Methods for producing phosphate and sulfate products

Abstract

The present invention (a) A step of reacting a phosphorus-containing material with sulfuric acid in the absence of a solvent to form a reaction mixture containing phosphoric acid, residual sulfuric acid and residual material, (b) A step of separating the generated phosphoric acid and residual sulfuric acid from the residual material by adding ethanol, thereby forming an ethanol slurry in which both acids are dissolved and a solid residual material. (c) A step of separating solid residue from ethanol in which the acid has been dissolved, (d1) Reacting both acids with ammonia to produce ammonium phosphate and ammonium sulfate, and separating ammonium phosphate and ammonium sulfate from ethanol, and / or (d2) A step of separating both acids from ethanol to produce phosphoric acid and sulfate products, (e) A process in which the separated ethanol is recycled back to process (b). The present invention relates to a method for producing a mixture of phosphate and sulfate products, including [specific components].

Description

Technical Field

[0001] The present invention relates to a method for producing a mixture of phosphate products and sulfate products. Further, it relates to a method for producing phosphoric acid and its products. In addition, the present invention particularly relates to the production and use of phosphoric acid and derivative salts from secondary phosphates such as waste streams. The present invention also relates to the production of ammonium phosphate salts combined with ammonium sulfate salts and the use of such salts as, for example, fertilizer raw materials, flame retardants, feed additives, and nutrients.

Background Art

[0002] In the production of phosphorus-containing products, in recent years, phosphorus resources have become increasingly scarce. One of the reasons is that phosphorus is a major component of fertilizers, animal feeds, detergents, and flame retardants. Phosphate is mined from phosphate rock, and China is the largest producer. The quality of phosphate rock varies. For example, phosphate rock in the United States contains 28.5 - 29.0% P2O5.

[0003] Phosphate mining has a great impact on the environment. For every ton of phosphoric acid produced by processing phosphate rock, usually 5 tons of waste is generated. This waste takes the form of radioactive solids containing impurities called phosphogypsum, which is of no use. Furthermore, the by-products of phosphate mining methods include fluoride, uranium, vanadium, etc.

[0004] Phosphate mines around the world are rapidly depleting. Therefore, there is a technical need for a more sustainable method that can recover phosphorus from, for example, waste resources, especially solid phosphorus sources. An example of a solid phosphorus source is struvite. This is a solid mineral that exists, for example, in wastewater treatment facilities, wastewater from the food processing industry, and other waste streams. Other solid phosphorus-containing waste resources include sewage sludge ash, meat and bone meal ash, compost ash, etc.

[0005] Generally, phosphoric acid, the basic raw material for phosphate fertilizers, is obtained by acid treatment (sulfuric acid, with the exception of hydrochloric acid) of phosphate rock (Ullmann's Technical Encyclopedia). This technique has been known for over a century and forms the basis of phosphoric acid and most derived phosphate-containing compounds (mainly for fertilizers, and also for industrial, animal feed, and food phosphates).

[0006] Ammonium sulfate ((NH4)2SO4) is an inorganic salt with numerous commercial uses. Its most common use is as a soil fertilizer for alkaline soils. It contains 21% nitrogen and 24% sulfur. Ammonium ions are released in the soil, lowering the soil's pH balance by forming a small amount of acid, while simultaneously supplying nitrogen essential for plant growth. It can also be used as an agricultural spraying aid for water-soluble insecticides, herbicides, and fungicides. In this case, it functions to bind iron and calcium cations present in well water and plant cells. Ammonium sulfate has also been used in flame retardant compositions, exhibiting similar effects to diammonium phosphate. As a flame retardant, it increases the combustion temperature of materials, reduces the maximum weight loss rate, and increases the formation of residues or charred materials.

[0007] Ammonium sulfate can be produced by treating ammonia with sulfuric acid, or it can be produced from gypsum (CaSO4·2H2O). In the latter case, fine gypsum is added to an ammonium carbonate solution. Calcium carbonate precipitates as a solid, leaving ammonium sulfate in the solution. Currently, sulfur resources are not depleted.

[0008] Methods for recovering phosphorus in the form of phosphate from a solid phosphorus source are known as prior art. Generally, these methods involve leaching phosphorus from the solid phosphorus source using an aqueous medium, and then recovering the phosphorus from the leachate.

[0009] For example, U.S. Patent No. 3,298,782 describes a method for extracting phosphates from phosphate rock after decomposing it with sulfuric acid, using a mixture of an alcohol immiscible with water and an amine-based extractant.

[0010] French Patent No. 1480663 discloses a conventional method for producing phosphoric acid by acid-treating phosphate rock. This method is an extension of the usual water-based phosphoric acid production method used on a large scale in industry. This method requires preheating of the phosphate rock, and as the examples in French Patent No. 1480663 demonstrate, the effectiveness of the procedure without heating is unacceptably low. Heating large quantities of phosphorus sources is costly in terms of both investment and operating costs.

[0011] International Publication No. 2020 / 169708 describes a method for producing phosphoric acid from solid phosphorus-containing materials. The solid phosphorus-containing material is contacted with a strong acid in a single-phase reaction medium containing an organic solvent, forming a phosphoric acid solution in the organic solvent and a residual solid material. The phosphoric acid solution in the organic solvent is then separated from the residual solid material. This method has been shown to allow for the recovery of phosphoric acid from solid phosphorus-containing materials with high purity and efficiency. A drawback of the method described in International Publication No. 2020 / 169708 is the need to use a strong acid diluted with an organic solvent for extraction. Dilution of the acid reduces the phosphorus recovery efficiency in complex materials such as sewage sludge ash. Therefore, the construction and operation of such methods are expensive. Furthermore, it is well known that such methods are sensitive to interference, such as fluctuations in input parameters.

[0012] International Publication No. 2022 / 098241 relates to a method for producing phosphoric acid, which involves reacting a phosphorus-containing material with an acid to form a reaction mixture containing phosphoric acid, without using an organic solvent. Here, the pKa of the acid is 3.5 or less, and then an organic solvent is added to the reaction mixture to extract phosphoric acid from the reaction mixture, thereby forming a phosphoric acid solution. Here, the amount of free water added to the reaction mixture is 20% by weight or less of the total weight of the reaction mixture, and the phosphorus-containing material includes a secondary raw material containing a phosphate salt.

[0013] U.S. Patent No. 3,663,168 describes a method for producing concentrated phosphoric acid from monocalcium phosphate present in single or triple superphosphates. This method involves mixing monocalcium phosphate with methanol and an acidic sulfate. Monocalcium phosphate has long been produced in the form of single or triple superphosphates by acid treatment of phosphate rock. Many plants use sulfuric acid as an acidifying agent in the production of single superphosphates. To produce phosphoric acid, the superphosphate raw material is mixed with methanol, and then sulfuric acid or ammonium sulfate is added. Fresh methanol was used for washing. A drawback of this method is that methanol is highly susceptible to degradation in the presence of concentrated sulfuric acid. Furthermore, the toxicity and handling safety issues of methanol make it unsuitable for industrial-scale use.

[0014] The literature discussed above discloses methods that are complex to implement. Therefore, there is a demand for optimized methods for producing high-quality ammonium phosphate, ammonium sulfate, and / or phosphoric acid that are easier to implement. Furthermore, there is a demand for methods for extracting phosphorus compounds that produce fewer low-quality by-products. [Prior art documents] [Patent Documents]

[0015] [Patent Document 1] U.S. Patent No. 3,298,782 [Patent Document 2] French Patent No. 1480663 [Patent Document 3] International Publication No. 2020 / 169708 [Patent Document 4] International Publication No. 2022 / 098241 [Patent Document 5] U.S. Patent No. 3663168 [Overview of the project]

[0016] An object of the present invention is to solve one or more drawbacks faced by the prior art. Another object of the present invention is to provide an alternative to two-phase extraction systems and to avoid additional complexity. Other objects include avoiding the formation of undesirable by-products. In particular, an object is to provide an efficient and low-cost method for producing phosphoric acid that prevents the effects of contamination of the processing equipment.

[0017] Therefore, the present invention is (a) A step of reacting a phosphorus-containing material with sulfuric acid in the absence of a solvent to form a reaction mixture containing phosphoric acid, residual sulfuric acid and residual material, (b) A step of separating the generated phosphoric acid and residual sulfuric acid from the residual material by adding ethanol, thereby forming an ethanol slurry in which both acids are dissolved and a solid residual material. (c) A step of separating solid residue from ethanol in which the acid has been dissolved, (d1) Reacting both acids with ammonia to produce ammonium phosphate and ammonium sulfate, and separating ammonium phosphate and ammonium sulfate from ethanol, and / or (d2) A step of separating both acids from ethanol to produce phosphoric acid and sulfate products, (e) A process in which the separated ethanol is recycled back to process (b). The present invention relates to a method for producing a mixture of phosphate and sulfate products, including [specific components].

[0018] Furthermore, the present invention relates to a product in which the total amount of ammonium phosphate and ammonium sulfate is at least 80% by weight, and the salts of iron, aluminum, and magnesium are at most 20% by weight, and the P:S ratio is in the range of 1:0.5 to 1:2, preferably in the range of 1:1 to 1:2.

[0019] The present invention also relates to using such products as fertilizer raw materials, flame retardants, feed additives, or yeast nutrients. [Brief explanation of the drawing]

[0020] To illustrate the present invention, the following non-limiting examples are shown. [Figure 1] A box plot of the phosphorus conversion rate (using sludge ash as a phosphorus-containing raw material) when the ratio of sulfuric acid to sludge ash is changed is shown. [Figure 2] Two NMR spectra of acetone after acid treatment are shown, indicating that a distinct decomposition peak of acetone can be confirmed after 4 days. [Figure 3] Two NMR spectra of ethanol after acid treatment are shown, indicating that the decomposition peak of ethanol is not confirmed after 4 days. [Figure 4] Results of phosphoric acid and residual solid samples analyzed by ICP analysis using methanol, ethanol, and acetone as solvents are shown. The comparison is based on the elemental yield into the solution. [Figure 5] Results of phosphoric acid and residual solid samples analyzed by ICP analysis using methanol, ethanol, and acetone as solvents are shown. The comparison target is the element retained in the solid content. [Figure 6] Results of phosphoric acid samples in various tests are shown.

Mode for Carrying Out the Invention

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this invention belongs. The terms used in the description of the invention herein are for the purpose of describing particular embodiments and are not intended to limit the invention.

[0022] As used herein, the term “free water” includes water that is not bound to a solid material, such as a crystalline skeleton or the phosphorus-containing material described herein. In particular, this term refers to water that is added as is and / or as part of a solution. Unlike conventional wet methods, it is desirable that the water added to the reaction mixture be in very small amounts (preferably 20% by weight or less, more preferably 10% by weight or less), and even more preferably none, so that the phosphoric acid produced is of high concentration and high purity as described herein. In particular, it is desirable that the free water introduced into the method by the phosphorus-containing material and / or acid be 10% by weight or less, more preferably 5% by weight or less, or none at all. Free water may be introduced into the reaction mixture by using a low concentration of acid, such as 93% concentrated sulfuric acid.

[0023] As used herein, the term “phosphoric acid” is intended to refer to phosphorus oxoacids. In particular, the term refers to phosphoric acid in which each phosphorus atom is bonded to four oxygen atoms (one of which is via a double bond), with the atoms positioned at the vertices to form a tetrahedral molecule. The oxidation state of phosphorus may be +5. Furthermore, phosphoric acid may contain one or more PO4 tetrahedra, thereby forming linear or branched, cyclic, or more complex structures. Examples of such phosphoric acids include oligophosphates such as phosphoric acid, pyrophosphate, triphosphate, superphosphate, and polyphosphate.

[0024] As used herein, the term “crystalline framework” includes, for example, the crystalline framework of a salt. The crystalline framework may be derived at least in part from a phosphorus-containing material. Water may be present within the crystalline framework. Such water may be removed, for example, by heating or solubilizing the crystalline framework. Therefore, the expression “water derived from the crystalline framework” is used. The water content of a compound can be measured by thermogravimetric analysis, nuclear magnetic resonance spectroscopy, near-infrared spectroscopy, and X-ray diffraction crystallography.

[0025] As used herein, the term “phosphate products” includes phosphoric acid as described above and phosphates produced during the process of the present invention. Phosphates include various forms of ammonium phosphate, iron(II) phosphate, iron(III) phosphate and their polymorphs (which may include hydrate forms), all forms of magnesium phosphate (including monomagnesium phosphate, dimagnesium phosphate, and trimagnesium phosphate; which may include hydrate forms), all forms of zinc phosphate, all forms of calcium phosphate (calcium hydrogen phosphate, dihydrogen phosphate, monocalcium phosphate, dihydrogen phosphate, polycalcium phosphate, hydroxyphosphates and oxophosphates which may include hydrate forms, all forms of silicon phosphate which may include hydrate forms, and aluminum phosphate, nickel phosphate or copper phosphate.

[0026] As used herein, the term “sulfate products” includes sulfuric acid and sulfates produced in the methods of the present invention. Sulfates include ammonium sulfate, ferric sulfate, ferric sulfate and all their polymorphs (which may include hydrates), magnesium sulfate (which may include hydrates), zinc sulfate, calcium sulfate (which may include hydrates), silicon sulfate (which may include hydrates), and all forms of aluminum sulfate, nickel sulfate, and copper sulfate.

[0027] As used herein, the term “residual solids” refers to materials that do not dissolve or react with sulfuric acid and remain solid or precipitate at least partially in ethanol. These residual solids may include some sulfate products such as zinc sulfate, calcium sulfate, silicon sulfate, nickel sulfate, or copper sulfate. The exact composition depends on the composition of the phosphorus-containing material used first. For example, using sewage sludge ash will result in more silica, iron sulfate, and aluminum sulfate, while using meat and bone meal ash will result in more calcium sulfate. Using dairy waste from whey processing will result in more calcium sulfate. Residual solids rich in sulfates, Ca, Si, Fe, and Al can be used, for example, in the manufacture of building materials. In concrete manufacturing, they may have beneficial properties that contribute to hardening acceleration and reaction acceleration.

[0028] The innovative extraction method of the present invention relates to the single-phase extraction of phosphates and provides a simple and economically attractive extraction method that is ideally suited, for example, to the production of phosphoric acid required for fertilizers.

[0029] The method for preparing a mixture of ammonium phosphate and ammonium sulfate according to the present invention involves reacting a phosphorus-containing material with sulfuric acid in the presence of a solvent. The reaction of the phosphorus-containing material with the acid forms a reaction mixture containing phosphoric acid. The reaction is carried out without the use of organic solvents. That is, the reaction mixture may contain 2% by weight or less of organic solvent relative to the total weight of the reaction mixture. Preferably, the reaction is carried out without any organic solvents. The phosphorus-containing material is acid-treated by directly adding sulfuric acid to the material or by the reverse method. During acid treatment (acid attack), the structure of the phosphorus-containing material may be destroyed at least partially (chemically and / or physically). Direct acid treatment of the phosphorus-containing material allows for reaching high reaction temperatures, which further accelerates the reaction in a short time. This, combined with a low free water content in the reaction mixture (e.g., 10% by weight or less, more preferably 5% by weight or less), significantly accelerates the reaction. Such decomposition of the phosphorus-containing material is represented by a series of reactions between the acid and the components of the phosphorus-containing material. When sulfuric acid is used, phosphates (e.g., calcium phosphate) are converted at least partially to calcium sulfate and phosphoric acid. The advantage of this solvent-free system lies in the formation of a reaction mixture consisting of phosphoric acid, residual sulfuric acid, and residual materials. The resulting reaction mixture is preferably a slurry with a viscosity intermediate between that of wet sand and coffee grounds.

[0030] In addition to sulfuric acid, one or more inorganic acids may be included. Examples of inorganic acids include nitric acid, hydrochloric acid, phosphoric acid, and perchloric acid. Sulfuric acid can be selected at any concentration, particularly at least about 70%, preferably at least about 80%, and more preferably at least about 96% or 98%. Nitric acid may have a concentration of about 68% or more. Hydrochloric acid may be selected at any concentration, preferably at least 30%. Phosphoric acid may be selected at any concentration, for example, in the range of about 75-85%. Perchloric acid may be selected at any concentration, preferably about 60% or more, more preferably about 70% or more.

[0031] Preferably, the acid comprises sulfuric acid plus one or more acids selected from phosphoric acid, nitric acid, and hydrochloric acid. More preferably, the acid comprises sulfuric acid alone, for example, sulfuric acid at a concentration of about 96-98%.

[0032] The reaction between phosphorus-containing materials and sulfuric acid is a spontaneously exothermic reaction. Typically, active heating is not required for the reaction. The reaction temperature depends on the starting temperature, the amount of heat generated, the water content, and the cooling / heating methods applied to the reaction environment. The temperature should be sufficient to effectively convert the phosphorus-containing material into phosphoric acid. For this reason, the reaction mixture may be actively heated. The reaction temperature is in the range of 50°C to 250°C, more preferably 90°C to 210°C. Below 50°C, the reaction rate is slow, and a complete reaction may not be achieved. After the reaction, the temperature of the reaction mixture is usually allowed to decrease naturally, for example, to about 100°C at most.

[0033] In the next step (b), the generated phosphoric acid and the remaining sulfuric acid are separated from the residue by adding ethanol, forming an ethanol slurry with dissolved acids and the residue. Using ethanol allows for easy separation of the product and by-products. This overcomes the separation problems that occurred in conventional wet methods. With ethanol, phosphoric acid and sulfuric acid dissolve, but by-products such as calcium sulfate dissolve only slightly or become insoluble. Aluminum sulfate, iron sulfate, and magnesium sulfate remain quite soluble in ethanol.

[0034] The use of ethanol overcomes problems that arise with other solvents. A drawback of the method described in International Publication No. 2022 / 098241 is that in the separation step, acetone was added to the partially solidified cooled reaction mixture to extract phosphoric acid. The resulting reaction mixture contained a solid residue and phosphoric acid dissolved in acetone. The solid residue was separated from the solvent by filtration. As a further extraction and washing step, additional acetone was added to the reactor and filtered. The total concentration of H3PO4 in the acetone from the filtrates from all filtration steps was 6.5%. The acetone was evaporated in a solvent evaporator to obtain pure solvent-free phosphoric acid. The total yield of pure phosphoric acid was 96% (calculated as phosphorus based on the phosphorus content in the raw materials).

[0035] The acetone used to dissolve the formed phosphoric acid was found to be unusable in this method because its decomposition causes the acetone itself and the resulting products to be stained yellow, dark brown, and even black. The decomposition of acetone can also produce a black, tar-like material after several recyclings, which is unusable in the method of this invention.

[0036] A drawback of the process described in U.S. Patent No. 3,663,168 is that methanol is used in both the reaction and separation stages. Furthermore, fresh methanol was used for washing. The disadvantage of methanol use is that it is highly susceptible to degradation in the presence of concentrated sulfuric acid. In addition, due to its toxicity and handling safety, the use of methanol on an industrial scale is not easy.

[0037] The use of ethanol results in a far superior overall method. Since ethanol does not decompose or decomposes only very partially, losses are limited. In step (e) of the method, the separated ethanol is recycled to step (b). To compensate for the loss of ethanol, it is possible to add, preferably up to 5% by weight, more preferably up to 2% by weight, of ethanol relative to the total amount of ethanol recycled. The separated ethanol recycled may contain some water. Preferably, the recycled ethanol contains water in the range of 1 to 20% by weight, more preferably 2 to 15% by weight, even more preferably 3 to 10% by weight, and even more preferably 4 to 7% by weight. If the amount of water in the recycled ethanol is too low, additional water may be added to the recycled ethanol.

[0038] In this context, ethanol refers to the alcohol used in step (b). Other alcohols may be present in trace amounts of 20% by weight or less, preferably 10% by weight or less, more preferably 5% by weight or less, and even more preferably 2% by weight or less. Most preferably, no other alcohols are present besides ethanol.

[0039] The favorable results with ethanol were unexpected. International Publication No. 2022 / 098241 describes particularly good extraction results obtained using solvents that do not form azeotropic mixtures with water. Since ethanol forms azeotropic mixtures with water, the favorable results with ethanol are unpredictable.

[0040] In the next step, the residue is separated from the ethanol in which the acid has dissolved. Suitable separation techniques for this step include filtration, centrifugation, and / or decantation, or a combination thereof. Furthermore, it has been found that water may improve filtration. Preferably, filtration is performed by shear-enhanced filtration using a nudge filter, a dynamic filter press, and / or a bocross filter. If necessary, a pre-coating agent or filter aid can be added to improve filtration efficiency. After separation, it is possible to repeat the process of reslurrying with ethanol to improve recovery. In this process, it is preferable to backflow the ethanol. It is desirable to return the clean solvent after separation to the previous step for reslurrying.

[0041] The addition of water may improve filtration and / or centrifugation by promoting flocculation and / or coagulation and / or crystallization. This water is added to ethanol, preferably in a ratio of 0.05 to 0.7, more preferably 0.05 to 0.3, relative to the phosphorus-containing material. It is believed that the addition of a certain amount of water produces magnesium sulfate, calcium sulfate, aluminum sulfate and / or iron sulfate containing x molecules of crystal water, which are easily filtered, where x is preferably an integer from 1 to 24. Sulfates up to the maximum amount of crystal water have excellent properties with respect to filtration.

[0042] It is possible to add water at the start of the reaction, and it is preferable to use more diluted sulfuric acid. It is also possible to add water at the end of the acid treatment reaction, during the separation of phosphoric acid. Furthermore, it is possible to add water before the separation of the existing solids and liquids.

[0043] Increasing the solid content reduces drying energy. This is because an increase in solid content reduces the amount of solvent needed, thus decreasing the amount of solvent that needs to be evaporated. Therefore, when a dried cake is obtained by solid-liquid separation, the amount of solvent that needs to be evaporated decreases.

[0044] In step (d1), the acid reacts with ammonia to produce ammonium phosphate and ammonium sulfate, which are separated from ethanol. Since the products are readily soluble in water, there is little to no water present. Preferably, the maximum amount of water present is 20% by weight, more preferably 10% by weight, and even more preferably 8% by weight. The precipitate can be separated from ethanol using commercially available techniques. When the ethanol in which the acid has been dissolved is ammonia-treated (treated with ammonia and / or its derivatives), a mixed precipitate of ammonium phosphate and ammonium sulfate is formed, which can be easily removed by filtration. This product may contain metals such as Mg, Fe, and Al. The precipitate is further dried or washed and dried to recover the ethanol and produce a solid suitable for commercial sale. Vacuum drying with steam recovery is preferably used for further drying of the precipitate. This water-soluble compound is, for example, a very valuable fertilizer. Because ammonium phosphate and ammonium sulfate are extremely insoluble in ethanol, this precipitate is remarkably different from precipitates in conventional aqueous systems. In conventional methods, ammonium phosphate and ammonium sulfate exhibit high solubility, requiring crystallization by evaporating large amounts of water. This was an unexpected result because ethanol forms an azeotropic mixture with water. While conventional aqueous systems for precipitation of ammonium phosphate are energy inefficient (energy-intensive), the present invention makes it possible to easily precipitate ammonium phosphate and ammonium sulfate in high purity. Furthermore, conventional aqueous systems for precipitation of ammonium phosphate produce a highly contaminated mother liquor containing a large amount of phosphoric acid that cannot be used to produce pure ammonium phosphate and cannot be discarded due to its value. The recovered ethanol according to the present invention is of extremely good quality and can be reused in step (b), and preferably can be reused multiple times.

[0045] In place of or in addition to step (d1), the acid is separated from the ethanol in step (d2) to produce phosphoric acid and sulfate products. Here again, the recovered ethanol is of very good quality and can be reused in step (b), preferably multiple times. Step (d2) is preferable to step (d1).

[0046] Advantageously, in step (a), an excess amount of sulfuric acid is added relative to the cations present in the phosphorus-containing material. More advantageously, the excess amount of sulfuric acid relative to the cations present in the phosphorus-containing material is in the range of 1.01 to 1.5, preferably in the range of 1.05 to 1.3. By using an excess amount of sulfuric acid relative to the cations in the phosphorus-containing material, the conversion rate of phosphorus in the phosphorus-containing material is increased to a level in which a conversion rate of at least 0.80 is achieved. The cations present are generally Ca, Fe, Al, Mg, and K. Other cations may be present as trace components at low concentrations.

[0047] The method may further include a step of cooling the reaction mixture before extraction. Preferably, the cooling step includes external cooling. The cooling step causes the dissolved salts to crystallize, facilitating the filtration of the precipitate and / or allowing the organic solvent to be mixed with the reaction mixture without the loss of most of the extraction solvent by evaporation. Preferably, the reaction mixture is cooled before step (b) via a jacket or by rapid cooling with a liquid, preferably with ethanol. Preferably, ethanol and / or additional ethanol are added to the reaction mixture at a temperature of 78°C or lower under atmospheric pressure, more preferably 55°C or lower under atmospheric pressure. This temperature can be reached by using external cooling or by allowing the mixture to cool for a certain period of time.

[0048] The use of other alcohols, such as n-propanol or isopropanol, may be considered as additional alcohols, but is not preferred. The use of a mixture of two or more different alcohols may also be considered.

[0049] Advantageously, in addition to ethanol, water is added to the reaction mixture in step (b) or step (c). The addition of water is advantageous for the formation of sulfates. Water is formed by the incorporation of water into the sulfate crystal structure; for example, up to 6 molecules of water are present in iron(III) sulfate hexahydrate, 7 molecules in magnesium(II) sulfate heptahydrate, and 2 molecules in calcium(II) sulfate dihydrate. The addition of water is also advantageous for the depolymerization of polyphosphate. The amount of water added is determined for each type of raw material. For example, depending on the components and form of Ca, Fe, Mg, Al, etc. in the sewage sludge ash, MeSO4·xH2O with a metal-dependent x is produced. Preferably, the amount of water added is sufficient to replace all of the crystal water x, and little free water remains in the ethanol after sulfate formation.

[0050] The present invention is applicable, for example, to the extraction of phosphates from secondary raw materials containing phosphates or from phosphate rock. The present invention enables the supply of high-purity, high-concentration phosphoric acid, phosphate derivatives, and sulfate derivatives, as defined herein, to local markets without relying on remote and unreliable mines. The present invention makes it possible to process large-scale raw material sources containing recycled phosphorus, such as struvite or sewage sludge ash, and extract phosphates.

[0051] The phosphorus-containing material may include secondary raw materials containing phosphates and / or phosphate rock. In particular, the phosphorus-containing material includes secondary raw materials containing phosphates. The secondary raw materials containing phosphates are any suitable poor, used, discarded, or depleted raw materials containing phosphates, such as agricultural food industry waste and sludge, and are reusable. For example, the secondary phosphate-containing material may be supplied from a phosphate recovery process. Preferably, the phosphorus-containing material includes one or more selected from apatite, calcium phosphate, struvite, vivienite, sewage sludge ash, meat and bone meal ash, dairy waste from whey processing, and fertilizer ash, and more preferably, one or more selected from struvite, vivienite, sewage sludge ash, meat and bone meal ash, calcium phosphate, and dairy waste from whey processing. Even more preferably, the phosphorus-containing material includes sewage sludge ash, meat and bone meal ash, and / or dairy stream from whey processing. The method of the present invention has been found to be particularly suitable for phosphorus-containing materials that have been heat-treated to convert the original material into ash. Most preferably is sewage sludge ash.

[0052] In the method of the present invention, the molar ratio of phosphorus (calculated as P) to sulfuric acid (calculated as protons) in the phosphorus-containing material is preferably 1:1 or higher, more preferably 1:1 to 15:1. More preferably, the molar ratio of sulfuric acid (calculated as protons) to phosphorus (calculated as P) in the phosphorus-containing material is 3:1 to 12:1. When using either sewage sludge ash or meat and bone meal ash, the molar ratio of sulfuric acid (calculated as protons) to phosphorus (calculated as P) in the phosphorus-containing material is even more preferably 4:1 to 8:1, and the exact ratio depends on the exact composition of the ash.

[0053] The inventors have discovered that acid treatment of phosphorus-containing materials, particularly secondary phosphates (secondary raw materials containing phosphates), with sulfuric acid generates autothermia in materials containing iron and / or aluminum, such as sewage sludge ash, especially in the presence of water. This heat is sufficient to convert the material into phosphoric acid and residual sulfuric acid in high yield. The phosphoric acid and sulfuric acid can then be selectively extracted using ethanol. As a result, the present invention avoids the complexity and cost of conventional methods as described in the prior art herein. Advantageously, phosphoric acid is formed by a spontaneous exothermic reaction between the phosphorus-containing material and sulfuric acid.

[0054] Preferably, 20% by weight or less of free water relative to the total weight of the reaction mixture is added to the reaction mixture. The amount of free water added to the reaction mixture may be 15% by weight or less, for example, 14% by weight or less, 13% by weight or less, 12% by weight or less, 11% by weight or less, or 10% by weight or less. Preferably, the amount of free water added to the reaction mixture is 5% by weight or less, for example, 4% by weight or less, or 3% by weight or less. More preferably, the amount of free water added to the reaction mixture is 2% by weight or less, such as 1% by weight. Even more preferably, substantially no free water is added to the reaction mixture (i.e., about 0% by weight of the reaction mixture). Although not bound by theory, it is thought that a small amount of free water added to the reaction mixture contributes to obtaining soluble phosphoric acid and / or phosphate compounds in high yield and high purity as described herein. One reason for adding 20% ​​by weight or less of free water to the reaction mixture is that it is desirable to obtain high concentrations of phosphoric acid as described herein, which can be transported at minimal cost, for example. Furthermore, by adding such a small amount of free water to the reaction mixture, the extraction process yields a solvent that can be reused in subsequent cycles, particularly with a desirable low water content.

[0055] Preferably, the amount of free water is 10% by weight or less, more preferably 5% by weight or less, and even more preferably 2% by weight or less. In addition to free water, the reaction mixture may contain water that was originally present in the crystalline skeleton, for example. For example, the amount of water derived from the crystalline skeleton may vary depending on the composition of the phosphorus-containing material. Therefore, in the case of sewage sludge, for example, the reaction mixture may contain approximately zero% by weight of water relative to the total weight of the reaction mixture, or at least 30% by weight or more of water derived from the crystalline skeleton. In particular, the reaction mixture may contain 40% or more by weight of water derived from the crystalline skeleton, such as 45% or 50% or more by weight.

[0056] Free water may be present in phosphorus-containing materials. Phosphorus-containing materials and / or acids may contain free water. The amount of free water contained in either may vary depending on the composition of the phosphorus-containing material and / or acid. In particular, a mixture of phosphorus-containing material and acid may contain 20% by weight or less of free water, for example, 15% by weight or less, 13% by weight or less, or 11% by weight or less, relative to the total weight of the phosphorus-containing material and acid. Preferably, the amount of free water in a mixture of phosphorus-containing material and acid is 10% by weight or less, for example, 9% by weight or less, 8% by weight or less, 7% by weight or less, or 6% by weight or less. More preferably, the amount of free water in a mixture of phosphorus-containing material and acid is 5% by weight or less, for example, 4% by weight. It is believed that such an amount of free water in a mixture of phosphorus-containing material and acid contributes to the direct acid treatment of the phosphorus-containing material and the exothermic reaction between the material and the acid. Therefore, the amount of heat required to promote the acid treatment reaction is small or no heat is required at all. Therefore, by keeping the amount of free water in the mixture of phosphorus-containing material and acid low, the reaction between the material and the acid may become spontaneous and / or exothermic.

[0057] Using ethanol instead of water prevents the formation of compounds like silica gel. Silica gel can cause harmful contamination (or fouling) within the method apparatus. Water induces hydrolysis of silica, leading to polymerization. Free water in the solvent should be minimized and preferably avoided.

[0058] The sulfuric acid used in the method of the present invention is preferably industrial-grade sulfuric acid. The concentration of the sulfuric acid is preferably 70% or higher, more preferably 80% or higher, even more preferably 90% or higher, and most preferably at least 96%.

[0059] This process may further include the addition of phosphoric acid. Phosphoric acid may be added, for example, to the reaction mixture of step (a) at the stage of step (a) (prior to the extraction step of step (b)), added between steps (a) and (b), and / or added during the extraction step of step (b), for example, before the addition of ethanol to the reaction mixture, simultaneously with the addition of ethanol, and / or after the addition of ethanol. Phosphoric acid may consist of all or part of the phosphoric acid formed by the method. For example, phosphoric acid may consist of 5% by weight or more of the phosphoric acid formed relative to the total weight of phosphoric acid, for example, 10% by weight or more, 15% by weight or more, 20% by weight or more, 25% by weight or more, or 30% by weight or more. Phosphoric acid may be 95% by weight or less of the produced phosphoric acid relative to the total weight of phosphoric acid, for example, 90% by weight or less, 85% by weight or less, 80% by weight or less, 75% by weight or less, or 70% by weight or less. In particular, phosphoric acid may contain 10 to 90% by weight of the produced phosphoric acid. For example, the solid-liquid ratio may be 20-80% by weight or 30-70% by weight. For example, by imparting a solid-liquid ratio to the reaction mixture as described herein, it is possible to improve the homogeneity of the reaction mixture and / or the extraction efficiency of phosphoric acid.

[0060] After extracting phosphoric acid and sulfuric acid from the reaction mixture, the acidic solution may still contain trace amounts of sulfate. Extraction is preferably carried out by evaporating ethanol in step (d2), and the recovered ethanol is recycled back into steps (e) through (b). The solids remaining in the acidic solution after extraction consist mainly of calcium sulfate and trace impurities derived from the phosphorus-containing raw materials. Any conventional filtration apparatus can be used to separate the phosphoric acid-containing solution from the solids. Further continuous washing steps can be performed to optimally separate the dissolved phosphoric acid and sulfuric acid from the solids. The production of high-purity phosphoric acid and sulfuric acid is desired. The amount of sulfate in the solution can be reduced by partial evaporation of ethanol. This process causes the sulfates to precipitate, which can then be removed by further filtration. However, since the amount of sulfate in the solution may be very small, this further purification step is not always necessary for all applications. Because the extraction method is highly selective, most other components present in the phosphorus-containing material (such as silica, calcium, copper, zinc, and iron) are not extracted in significant amounts and are filtered out as solids along with sulfates during the primary filtration process.

[0061] The present invention enables the production of high concentrations of phosphoric acid and sulfuric acid, particularly by minimizing the water content during the oxidation reaction. High concentrations of phosphoric acid include, for example, superphosphate and polyphosphate. Conventionally, producing such phosphoric acid required a large amount of thermal energy to remove water from ordinary phosphoric acid, or the addition of phosphorus pentoxide produced through an energy-intensive white phosphorus synthesis pathway. To obtain phosphoric acid from a solution, reuse by evaporation and recovery of the solvent is preferred. Distillation or evaporation of the solvent may produce phosphoric acid and phosphorus pentoxide (P2O5) of different concentrations. The phosphoric acid may have a P2O5 content of at least 35% by weight. For example, in the range of about 35% by weight P2O5 to about 70% by weight P2O5, specifically in the range of about 35% by weight P2O5 to about 65% by weight P2O5. The phosphoric acid may have a P2O5 concentration of 40% by weight or more, for example, 45% by weight or more, 50% by weight or more, 55% by weight or more, or 60% by weight or more, and / or for example, 70% by weight or less, 65% by weight or less. For example, phosphoric acid may have a P2O5 concentration of 40-70% by weight, for example, 55-70% by weight, or 60-65% by weight. More preferably, phosphoric acid has a P2O5 content of 60% by weight or more, for example, 65% by weight or more, for example, 60-70% by weight. The concentration of phosphoric acid depends on the amount of water added to or present in the reaction mixture, etc. Phosphoric acid can be easily further concentrated, for example, by heating the acid to evaporate the water.

[0062] After phosphoric acid and sulfuric acid are extracted from the reaction mixture, they react with ammonia to produce ammonium phosphate and ammonium sulfate. The present invention also relates to the resulting product, in which the total of ammonium phosphate and ammonium sulfate is at least 80% by weight, the P:S ratio is in the range of 1:1 to 1:2, and the product contains up to 20% by weight of salts of iron, aluminum, and magnesium.

[0063] Preferably, the salts of iron, aluminum, and magnesium are hydrated iron(II) sulfate, hydrated aluminum sulfate, and hydrated magnesium sulfate, or phosphates.

[0064] In the most preferred embodiment of the present invention, ethanol is used as the solvent to convert the acid into an ammonium salt product. That is, the method for producing a mixture of the phosphate product and the sulfate product is as follows: (a) A step of reacting a phosphorus-containing material with sulfuric acid in the absence of a solvent to form a reaction mixture containing phosphoric acid, residual sulfuric acid and residual material, (b) A step of separating the generated phosphoric acid and residual sulfuric acid from the residual material by adding ethanol, thereby forming an ethanol slurry in which both acids are dissolved and a solid residual material. (c) A step of separating solid residue from ethanol in which the acid has been dissolved, (d1) Reacting both acids with ammonia to produce ammonium phosphate and ammonium sulfate, and separating ammonium phosphate and ammonium sulfate from ethanol, and / or (d2) A step of separating both acids from ethanol to produce phosphoric acid and sulfate products, (e) A process in which the separated ethanol is recycled back to process (b). Includes.

[0065] The animal feed may be provided by adding a calcium compound to an organic solvent as a calcium ion source for precipitating calcium phosphate. Neutralization of the extraction solvent with sodium hydroxide may precipitate sodium phosphate, a commercially valuable product. Neutralization with a potassium compound such as potassium hydroxide produces a precipitate of potassium phosphate, which is useful for industrial and food applications. Thus, it can be seen that phosphoric acid can be easily separated from the solution, for example by evaporation and / or precipitation in the form of a salt. Therefore, the method may further include the step of adding a reactant (e.g., any of the reactants described above) that reacts with phosphoric acid to form a phosphate to the phosphoric acid solution. The reactant is selected from calcium compounds, sodium compounds, and / or potassium compounds, preferably any of the compounds described herein. For example, the method may further include the step of treating the phosphoric acid solution with ammonia to form an ammonium phosphate salt. Thus, an ammonium phosphate salt obtained by the method is also provided, and the method further includes the step of treating the phosphoric acid solution with ammonia to form an ammonium phosphate salt.

[0066] Mixtures of ammonium phosphate and ammonium sulfate may contain impurities similar to those found in phosphoric acid, such as metals like aluminum, magnesium, iron, and calcium, fluorides, unreacted phosphoric acid, solvents, and acids. In particular, mixtures of ammonium phosphate and ammonium sulfate contain impurities of 20% by weight or less, based on the total weight of ammonium phosphate and ammonium sulfate. Preferably, mixtures of ammonium phosphate and ammonium sulfate contain impurities of 10% by weight or less, such as 5% by weight or less. More preferably, mixtures of ammonium phosphate and ammonium sulfate contain impurities of 3% by weight or less, for example, 2% by weight or less, or 1% by weight or less.

[0067] The present invention further relates to the use of a mixture of ammonium phosphate and ammonium sulfate (with a P / S ratio in the range of 1:0.5 to 1:2, preferably in the range of 1:1 to 1:2, and containing up to 20% by weight of salts of iron, aluminum, and magnesium) as a fertilizer raw material, flame retardant, feed additive, or yeast nutrient.

[0068] The present invention also provides for the use of ammonium phosphate salts obtained by methods defined herein as fertilizer materials, flame retardants, feed additives, or yeast nutrients (e.g., for winemaking). This step may also follow the steps of a first aspect of the present invention and further include adding a reactant that reacts with phosphoric acid to form an ammonium phosphate salt to a phosphoric acid solution. This method may also follow the methods for producing ammonium phosphate salts described herein. In particular, monoammonium phosphate and / or diammonium phosphate salts may be used as fertilizer materials, while monoammonium phosphate or diammonium phosphate salts may be used as precursors for producing flame retardants such as polyammonium phosphate, or as flame retardants themselves. [Examples]

[0069] (Example 1a): Laboratory test 50 g of sewage sludge ash (SSA) was placed in a beaker. 53 g of 96% sulfuric acid (SA) was added to the beaker. The contents of the beaker were stirred for 10 minutes. The temperature rapidly rose to 180°C and then began to decrease. The mixture was cooled to 50°C using a water bath, and then 250 mL of ethanol was added. The resulting slurry was mixed with ULTRA-TURRAX® for 10 minutes. The slurry was poured into a Buchner funnel, and the phosphoric acid solution was separated from the solid by vacuum filtration through filter paper. After the cake surface dried, an additional 50 mL of ethanol was poured onto the filtered cake to improve the phosphorus recovery rate from the solid. This operation was repeated twice. The measured phosphorus removal rate from the solid was 83%. Figure 1 shows the relationship between the phosphorus recovery rate from the solid and the SA:SSA ratio. From the figure, it can be concluded that 80% recovery from SSA is possible if this procedure is performed with an SA:SSA ratio of 1:1.

[0070] (Example 1b): Laboratory test Laboratory experiments were repeated using three types of ore samples (Egyptian rocks) with different P2O5 content. Specifically, the P2O5 content was 13.6% (Sample A), 18.6% (Sample B), and 19.6% (Sample C). The received ore was first ground into a fine powder to be used as input material. Sulfuric acid (SA) was added to this fine powder in a 1:1 ratio. Specifically, 10 grams of ore powder per 10 grams of sulfuric acid. After the addition of sulfuric acid, significant "foaming" occurred at the site where the ore powder and acid came into contact, and a foamy material was formed (thought to be due to the trapping of generated gas). At the same time, a large amount of heat was released. After continuous stirring, the reaction was confirmed to be complete by the homogenization of the mixture, and the reaction finished in about 10 minutes. This mixture is called the acid-treated solution. To measure the amount of extracted phosphate, the acid-treated solution was washed and separated from the residual solid. Specifically, the acid treatment solution was suspended in a solvent (ethanol-EtOH) and centrifuged. This separated the liquid EtOH portion containing extracted phosphoric acid (PA) from the solid residue called cake. To measure the amount of residual PA in the cake, the cake was dried overnight in an oven and then ground into a fine powder called coarse salt (CS). The phosphorus removal rates from the solid were 40% for sample A, 42% for sample B, and 54% for sample C.

[0071] (Example 2): Pilot plant scale 8 kg of sewage sludge ash was added to the acid treatment reactor. 4.4 L of 96% sulfuric acid was added over 10 minutes while stirring. The reaction, which liberates phosphates from the ash as phosphoric acid, raised the temperature to 134°C above the ambient temperature. Twelve minutes after stopping the sulfuric acid addition, the reactor was cooled by flowing water into the cooling mantle. After 48 minutes of cooling, when the temperature fell below 50°C, ethanol was added to dissolve the generated phosphoric acid, and stirring was intensified. The resulting slurry was filtered to separate the phosphoric acid solution and residual sulfuric acid from the solids, and transferred to the next step. The filtered cake was washed again and the solids were filtered, removing more than 80% of the phosphorus from the solids. In the next step, the phosphoric acid solution was reacted with ammonia to produce ammonium phosphate and ammonium sulfate, which were separated from the ethanol by filtration. The ethanol was reused in the oxidation reactor to dissolve the phosphoric acid.

[0072] When ethanol was used as the solvent, a clear liquid was obtained without significant discoloration or visible decomposition products. Ethanol was used multiple times. Experiments were also conducted using acetone as the solvent. For example, when acetone was used as the solvent, the liquid turned brown due to decomposition, and eventually became black. The composition of the solvent mixture after acid treatment was measured by NMR four days later. Decomposition (peaks) was clearly observed with acetone, but not with ethanol. The results are shown in Figures 2 and 3.

[0073] (Example 3): Comparison of degradation with different solvents Before starting the experiment, sewage sludge ash and sulfuric acid were mixed in a ratio of 1:0.73 and stirred to prepare the acid treatment solution. Since acid treatment is an exothermic reaction, the acid treatment solution was cooled to room temperature before the experiment. 23 g of the oxidizing solution and 70 mL of solvent were poured into a beaker. The contents of the beaker were mixed in an immersion blender for 5 minutes. The mixed sample was subjected to solid-liquid separation using filter paper. The time required for solid-liquid separation must be recorded. The residual solids on the filter paper were heated on a heating plate to promote the evaporation of the residual solvent. The residual liquid after paper filtration mainly consisted of the solvent and extracted phosphoric acid. Heat was added to the liquid to evaporate the solvent, leaving the phosphoric acid sample. The phosphoric acid and residual solid sample were analyzed by ICP analysis.

[0074] The analysis results are shown in Figures 4 and 5. The yields of ethanol, methanol, and acetone are similar. While the degradation of ethanol and methanol is negligible and visible to the naked eye, significant degradation and the formation of black products are observed in acetone and propanol. This is clearly visible in Figure 6. Figure 6 shows the results of phosphoric acid samples in various tests. Each letter represents the test results using different solvents: A: acetone B: Ethanol C: Methanol D: Ethanol E: methanol F: 1-propanol G: 1-Propanol H:2-propanol I:2-propanol J: Acetone K: Acetone

[0075] Ethanol and methanol clearly show superior results in terms of decomposition, while products using acetone, 1-propanol, or 2-propanol show clear decomposition and dark-colored products.

Claims

1. (a) A step of reacting a phosphorus-containing material with sulfuric acid in the absence of a solvent to form a reaction mixture containing phosphoric acid, residual sulfuric acid and residual material. (b) A step of separating the generated phosphoric acid and residual sulfuric acid from the residual material by adding ethanol, thereby forming an ethanol slurry in which both acids are dissolved and a solid residual material. (c) A step of separating solid residue from ethanol in which the acid has been dissolved, (d1) A step of reacting both acids with ammonia to produce ammonium phosphate and ammonium sulfate, and separating ammonium phosphate and ammonium sulfate from ethanol, and / or (d2) A step of separating both acids from ethanol to produce phosphoric acid and sulfate products, (e) A process in which the separated ethanol is recycled back to process (b). A method for producing a mixture of phosphate and sulfate products containing [the specified compound].

2. The method according to claim 1, wherein in step (a), an excess amount of sulfuric acid is added to the phosphorus in the phosphorus-containing material.

3. The method according to claim 2, wherein the amount of excess sulfuric acid relative to the cations present in the phosphorus-containing material is in the range of 1.01 to 1.5, preferably in the range of 1.05 to 1.

3.

4. The method according to any one of claims 1 to 3, wherein the reaction mixture is cooled before step (b) by cooling through a jacket or by rapid cooling with a liquid, preferably with ethanol.

5. The method according to any one of claims 1 to 4, wherein ethanol is added to the reaction mixture at a temperature of 78°C or lower, preferably 55°C or lower, under atmospheric pressure.

6. The method according to any one of claims 1 to 5, wherein in step (b) or (c), water is added to the reaction mixture in addition to ethanol.

7. The method according to any one of claims 1 to 6, wherein in step (b), ethanol is added to the reaction mixture in step (b).

8. The method according to any one of claims 1 to 7, wherein the phosphorus-containing material comprises one or more selected from apatite, struvite, vivienite, sludge ash, meat and bone meal ash, whey processing-derived dairy waste, and compost ash, preferably comprising one or more selected from struvite, vivienite, sludge ash, meat and bone meal ash, calcium phosphate, whey processing-derived dairy waste, and compost ash.

9. The method according to claim 8, wherein the phosphorus-containing material includes sludge ash, meat and bone meal ash, and / or dairy waste derived from whey processing.

10. The method according to any one of claims 1 to 9, wherein the molar ratio of sulfuric acid calculated as a proton to phosphorus in the phosphorus-containing material calculated as P is 1:1 or greater, preferably 1:1 to 15:

1.

11. The method according to claim 10, wherein the molar ratio is 3:1 to 12:

1.

12. The method according to any one of claims 1 to 11, wherein phosphoric acid is formed by a spontaneous exothermic reaction between a phosphorus-containing material and sulfuric acid.

13. The method according to any one of claims 1 to 12, wherein the amount of free water is 10% by weight or less, preferably 5% by weight or less, and more preferably 2% by weight or less.

14. The method according to any one of claims 1 to 13, wherein the sulfuric acid is industrial sulfuric acid.

15. A product in which the total amount of ammonium phosphate and ammonium sulfate is at least 80% by weight, and the total amount of iron, aluminum and magnesium salts is at most 20% by weight, and the P:S ratio is in the range of 1:0.5 to 1:2, preferably in the range of 1:1 to 1:

2.

16. A product in which the total amount of phosphoric acid and sulfuric acid and / or sulfates is at least 80% by weight, and the total amount of iron, aluminum and magnesium salts is at most 20% by weight, wherein the P:S ratio is in the range of 1:0.5 to 1:2, preferably in the range of 1:1 to 1:

2.

17. The product according to claim 15 or 16, wherein the iron, aluminum, and magnesium salts are iron(III) sulfate, aluminum sulfate, and magnesium sulfate.

18. Use of the product according to any one of claims 15 to 17 as a fertilizer raw material, flame retardant, feed additive, or yeast nutrient.

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