WO2025040609A1

WO2025040609A1 - Process for producing dicalcium phosphate feed with low fluoride content

Info

Publication number: WO2025040609A1
Application number: PCT/EP2024/073167
Authority: WO
Inventors: Hosam ELSAYED; Mohamed MAHROUS; Khaled DIAA
Original assignee: Evergrow For Specialty Ferti Lizers; Proferty Monoprosopi AE
Current assignee: Evergrow For Specialty Ferti Lizers; Proferty Monoprosopi AE
Priority date: 2023-08-21
Filing date: 2024-08-19
Publication date: 2025-02-27
Anticipated expiration: 2026-02-21

Abstract

The present disclosure provides a process for producing low-fluoride dicalcium phosphate. The process involves selecting phosphate rocks with variable phosphorus contents, treating the selected phosphate rocks with hydrochloric acid at a low pH to produce phosphoric acid and other compounds, adding calcium carbonate aqueous mixture to the reaction product to form insoluble calcium fluoride, separating the insoluble calcium fluoride from the mixture, forming dicalcium phosphate at a specific pH, and separating it by filtration. The addition of calcium carbonate is controlled by using calcium carbonate aqueous solutions of specific concentration of calcium carbonate to increase the precipitation process and control the fluoride content. The process results in a dicalcium phosphate product with a low fluoride content and high P/F ratio.

Description

PROCESS FOR PRODUCING DICALCIUM PHOSPHATE FEED WITH LOW FLUORIDE CONTENT

FIELD OF INVENTION

The present disclosure relates to the production of dicalcium phosphate, and more particularly to a process for producing low-fluoride dicalcium phosphate feed with a high P/F (phosphorus/fluoride) ratio controlled by selection of calcium carbonate aqueous mixture of advantageous concentration.

BACKGROUND

Phosphorus (P) is a nutrient that is indispensable for the growth of plants and animals. It plays a central role in energy exchange, the synthesis of nucleic acids, and bone formation. Dicalcium phosphate (DCP) is a calcium phosphate salt that is commonly used as a food additive due to its active properties and positive anticoagulant effect. It is also a component of animal feed, serving as a source of phosphorus and a feed corrector. The use of DCP in animal feed helps meet the nutritional requirements of animals and contributes to their growth and fertility.

DCP is typically obtained from phosphoric acid with the addition of calcium hydroxide. Another method involves treating crude phosphate rocks, which contain phosphorus in proportions ranging from 24% to 30% with mineral acids.

The quality of rock phosphate seems to be one of the greatest future challenges related to production of dicalcium phosphate (DCP). Global scarcity, demand, prices and feed security, as well as manufacture of critical phosphorous (P) materials in industry show critical pressure. Optimization process of phosphate rock (PR) resources is required where phosphorous contents in PR are variable (24-30%).

Calcium carbonate is often added after phosphate rock acidic treatment to precipitate fluorides and silica, which are then removed by filtration as precipitated solids. However, the control of fluoride content and the increase of yield in the sedimentation process remain challenging. Therefore, there is a continuous demand for improved processes of low-fluoride DCP production with a high P/F (phosphorus/fluoride) ratio.

SUMMARY

In view of this, a process for the production of dicalcium phosphate with a fluoride content of less than 0.1 % w/w is provided. The process comprises the steps of:

• reacting a phosphate rock with hydrochloric acid to form a mixture comprising an aqueous phase with pH between 0.1-0.5,

• adding a first portion of a calcium carbonate aqueous mixture 20-23 % VJ/VJ to the aqueous phase until pH is between 1.0-1.5 to precipitate fluoride salts;

• separating the precipitated fluoride salts from the mixture, thereby obtaining a filtrate;

• raising the pH of the filtrate by addition of a second portion of a calcium carbonate aqueous mixture 20-23% w/w until pH reaches 2.5 to 3.0 to precipitate dicalcium phosphate;

• separating the dicalcium phosphate from the aqueous phase; and

• drying the separated dicalcium phosphate to produce a final product of dicalcium phosphate with fluoride content of less than 0.1 % VJ/VJ.

The mixture formed by reacting the phosphate rock with hydrochloric acid may also comprise an insoluble solid phase containing impurities. In this case, after the step of reacting the phosphate rock with hydrochloric acid and before the step of adding a first portion of a calcium carbonate aqueous mixture, the aqueous phase may be optionally separated from the insoluble solid phase. This has the advantage that the next step can be executed more effectively. It is further understood that, in the case where the mixture comprises both an aqueous phase and an insoluble solid phase but the aqueous phase is not separated from insoluble solid phase, the feature "adding a first portion of a calcium carbonate aqueous mixture 20-23 % VJ/VJ to the aqueous phase to precipitate fluoride salts" can be understood as adding a first portion of a calcium carbonate aqueous mixture 20-23 % VJ/VJ to the mixture and thus consequently also to the aqueous phase to precipitate fluoride salts.

The step of raising the pH of the filtrate by addition of a second portion of a calcium carbonate aqueous mixture 20-23%w/w until pH reaches 2.5 to 3.0 to precipitate dicalcium phosphate may in particular also be understood as adding a second portion of a calcium carbonate aqueous mixture 20- 23%w/w for raising the pH until pH reaches 2.5 to 3.0 to precipitate dicalcium phosphate.

After separating the dicalcium phosphate from the aqueous phase and before the drying step described above, the separated dicalcium phosphate may optionally be washed. This has the advantage that further impurities may be removed. It is understood that, when the washing step takes place, the feature "drying the separated dicalcium phosphate to produce a final product of dicalcium phosphate with fluoride content of less than 0.1 % VJ/VJ" can be understood as drying the washed separated dicalcium phosphate to produce a final product of dicalcium phosphate with fluoride content of less than 0.1 % VJ/VJ. It is noted that the drying step takes place regardless of whether the washing step has been executed, as the produced dicalcium phosphate comprises moisture. In particular, it is preferable that the produced dicalcium phosphate is dried so as to comprise not more than 3.0 % VJ/VJ of moisture content.

Further details and aspects are provided in the claims and the part of the detailed description.

TECHNICAL EFFECTS AND ADVANTAGES

The disclosed process for producing low-fluoride content dicalcium phosphate (DCP) presents several technical advantages.

Firstly, controlling the addition of calcium carbonate by selecting appropriate % VJ/VJ value of the calcium carbonate aqueous mixture enhances the sedimentation process and effectively manages the fluoride content. This results in a DCP product with a low fluoride content, which is beneficial due to the toxic effects of fluoride.

Secondly, the process allows for the production of DCP with a high phosphorus to fluoride (P/F) ratio, which is desirable in animal feed for promoting growth and fertility.

The process can also accommodate phosphate rocks with variable phosphorus contents, ranging from 26.0 to 30.0 % / , preferably from 26.0 to 28.5 % / , more preferably from 26.0 to 28.0 % VJ/VJ, providing flexibility in the selection of raw materials.

Furthermore, the process can be designed to operate at specific pH levels, ensuring the efficient formation and separation of DCP.

The resulting DCP product conforms to international standards such as Good Manufacturing Practice for Feed Safety (GMP+) and Hazard Analysis Critical Control Point, demonstrating its high quality and suitability for use in various applications, such as compound feeds, premixes, and concentrates for poultry, ruminants, pets, and aquatic animals. These technical advantages collectively contribute to an improved process for producing low-fluoride DCP.

DEFINITIONS

As per IUPAC, the term "content" is an amount of substance of a component in a system divided by the mass of the system, whereas the term "concentration" characterizes the composition of a mixture with respect to the volume of the mixture (mass, amount, volume and number concentration).

A phosphate rock is in particular a rock with phosphorus content ranging between 26 and 30 % w/w. Phosphorus content of phosphate rock is defined as P2O5 and the unit is w/w, referring to all the phosphorus oxides in a material. It is understood that all related phosphorus compounds are collectively described as "P2O5 content". In addition, when phosphorus content is measured as P2O5, this is indicated as such (P2O5). Otherwise, if phosphorus is measured simply as phosphorus, then the symbol of the element is indicated (P). Phosphorus (P) is measured with spectro-photometer in the DCP product.

Dicalcium phosphate (DCP) is expressed by the chemical formula CaHPO₄. DCP may be in the form of the dihydrate. Within the context of the present invention, DCP is not limited to the dihydrate form but may also include other known forms of DCP, such as the anhydrous form. Heat of drying influences the form of DCP.

A mixture may refer to a slurry, a solution or any physical mixture between two or more components. A slurry solution refers to a kind of mixture wherein the liquid phase comprises insoluble matter and it may also be described as suspension. "Slurry solution" and "mixture" can be used interchangeably within the context of the present invention.

A reaction mixture may refer to a mixture wherein certain changes in its chemical composition have taken place, such as for example digestion of the phosphate rock with hydrochloric acid, pH adjustment with calcium carbonate aqueous mixture either for precipitation of calcium fluoride or for precipitation of DCP.

Feed grade dicalcium phosphate (DCP) that is a specific form of DCP used in animal feed refers to dicalcium phosphate with phosphorus content of at least 18.0% w/w. Feed grade DCP is defined in accordance with Good Manufacturing Practice for Feed Safety and Hazard Analysis Critical Control Point (GMP+).

P/F ratio is the ratio of phosphorus content to fluoride content. For the calculation of P/F ratio, phosphorus content is measured as P with spectro-photometer method and fluoride content is measured as F with fluoride-selective electrode method. Suitable analytical methods for those measurements are well known in the art, for example AOAC (Association of Official Agricultural Chemists). High P/F ratio means more than 200, preferably more than 300, still more preferably more than 400 and even more preferably 500.

When the fluoride content is measured in solutions, ion selective fluoride meter method according to IS 5470 : 2002 is used.

Low fluoride content DCP refers to DCP wherein the fluoride content is less 0.1% w/w, still more preferably less than 0.05% w/w and even more preferably less than 0.04 % w/w.

DETAILED DESCRIPTION

The present invention discloses a process for the production of dicalcium phosphate (DCP) with low fluoride content.

In a preferred embodiment the DCP produced according to the present invention has a fluoride content of less than 0.1% w/w. The fluoride content may in particular be measured by fluorideselective electrode method. More preferably, the fluoride content may be less than 0.05% w/w. Still more preferably, the fluoride content may be less than 0.04% w/w.

The process comprises the following steps: a. reacting a phosphate rock with hydrochloric acid to form a mixture comprising an aqueous phase with pH from 0.1 to 0.5, and optionally an insoluble solid phase containing impurities; b. optionally separating the aqueous phase from the insoluble solid phase; c. adding a first portion of a calcium carbonate aqueous mixture 20-23 % w/w to the aqueous phase until the pH is from 1.0 to 1.5 to precipitate fluoride salts; d. separating the precipitated fluoride salts and optionally separating the insoluble solid phase from the mixture thereby obtaining a filtrate; e. raising the pH of the filtrate by addition of a second portion of a calcium carbonate aqueous mixture 20-23 % w/w until pH reaches 2.5 to 3.0 to precipitate dicalcium phosphate; f. separating the dicalcium phosphate from the aqueous phase; g. optionally washing the separated dicalcium phosphate, in order to obtain a lower chloride content in the final product ; and h. drying the separated dicalcium phosphate to produce a final product of dicalcium phosphate with fluoride content of less than 0.1 % VJ/VJ.

In step a, the phosphate rock may have a phosphorus content of between 26 % and 30 % VJ/VJ, preferably between 26.0 and 28.5 % VJ/VJ, more preferably between 26 and 28.0% VJ/VJ. The phosphate rock may comprise further organic and inorganic components in different forms (salts or oxides for example), as well as various ions, such as Na, Ca, K, Mg, Al and Fe. Examples of said components are CasfPCUh (calcium phosphate), CaCOs (calcium carbonate), SiOj (silicon dioxide or silica), CaFj (calcium difluoride), MgO (magnesium oxide), iron and AI2O3 (aluminum oxides), sodium chloride, potassium oxide. Heavy metals may also be present. The phosphate rock used in the present process is characterized as "low calcium carbonate content" if it comprises less than 14% VJ/VJ of calcium carbonate and "high calcium carbonate content" if it comprises equal to or more than 14% VJ/VJ of calcium carbonate, in particular as measured by complex-metric titration or gravimetric analysis. The amount of silica (SiOz) may also vary and it is usually decreasing when calcium carbonate is increasing. In other words, the amount of silica may in particular be in an inverse relationship to the amount of calcium carbonate, meaning that the amount of silica is higher when the amount of calcium carbonate is lower, and lower when the amount of calcium carbonate is higher. This amount of silica per se is not important for the process, as long as the amount of calcium carbonate is quantified and the pH adjustment in step c is as described below. Silica as well as other components of the phosphate rock beyond phosphorus compounds and calcium carbonate may have variable contents and are either solubilized by the treatment with the hydrochloric acid in step a, and/or removed as insoluble matter in step b.

Upon reaction with hydrochloric acid, the resulting mixture comprises an aqueous phase which comprises phosphoric acid, phosphate ions, chloride ions, and calcium ions.

The hydrochloric acid of step a may be used at a concentration of 11-13% w/v, preferably 12% w/v. The resulting pH of the resulting reaction mixture upon addition of said hydrochloric acid may range from 0.1 to 0.5, preferably from 0.1 to 0.3. Hydrochloric acid is added until the phosphate rock is digested, and phosphorus is transferred from insoluble into soluble form. Upon treatment of the phosphate rock with hydrochloric acid, phosphoric acid (H₃PO₄) is produced with other compounds such as Ca(H2PO₄)2 (monocalcium phosphate), CaCL (calcium chloride), HF (hydrogen fluoride) and optionally non-reactive substances, such as for example silica. In case an insoluble solid phase remains after the treatment with the hydrochloric acid in step a, it may be desirable the insoluble parts to be separated from the liquid, for example by filtration, according to step b. Preferably, the reaction with hydrochloric acid forms a mixture comprising an aqueous phase as defined herein and an insoluble solid phase containing impurities

The calcium carbonate aqueous mixture of steps c and e may be used at a concentration of 20-23%, preferably 20-22%, even more preferably 20-21%, still more preferably 20% w/w. This is the "dilution" of calcium carbonate controlled by the present process to advantageously minimize fluoride content in the final product while achieving favourable yields. It is not necessary to use the same concentration in both steps, as long as the range 20-23 % w/w is applied and the pH values at steps c and e are as described below for steps c and e. However, the same concentration can be used and unless otherwise specified, throughout the examples and figures the same concentration of calcium carbonate aqueous mixture is used in both steps. It is therefore understood that the present invention comprises an embodiment wherein a first portion of a calcium carbonate aqueous mixture of a concentration of 20-23%, preferably 20-22%, more preferably 20-21% and still more preferably 20% w/w is used and wherein a second portion of a calcium carbonate aqueous mixture of a concentration of 20-23%, preferably 20-22%, more preferably 20-21% and still more preferably 20% w/w is used. In a preferred embodiment the first and second portions of calcium carbonate aqueous mixture are used from a single calcium carbonate aqueous mixture with a concentration of 20-23%, preferably 20-22%, more preferably 20-21% and still more preferably 20% w/w of calcium carbonate. It is noted that the characterization of the portions of the aqueous mixtures as "first portion" and "second portion" is made so that reference can simply be made to the "first portion" and the "second portion" without having to repeat the term "calcium carbonate aqueous mixture". It is also noted that the following expressions could be used: "a portion of a first calcium carbonate aqueous mixture" and "a portion of a second calcium carbonate aqueous mixture". In the case of a single calcium carbonate aqueous mixture as described above, the first calcium carbonate aqueous mixture and the second calcium carbonate aqueous mixture are the same/single calcium carbonate aqueous mixture. In this case, the expression "a portion of a first calcium carbonate aqueous mixture" and "a portion of a second calcium carbonate aqueous mixture" could also be understood as "a first portion of a calcium carbonate aqueous mixture" and "a second portion of the calcium carbonate aqueous mixture".

The concentration of calcium carbonate in the calcium carbonate aqueous mixture used in the novel process increases the formation of calcium fluoride precipitating from the mixture, thereby minimizing the final fluoride content of the DCP product. And for this reason, the concentration of calcium carbonate in the calcium carbonate aqueous mixture is controlled to optimize the precipitation of fluoride salts and maximize the formation of pure dicalcium phosphate.

In step c, a first portion of a calcium carbonate aqueous mixture is added until the pH of the resulting mixture is 1.00-1.50. When the phosphate rock used in the process is a "low calcium carbonate content", meaning that it comprises less than 14% w/w of calcium carbonate, then the first portion of calcium carbonate aqueous mixture is added until the pH of the resulting mixture is 1.00-1.25. In a preferable embodiment, the resulting pH is 1.00-1.20. When the phosphate rock used in the process is a "high calcium carbonate content", meaning that it comprises equal to or more than 14% w/w of calcium carbonate, then the first portion of calcium carbonate aqueous mixture is added until the pH of the resulting mixture is 1.26-1.50. In a preferred embodiment, the resulting pH is 1.30-1.50.

During step c, fluoride anions precipitate as CaFj. Other forms of fluoride salts may also be comprised in the precipitate of step c.

In step d, the precipitate of step c is separated from the mixture. The resulting solution is used in step e. In case the insoluble solid phase of step a is not separated, i.e. in case step b is omitted, it may be preferable to separate said insoluble solid phase in step d, together with the precipitated fluoride salts.

In step e, the second portion of a calcium carbonate aqueous mixture may be added until the pH is between 2.5 and 3.0, preferably 2.6-2.9, more preferably 2.7-2.8. In this step, DCP is precipitated from the mixture.

In step f, the DCP is separated from the mixture, for example by filtration.

Step g comprises washing of the separated DCP. Water is preferred for the washing step. In a preferred embodiment the separated dicalcium phosphate is washed.

Step h comprises drying of the separated DCP. The drying step of the present invention has no specific requirements as long as the filtered mass is dry enough to be processed, analyzed or packaged. Drying may for example be achieved either by extended application of vacuum during filtration or by heating at 60-80 °C or combination of application of vacuum with heating. In any case, the drying temperature shall not exceed 80 °C. When heating is applied, the dried product may optionally be cooled, for example by air, e.g. to 25-30 °C. Appropriate methods for drying are well known to the skilled person. The DCP resulting from step h, which can also be characterized as the final product within the present invention, has low fluoride content, low fluoride content being defined as less than 0.1% w/w, preferably less than 0.05% w/w, more preferably less than 0.04% w/w. The final product of DCP is further characterized by a high P/F ratio, particularly of more than 200, preferably of more than 300, more preferably of more than 400, even more preferably of more than 500. Analysis of DCP produced as per the present process is shown in Table 2.

The filtration used in various steps of the inventive process may be performed by any filter apparatus appropriate for the batch size manufactured. Belt filters are convenient when slurry mixtures require filtration. Press filters may also be used. However, any other type of filtering device may also be envisaged, as long as it is able to separate solids from liquid components in accordance with the batch size and the texture of the mixture to be separated. Preferably, the filtration in steps b and d of the process are performed by a pressure filter and the filtration in step f is performed by a belt filter.

Whenever desirable, washing may be performed to remove remaining quantities of the filtrate onto the filtered mass. Washing is a well-known procedure for the skilled person. Water is preferable, but other solvents as well as aqueous solutions can be used.

In another aspect of the present invention, DCP with low fluoride content obtainable according to the disclosed process is provided. DCP is characterized by low fluoride content, low fluoride content being define as less than 0.1% w/w, preferably less than 0.05% w/w, more preferably less than 0.04% w/w. DCP is further characterized by a high P/F ratio, particularly of more than 200, preferably of more than 300, more preferably of more than 400, even more preferably of more than 500.

In another aspect of the present invention, DCP with low fluoride content prepared according to the disclosed process is provided.

The DCP produced by the present process conforms to international standards for feed grade dicalcium phosphate.

In another embodiment the present invention may be described as follows.

The first step of the invention is the selection of phosphate rocks (PR) where the phosphorus contents in the stone are variable (26%-28%) involved with organic and inorganic substances in different forms as well as various ions such as Ca, K, Mg and Fe and the impurities were for example Cas (PO₄) 2, CaCOs, SiC , CaF2, hydrochloric acid (12% w/v) is used where the reaction is carried out at a low pH (0.1). From the reaction product, phosphoric acid is produced with other compounds such as Ca (HjPCUh, CaCL, HF and non-reactive substances from the acidification of phosphate rocks.

The addition of different concentrations of calcium carbonate (20%) at pH (1.0) resulted in the formation of insoluble calcium fluoride and is separated by special filters. To control the quality of the process for the production of low-fluoride feed, the sedimentation process is carried out when certain dilutions are used, the reaction tends to increase the formation of calcium fluoride deposits and then remove them upon separation by pressure filter.

After fluoride separation, dicalcium phosphate (DCP) is formed at pH 2.5 to 3.0 and then separated by filtration using a special filter.

After that, the product is washed and airdried, and by analyzing the final product, it was of high quality, low fluoride concentration, and high-quality international standards.

Phosphorus (P) as a nutritious element is vital to the growth of plants and animals. The quality of rock phosphate seems to be one of the greatest challenges in future related to production of dicalcium phosphate (DCP). Global scarcity, demand, prices and feed security, as well as manufacture of critical phosphorous (P) materials in industry show critical pressure. Optimization process of phosphate rock (PR) resources is required where phosphorous contents in PR are variable (24-30%). Also, organic and inorganic matters occur in various forms, and different Ca, K, Mg and Fe ions. P2O5 is highly enriched in local PR (26%-28%) as its concentrations are also highly variable e.g. Ca3(PO₄h, CaCOs, SiOz, CaF2, and organic compounds. In contrast to phosphate, the water-soluble P proportions are limited due to the formation of less mobile P phases.

With usage of HCI (12% w/v) wherein the reaction is conducted in low pH (0.1), phosphoric acid, Ca(H2PO₄)2, CaCL, HF and unreacted substances are produced from the acidification of phosphate rock. Addition of calcium carbonate slurry in different concentrations led to form soluble DCP and low phosphate gypsum. For control fluoride content, precipitation process is conducted at certain dilution as silicofluoride complexes and then removed on separation by press filter.

In order to control the quality of the process to produce low fluoride fertilizer, a sedimentation process is carried out when certain dilutions are used. The reaction tends to form precipitates and then remove them upon separation by means of a press filter. After that, the product is washed and air dried. The DCP final product analysis shows high quality with high P/F ration and conforming to international standards. Process description

Process for the production of DCP which comprises the steps of:

(a) The characterization of phosphate rocks shows high content of phosphate as shown in Table 1.

(b) Performing an attack of phosphate rock with a solution of hydrochloric acid with final pH 0.1 to form a slurry comprising that leads an aqueous phase containing phosphoric acid in solution, phosphate ions, chloride ions and calcium ions and an insoluble solid phase containing impurities as Eq #1.

(c) Performing a neutralization of the aqueous phase by addition of a calcium carbonate with final pH 1.1 to separate fluoride salts from phosphate solution.

(d) Separating the aqueous phase (filtrate) comprising in solution, phosphate ions, chloride ions and calcium ions, and the insoluble solid phase as figure 1.

(e) After filtration and pH were raised to 2.5-3.0 by Calcium carbonate slurry solution to form Dicalcium phosphate being insoluble in water. Separating the calcium phosphate, which may be used in the process as a first phosphate salt, and the aqueous phase containing, in solution, calcium ions and fluoride ions as figure 2 and Eq #2

(f) After washing, the results DCP with high concentration of phosphate with a second solid phase containing low impurities as figure 3 and Eq #3

(g) Separating the phosphate salt from the second solid phase

(h) Precipitation the DCP with drying and air cooling to form DCP final products with low Fluoride impurities as figure 3 and Equation 3

(i) Washing solid phase by water to remove more chloride impurities and high quality DCP production as figure 1

(k) Air drying the DCP precipitates containing a very low concentration of impurities as figure 1.

In another embodiment, the present invention may be described as follows.

The new system deals with how to control the commercial products of DCP with feed grade specs. Many variable parameters are participated in the production process. The patent focus how we manage the selection of certain concentration of CaCOs depending on the specs of powder. In laboratory, we tested the suitable concentration with resulted pH to decrease the fluoride concentration comparing with phosphate concentration ((P/F ratio) in the final products.

The first step of the invention is the selection of phosphate rocks (PR) where the phosphorus contents in the stone are variable (26%-28%) involved with organic and inorganic substances in different forms as well as various ions such as Ca, K, Mg and Fe and the impurities were for example Cas (PO₄) 2, CaCOs, SiC , CaF2, hydrochloric acid (12%) is used where the reaction is carried out at a low pH (0.1). From the reaction product, phosphoric acid is produced with other compounds such as Ca(H2PO₄)2, CaCL, HF and non-reactive substances from the acidification of phosphate rocks.

The addition of different concentrations of calcium carbonate at pH (1.0) - 1.2 resulted in the formation of insoluble calcium fluoride and is separated by special filters. To control the quality of the process for the production of low-fluoride feed, the sedimentation process is carried out when certain dilutions are used, the reaction tends to increase the formation of calcium fluoride deposits and then remove them upon separation by pressure filter (press filter).

After fluoride separation, dicalcium phosphate (DCP) is formed at pH 2.5 to 3.0 and then separated by filtration using a special filter (Belt filter). After that, the product is washed and air dried, and by analyzing the final product, it was of high quality, low fluoride concentration, and high-quality international standards.

BRIEF DESCRIPTION OF FIGURES

FIG. 1 illustrates a flowchart of the process for producing dicalcium phosphate with varying calcium carbonate concentrations, according to an embodiment.

FIG. 2 depicts a graph comparing fluoride concentration (% w/w) in the reaction mixture after completing step d and final products under different calcium carbonate concentrations (% w/w), according to an embodiment.

FIG. 3 shows a graph detailing the phosphate/fluoride ratio in the reaction mixture after completing step d, according to an embodiment. P and F are expressed as % VJ/VJ.

FIG. 4 presents a graph of phosphorus (expressed as P2O5 % VJ/VJ and P % VJ/VJ) and fluoride content (expressed as % VJ/VJ) in final product after treatment with different concentrations of calcium carbonate, according to an embodiment. FIG. 5 illustrates a graph showing the ratio of phosphate and fluoride (ratio of P/F, P as % w/w and F as % VJ/VJ) in the mixture after completing step d and final dicalcium phosphate products as a function of varying calcium carbonate concentration, according to an embodiment.

FIG.6 illustrates a graph showing the pH of final phosphate solution after removal of calcium fluoride by using different concentrations of slurry calcium carbonate and phosphate rock with low calcium carbonate content.

FIG.7 illustrates the relationship between P2O5 (% w/w) and F (ppm) of phosphate solutions and calcium carbonate concentrations in the calcium carbonate aqueous mixture used in steps c and e.

EXAMPLES

The following examples show analysis data for the starting material (phosphate rock) and the final product according to the disclosed process. A flowchart of the process is shown in Fig.1, and analytical data of several parameters in relation to calcium carbonate aqueous mixtures of variable concentrations are presented in example 1.

EXAMPLE 1

Table 1: Analysis data of Phosphate rocks used in production of DCP

Standard test methods for phosphate rock used in the below examples are: a) Phosphate rock with calcium carbonate less than 14% w/w (Unit of components reported with % are w/w):

Table 1a

b) Phosphate rock with calcium carbonate equal or greater than 14% w/w (Unit of components reported with % are w/w):

Table 1b

In the following, figure 1 is described.

Figure 1 presents the process of DCP production according to a specific embodiment. It is noted that references to the steps of the general method as described are included in brackets for a better understanding of the embodiment.

Equation 1: The phosphate rock is treated with hydrochloric acid (at a concentration of 12% w/v in this specific embodiment) to form a mixture (step a), any insoluble parts or unreacted substances are optionally separated to obtain the aqueous phase (step b).

Equation 2: A first portion of a calcium carbonate aqueous mixture is added to the aqueous phase (liquid phase) to precipitate fluoride salts (step c). The precipitated solids are separated from the mixture thereby obtaining a filtrate (step d).

The pH of the filtrate is further raised by addition of a second portion of a calcium carbonate aqueous mixture until pH reaches 2.5 to 3.0 whereby DCP is precipitated (step e) and separated from the mixture (step f). DCP may optionally be washed (step g) and then drying is followed to provide the final product (step h), DCP with low fluoride content. Following the disclosed method and by using different concentrations of calcium carbonate aqueous mixture (expressed as % w/w) the fluoride content (F in ppm) and yield of the precipitated DCP (% P2O5 yield) obtained varies as shown in the below results. P2O5 is expressed as % w/w and weight of filtrate and P2O5 in filtrate are expressed in grams.

Reaction between phosphate rock (PR), HCI (12 w/v %)

The results after reaction of step a are the following:

1) Treatment with 24 gm calcium carbonate in slurry mixture (30%), filter Filtrate solution analysis:

2) Treatment with 24 gm calcium carbonate in slurry mixture (25%), filter Filtrate solution analysis:

3) Treatment with 24 gm calcium carbonate in slurry mixture (20%), filter Filtrate solution analysis:

4) Treatment with 24 gm calcium carbonate in slurry mixture (19%), filter Filtrate solution analysis:

) Treatment with 24 gm calcium carbonate in slurry mixture (18%), filter Filtrate solution analysis:

) Treatment with 24 gm calcium carbonate in slurry mixture(17%), filter Filtrate solution analysis:

) Treatment with 24 gm calcium carbonate in slurry mixture (16%), filter Filtrate solution analysis:

) Treatment with 24 gm calcium carbonate in slurry mixture (15%), filter Filtrate solution analysis:

) Treatment with 24 gm calcium carbonate in slurry mixture (10%), filter Filtrate solution analysis:

In the following table 2, average analysis data of final DCP products (produced by phosphate rock with high or low calcium carbonate content) are presented.

Table 2

Claims

1. A process for the production of dicalcium phosphate with a fluoride content of less than 0.1 % w/w, the process comprising: a) reacting a phosphate rock with hydrochloric acid to form a mixture comprising an aqueous phase with pH from 0.1 to 0.5, and optionally an insoluble solid phase containing impurities; b) optionally separating the aqueous phase from the insoluble solid phase; c) adding a first portion of a calcium carbonate aqueous mixture 20-23 % w/w to the aqueous phase until pH is 1.0-1.5 to precipitate fluoride salts; d) separating the precipitated fluoride salts from the mixture thereby obtaining a filtrate; e) raising the pH of the filtrate by addition of a second portion of a calcium carbonate aqueous mixture 20-23%w/w until pH reaches 2.5 to 3.0 to precipitate dicalcium phosphate; f) separating the dicalcium phosphate from the aqueous phase; g) washing the separated dicalcium phosphate; and h) drying the separated dicalcium phosphate to produce a final product of dicalcium phosphate with fluoride content of less than 0.1 % w/w.

2. The process of claim 1, wherein the phosphate rock has a phosphorus content ranging from 26 to 30% w/w, preferably from 26.0% to 28.5% w/w.

3. The process of claim 2, wherein when the phosphate rock comprises calcium carbonate in a content of less than 14 % w/w, then the first portion of a calcium carbonate aqueous mixture in step c is added to the aqueous phase until pH of the aqueous phase is from 1.26 to 1.50.

4. The process of claim 4, wherein when the phosphate rock comprises calcium carbonate in a content of equal to or more than 14 % w/w, then the first portion of a calcium carbonate aqueous mixture in step c is added until pH is from 1.00 to 1.25.

5. The process of any of the preceding claims, wherein the aqueous phase of step a comprises phosphoric acid, phosphate ions, fluoride ions, and calcium ions.

6. The process of any of the preceding claims, wherein the dicalcium phosphate is separated from the aqueous phase in step f by filtration using a belt filter.

7. The process of any of the preceding claims, wherein the dicalcium phosphate is dried at a temperature of 60-80°C and subsequently cooled by air to 25-30° C.

8. The process of any of the preceding claims, wherein the concentration of calcium carbonate in the calcium carbonate aqueous mixture is controlled to optimize the precipitation of fluoride salts and the formation of dicalcium phosphate.

9. The process of any of the preceding claims, wherein the calcium carbonate aqueous mixture has a calcium carbonate concentration between 20 and 22 % w/w, preferably 20 and 21% w/w, more preferably 20% w/w.

10. The process of any of the preceding claims, wherein the addition of the second portion of a calcium carbonate aqueous mixture results in a pH of 2.6-2.9, preferably 2.7-2.8.

11. The process of any of the preceding claims, wherein the fluoride content is less than 0.05 % w/w, preferably 0.04 % w/w.

12. Dicalcium phosphate obtainable by a process as defined by any of the preceding claims.