Method for producing phosphoric acid, a monovalent cation sulfate and calcium carbonate

Abstract

The invention relates to a method for producing phosphoric acid, a monovalent cation sulfate and calcium carbonate, comprising a first treatment of a phosphate source with an inorganic acid solution, a second treatment for obtaining calcium sulfate, recovery of phosphoric acid and calcium sulfate to be treated in a treatment with a monovalent cation carbonate solution, and recovery of calcium carbonate and a monovalent cation sulfate.

Description

Process for the production of phosphoric acid, monovalent cationic sulfate, and calcium carbonate FIELD OF INVENTION

[0001] The present invention relates to a process for the production of phosphoric acid, monovalent cationic sulfate and calcium carbonate. TECHNOLOGICAL BACKGROUND

[0002] The wet processing of phosphoric acid from rocks results in the production of a significant quantity of calcium sulfate, the purity of which reflects the quality of the phosphate rock and the transformation process. This reaction byproduct has little commercial value and is often sent to landfill. The production of one tonne of phosphoric acid generates several tonnes of calcium sulfate. This substantial amount of material to manage has led to the exploration of valorization methods to reduce the amount of material sent to landfill and to convert the calcium sulfate into a product with higher commercial value.

[0003] For example, US patent 3004827 describes a process for treating gypsum, a byproduct of phosphoric acid production, to produce ammonium sulfate and calcium carbonate. The process involves producing gypsum from rock, which implies the presence of impurities that lead to poor reaction yields. To overcome this problem, the patent describes a hydrocyclone purification of the gypsum to obtain purified gypsum.

[0004] Unfortunately, this type of process consumes a lot of water and requires a complex installation as part of an industrial production of phosphoric acid, which is ultimately planned for the sole purpose of valorizing a by-product.

[0005] Document W02005 / 118222A discloses a process for treating phosphogypsum to recover its calcium content. The process produces calcium carbonate and ammonium sulfate. The phosphogypsum is obtained from the treated rock, from which phosphoric acid is extracted and which contains the inherent impurities of the rock. According to this document, residual impurities remain in the incoming phosphogypsum and are then transferred to the calcium carbonate phase, which is subsequently treated with an organic acid to produce, on the one hand, a liquid phase consisting of a liquid calcium salt of the organic acid and, on the other hand, impurities that have not reacted in solid form. The calcium salt of the organic acid is consumed via one or two additional steps, such as a reaction with phosphoric acid or a reaction with ammonium sulfate.

[0006] Unfortunately, in addition to their inherent complexity, the valorization methods do not meet market needs unless generating a concentrating stream is desirable, beyond simply increasing the yield of phosphoric acid extraction. In any case, the complexity of processing phosphogypsum in an industrially viable manner is clear.

[0007] The US3493340 document describes a purification operation of a phosphate source prior to source treatment, including leaching, or partial attack of the phosphate source in order to dissolve a maximum of impurities in the liquid phase while maintaining a maximum of phosphorus in the solid phase.

[0008] The US3552919 document describes a treatment of a phosphate source with sulfuric acid to obtain a solid phase comprising calcium sulfate dihydrate, to which ammonium carbonate is added to obtain a liquid phase comprising ammonium sulfate and a solid phase of CaCCh.

[0009] Document CN101269823 also describes a process for converting phosphogypsum into calcium carbonate and ammonium sulfate. This document also highlights the need to purify the calcium sulfate before it can be processed.

[0010] As can be seen, several valorization pathways for calcium sulfate or phosphogypsum have been described, some of which lead to the production of calcium carbonate and monovalent cationic sulfate. These latter two offer certain advantages, such as the possibility of marketing monovalent cationic sulfate at a higher added value. Furthermore, the quantity of residual calcium carbonate after phosphogypsum processing is generally lower in tonnage (weight of calcium carbonate versus weight of phosphogypsum), resulting in lower landfill costs.

[0011] As can be seen, while the valorization of phosphogypsum into ammonium sulfate and calcium carbonate seems promising, it is hampered by the presence of impurities in the phosphogypsum preventing the production of commercially viable products, or limiting subsequent uses, or it requires the use of complex and / or costly purification techniques.

[0012] The invention aims to overcome at least partially the disadvantages of the prior art by providing a process for producing phosphoric acid, monovalent cationic sulfate and calcium carbonate in a simple and industrially viable manner with sufficient degrees of purity to allow their commercialization. SUMMARY OF THE INVENTION

[0013] To solve this problem, the invention provides a process as indicated at the beginning comprising the following steps: a first treatment (T1) of a phosphate source comprising phosphorus and calcium with an inorganic acid solution to obtain a first slurry consisting of a first acidic liquid phase and a first solid phase comprising calcium, preferably in the form of calcium sulfate, predominantly hemi- or dihydrate (HH, DH), a second treatment (T2) of said first slurry (1B) and / or the first solid phase (1S) comprising calcium with a sulfuric solution to obtain a second slurry consisting of phosphoric acid and a second solid phase (2S) comprising calcium sulfate, preferably with a degree of hydration different from that of the calcium sulfate of the first solid phase (1S),recovery of phosphoric acid and the second solid phase by separation of phosphoric acid and the second solid phase, a third treatment of the second solid phase with a solution of monovalent cationic carbonate, said monovalent cation being chosen from the group comprising lithium ion, sodium ion, potassium ion, ammonium ion, allowing a third slurry to be obtained consisting of a liquid phase of monovalent cationic sulfate and a third solid phase of calcium carbonate, recovery of the calcium carbonate and monovalent cationic sulfate from said third slurry by separation of the liquid phase of monovalent cationic sulfate and said third solid phase of calcium carbonate. BRIEF DESCRIPTION OF THE FIGURES

[0014] Based on these figures, FIG.1 illustrates a first variant of the present invention FIG.2 illustrates a second variant of the present invention with a separation of the first porridge. FIG.3 illustrates a third variant of the present invention with a fourth treatment. FIG.4 illustrates a fourth variant of the present invention comprising a preliminary purification step of the phosphate source. FIG.5 illustrates a fifth variant of the present invention comprising an alternative step to that of Figure 4 of preliminary purification of the phosphate source. DETAILED DESCRIPTION OF THE INVENTION

[0015] As can be seen in Figures 1 to 4, the process according to the present invention comprises a first treatment of a phosphate source comprising phosphorus and calcium with an inorganic acid solution including concentrated sulfuric acid, and a second treatment of the first solid phase (1S) low in phosphorus and / or the first slurry (1B) thus produced during the first treatment with sulfuric acid, yielding, among other things, calcium sulfate. These two treatment steps result in a solid phase comprising purified calcium sulfate with a reduced impurity level.

[0016] Indeed, the first treatment (T1) dissolves some of the impurities present in the phosphate source, including phosphorus and calcium. The recovered solid (1S), containing calcium, has a reduced impurity content due to the dissolution of some of the impurities initially present in the phosphate source.

[0017] The first treatment (T1) is characterized by • The inorganic acid solution used in the first treatment (T1) is an acidic solution comprising concentrated sulfuric acid greater than 80%, preferably greater than 90%, of H2SO4. • The first treatment (T1) is performed with a molar ratio, H+ / Ca > 1.8 and, • the first liquid phase (1 L) rich in phosphorus comprises at least 90% by weight of P2O5 relative to the weight of P2O5 included in the phosphate source.

[0018] This first solid phase (1S), containing calcium, is low in phosphorus and is then subjected to the second treatment (T2) in which it is treated with sulfuric acid. This second treatment (T2) dissolves a further portion of impurities and allows for the recovery of P₂O₅ trapped in the first solid phase (1S) containing calcium, which could not pass into the first liquid phase (1L). These impurities and the P₂O₅ initially present in the phosphate source are also recovered. The presence of impurities within the second solid phase (2S) is reduced by dissolving the impurities resulting from the second sulfuric acid treatment (T2).This second treatment (T2) of the first solid phase (1S) comprising calcium with sulfuric acid therefore forms on the one hand a second solid phase (2S) crystallized comprising calcium sulfate and exhibiting very few impurities and on the other hand a second liquid phase (2L) comprising phosphoric acid.

[0019] The first and second treatments (T1, T2) indicated above are two treatments of the phosphate source and the first solid phase (1S), respectively. Either one or the other These processes allow the transfer of impurities from the solid phase (1 S, 2 S) to the corresponding liquid phase (1 L, 2 L). This enables the production of calcium sulfate with a relatively low impurity level, allowing for the valorization of the calcium sulfate without requiring a post-formation purification step. Dissolving the impurities transfers those impurities from the first and second solid phases (1 S, 2 S) to the first and second liquid phases (1 L, 2 L), respectively, either to the first acidic liquid phase (1 L) to be treated, to the second liquid phase (2 L) containing phosphoric acid, or to an acidic liquid phase to be recycled. These liquid phases are simpler to purify than a solid phase; purification can be achieved, for example, by selective precipitation, by liquid-solid separation with or without the addition of additives, and / or by solvent extraction.

[0020] As can be seen, contrary to the teachings of the cited documents, the impurities are extracted from the phosphate source and the first solid phase (1 S), which avoids complex solid phase purification treatments and simplifies the valorization of gypsum, a by-product of phosphoric acid production.

[0021] Next, in the process according to the present invention, the second solid phase (2S) comprising calcium sulfate undergoes a third treatment (T3) with a solution of a monovalent cationic carbonate, said monovalent cation being selected from the group comprising lithium ions, sodium ions, potassium ions, and ammonium ions. This treatment dissolves the calcium sulfate and forms calcium carbonate as a third solid phase (3S). The monovalent cationic sulfate remains in solution in the third liquid phase (3L).

[0022] As previously mentioned, thanks to the two-step treatment of the phosphate source, the calcium sulfate exhibits a very low level of impurities. Thus, upon its dissolution in the aforementioned monovalent cationic carbonate solution, few impurities are released. The precipitation of calcium carbonate following the dissolution of the calcium sulfate therefore necessarily results in few impurities in the solid phase of calcium carbonate. Surprisingly, and contrary to the processes described in the prior art, the calcium carbonate is sufficiently pure to reach a level of purity that makes it suitable for technical or even food applications.

[0023] Indeed, the separation of the third liquid phase (3L) of monovalent cationic sulfate and the said third solid phase (3S) of calcium carbonate makes it possible to obtain on the one hand high purity calcium carbonate, which can be marketed in a simple and industrially viable way and on the other hand high purity monovalent cationic sulfate, with the same advantages as calcium carbonate, namely in a simple, industrially viable way and whose quality allows for marketing.

[0024] Furthermore, the transformation of calcium sulfate into calcium carbonate and monovalent cationic sulfate also reduces the quantity of compounds that are difficult to recycle. The product typically considered the least valuable is calcium carbonate. The theoretical mass balance indicates that the reaction consumes 1,000 tons of gypsum to form 767 tons of calcium carbonate. Thus, even if the recycling of calcium carbonate is not locally feasible, the process according to the invention reduces the mass of the compound sent to landfill by almost 25%.

[0025] The phosphate source comprising phosphorus and calcium may be of sedimentary or igneous origin; it may be phosphate ore rock, phosphate mine tailings or beneficiation tailings, phosphate slime, a phosphate salt, a calcium salt, a calcium phosphate salt, such as monocalcium phosphate (MCP), dicalcium phosphate (DCP), tricalcium phosphate (TCP), hydroxyapatite, phosphorite, apatite, chlorapatite, fluorapatite, calcium phosphate, incineration ash, or mixtures thereof.

[0026] The phosphate source, comprising phosphorus and calcium, can be in solid form, in the form of sludge, or in the form of an aqueous suspension.

[0027] The inorganic acid solution of the first treatment step comprises sulfuric acid and may comprise phosphoric acid, sulfophosphoric acid, hydrochloric acid and / or a mixture thereof, preferably sulfuric acid alone, even more preferably sulfuric acid and / or sulfophosphoric acid.

[0028] The sulfuric acid introduced into the inorganic acid solution of the first treatment step (T1) is a concentrated sulfuric acid solution, namely with a concentration greater than 80%, preferably greater than 90%, preferably greater than 95%, and preferably greater than 98% by weight relative to the total weight of the solution. In an alternative process to the present invention, it is possible to use a dilute acid solution, namely with a concentration between 5 and 20%, preferably between 7 and 15%, and preferably between 8 and 10% by weight relative to the weight of the solution. The inorganic acid solution is the solution introduced in the first treatment step.

[0029] Preferably, the inorganic acid solution in the first treatment step (T1) is sulfuric acid and is a concentrated solution, namely with a concentration greater than 80%, preferably greater than 90%, preferably greater than 95%, and preferably greater than 98% by weight relative to the total weight of the solution. The inorganic acid solution is the solution introduced in the first treatment step (T1). Preferably, sulfuric acid is used in combination with phosphoric acid.

[0030] The first solid phase (1S) comprising calcium resulting from the first treatment step (T1) can be anhydrous calcium sulfate, calcium sulfate hemihydrate (HH), calcium sulfate dihydrate (DH).

[0031] More specifically, the first solid phase (1S) comprising calcium resulting from the first treatment step is predominantly anhydrous calcium sulfate, calcium sulfate hemihydrate, calcium sulfate dihydrate.

[0032] The sulfuric acid solution used in the second treatment (T2) can be a sulfuric acid solution at various concentrations, such as a concentrated sulfuric acid solution, namely having an H₂SO₄ content greater than 80%, preferably greater than 90%, preferably greater than 95%, and preferably greater than 98% by weight relative to the total weight of the solution. In an alternative process to the present invention, the sulfuric acid solution can be a dilute sulfuric acid solution, namely having an H₂SO₄ content between 5 and 20% by weight relative to the weight of the dilute sulfuric acid solution.

[0033] The calcium sulfate present in the second solid phase (2S) from said second treatment (T2) may be crystalline calcium sulfate hemihydrate, crystalline calcium sulfate dihydrate, or mixtures thereof, typically consisting of a phase predominantly containing calcium sulfate hemihydrate, or a phase predominantly containing calcium sulfate dihydrate. Preferably, the calcium sulfate present in the second solid phase from said second treatment is predominantly crystalline calcium sulfate hemihydrate, crystalline calcium sulfate dihydrate, or mixtures thereof, typically consisting of a phase predominantly containing calcium sulfate hemihydrate, or a phase predominantly containing calcium sulfate dihydrate.

[0034] By the terms "majority comprising" such as for example a "phase majorly comprising" a compound or the terms "rich in" a compound, we mean to include more than 90% by weight, preferably more than 92% by weight, more particularly more than 95% by weight and even more preferably more than 97% by weight such as for example that the phase comprises more than 90% by weight, preferably more than 92% by weight, more particularly more than 95% by weight and even more preferably more than 97% by weight of the compound.

[0035] Advantageously, the said separation of the second liquid phase (2L) comprising phosphoric acid and the second solid phase (2S) can advantageously be carried out under vacuum using a separation device such as a belt filter or a tilting cell filter.

[0036] Preferably, the monovalent cation carbonate solution in the third treatment (T3) is an ammonium carbonate solution. This ammonium carbonate solution can be formed by bubbling carbon dioxide and ammonia in an aqueous solution.

[0037] The said separation of the third liquid phase (3L) of monovalent cation sulfate and the said third solid phase (3S) of calcium carbonate can advantageously be carried out using a separation device such as a filter, a filter press, a drum filter, a centrifuge, a belt filter, or even a rotary filter.

[0038] Advantageously and as illustrated in Figure 3, the third liquid phase (3L) of monovalent cation sulfate can be acidified with an acid solution (Ac4) to extract the dissolved CO2 and possibly concentrated to generate a fourth solid phase (4S) comprising a crystalline monovalent cation sulfate which can be recovered by filtration or directly dried by industrial drying devices such as spray dryer, flash dryer, calciner.

[0039] Advantageously, and as illustrated in Figure 1, the process according to the present invention does not involve recovering said first acidic liquid phase (1 L), and the acidic liquid phase (1 L) is sent to the second treatment (T2) with the first solid phase (1 S) without separating the first slurry (1 B). Advantageously, said first slurry (1 B) is sent directly to the second treatment.

[0040] Alternatively, and as illustrated in Figure 2, the process according to the present invention comprises a separation, in whole or in part, of the first slurry (1B) allowing recovery of said first acidic liquid phase (1L) and the first solid phase (1S), preferably by filtration. Filtration yields a filtrate containing said first acidic liquid phase (1L) and a filter cake containing said first solid phase (1S) comprising said calcium. Advantageously, said recovery of the first solid phase can be carried out using a separation device such as a filter press, a belt filter, a rotary filter, or a tilting cell filter. Advantageously, a portion of the first slurry (1B) is sent, along with the first solid phase (1S), to the second treatment (T2).

[0041] Preferably, said first acidic liquid phase (1 L) comprises monocalcium phosphate in solution and / or phosphoric acid and / or sulfophosphoric acid. Preferably, said first acidic liquid phase (1 L) comprises predominantly phosphoric acid.

[0042] Preferably, and as illustrated in Figure 3, the process includes a fourth treatment (T4) for neutralizing said third liquid phase (3L) of cationic sulfate monovalent cation sulfate is dissolved by a mineral acid (Ac4), forming a fourth slurry (4B) composed of a fourth solid phase (4S) of monovalent cation sulfate and a fourth neutralized liquid phase (4L), with recovery of the monovalent cation sulfate. According to the present invention, the fourth slurry (4B) is a suspension that becomes increasingly concentrated in solid matter as the process progresses. More specifically, the cation sulfate is recovered by concentration (e.g., evaporation) followed by separation between the liquid and solid phases. Preferably, said mineral acid (Ac4) is selected from sulfuric acid, nitric acid, hydrochloric acid, and fluorosilicic acid. 1 ère solid phase (1S) in the 1 ère porridge (1 B) = DH

[0043] In a first advantageous embodiment, said first treatment (T1) is an attack on the phosphate source, preferably phosphate rock or DCP, by concentrated sulfuric acid with a ratio H + / Ca > 1.8, preferably a ratio H + / Ca > 2, Le., in superstoichiometry, possibly in combination with phosphoric acid, wherein said first acidic liquid phase (1 L) comprises at least 90% by weight of P2O5 relative to the weight of P2O5 contained in the phosphate source and is a phase containing phosphoric acid, and wherein said first solid phase (1 S) containing calcium is a solid phase of dihydrated calcium sulfate crystals. The first acidic liquid phase (1 L) of the first slurry (1 B) is then a phase containing phosphoric acid, predominantly containing phosphoric acid, and the first solid phase (1 S) containing calcium of the first slurry is a solid phase comprising predominantly dihydrated calcium sulfate crystals.

[0044] In this first advantageous embodiment, the concentration of H2SO4 in the concentrated sulfuric acid fed for the first treatment has a concentration of H2SO4 preferably greater than 80%, preferably greater than 90%, preferably greater than 95%, preferably greater than 98% by weight relative to the total weight of the inorganic acid solution.

[0045] Advantageously, in some cases, during the first treatment (T1), an addition of a fluoride source in the first slurry (1 B) at a content of 1% to 5% by weight of F relative to the P2O5 contained in the phosphate source is provided.

[0046] The first treatment (T1) of this first advantageous embodiment has a duration of between 3 and 6 hours, preferably between 4 and 5 hours. The temperature during the first treatment (T1) of this first advantageous embodiment is between 65 and 95°C, preferably between 70 and 90°C, and preferably between 75 and 85°C. 1 ère solid phase (1S) in the 1 ère porridge (1 B) = HH, 2 ème solid phase (2S) = DH

[0047] In a second advantageous embodiment, said first treatment (T1) is an attack on the phosphate source, preferably phosphate rock or DCP, with concentrated sulfuric acid, optionally in combination with phosphoric acid, wherein said first liquid phase (1 L) of the acid is a phase containing predominantly phosphoric acid and wherein said first solid phase (1 S) containing calcium is a solid phase comprising predominantly calcium sulfate hemihydrate crystals. In this second advantageous embodiment, the concentrated sulfuric acid has a H2SO4 concentration preferably greater than 80%, preferably greater than 90%, preferably greater than 95%, and preferably greater than 98% by weight relative to the total weight of the inorganic acid solution.In this second advantageous embodiment, the first treatment preferably lasts between 2 and 11 hours, and more preferably between 6 and 10 hours, depending on the cooling rate. The temperature during this first treatment in this second advantageous embodiment is between 80 and 110°C, preferably between 85 and 105°C, and more preferably between 90 and 100°C.

[0048] The first treatment (T1) according to the present invention should not be confused with leaching a phosphate rock with a dilute inorganic acid solution. Such a leaching operation can be applied prior to the first treatment (T1) in a purification operation, an example of which is illustrated in Figure 4 with an example of the treatment of a crude phosphate source (21) by leaching.For example, in a leaching operation, the inorganic acid solution (24) may have a concentration of less than 50% by weight of inorganic acid relative to the weight of the solution, preferably less than 30% by weight, preferably less than 20% by weight, more particularly less than 15% by weight, and even more particularly less than 10% by weight of inorganic acid relative to the weight of the solution, and wherein said solid phase containing the calcium is a solid phase formed from the leached rock and / or calcium phosphate. More particularly, such leaching may be carried out with a molar ratio of H₂P₂O₅ between 0.05 and 5, preferably between 0.06 and 1.75. Preferably, the inorganic acid solution used to leach the crude phosphate source may be a dilute sulfuric acid solution. Advantageously, the pretreatment step (25) is a leaching step.

[0049] Advantageously, in the pretreatment step (25), the inorganic acid solution (24) is diluted and may preferably contain sulfuric acid, phosphoric acid, hydrochloric acid, hydrofluoric acid, hexafluorosilicic acid, or any combination thereof. In particular, the pretreatment step (25) has a duration of between 5 and 300 minutes, preferably between 10 and 200 minutes, and preferably between 15 and 180 minutes. Advantageously, the pretreatment step (25) is carried out at a temperature between 25 and 90°C, preferably between 30 and 85°C, and preferably between 40 and 80°C.

[0050] Advantageously, said second treatment (T2) is an attack of the first solid phase (1S) comprising calcium and / or slurry (1B) by concentrated sulfuric acid, optionally in combination with phosphoric acid and wherein said second solid phase (2S) comprising calcium sulfate is a second solid phase comprising predominantly crystals of dihydrated calcium sulfate.

[0051] Indeed, according to the present invention, in certain embodiments, the first solid phase (1S), comprising calcium from the first treatment (T1), is a crystalline calcium sulfate to which a second treatment (T2) is applied to form predominantly dihydrated crystalline calcium sulfate. This double crystallization increases the purity of the calcium sulfate obtained after the second treatment (T2). Advantageously, the first solid phase (1S) is a hemihydrated calcium sulfate and the second solid phase (2S) is a dihydrated calcium sulfate.

[0052] The concentration of H2SO4 in concentrated sulfuric acid during second treatment (T2) is more particularly greater than 80%, preferably greater than 90%, preferably greater than 95%, preferably greater than 98% by weight relative to the weight of the concentrated sulfuric acid solution.

[0053] The second treatment (T2) preferably lasts between 3 and 6 hours, and preferably between 4 and 5 hours. The temperature during the second treatment is preferably between 65 and 95°C, preferably between 70 and 90°C, and preferably between 75 and 85°C.

[0054] Advantageously, said second treatment (T2) is an attack of the solid phase containing calcium by concentrated sulfuric acid and in which said second solid phase (2S) comprising calcium sulfate is a second solid phase comprising predominantly crystals of calcium sulfate hemihydrate.

[0055] According to the present invention, in certain embodiments, the first solid phase (1S), comprising calcium from the first treatment (T1), is a crystalline calcium sulfate to which a second treatment (T2) is applied to form predominantly hemihydrated crystalline calcium sulfate. This double crystallization increases the purity of the calcium sulfate obtained after the second treatment. Advantageously, the first solid phase (1S) is dihydrated calcium sulfate and the second solid phase (2S) is hemihydrated calcium sulfate.

[0056] The second treatment (T2) preferably has a duration of between 0.2 and 11 hours, preferably between 0.5 and 1 hour. The temperature during the second treatment is more particularly between 80 and 110°C, preferably between 85 and 105°C, preferably between 90 and 100°C, preferably between 95 and 100°C.

[0057] Advantageously, the process further comprises, prior to said first treatment, a pretreatment step, advantageously at least one step of purification or suspension of a crude phosphate rock with obtaining said phosphate source comprising calcium.

[0058] Advantageously, the pretreatment step in the tank (25) is a partial attack or leaching of a raw phosphate rock with dilute sulfuric acid, optionally followed by at least one neutralization step using a base, for example, quicklime or slaked lime and / or calcium hydroxide and / or calcium carbonate. Advantageously, said phosphate source containing calcium is a phosphate rock or a leached rock or calcium phosphate or a mixture thereof.

[0059] Advantageously, the concentration of H2SO4 in the dilute sulfuric acid is less than 50%, advantageously between 5 and 20% by weight relative to the weight of the dilute sulfuric acid solution.

[0060] Advantageously, the pretreatment step in the tank (25) is a complete attack of raw phosphate rock with hydrochloric acid of a concentration of less than 50% by weight and / or dilute sulfuric acid, followed by at least one neutralization step using a base, for example, quicklime or slaked lime and / or calcium carbonate, in order to obtain the phosphate source to be treated according to the process of the present invention. The calcium-containing phosphate source thus formed is preferably calcium phosphate, MCP, DCP, or mixtures thereof. Preferably, the hydrochloric acid concentration of the dilute hydrochloric acid is between 5 and 20%.

[0061] In another variant, the pretreatment step (25) is partial attack or leaching of crude phosphate rock with hydrochloric acid of a concentration of less than 50 wt%, optionally followed by at least one neutralization step using calcium carbonate, wherein said calcium-containing phosphate source is formed from the leached rock and / or calcium phosphate and / or the phosphate rock. Preferably, the hydrochloric acid concentration of the dilute hydrochloric acid is between 5 and 20 wt%.

[0062] Advantageously, said separation of the second liquid phase (2L) containing phosphoric acid and of the second solid phase (2S) from the second boil (2B) is a separation by vacuum filtration allowing to obtain a filtrate comprising phosphoric acid and a filtration cake formed from the second solid phase.

[0063] Preferably, said separation of the third liquid phase (3L) of monovalent cation sulfate and said third solid phase (3S) of calcium carbonate is a separation by filtration or dewatering allowing to obtain a filtrate formed of the third liquid phase (3L) of monovalent cation sulfate and a filtration cake formed from the third solid phase (3S) of calcium carbonate.

[0064] Preferably, the process further includes a washing step of the filter cake from the first treatment (T1) with recovery of a washed filter cake and an acidic washing filtrate.

[0065] Preferably, the process further includes a washing step of the filter cake from the second treatment (T2) with recovery of a washed filter cake and a washing filtrate containing soluble phosphorus.

[0066] Advantageously, the acid wash filtrate from the filter cake of the first and / or second treatment (T1, T2) is introduced at the first treatment stage or the second treatment stage or even at the pretreatment stage.

[0067] The process according to the present invention makes it possible to produce in a simple and industrially viable way phosphoric acid, monovalent cationic sulfate and calcium carbonate having high degrees of purity allowing their commercialization.

[0068] As can be seen in Figures 1 and 2, the process first includes a first treatment (T1) in which an acid in solution is fed via a feed line 1 and in which a phosphate source containing phosphorus and calcium is fed via a feed line (2) into a tank (4), which forms a first slurry (1 B).

[0069] The first slurry (1 B) contains at least a first solid phase (1 S) comprising calcium and a first acidic liquid phase (1 L), comprising P2O5.

[0070] The first solid phase (1S) comprising calcium and / or the first slurry is then subjected to a second treatment (T2) by a sulfuric solution supplied by a feed duct (5) which forms a second slurry (2B) consisting of a second liquid phase (2L) of phosphoric acid and a second solid phase (2S) comprising calcium sulfate.

[0071] The second slurry (2B) is then subjected to separation on a first separation device (7). The separation results in the separation, on the one hand, of the second liquid phase (2L) of phosphoric acid and, on the other hand, of the second solid phase (2S).

[0072] In a third treatment (T3), a monovalent cation carbonate solution, said monovalent cation being chosen from the group comprising lithium ion, sodium ion, potassium ion, and ammonium ion, is fed via a feed line (11) into the tank (10) containing the second solid phase (2S). The reaction of the second solid phase (2S) and the monovalent cation carbonate solution will lead to the dissolution of a portion of the second solid phase (2S) and the formation of a third slurry (3B) consisting of a third liquid phase (3L) of monovalent cationic sulfate and a third solid phase (3S) of calcium carbonate.

[0073] The third slurry (3B) is then subjected to separation on a second separation device (13). The separation results in the separation, on the one hand, of the third solid phase (3S) of calcium carbonate and, on the other hand, of the third liquid phase (3L) of monovalent cationic sulfate 1 ère solid phase (1S) in the 1 ère porridge (1 B) = DH, 2 ème solid phase (2S) = HH

[0074] In one embodiment of the process for producing phosphoric acid, monovalent cationic sulfate, and calcium carbonate according to the invention, illustrated in Figure 1, the first treatment (T1) is a treatment based on concentrated sulfuric acid, resulting in the formation of the first solid phase (1S) comprising calcium sulfate dihydrate crystals suspended in the first liquid phase (1L) comprising mainly phosphoric acid, forming the first slurry (1B). The second treatment (T2) is a treatment based on concentrated sulfuric acid, resulting in the formation of calcium sulfate hemihydrate crystals as a second solid phase (2S) suspended in the second liquid phase (2L) of phosphoric acid, forming the second slurry (2B).As can be seen in Figure 1, in this embodiment, the process first includes a step in which sulfuric acid or an acid mixture containing sulfuric acid and phosphoric acid is fed via a feed line (1) with an inorganic acid solution and in which a phosphate source comprising phosphorus and calcium is fed via a feed line (2) into a tank (4), which forms a first slurry (1 B).

[0075] The phosphate source comprising phosphorus and calcium may be of sedimentary or igneous origin; it may be phosphate ore rock, phosphate mine tailings or beneficiation tailings, phosphate slime, a phosphate salt, a calcium salt, a calcium phosphate salt, such as monocalcium phosphate (MCP), dicalcium phosphate (DCP), tricalcium phosphate (TCP), hydroxyapatite, phosphorite, apatite, chlorapatite, fluorapatite, calcium phosphate, incineration ash, or mixtures thereof.

[0076] In this embodiment, the first slurry (1 B) contains at least some calcium sulfate dihydrate crystals (= first solid phase (1 S)) suspended in an acidic aqueous phase formed by the sulfuric or sulfo-phosphoric acid treatment of the rock (= first liquid phase (1 L)). The residence time of the first treatment step (T1) of said phosphate source is between 60 and 300 minutes, preferably between 90 and 270 minutes, and more particularly between 120 and 240 minutes. The first treatment can be carried out in a leaching tank or in a leaching tank followed by a digestion tank. The time of the indicated stay being the stay time in the attack tank or the stay time in the attack tank and in the digestion tank.

[0077] In the embodiments that can be implemented in the apparatus of Figure 1, advantageously (not shown), a fluorine source is added to the first slurry (1B) during the initial treatment (T1) at a concentration of 1% to 5% by weight of F relative to the P2O5 content of the phosphate rock. Antifoaming agents and crystallization modifiers may also be added.

[0078] The first slurry (1 B) also contains phosphoric acid following the reaction below (I), typically also containing 1.5 to 3% free SO3, resulting from the slight excess of sulfuric acid relative to the amount of phosphate source introduced into the conduit (2).

[0079] Furthermore, in the illustrated embodiment, and under the aforementioned conditions, the first slurry (1 B) has a temperature between 70 and 90°C.

[0080] The first boil (1 B) is then engaged in the second treatment step (T2) via a transfer conduit (31) into a conversion tank (17), in which sulfuric acid is fed via a feed conduit (5) to come into contact with said first boil (1 B) and react with the calcium sulfate dihydrate crystals of the first boil (1 B) and form a second boil (2B).

[0081] The second slurry (2B) contains at least calcium sulfate hemihydrate crystals (= second solid phase (2S)) suspended in phosphoric acid (= second liquid phase (2L)). The residence time of the second treatment step (T2) of the sulfate dihydrate crystals (= first solid phase (1S)) in the conversion tank (17) is between 15 and 150 minutes, preferably between 30 and 120 minutes.

[0082] The second liquid phase (2L) of phosphoric acid from the second slurry (2B) also contains between 5 and 8% free SO3, resulting from the addition of sulfuric acid during the second treatment step (T2).

[0083] The second slurry (2B) is then separated by filtration using a filtration device (7). Filtration results in the separation of, on the one hand, the second liquid phase (2L) of phosphoric acid, which has a P2O5 equivalent concentration of between 20 and 50% by weight relative to the weight of phosphoric acid, and on the other hand, a second solid phase (2S) containing calcium, in this case, a filter cake of calcium sulfate hemihydrate, which is then recovered. The calcium sulfate hemihydrate rehydrated or not can then be transferred via a transfer line (18) into the tank (10).

[0084] For example, a solution of ammonium carbonate (or other monovalent cationic carbonate) is fed into the tank (10) via a feed line (11). The reaction of calcium sulfate in the second solid phase (2S) and the ammonium carbonate solution dissolves the calcium sulfate and precipitates a third solid phase (3S) of calcium carbonate, thus forming a third slurry (3B). The third slurry (3B) is therefore composed of a third liquid phase (3L) of ammonium sulfate and a third solid phase (3S) of calcium carbonate.

[0085] The third slurry (3B) is then subjected to separation using a separation device (13), such as a filter, filter press, centrifuge, belt filter, or rotary filter. The separation results, on the one hand, in the third solid phase (3S) of calcium carbonate and, on the other hand, in the third liquid phase (3L) of ammonium sulfate. 1 èresolid phase (1S) in the 1 ère porridge (1 B) = DH, 2 ème solid phase (2S) = HH

[0086] In another embodiment of the process for producing phosphoric acid, monovalent cationic sulfate, and calcium carbonate according to the invention, which can be implemented in the apparatus illustrated in Figure 1, the first treatment is a treatment based on concentrated sulfuric acid leading to the formation of calcium sulfate dihydrate crystals (= first solid phase (1S)) suspended in a first liquid phase (1L) comprising mainly phosphoric acid, forming the first slurry (1B). The second treatment (T2) is a treatment based on concentrated sulfuric acid leading to the formation of calcium sulfate hemihydrate crystals as a second solid phase (2S) suspended in the second liquid phase (2L) of phosphoric acid.As can be seen in Figure 1, the process first comprises a first treatment (T1) in which sulfuric acid or an acid mixture containing sulfuric and phosphoric acids is fed via a feed line (1) with an inorganic acid solution, and in which a phosphate source comprising phosphorus and calcium is fed via a feed line (2) into a tank (4), forming a first slurry (1B). In the described embodiment, the phosphate source is preferably a rock.

[0087] In the embodiments implementable in the apparatus of Figure 1, advantageously (not illustrated), it is provided during the attack of the first treatment (T1), an addition of a source of fluorine in the first slurry (1 B) at a content of 1% to 5% by weight of F relative to the P2O5 contained in the phosphate rock.

[0088] The first slurry (1 B) contains at least some crystals of calcium sulfate dihydrate (= first solid phase (1 S)) suspended in the first acidic aqueous phase (1 L) formed by sulfuric or sulfo-phosphoric acid etching of the rock. The residence time of the first treatment stage (T1) of said phosphate source is between 60 and 300 minutes, preferably between 90 and 270 minutes, and more particularly between 120 and 240 minutes. The first treatment (T1) can be carried out in a leaching tank or in a leaching tank followed by a digestion tank. The residence time indicated is the residence time in the leaching tank or the residence time in the leaching tank and in the digestion tank.

[0089] The first slurry (1 B) also contains phosphoric acid typically containing 1.5 to 3% free SO3, resulting from the slight excess of sulfuric acid relative to the amount of phosphate source introduced through the conduit (2).

[0090] Furthermore, in this embodiment, and under the aforementioned conditions, the first slurry (1 B) has a temperature between 70 and 90°C.

[0091] The first boil (1 B) is then engaged in the second treatment step (T2) via a transfer conduit (16) into a conversion tank (17), in which sulfuric acid is fed via a feed conduit (5) to come into contact with said first boil (1 B) and react with the calcium sulfate dihydrate crystals of the first boil (1 B) and form a second boil (2B).

[0092] The second slurry (2B) contains at least calcium sulfate hemihydrate crystals (= second solid phase (2S)) suspended in the second liquid phase (2L) of phosphoric acid. The residence time of the second treatment step (T2) of the calcium sulfate dihydrate crystals in the conversion tank (17) is between 30 and 150 minutes, preferably between 60 and 120 minutes.

[0093] The phosphoric acid in the second boil (2B) also contains between 5% and 8% free SO3, resulting from the addition of sulfuric acid during the second treatment step (T2).

[0094] The second slurry (2B) is then subjected to separation by filtration on a filtration device (7). Filtration results in the separation of, on the one hand, the second liquid phase (2L) of phosphoric acid which has a concentration of P2O5 equivalent between 25 and 50% by weight relative to the weight of phosphoric acid and, on the other hand, a second solid phase (2S) comprising calcium, in this case, a filter cake of calcium sulfate hemihydrate which is then rehydrated or not and then transferred via a transfer line (18) into the tank (10).

[0095] In the third treatment (T3), a potassium carbonate solution is fed into the tank (10) via a feed line (11). The reaction of calcium sulfate and the potassium carbonate solution dissolves the calcium sulfate and precipitates a third solid phase (3S) of calcium carbonate, thus forming a third slurry (3B). The third boil (3B) is therefore formed of a third liquid phase (3L) of potassium sulfate and a third solid phase (3S) of calcium carbonate.

[0096] The third slurry (3B) is then subjected to separation using a separation device (13), such as a filter, filter press, centrifuge, belt filter, or rotary filter. The separation results, on the one hand, in a third solid phase (3B) of calcium carbonate and, on the other hand, in a third liquid phase (3L) of potassium sulfate. 1 ère solid phase (1S) in the 1 ère porridge (1 B) = DH, 2 ème solid phase (2S) = HH

[0097] In another embodiment of the process for producing phosphoric acid, monovalent cationic sulfate and calcium carbonate according to the invention, which can be implemented in an apparatus illustrated in Figure 2, the first treatment (T1) is a treatment based on concentrated sulfuric acid leading to the formation of calcium sulfate dihydrate crystals, said first treatment is followed by a step of separating the first liquid phase (1 L) acid and the first solid phase (1 S) comprising calcium and said first solid phase (1 S) comprising calcium is then engaged in the second treatment (T2) which is a treatment based on concentrated sulfuric acid leading to the formation of calcium sulfate hemihydrate crystals.As can be seen in Figure 2, the process first comprises a first treatment (T1) in which sulfuric acid or an acid mixture containing sulfuric and phosphoric acid is fed via a feed line (1) and in which a phosphate source comprising phosphorus and calcium is fed via a feed line (2) into a tank (4), forming a first slurry (1B). In the described embodiment, the phosphate source is a rock.

[0098] The first slurry (1B) contains at least calcium sulfate dihydrate crystals suspended in an acidic aqueous phase formed by the sulfuric and / or sulfophosphoric acid leaching of the rock. The residence time of the first treatment stage of said phosphate source is between 60 and 300 minutes, preferably between 120 and 250 minutes, and more particularly between 150 and 180 minutes. The first treatment (T1) can be carried out in a leaching tank or in a leaching tank followed by a digestion tank. The residence time indicated is the residence time in the leaching tank or the residence time in the leaching tank and in the digestion tank.

[0099] The first liquid phase (1 L) of the first slurry (1 B) also contains phosphoric acid and typically contains less than 2%, preferably less than 1%, of free SO3, resulting from the slight excess of sulfuric acid relative to the amount of phosphate source introduced during the first treatment (T1). Furthermore, under the aforementioned conditions, the first slurry (1 B) has a temperature between 70 and 90°C.

[0100] All or part of the first slurry (1 B) is separated by filtration using an intermediate separation device (22). Filtration results in the separation of, on the one hand, the first liquid phase (1 L) of phosphoric acid and, on the other hand, a filter cake containing the first solid phase (1 S) of calcium sulfate dihydrate, which is collected in an intermediate tank (17). Advantageously, the unfiltered portion of the first slurry is collected in the intermediate tank (17) via a feed line (31).

[0101] The said intermediate tank (17) is supplied with sulfuric acid via a feed line (5) to react with the filter cake containing the first solid phase (1S) of calcium sulfate dihydrate and possibly with the unfiltered part of said first slurry (1B) to form a second slurry (2B).

[0102] The second slurry (2B) contains at least calcium sulfate hemihydrate crystals (= second solid phase (2S)) suspended in an acidic aqueous second liquid phase (2L). The residence time of the second treatment step for the calcium sulfate dihydrate crystals is between 20 and 150 minutes, preferably between 30 and 60 minutes. The second slurry (2B) also contains phosphoric acid, typically containing between 5 and 8% free SO3, resulting from the addition of sulfuric acid during the second treatment step (T2).

[0103] The second slurry (2B) is then separated by filtration using a filtration device (7). Filtration results in the separation of, on the one hand, the second liquid phase (2L) of phosphoric acid, which has a P₂O₅ equivalent concentration of between 25 and 50% by weight relative to the weight of phosphoric acid, and, on the other hand, a second solid phase (2S) containing calcium, in this case, a filter cake of calcium sulfate hemihydrate, which is then collected in a tank (10). Preferably, the calcium sulfate hemihydrate filter cake is washed, and the washing filtrates are mixed with the second liquid phase (2L) to obtain a dilute liquid phase (2L) with a mass concentration of between 10 and 20% by weight of P₂O₅. Advantageously, the second liquid phase (2L), diluted or undiluted, is recovered in the first treatment (T1) to constitute the inorganic acid.

[0104] In the third treatment (T3), a solution, for example, of ammonium carbonate (or carbonate of another monovalent cation) is fed via a feed line (11) into the tank (10). The reaction of the second solid phase (2S) and the solution of the monovalent cation carbonate leads to the dissolution of the second solid phase (2S) and the formation of a third slurry (3B) consisting of a third liquid phase (3L) of ammonium sulfate and a third solid phase (3S) of calcium carbonate.

[0105] The third slurry (3B) is then subjected to separation on a separation device (13). The separation results in the separation, on the one hand, of a third solid phase (3S) of calcium carbonate and, on the other hand, of a third liquid phase (3L) of ammonium sulfate. Process with purification pretreatment according to FIG.4

[0106] In another embodiment of the process for producing phosphoric acid, monovalent cation sulfate, and calcium carbonate according to the invention, which can be implemented in an apparatus illustrated in Figure 4, the first treatment is preceded by a pretreatment step involving the complete attack of the raw rock. As can be seen in Figure 4, the process first comprises a step in which dilute sulfuric acid and / or hydrochloric acid having a concentration of less than 50% by weight of solution is fed via a feed line (24), and in which raw rock is fed via a feed line (21) into a tank (25), forming a mixture (01B) of an acidic liquid phase (01L) containing dissolved MCP and a solid (01S) containing impurities. A liquid / solid separation allows the recovery of the liquid phase (01L) containing phosphorus, primarily in the form of dissolved MCP.

[0107] The liquid phase (01 L) is then transferred via a transfer line (27) to a neutralization tank (34) in which a base, for example calcium carbonate and / or quicklime or slaked lime and / or sodium hydroxide, is added, preferably in liquid form (suspension and / or solution) via a feed (35) to form a neutralized mixture (03B). The mixture (03B) is transferred to a separation device (37) to collect, on the one hand, a solid phase (03S) which, after optional washing of the cake, is the phosphate source and is predominantly in the form of calcium phosphate salt and / or dicalcium phosphate (DCP), and a liquid phase (03L). The solid phase (03S) collected after separation forms the phosphate source, which is transferred to the tank (4) by means of the line (2).

[0108] A sulfuric acid or an acid mixture containing sulfuric acid and phosphoric acid is fed via the feed line (1) into the tank (4) and reacts with the phosphate source, in the embodiment described, the phosphate source is DCP which forms a first slurry (1 B).

[0109] The first slurry (1B) contains at least calcium sulfate dihydrate crystals suspended in an acidic aqueous phase formed by the sulfuric or sulfo-phosphoric acid treatment of the rock. The residence time of the first treatment stage (T1) of said phosphate source is between 60 and 300 minutes, preferably between 90 and 270 minutes, and more particularly between 120 and 240 minutes. The first treatment (T1) can be carried out in a leaching tank or in a leaching tank followed by a digestion tank. The residence time indicated is the residence time in the leaching tank or the residence time in the leaching tank and in the digestion tank. The first slurry (1B) thus also contains of phosphoric acid, typically also containing 1.5 to 3% free SO3, resulting from the slight excess of sulfuric acid relative to the amount of phosphate source introduced during the first treatment (T1). Furthermore, in the illustrated embodiment, and under the aforementioned conditions, the first slurry (T1) has a temperature between 70 and 90°C.

[0110] Optionally, the first slurry (1 B) can be filtered in whole or in part before being sent to the second treatment step (T2). Filtration results in the separation of a first acidic aqueous liquid phase (1 L) and, on the other hand, a filter cake containing the first solid phase (1 S) which contains at least some calcium sulfate dihydrate crystals.

[0111] In embodiments implementable in the apparatus of Figure 4, advantageously (not illustrated in the Figures), during the initial treatment (T1), a fluorine source is added to the first slurry (1B) at a concentration of 1% to 5% by weight of F relative to the P2O5 contained in the phosphate rock. Antifoaming agents and crystallization modifiers can also be added.

[0112] The first boil (1 B) and / or the filter cake comprising the aforementioned first solid phase (1 S) which contains at least some calcium sulfate dihydrate crystals is then engaged in the second treatment step (T2) via a transfer line (16, 31) into a conversion tank (17), in which concentrated sulfuric acid is fed via a feed line (5) to come into contact with said first boil (1 B) and react with the calcium sulfate dihydrate crystals of the first boil (1 B) or of the first solid phase (1 S) and form a second boil (2B).

[0113] The second slurry (2B) contains at least one second solid phase (2S) of calcium sulfate hemihydrate crystals suspended in phosphoric acid. The residence time of the second treatment step (T2) of the dihydrate sulfate crystals in the conversion vessel (17) is between 15 and 150 minutes, preferably between 30 and 90 minutes. The phosphoric acid in the second slurry (2B) also contains between 5 and 8% free SO3, resulting from the addition of sulfuric acid during the second treatment step.

[0114] The second slurry (2B) is then separated by filtration using a filtration device (7). Filtration results in the separation of, on the one hand, the second liquid phase (2L) of phosphoric acid, which has a P2O5 equivalent concentration of between 25 and 50% by weight relative to the weight of phosphoric acid, and, on the other hand, a second solid phase (2S) containing calcium, in this case, a calcium sulfate hemihydrate filter cake, which is then recovered. Preferably, the calcium sulfate hemihydrate filter cake is washed, and the washing filtrates are mixed with the second liquid phase (2L) to obtain a dilute liquid phase (2L) with a mass concentration between 10 and 20% by weight of P2O5. Advantageously, the second liquid phase (2L), diluted or not, is recovered in the first treatment (T1) to constitute the inorganic acid.

[0115] The second solid phase (2S), calcium sulfate hemihydrate, is rehydrated or not (not shown) to be transferred via a transfer line (18) into the tank (10).

[0116] A potassium carbonate solution is fed into the tank (10) via a feed line (11). The reaction between the second solid phase (2S) of calcium sulfate and the potassium carbonate solution dissolves the calcium sulfate and precipitates a third solid phase (3S) of calcium carbonate, thus forming a third slurry (3B). The third slurry (3B) is therefore composed of a third liquid phase (3L) of potassium sulfate and a third solid phase (3S) of calcium carbonate. The third slurry (3B) is then separated using a separation device (13), such as a filter, filter press, centrifuge, belt filter, or rotary filter. The separation yields, on the one hand, a third solid phase (3S) of calcium carbonate and, on the other hand, a third liquid phase (3L) of potassium sulfate. Process with purification pretreatment according to FIG.5

[0117] In another embodiment of the process for producing phosphoric acid, monovalent cationic sulfate, and calcium carbonate according to the invention, which can be implemented in an apparatus illustrated in Figure 5, the first treatment is preceded by a pretreatment step of leaching the raw rock (or partial attack). As can be seen in Figure 5, the process first comprises a step in which dilute sulfuric acid and / or hydrochloric acid having a concentration of less than 25% by weight of solution is fed via a feed line (24), and in which raw rock is fed via a feed line (21) into a tank (25), forming a mixture (01B) of a liquid phase (01L) and a solid phase (01S) containing predominantly P2O5.

[0118] Preferably, the slurry (01 B) is transferred to a tank 26 or maintained in the tank (25), and advantageously, a base is added to obtain a slurry (02 B) consisting of a liquid phase (02 L) and a solid phase (02 S). The base is preferably added in liquid form (suspension and / or solution). Preferably, the base is selected from the group of calcium carbonate, quicklime, slaked lime, sodium hydroxide, and mixtures thereof.

[0119] A liquid / solid separation allows the recovery of the solid phase (O1S) or (O2S) containing the phosphorus that comprises the leached rock. Following the separation, the solid phase (O1S) (not shown) or (O2S) is transferred to the tank (4) by means of the pipe (2).

[0120] Sulfuric acid or an acidic mixture containing sulfuric acid and phosphoric acid is fed via the feed line (1) into the tank (4) and reacts with the Phosphate source, in the embodiment described, the phosphate source is leached rock which forms a first slurry (1 B).

[0121] The first slurry (1B) contains at least calcium sulfate dihydrate crystals suspended in an acidic aqueous phase formed by the sulfuric or sulfo-phosphoric acid treatment of the rock. The residence time of the first treatment step (T1) of said phosphate source is between 60 and 300 minutes, preferably between 90 and 270 minutes, and more particularly between 120 and 240 minutes. The first treatment (T1) can be carried out in a leaching tank or in a leaching tank followed by a digestion tank. The residence time indicated is the residence time in the leaching tank or the residence time in the leaching tank and in the digestion tank. The first slurry (1B) thus also contains phosphoric acid, typically also containing 1.5 to 3% free SO3, resulting from the slight excess of sulfuric acid relative to the quantity of phosphate source introduced during the first treatment (T1).Furthermore, in the illustrated embodiment, and under the aforementioned conditions, the first slurry 3 has a temperature between 70 and 90°C.

[0122] Optionally, the first slurry (1 B) can be filtered in whole or in part before being sent to the second treatment step (T2). Filtration results in the separation of a first acidic aqueous liquid phase (1 L) and, on the other hand, a filter cake containing the first solid phase (1 S) which contains at least some calcium sulfate dihydrate crystals.

[0123] In the embodiments implementable in the apparatus of Figure 1, advantageously (not shown), it is provided that during the initial treatment (T1), a fluorine source is added to the first slurry (1B) at a concentration of 1% to 5% by weight of F relative to the P2O5 contained in the phosphate rock. Antifoaming agents, crystallization modifiers, etc., can also be added.

[0124] The first boil (1 B) and / or the filter cake comprising the aforementioned first solid phase (1 S) which contains at least some calcium sulfate dihydrate crystals is then engaged in the second treatment step (T2) via a transfer line (16, 31) into a conversion tank (17), in which concentrated sulfuric acid is fed via a feed line (5) to come into contact with said first boil (1 B) and react with the calcium sulfate dihydrate crystals of the first boil (1 B) or of the first solid phase (1 S) and form a second boil (2B).

[0125] The second slurry (2B) contains at least one second solid phase (2S) of calcium sulfate hemihydrate crystals suspended in phosphoric acid. The residence time of the second treatment step (T2) of the dihydrate sulfate crystals in the conversion tank (17) is between 15 and 150 minutes, preferably between 30 and 90 minutes. The phosphoric acid from the second boil (2B) also contains between 5 and 8% free SO3, resulting from the addition of sulfuric acid during the second treatment step.

[0126] The second slurry (2B) is then separated by filtration using a filtration device (7). Filtration results in the separation of, on the one hand, the second liquid phase (2L) of phosphoric acid, which has a P₂O₅ equivalent concentration of between 25 and 50% by weight relative to the weight of phosphoric acid, and, on the other hand, a second solid phase (2S) containing calcium, in this case, a filter cake of calcium sulfate hemihydrate, which is then recovered. Preferably, the calcium sulfate hemihydrate filter cake is washed, and the washing filtrates are mixed with the second liquid phase (2L) to obtain a dilute liquid phase (2L) with a mass concentration of between 10 and 20% by weight of P₂O₅. Advantageously, the second liquid phase (2L), diluted or undiluted, is recovered in the first treatment (T1) to constitute the inorganic acid.

[0127] The second solid phase (2S), calcium sulfate hemihydrate, is rehydrated or not (not shown) to be transferred via a transfer line (18) into the tank (10).

[0128] A potassium carbonate solution is fed into the tank (10) via a feed line (11). The reaction between the second solid phase (2S) of calcium sulfate and the potassium carbonate solution dissolves the calcium sulfate and precipitates a third solid phase (3S) of calcium carbonate, thus forming a third slurry (3B). The third slurry (3B) is therefore composed of a third liquid phase (3L) of potassium sulfate and a third solid phase (3S) of calcium carbonate. The third slurry (3B) is then separated using a separation device (13), such as a filter, filter press, centrifuge, belt filter, or rotary filter. The separation yields, on the one hand, a third solid phase (3S) of calcium carbonate and, on the other hand, a third liquid phase (3L) of potassium sulfate.

Claims

DEMANDS 1. A process for the production of phosphoric acid, monovalent cationic sulfate, and calcium carbonate comprising the following steps: A first treatment (T1) of a phosphate source comprising phosphorus and calcium using an inorganic acid solution to obtain a first slurry (1 B) consisting of a first acidic liquid phase (1 L) rich in phosphorus and a first solid phase (1 S) comprising calcium in the form of calcium sulfate and poor in phosphorus, A second treatment (T2) of the first slurry (1B) and / or the first solid phase (1S) with a concentrated sulfuric acid solution to obtain a second slurry (2B) consisting of a second liquid phase (2L) comprising phosphoric acid and a second solid phase (2S) comprising calcium sulfate, separation of the second liquid phase (2L) and the second solid phase (2S) preferably by vacuum filtration, a third treatment of the second solid phase (2S) with a solution of monovalent cation carbonate, said monovalent cation being chosen from the group comprising lithium ion, sodium ion, potassium ion, ammonium ion, to obtain a third slurry (3B) consisting of a liquid phase (3L) of monovalent cation sulfate and a third solid phase (3S) of calcium carbonate, separation of the third solid phase (3S) and the third liquid phase (3L) forming the third slurry (3B),characterized in that, • The inorganic acid solution used in the first treatment (T1) is an acidic solution comprising concentrated sulfuric acid greater than 80%, preferably greater than 90%, of H2SO4, in that • The first treatment (T1) is performed with a molar ratio, H + / Ca > 1.8, preferably H + / Ca > 2 and in that, • the first liquid phase (1 L) rich in phosphorus comprises at least 90% by weight of P2O5 relative to the weight of P2O5 included in the phosphate source.

2. A process according to claim 1, further comprising recovery of the first acidic liquid phase (1 L) by separating all or part of the first slurry (1 B) into the first acidic liquid phase (1 L) and the first solid phase (1 S) comprising calcium, preferably by filtering the first slurry to obtain a filtrate comprising the first acidic liquid phase (1 L) and a filter cake comprising the first solid phase (1 S) comprising calcium.

3. Process according to claim 1 or 2, comprising a neutralization (T4) of the third liquid phase (3L) of monovalent cation sulfate by a mineral acid (Ac4) forming a fourth slurry (4B) consisting of a fourth solid phase (4S) comprising monovalent cation sulfate and a neutralized fourth liquid phase (4L) and a recovery of the monovalent cation sulfate.

4. A process according to any one of the preceding claims, wherein the phosphate source comprises phosphate rock and / or a calcium phosphate salt, preferably dicalcium phosphate (DCP).

5. A process according to any one of the preceding claims, wherein in addition to concentrated sulfuric acid, the inorganic acid solution used in the first treatment (T1) also comprises phosphoric acid and wherein the first liquid phase (1 L) acid is a phase containing phosphoric acid.

6. A process according to any one of the preceding claims, wherein the first solid phase (1S) containing calcium is a solid phase of calcium sulfate hemihydrate (HH) or dihydrate (DH) crystals, preferably dihydrate (DH).

7. A process according to any one of the preceding claims, wherein the second solid phase (2S) is a solid phase of calcium sulfate crystals hemihydrate (HH) or dihydrate (DH), preferably of a different degree of hydration than the first solid phase (1S) and preferably hemihydrate.

8. A process according to any one of the preceding claims, further comprising prior to the first treatment (T1), at least one pretreatment step of a crude phosphate source with obtaining the phosphate source comprising calcium.

9. A method according to any one of the preceding claims, wherein the separation of the second liquid phase (2L) and the second solid phase (2S) from the second boil (2B) is a separation by filtration allowing to obtain a filtrate formed of the second liquid phase (2L) containing phosphoric acid and a filtration cake formed of the second solid phase (2S).

10. A process according to any one of the preceding claims, wherein the separation of the third liquid phase (3L) of monovalent cation sulfate and the third solid phase (3S) of calcium carbonate is a separation by filtration or centrifugation allowing to obtain a filtrate formed of the third liquid phase (3L) of monovalent cation sulfate and a filtration cake formed of the third solid phase (3S) of calcium carbonate.

11. A process according to any one of claims 2 and 3 to 10 when they depend on claim 2, further comprising a washing step of the filter cake(s) forming the first solid phase (1S) and / or the second solid phase (2S) and / or the third solid phase (3S) following the first, second and / or third treatments (T1-T3), respectively, with recovery of a washed filter cake and a liquid washing phase.

12. A process according to claim 11, wherein the liquid washing phase of the second treatment (T2) is introduced at the first treatment step (T1) or at the second treatment step (T2) or even at a pretreatment step according to claim 9.

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