BE1021886B1 - NEW PHOSPHATE SOURCE FOR AGRICULTURE AND FOOD. - Google Patents

Abstract

Disclosed is a phosphate salt in solid form of the formula Mn (HPO4) y.zH20 wherein M is Na, K, NH4, n = 2, and y = 1; or M is Ca, n = 1, y = 1; or M is Al or Fe, n = 2, y = 3; and wherein z is 0, 1 or 2; said phosphate salt has a phosphate content expressed as a P205 content of between 30 and 50% by weight of the phosphate salt, characterized in that it has a cadmium content of less than 0.40 ppm.

Description

NEW PHOSPHATE SOURCE FOR AGRICULTURE AND

FOOD

Technical area

The present invention relates to a phosphate salt having a high purity, that is to say a low content of impurities mainly radioactive impurities and / or from heavy metals or transition metals of the periodic table of the elements. The present invention also relates to a process for the preparation of this phosphate salt and its use in a formulation or composition intended for agriculture or in foodstuffs or for the preparation thereof. Preferably, said phosphate salt can be used for the preparation of single superphosphate (SSP), triple superphosphate (TSP), monoammonium phosphate (MAP), diammonium phosphate (DAP), phosphoric acid, NPK fertilizer, monocalcium phosphate (MCP) or mono-dicalcium phosphate (PCAP).

Technological background of the invention

Phosphate salts are regularly used in fertilizer compositions such as fertilizers or food compositions to facilitate the supply of phosphorus respectively in the soil or in animal or human food.

In the field of agriculture, fertilizers are nevertheless compounds that can cause serious environmental contaminations including cultivated soils. Mineral fertilizers, in view of their intensive use to increase the supply of nutrients such as nitrogen or phosphorus, can permanently contaminate soils if they contain excessive impurities. Phosphates are a preferred source for bringing phosphorus to the soil. These are usually produced or derived from phosphate ore which naturally contains high levels of metals including cadmium, lead, mercury, uranium, chromium or arsenic. The dispersion of these toxic elements in the cultivated soils will promote a sustainable environmental pollution of said cultivated soils. In addition, some of these elements may be found in foods grown on these soils, in water and ultimately in the human or animal body. Several types of gastrointestinal, pulmonary or renal diseases are known to be caused by the excessive presence of toxic elements.

Among the phosphate salts commonly used in agriculture are single superphosphate (SSP), triple superphosphate (TSP), or calcium phosphate salts such as dicalcium phosphate (DCP). Dicalcium phosphate is prepared from phosphate ore. For example, WO2004 / 002888 discloses the preparation of phosphate salts by a process comprising the following steps: at least one attack of phosphate ore by a first aqueous solution of hydrochloric acid, with the formation of a liquor of attack a first separation, in the etching liquor, between an insoluble solid phase containing impurities and a separated aqueous phase comprising, in solution, phosphate ions, chloride ions and calcium ions; an extraction of an aqueous solution containing phosphate ions, chloride ions and calcium ions by an organic extraction agent, to form an aqueous extraction phase comprising chlorine ions and calcium ions and an organic extraction phase containing phosphoric acid, and - reextraction of the organic extraction phase with an aqueous stripping agent, to isolate an aqueous reextraction phase containing phosphate ions, and, optionally only a concentration of the aqueous stripping phase to form an aqueous solution of pure phosphoric acid.

By this process carried out at room temperature, a dicalcium phosphate having a P 2 O 5 content of 36.27% by weight and a Ca content of 28.9% by weight is obtained. The content of impurities, mainly heavy metals among which cadmium, arsenic, nickel or lead are respectively 0.65 ppm, 2.01 ppm, 3.5 ppm and 3.7 ppm. The implementation of this salt in the field of fertilizers or livestock feed is envisaged.

Also known from WO2005 / 066070 is another process for attacking phosphate ore at room temperature to form a dicalcium phosphate precipitate. The process comprises in particular the steps of: - digestion of phosphate ore with an aqueous solution of hydrochloric acid, with formation of an etching liquor consisting of an aqueous phase, in which calcium phosphate is in solution, and an insoluble solid phase, containing impurities, - a first separation between the insoluble solid phase and the aqueous phase of the etching liquor, - a prior neutralization of an aqueous medium containing calcium phosphate in solution at a temperature of first pH below the pH at which a significant part of this calcium phosphate in solution precipitates in the form of calcium monohydrogenphosphate (DCP), with precipitation of impurities, - an isolation of impurities precipitated from the previously neutralized aqueous medium, - a neutralization said aqueous medium previously neutralized at a second pH higher than the aforementioned first pH, with precipitation of DCP, and a second separation between the subsequently neutralized aqueous medium, which is an aqueous solution of calcium chloride, and the precipitated DCP.

The Applicant has notably observed that the precipitated DCP obtained by this process contained a cadmium content of 0.46 ppm.

FR2115244 also discloses a process for the preparation of precipitated DCP produced from an attack of phosphate ore with dilute hydrochloric acid. The insoluble materials resulting from this reaction are separated while the liquid phase is subjected to two neutralization steps in the presence of a basic compound allowing the precipitation of the DCP. The Applicant has observed that the heavy metal contents in the DCP resulting from this process were higher than in the DCP resulting from the method of WO2005 / 066070 described above. The cadmium content was in particular 1.3 ppm.

Casacuberta et al., Journal of hazardous materials, 2009, 170, 814-823, also discloses the levels of radioactive elements in several samples of dicalcium phosphate (DCP). The DCP samples 1-4, 9 and 10 mentioned herein were prepared by digestion of the phosphate ore in the presence of hydrochloric acid and then neutralization of the resulting aqueous phase to precipitate the DCP. The contents of U234, U238 and Pb210 are high, respectively of the order of 900 Bq / kg, 1100 Bq / kg and 2000 Bq / kg, ie almost 4000 Bq / kg on these three radioactive elements only. Casacuberta et al. explain that these high levels of uranium and lead are due to the solubility of these elements in acidic medium and their precipitation in the form of salts concomitantly with the precipitation of dicalcium phosphate during the preparation process of the latter. The cadmium content in these samples ranges from 0.44 ppm to 6.5 ppm.

Under certain conditions, the magnesium content must also be controlled. The magnesium present in dicalcium phosphate (DCP) comes from the phosphate source used to produce DCP. A magnesium content in the phosphate source which is too high, greater than 1% by weight of magnesium in the phosphate source, causes problems of treatment of the etching liquor during the leaching of the phosphate source by an acid. The phosphate salts are therefore generally prepared from a low magnesium phosphate source (less than 1% by weight in the phosphate source).

The levels of radioactive elements or metals of phosphate salts such as dicalcium phosphate can be reduced to limit the risks of contamination of soil or food grown in these soils while using a wide variety of phosphate sources.

The present invention aims to provide a phosphate salt suitable for use in a formulation or composition intended for agriculture or food or suitable for use in the preparation of a formulation, a composition for in agriculture or food, and in which at least a portion of the contents of radioactive elements or metal impurities of heavy metals or transition metals, is reduced. The present invention also aims to provide a process for preparing this flexible phosphate salt, that is to say that can use a wide range of phosphate source regardless of the quality thereof. Summary of the invention

According to a first aspect, the present invention relates to a phosphate salt in solid form of formula Mn (HPO 4) y · ZH 2 O wherein M is Na, K, NH 4, n = 2, and y = 1; or M is Ca, n = 1, y = 1; or M is Al or Fe, n = 2, y = 3; and wherein z is 0, 1 or 2; said phosphate salt has a phosphate content expressed as P205 content of between 30 and 50% by weight of the phosphate salt.

Said phosphate salt according to the present invention may have a cadmium content of less than 0.4 ppm. Said phosphate salt according to the present invention may have a magnesium content less than or equal to 20 ppm, advantageously less than 15 ppm, preferably less than 10 ppm.

Said phosphate salt according to the present invention may also have a Po210 content of less than 500 Bq / kg, advantageously less than 300 Bq / kg, preferably less than 200 Bq / kg.

Said phosphate salt according to the present invention may have a Ra226 content of less than 50 Bq / kg, advantageously less than 25 Bq / kg, preferably less than 10 Bq / kg, in particular less than 5 Bq / kg.

Preferably, said phosphate salt may have a uranium content of less than 1500 Bq / kg, preferably less than 1000 Bq / kg, in particular less than 800 Bq / kg. The uranium content is determined by the sum of the respective U234, U235 and U238 contents.

Said phosphate salt may have a Pb210 content of less than 1500 Bq / kg, advantageously less than 1000 Bq / kg, preferably less than 800 Bq / kg, in particular less than 500 Bq / kg.

The contents of uranium (U234, U235 and U238), Pb210, Po210, Ra226 or magnesium or cadmium in said phosphate salt according to the invention are significantly decreased relative to equivalent phosphate salts of the art prior. Thus, as mentioned above, Casacuberta et al. described a series of DCP samples, obtained by a wet process, whose uranium contents (U234 and U238), Po210, Pb210 and magnesium were respectively of the order of 2000 Bq / kg, 1000 Bq / kg, 2000 Bq / kg and 200 ppm. Said phosphate salt according to the present invention has low levels of radioactive element for use in agriculture or animal feed or human. Said phosphate salt according to the present invention may have one or more of the levels of radioactive elements mentioned in the present invention in combination with one or more of the metal contents mentioned in the present invention. In addition to a low cadmium content, said phosphate salt may have one or more of the contents of Po210, Pb210, U234, U235, U238, Ra226, Ra228, K40, Th228, Th230 or Th232 mentioned in the present application. The content expressed in relation to a radioactive element, i.e. a radionuclide, corresponds to the Bq activity of the radionuclide per kg of the product under consideration, for example per kg of phosphate salt according to the invention.

According to a second aspect of the present invention, a process for preparing said phosphate salt is provided. The process is a wet and non-thermal process (i.e. by calcination of phosphate ore). The process according to the present invention comprises the steps of: a) digesting a phosphate source with a first aqueous solution of hydrochloric acid with formation of an etching liquor consisting of an aqueous phase comprising phosphate ions and chloride ions in solution, and a first insoluble solid phase containing impurities, b) a first separation between the aqueous phase comprising phosphate ions and chloride ions in solution and the first insoluble solid phase containing impurities, c) a neutralizing said aqueous phase comprising phosphate ions and chloride ions in solution at a pH sufficient to form an aqueous medium comprising chloride ions and for precipitating the phosphate ions in the form of said phosphate salt, d) a second separation between said aqueous medium comprising chloride ions and said phosphate salt, characterized in that steps a) and b) are carried out at a temperature of between 50 ° C and 70 ° C.

Said phosphate salt has levels of radioactive elements, such as uranium, polonium or Pb210, and metals, such as magnesium or cadmium, reduced compared to the prior art through the implementation of the steps a) and b) of the present process at a temperature of 50 ° C and 70 ° C. Step a) of digestion of the phosphate source may have a duration of less than one hour, advantageously less than 30 minutes, preferably between 5 minutes and 20 minutes, in particular 15 minutes. The content of radioactive or metallic elements can also be controlled by this relatively short period of digestion of the phosphate source. By controlling the temperature and / or time of digestion of the phosphate source, the amount of impurities (radioactive elements or metals) dissolved in step a) is lower while maintaining a fast and economically viable reaction.

The duration of the neutralization carried out in step c) may be less than four hours, advantageously less than two hours, preferably less than one hour, in particular between 35 minutes and 50 minutes.

In view of its purity, i.e. thanks to its low content of radioactive elements, said phosphate salt according to the present invention can be used directly as one of the constituents of a composition intended for agriculture or a food composition. Said phosphate salt according to the present invention can also be used for the preparation of monoammonium phosphate or diammonium phosphate. Said phosphate salt according to the present invention can also be used for the preparation of triple superphosphate or simple superphosphate. Said phosphate salt according to the present invention can also be used to prepare a high purity phosphoric acid, especially having a low content of radioactive elements. Said phosphate salt according to the present invention can also be used to prepare calcium sulfate or calcium chloride preferably having reduced uranium, Po210, Pb210 and / or cadmium contents. Said phosphate salt according to the present invention can also be used to prepare monocalcium phosphate or mono-dicalcium phosphate (MDCP).

The present invention also provides compositions comprising said phosphate salt or one of the compounds as mentioned above and prepared from said phosphate salt according to the present invention.

The method according to the present invention also makes it possible to use a phosphate source of low quality, that is to say having a phosphate content, expressed as a percentage by weight of P205 in the phosphate source, which is low or contains high impurity content unlike the method described in the prior art.

Brief description of the drawings

Figure 1 shows a block diagram of the process for the preparation of said phosphate salt according to a particular embodiment of the present invention.

Detailed description of the present invention

According to the present invention, a phosphate salt depleted of metallic or radioactive impurities is provided. Said phosphate salt has a phosphate content expressed as P205 content of between 30 and 50% by weight of the phosphate salt, preferably 36 to 45% by weight of the phosphate salt. Said phosphate salt may be in solid form. Said phosphate salt may be of formula Mn (HPO 4) y · ZH 2 O wherein M is Na, K, NH 4, n = 2, and y = 1; or M is Ca, n = 1, y = 1; or M is Al or Fe, n = 2, y = 3; and wherein z is 0, 1 or 2.

Said phosphate salt according to the present invention may have a uranium content of less than 1500 Bq / kg, preferably less than 1000 Bq / kg, in particular less than 800 Bq / kg. The uranium content is determined by the respective U234, U235 and U238 contents. Said phosphate salt may have a uranium U234 content of less than 800 Bq / kg, advantageously less than 600 Bq / kg, preferably less than 500 Bq / kg, in particular less than 400 Bq / kg. Said phosphate salt may have a uranium U238 content of less than 900 Bq / kg, advantageously less than 700 Bq / kg, preferably less than 500 Bq / kg, in particular less than 400 Bq / kg. Said phosphate salt may have a uranium U235 content of less than 100 Bq / kg, advantageously less than 75 Bq / kg, preferably less than 50 Bq / kg, in particular less than 20 Bq / kg.

Said phosphate salt according to the present invention may have a Pb210 content of less than 1500 Bq / kg, advantageously less than 1000 Bq / kg, preferably less than 800 Bq / kg, in particular less than 500 Bq / kg.

Said phosphate salt according to the present invention may have a Po210 content of less than 500 Bq / kg, advantageously less than 300 Bq / kg, preferably less than 200 Bq / kg, in particular less than 150 Bq / kg.

Said phosphate salt according to the present invention may have a Th228 content of less than 100 Bq / kg, advantageously less than 50 Bq / kg, preferably less than 25 Bq / kg, in particular less than 10 Bq / kg. Said phosphate salt according to the present invention may have a Th230 content of less than 100 Bq / kg, advantageously less than 50 Bq / kg, preferably less than 25 Bq / kg, in particular less than 10 Bq / kg. Said phosphate salt according to the present invention may have a Th232 content of less than 50 Bq / kg, advantageously less than 25 Bq / kg, preferably less than 10 Bq / kg, in particular less than 1 Bq / kg. Said phosphate salt according to the present invention may have a thorium content, determined by the respective contents of Th230, Th228 and Th232, of less than 150 Bq / kg, advantageously less than 100 Bq / kg, preferably less than 50 Bq / kg. , in particular less than 20 Bq / kg.

Said phosphate salt according to the present invention may have a Ra226 content of less than 50 Bq / kg, advantageously less than 25 Bq / kg, preferably less than 10 Bq / kg, in particular less than 5 Bq / kg. Said phosphate salt according to the present invention may have a Ra228 content of less than 50 Bq / kg, advantageously less than 25 Bq / kg, preferably less than 10 Bq / kg, in particular less than 5 Bq / kg and more particularly lower at 1 Bq / kg. Said phosphate salt according to the present invention may have a radium content, determined by the respective Ra226 and Ra228 contents, of less than 100 Bq / kg, advantageously less than 50 Bq / kg, preferably less than 20 Bq / kg, especially less than 10 Bq / kg and more particularly less than 5 Bq / kg.

Said phosphate salt according to the present invention may have a K40 content of less than 25 Bq / kg, advantageously less than 10 Bq / kg, preferably less than 5 Bq / kg.

Advantageously, said phosphate salt according to the present invention is a calcium phosphate salt of formula Ca (HPO 4) .zH 2 O where z is 0, 1 or 2; in particular a calcium phosphate salt of formula Ca (HPO4) .2H2O. Said calcium phosphate salt may thus have a phosphate content expressed as P205 content of between 30 and 50% by weight of the phosphate salt and a calcium content of between 15 and 30% by weight of the phosphate salt. Advantageously, said calcium phosphate salt may have a phosphate content expressed as a P205 content of between 33 to 45% by weight of the phosphate salt and a calcium content of between 15 and 30% by weight of the phosphate salt. Preferably, said calcium phosphate salt may have a phosphate content expressed as a P205 content of between 36 to 45% by weight of the phosphate salt and a calcium content of between 15 and 30% by weight of the phosphate salt.

In addition to low levels of radioactive impurities, said radioactive impurities including one or more of the radioactive elements detailed above, eg U234, u235, U238, Po210, Th228, Th230, Th232, K40, Ra226, Ra228 or Pb210, said phosphate salt according to the present invention may have low levels of metal impurities, eg heavy metals and transition metals. Alternatively or concomitantly with the contents of one or more radioactive elements described in the present application, said phosphate salt may have one or more of the metal contents mentioned below.

In particular, said phosphate salt may have a strontium content of less than 300 ppm, advantageously less than 280 ppm, preferably less than 250 ppm, in particular less than 100 ppm.

Said phosphate salt may have a barium content of less than 50 ppm, advantageously less than 25 ppm, preferably less than 10 ppm.

Said phosphate salt may have a cobalt content of less than 10 ppm, advantageously less than 5 ppm, preferably less than 1 ppm.

Said phosphate salt may have a mercury content of less than 10 ppm, advantageously less than 5 ppm, preferably less than 1 ppm.

Said phosphate salt may have an arsenic content of less than 5 ppm, advantageously less than 3 ppm, preferably less than 1.6 ppm, in particular less than 1 ppm.

Said phosphate salt may have a copper content of less than 10 ppm, advantageously less than 5 ppm, preferably less than 1 ppm.

Said phosphate salt may have a zinc content of less than 100 ppm, advantageously less than 50 ppm, preferably less than 35 ppm.

Said phosphate salt may have a chromium content of less than 150 ppm, advantageously less than 100 ppm, preferably less than 75 ppm.

Said phosphate salt may have a nickel content of less than 3 ppm, preferably 2.5 ppm.

Said phosphate salt may have a thallium content of less than 5 ppm, advantageously less than 2.5 ppm, preferably less than 1 ppm.

Said phosphate salt may have a lead content of less than 3 ppm, advantageously less than 2 ppm, preferably less than 1.5 ppm.

Said phosphate salt may have a cadmium content of less than 0.40 ppm, preferably less than 0.30 ppm, preferably less than 0.10 ppm.

Said phosphate salt may have a manganese content of less than 20 ppm, advantageously less than 15 ppm, preferably less than 10 ppm, in particular less than 5 ppm.

Said phosphate salt may have a molybdenum content of less than 3 ppm, advantageously less than 2 ppm, preferably less than 1 ppm.

Said phosphate salt according to the present invention may also have a magnesium content less than or equal to 20 ppm, advantageously less than 15 ppm, preferably less than 10 ppm. Said phosphate salt may contain less than 5% by weight of the magnesium initially included in said source of phosphate, preferably less than 3%, preferably less than 2.5%, in particular less than 1%.

Said phosphate salt according to the present invention may optionally have a metal impurity content of less than 1000 ppm, preferably less than 750 ppm, in particular less than 500 ppm, said metal impurity content being determined from the respective barium contents, cobalt, mercury, manganese, magnesium, molybdenum, strontium, thallium, cadmium, arsenic, copper, lead, zinc, nickel and chromium in said phosphate salt.

Said phosphate salt according to the present invention may be in the form of aggregates of solid particles having a diameter of between 500 μm and 5 mm, advantageously between 500 μm and 3 mm, and preferably between 1 mm and 2 mm.

Alternatively, said phosphate salt according to the present invention may be in the form of aggregates of solid particles having a diameter less than 500 μm, advantageously a diameter of between 50 and 500 μm, preferably between 100 μm and 200 μm.

Preferably, said phosphate salt can be produced from a phosphate source selected from the group consisting of phosphate ore or secondary phosphate sources such as ash, for example fly ash (bone ash or slurry, or ashes resulting from the incineration of sewage sludge) or any other raw material containing more than 10% of phosphate expressed as P205 content (ie any other raw material containing 10% by weight of P205). The phosphate ore and the secondary phosphate sources typically comprise more than 10% by weight of P 2 O 5, advantageously more than 15% by weight of P 2 O 5, preferably more than 20% by weight of P 2 O 5.

Said phosphate salt according to the present invention may have a solubility in water at room temperature (20 ° C) of between 0.01 and 2% by weight. When said phosphate salt is a calcium phosphate salt, it may have a solubility in water at room temperature (20 ° C) of between 0.01 and 0.1% by weight.

Said phosphate salt according to the present invention, preferably when in the form of a salt of calcium phosphate, can be used as an ingredient in a composition intended for agriculture, in a food composition, or as a product of starting material for the preparation of phosphoric acid, single superphosphate or triple superphosphate, monocalcium phosphate (MCP), mono-dicalcium phosphate (MDCP), ammonium phosphate salts (monoammonium or diammonium), phosphate potassium, or NPK-type fertilizer compounds.

Said phosphate salt according to the present invention, preferably when in the form of a calcium phosphate salt, can be brought into contact with one or more of the compounds selected from water, sulfuric acid, water, phosphoric acid, a source of nitrogen or a source of potassium, or mixtures thereof, and mixing with them to advantageously form aggregates of solid particles suitable for use as an ingredient in compositions for agricultural purposes or compositions food. Said nitrogen source may be ammonia, urea, a nitrate, an ammonium salt such as ammonium sulphate, ammonium chloride, ammonium nitrate or mixtures thereof, or any another source of organic or inorganic nitrogen comprising a nitrogen atom. Said source of potassium may be a potassium salt such as potassium chloride, potassium sulphate, potassium nitrate, a mixture of potassium sulphate and magnesium sulphate, or mixtures thereof. Aggregates of solid particles may comprise said phosphate salt of the present invention if the reaction with any of the above reagents is not complete. When said phosphate salt is contacted with sulfuric acid, and optionally with water, simple superphosphate (SSP) may be formed. When said phosphate salt is contacted with phosphoric acid, and optionally with water and sulfuric acid, triple superphosphate (TSP) may be formed. The weight ratio of phosphoric acid to phosphate salt is from 0.5 to 0.65. The phosphate content in the TSP is generally between 40% and 55% by weight of P2O5. When said phosphate salt is brought into contact with sulfuric acid, said source of nitrogen, and optionally water and / or phosphoric acid, monoammonium phosphate (MAP), diammonium phosphate ( DAP) or a mixture of both can be formed. When said phosphate salt is contacted with sulfuric acid and a source of potassium and optionally with water and / or phosphoric acid, potassium phosphate salt may be formed. When said phosphate salt is brought into contact with said source of nitrogen and said potassium source, and optionally water and / or phosphoric acid and / or sulfuric acid, a composition of "NPK type Can be formed. The term "NPK" refers to a composition comprising nitrogen, potassium, phosphorus or mixtures thereof. Preferably, the NPK composition may comprise a content by weight different or equal in phosphorus, nitrogen or potassium based on the total weight of the composition. The phosphorus, nitrogen or potassium content may be adjusted depending on the compounds contacted and their respective proportions. When said phosphate salt is contacted with an adequate amount of phosphoric acid, monocalcium phosphate may be formed. The weight ratio of phosphoric acid to phosphate salt is from 0.5 to 0.65. When said phosphate salt is contacted with an adequate amount of phosphoric acid, a mono-dicalcium phosphate may be formed. The weight ratio of phosphoric acid to phosphate salt is less than 0.5. The phosphoric acid used in the various processes above preferably has a phosphate content expressed as a percentage by weight of P2O5 of between 45% and 60%, advantageously between 50% and 55%, and preferably about 54%.

Said phosphate salt according to the present invention can be prepared by the process comprising the following steps: a) a digestion of a phosphate source with a first aqueous solution of hydrochloric acid with formation of an attack liquor consisting of an aqueous phase comprising phosphate ions and chloride ions in solution, and a first insoluble solid phase containing impurities, b) a first separation between the aqueous phase comprising phosphate ions and chloride ions in solution and the first solid phase insoluble material containing impurities; c) neutralization of said aqueous phase comprising phosphate ions and chloride ions in solution at a pH sufficient to form an aqueous medium comprising chloride ions and for precipitating the phosphate ions in the form of said phosphate salt, d a second separation between said aqueous medium comprising the chloride ions and said phosphate salt, characterized in that steps a) and b) are carried out at a temperature of between 50 ° C and 70 ° C.

Said method according to the present invention may also comprise a step of drying said phosphate salt obtained in step d). Step a) of digestion of the phosphate source may have a duration of less than one hour, advantageously less than 30 minutes, preferably between 5 minutes and 20 minutes, in particular 15 minutes.

The duration of the neutralization carried out in step c) may be less than four hours, advantageously less than two hours, preferably less than one hour, in particular between 35 minutes and 50 minutes.

The impurities contained in the solid phase obtained in step a) and separated in step b) may be metal impurities or radioactive elements or insoluble materials. The radioactive elements contained in this solid phase may be one or more of U234, U235, U238, Po210, Th228, Th230, Th232, K40, Ra226, Ra228 or Pb210. The metal elements may be any of the following metal elements: barium, cobalt, mercury, manganese, magnesium, molybdenum, strontium, thallium, cadmium, arsenic, copper, lead, zinc, nickel and chromium. The implementation of steps a) and b) at a temperature between 50 ° C and 70 ° C, preferably between 55 ° C and 65 ° C, to control the precipitation of radioactive impurities or not. In addition, even in the presence of a source of magnesium-rich phosphate, the implementation of the process at a temperature between 50 ° C. and 70 ° C. makes it possible to control the viscosity of the etching liquor and avoid the problems of processing. of the leaching reaction of the rock. When steps a) and c) are carried out during a short reaction time as mentioned above, the purity of said aqueous medium comprising the chloride ions and said phosphate salt obtained in step d) is increased. Thus, the presence of radioactive impurities and / or metals is strongly limited in said aqueous medium comprising the chloride ions and said phosphate salt obtained in step d) by the process according to the present invention.

Said phosphate source used in step a) may be selected from the group consisting of phosphate ore or secondary phosphate sources such as ash, for example fly ash (bone or slurry ashes or slurries). ashes resulting from the incineration of sewage sludge) or any other raw material containing more than 10% of phosphate expressed as a percentage by weight of P205 in said raw material. Ashes as used herein may comprise more than 10% by weight of phosphate expressed as a percentage by weight of P 2 O 5 in the ash, advantageously more than 15% by weight of P 2 O 5.

Said source of phosphate may contain a magnesium content greater than 1.5% by weight based on the total weight of the phosphate source. Advantageously, the magnesium content of said source of phosphate may be between 1.5% and 20% by weight based on the total weight of the phosphate source, preferably between 1.5 and 10% by weight.

Said first aqueous solution of hydrochloric acid used in step a) of the present process may have an HCl concentration of less than or equal to 15% by weight, advantageously 8 to 13%, preferably 12% by weight of the first. aqueous solution. The use of a solution of HCl at a concentration of between 8 and 13% by weight or of the order of 12% by weight makes it possible to carry out step a) in a dilute medium favoring the treatment of rich rock. in magnesium.

Preferably, in the etching liquor, the molar ratio between HCl and Ca is between 1.2 and 2.6.

Said neutralization of step c) can be carried out in the presence of a base, advantageously calcium carbonate, calcium hydroxide, calcium oxide or one or more salts of calcium, of sodium, of potassium or ammonium. Preferably, said neutralization of step c) is carried out in the presence of calcium carbonate, calcium hydroxide, calcium oxide or a calcium salt. In this case, said precipitated phosphate salt is a calcium phosphate salt and said aqueous medium, in step d), comprises chloride ions and calcium ions. Said aqueous medium is preferably a solution of calcium chloride having a calcium chloride content of between 8 and 20% by weight of the solution, advantageously between 12 and 18% by weight, preferably about 15% by weight.

Alternatively, the use in step c) of a salt of sodium, potassium or ammonium allows the preparation respectively of a salt of sodium phosphate, potassium or ammonium. The appropriate use of an aluminum or iron salt or hydroxide allows the preparation of the corresponding phosphate salt.

Said neutralization carried out in step c) can be carried out at a pH of less than 5, advantageously between 2.0 and 5.0, preferably between 2.5 and 4.0, in particular between 2.5 and 3.0. When the neutralization is carried out at a pH between 2.5 and 3.0, the magnesium remains in solution without precipitating concomitantly with said phosphate salt. Preferably, this neutralization step can be carried out at room temperature or at a temperature of between 50 and 70 ° C.

Said phosphate salt obtained in step d) may contain less than 5% by weight of the magnesium initially included in said source of phosphate, preferably less than 2.5%, preferably less than 1%.

According to a particular embodiment, the process according to the present invention further comprises the steps: e) an attack of all or part of said phosphate salt obtained in step d) by an aqueous solution of strong acid to form a suspension a first phosphoric acid in solution and a second solid phase, f) a third separation between the first phosphoric acid and said second solid phase.

Preferably, step e) can be carried out at a temperature above 80 ° C, in particular at a temperature between 80 ° C and 100 ° C. The implementation of step e) at a temperature above 80 ° C., preferably at a temperature of between 80 ° C. and 100 ° C., makes it possible to control the viscosity of the reaction medium obtained in step e). Preferably, when said phosphate salt used in step e) is a calcium phosphate salt, said aqueous solution of strong acid may be sulfuric acid. Thus, the second solid phase of step e) comprises calcium sulfate hemihydrate. Alternatively, when said phosphate salt used in step e) is a calcium phosphate salt and step e) is carried out at a temperature below 80 ° C, preferably between 60 ° C and 80 ° C, said aqueous solution of strong acid may be sulfuric acid and said second solid phase of step e) comprises calcium sulfate dihydrate.

Preferably, in step e) the molar ratio between the aqueous solution of strong acid and said phosphate salt obtained in step d) may be between 0.6 and 1.6.

The first phosphoric acid obtained in step f) may be treated with activated charcoal or a sulfide compound or may be concentrated. Said first phosphoric acid may be used in a composition intended for agriculture, for example a fertilizer composition, or used in the preparation of a food composition. Said first phosphoric acid may be used for the preparation of a triple superphosphate or superphosphoric acid. The content of radioactive elements or metallic elements in the products thus prepared will be reduced.

According to a preferred embodiment, said aqueous medium comprising chloride ions and obtained in step d) can be treated with a basic compound to form a purified aqueous phase and a solid phase comprising impurities. Said purified aqueous phase comprises chloride ions and preferably has a pH of between 8 and 12, advantageously between 9 and 10. Advantageously, when the aqueous medium obtained in step d) comprises chloride ions and calcium ions, the compound basic is selected from calcium hydroxide, calcium oxide and calcium, sodium, potassium or ammonium salts to form a purified aqueous phase comprising calcium chloride. Said solid phase comprising impurities may comprise magnesium salts or radioactive elements or metallic impurities. The treatment of said aqueous medium comprising chloride ions and obtained in step d) by a basic compound thus makes it possible to obtain a solution of purified calcium chloride, i.e. having a lower content of radioactive elements and magnesium. This treatment can be carried out at a temperature between 50 and 70 ° C. Alternatively, this treatment can be performed at room temperature. Preferably, said purified aqueous phase has a calcium chloride content of between 10 and 30% by weight of the purified aqueous phase, advantageously between 12 and 20% by weight, preferably about 15%.

Thus, the present invention also relates to a calcium chloride depleted of radioactive elements. The calcium chloride can be in solution or in solid form. Said calcium chloride may have a uranium content of less than 1 Bq / kg, preferably less than 0.1 Bq / kg, the uranium content being determined by the respective U234, U235 and U238 contents. Said calcium chloride may also have a Po210 content of less than 500 Bq / kg, advantageously less than 250 Bq / kg, preferably less than 100 Bq / kg. Said calcium chloride may also have a radium content, determined by the respective Ra226 and Ra228 contents, less than 10 Bq / kg, advantageously less than 1 Bq / kg, preferably less than 0.5 Bq / kg. Said calcium chloride may also have a Pb210 content of less than 100 Bq / kg, preferably less than 50 Bq / kg. Said calcium chloride may also have a thorium content determined by the respective contents of Th228, Th230 and Th232, less than 10 Bq / kg, preferably less than 1 Bq / kg. Said calcium chloride may be obtained by the process according to the present invention, for example by steps a) to d) of the present process wherein step c) is carried out in the presence of a calcium salt, hydroxide or calcium oxide to obtain in step d) an aqueous medium comprising chloride ions and calcium ions, thereby forming an aqueous medium comprising calcium chloride. This aqueous medium comprising calcium chloride can be dried or concentrated.

Advantageously, said aqueous medium comprising calcium chloride, and obtained in step d), can be purified to present even lower levels of different radioactive elements or metals. Thus, said calcium chloride may have a uranium content of less than 0.05 Bq / kg, the uranium content being determined by the respective U234, U235 and U238 contents. Said calcium chloride may also have a Po210 content of less than 50 Bq / kg, advantageously less than 10 Bq / kg, preferably less than 5 Bq / kg. Said calcium chloride may also have a radium content, determined by the respective Ra226 and Ra228 contents, of less than 1 Bq / kg, advantageously less than 0.5 Bq / kg, preferably less than 0.1 Bq / kg. Said calcium chloride may also have a Pb210 content of less than 10 Bq / kg. Said calcium chloride may also have a thorium content determined by the respective contents of Th228, Th230 and Th232, less than 0.1 Bq / kg, preferably no trace of thorium is detected. Preferably, said purified calcium chloride can be prepared by the present process by treating the previously obtained calcium chloride solution with a basic compound, chosen for example from calcium hydroxide, calcium oxide and calcium salts. , sodium, potassium or ammonium as described in the present application. The purified calcium chloride solution thus obtained may have a pH greater than 10. Said solution of purified calcium chloride may be concentrated and / or dried. Thus, a solution of calcium chloride having a CaCl 2 concentration of 35-40% by weight of the total solution can be obtained. Alternatively, CaCl 2 granules having a CaCl 2 content greater than 95% by weight based on the total weight of the granules can be obtained. Alternatively, petals of CaCl2 having a CaCl2 content greater than 70% by weight based on the total weight of the petals can be obtained, preferably a content of between 70 and 80% by weight.

The second solid phase of step e) and separated in step f) comprises calcium sulfate hemihydrate or calcium sulfate dihydrate or a mixture of both. The calcium sulfate hemihydrate, the calcium sulfate dihydrate or their mixture may be mixed with an acid solution, preferably a strong acid, to form a solid phase comprising calcium sulfate dihydrate and an aqueous phase comprising phosphate ions. The calcium sulfate hemihydrate is thus converted into calcium sulfate dihydrate. The acid solution may be a solution of hydrochloric acid, and thus the aqueous phase obtained is a solution of hydrochloric acid also comprising phosphate ions. Alternatively, the strong acid solution may be a sulfuric acid solution and the second solid phase separated in step f) may also be mixed with said purified aqueous phase, preferably said purified calcium chloride solution, or said aqueous medium comprising chloride ions obtained in step d), preferably said aqueous medium comprising chloride ions and calcium ions obtained in step d), or their mixture. A solid phase comprising calcium sulfate dihydrate and an aqueous phase comprising hydrochloric acid are then obtained. The aqueous phase comprising hydrochloric acid may be recycled to form all or part of said first aqueous hydrochloric acid solution used in step a).

Thus, the present invention enables the preparation of calcium sulfate dihydrate with a low content of radioactive elements. Said calcium sulphate thus prepared may have a K40 content of less than 50 Bq / kg, advantageously less than 30 Bq / kg, preferably less than 16 Bq / kg. Said calcium sulphate may have a Ra228 content of less than 50 Bq / kg, advantageously less than 25 Bq / kg, preferably less than 10 Bq / kg, in particular less than 5 Bq / kg. Said calcium sulphate may have a Ra226 content of less than 50 Bq / kg, advantageously less than 25 Bq / kg, preferably less than 10 Bq / kg, in particular less than 5 Bq / kg. Said calcium sulphate may have a Th228 content of less than 50 Bq / kg, advantageously less than 25 Bq / kg, preferably less than 10 Bq / kg, in particular less than 5 Bq / kg. Said calcium sulphate may have a U235 content of less than 50 Bq / kg, advantageously less than 25 Bq / kg, preferably less than 10 Bq / kg, in particular less than 5 Bq / kg. Said calcium sulphate may have a U238 content of less than 50 Bq / kg, advantageously less than 25 Bq / kg, preferably less than 15 Bq / kg.

According to a third aspect of the present invention, said phosphate salt according to the present invention can be used, preferably in solid form, in a composition or for the preparation thereof. The composition may be a composition intended for agriculture or a food composition. Advantageously, said composition intended for agriculture is a liquid fertilizing composition, or a fertilizing composition partially or totally soluble in water. Said food composition is a composition for animal feed or livestock or human. Preferably, said phosphate salt thus used is prepared by the process according to the present invention.

According to a fourth aspect of the present invention, a composition for agriculture or a food composition comprising said phosphate salt according to the present invention is provided.

Said food composition may also further comprise a basic food substance. Said food composition may be prepared by a process comprising the steps of: A) preparing said phosphate salt according to the present invention by the method according to the present invention, B) mixing said phosphate salt thus prepared with a basic food substance.

Said composition intended for agriculture may also comprise a potassium source and / or a nitrogen source, diammonium phosphate, monoammonium phosphate, potassium phosphate, simple superphosphate, monocalcium phosphate, mono phosphate -dicalcium or triple superphosphate. Said composition intended for agriculture may be a fertilizing composition, preferably a liquid fertilizing composition, or a fertilizing composition partially or totally soluble in water. Said nitrogen source may be ammonia, urea, a nitrate, an ammonium salt such as ammonium sulphate, ammonium chloride, ammonium nitrate or mixtures thereof, or any another source of organic or inorganic nitrogen comprising a nitrogen atom. Said source of potassium may be a potassium salt such as potassium chloride, potassium sulphate, potassium nitrate, potassium hydrogen sulphate, a mixture of potassium sulphate and magnesium sulphate, or mixtures thereof. Said composition intended for agriculture may be prepared by a process comprising the steps of: A) preparing said phosphate salt according to the present invention, preferably by the process according to the present invention, B) mixing said phosphate salt obtained in A) with one or more of the following: a source of nitrogen or a source of potassium or a mixture thereof, water, sulfuric acid or phosphoric acid to form said composition.

In the various compositions described in the present application, said phosphate salt according to the present invention is preferably a calcium phosphate salt (CaHPO 4 .zH 2 O where z is 0, 1 or 2, preferably z is 2).

According to a particular embodiment of the invention, a process for the preparation of simple superphosphate (SSP) is provided and comprises the steps of: A) preparing said phosphate salt according to the present invention, preferably by the method according to the present invention. invention, B) addition of sulfuric acid and optionally phosphoric acid, water to said phosphate salt to form single superphosphate (SSP).

The molar ratio between the sulfuric acid and the said phosphate salt is between 0.1 and 1. The molar ratio between the phosphoric acid and the said phosphate salt is between 0 and 1.

According to a particular embodiment of the invention, a process for the preparation of triple superphosphate (TSP) is provided and comprises the steps of: A) preparing said phosphate salt according to the present invention, preferably by the method according to the present invention. invention, B) addition of phosphoric acid, and optionally sulfuric acid and / or water to said phosphate salt to form TSP.

The molar ratio between the sulfuric acid and the said phosphate salt is between 0 and 1, preferably between 0.1 and 0.5. The molar ratio between the phosphoric acid and said phosphate salt is between 0.1 and 1, preferably between 0.1 and 0.5.

According to a particular embodiment of the invention, a process for the preparation of monoammonium phosphate (MAP) or diammonium phosphate (DAP) is provided and comprises the steps of: A) preparation of a phosphate salt according to the the present invention, preferably by the method according to the present invention, B) addition of sulfuric acid and ammonia or an ammonium salt to said phosphate salt to form monoammonium phosphate or diammonium phosphate.

Preferably, the addition of sulfuric acid may be prior to that of ammonia or ammonium salt. Preferably, filtration is performed after the addition of sulfuric acid to separate an aqueous phase comprising phosphoric acid and a solid phase comprising calcium sulfate. The addition of the ammonia or the ammonium salt is carried out on the filtrate resulting from said filtration, i.e. on the aqueous phase comprising phosphoric acid. The molar ratio between the sulfuric acid and the said phosphate salt is between 0.5 and 1.5, preferably between 0.8 and 1.2. Preferably, the molar ratio between the ammonia or the ammonium salt and the said phosphate salt is between 0.5 and 2.5.

According to a particular embodiment of the invention, a process for the preparation of potassium phosphate is provided and comprises the steps of: A) preparing a phosphate salt according to the present invention, preferably by the method according to the present invention invention, B) adding a source of potassium to said phosphate salt, and optionally an acid, to form said potassium phosphate salt. The acid may be phosphoric acid or sulfuric acid. Preferably, when the sulfuric acid is added, this addition may be prior to that of the potassium source. Filtration is advantageously carried out after the addition of sulfuric acid to separate an aqueous phase comprising phosphoric acid and a solid phase comprising calcium sulphate. The addition of the potassium source can then be carried out on the filtrate resulting from said filtration, i.e. on the aqueous phase comprising phosphoric acid. Alternatively, filtration can be performed after the implementation of step b). The molar ratio between the sulfuric acid and the said phosphate salt is between 0.5 and 1.5, preferably between 0.8 and 1.2. Preferably, the molar ratio between the potassium source and the said phosphate salt is between 0.5 and 2.5, preferably between 1 and 2. The process is particularly applicable to the preparation of monopotassium phosphate (MKP - KH2PO4). In this case, the potassium source may preferably be potassium chloride, potassium sulphate, potassium hydrogen sulphate (KHSO4) or another potassium salt. The molar ratio between the acid and the said phosphate salt is between 0 and 1. The molar ratio between the potassium source and the said phosphate salt is between 0.5 and 2.5, preferably between 1 and 2. In particular, the acid supply is optional when the potassium source is potassium hydrogen sulphate.

Said phosphate salt according to the present invention, when it is preferably prepared according to the method of the present invention, can be used in a composition intended for agriculture or in a food composition, or serve as a starting product for the preparation said compositions. These can be prepared according to the methods described above. The present invention also allows the preparation of "NPK" type composition. This type of compositions is frequently used as fertilizer in agriculture. The present invention therefore provides compositions having low levels of impurities (radioactive elements or metal) avoiding contamination of soils and crops where these compositions can be used.

According to a particular embodiment of the invention, a process for the preparation of NPK composition is provided and comprises the steps of: A) preparing a phosphate salt according to the present invention, preferably by the method according to the present invention , B) adding sulfuric acid, a nitrogen source and / or a potassium source, to said phosphate salt to form an NPK composition.

The molar ratio between the sulfuric acid and the said phosphate salt is between 0.1 and 1.5.

According to a particular embodiment of the invention, a process for the preparation of monocalcium phosphate (MCP) is provided and comprises the steps of: A) preparing a phosphate salt according to the present invention, preferably by the method according to the present invention, B) adding an adequate amount of phosphoric acid to obtain a monocalcium phosphate.

The adequate amount of phosphoric acid is determined according to the weight of phosphate salt. The weight ratio of phosphoric acid to phosphate salt is from 0.5 to 0.65.

According to a particular embodiment of the invention, a process for the preparation of mono-dicalcium phosphate (MDCP) is provided and comprises the steps of: A) preparing a phosphate salt according to the present invention, preferably by the process according to the present invention, B) adding an adequate amount of phosphoric acid to obtain mono-dicalcium phosphate.

The adequate amount of phosphoric acid is determined according to the weight of phosphate salt. The weight ratio of phosphoric acid to phosphate salt is less than 0.5.

Advantageously, the process according to the invention is carried out continuously.

Figure 1 shows a block diagram of the process for preparing said phosphate salt according to a particular embodiment of the present invention. The particular embodiment described below concerns in particular the preparation of dicalcium phosphate having a low content of radioactive elements, but also the preparation of calcium chloride solutions or the preparation of calcium sulfate also having a low content of radioactive elements. The process can be applied to the preparation of other types of phosphate salts, for example sodium, potassium, ammonium, aluminum or iron phosphate salts.

The source of phosphate 1, for example phosphate ore, is treated with a hydrochloric acid solution 2 during a step of digestion of the phosphate source at 3. The treatment is carried out at a temperature of between 50 and 70 ° C. C for less than one hour, preferably less than 30 minutes, preferably between 5 minutes and 20 minutes. The reaction medium 4 resulting from the digestion 3 comprises a solid phase comprising impurities (radioactive elements and / or metallic impurities) and a liquid phase comprising phosphate ions and chloride ions. The reaction medium 4 is filtered to separate the solid phase 4 'comprising the metal impurities and / or radioactive elements from the aqueous phase comprising phosphate ions and chloride ions.

The aqueous phase comprising phosphate ions and chloride ions is then treated, at 13, with a base 14, for example CaCO 3, to form a dicalcium phosphate precipitate 16 and an aqueous solution comprising chloride ions and calcium ions forming thus a solution of calcium chloride. The dicalcium phosphate precipitate 16 and the aqueous solution are separated by filtration, for example by means of a belt filter. The dicalcium phosphate thus obtained is a phosphate salt according to the present invention, i.e. depleted of radioactive elements in particular. This dicalcium phosphate 16 may be used as a raw material in a composition intended for agriculture or in a food composition. It can also be used as a starting reagent for the preparation of compounds such as for example single or triple superphosphate, monoammonium phosphate or diammonium phosphate, or potassium phosphate, monocalcium phosphate (MCP) or phosphate mono-dicalcium (MDCP).

The dicalcium phosphate 16 may also be treated, preferably at a temperature above 80 ° C, with a solution of sulfuric acid 18 at 17 to form a solid phase comprising calcium sulphate and an aqueous phase comprising phosphoric acid , subsequently separated from each other for example by filtration. The calcium sulphate 24 thus obtained comprises calcium sulphate hemihydrate which can be treated at 31 with a hydrochloric acid solution 30. After separation, an aqueous solution of hydrochloric acid 32 and a solid phase of calcium sulphate dihydrate 33 are obtained. The solid phase of calcium sulfate dihydrate 33 has low levels of radioactive elements or metallic elements. Calcium sulfate dihydrate 33 can thus be used in a paper bleaching process or in the preparation of plaster or compositions for construction. The aqueous solution of hydrochloric acid 32 also comprises residual phosphate ions.

The calcium chloride solution can be purified at 26 by the addition of a base 25, for example calcium hydroxide. After separation, for example by filtration, a solid phase 27 comprising impurities and a purified aqueous phase comprising calcium chloride 28 are obtained. The purified aqueous phase comprising calcium chloride 28 can be concentrated and / or dried to obtain calcium chloride in different forms (solution or solid) at different concentrations. The purified aqueous phase comprising calcium chloride 28 can also be treated at 29 with a sulfuric acid solution 34. The calcium chloride solution and calcium sulfate 24 can also be added at 29 to form an aqueous phase. hydrochloric acid and a solid phase comprising calcium sulfate dihydrate 36. The hydrochloric acid solution 35, as well as the hydrochloric acid solution 32, can be recycled for use at 3 in the digestion step of the source of phosphate. The solid phase comprising calcium sulfate dihydrate 36 can be used as calcium sulfate dihydrate 33.

In addition to a phosphate salt depleted in radioactive elements, the present process allows the preparation of calcium chloride, in solution or in solid form, and / or calcium sulfate dihydrate each having low radioactive element contents. The preparation of these compounds and their subsequent use is another advantage of the present invention.

According to an alternative aspect of the invention, when said source of phosphate used in step a) of the present process is a source of secondary phosphate such as fly ash from the incineration of bone, slurry or sludge. purification as described in the present application, the digestion with a hydrochloric acid solution (step a)) forms an aqueous solution comprising phosphate ions and chloride ions in solution. This can be isolated after step b) of the process. This solution is purified to remove chloride ions to produce phosphoric acid or PCM. The removal of chloride ions can be done according to the purification techniques known to those skilled in the art.

Examples

Procedure for determining radioactive element contents by gamma spectrometry

The contents of Pb210, K40, Ra226 and Ra228 were determined by gamma spectrometry. The measurements were carried out in the presence of a detector comprising a Canberra utra-pure germanium crystal (HPGe) (HPGe XtRa 50% relative efficiency or HPGe BEGe 34% relative efficiency) and disposed of inside a measuring device containing a lead shield. Measurements are performed between 3 keV and 3 MeV for a BEGe detector or between 3keV and> 10 MeV for an XtRa detector. The detector is calibrated using samples placed in Marinelli ™ containers with a capacity of 1 mL to 2.5 L. The Ra226 content was determined by measuring radionuclide daughter Ra226. The sample to be analyzed is brought into contact with activated charcoal in the water to absorb the Ra226 present in the sample. The solid residue was placed in a container (coaxial HDPE - 250 mL) for 21 days. The measurement of Ra226 was performed using a Lucas cell type detector. The K40 content is determined by the emission line at 1460.82 keV. The Ra226 content was determined from the daughter radionuclides Bi214 and Pb214, the emission lines of which are respectively 609.31 keV, 1120.28 keV and 1764.5 keV for Bi214 and 241.99 keV, 295 22 keV and 351.93 keV for Pb214. The Ra228 content was determined by considering the emission lines of Ac228 at 338.32 keV, 911.19 keV and 968.96 keV. The Pb210 content was determined by considering the emission line at 46.5 keV.

Procedure for Determining Radioactive Content by Alpha Spectrometry

The contents of Po210, Th228, Th230, Th232, U234, U235, U238 were determined by alpha spectrometry. The detector is a silicon detector also called "PIPS detector" brand Canberra. When the sample to be analyzed is solid (for example DCP or CaSO4), 1 g of it is previously digested with microwaves in the presence of a mixture comprising 5 ml of hydrofluoric acid, 5 ml of hydrochloric acid and 5 ml. nitric acid. When the sample to be analyzed is liquid, it (10 mL) is treated with an aqueous solution of FeCl3 (1 mL of a solution prepared from 7.3 g / 100 mL). The precipitate is centrifuged and calcined. To determine the content of polonium Po210, the sample previously treated as mentioned above is mixed with 0.25 L of water and 20 ml of hydrochloric acid (6 M), ascorbic acid before being deposited. on a silver surface with stirring at a temperature between 80 ° C and 90 ° C for 6 hours. To determine the uranium and thorium contents, the sample is purified on an ion exchange resin (Biorad AG) in the presence of a tracer (Po208 or Po209) to remove the polonium and subjected to a second separation between the uranium and thorium on a column comprising a UTEVA® type resin (Eichrom) in the presence of a U232 and Th229 tracer.

Procedure for determining the contents of transition metals

The metal contents in a sample are determined by optical emission spectrometry (ICP-OES) using an Agilent 710 Axial Serial ICP optical emission spectrometer equipped with a nebulizer (One Neb insert concentric ICP) and a plasma torch (lo-flw, Quartz, inlet tbg, axial). Samples and standards are prepared in containers previously cleaned with a dilute solution of nitric acid (193 g of 96% nitric acid, diluted to 1000 mL with distilled water). The equipment is calibrated by the following protocol using standard solutions of Pb (N03) 2 with a lead concentration of 100 mg / L, Cd (N03) 2 with a cadmium concentration of 100 mg / L, Hg (N03) 2 with a mercury concentration of 100 mg / L, H3As04 with an arsenic concentration of 100 mg / L, and Y (N03) 3 with an yttrium concentration of 100 mg / L. From each of the solutions of Pb (NO 3) 2, Cd (NO 3) 2, Hg (NO 3) 2 and H 3 AsO 4 a series of 7 calibration samples at 0.01 ppm, 0.05 ppm, 0.1 ppm, 0 5 ppm, 1 ppm and 5 ppm are prepared. In each sample, 200 μl of the standard solution of Y (N0 3) 3 is added and then each sample is diluted with the diluted nitric acid solution above to reach a volume of 100 ml.

Preparation of CaCI2 samples to be analyzed by ICP-OES

In a 100 ml flask containing 50 ml of the dilute nitric acid solution as prepared above, 10 g of CaCl 2 and then 200 of the standard solution of Y (NO 3) 3 are added. The volume is then adjusted to 100 mL by the addition of the dilute nitric acid solution. The solution thus obtained is stirred vigorously.

Preparation of phosphate salt samples according to the present invention, DCP and gypsum to be analyzed by ICP-OES

In a 100 mL flask containing 25 mL of the dilute nitric acid solution as prepared above, 2 g of the sample to be analyzed and then 10 mL of a 37% hydrochloric acid solution are added. If necessary, the resulting solution can be boiled to dissolve the sample to be analyzed. 200 μl of the standard solution of Y (N0 3) 3 are added and the volume is adjusted to 100 ml by the addition of the dilute nitric acid solution. The solution thus obtained is stirred vigorously and optionally filtered before analyzing it if necessary.

Example 1

North African phosphate ore having a P 2 O 5 content of 29% by weight is used. The etching of the ore is carried out using an aqueous solution having a weight content of 12% HCl at a temperature of 60 ° C. The amount of HCI added is determined by a molar ratio between the HCl added to the ore and the Ca present therein. The attack of the ore is carried out at a ratio HCI / Ca of 1.8. The residence time in the etching reactor is 15 minutes. The etching liquor is then transferred to a filter press where the insoluble materials (noted residues in Table 1 below) are separated from the aqueous phase. The temperature is maintained at 60 ° C for filtration. The solution leaving the filter press is conveyed to a neutralization reactor. Calcium carbonate is added at a Ca / P molar ratio of 1 and a pH of 2.5-3.0. After 45 minutes of reaction and formation of dicalcium phosphate (DCP), the neutralized reaction medium is then directed to a band filter. The cake obtained is dried and consists of DCP having the characteristics mentioned below, i.e. a low content of radioactive elements and / or low levels of metals. The DCP has a P205 content of 44% by weight (on a dry weight basis) and a calcium content of 24% by weight (on a dry weight basis). The filtrate is an aqueous solution of calcium chloride at 15% by weight. The calcium chloride solution can be purified by the addition of calcium hydroxide until the pH of the solution is between 9 and 10. Insoluble materials mainly comprising magnesium salts and radioactive elements precipitate, thus depleting the calcium chloride solution in radioactive elements. A solution of purified calcium chloride (15% by weight) is thus obtained.

Table 1 details the radioactive element levels of the ore, the dicalcium phosphate (DCP) obtained, the calcium chloride solution (CaCl2) and the purified calcium chloride solution (CaCl2p) and the residues from the filtration after the ore digestion step (ie first solid phase). Example 1 was repeated three times and the various compounds above were analyzed each time. For each radioactive element, an average value over the three tests was determined and is shown below in Table 1.

Table 1 - Content of radioactive elements (Bq / kg) in rock, DCP, CaCl2, CaCl2p and residues from the etching liquor according to the method of the present invention.

(0 = content of the element considered below the limit of detection)

The results shown in Table 1 demonstrate unequivocally that the process according to the present invention allows the preparation of a phosphate salt depleted of radioactive elements, i.e. a lower radionuclide concentration. A large majority of the radioactive elements are precipitated in the insoluble materials resulting from the filtration of the attack liquor. The implementation of the step of digestion of the ore at a temperature between 50 and 70 ° C, for example 60 ° C, promotes the precipitation of radioactive elements. Thus, in addition to dicalcium phosphate, calcium chloride, purified or not, having concentrations of radionuclides, i.e. radioactive elements, is also low. The levels of radioactive elements in the dicalcium phosphate obtained according to the invention are lower than the levels mentioned for different DCP samples by Casacuberta et al. (Journal of hazardous materials, 2009, 170, 814-823). The phosphate salt according to the present invention is therefore purer than the DCP of the prior art, when the content of radioactive elements is taken into account. In addition, the cadmium content in the DCP obtained according to the present invention was 0.26 ppm.

Example 2 (Comparative) Example 1 is reproduced by etching the etch and filtering the etching liquor at room temperature. The contents of radioactive elements are clearly higher than those obtained in dicalcium phosphate according to the present invention, ie when steps a) and b) of the present process according to the invention are carried out at a temperature of between 50 ° C. and 70 ° C. . The uranium content was greater than 1500 Bq / kg. In particular, the content in the DCP obtained according to Example 2 in K40, Ra228, Th232, Pb210 and U234 were respectively 9 Bq / kg, 580 Bq / kg, 72 Bq / kg, 1170 Bq / kg and 900 Bq / kg. kg. The Po210 polonium content was 840 Bq / kg.

Example 3 Example 1 is reproduced from ore of Syrian origin containing a P205 content of 30.9%. A dicalcium phosphate having a P 2 O 5 content of 42% by weight and calcium of 27% by weight is obtained. The dicalcium phosphate obtained in Example 3 has the same characteristics, in terms of levels of radioactive elements, as the dicalcium phosphate of Example 1. Table 2 below details the metal contents in the dicalcium phosphate obtained according to US Pat. Example 3. The table also details the metal contents of a dicalcium phosphate described in WO2004 / 002888 produced by a comparative method in which the digestion and filtration steps of the etching liquor are carried out at room temperature.

Table 2 - Content (in ppm) of metals in the dicalcium phosphate of Example 3 and in the dicalcium phosphate of WO2004 / 002888

The process according to the present invention makes it possible to produce a phosphate salt such as a dicalcium phosphate in which the metal contents are reduced. The contents of cadmium, arsenic and lead are greatly reduced in the dicalcium phosphate prepared by the present invention. The magnesium content in the DCP represents less than 1% of the magnesium initially present in the phosphate ore.

Example 4 - Preparation of SSP simple superphosphate

The dicalcium phosphate prepared according to Example 1 can be used for the preparation of simple superphosphate. The dicalcium phosphate was mixed with a solution of sulfuric acid (0.5 molar equivalents relative to the amount of dicalcium phosphate) in a counter-rotating twin-helix mixer. The simple superphosphate (Ca (H 2 PO 4) 2) obtained with a P 2 O 5 content of between 32 and 37% by weight is dried and then sieved. The simple superphosphate can be used as such as a fertilizer in a composition intended for agriculture. The amount of sulfuric acid may be adapted to form, in the presence of a mass agent, simple superphosphate having a P205 content of between 16 and 18%.

Example 5 - Preparation of TSP triple superphosphate

The dicalcium phosphate prepared according to Example 1 can be used for the preparation of triple superphosphate. The dicalcium phosphate was mixed with a solution of sulfuric acid (0.33 molar equivalents relative to the amount of dicalcium phosphate) and phosphoric acid (0.33 molar equivalents relative to the amount of dicalcium phosphate) in a mixer with double helix in opposite direction. The triple superphosphate (Ca (H 2 PO 4) 2) obtained with a P 2 O 5 content of 45% by weight is dried and then sieved. The triple superphosphate thus obtained can be used as such as a fertilizer in a composition intended for agriculture.

Example 6 - Preparation of monoammonium phosphate and diammonium phosphate (MAP / DAP)

The dicalcium phosphate prepared according to Example 1 can be used for the preparation of monoammonium phosphate and diammonium phosphate. The dicalcium phosphate was mixed with a sulfuric acid solution (1 molar equivalent based on the amount of dicalcium phosphate) to form solution phosphoric acid and a calcium sulfate precipitate. After filtration, ammonia (between 1 and 2 molar equivalents relative to the amount of dicalcium phosphate) is added to the phosphoric acid solution. The proportion between monoammonium phosphate and diammonium phosphate may vary depending on the amount of ammonia added. After drying and granulation, monoammonium phosphate and diammonium phosphate are used as such as fertilizer in a composition intended for agriculture.

Example 7 Preparation of an NPK-type Composition

The dicalcium phosphate prepared according to Example 1 can be used for the preparation of NPK composition. The dicalcium phosphate was mixed with a solution of sulfuric acid (1 molar equivalent relative to the amount of dicalcium phosphate) and then with ammonia and potassium chloride. The amounts of ammonia and potassium chloride added are determined according to the desired nitrogen and potassium contents in the final NPK composition. NPK compositions 15/15/15, 10/10/10, 10/5/10 and 20/20/20 have been prepared in particular. The phosphorus and potassium values represent the amount of oxide in the form of P205 or K20 that would have been present in the composition if all the phosphorus or elemental potassium had been oxidized in these forms. The nitrogen value is that by weight of elemental nitrogen in the composition.

Example 8 Example 1 was reproduced from a phosphate rock comprising 2.3% by weight of magnesium. The dicalcium phosphate obtained had the same characteristics as those of the dicalcium phosphate of Example 1 in terms of levels of radioactive elements and cadmium. In addition, less than 0.7% by weight of the magnesium present in the phosphate rock initially was present in this dicalcium phosphate.

Example 9

The purified calcium chloride solution (CaCl 2 P) obtained in Example 1 is treated with a sulfuric acid solution (96% by weight) to form gypsum dihydrate CaSO 4, 2H 2 O and a solution of hydrochloric acid. The gypsum dihydrate CaSO 4, 2H 2 O is analyzed and the contents of metals and radioactive elements are listed below in Table 3. The gypsum dihydrate CaSO 4, 2H 2 O comprises a CaO content of 32.7% by weight and S0 3 of 46%. , 4% by weight.

Table 3 - Content of metals (in ppm) and radioactive elements (Bq / kg) in gypsum dihydrate CaSO 4, 2H 2 O according to Example 9

The process according to the present invention allows the preparation of gypsum having a very low radioactive element content.

EXAMPLE 10 Example 1 is repeated using as ash source ashes resulting from the calcination of sewage sludge. The phosphate content in the phosphate source is 23.6% by weight P 2 O 5 of the phosphate source. The phosphate salt obtained is a dicalcium phosphate comprising a phosphate content of 33.1% by weight of P205 and 15% by weight of calcium in dicalcium phosphate. The contents of cadmium, chromium and mercury in the DCP obtained are respectively 0.28 ppm, 50 ppm and less than 0.1 ppm. The contents of radioactive elements are similar to those obtained for the DCP obtained in Example 1.

Claims (48)

claims A phosphate salt in solid form of the formula Mn (HPO 4) y · ZH 2 O wherein M is Na, K, NH 4, n = 2, and y = 1; or M is Ca, n = 1, y = 1; or M is Al or Fe, n = 2, y = 3; and wherein z is 0, 1 or 2; said phosphate salt having a phosphate content expressed as P205 content of between 30 and 50% by weight of the phosphate salt, preferably 36 to 45% by weight, characterized in that the cadmium content in said salt of phosphate, is less than 0.40 ppm. 2. phosphate salt according to claim 1 characterized in that the Ra226 content in said phosphate salt is less than 100 Bq / kg, preferably less than 50 Bq / kg, preferably less than 10 Bq / kg, in particular lower than at 5 Bq / kg. 3. phosphate salt according to claim 1 or 2 characterized in that the magnesium content is less than or equal to 20 ppm. 4. Phosphate salt according to any one of the preceding claims, characterized in that the uranium content in said phosphate salt is less than 1500 Bq / kg, preferably less than 1000 Bq / kg, in particular less than 800 Bq / kg. kg, the uranium content being determined by the respective U234, U235 and U238 contents. 5. phosphate salt according to any one of the preceding claims characterized in that the content of Pb210 in said phosphate salt is less than 1500 Bq / kg, preferably less than 1000 Bq / kg, preferably less than 800 Bq / kg. , in particular less than 500 Bq / kg. 6. Phosphate salt according to any one of the preceding claims characterized in that the content of polonium Po210 in said phosphate salt is less than 300 Bq / kg, preferably less than 200 Bq / kg, preferably less than 150 Bq / kg. 7. phosphate salt according to any one of the preceding claims, characterized in that the phosphate salt is a calcium phosphate salt preferably having a calcium content of between 15 and 30% by weight. 8. phosphate salt according to any one of the preceding claims, characterized in that it is in the form of aggregates of solid particles having a diameter of between 500 μm and 5 mm, advantageously between 500 μm and 3 mm, preferably between 1 mm and 2 mm. 9. phosphate salt according to any one of claims 1 to 7, characterized in that it is in the form of aggregates of solid particles having a diameter of less than 500 μm, advantageously a diameter of between 50 μm and 500 μm, preferably between 100 pm and 200 pm. 10. Phosphate salt according to any one of the preceding claims, characterized in that it also has one or more of the following metal impurity contents: the strontium content is less than 280 ppm or the nickel content is less than 3. ppm or the thallium content is less than 5 ppm or the lead content is less than 3 ppm or a manganese content less than 15 ppm or less than 3 ppm molybdenum content. 11. phosphate salt according to any one of the preceding claims characterized in that it is produced from a phosphate source selected from the group consisting of phosphate ore or secondary sources of phosphate such as ash or any other raw material containing more than 10% of phosphate, expressed as the content by weight of P205 in the source of phosphate. 12. Use of a phosphate salt according to any preceding claim as an ingredient in a composition intended for agriculture, in a food composition, or as starting material for the preparation of phosphoric acid, monocalcium phosphate, mono-dicalcium phosphate, single superphosphate or triple superphosphate, ammonium phosphate salts, potassium phosphate salts, or fertilizer compounds comprising a phosphate group. Process for the preparation of a phosphate salt according to any one of the preceding claims 1 to 12 comprising the following steps: a) digestion of a phosphate source with a first aqueous solution of hydrochloric acid with formation of an etching liquor consisting of an aqueous phase comprising phosphate ions and chloride ions in solution, and a first insoluble solid phase containing impurities, b) a first separation between the aqueous phase comprising phosphate ions and chloride ions in solution and the first insoluble solid phase containing impurities, c) neutralization of said aqueous phase comprising phosphate ions and chloride ions in solution at a pH sufficient to form an aqueous medium comprising chloride ions and to precipitate the ions phosphates in the form of said phosphate salt, d) a second separation between said aqueous medium comprising the ions chl and said phosphate salt, characterized in that steps a) and b) are carried out at a temperature between 50 ° C and 70 ° C. 14. Method according to the preceding claim characterized in that step a) has a duration less than one hour, preferably less than 30 minutes, preferably between 5 and 20 minutes. 15. Method according to any one of claims 13 or 14 characterized in that the neutralization performed in step c) has a duration of less than four hours, preferably less than two hours, preferably less than one hour. 16. Method according to any one of claims 13 to 15 characterized in that said phosphate source comprises a magnesium content greater than 1.5% by weight based on the total weight of the phosphate source. 17. Method according to any one of claims 13 to 16 characterized in that said phosphate salt contains less than 5% by weight of magnesium initially included in said source of phosphate. 18. A process according to any one of claims 13 to 17 characterized in that said phosphate source of step a) is selected from the group consisting of phosphate ore or secondary phosphate sources such as ash or any other raw material containing more than 10% of phosphate expressed as the content by weight of P205 in the source of phosphate. 19. Method according to any one of claims 13 to 18 characterized in that said first aqueous solution of hydrochloric acid has a concentration of HCl less than or equal to 15% by weight, preferably 8 to 13% by weight, preferably 12% by weight. 20. Process according to any one of claims 13 to 19 characterized in that in the etching liquor, the molar ratio between HCl and Ca is between 1.2 and 2.6. 21. Method according to any one of claims 13 to 20 characterized in that said neutralization of step c) is carried out in the presence of calcium carbonate, calcium hydroxide, calcium oxide or a or more calcium, sodium or ammonium salts. 22. Method according to any one of claims 13 to 21 characterized in that said neutralization of step c) is carried out in the presence of calcium carbonate, calcium hydroxide, calcium oxide or a calcium salt soluble in water; said precipitated phosphate salt being a calcium phosphate salt and said aqueous medium comprises chloride ions and calcium ions. 23. Method according to any one of claims 13 to 22 characterized in that in step c), the pH is less than 5, preferably between 2.0 and 5.0, preferably between 2.5 and 4 , 0, preferably between 2.5 and 3.0. 24. Method according to any one of claims 13 to 23 characterized in that said neutralization of step c) is carried out in the presence of calcium carbonate, calcium hydroxide, calcium oxide or a calcium salt soluble in water; said precipitated phosphate salt being a calcium phosphate salt and said aqueous medium is a calcium chloride solution having a calcium chloride content of between 8 and 20% by weight of the solution, preferably between 12 and 20% by weight preferably 15% by weight. 25. A method according to any one of claims 13 to 24 characterized in that a basic compound is added to said aqueous medium comprising chloride ions obtained in step d) to form a purified aqueous phase comprising chloride ions and pH included between 8 and 12, preferably between 9 and 10, and a solid phase comprising impurities. 26. Method according to any one of claims 13 to 25 characterized in that said neutralization of step c) is carried out in the presence of calcium carbonate, calcium hydroxide, calcium oxide or a calcium salt soluble in water; said precipitated phosphate salt being a calcium phosphate salt and said aqueous medium comprises chloride ions and calcium ions forming a calcium chloride solution; and in that a basic compound selected from calcium hydroxide, calcium oxide and calcium, sodium, potassium or ammonium salts is added to said calcium chloride solution to form a purified solution calcium chloride having a pH of from 8 to 12, and a solid phase comprising impurities including magnesium salts. 27. Method according to any one of the preceding claims 13 to 26 characterized in that it further comprises the steps: e) an attack of all or part of said phosphate salt obtained in step d) by an aqueous solution of strong acid to form a suspension of a first phosphoric acid in solution and a second solid phase, f) a third separation between the first phosphoric acid and said second solid phase. 28. The method of claim 27 characterized in that in step e) the molar ratio between the aqueous solution of strong acid and said phosphate salt obtained in step d) is between 0.6 and 1.6 . 29. A method according to any one of claims 27 or 28 characterized in that the aqueous solution of strong acid used in step e) is an aqueous solution of sulfuric acid and the second solid phase formed in step e ) comprises calcium sulfate hemihydrate, calcium sulfate dihydrate or a mixture thereof. 30. Method according to any one of claims 27 to 29 characterized in that the second solid phase obtained in step f) and comprising calcium sulfate hemihydrate, calcium sulfate dihydrate or a mixture thereof, is mixed with an acid solution to form a solid phase comprising calcium sulfate dihydrate and an acidic aqueous phase comprising phosphate ions. 31. Method according to the preceding claim characterized in that the acid solution is a sulfuric acid solution and the second solid phase obtained in step f) is also mixed with said purified aqueous phase according to claim 25 or 26, or said an aqueous medium comprising chloride ions obtained in step d) or said aqueous medium comprising chloride ions and calcium ions according to claim 24, or mixtures thereof to form a solid phase comprising calcium sulfate dihydrate and an aqueous phase comprising hydrochloric acid. 32. The method of claim 30 or 31 characterized in that the aqueous phase comprising hydrochloric acid is recycled to form all or part of said first aqueous hydrochloric acid solution used in step a). 33. Method according to any one of claims 13 to 32 characterized in that it is carried out continuously. 34. Use of the phosphate salt according to claim 12 characterized in that said phosphate salt is prepared by the process as defined according to any one of claims 13 to 33. 35. Use according to claim 12 or 34 characterized in that said composition intended for agriculture is a liquid or water-soluble fertilizing composition or said food composition is a composition for animal feed or livestock or human. 36. A composition comprising a phosphate salt according to any one of claims 1 to 11. 37. Composition according to the preceding claim characterized in that it is a food composition and further comprises a basic food substance. 38. A process for the preparation of the composition according to the preceding claim characterized in that it comprises the steps: A) preparation of said phosphate salt according to any one of claims 1 to 11 preferably by the method according to any one of claims 13 to 33, B) mixing said phosphate salt obtained in A) with a basic food substance. 39. A composition according to claim 36 characterized in that it is a composition intended for agriculture further comprising a potassium source and / or a nitrogen source to form preferably a fertilizer composition, in particular a liquid fertilizer composition. , or a composition partially or wholly soluble in water. 40. Process for the preparation of the composition according to the preceding claim, characterized in that it comprises the steps: A) preparation of said phosphate salt according to any one of claims 1 to 11, preferably by the process according to any one of claims 13 to 33, B) mixing said phosphate salt with a potassium source and / or a nitrogen source; 41. A process for the preparation of a single superphosphate (SSP) comprising the steps of: A) preparing a phosphate salt according to any one of claims 1 to 11, preferably by the method according to any one of claims 13 to 33, B) addition of sulfuric acid and optionally phosphoric acid, water, to said phosphate salt obtained in A) to form SSP. 42. Process for preparing monoammonium phosphate (MAP) or diammonium phosphate (DAP) comprising the steps of: A) preparing a phosphate salt according to any one of claims 1 to 11, preferably by the process according to any one of claims 13 to 33, B) adding sulfuric acid and ammonia or an ammonium salt to said phosphate salt obtained in A) to form monoammonium phosphate or diammonium phosphate, preferably the sulfuric acid is added beforehand to the ammonia. 43. A process for preparing an NPK-type composition comprising the steps of: A) preparing a phosphate salt according to any one of claims 1 to 11, preferably by the method according to any one of claims 13 at 33, B) adding sulfuric acid, a source of nitrogen or a source of potassium or both to said phosphate salt obtained in A) to form said NPK composition. 44. A process for preparing phosphoric acid comprising the steps of: A) preparing a phosphate salt according to any one of claims 1 to 11, preferably by the method according to any one of claims 13 to 33, B) adding sulfuric acid to said phosphate salt obtained in A) and optionally water to form phosphoric acid, the molar ratio of sulfuric acid to said phosphate salt is 0.9 to 1.1 . 45. A process for the preparation of a triple superphosphate (TSP) comprising the steps of: A) preparing a phosphate salt according to any one of claims 1 to 11, preferably by the process according to any one of claims 13 to 13. 33, B) addition of phosphoric acid and optionally sulfuric acid, water, said phosphate salt obtained in A) to form the TSP. 46. A process for preparing monocalcium phosphate (MCP) comprising the steps of: A) preparing a phosphate salt according to any one of claims 1 to 11, preferably by the process according to any one of claims 13 to 33, B) addition of phosphoric acid to said phosphate salt obtained in A) to form the monocalcic phosphate, the weight ratio between the phosphoric acid and said phosphate salt is between 0.5 and 0.65. 47. A process for preparing mono-dicalcium phosphate (MDCP) comprising the steps of: A) preparing a phosphate salt according to any one of claims 1 to 11, preferably by the process according to any one of the claims 13 to 33, B) adding phosphoric acid to said phosphate salt obtained in A) to form the monocalcium phosphate, the ratio by weight between the phosphoric acid and said phosphate salt is less than 0.5. 48. A process for the preparation of potassium phosphate comprising the steps of: A) preparing a phosphate salt according to any one of claims 1 to 11, preferably by the process according to any one of claims 13 to 33, B) adding a source of potassium to said phosphate salt obtained in A) and optionally an acid to form said potassium phosphate.