OA21971A - Process for producing a phosphate containing product from a phosphate source. - Google Patents

Abstract

The present invention concerns a process for producing a phosphate containing product from a phosphate source (PO), the process comprising the following steps: • feeding aone or more reactors with a raw material (PCI) comprising phosphate in amounts of at least 5 wt.% P2O5, and calcium in amounts of at least 0.7 wt.% CaO, • digesting the raw material (PCI) with a digestion liquor (L) in the one or more reactors, wherein the digestion liquor (L), - is an aqueous solution of sulphuric acid (H2SO4) and a mineral acids (HX), in a ratio (H+(SA) / H+(L) comprised between 2 and 75%, wherein H+(SA) and H+(L) are the mole content of H+ issued from the sulphuric acid and the digestion liquor (L), respectively, - is added to the raw material (PC 1) to form a digested suspension (PC2) in amounts such that the molar ratio H+(L) / Ca is comprised between 0.8 and 1.95, wherein Ca is the mole content of calcium present in the digested suspension (PC2), and • separating the digested suspension (PC2) into, on the one hand, the aqueous phosphate rich solution (PI) and, on the other hand, the first solid phase (C1).

Description

PROCESS FOR PRODUCING A PHOSPHATE CONTAINING PRODUCT FROM A PHOSPHATE SOURCE

FIELD OF THE INVENTION

The présent invention relates to a process for producing a phosphate containing product from a phosphate source (PO). The phosphate source can comprise phosphate ores or ashes from different origins, industrial or municipal. The présent invention enhances filtration after digestion of the raw material issued from the phosphate source and prevents losses of P2O5 in the cake with CaSO4.nH2O while maintaining an acceptable efficacy.

BACKGROUND OF THE INVENTION

Phosphate sources can be issued from ore, typically containing apatite, or from ashes from the incinération of sewage, animal bones, and the like. These phosphate sources comprise numerous other components which need be separated to reach the levels of purity required by the corrcsponding end applications. To this purpose, raw material issued from the phosphate source can be digested in a first step in a digestion liquor to solubilize the phosphate ions and maintain as many other components as possible insoluble. This digestion step is often followed by a séparation step, to separate a solid residue mainly composed of insoluble components from a liquid filtratc containing the dissolved phosphates. The sélection of the conditions used in this first step, including the composition of the digestion liquor, the duration of the digestion, the température, the pH, etc., is often a trade-off between ensuring that ail the phosphates présent in the raw material are indeed solubilized and présent in the liquid filtratc after séparation, and preventing as many other components as possible from solubilizing too and thus remaining in the solid residue. If the digestion is too weak, phosphates can be retained in the raw material in the insoluble form and if, on the other hand, digestion is too strong, many impurities will be dissolved too and entrained with the phosphates in the liquid filtrate.

Most ores and many ashes comprise certain amounts of CaO and / or sulphates (SO4²). Undesired calcium can be precipitated as calcium sulphates (= CaSO4.nH2O) by addition of sulphuric acid (= H2SO4). Digesting the raw material with sulphuric acid alone can, however, be detrimental to the efficacy of the process, and co-precipitation of calcium phosphates may occur. IN particular, addition of sulphuric acid introduces sulphate ions (SO4²·) which need be eliminated and may require in some cases addition of Ca²⁺ ions to precipitate calcium sulphates (CaSOT.nHiO) with different degrees of hydration (i.e., n = 0 to 2). If calcium sulphates coprecipitate with substantial amounts of P2O5, the yield in phosphates is decreased accordingly, as they cannot casily be dissociated after co-precipitation. The reaction of calcium phosphates (Ca3(PO4)2) with sulphuric acid (H2SO4) yields more calcium sulphates than phosphoric acid, i.e., more side products than end-products.

Ca₃(PO4)2 + 3 H?SO4 +6H2O 4 3 CaSO₄.2H2O +2 H3PO4

Digesting raw material with sulphuric acid may also lead to the formation of hemihydrate or anhydride calcium sulphate. Calcium sulphate hemihydrate (= CaSCU./^O) is prompt to rehydrate and set to form dihydrate plaster (= CaSO4.2H2O) which can block the production line, generating extra costs either by stopping the production for the time required to unclog and clean the equipment or by including spare pièces of equipment to switch the production through the spare pièces. Anhydride (= CaSO4) is difficult to filter, thus hindering the séparation of liquid from solid phases.

Digestion liquors comprising hydrochloric acid (= HCl) alone are used in the art. HCl has the major inconvénient of introducing chlorine (Cl) into the system, which is banned from many applications. As HCl is a strong acid, the equipment, such as reactors, tanks, tuns, tubing must be made of corresponding résistant materials, which increases the cost of the production line accordingly. Finally, HCl dissolves components forming soluble salts without forming précipitâtes, such that ail that is dissolved from the raw material is présent in the liquid filtrate together with the phosphates.

Phosphoric acid (= H3PO4) is also commonly used in digestion liquors. Like HCl, H3PO4 dissolves components forming soluble salts without forming précipitâtes, such that ail that is dissolved from the raw material is présent in the liquid filtrate together with the phosphates. Phosphoric acid is a weaker acid than H2SO4 or HCl discussed supra, which could lead to dissolution of only part of the phosphates présent in the raw material.

EP3066048 proposes to first digest ashes with phosphoric acid and / or nitric acid, separate the solid from the liquid filtrate, and reacting in a separate step the liquid filtrate with sulphuric acid (= H2SO4) to precipitate calcium sulphates (= CaSO4.nH?O). Similariy, EP3296258 describes a similar two- (or more-) step process. These processes require two consecutive digestions, requiring heavy apparatuses, various reactants and longer times.

There is a need in the art for a simple nd reliable process for extracting phosphates efficiently from a raw material containing certain amounts of undesired CaO. The present invention proposes such simple process which allows undesired calcium to be precipitated as calcium sulphate without impairing the efficacy of the process. The séparation by filtration step which follows is thus facilitated by the presence in the solid of crystallized compounds. These and other advantages of the present invention are explained more in detail in the following sections.

SUMMARY OF THE INVENTION

The objectives of the present invention hâve been reached with a process for producing a phosphate containing product from a phosphate source (PO), the process comprising the following steps:

• feedingone or more reactors with at least one raw material (PCI) issued from the phosphate source (PO), the at least one raw material comprising a phosphate required amount expressed in équivalent P2O5 amounts (= wt.% P2O5) of at least 5 wt.% P2O5, and a required calcium amount expressed in équivalent CaO amounts (= wt.% CaO) of at least 0.7 wt.% CaO, • in a digestion step (Dl), digesting the at least one raw material (PCI) with a digestion liquor (L) in the one or more reactors, wherein the digestion liquor (L), o is an aqueous solution of sulphuric acid (H2SO4) and of one or more minerai acids (HX), wherein a ratio (H⁺(SA) / H (L)) of a mole content of H* issued from the sulphuric acid (= H^SA)) to a total mole content of H' ions in the digestion liquor (L) (= H¹ (LJ) is comprised between 2 and 75%, o is added to the at least one raw material (PCI ) in amounts such that a molar ratio (H⁺(L) / Ca) of the total amount of H⁺ ions in the digestion liquor (L) (= H⁺( L)) to a total amount of Ca atoms (= Ca) present in both digestion liquor (L) and at least one raw material (PCI) is comprised between 0.8 and 1.95 (i.e., 1C(L) ! Ca = 0.8 - 1.95), to form a digestcd suspension (PC2) comprising an aqueous phosphate rich solution (PI) comprising phosphate ions and a first solid phase (Cl) containing calcium sulphate and impurities, wherein the digestion step (Dl) occurs at a température lowcr than 100°C and has a duration lower than 180 min, • In a séparation step (SI), separating the digested suspension (PC2) into, on the one hand, the aqueous phosphate rich solution (P 1 ) and, on the other hand, the first solid phase (C 1 ).

In a preferrcd embodiment, the solid phosphate source (PO) either:

• contains calcium in an amount of at least the required calcium amount and thus forms the at least one raw material (PCI) (i.e., PCI = PO), or • contains less than the required calcium amount, and the at least one raw material (PCI) is formed in a raw material formation step (MO) by addition of a calcium compound (CO) to the phosphate source (PO) to form the at least one raw material (PCI ) with the required amounts of calcium (i.e., PCI c PO + CO), wherein the calcium compound is chosen among:

o lime dérivatives including quick lime, slaked lime, pulverized lime, lime milk, fïnely ground limestone as pure product or as residue, o calcium carbonate, o calcium phosphates salts (mono di-; tri-), o kaolin, o calcium hydroxide, o calcium sulphate, o calcium fluoride, e a second phosphate source (P02) containing calcium, o the aqueous phosphate rich solution (Pl ), o phosphoric acid,or o a mixture thereof.

The one or more minerai acids (HX) can be chosen among hydrochloric acid, phosphoric acid, tluosilic acid, hydrofluoric acid, the aqueous phosphate rich solution (PI), the wash fîltrate of the residue or a combination thereof, and preferably comprises hydrochloric acid, more preferably, hydrochloric acid alone.

In a preferred embodiment, a portion of the aqueous phosphate rich solution (PI) is recirculated into the digestion step (Dl) as a component of the digesting liquor or as a calcium source, wherein the portion of the aqueous phosphate rich solution (PI) being recirculated is preferably comprised between l and 50%, more preferably between 5 and 30%, most preferably between 10 and 20%.

The at least one raw material (PC l ) can comprise phosphate in amounts comprised between !0and50wt.% P2O5, preferably between 12 and 45 wt.% P2O5, more preferably between 14 and 40 wt.% P2O5, more preferably between 15 and 38 wt.% P2O5, more preferably between and 35 wt.% P2O5, more preferably between 19 and 30 wt.% P2O5, more preferably between 20 and 27.5 wt.% P2O5, more preferably between 22.5 and 25 wt.% P2O5.

The at least one raw material (PCI) can comprise hydroxy and/or fluoro apatite m amounts comprised between 4wt.% and 91.5 wt.%, preferably between I0 and 90 wt.%, more preferably between 15 and 85 wt.% P2O5, most preferably between 20 and 75 wt.%, preferably between 40 and 60 w^rt.%.

The phosphate source (PO) can be choscn among one or more of the following origins:

• phosphate ores, • phosphate salts, • ashes, preferably ashes from one or more of incinerated sewage sludge, bones, manure.

The phosphate source (PO) can be used alone or admixed with a second phosphate source (P02) of different origin than the phosphate source, wherein the admixing occurs either prior to feeding into the one or more reactors, or in the one or more reactors.

An advantage of the present invention is that the digestion step (Dl) can occur at atmospheric pressure and at a température lower than l00°C, and even lower than 70°C, preferably between 30°C and 65°C; more preferably between 40°C and 60°C; more preferably between 45°C and 50°C. The digestion step (Dl) has a duration lower than 180 min, preferably lower than 90 min, more preferably lower than 60 min, more preferably lower than 45 min, and wherein the duration is preferably at least 5 min, more preferably at least 10 min.

A combined concentration of the sulphuric acid and the one or more minerai acids in the digestion liquor (L) is preferably less than 20 wt.%, preferably less than 15 wt.%, more preferably less than 10 wt.%, and is preferably at least 2%, more preferably at least 5%.The ratio (ΙΓ(5Α) / H⁺(L)) of the mole content of H' issued from the sulphuric acid (= H⁺(SA)) to the total amount of H⁺ ions in the digestion liquor (L) (= H‘(L) is preferably comprised between 5% and 70%, preferably between 7% and 60%, more preferably between 10 and 50%, more preferably between 12% and 40%; more preferably between 15% and 30%, most preferably between 18% and 25%.

In the digesting (Dl ) step, a molar ratio (H⁺(L)/ Ca) of the H⁺-ions (H‘(L)) in the digestion liquor (L) to the calcium atoms in both digestion liquor and at least one raw material (PCI ) can be comprised between 1.3 and 1.9, preferably l ,7 and l ,8, more preferably between 1.5 and 1.6.

The process can comprise an additional step, wherein the aqueous phosphate rich solution (PI) is neutralized in a neutralizing step (NI) to form dicalcium phosphate (DCP), wherein the neutralisation step (NI) is performed in presence of a source of calcium (Bl ) to reach a pH preferably comprised between 3 and 6, wherein the source of calcium (B l ) is chosen among, • lime derivatives including quick lime, slaked lime, puiverized lime, lime milk, • calcium carbonate or fînely ground limcstone, • calcium hydroxide, • calcium phosphate, or • a mixture thereof.

The DCP thus produced can be further processcd to produce, • a fertilizer, preferably of type monoammonium phosphate (MAP), diammonium phosphate (DAP), Ammonium-Potassium Phosphate fertilizer (NPK fertilizer), • animal feed, • food grade products, • merchant grade or purified phosphoric acid or technical grade phosphoric acid.

In a preferred embodiment, the one or more reactors are fed with,:

• the digestion liquor formed by mixing the aqueous solution of sulphuric acid (H2SO4) and the aqueous solution of one or more minerai acids (HX) prior to feedîng into the one or more reactors; or • the aqueous solution of sulphuric acid (H2SO4) first, followed by the aqueous solution of one or more minerai acids (HX), • the aqueous solution of one or more minerai acid (HX) first, followed by the aqueous solution of sulphuric acid (H2SO4),

With substantîal amounts of impurities, the process is more efficient if as much P2O5 contained in the raw material be dissolved in the digested suspension (PC2) and as little as possible remains undissolved and be part of the first solid phase (Cl) after the séparation step (SI). This can be quantified by a P2O5-IOSS ratio (m(P2Û5)ci / m(P2O5)pci) of a total mass (mfPiOsjci) of phosphorus in the first solid phase (Cl) to a total mass (m(P2Oj)pci) of phosphorus in the raw material (PCI). For example, the P2O5-IOSS ratio can be comprised between l % and 30%, preferably between l .5% and 25 %, more preferably between 2% and 20%, most preferably between 2.5 % and I5 %; most preferably between 3 and 10%; most preferably 5 and 8%, most preferably 6 and 7%.

The efficacy of the process also dépends on the amounts of impurities other than CaO which can be separated from the digested suspension (PC2). The reaction of CaO with H2SO4 précipitâtes calcium sulphates which are separated from the digested suspension (PC2) at the séparation step (SI). The lower the proportion of calcium sulphate in the cake (= first solid phase (Cl), the higher the amounts of impurities other than CaO hâve been separated from the digested suspension (PC2). This can be quantified with a calcium sulphate weight ratio (m(CaSO4) / m(Cl )) of a total mass (m(CaSO4) of CaSO4.nHjO (with n = 0 to 2) in the first solid phase (Cl ) to a total mass (m(Cl)) of the first solid phase (Cl ). A low value of the calcium sulphate weight ratio is représentative of a high amount of impurities other than CaO in the cake. For example, the calcium sulphate weight ratio can be less than 97 wt.%, preferably comprised between 5 wt.% and 90 wt.%, between 10 wt.% and 85 wt.%, between 15 wt.% and 75 wt.%, more preferably between 50 wt.% and 70 wt.%.

BRIEF DESCRIPTION OF THE FIGURES

On these figures,

Fig. I shows the process steps of the présent invention in its broadest scope.

Fig. 2 shows the process steps of a preferred embodiment of the présent invention.

Fig. 3 shows the process steps of another preferred embodiment.

Fig. 4 shows the process steps of yet another preferred embodiment.

Fig. 5 shows a graph plotting the filtering time and P2O5 loss as a function of the ratio H*(SA) / FT(L).

DETAILED DESCRIPTION.

As shown in Figure l, the process of the présent invention for producing a phosphate containing product from a phosphate source (PO) comprises the following steps.

One or more reactors are fed with at least one raw material (PCI) issued from the phosphate source (PO). The at least one raw material (PCI) comprises, • a phosphate required amount expressed in équivalent P2O5 amounts (= wt.% P2O5) of at least 5 wt.% P2O5, and • a required calcium amount expressed in équivalent CaO amounts (= wt.% CaO) of at least 0.7 wt.% CaO.

In a digestion step (Dl ), the at least one raw material (PCI ) is digested with a digestion liquor (L) in the one or more reactors. The digestion liquor (L) is an aqueous solution of sulphuric acid (H2SO4) and of one or more minerai acids (HX), wherein a ratio (H^SA) / H*(L)) of a mole content of H' issued from the sulphuric acid (= H⁺(SA)) to a total mole content of H' ions in the digestion liquor (L) (= H(L)) is comprised between 2 and 75%.

The digestion liquor (L) is added to the at least one raw material (PCI ) in amounts such that a molar ratio (H (L) / Ca) of the total amount of H⁺ ions in the digestion liquor (L) (= H*(L)) to a total amount of Ca atoms (= Ca) présent in both digestion liquor (L) and at least one raw material (PCI) is comprised between 0.8 and 1.95 (i.e., H '(L) / Ca = 0.8 - L95), to form a digested suspension (PC2) comprising an aqueous phosphate rich solution (PI ) comprising phosphate ions and a first solid phase (C l ) containing calcium sulphate and impurities.

In a séparation step (SI), the digested suspension (PC2) is separated into, on the one hand, the aqueous phosphate rich solution (PI) (= filtrate) and, on the other hand, the first solid phase (Cl ) (= residue).

In a preferred embodiment, the first solid phase (Cl) is washed with water (counter- or co-current washing) before being stored or used.

PHOSPHATE SOURCE (PO) AND RAW MATERIAL (PCI)

The phosphate source (PO) can be an ore or rock containing in particular calcium phosphate in the form of apatite (and dérivatives thereof including fluoro, chloro, hydroxy, ... - apatite) or tri-calcium phosphate or dicalcium phosphate. It can be a phosphate sait such as ammonium phosphate salts, sodium phosphate salts, aluminium phosphate salts, iron phosphate salts, aluminium and iron phosphates salts, struvite or a mixture of salts and the like, or it can be a phosphate containing ash obtained by buming in a waste incinération plant phosphate-containing sewage sludgcs, bio-degradable wastes, bio-wastes and/or animal wastes, in particular animal bones. A given phosphate source (PO) can be used alone or admixed with a second or more phosphate source(s) (P02) of different origin(s). The admixing can occur either prier to feeding the phosphate sources (PO, P02) into the one or more reactors, or in the one or more reactors.

ln one embodiment, the phosphate source (PO) contains calcium in an amount of at least the required calcium amount. This can typically be the case if the phosphate source is a phosphate ore. In this case, the phosphate source (PO) forms the at least one raw material (PCI) and needs not be treated by addition of any calcium source (i.e., PCI = PO).

In an alternative embodiment, the phosphate source (PO) contains less than the required calcium amount. This can be the case with ashes, depending on their origins and with ammonium or sodium salts. In these cases, the at least one raw material (PCI) is formed in a raw material formation step (MO) illustrated in Figures 2 to 4 by addition of a calcium compound (CO) to the phosphate source (PO) to form the at least one raw material (PCI) with the required amounts of calcium (i.e., PCI c PO + CO). The calcium compound can be chosen among, • lime dérivatives including quick lime, slakcd lime, pulverized lime, lime milk, finely ground limestone, as a pure product or as a residue, • calcium carbonate, • calcium phosphates (mono-, di-, tri), • kaolin, • calcium hydroxîde, • calcium sulphate, • calcium fluoride, • a second phosphate source (P02) containing calcium, • the aqueous phosphate rich solution (PI), or • a mixture thereof.

Alternat!vely, or concomitantly, a portion of the aqueous phosphate rich solution (PI) can be recirculated into the digestion step (Dl) as a component of the digesting liquor or as a calcium source. The portion ofthe aqueous phosphate rich solution (PI) which is recirculated is preferably comprised between l and 50 wt.%, more preferably between 5 and 30 wt.%, most preferably between 10 and 20 wt. %.

Alternative! y, or concomitantly, the entire wash filtrate quantity or a portion ofthe wash filtrate of the first solid phase can be recirculated into the digestion step (Dl) as a component of the digesting liquor or as a calcium source. The portion of the wash filtrate which is recirculated is preferably comprised between l and 75 wt.%, more preferably between 5 and 50 wt.%, more preferably between 10 and 30 wt.%, most preferably between 15 and 20 wt. %.

Regardless of the origin of the calcium, the at least one raw material (PCI ) comprises calcium in amounts preferably comprised between 0.7 wt.% and 60 wt.% CaO, more preferably between l and 57.5 wt.% CaO; more preferably between 1.5 and 55 wt.% CaO, more preferably between 2 and 52,5 wt.% CaO; niore preferably between 3 and 50 wt.% CaO; more preferably between 6 and 47,5 wt.% CaO more preferably between 10 and 45 wt.% CaO, more preferably between 15 and 35 wt.% CaO, and most preferably between l 7.5 and 30 wt.% CaO.

The at least one raw material (PCI) can comprise a total amount as P2O5 of phosphate preferably comprised between 10 and 50 wt.% P2O5, preferably between 12 and 45 wt.% P2O5, more preferably between 14 and 40 wt.% P2O5, more preferably between 15 and 38 wt.% P2O5, more preferably between 18 and 35 wt.% P2O5, , more preferably between 19 and 30 wt.% P2O5, more preferably between 20 and 27.5 wt.% P2O5, more preferably between 22.5 and 25 wt.% P2O5.

DIGESTION STEP (Dl) AND DIGESTION LIQUOR (L)

The digestion liquor (L) used in the digestion step (Dl) must comprise sulphuric acid (H2SO4) and one or more minerai acids (HX). The sulphuric acid is présent in an amount such that a ratio (H⁺(SA) / H⁺(L)) of a mole content of H⁺ issued from the sulphuric acid (= H⁺(SA)) to a total mole content of H* ions in the digestion liquor (L) (= 1T(L)) is comprised between 2 and 75%, preferably between 5% and 70%, preferably between 7% and 60%, more preferably between 10 and 50%, more preferably between 12% and 40%; more preferably between 15% and 30%, most preferably between 18% and 25%.

Sulphuric acid can be pure or residual, i.e. generated by washing installations or during routine production or maintenance operations in industries such as metallurgy, food processing, pharmaceuticals, Chemicals, and particularly sulphuric acid production or phosphoric acid production.

The one or more minerai acids (HX) can be chosen among hydrochloric acid, nitrie acid, phosphoric acid, fluosilicic acid, hydrofluoric acid, the aqueous phosphate rich solution (PI), the wash filtrate of the first solid phase (C l ) or a combination thereof.

The one or more minerai acids can be derived from aqueous solutions of acidic calcium chloride. For cxample, an aqueous phase (Al ) resulting from a DCP séparation step (S2) discussed more in detail in continuation, after précipitation ofdicalcium phosphate (= DCP) by neutralisation (N l ) with a base, which can be recirculated from the same process line, or from a separate process line.

The one or more minerai acids can also be derived from a residual aqueous solution containing POq-ions from industries or agro-industries, qualified as residual because they contain impurities of the following types: heavy metals, fluorescents, carbons, chlorides, and the like or because the P2O5 content of these solution is too low (such as for cxample, less than 20wt %, or less than I5wt %, less than IO wt %, preferably less than 5wt%). Such solutions can generally not be used as such in the production of pure phosphoric acid or in the production of pure phosphate salts.

This solution can be generated by washing installations or during routine production or maintenance operations in industries such as metallurgy, food processing, pharmaceuticals, Chemicals, and particularly in the production of phosphate salts or fertilisers or the production of DCP (for example with the présent process).

The one or more minerai acids can comprise any one of the foregoing acids, and any mixture thereof. In a preferred embodiment, however, the minerai acid (HX) comprises hydrochloric acid, and preferably, hydrochloric acid alone. In an alternative embodiment, the minerai acid (HX) comprises hydrofluoric acid, and preferably, hydrofluoric acid alone. In yet an alternative embodiment, the minerai acid (HX) comprises fluosilicic acid, and preferably, fluosilicic acid alone.

The digestion step (Dl ) can advantageously occur at atmospherie pressure. The digestion température can be quite low, as it is lower than l00°C, preferably lower than 70°C, more preferably between 30°C and 65°C; more preferably between 40°C and 60°C; more preferably between 45°C and 50°C.

The digestion step (Dl) can be quite rapid with a duration and is lower than 180 min, preferably lower than 90 min, more preferably lower than 60 min, more preferably lower than 45 min, and wherein the duration is preferably at least 5 min, more preferably at least IO min.

The acid concentrations in the digestion liquor (L) needs be controlled. For example, a combined concentration of the sulphuric acid and the one or more minerai acids in the digestion liquor (L) can be less than 20 wt.%, preferably less than 15 wt.%, more preferably less than IO wt.%. The combined concentration can be at least 2%, more preferably at least 5%.

The amounts of acids in the digestion Iiquor (L) can be related to the amount of undesired calcium to be removed from the system. For example, a molar ratio (H*(L)/Ca) of the mole content of H⁺ présent in the digestion Iiquor ( = H⁺(L)) to the calcium atoms in both digestion iiquor and at least one raw material (PC l ) is comprised between l .3 and l .9, preferably l .7 and l .8, more preferably between 1.5 and I.6.

The one or more reactors can be fed in different manners. In a first embodiment, the digestion Iiquor is formed by mixing the aqueous solution of sulphuric acid (H2SO4) and the aqueous solution of one or more minerai acids (HX) prior to feeding into the one or more reactors.

In an alternative embodiment, the digestion Iiquor can be formed and mixed in the one or more reactors. For example, the aqueous solution of sulphuric acid (H2SO4) can first be fed to the one or more reactors, followed by the aqueous solution of one or more minerai acids (HX). Altcmatively, the aqueous solution of one or more minerai acids (HX) can be fed first to the one or more reactors, followed by the aqueous solution of sulphuric acid (H2SO4). Finally, the aqueous solution of sulphuric acid (H2SO4) and the aqueous solution of one or more minerai acids (HX) can be fed to the one or more reactors simultaneously, without being mixed beforehand. in another alternative embodiment, one reactor is fed with the aqueous solution of sulphuric acid (H2SO4) and the aqueous solution of one or more minerai acids (HX) simultaneously, without being mixed beforehand and the digested suspension (PC2) is fed into one or more reactors before being separated. More than one reactor can be arranged in sériés. The raw material (PCI ) and digestion Iiquor (L) can be fed to a first reactor, and the thus formed suspension can be transferred from the first reactor to the following reactors in sériés. This method increases the digestion time accordingly. In an alternative embodiment, the sulphuric acid or ail or a sélection of the one or more minerai acids (HX) can be fed in the first reactor with the raw material, and the remaining acid components forming the digestion Iiquor can be added to successive reactors, as the suspension traveis from one reactor to the next one. It is, however, preferred to contact the raw material (PCI) with ail the components of the digestion Iiquor (L) in the first reactor.

The présent invention applies to any raw material (PCI), including raw materials comprising substantial amounts of impurities. In a raw material (PCI) comprising substantial amounts of impurities, it is advantageous that as much P2O5 be dissolved in the aqueous phosphate rich solution (P l ), and as much impurities as possible do not dissolve and remain in the first solid phase (Cl) separated from the aqueous phosphate rich solution (PI) after the séparation step (SI)..

For example, the efficacy ofthe P2O5 recovery from the raw material can be quantified by a P2O5-IOSS ratio (m(P2Oj)ci / m(P2O5)pci) of a total mass (mfPjO.Qci) of phosphorus in the first solid phase (Cl) to a total mass (m(P2O5)pci) of phosphorus in the raw material (PCI). The P2O5-IOSS ratio defines the amount of P2O5 which does not dissolve and remains in the first solid phase (C l ). The P2O5-IOSS ratio can be comprised between I % and 30 %, preferably between l .5% and 25 %, more preferably between 2% and 20%, most preferably between 2.5 % and I5 %; most preferably between 3 and 10%; most preferably 5 and 8%, most preferably 6 and 7%. Altematively, the first solid phase (Cl) can comprised between 0.25 wt.% and 10 wt.% P2O5, preferably between 0.3 wt.% and 7 wt.% P2O5, more preferably between 0.5 wt.% and 5 wt.% P2O5, most preferably between 0.7 wt.% and 3 wt.% P2O5..

Since substantially ail CaO présent in the raw material which reacts with H2SO4 précipitâtes as calcium sulphate, the cake, which forms the first solid phase (Cl), comprises substantial amounts of calcium sulphates, depending on the amounts of CaO présent in the raw material (PC l ) relative to the impurities. It follows that a raw material comprising Iittle impurities other than CaO, will form a cake comprising high proportions of calcium sulphates, whilst the proportion of calcium sulphates in the cake decreases with increasing amounts of impurities in the raw material which are successfully separated into the first solid phase (Cl). The proportion of calcium sulphates présent in the cake (or first solid phase (Cl )) can be quantified by a calcium weight ratio (m(CaSO4) / m(Cl)) of a total mass (m(CaSO4) of CaSO4.nH2O (with n = 0 to 2) in the first solid phase (Cl) to a total mass (m(Cl)) of the first solid phase (Cl). For example, the calcium weight ratio (m(CaSO4) ! m(C l )) can be less than 97 wt.%, preferably comprised between 5 wt.% and 90 wt.%, between l0wt.% and 85 wt.%, between 15 wt.% and 75 wt.%, more preferably between 50 wt.% and 70 wt.%.

SEPARATION STEP (SI)

Digestion of the raw material (PCI) forms a digested suspension (PC2) comprising an aqueous phosphate rich solution (PI) comprising phosphate ions and a first solid phase (Cl) containing among others calcium sulphate and impurities. The aqueous phosphate rich solution (PI) must be separated from the first solid phase (Cl) in a séparation step (SI) as shown in Figures l to 4. The séparation step (S l ) can be carried out in a séparation unit selectcd among any one of a décantation unit, a vacuum belt filter, a press filter, a membrane press filter, or a centrifuge.

Comparée! with a dîgested suspension of the prior art treated with hydrochloric acid (= HCl) alone, the digested suspension (PC2) of the présent invention obtained with the présent digestion step (Dl ) can be filtcrcd quicker and more efficîently. Without wishing to be bound by any theory, it is believed that this is due to the presence in the solid phase (Cl) of crystallized solids (calcium sulphate and preferably gypsum) rather than a mud of impurities obtained with the prior art digestion steps with e.g., HCl alone.

The solid phase (Cl) can be discarded or further processed for other applications. Depending on the nature of the phosphate source (PO) and the amounts of impurities présent therein, the aqueous phosphate rich solution (PI) can be further processed to yield desired phosphate containing end-products of desired purifies. For example, the aqueous phosphate rich solution (PI) can be concentrated and purified by means of well-known phosphoric acid purification steps. In an alternative embodiment, the aqueous phosphate rich solution (PI ) can be neutralized in a neutralization step (NI) described in continuation.

NEUTRALIZATION STEP (NI) OF THE AQUEOUS PHOSPHATE RICH SOLUTION (PD

The process of the présent invention can be used for the préparation of a dicalcium phosphate (DCP). To this purpose, the process illustrated in Figures 3 and 4 further comprises a neutralization step (NI), wherein the aqueous phosphate rich solution (PI) is neutralized at a pH sufficient to form a DCP-suspension (P2) comprising an aqueous phase (Al) and a DCP-rich solid phase (P3) comprising DCP. The DCP-rich solid phase (P3) is separated from the aqueous phase (Al) of the DCP-suspension (P2) in a DCP séparation step (S2).

The neutralisation step (N I ) is performed in presence of a source of calcium (Bl ) to reach a pH preferably comprised between 3 and 6. The source of calcium (Bl) can be chosen among, • Lime dérivatives including quick lime, slaked lime, lime, lime milk, as pure product or as residue.

• calcium carbonate or limestone, • calcium hydroxide as pure product or as residue, • calcium phosphate, • a mixture thereof.

In an embodiment ofthe process illustrated in Figure 4, the aqueous phosphate rich solution (PI) or the DCP-rich solid phase (P3) is further processed in an end process (EP) to produce an end-product (P4) selected among, • a fertilizer, preferably of type monoammonium phosphate (MAP), diammonium phosphate (DAP), Ammonium-Potassium Phosphate fertilizer (NPK fertilizer), • animal feed, • food grade product, • merchant grade or purified phosphoric acid or technical grade phosphoric acid.

EXAMPLE

A rock (ore) from Morocco referenced as K09 was used as phosphate source (PO) and as raw material (PCI) for the following examples (= Ex. 2 to 5) and comparative examples (= CEx.l and 6). The analyses results of a sélection of compounds contained in the rock are listed in Table l.

Samples of m = 100 g ofthe K09-rock were digested in different digestion liquors as listed in Table 2, for a duration t = 30 min at a température T = 60°C. In ail cases the acids concentration, both HX and H2SO4, was 6 wt.%, and the ratio (H⁺(L) / Ca) of the total amount of ΙΓ ions in the digestion liquor (L) (= H⁺(L)) to the total amount of Ca atoms (=Ca) présent in the rock (the digestion liquors (L) did not comprise any Ca atoms) was equal to l .8.

Table 1: analyses results of a sélection of compounds contained in ore front

Morocco (ref. K09) used in the présent examples

A12O3 wt.%	CaO wt.%	FeiO? wt.%	MgO wt.%	P2O5 wt.%
0.35	50	0.231	0.785	29.7

The liquors of (comparative) Examples 1 to 6 were ail composed of sulphuric acid and hydrochloric acid in the molar concentrations listed in Table 2. Table 2 also lists the filtration times and P2O5 losses (calculated from the solid masses and P2O5 in the solid). P2O5 losses are defined in this step as P2O5 masses lost in solid phase divided by P2O5 masses coming from raw materials (here phosphate sources). Filtration is carried out with a Buchner filter and ail filtration parameters (surface, pore diameter, and the like) are maintained constant.

Table 2: compositions of the liquors and filter limes and P2O5 loss in (comparative) Exantples 1 (o 6

#	H+(SA) mol.%	H(HC 0 mol.%	Filter time s	cake σ &	P2O5 in cake wt.%	P2O5 losses wt.%
C.Ex 1	0	100	740	27.2	2.36	2
Ex.2	6.75	93.25	54	23.05	3.5	3
Ex. 3	12.5	87.5	26	28.7	3.85	4
Ex.4	25	75	35	44.2	2.4	4
Ex.5	75	25	25	115.5	2.19	9
CEx. 6	100	0	12	138.7	3.4	16

Table 2 lists the liquor compositions used in the examples and comparative examples. The liquors in CEx. 1 and CEx.6 comprise sulphuric acid only and hydrochloric acid only, respectively, 5 and are therefore not according to the présent invention. The liquors of Ex.2 to Ex.5 comprise both sulphuric acid and hydrochloric acid and are according to the présent invention.

Table 2 lists for each of the (comparative) examples 1 to 6 the filtration times required for separating the digested suspension (PC2) into, on the one hand, the aqueous phosphate rich solution (P 1 ) and, on the other hand, the first solid phase (C1 ). Table 2 also lists the resulting P2O5 10 losses which remained in the first solid phase and is not dissolved in the aqueous phosphate rich solution (PI). Figure 5 illustrâtes graphically the results listed in Table 2, showing the filtration times (= black circles, solid line - left-hand ordinate axis) and P2O5 losses (= white circles, dashed line - right-hand ordinate axis) as a function of the amount of sulphuric acid in the digestion liquor expressed in ternis of the ratio (ET(SA) / H⁺(L)) of the mole content of H⁺ issued from the 15 sulphuric acid (= H (SA)) to the total mole content of H⁺ ions in the digestion liquor (L) (= H⁺(L)). Note that for sake of clarity, the maximum of the left-hand ordinate axis of filter time is set to 100 s, well below the filter time of 740 s measured with CEx. 1.

It can be seen from Table 2 and Figure 5, that digesting a rock with a digestion liquor (L) comprising HCl only (i.e., CEx.l with H⁺(SA) / Η'(Ε) = 0) has the effect of increasing substantially the filtering time to 740 s versus 12 s when the digestion liquor (L) comprises H2SO4 only (i.e., CEx.6 with H~(SA) / H⁺(L) = 100%). Digesting the rock with a liquor comprising H2SO4 only (i.e., CEx.6 with H (SA) / H^r ( L) = 100%), however, încreases the P2O5 losses to 16% versus 2% when the digestion liquor (L) comprising HCl only (i.e., CEx.l with H*(SA) / H (L) = 0).

Using a digestion liquor (L) comprising a mixture of H2SO4 with a minerai acid (HX) (here

HX = HCl) yields a digested suspension (PC2) which can be separated within industrialisable time durations (Ex.2 to Ex.5: t = 12 to 35 s), with limited losses of P2O5 (Ex.2 to Ex.5: P2O5 loss = 2 to 9 wt.%). These results clearly demonstrate that the method of the présent invention, including digesting a source of phosphate with a digestion liquor comprising both H2SO4 and a minerai acid (HX) présent in a ratio ratio, H’(SA) / H⁺(L), comprised between 2 and 75% is clearly advantageous over digestion liquors comprising both components outside the claimed ratio. The method of the présent invention is therefbre unexpectedly advantageous over prior art methods.

REF	DESCRIPTION
Al	Aqueous phase (after step NI)
CO	Calcium compound
CI	First solid phase containing calcium sulphate and impuritics
Ca	Total amount of Ca atoms
DI	Digestion step
DCP	Dicalcium phosphate
EP	End process
HX	Minerai acid
H+(L)	Mole content of H' issued from both sulphuric acid and one or more minerai acids
H'(SA)	Mole content of H4 issued from the sulphuric acid
MO	Raw material formation step
NI	Neutralization step
PO	Phosphate source
PI	Aqueous phosphate rich solution (after step S1 )
P2	DCP-suspension (after step NI )
P3	DCP-rich solid phase (after step S2)
P4	End product
PCI	Raw material
PC2	Digested suspension (after step DI )
SI	Séparation step
S2	DCP séparation step

Claims (15)

1. l. A process for producing a phosphate containing product from a phosphate source (PO), the process comprising the following steps:

   • teeding one or more reactors with at least one raw material (PCI) issued from the phosphate source (PO), the at least one raw material comprising a phosphate required amount expressed in équivalent P2O5 amounts (= wt.% P2O5) of at least 5 wt.% P2O5, and a required calcium amount expressed in équivalent CaO amounts (= wt.% CaO) of at least 0.7 wt.% CaO, • in a digestion step (Dl), digesting the at least one raw material (PCI) with a digestion liquor (L) in the reactor, wherein the digestion liquor (L), o is an aqueous solution of sulphuric acid (H2SO4) and of one or more minerai acids (HX), wherein a ratio (H (SA) / H⁺(L)) of a mole content of H⁺ issued from the sulphuric acid (= H⁺(SA)) to a total mole content of H ' ions in the digestion liquor (L) (= H (L)) is comprised between 2 and 75%, o is added to the at least one raw material (PC l ) in amounts such that a molar ratio (H*(L) / Ca) of the total amount of H’ ions in the digestion liquor (L) (= H (I.)) to a total amount of Ca atoms (= Ca) présent in both digestion liquor (L) and at least one raw material (PCI ) is comprised between 0.8 and 1.95 (i.e., H*(L) / Ca = 0.8 - l .95), to fonn a digested suspension (PC2) comprising an aqueous phosphate rich solution (PI) comprising phosphate ions and a first solid phase (Cl ) containing calcium sulphate and impurities, wherein the digestion step (Dl) occurs at a température lower than l00°C and has a duration lower than 180 min, • In a séparation step (SI), separating the digested suspension (PC2) into, on the one hand, the aqueous phosphate rich solution (PI ) and, on the other hand, the first solid phase (Cl ).
2. 2. Process according to claim l, wherein the solid phosphate source (PO) either:

   • contains calcium in an amount of at least the required calcium amount and thus forms the at least one raw material (PCI) (i.e., PCI = PO), or • contains less than the required calcium amount, and the at least one raw material (PCI) is formed in a raw material formation step (MO) by addition of a calcium compound (C0) to the phosphate source (PO) to form the at least one raw material (PCI) with the required amounts of calcium (i.e., PCI c PO + CO), wherein the calcium compound is chosen among:

   o lime dérivatives including quick lime, slaked lime, pulverized lime, lime milk, finely ground limestone o calcium carbonate, o calcium phosphates salts (mono di-; tri-), o kaolin, o calcium hydroxide, o calcium sulphate, o calcium fluoride, θ a second phosphate source (P02) containing calcium, o the aqueous phosphate rich solution (PI), o phosphoric acid.or o a mixture thereof.
3. 3. Process according to claim l or 2, wherein the one or more minerai acids (HX) are chosen among hydrochloric acid, phosphoric acid, fluosilic acid, hydrofluoric acid, the aqueous phosphate rich solution (PI), the wash fîltrate of the first solid phase (Cl), or a combination thereof, and preferably comprises hydrochloric acid, more preferably, hydrochloric acid alone
4. 4. Process according to any one of the preceding claims, wherein a portion of the aqueous phosphaterich solution (PI) is recirculated into the digestion step (Dl) as a component of the digesting liquor or as a calcium source, wherein the portion of the aqueous phosphate rich solution (PI ) being recirculated is preferably comprised between l and 50%, more preferably between 5 and 30%, most preferably between 10 and 20%.
5. 5. Process according to any one of the preceding claims, wherein the at least one raw material (PCI) comprises phosphate in amounts comprised between 10 and 50 wt.% P2O5, preferably between 12 and 45 wt.% P2O5, more preferably between 14 and 40 wt.% P2O5, more preferably between 15 and 38 wt.% P2O5, more preferably between 18 and 35 wt.% P2O5, , more preferably between 19 and 30 wt.% P2O5, more preferably between 20 and 27.5 wt.% P2O5, more preferably between 22.5 and 25 wt.% P2O5.
6. 6. Process according to any one ofthe preceding daims, wherein the phosphate source (PO) is chosen among one or more of the following origins:

   • phosphate ores, • phosphate salts, • ashes, preferably ashes from one or more of incinerated sewage sludge, bones, manure, and wherein the phosphate source (PO) is used alone or admixed with a second phosphate source (P02) of different origin than the phosphate source, wherein the admixing occurs either in the reactor or prior to feeding the phosphate source (PO) into the reactor.
7. 7. Process according to any one of the preceding daims, wherein the digestion step (D l ) occurs at atmospheric pressure and at a température lower than 70°C, preferably between 30°C and 65°C; more preferably between 40°C and 60°C; more preferably between 45°C and 50°C.
8. 8. Process according to any one of the preceding daims, wherein the digestion step (Dl ) has a duration lower than 90 min, preferably lower than 60 min, more preferably lower than 45 min, and wherein the duration is preferably at least 5 min, more preferably at least 10 min.
9. 9. Process according to any one of the preceding daims, wherein a combined concentration of the sulphuric acid and the one or more minerai acids in the digestion liquor (L) is less than 20 wt.%, preferably less than 15 wt.%, more preferably less than 10 wt.%, and is preferably at least 2%, more preferably at least 5%.
10. 10. Process according to any one of the preceding daims, wherein the ratio (H'(SA) / H⁺(L)) of the mole content of H⁺ issued from the sulphuric acid (= H⁺(SA)) to the total amount of H ions in the digestion liquor (L) (= H*(L) is comprised between 5% and 70%, preferably between 7% and 60%, more preferably between 10 and 50%, more preferably between 12% and 40%; more preferably between 15% and 30%, most preferably between 18% and 25%.
11. 11. Process according to any one of the preceding daims, wherein, in the digesting (Dl) step, a molar ratio (H⁺(L)/ Ca) ofthe H⁺-ions (H (L)) in the digestion liquor (L) to the calcium atoms in both digestion liquor and at least one raw material (PCI ) is comprised between l .3 and l .9, preferably l .7 and l .8, more preferably between l .5 and l .6.

    J
12. 12. Process according to any onc of the preceding claims, wherein the aqueous phosphate rich solution (PI) is neutralized in a neutralizing step (NI) to form dicalcium phosphate (DCP), wherein the neutralisation step (NI ) is performed in présence of a source of calcium (Bl) to reach a pH preferably comprised between 3 and 6, wherein the source of calcium (BI) is chosen among, • lime dérivatives including quick lime, slaked lime, pulverized lime, lime milk, • calcium carbonate or finely ground limestone, • calcium hydroxide, • calcium phosphate, or • a mixture thereof.
13. 13. Process according to claim I2, wherein the DCP is further processed to produce, • a fertilîzer, preferably of type monoammonium phosphate (MAP), diammonium phosphate (DAP), Ammonium-Potassium Phosphate fertilîzer (NPK fertilîzer), • animal feed, • food grade products, • merchant grade or purified phosphoric acid or technical grade phosphoric acid.
14. 14. Process according to any one of the preceding claims, wherein the reactor is fed with:

    • the digestion liquor formed by mixing the aqueous solution of sulphuric acid (H2SO4) and the aqueous solution of one or more minerai acids (HX) prior to feeding into the reactor; or • the aqueous solution of sulphuric acid (H2SO4) first, followed by the aqueous solution of one or more minerai acids (HX), or • the aqueous solution of one or more minerai acids (HX) first, followed by the aqueous solution of sulphuric acid (H2SO4), or • the aqueous solution of sulphuric acid (H2SO4) and the aqueous solution of one or more minerai acids (HX) simultaneously, without being mixed before.
15. 15. Process according to any one of the preceding claims, wherein • a P₂O₅-loss ratio (m(P2O5)ci ! m(P₂O5)pci) of a total mass (m(P2O5)ci) of phosphorus in the first solid phase (Cl) to a total mass (m(P₂O5)pci) of phosphorus in the raw material (PCI ) is comprised between between l % and 30 %, preferably between l .5% and 25 %, more preferably between 2% and 20%, most preferably between 2.5 % and 15 %; most preferably between 3 and 10%; most preferably 5 and 8%, most preferably 6 and 7%, and or • a calcium weight ratio (m(CaSO4) / m(C 1 )) of a total mass (m(CaSÛ4) of CaSO4.nH₂O

    5 (with n = 0 to 2) in the first solid phase (C1 ) to a total mass (m(C 1 )) of the first solid phase (Cl ) is less than 97 wt.%, preferably comprised between 5 wt.% and 90 wt.%, between 10 wt.% and 85 wt.%, between 15 wt.% and 75 wt.%, more preferably between 50 wt.% and 70 wt.%