Process for producing superphosphate products from different phosphate sources

Abstract

The invention relates to a process for the preparation of super phosphate, comprising: a) reacting at least a first phosphorus containing material with sulfuric acid, thereby forming a reaction mixture comprising phosphoric acid, remaining sulfuric acid and residual material; b) separating the produced phosphoric acid and remaining sulfuric acid from the residual material by adding a solvent, thereby forming a slurry wherein at least the acids are dissolved and solid residual material; c) separating the solid residual material from the solvent wherein at least the acids are dissolved; d) recovering the solvent from the acids to produce a liquid product comprising at least phosphoric acid, sulfuric and sulfurous acid and dissolved metal sulphate and phosphate salts; and e) reacting at least part of the liquid product with at least one second phosphorus containing material to form super phosphate.

Description

[0001] PROCESS FOR PRODUCING SUPERPHOSPHATE PRODUCTS FROM DIFFERENT PHOSPHATE SOURCES

[0002] Field of the invention

[0003] The present invention relates to a process for the preparation of super phosphate. It furthermore relates to the production and uses of superphosphate, specifically from secondary phosphates, such as waste streams. The invention also relates to the uses of the super phosphates as fertilizer material, feed additive or nutrient.

[0004] Background of the invention

[0005] In the production of phosphorus comprising products, resources of phosphor become more scarce nowadays. One of the reasons is that phosphorus is a major element in fertilizer, in animal feed, detergents and flame retardants. Phosphate is being mined from phosphate rock, or phosphorite, with Marocco being the biggest producer. The grade of phosphate rock varies, phosphorite in the US for example contains from 28.5 to 29.0 percent P2O5.

[0006] Phosphate mining has a huge environmental impact. For each ton of phosphoric acid produced by the processing of phosphate rock, generally five tons of waste are generated. This waste takes the form of impure, useless, radioactive solid called phosphogypsum. Furthermore, byproducts of the phosphate mining process are for example fluoride, uranium and vanadium.

[0007] Phosphorus mines around the world are rapidly exhausting. There is thus a need in the art for a process which is more sustainable and able to recover phosphorus from for example waste resources, in particular from solid phosphorus sources. An example of a solid phosphorus source is struvite, which is a solid mineral which can be found in, for example, wastewater treatment units, wastewater from food processing industries, and other wastewater streams. Further solid phosphorus-containing waste resources include sewage sludge ash, meat and bone meal ash, and manure ash.In general, phosphoric acid, the basic feedstock for phosphate fertilizers, is obtained through acid attack (sulfuric acid, or exceptionally hydrochloric acid) on phosphate rock (Ullmann's Technical Encyclopedia). This technology has been known for over a century and forms the basis of phosphoric acid and most derivative phosphate containing compounds, chiefly fertilizers but also technical, feed and food grade phosphates.

[0008] The recovery of phosphate from various sources is for example described in WO-A-2024227815. In there is described a process for producing various phosphate and sulphate products, to be used as fertilizer material, flame retardant feed additive or yeast nutrient. To be used as fertilizer material in for example phosphate fertilizers, the phosphate products of WO-A-2024227815 might be less suitable as such.

[0009] However, there remains a need for the development of alternative processes and the production of suitable products to be used in phosphate fertilizers.

[0010] of the invention

[0011] It is an objective of the invention to address one or more of the disadvantages faced in the prior art. It is another objective of the invention to provide an alternative process for producing ingredients for phosphate fertilizers. A particular objective is to provide an efficient process for the production of phosphate comprising fertilizers starting from secondary phosphate sources.

[0012] Accordingly, the present invention relates to a process for the preparation of super phosphate, comprising:

[0013] a) reacting at least a first phosphorus containing material with sulfuric acid, thereby forming a reaction mixture comprising phosphoric acid, remaining sulfuric acid and residual material;

[0014] b) separating the produced phosphoric acid and remaining sulfuric acid from the residual material by adding a solvent, thereby forming a slurry wherein at least the acids are dissolved and solid residual material;

[0015] c) separating the solid residual material from the solvent wherein at least the acids are dissolved;d) recover the solvent from the acids to produce a liquid product comprising at least phosphoric acid, sulfuric and sulfurous acid and dissolved metal sulphate and phosphate salts; and

[0016] e) reacting at least part of the liquid product with at least one second phosphorus containing material to form super phosphate.

[0017] The present invention further relates to a product comprising at least in the range of from 10 up to 30 wt% of P2O5, at least in the range of from 10 up to 25 wt% of neutral ammonium citrate soluble P2O5 and at least in the range of from 5 up to 30 wt% of sulphate salts.

[0018] The present invention also relates to a use of the super phosphate comprising product, as fertilizer material and / or as ammonia binder.

[0019] Applicants have surprisingly found that the superphosphate as produced by the process of the invention has improved properties for the production of certain phosphate comprising fertilizers. These improved properties include a certain stickiness of the material that is advantageous in the formation of fertilizer particles. It is believed that these improved properties are the result of additional sulphate salts present due to process of the invention. Furthermore, by integrating the process of the invention to produce super phosphate with the production of a liquid product comprising at least phosphoric acid, for the same amount of phosphorus containing material, energy consumption is reduced by around 50% compared to acid production alone from the same amount of starting material. This was not foreseen, and it is a huge benefit for the environment. Also less complicated equipment is required, for the same amount of phosphorus containing material at the start, specially in the case of sewage sludge ash as phosphorus containing material.

[0020] Detailed description of 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 art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.The term "phosphoric acid" as used in this disclosure is meant to refer to phosphorus oxoacid. In particular, the term is used to refer to phosphoric acids, wherein each phosphorus atom is bonded to four oxygen atoms, one of them through a double bond, and arranged at the corners to form a tetrahedron-shaped molecule. The phosphorus may have an oxidation state of +5. In addition, the phosphoric acid may comprise one or more PO4 tetrahedra, thereby forming linear or branched chains, cycles, or more complex structures. Examples of such phosphoric acids are orthophosphoric acid, pyrophosphoric acid, oligophosphoric acid, such as triphosphoric acid, super phosphoric acid and polyphosphoric acid.

[0022] The term “phosphate products” as used herein, includes phosphoric acid as described above and phosphate salts that are being formed during the process of the invention. The phosphate salts may include the various forms of ammonium phosphate, iron (II) phosphate and iron (III) phosphate and its polymorphs, possibly in their hydrated form, all forms of magnesium phosphate including monomagnesium phosphate, dimagnesium phosphate and trimagnesium phosphate, possibly in their hydrated form, all forms of zinc phosphate, all forms of calcium phosphate including orthophosphates, di- and monohydrogen phosphates, di- and polyphosphates, hydroxy- and oxophosphates, possibly in their hydrated form, all forms of silicon phosphate, possibly in their hydrated form, and aluminum, nickel or copper phosphates, possibly in their hydrated form.

[0023] The term “super phosphate” as used herein, includes all formulations of super phosphate or superphosphate that contain a significant proportion of soluble and available phosphate ions which is the key quality property. Super phosphate includes single superphosphate, double superphosphate and triple superphosphate. Single superphosphate is generally produced using the traditional method of extraction of phosphate rock with sulfuric acid, an approximate 1:1 mixture of Ca(H2PC>4)2 and CaSC . Double superphosphate generally refers to a mixture of triple and single superphosphate, resulting from the extraction of phosphate rock with a mixture of phosphoric and sulfuric acids. Triple superphosphate is a component of many proprietary fertilizers. It primarily consists of monocalcium phosphate, Ca(H2PO4)2. It is obtained by treating phosphate rock with phosphoric acid. Many proprietary fertilizers are derived fromtriple superphosphate, for example by blending with ammonium sulphate and potassium chloride. Typical fertilizer-grade triple superphosphate contains 45% P2O5 eq, single superphosphate 20% P2O5 eq.

[0024] The term “sulphate products” as used herein, includes sulfuric acid and sulphate salts that are being formed during the process of the invention. The sulphate salts may include all forms of ammonium sulphate, iron (II) sulphate and iron (III) sulphate and all its polymorphs, possibly in their hydrated form, all forms of magnesium sulphate, possibly in their hydrated form, all forms of zinc sulphate, all forms of calcium sulphate, possibly in their hydrated form, all forms of silicon sulphate, possibly in their hydrated form, and aluminum, nickel or copper sulphates, possibly in their hydrated form.

[0025] The term “residual solid material” as used in this disclosure is meant to refer to the material that does not dissolve or hardly reacts anymore with sulfuric acid and remains solid or precipitates at least partly in solvent. This residual solid material may include some of the sulphate products, such as zinc sulphate, calcium sulphate, silicate, iron sulphate, aluminium sulphate, and nickel or copper sulphates. The exact composition depends on the composition of the phosphorus containing material that is being used to start with. If for example sewage sludge ash is being used, more silica, iron sulphate and aluminium sulphate is present whereas if meat and bone meal ash is being used, more calcium sulphate is present. If dairy waste from whey processing is being used, more calcium sulphate is being present. The residual solid material, being rich in sulphate, Ca, Si, Fe and Al, can be used for example for the production of building materials. In the production of concrete, it may have positive properties which contribute to faster curing and / or acceleration of the reaction.

[0026] The term “free water” as used herein, includes water that originates from a state wherein the water is not bound to, for example, solid matter, such as crystalline frameworks or phosphorus-containing material as described in this disclosure. In particular, the term refers to water that is added as such and / or as part of a solution. Unlike the traditional wet process, there is preferably very little, preferably 20 wt.% or less, more preferably 15 wt% or less, even more preferably 10 wt% or less is added to the reaction mixture so that the phosphoric acid produced is of high concentration and high purity as described in this disclosure.In particular, very little free water, such as 15 wt% or less, more preferably 10 wt.% or less of free water, may be introduced into the process by the phosphorus-containing material and / or acid. Free water might be introduced to the reaction mixture by using a less concentrated acid, for example a 93% concentrated sulfuric acid. Some free water is advantageous in order to mobilize the protons of sulfuric acid.

[0027] The term "crystalline frameworks" as used herein, includes crystalline frameworks of, for example, a salt. The crystalline frameworks can originate, at least in part, from the phosphorus-containing material. Water can be found in crystalline frameworks. Such water can be removed from a crystalline framework by, for example, heating or solubilizing the crystalline framework. Hence, the phrase "water originating from crystalline frameworks". The water content of compounds can be determined with thermogravimetric analysis, nuclear magnetic resonance spectroscopy, near infrared spectroscopy and even X-ray diffraction crystallography.

[0028] The innovative process of the invention relates to extraction of phosphate to provide a straightforward and economically interesting process for producing phosphoric acid and super phosphate, that is very suitable for use in for example, fertilizers. First at least a first phosphorus containing material which is reacted with sulfuric acid, thereby forming a reaction mixture comprising phosphoric acid, remaining sulfuric acid and residual material. Depending on the concentration of the sulfuric acid and the addition of water, more or less water will be present during this first step. A further solvent might be present, such as ethanol, or acetone, or other organic solvents. Also additional water might be present as solvent.

[0029] Suitably, step a) is being executed in the absence of a solvent. With the reaction between the phosphorus-containing material and the acid, a reaction mixture is formed that comprises phosphoric acid. The reaction is preferably performed in the absence of an organic solvent, that is the reaction mixture may comprise 2 wt.% or less of organic solvent by total weight of the reaction mixture. More preferably, the reaction is performed in the absence of any organic solvent. The phosphorus-containing material is acidulated directly by adding the sulfuric acid to the material or vice versa. During acidulation, or acid attack, the structureof the phosphorus-containing material may at least partially be (chemically and / or physically) destroyed. By directly acidulating the phosphorus-containing material, high reaction temperatures may be reached that further drive the reaction forward in a short time span. This, in combination with a low free water content of the reaction mixture (e.g., 5 wt.% or less), will significantly drive the reaction forward. Such destruction of phosphorus-containing material may be represented by a series of reactions between the acid and components of the phosphorus-containing material. With sulfuric acid, phosphate salts, such as calcium phosphate, will be converted at least partially to calcium sulphate and phosphoric acid. The advantage of this solvent free system is that a reaction mixture is being formed comprising phosphoric acid, remaining sulfuric acid and residual material. The formed reaction mixture has preferably the appearance of a slurry, between moist sand and clay.

[0030] Besides sulfuric acid the acid may comprise one or more other inorganic acids. Examples of inorganic acids include nitric acid, hydrochloric acid, phosphoric acid, and perchloric acid. Sulfuric acid may be selected having any concentration, particularly of at least about 70 %, preferably at least about 80 %, more preferably at least about 96 % or 98 %. Nitric acid may have a concentration of about 68 % or higher. Hydrochloric acid of any concentration may be selected, preferably of at least 30 %. Phosphoric acid of any concentration may be selected, such as in the range of about 75-85 %. Perchloric acid of any concentration may be selected, preferably of about 60 % or higher, more preferably of about 70 % or higher.

[0031] Preferably, the acid comprises besides sulfuric acid one or more selected from phosphoric acid, nitric acid and hydrochloric acid. More preferably, the acid comprises solely sulfuric acid, such as sulfuric acid having a concentration of about 96-98 %.

[0032] More preferably, the amount of sulfate anions from sulfuric acid towards cations present in the phosphorus containing material is in the range of from 0.5 up to 1.5, more preferably of from 0.8 up to 1.5, more preferably of from 0.8 up to 1.4, even more preferably in the range of from 0.9 up to 1.3. By using this amount of sulfuric acid, the conversion of phosphorus in the phosphorus containing material is higher, even at such a level that a conversion of at least0.80 was reached. More suitably, in step a) an excess amount of sulfuric acid towards phosphorus in the phosphorus containing material is added. The cations are preferably defined as the ions of calcium, iron, aluminium, magnesium, potassium, sodium, zinc and copper. The cation of silicium is too inert and not taken into account in this ratio.

[0033] The reaction between the phosphorus-containing material and sulfuric acid is a spontaneous exothermic reaction. The reaction typically does not require active heating. The temperature at which the reaction proceeds depends among others on the starting temperature, the heat generated in the reaction, the moisture content and the cooling / heating means applied externally to the reaction. The temperature should be sufficient to effectively convert the phosphorus-containing material to form phosphoric acid. Thereto, the reaction mixture may be actively heated. The temperature at which the reaction occurs may be between 50°C and 250°C, more preferably between 90°C and 210°C. At temperatures below 50°C, the reaction occurs slowly and may not reach completion. After the reaction, the temperature of the reaction mixture is typically allowed to drop, thereby reaching, for example, a temperature of at most about 150°C, more preferably about 120°C, more preferably about 100 °C.

[0034] Suitably, the reaction mixture is cooled before step b) via a jacket or by quenching with a liquid, preferably by quenching with water.

[0035] In the next step, step b), the produced phosphoric acid and remaining sulfuric acid are being separated from the residual material by adding a solvent, thereby forming a slurry wherein the acids are dissolved and residual material. This solvent can be an organic solvent, like methanol, ethanol, acetone etc, or water.

[0036] Suitably, the solvent in step b) is ethanol or acetone, more preferably ethanol. By using ethanol or acetone, products and by-products are separated in an uncomplicated manner. Separation problems encountered with traditional wetprocesses are overcome now. By using ethanol or acetone, phosphoric acid and sulfuric acid are soluble therein, but the by-products, such as sulphates of calcium are only sparingly soluble, or insoluble. Aluminium, iron and magnesium sulphates are still fairly soluble in ethanol or acetone. Although acetone works really well for the separation of the produced phosphoric acid and remainingsulfuric acid from the residual material, it is less suitable for multiple use in the process of the invention. This leads to a preference for ethanol as solvent in this step. The use of ethanol results in a far better overall process; ethanol shows no or only very limited degradation, resulting in limited losses when ethanol is preferably re-used. To make up for any losses of ethanol, more preferably a maximum of 5 wt%, even more preferably a maximum of 2 wt% relative to the total of recycled ethanol may be added. Methanol also shows no or only very limited degradation, resulting in limited losses. Ethanol is preferred over methanol, as methanol is more difficult to handle.

[0037] In step c) the solid residual material is separated from the solvent wherein at least the acids are dissolved. Separation techniques that are suitable for this step are filtration, centrifuge and / or decanting or a combination thereof. We furthermore found that water may improve filtration. Preferably, filtration is done using shear enhanced filtration like using a nudge filter, a dynamic filter press and / or a bocross filter. When necessary, pre-coats or filter aids can be applied to improve the filtration. Separation may be followed by re-slurrying with ethanol and / or methanol and separating to increase recovery, and again if so required. Preferably the solvent, more preferably ethanol or aceton, more preferably ethanol is moved countercurrent in this processing. Preferably clean solvent is moved after separation to the previous step for reslurrying.

[0038] The addition of water may improve filtration and / or centrifugation by causing enhanced flocculation and I or coagulation. This water can be added to ethanol or acetone, preferably in ratios between 0.05 up to 0.7 water to the phosphorus containing material, more preferably in ratios between 0.05 up to 0.3 water to the phosphorus containing material. It is believed that the addition of certain amounts of water causes the formation of magnesium sulphate, calcium sulphate, aluminium sulphate and / or iron sulphate with x molecules of crystal water, which is easier to filter, wherein x is preferably an integer between 1 and 24. The sulphate salts with up to their maximum of crystal water have superior properties with respect to filtration. Improvement of solid content will reduce energy for drying, as more solids results in less solvent and less solvent needs to be evaporated. So, if the solid - liquid separation results in a drier cake less solvent needs to be evaporated.In the next step, in step d), the solvent is recovered from the acids to produce a liquid product comprising at least phosphoric acid, sulfuric and sulfurous acid and dissolved metal sulphate and phosphate salts. In the preferred embodiment of the invention that as solvent ethanol is used, the recovered ethanol is of such a good quality that it can be reused in step b), preferably multiple times.

[0039] In step e) at least part of the liquid product comprising at least phosphoric acid, sulfuric and sulfurous acid and dissolved metal sulphate and phosphate salts is reacted with at least one second phosphorus containing material to form super phosphate. This super phosphate is preferably mostly single superphosphate.

[0040] Preferably, the temperature at which the least phosphoric acid, sulfuric and sulfurous acid and dissolved metal sulphate and phosphate salts is reacted with the at least one second phosphorus containing material in step e) is at least 60°C, more preferably at least 70°C, even more preferably at least 80°C. Below these temperatures the reaction also proceeds, however, to optimise the speed of reaction the higher temperatures are preferred. In order to reach the temperatures, one or more reactants may be heated.

[0041] Advantageously, the solvent as separated in step d) is recycled to step b) of the process. Not all solvents are evenly suitable to recycle one or more times. Most advantageously, ethanol is used as solvent and recycled multiple times. Ethanol hardly shows any degradation, like change of color etcetera. Thus also the make up for any losses of ethanol, is preferably limited to a maximum of 5 wt%, even more preferably a maximum of 2 wt% relative to the total of recycled ethanol. This makes it attractive from both an environmental perspective as well as from an economic perspective.

[0042] The process may further comprise a step of cooling the reaction mixture prior to the extraction. Preferably, the cooling step comprises external cooling. With the cooling step, dissolved salts may crystallize such that the filtration of precipitates becomes easier and / or mixing of the organic solvent with the reaction mixture is made possible without losing a significant part of the solvent intended for the extraction by evaporation. Preferably, the reaction mixture is cooled beforestep b) via a jacket or by evaporation of a liquid, preferably water. Vacuum can be applied to enhance the evaporation.

[0043] Preferably, ethanol and / or additional ethanol is added to the reaction mixture at a temperature at or below 78°C, more preferably at a temperature at or below 55°C. This temperature can be reached by the use of external cooling or by letting the mixture cool down by waiting a certain time.

[0044] The use of another alcohol like n-propanol or isopropanol might be considered, possibly as additional alcohol, but is not preferred. The use of mixtures of more than 2 different alcohols might also be considered.

[0045] Advantageously, besides a solvent, more preferably ethanol, water is added to the reaction mixture in step a) or in step b). The addition of water is advantageous for the formation of the sulphate salts. To form these, water is being built in the sulphate salt crystal framework up to 6 water molecules in for example iron(lll)sulphate hexahydrate, 7 water molecules for magnesium(ll)sulphate heptahydrate, and 2 water molecules in case of calcium(ll)sulphate dihydrate. Water addition may also be advantageous to depolymerize polyphosphoric acid. The amount of water advantageously added is determined per kind of source material. Depending on the components and form of Me, being for example Ca, Fe, Mg, and / or Al in for example sewage sludge ash, MeSC .xF O is formed, where x depends on the metal. Advantageously, the amount of water is sufficient to make up for all crystal water x, and almost no free water is left in the ethanol and / or methanol after formation of the sulphate salts.

[0046] The invention is applicable to the extraction of phosphate from, for example, secondary raw material comprising phosphate, and phosphate rock. The invention can provide local markets with a supply of super phosphate. The invention can provide local markets also with a supply concentrated phosphoric acid, phosphate derivatives and sulphate derivatives as defined in this disclosure, without relying on mines that may be far away and whose supply is difficult to secure. The invention makes it available to process large sources of, for example, recycled phosphorus, such as struvite and / or sewage sludge ash, for the extraction of phosphate.The phosphorus-containing material may comprise secondary raw material comprising phosphate, and / or phosphate rock. In particular, the phosphorus-containing material comprises secondary raw material comprising phosphate. Secondary raw material comprising phosphate can be any suitable poor, used, rejected and / or depleted material, comprising phosphate, such as wastes from the agri-food industry, sludge, etc., for further use. For example, the secondary phosphate-containing material may be provided from a phosphate recovery operation.

[0047] Preferably, the first phosphorus containing material comprises one or more selected from waste streams comprising calcium phosphate, struvite, vivianite, sewage sludge ash (SSA), meat and bone meal ash, dairy waste stream from whey processing and manure ash. These waste streams are all circular waste streams, so no virgin material from the earth are taken to produce the products of the invention. Furthermore, Europe and many other countries rely on sourcing from Marocco. By recovering phosphorus from SSA this dependence is reduced. The product is competitive and in addition does not contain cadmium and uranium, which are pollutants of soil. Fertilizer companies also like the stickiness of the product starting with these phosphorus containing material from waste streams, more specifically starting from SSA, saving them additives to produce fertilizer.

[0048] Preferably, the second phosphorus containing material comprises one or more selected from waste streams comprising calcium phosphate, struvite, vivianite, sewage sludge ash, meat and bone meal ash, dairy waste stream from whey processing and manure ash, more preferably one or more selected from struvite, vivianite, sewage sludge ash, meat and bone meal ash, calcium phosphate, dairy waste stream from whey processing and manure ash.

[0049] More suitably, both the first and / or second phosphorus containing material comprises sewage sludge ash, meat and bone meal ash, and / or dairy waste from whey processing. We found that the process of the invention is especially suitable for phosphorus-containing material that have undergone heat treatment to convert the original material to its ashes. Most preferred is sewage sludge ash, for both first and second phosphorus containing material. The amount of monocalcium phosphate is in this case limited, which is advantageous for theproduction and use of super phosphate. Other advantages are that the equipment for producing phosphoric acid is much more complicated. For the conversion of the same amount of ash, the plant that produces single super phosphate is 15 to 30% cheaper, and the energy consumption is reduced by around 50% compared to acid production, which is beneficial to the environment. The resulting single super phosphate product is perceived much better by fertilizer producers compared to the acid product. The product produced from this process is circular and can replace fossil single super phosphate. The product is competitive and in addition does not contain cadmium and uranium, which are pollutants of soil.

[0050] With the process of the invention, it is preferred to have a molar ratio between sulfuric acid, calculated as protons, and phosphorus in the phosphorus-containing material, calculated as P, of 1:1 or more, preferably 1:1 to 15:1. It is even more preferred to have a molar ratio between sulfuric acid, calculated as protons, and phosphorus in the phosphorus-containing material, calculated as P, of 3:1 to 12:1. If one of the ashes is being used, sewage sludge ash or meat and bone meal ash, it is even more preferred to have a molar ratio between sulfuric acid, calculated as protons, and phosphorus in the phosphorus-containing material, calculated as P, of 4:1 to 8:1, the exact ratio depending on the exact composition of the ashes.

[0051] The inventors found that by acidulating phosphorus-containing material with sulfuric acid, in particular secondary phosphates (secondary raw material comprising phosphate) that comprise, for example, iron and / or aluminium, such as sewage sludge ashes, especially in the absence of water, autogenous heating occurs, which is sufficient to allow high-yield conversion of the material to phosphoric acid and remaining sulfuric acid. Subsequently, the phosphoric acid and sulfuric acid can be selectively extracted using ethanol and / or methanol. As a result, the invention avoids the complexity and costs of traditional processes, such as those described in the prior art mentioned in this disclosure. Thus, advantageously, the phosphoric acid is formed by a spontaneous, exothermic reaction between the phosphorus-containing material and sulfuric acid.

[0052] The sulfuric acid used in the process of the invention is preferably a technical grade sulfuric acid. Preferably, the concentration of sulfuric acid is morethan 70%, more preferably more than 80%, even more preferably more than 90%, most preferably at least 96%.

[0053] The process may further comprise adding phosphoric acid. The phosphoric acid may be added either prior to extraction step b), such as to step a), for example, to the reaction mixture under step a); between steps a) and b); and / or during extraction step b), such as prior to adding solvent to the reaction mixture, at the same time as adding solvent and / or after adding solvent. The phosphoric acid may comprise entirely of phosphoric acid formed by the process or in part. For example, the phosphoric acid may comprise 5 wt.% or more of the formed phosphoric acid by total weight of the phosphoric acid, such as 10 wt.% or more, 15 wt.% or more, 20 wt.% or more, 25 wt.% or more, or 30 wt.% or more. The phosphoric acid may comprise 95 wt.% or less of the formed phosphoric acid by total weight of the phosphoric acid, such as 90 wt.% or less, 85 wt.% or less, 80 wt.% or less, 75 wt.% or less, or 70 wt.% or less. In particular, the phosphoric acid comprises 10-90 wt.% of the formed phosphoric acid, such as 20-80 wt.% or 30-70 wt.%. By adding phosphoric acid to the process, for example, the ratio between solids and liquids, such as those described in this disclosure, in the reaction mixture may be favourably affected, thereby improving the homogeneity of the reaction mixture and / or the extraction of phosphoric acid.

[0054] Advantageously, an additional step is added to the process, to obtain a more transferable end product. Preferably, in step e) or in a sequential step f) a carbonate is added, preferably calcium carbonate, magnesium carbonate, sodium carbonate and / or potassium bicarbonate, more preferably calcium carbonate. If a carbonate is added in step e) it is preferably done simultaneously with the addition of the at least one second phosphorus containing material, even more preferably mixed first with the second phosphorus containing material. More preferably, the carbonate is added in step e). Carbonic acid might also be used, although a bit less practical, to be added under pressure to step e) of the process, followed by releasing the pressure. The carbonate ensures that the super phosphate formed has a more open structure, and is easier to handle. Most preferred is the use of calcium carbonate because it is abundantly present.

[0055] Suitably, in step a), in step e) or in a sequential step f) one or more surfactants are added. More suitably, according to a preferred embodiment, instep a), the acidulation step, a first phosphorus containing material is mixed with sulfuric acid, optionally together with a surfactant to provide an intermediate product. In an alternative preferred embodiment, in step e) at least part of the liquid product is reacted with at least one second phosphorus containing material and one or more surfactants are added. Preferred surfactants according to the invention are fatty amines, more preferred is ethyl fatty amine.

[0056] Suitably, in step a) or in step e) next to CaCOa and surfactant water may be added in an amount less than 0.5 kg per kg of ash, more preferably less than 0.25 kg per kg of ash. The water suitably originates from the bleed from an exhaust scrubber used in the process of the invention.

[0057] Suitably, the super phosphate as produced according to the invention is processed into granulates. More suitably, granulation is done by breakage of the more open structure of the super phosphate formed, followed by ripening or curing it.

[0058] The present invention is also directed to a product comprising at least in the range of from 10 up to 30 wt% of P2O5, more preferably in the range of from 10 up to 25 wt% of P2O5, at least in the range of from 10 up to 25 wt% of neutral ammonium citrate soluble P2O5 and at least in the range of from 5 up to 30 wt% of sulphate salts, more preferably up to 26 wt% of sulphate salts, even more preferably up to 20 wt% of sulphate salts. Preferably, the sulphate salts are iron, aluminium and / or magnesium sulphate salts. It is thought that these sulphate salts provide a stickiness to the super phosphate material that has many advantages in the production of granular fertilizer. The P2O5 can also be in the form of phosphate salts with the same cations.

[0059] Advantageously, the aluminium, iron and magnesium sulphate salts in the product come from two sources, namely they originate from phosphoric acid used for the production of the product for in between 1 up to 15 wt% and from a second phosphorus containing material for in between 5 up to 25 wt% relative to the total amount of the product. By integrating the process streams of the invention, the product is more preferably made using the phosphoric acid originating from step d) of the process according to the invention. Some potassium and sodium sulphate salts might also be present.By integrating the process streams of the invention even further, the product is more preferably made using as the second phosphorus containing material the same material as the first phosphorus material used in step a) of the process of the invention. It is believed that the resulting product comprises good sticking properties due to the accumulation of all the sulphate salts.

[0060] The present invention is also directed to a use of the product comprising at least in the range of from 5, more preferably of from 10 wt% up to 30 wt%, more preferably 25 wt% of P2O5, at least in the range of from 5, more preferably of from 10 wt% up to 25 wt% of neutral ammonium citrate soluble P2O5 and at least in the range of from 5 up to 20 wt% of sulphate salts as ingredient for fertilizer material. The advantage of these superphosphate fertilizers is that a significant proportion of the phosphate content is soluble and is immediately available to plants and another part that is slowly released over months, which is the key quality property. It thus provides a very quick boost to plant growth. However, the complex soil dynamics tend to immobilize phosphate in mineral complexes or organic ligands reducing the availability to plants.

[0061] The following, non-limiting figures and examples are provided to illustrate the invention.

[0062] Fig. 1 illustrates a schematic representation of a preferred embodiment of the process of the invention.

[0063] Figure 1 demonstrates the process of the invention according to a preferred embodiment. In this embodiment both the first and the second phosphorus containing material comprise sewage sludge ash, that is in a vessel (1). A part of the sewage sludge ash is added to the acidulation reactor (2). Also added to the reactor is a calculated amount of sulfuric acid from vessel (3). The mixture is transported to a next vessel (4) where washing takes place with ethanol to isolate produced phosphoric acid and remaining sulfuric acid from the residual material by adding ethanol from vessel (5), thereby forming a slurry wherein at least the acids are dissolved and solid residual material. Next, the material is transported to a separator (6), where the formed solid residual material is separated from ethanol wherein at least the acids are dissolved. The solid residual material is sent to a drier (8), and dried residual solids are produced. Theethanol wherein at least the acids are dissolved, is sent to an evaporation step, where ethanol is recovered from the acids. The ethanol recovered from the evaporation and from the drier is reused and sent to vessel (5). The produced liquid product comprising at least phosphoric acid, and sulfurous acid and dissolved metal sulphate and phosphate salts is transported to reactor (9), where the other part of the sewage sludge ash is added to the liquid product, at increased temperature. After stirring for a certain period of time single super phosphate is formed as product.

[0064] Examples

[0065] Example 1:

[0066] For the production of single superphosphate an experiment was done starting from step d of the process. Phosphoric acid from step d) was weighed to an amount of 125 g and pre-heated to 120°C. 8 droplets of a surfactant were added to a beaker at ambient temperature where the reaction happens. 200 g of sewage sludge ash (SSA) was weighed and 18 g of CaCOs was pre-mixed with the SSA. The phosphoric acid was added to the beaker for the reaction and the mixer was turned on, with a stirring speed of 450 rpm. The SSA was added to the mixer as fast as possible (in one go) and mixing was kept for 10 seconds. The mixing was then stopped, the blade was removed from the mixture and the mixture was left for hardening overnight in the beaker. The product has hardened and an open structure was observed. Samples were taken for analysis the next day and the product was stored.

Claims

CLAIMS1. Process for the preparation of super phosphate, comprising:a) reacting at least a first phosphorus containing material with sulfuric acid, thereby forming a reaction mixture comprising phosphoric acid, remaining sulfuric acid and residual material;b) separating the produced phosphoric acid and remaining sulfuric acid from the residual material by adding a solvent, thereby forming a slurry wherein at least the acids are dissolved and solid residual material;c) separating the solid residual material from the solvent wherein at least the acids are dissolved;d) recovering the solvent from the acids to produce a liquid product comprising at least phosphoric acid, sulfuric and sulfurous acid and dissolved metal sulphate and phosphate salts; ande) reacting at least part of the liquid product with at least one second phosphorus containing material to form super phosphate.

2. Process according to claim 1 , wherein the amount of sulfuric acid towards cations present in the phosphorus containing material is in the range of from 0.5 up to 1.5, preferably in the range of from 0.9 up to 1.3.

3. Process according to any of the previous claims, wherein step a) is being executed in the absence of a solvent.

4. Process according to any of the previous claims, wherein the solvent in step b) is ethanol or acetone, preferably ethanol.

5. Process according to any of the previous claims, wherein the solvent as separated in step d) is recycled to step b) of the process.

6. Process according to any of the previous claims, wherein the reaction mixture is cooled before step b) via a jacket or by quenching with a liquid, preferably by quenching with water.

7. Process according to claim 4, wherein ethanol is added to the reaction mixture at a temperature at or below 78°C at atmospheric pressure, preferably at a temperature at or below 55°C at atmospheric pressure.

8. Process according to claims 4 and 7, wherein besides ethanol water is added to the reaction mixture in step b) or in step c).

9. Process according to any of the previous claims, wherein the first phosphorus containing material comprises one or more selected from calcium phosphate, struvite, vivianite, sewage sludge ash, meat and bone meal ash, dairy waste stream from whey processing and manure ash.

10. Process according to any of the previous claims, wherein the second phosphorus containing material comprises one or more selected from apatite, calcium phosphate, struvite, vivianite, sewage sludge ash, meat and bone meal ash, dairy waste stream from whey processing and manure ash, preferably one or more selected from struvite, vivianite, sewage sludge ash, meat and bone meal ash, calcium phosphate, dairy waste stream from whey processing and manure ash.

11. Process according to claims 9 or 10, wherein the first and / or second phosphorus containing material comprises sewage sludge ash, meat and bone meal ash, and / or dairy waste from whey processing.

12. Process according to any of the previous claims, wherein the phosphoric acid is formed by a spontaneous, exothermic reaction between the phosphorus-containing material and sulfuric acid.

13. Process according to any one of the previous claims, wherein the sulfuric acid is a technical grade sulfuric acid.

14. Process according to any of the previous claims, wherein in step e) or in a sequential step f) a carbonate is added, preferably calcium carbonate, magnesium carbonate, sodium carbonate and / or potassium bicarbonate, more preferably calcium carbonate.

15. Process according to any of the previous claims, wherein in step a), in step e) or in a sequential step f) one or more surfactants are added.

16. Process according to any of the previous claims, wherein the super phosphate is processed into granulates.

17. Product comprising at least in the range of from 10 up to 30 wt% of P2O5, at least in the range of from 10 up to 25 wt% of neutral ammonium citrate soluble P2O5 and at least in the range of from 5 up to 30 wt% of sulphate salts.

18. Product according to claim 17, wherein the sulphate salts are iron, aluminium and / or magnesium sulphate salts.

19. Product according to claim 18, wherein the aluminium, iron and magnesium sulphate salts originate from phosphoric acid used for the production of the product for in between 1 up to 15 wt% and from a second phosphorus containing material for in between 5 up to 25 wt% relative to the total amount of the product.

20. Product according to claim 19, wherein the phosphoric acid is originating from step d) of the process of claims 1 to 16.

21. Product according to claim 19 or 20, wherein the second phosphorus containing material is the same material as the first phosphorus material used in step a) of the process of claims 1 to 16.

22. Use of the product according to claims 17 to 21 , as ingredient for fertilizer 5 material.

Images