About fifty percent of particulates at this point in the system are less than 0.5 pm, and the burden of removal is shifted to subsequent activated carbon filters resulting in escalation in downtime, loss of productivity, escalated costs to replace carbon, and further escalation in hazardous transportation and disposable costs.

[0026] The present invention pertains to the removal of these dissolved and suspended materials. The term PA herein refers to all forms of aqueous phosphoric acid regardless of which of the many processes is used for its production and its specific location within these various processes. Process details concerning oxidation, reduction and precipitation via an electrolytic process and apparatus are described in the present inventor’s U.S. Patent Nos. 6,719,894 and 7,087,176, which are incorporated by reference in their entirety for all purposes. The filtration process described herein is applicable in multiple process locations requiring liquid-solids separation and may be used with chemical, electrochemical, and/or assisted precipitation techniques. Assisted precipitation includes a combination of chemical and electrolytic precipitation techniques. Unit process locations include desulfation, dearsenication or sulfiding, defluorination and decolorization, all of which may be applicable as pre-treatment and post-treatment scenarios. This electrolytic redox - membrane filtration technique may also be applied in other mineral extraction processes to recover beneficial materials and rare earth species from acids, alkalis, brines and other aqueous solvents and solutions.

|0027] The filtration process described herein may be a microfiltration process or an ultrafiltration process. Thus, the filtration system as disclosed herein may provide for microfiltration or ultrafiltration. In one embodiment, the filtration process is a microfiltration, and in another embodiment, the filtration process is an ultrafiltration.

[0028] Systems for filtration according to the present invention preferably comprise a porous ceramic membrane. The membrane provides filtration by allowing the permeate through the pores. Materials that do not pass through the pores are retained and form a retentate. The porous ceramic membrane may comprise silicon carbide SiC or zirconium oxide (ZrO2)or a combination SiC and ZrO2. In one embodiment, the porous ceramic membrane comprises SiC and has a pore size suitable for microfiltration. In another embodiment, the porous ceramic membrane comprises ZrO2 and has a pore size suitable for ultrafiltration.

[0029] The filtration system and the electrochemical process may be combined in different ways. In one embodiment, the electrochemical treatment takes place before the filtration system. In another embodiment, the electrochemical treatment is combined with the filtration system within a single reactor. Treating the permeate and/or the retentate with an electrochemical treatment may also be advantageous to remove impurities. Thus, in one embodiment, the permeate is treated with an electrochemical treatment. In one embodiment, the retentate is treated with an electrochemical treatment. In one embodiment, the retentate is recirculated and fed back to the filtration system.

|0030| In one embodiment, the electrochemical treatment is provided by one or more electrolytic units configured to provide an electromotive force and/or and electric field across the porous ceramic membrane surface. In one embodiment, the electrochemical treatment is provided by one or more electrolytic units configured to provide an electromotive force and/or and electric field to the crude phosphoric acid, the permeate or the retentate. In one embodiment, the electrochemical treatment is provided by an electrode configured to provide an electormotive force and/or an electric field to the crude phosphoric acid, the permeate or the retentate. In one embodiment, the electrode comprises a material selected from the group consisting of titanium suboxide (Ti4O7), boron doped diamond (BDD), iron (Fe), stainless steel (SS) and iridium or any combination thereof. [0031] Fig. 1 is a block flow diagram showing a process 10 for the refining of PA / MGA feedstock. PA feedstock, which is typically 45% - 55% phosphoric acid when received, is stored in a heated equalization vessel 12. In one embodiment, PA is transferred to an agitated mixing tank 14 where a chemical precipitating agent is metered and mixed into the acid stream for the reduction and precipitation of various dissolved metal contaminates. Chemical precipitants that may be used include calcium carbonate, calcium hydroxide, hydrogen sulfide gas or a variety of sodium salts including sulfide, sulfite, metabisulfite and hydrosulfite.

[0032] A mixture of the PA and the chemical precipitating agent from mixing tank 14 is transferred to an agitated reaction vessel 16. Chemical reactions are allowed to occur, particularly for reduction and oxidation of dissolved metal species, thereby causing dissolved species to form solid particulates, which can be removed from the PA stream.

[0033] In another embodiment, an electrolytic or electrocoagulation reactor 18 is used to reduce the dissolved metal contaminates. In one embodiment, the electrolytic or electrocoagulation reactor comprises one or more electrode(s) as described herein. An apparatus and a process for electrocoagulation is described in U.S. Patent Nos. 6,719,894 and 7,087,176 issued to Gavrel et al. A commercial embodiment of an electrocoagulation reactor is sold under the brand name E-FLOC® and can be purchased from Ecolotron, Inc., which has a place of business at 4730 FM646, Dickinson, TX 77539. Ecolotron has a website at https://ecolotron.com. E-FLOC® electrolytic technology incorporates a low-voltage direct current applied to a series of parallel electrodes through which a treatment fluid, in this case PA, flows and is exposed to the electric current. As an electric current is a flow of electrons, multi- valent metal species in solution may gain electrons from the applied current and thus be reduced. Other species including organics may be oxidized as reduction and oxidation occur simultaneously, and one may not occur without the other. Difficult-to-remove multi-valent metals in solution with PA include chromium, arsenic, selenium, vanadium, iron and copper among others. These species should be reduced or oxidized to the correct oxidation state before precipitation or co-precipitation occurs. A discharge stream of PA from the electrocoagulation reactor 18 is fed to the reaction vessel 16.

[0034] Mixing tank 14 can be used for chemical precipitation of dissolved species. Electrocoagulation reactor 18 can be used as an electrochemical technique for removing dissolved species. Either or both of the chemical and electrochemical techniques may be used to treat the PA / MGA feedstock in the heated equalization vessel 12. Some applications may be best handled by a combination of chemical and electrochemical techniques, and an apparatus that combines this functionality can be substituted for the mixing tank 14 and the electrocoagulation reactor 18 or can be added to the process. After chemical and/or electrochemical treatment, an adequate reaction time is provided in the reaction vessel 16 to allow dissolved contaminates to precipitate. By-product gases that form in the oxidation and reduction reactions are fed to an off-gas scrubber 20 for cleaning prior to discharge to the atmosphere.

[0035] After precipitation, the PA containing the precipitated material is transferred to an agitated balance tank 22 to be metered to an ultrafiltration (UF) system 24 for liquidsolids separation. In some cases, an electrolytic reactor may be included at this point for the recirculation of the balance tank (22) for continued treatment of the aqueous suspension before transfer to the ultrafiltration (UF) system (24). Although not shown, a coarse-solids removal component may be used as a pre-filtration step to remove larger particulates or aggregates. Coarse-solids removal components include settling tanks, hydrocyclones, strainers and centrifuges. In particular, a centrifuge can be included in the process to receive feed from the reaction vessel 16 and to separate the stream into a lighter fraction, which is fed to the balance tank 22, and a heavier fraction that contains removed particulates, which can be fed to a retentate tank 32, which is discussed below. The suspended solids content after precipitation is typically from 0.5% to 4.0%. The mixture of PA and particulates in the reaction vessel 16 and the balance tank 22 has a high viscosity, and the mixture is typically heated to a temperature of about 40°C to about 60°C to improve hydraulics and flow characteristics. The mixture of PA and particulates in balance tank 22 has a low pH since it is an acid stream and typically has a pH of between about 0.1 and 1.5. The low pH and the hot temperature makes it very challenging to separate the solid particulates that are formed from the phosphoric acid, which is the desired product. Conventional polymeric membranes are not satisfactory for use in these conditions. Diatomaceous earth, perlite, zeolite, pumice and ash have been used as a filter media.

[0036] The ultrafiltration (UF) system 24 comprises a plurality of filtration units, where each unit comprises a plurality of membrane tubes in a housing. The membrane tubes are preferably highly porous and are preferably made of a silicon carbide (SiC) ceramic material and/or of a hybrid silicon carbide and zirconium oxide (ZrCh) material. The ceramic membrane tubes preferably further comprise titanium sub-oxide (TiuO?) or boron doped diamond (BDD). The ceramic membrane tubes comprise SiC, ZrC>2, BDD and Ti4O? in one embodiment. In one embodiment, the system comprises electrodes made from a material selected from the group consisting of: titanium suboxide (Ti4O?), boron doped diamond (BDD), iron (Fe), stainless steel (SS) and iridium or any combination thereof. The ceramic membrane tubes are preferably chemically inert at a pH range of 0.0 to 14.0 and stable to a temperature up to 800°C. Manufacturers for a suitable UF system 24 include LiqTech Holdings A/S of Denmark, particularly LiqTech Ceramics, Alsys Group of France, particularly Ceramem LLC in Waltham, Massachusetts, USA, and Kemco Systems Co., LLC of Clearwater, Florida, USA.

[0037] The mixture of PA and particulates flows into ends of the tubes within a particular housing and through the porous ceramic tubes. Particulates of a sufficient size do not pass through a porous side wall of a tube, but liquid phosphoric acid does pass through the porous side wall and is collected in the housing and outside the tubes and discharged from each housing as a permeate, which is collected in a permeate tank 26. UF system 24 removes a substantial portion of solid particles having a size of less than one micron. The permeate is considered to be a solids-free PA stream. The solids-free PA in the permeate tank 26 is discharged to a carbon filter unit 28 for decolorization and then concentrated in an evaporation unit 30, where evaporators are used to evaporate water, thereby concentrating the phosphoric acid.

|0038| Particulates that cannot pass through the porous side walls of the tubes flow through the length of the tubes and are discharged in a retentate stream, which is recirculated. After the retentate is concentrated to a predetermined critical concentration, it is wasted and collected in a retentate tank 32. The retentate collected in the retentate tank 32 has a much higher concentration of particulates than in the PA in balance tank 22. The wasted retentate, which is also called reject, contains the precipitated material that is retained by the membrane tubes. Although not shown in Fig. 1, this up-concentrated stream remains within a recirculation loop for further filtration until it reaches a critical concentration, after which it is discharged as a waste stream to a filter press 34 for water washing and dewatering to produce a dry filter cake 36 for disposal. A liquid filtrate 38, which is a dilute PA stream, from filter press 34 is returned to the feedstock tank, which is equalization vessel 12, or to mixing tank 14 or to the electrolytic reactor 18 to reclaim additional PA product from the filtrate.

[0039] Fig. 2 is very similar to Fig. 1 and is a block flow diagram showing a process 10a for the refining of a PA / MGA feedstock that is received in a feedstock tank 12a. The feedstock is fed to a chemical precipitant mixing vessel 14a and/or to an electrolytic or electrocoagulation reactor 18a, after which a PA stream is discharged to a balance tank 22a. Although not shown, the mixing vessel (14a) may contain a recirculation loop for continuous recirculation of PA/MGA through the electrolytic reactor (18a). A process feed pump 40 pumps a PA slurry from the balance tank 22a to a UF system 24a. The process feed pump 40 provides about 60 psi pressure to a recirculation loop 42. A recirculation pump 44 generates crossflow through a membrane housing 24b and through the recirculation loop 42 to maintain a continuous, crossflow velocity. Pressures and flowrates inside the system are controlled by adjusting the position of regulating valves 46a and 46b and pump speeds for pumps 40 and 44. The membrane housing 24b preferably contains from about 20 to about 200 tubular membrane elements arranged such that the PA enters through one end, travels through the length of the internal channels and exits from the opposite end of the membrane elements to be returned to the suction of the recirculation pump 44 as retentate.

[0040] The pressure within the recirculation loop 42 provides the force required to push the filtrate through the membrane (inside - out), where it collects within the housing 24b to be released from the system by a discharge valve 48 as a permeate. The pressure differential between the internal recirculation loop 42 and the permeate side is known as the transmembrane pressure (TMP). The retentate, which comprises the solids rejected by the membrane, remains within the recirculation loop 42 until the concentration reaches a critical point, after which it is discharged from the system as reject or retentate waste 50. The concentrated reject is sent to a filter press 34a, where it is dewatered and water washed to reclaim remaining acid product for return to the headworks 12a of the system. The remaining solids are dewatered to produce a dry filter cake for disposal. The permeate is transferred to an activated carbon filtration system 28a and/or to an evaporator 30a for concentration. The UF system 24a includes a backwash pump (not shown) for the periodic backwashing of the membrane elements with stored permeate or water and a chemical clean-in-place module (not shown) for periodic cleaning as required.

[0041] Parameters monitored for control of UF system 24a include: flowrate of influent feed, permeate discharge and crossflow within the recirculation loop 42; pressure of the influent feed, retentate in the recirculation loop 42 and the permeate discharge; and temperature of the influent feed and the retentate in the recirculation loop 42. [0042] Ultrafiltration (UF) systems 24 and 24a use a crossflow filtration method. In crossflow filtration, the liquid feed stream runs tangential to the membrane, establishing a pressure differential across the membrane. This creates a flow of liquid through the membrane. The particles in solution continue to flow along the surface of the membrane. In contrast to conventional, dead-end filtration practices, the use of a turbulent, tangential flow tends to prevent particles from building up as a filter cake, and particulates are continuously removed from the process. This mode is particularly suitable for a high particle concentration in a feed stream.

[0043] The trans membrane pressure (TMP) is the driving force across the membrane; the pressure required to push liquid through the membrane. TMP is defined as the [(inlet pressure minus the outlet pressure) divided by two] minus the pressure of the permeate, or

|0044] Flux is a measure of the rate at which permeate passes through the membrane per unit membrane surface area. The unit is liters/m ² /hour and is typically called LMH. One determination of flux is a net flux and another is an instantaneous flux.

[0045] Crossflow velocity is defined as the velocity in the individual channels at the inlet of the membrane element. The cross flow removes the particles trapped at the surface of the membrane by a shear force. This shear force entails a pressure drop along the length of the membrane. This pressure drop can be up to 1 bar and depends on the liquid and the velocity.

[0046] Fig. 3 is very similar to Figs. 1 and 2 and is a process 10b for the refining and further purification of MGA / PA feedstock. Process 10b incorporates three additional electrolytic reactors as separate, add-on components that are placed throughout the system to be used for electro - reduction (ER), electro - oxidation (EOX) and/or electro - sorption (ES). Two electrolytic units 18b are placed within a retentate recirculation loop 42b of a UF system 24b and/or at the influent to the UF system 24b, not shown. As the retentate contains the rejected solids in a slurry with the MGA / PA, which is continuously recirculated within the retentate recirculation loop 42b, the aqueous phase may still contain heavy metals in solution that require reduction / precipitation so that they may be subsequently retained by the membranes to be discharged as wasted retentate 50. Because the retentate concentrates solids, electrodes within the retentate loop are best constructed as flat plates, rods, grids screens, etc. to avoid fouling that may occur with permeable reactive electrode membranes.

|0047] The two electrolytic reactors 18b provide for the continuing oxidation / reduction / adsorption / precipitation of these metals from the aqueous phase MGA / PA. These two electrolytic reactors 18b also provide an electromotive force (EMF) / electric field and applies charges to the suspended particulates present within the recirculated suspension to avoid and reduce fouling of the UF membranes. Membrane fouling is mitigated, and filtration mechanics are enhanced by the electrokinetic effects supplied by the EMF / electric field including: electroosmosis, electrophoresis, electrolysis, electro - sorption, as well as electro - reduction and electro - oxidation. Particulates within the retentate loop 42b also acquire an ionic charge (dielectric layer) to further assist in their rejection by the membranes. Furthermore, the simultaneous oxidation of organic species in the aqueous phase reduces the viscosity of the MGA / PA to further increase TMP / flux, reduce color, and increase the mass transport coefficient of ions within the aqueous phase. By including different electrodes used for reduction and/or oxidation into the redox reactors 18b located at each end of the membrane housing 24b, the influent liquid or feedstock and the recirculating retentate recirculate through these electrodes, thereby providing continuing treatment. The redox reactors 18b provide an EMF / electric field across the membranes, which mitigates fouling and also charges particulates within the recirculation loop to aid in rejection by the membranes and further aid prevention of fouling of the membranes.

|0048| A third electrolytic reactor 18b2 is placed in a post-filtration position for the further electro-oxidation / reduction / adsorption of the permeate to further remove organics, color, etc. and produce a purified product that is more applicable for food, pharma, cola and semi-conductor applications. The third permeate polishing reactor 18b2 may incorporate reactive electrode membranes (REM) 19b that are three dimensional and provide a permeable electrode structure. As electrolytic reactions occur at the liquid interface, porous, three- dimensional electrodes provide exponentially greater surface area for reactions to occur, and electrolytic activity is therefore increased exponentially. These membranes may be enclosed within a housing (not shown) and operate under positive pressure and/or be submerged within a permeate tank 26b in which case the permeate is withdrawn through REM 19b via a vacuum pump 27b. A permeate recirculation loop 27b-2 is included for the recirculation of permeate to the permeate tank 26b via control valve 27b-3. The permeate discharge is then transferred through a carbon media filter 28b and then concentrated via an evaporator 30b. A secondary discharge port with a discharge valve 27b-4 is included on the permeate tank 26b for the periodic backwashing and desorption of contaminates from REM 19b surfaces. A backwash pump is not shown.

[0049] EMBODIMENTS OF THE INVENTION

The present invention includes a number of different embodiments, including the following.

1. A method for removing impurities from aqueous crude phosphoric acid comprising the steps of: receiving aqueous crude phosphoric acid in a mixing tank or in a reaction vessel, wherein the crude phosphoric acid contains dissolved and suspended contaminates; mixing a chemical precipitating agent into the aqueous crude phosphoric acid; precipitating a portion of the dissolved contaminates thereby forming a first mixture; feeding the first mixture to an ultrafiltration (UF) system, wherein the UF system comprises a plurality of ceramic membrane tubes enclosed within a housing, wherein each ceramic membrane tube has a length, opposing first and second ends, a longitudinal axis and a porous side wall that defines a longitudinal bore between the opposing ends, wherein the first mixture is fed into first end of the tubes; collecting a permeate stream from the housing, wherein the permeate stream is a portion of the first mixture that flows through the porous side wall in each ceramic membrane tube; and collecting a retentate stream from the second end of the tubes.

2. The method of embodiment 1 , wherein the ceramic membrane tubes comprise silicon carbide.

3. The method of embodiment 2, wherein the ceramic membrane tubes further comprise zirconium oxide. 4. The method of embodiment 1, wherein the ceramic membrane tubes comprise silicon carbide (SiC), zirconium oxide (ZrC ), titanium sub-oxide (T14O7), and Boron Doped Diamond (BDD).

5. The method of embodiment 1, 2, 3 or 4, wherein the amount of solid particulate matter in the permeate stream is less than 60% of the amount of solid particulate matter in the amount of solid particulate matter in the retentate stream.

6. The method of embodiment 5, wherein the amount of solid particulate matter in the permeate stream is less than 50% of the amount of solid particulate matter in the amount of solid particulate matter in the retentate stream.

7. The method of embodiment 1 , 2, 3 or 4, further comprising a recirculation loop in which the retentate stream is added to the first mixture and fed to the UF system.

8. The method of embodiment 7, further comprising a filter press, wherein a portion of the retentate stream is fed to the filter press.

9. The method of embodiment 8, further comprising recovering a filtrate from the filter press and adding the filtrate to the aqueous crude phosphoric acid.

10. The method of embodiment 1, 2, 3 or 4, further comprising a carbon filter and passing the permeate stream through the carbon filter.

11. The method of embodiment 10, wherein a decolored permeate stream is discharged from the carbon filter, further comprising evaporating water from the decolored permeate stream.

12. A method for removing impurities from aqueous crude phosphoric acid comprising the steps of: receiving aqueous crude phosphoric acid in a mixing tank or in a reaction vessel, wherein the crude phosphoric acid contains dissolved and suspended contaminates; conveying the aqueous crude phosphoric acid through an electrocoagulation reactor; precipitating a portion of the dissolved contaminates thereby forming a first mixture; feeding the first mixture to an ultrafiltration (UF) system, wherein the UF system comprises a plurality of ceramic membrane tubes enclosed within a housing, wherein each ceramic membrane tube has a length, opposing first and second ends, a longitudinal axis and a porous side wall that defines a longitudinal bore between the opposing ends, wherein the first mixture is fed into first end of the tubes; collecting a permeate stream from the housing, wherein the permeate stream is a portion of the first mixture that flows through the porous side wall in each ceramic membrane tube; and collecting a retentate stream from the second end of the tubes.

13. The method of embodiment 12, wherein the ceramic membrane tubes comprise silicon carbide.

14. The method of embodiment 13, wherein the ceramic membrane tubes further comprise zirconium oxide.

15. The method of embodiment 12, wherein the ceramic membrane tubes comprise silicon carbide (SiC), zirconium oxide (ZrC ), titanium sub-oxide (U4O7), and Boron Doped Diamond (BDD).

16. The method of embodiment 12, 13, 14 or 15, wherein the amount of solid particulate matter in the permeate stream is less than 60% of the amount of solid particulate matter in the amount of solid particulate matter in the retentate stream.

17. The method of embodiment 16, wherein the amount of solid particulate matter in the permeate stream is less than 50% of the amount of solid particulate matter in the amount of solid particulate matter in the retentate stream.

18. The method of embodiment 12, 13, 14 or 15, further comprising a recirculation loop in which the retentate stream is added to the first mixture and fed to the UF system. 19. The method of embodiment 18, further comprising a filter press, wherein a portion of the retentate stream is fed to the filter press.

20. The method of embodiment 19, further comprising recovering a filtrate from the filter press and adding the filtrate to the aqueous crude phosphoric acid.

21. The method of embodiment 12, 13, 14 or 15, further comprising a carbon filter and passing the permeate stream through the carbon filter.

22. The method of embodiment 21, wherein a decolored permeate stream is discharged from the carbon filter, further comprising evaporating water from the decolored permeate stream.

23. The method of embodiment 12, 13, 14 or 15, further comprising mixing a chemical precipitating agent into the aqueous crude phosphoric acid.

24. The method of embodiment 23, wherein the amount of solid particulate matter in the permeate stream is less than 60%, preferably less than 50%, of the amount of solid particulate matter in the amount of solid particulate matter in the retentate stream.

25. The method of embodiment 23, further comprising a recirculation loop in which the retentate stream is added to the first mixture and fed to the UF system.

26. The method of embodiment 25, further comprising a filter press, wherein a portion of the retentate stream is fed to the filter press.

27. The method of embodiment 26, further comprising recovering a filtrate from the filter press and adding the filtrate to the aqueous crude phosphoric acid.

28. The method of embodiment 23, further comprising a carbon filter and passing the permeate stream through the carbon filter. 29. The method of embodiment 28, wherein a decolored permeate stream is discharged from the carbon filter, further comprising evaporating water from the decolored permeate stream.

30. A system for removing impurities from aqueous crude phosphoric acid comprising: a mixing tank or in a reaction vessel for receiving aqueous crude phosphoric acid, wherein the crude phosphoric acid contains dissolved and suspended contaminates. an injection apparatus for adding a chemical precipitating agent into the aqueous crude phosphoric acid and precipitating a portion of the dissolved contaminates to thereby form a first mixture; an ultrafiltration (UF) system for filtering the first mixture, wherein the UF system comprises a plurality of ceramic membrane tubes enclosed within a housing, wherein each ceramic membrane tube has a length, opposing first and second ends, a longitudinal axis and a porous side wall that defines a longitudinal bore between the opposing ends, wherein the first mixture is fed into first end of the tubes; piping for collecting a permeate stream from the housing, wherein the permeate stream is a portion of the first mixture that flows through the porous side wall in each ceramic membrane tube; and piping for collecting a retentate stream from the second end of the tubes.

31. The system of embodiment 30, wherein the ceramic membrane tubes comprise silicon carbide.

32. The system of embodiment 31, wherein the ceramic membrane tubes further comprise zirconium oxide.

33. The system of embodiment 30, wherein the ceramic membrane tubes comprise silicon carbide (SiC), zirconium oxide (ZrC>2), titanium sub-oxide (TiziO?), and Boron Doped Diamond (BDD). 34. The system of embodiment 30, 31, 32, or 33, further comprising a recirculation loop for adding the retentate stream to the first mixture before the first mixture is fed to the UF system.

35. The system of embodiment 34, further comprising a filter press for filtering a portion of the retentate stream.

36. The system of embodiment 35, further comprising piping for recovering a filtrate from the filter press and for adding the filtrate to the aqueous crude phosphoric acid.

37. The system of embodiment 30, 31, 32, or 33, further comprising a carbon filter for treating the permeate stream.

38. The system of embodiment 37, further comprising evaporation equipment downstream from the carbon filter for evaporating water from a treated permeate stream discharged from the carbon filter.

39. A system for removing impurities from aqueous crude phosphoric acid comprising: a mixing tank or in a reaction vessel for receiving aqueous crude phosphoric acid, wherein the crude phosphoric acid contains dissolved and suspended contaminates; an electrocoagulation reactor for treating the aqueous crude phosphoric acid and precipitating a portion of the dissolved contaminates to thereby form a first mixture; an ultrafiltration (UF) system for filtering the first mixture, wherein the UF system comprises a plurality of ceramic membrane tubes enclosed within a housing, wherein each ceramic membrane tube has a length, opposing first and second ends, a longitudinal axis and a porous side wall that defines a longitudinal bore between the opposing ends, wherein the first mixture is fed into first end of the tubes; piping for collecting a permeate stream from the housing, wherein the permeate stream is a portion of the first mixture that flows through the porous side wall in each ceramic membrane tube; and piping for collecting a retentate stream from the second end of the tubes. 40. The system of embodiment 39, wherein the ceramic membrane tubes comprise silicon carbide.

41. The system of embodiment 40, wherein the ceramic membrane tubes further comprise zirconium oxide.

42. The system of embodiment 39, wherein the ceramic membrane tubes comprise silicon carbide (SiC), zirconium oxide (ZrC ), titanium sub-oxide (T14O7), and Boron Doped Diamond (BDD).

43. The system of embodiment 39, 40, 41 or 42, further comprising a recirculation loop for adding the retentate stream to the first mixture before the first mixture is fed to the UF system.

44. The system of embodiment 43, further comprising a filter press for filtering a portion of the retentate stream.

45. The system of embodiment 44, further comprising piping for recovering a filtrate from the filter press and for adding the filtrate to the aqueous crude phosphoric acid.

46. The system of embodiment 39, 40, 41 or 42, further comprising a carbon filter for treating the permeate stream.

47. The system of embodiment 46, further comprising evaporation equipment downstream from the carbon filter for evaporating water from a treated permeate stream discharged from the carbon filter.

48. The system of embodiment 40, further comprising an injection apparatus for adding a chemical precipitating agent into the aqueous crude phosphoric acid.

49. A method for removing impurities from aqueous crude phosphoric acid comprising the steps of: receiving aqueous crude phosphoric acid in a mixing tank or in a reaction vessel, wherein the crude phosphoric acid contains dissolved and suspended contaminates; precipitating a portion of the dissolved contaminates thereby forming a first mixture, wherein either or both a chemical precipitating agent is mixed into the aqueous crude phosphoric acid or the aqueous crude phosphoric acid is passed through an electrocoagulation reactor; feeding the first mixture to an ultrafiltration (UF) system, wherein the UF system comprises a plurality of ceramic membrane tubes enclosed within a housing, wherein each ceramic membrane tube has a length, opposing first and second ends, a longitudinal axis and a porous side wall that defines a longitudinal bore between the opposing ends, wherein the first mixture is fed into first end of the tubes; collecting a permeate stream from the housing, wherein the permeate stream is a portion of the first mixture that flows through the porous side wall in each ceramic membrane tube; and collecting a retentate stream from the second end of the tubes.

50. The method of embodiment 49, wherein the ceramic membrane tubes comprise silicon carbide.

51 . The method of embodiment 50, wherein the ceramic membrane tubes further comprise zirconium oxide.

52. The method of embodiment 49, wherein the ceramic membrane tubes comprise silicon carbide (SiC), zirconium oxide (ZrC ), titanium sub-oxide (TiziO?), and Boron Doped Diamond (BDD).

53. The method of embodiment 49, 50, 51 or 52, wherein the amount of solid particulate matter in the permeate stream is less than 60% of the amount of solid particulate matter in the amount of solid particulate matter in the retentate stream. 54. The method of embodiment 53, wherein the amount of solid particulate matter in the permeate stream is less than 50% of the amount of solid particulate matter in the amount of solid particulate matter in the retentate stream.

55. The method of embodiment 49, 50, 51 or 52, further comprising a recirculation loop in which the retentate stream is added to the first mixture and fed to the UF system.

56. The method of embodiment 55, further comprising a filter press, wherein a portion of the retentate stream is fed to the filter press.

57. The method of embodiment 56, further comprising recovering a filtrate from the filter press and adding the filtrate to the aqueous crude phosphoric acid.

58. The method of embodiment 49, 50, 51 or 52, further comprising a carbon filter and passing the permeate stream through the carbon filter.

59. The method of embodiment 58, wherein a decolored permeate stream is discharged from the carbon filter, further comprising evaporating water from the decolored permeate stream.

|0050| Having described the invention above, various modifications of the techniques, procedures, materials, and equipment will be apparent to those skilled in the art. It is intended that all such variations within the scope and spirit of the invention be included within the scope of the appended claims.