Method for removing impurities from phosphate concentrate, high purity phosphate concentrate and use of a high purity phosphate concentrate

Abstract

The present invention relates to a method for removing impurities from phosphate concentrate, comprising leaching the phosphate concentrate with an acid and a reducing solution under controlled temperature, time period and pH to obtain a high purity concentrate. The invention further relates to the high purity phosphate concentrate obtained by said method and to use of the high purity phosphate concentrate in manufacturing phosphoric acid or phosphate products.

Description

METHOD FOR REMOVING IMPURITIES FROM PHOSPHATE CONCENTRATE, PHOSPHATE CONCENTRATE WITH A HIGH DEGREE OF PURITY, AND USE OF A PHOSPHATE CONCENTRATE WITH A HIGH DEGREE OF PURITY FIELD OF APPLICATION

[0001] The present invention relates to the dissolution and removal of metallic compounds, mainly oxides, carbonates and silicates, which are present in phosphate concentrates, as well as in phosphate rocks, and are solubilized during the phosphoric acid production process and contaminate fertilizer products. BACKGROUND OF THE INVENTION

[0002] Over the years, phosphoric acid consumption has increased due to its vast number of applications. Phosphoric acid can be used, for example, in the manufacture of acidulants for soft drinks (especially cola), sweets, salad dressings, jellies, biological yeasts, sugar refining, vegetable oil stabilization, chocolate factories, and in the food and pharmaceutical industries for insulin production, antibiotic production, fortifiers, and more. In the chemical industry, phosphoric acid is used in the manufacture of agricultural fertilizers, bi-calcium phosphate for animal feed, charcoal production, detergent formulations, pickling solutions, and rust inhibitors. Phosphoric acid is also used in biological effluent treatment (flocculation and precipitation) and in the chemical or electrochemical polishing of aluminum parts.

[0003] According to “LAPIDO-LOUREIRO, FEV; MELAMED R. Phosphorus in Brazilian agriculture: a mining-metallurgical approach”, the fertilizer industry is responsible for the consumption of approximately 90% of the industrial purity phosphoric acid produced in Brazil, with the remaining 10% being used by other segments.

[0004] Currently, phosphoric acid is obtained in industry by two different processes. In the first, the wet process, sedimentary rocks or soils containing the mineral apatite (phosphate rocks) react with inorganic acids, typically sulfuric acid, to form phosphoric acid and other byproducts. In the second process, the dry process, phosphorus is burned in open air, forming P4O10, which then undergoes hydrolysis, producing phosphoric acid. Of these two methods, the most commonly used method for obtaining phosphoric acid is the wet process.

[0005] Commercially available phosphate rocks and phosphate concentrates are generally contaminated with high levels of metallic elements that are partially or completely solubilized in the phosphoric acid manufacturing process, contaminating the final phosphate products.

[0006] The processing of these rocks or concentrates through mineral or chemical treatment has been a challenge for current researchers in the fertilizer industry.

[0007] The importance of the rock or concentrate treatment and purification process has also been very important due to the economic aspect, since through this preliminary treatment it is possible to increase the mineable reserves of phosphate ores and reduce the volume of material in the dump (a location selected for depositing excess material resulting from the excavation of cuts).

[0008] Furthermore, the treatment of rocks and concentrates allows for the reduction of impurity content, which is highly harmful in the manufacture of fertilizers and animal feed products.

[0009] Depending on the origin of the phosphate rock, purification treatment allows the removal of toxic and radioactive elements from the food chain, such as cadmium, arsenic, thorium, uranium, among others.

[0010] No less important, the purification treatment process of phosphate rocks and concentrates reduces phosphorus losses. that form insoluble compounds with some metals and are discarded in phosphogypsum, which is a byproduct of the production of phosphoric acid in the fertilizer and phosphate fertilizer industries.

[0011] During the manufacture of phosphoric acid with contaminated rocks and concentrates, there are several effects that negatively affect the phosphoric acid manufacturing process, increasing the cost and quality of the product, such as increased acid viscosity, increased filtration rate, need for additives to improve gypsum crystallization, increased heat exchanger cycling and incrustations, and also contamination of the final products, including contamination of the phosphogypsum generated in the plants.

[0012] The removal of impurities from phosphate rocks and concentrates through the acid or alkaline leaching process, to solubilize metallic impurities, has become a common practice and several publications have been found in the literature.

[0013] The use of dilute hydrochloric acid solutions in the process of leaching impurities from rocks or concentrates has become increasingly popular due to the high solubility of some metals in hydrochloric acid. For example, the solubility of ferric chloride is approximately 30 times greater than that of ferric sulfate.

[0014] During the leaching process, calcium carbonate present in rocks and concentrates is generally dissolved, producing highly soluble calcium chloride. When sulfuric acid is used, calcium reacts with sulfate, producing insoluble calcium sulfate, which contaminates the concentrate.

[0015] As is known in the art, several types of acids can be used in the process of leaching impurities from phosphate rock through hydrometallurgical processes, in which the rock comes into contact with a solution slightly acidified by sulfuric acid, acid nitric or hydrochloric acid without attacking the apatite.

[0016] The choice of acid depends on the minerals present in the concentrate, and how these minerals are released depends on the rock's grain size. For example, minerals present in the form of carbonatite cannot be leached with sulfuric acid due to the formation of completely insoluble calcium sulfate.

[0017] However, the amount of contaminating elements present in phosphate rocks is generally extremely high, such as the rock from the Catalão Alkaline Complex in the state of Goiás, Brazil, which contains more than 30 contaminating elements, including Ca, Sr, Mn, Mg, Zn, Fe, Ni, Cu, Sn, Na, K, Li, Al, U, Th, and Si, as well as rare earths and other heavy metals such as Pb, As, Cd, and Hg, among others. Most of these elements are solubilized during the production of phosphoric acid and are present throughout the phosphorus utilization chain, both in agriculture and in animal feed.

[0018] Some phosphate rocks, such as the source rock from the Catalão deposits, have a high iron content as a contaminant, primarily in the form of various iron oxides, such as hematite, limonite, goethite, and magnetite, with varying oxidation states. The dissolution of these iron oxides via leaching of phosphate rock has been investigated in acidic solutions with controlled pH. Various effects of particle size, residence time, temperature, and degree of agitation have been studied. The dissolution rate depends on the concentration of the H ion. + and the reaction temperature. The dissolution mechanism always follows an exothermic path. In some cases, the activation energy for the solubilization reaction reaches 13.63 kJ / mol, and the total iron removal from the ore reaches 92% in a time of up to 120 minutes with 12M HCl solution.

[0019] The basic iron dissolution reaction is as follows: Fe2O3+ 6H+ + Cl- 2FeCl3+ 3H2O (4)

[0020] To illustrate the field of this invention, below are some examples of patents that are directly or indirectly related to this work.

[0021] In the case of patent CA2965441C, a hydrometallurgical process is presented provided for the selective leaching of metals from ore, concentrates, tailings, slags or other contaminant-bearing solids, combining simultaneous leaching with commercial recovery of the contaminants and recycling of a portion of the leaching agent.

[0022] Patent KR101239026B1 discloses a method for leaching metals from ores comprising: leaching the ore in the presence of hydrochloric acid to form a soluble metal chloride salt in the leaching solution, adding sulfuric acid to the leaching solution, and a method is provided which includes recovering a metal sulfate salt from a leaching solution and regenerating hydrochloric acid.

[0023] The process presented in patent JPH11510559A comprises subjecting an ore or concentrate to oxidation under pressure in the presence of oxygen and an acidic solution containing halogen and sulfate or hydrogen sulfate or H2SO4 ions.

[0024] Patent CN106672930B relates to a method for directly leaching medium-low grade phosphorite with hydrochloric acid to prepare phosphoric acid via a wet process, which directly fills medium-low grade phosphorite powder into an ore column, prepares wet process phosphoric acid by leaching with hydrochloric acid, and then reacts the leachate with sulfuric acid to generate phosphogypsum.

[0025] In US Patent 3,490,811, phosphate rock is acidified in situ by injecting the acidifying agent into a subsurface phosphate rock positioned through an injection well. The phosphoric acid formed by the acidulation reaction is recovered in a production tank. Acidulation can be carried out with conventional acids such as sulfuric acid, nitric acid and hydrochloric acid.

[0026] US Patent 9,745,193 B2 describes a hydrochloric acid impurity removal process applied directly after phosphoric acid production. In this case, iron precipitation is performed directly in the phosphoric acid solution.

[0027] Patent RU2663034 C2 relates to the leaching processing of phosphorus-containing ores for the recovery of at least one metal. The method for concentrating phosphate compounds is described, comprising the steps of: dissolving the raw material containing sewage sludge ash, containing phosphorus and at least one metal such as iron or aluminum, in the liquid containing a hydrochloric acid solution.

[0028] The method presented in international publication WO2014178788A1 for removing impurities and concentrating phosphate compounds involves leaching the material in hydrochloric acid. The dissolved metals are separated, thus forming a first leaching solution. A molar ratio of phosphorus to the sum of iron and aluminum in the first leaching solution is maintained at greater than 1.0.

[0029] US 3,479,139 A describes a process for purifying phosphoric acid from iron impurities by reducing iron (III) contained in phosphoric acid to iron (II) using reducing agents. The change in the oxidation state of iron favors the removal of the element in the purification of phosphoric acid.

[0030] US 3,975,178 A refers to an improved process for the partial purification of wet-process phosphoric acid. The crude acid is treated with methanol and ammonia to precipitate most of the metallic impurities, primarily iron.

[0031] Document US 4,382,916 A presents a process of Recovery of hydrochloric acid as a byproduct of high-quality ferrous sulfate in various forms of hydrate from residual pickling liquor containing ferrous chloride. The residual hydrochloric liquor is concentrated in a crystallizer, and the free HCl reacts to form ferrous chloride, which precipitates.

[0032] The invention described in US 3,310,374 demonstrated that ferric ion is very difficult to remove from phosphoric acid, likely due to the formation of strong ferric-phosphate ion complexes. This difficulty is demonstrated by the fact that cation exchange resins do not remove ferric ion from phosphate solutions, even when iron is the only metal ion in the solution.

[0033] Chinese document CN113735081 A presents a process for the efficient recovery of a wide range of metals contained in phosphate minerals by leaching this ore with a dilute aqueous mixture of sulfuric and hydrochloric or nitric acid and precipitating phosphate values ​​as dicalcium phosphate.

[0034] In addition to the patent documents presented above, the following articles contribute to the understanding of the present invention in relation to the effects of reductive leaching processes, related to the solubilization of the iron element.

[0035] For example, the paper published by the "Depariameni of Metallurgical Engineering, Institut Teknologi Bandung, West Java, Indonesia, M.R.Kumiawan, et. al., examined the effectiveness of the method of producing synthetic rutile from ilmenite by means of a reductive leaching of ilmenite in hydrochloric acid.

[0036] The report, "New formulations for iron oxide dissolution. Hydrometallurgy, 27: 339-360, Chiarizia, R. and Horwitz", presents the dissolution of synthetic goethite containing 59% by weight of Fe in mineral acid solutions (HC1, HNO3, H2SO4). The effect of various reducing agents on the rate of iron dissolution by inorganic acids was evaluated.

[0037] The report, "Dissolution Kinetics of Iron Oxide in Clay in Hydrochloric Acid Solutions, Department of Materials and Metallurgical Engineering, Bangladesh, UK Sultana," presents a leaching process of a clay sample containing 8.15 wt.% FeiCh and 27.49 wt.% AI2O3 in hydrochloric acid. The effects of acid concentration, time, and temperature on the dissolution rate of iron contained in the clay sample were investigated.

[0038] The report "Reductive leaching of ilmenite ore in hydrochloric acid for the preparation of synthetic rutile, MHH Mahmoud, Central Metallurgical R&D Institute PO Box 87, Helwan, Cairo" presents the reactivity of ilmenite ore during leaching with hydrochloric acid. The leaching power can be significantly increased by solution reduction using metallic iron or a reducing agent.

[0039] For the leaching and removal of some metals in soluble form, such as iron, manganese, and some rare earths, it is essential to use oxidizing acid leaching or reducing acid leaching. This requires leaching with a mixture of the acid solution and an oxidizing or reducing agent solution.

[0040] The purpose of this invention is to remove various impurities from phosphate rocks or concentrates, which has the objective of manufacturing phosphoric acid, via acid leaching with a reducing substance.

[0041] As will be further detailed below, the present invention aims to solve the problems of the prior art described above in a practical and efficient manner. SUMMARY OF THE INVENTION

[0042] A first objective of the present invention is to provide a method for removing impurities from phosphate concentrate by acid leaching a phosphate concentrate with an acid and a reducing solution under controlled temperature, time and pH.

[0043] A second objective of the present invention relates to the phosphate concentrate with a high degree of purity prepared using the claimed method.

[0044] A third objective of the present invention relates to the use of the phosphate concentrate with a high degree of purity for the manufacture of phosphoric acid or phosphate products. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The figure shows the experimental scheme carried out in all acid leaching tests of the concentrate. DETAILED DESCRIPTION OF THE INVENTION

[0046] This invention relates to the purification of phosphate concentrates for the production of phosphoric acid or phosphate products. More specifically, it relates to the removal of iron, aluminum, magnesium, calcium, and other impurities present in phosphate rocks that affect the industrial production of phosphoric acid or phosphate products using the wet process.

[0047] Using the method of the present invention, a high-purity phosphate concentrate can be obtained from highly contaminated phosphates containing oxides of iron, aluminum, magnesium, calcium, and rare-earth elements, among others, by leaching the phosphate with dilute acid solutions. The phosphate concentrate can be phosphate rock or tailings produced in phosphate industries.

[0048] According to the invention, the purity of the concentrate is related to the quality of the phosphoric acid. In one embodiment, to obtain a higher-quality phosphoric acid, the P2O5 concentration in the phosphate concentrate is equal to or greater than approximately 32% by weight, and the concentration of impurities such as iron, aluminum, and magnesium must be equal to or less than approximately 0.2% by weight.

[0049] Ideally, a concentrate with a high degree of purity presents typically a P2O5 concentration between about 32% and about 36.5% by weight, preferably between about 33% and about 36% by weight and an impurity concentration ranging from 0% to about 0.2% by weight.

[0050] More specifically, the method described here comprises the phosphate concentrate leaching step, in which the phosphate concentrate is mixed with hydrochloric acid and a reducing solution under controlled temperature, time and pH, forming a pulp.

[0051] In one embodiment of the invention, the mixing step occurs at a temperature ranging from about 55 to about 95°C for a time of about 40 to about 80 minutes. The acid used is preferably a dilute solution of hydrochloric acid, nitric acid, sulfuric acid, citric acid, oxalic acid, formic acid, or fluorosilicic acid, or combinations thereof, having a concentration of about 1 to about 7 molar so as to maintain the mixture in the pH range of about 0.2 to about 6.

[0052] In a preferred embodiment, the acid used is a dilute solution of hydrochloric acid, nitric acid, sulfuric acid, or fluorosilicic acid or combinations thereof, having a concentration of about 1 to about 5 molar, so as to maintain the mixture in the pH range of about 0.5 to about 5.

[0053] In an even more preferred embodiment, the acid used is a dilute solution of hydrochloric acid and the temperature of the mixture varies between about 70 and 85°C, even more preferably about 80°C, for a period of about 50 to 70 minutes, even more preferably about 60 minutes.

[0054] The reducing solution of the present invention may be a sodium dithionite solution containing from about 5 to about 50% concentration. Alternatively, the reducing solution comprises sodium hydrosulfite in the form of a crystalline powder or in the form of a solution.

[0055] The pulp then undergoes a filtration stage, forming a cake. Typically, a vacuum filter, such as a vacuum belt filter, is used.

[0056] Afterwards, the cake is washed to remove the acidity and dried.

[0057] In another embodiment, the method comprises a second leaching step. The pulp obtained after the first leaching step is mixed again with an acid and a reducing solution at a temperature ranging from about 55 to 95°C (135 to 195°F) for a period of about 40 to 80 minutes. The acid used in the second leaching step is preferably a dilute solution of hydrochloric acid, nitric acid, sulfuric acid, citric acid, oxalic acid, formic acid, or fluorosilicic acid, or combinations thereof, and even more preferably, a dilute solution of hydrochloric acid, nitric acid, sulfuric acid, or fluorosilicic acid, or combinations thereof.

[0058] In a preferred embodiment, the acid used is a dilute solution of hydrochloric acid and the temperature of the mixture varies between about 70 and 85°C, even more preferably about 80°C, for a period of about 50 to 70 minutes, even more preferably about 60 minutes.

[0059] Alternatively, the second leaching step comprises mixing the pulp obtained in the first leaching step with an acid and an organic chelating agent.

[0060] Preferably, the organic chelating agent is selected from citric acid, oxalic acid, ethylenediaminetetraacetic acid (EDTA), dimercaptosuccinic acid, tartaric acid, sodium citrate, or a combination thereof. This chelating agent sequesters metal ions, such as calcium, magnesium, copper, iron, and manganese, found especially in water, by aggregating them into its chemical structure. This means that this compound removes metals. free heavy metals present in the medium, thus reducing the reactivity of these metals with the other components in the solution.

[0061] Furthermore, the leaching solution, which is a mixture of acid, preferably hydrochloric acid, with a reducing solution and which may contain a small amount of phosphorus, can be recovered in the form of dicalcium phosphate for animal feed or fertilizer phosphates.

[0062] Recovery is achieved by neutralizing the acidic pulp with a base, such as calcium hydroxide, to precipitate the dicalcium phosphate together with the purified concentrate.

[0063] From the present method, it is possible to remove a large amount of impurities, such as, for example, from about 35 to about 55% by weight of FeiCb, from about 30 to about 100% by weight of AI2O3 and from about 80 to about 100% by weight of MgO.

[0064] Furthermore, a removal rate of phosphoric acid-soluble FeiCb of about 60% to about 85% is achieved.

[0065] The following description will be based on a particular embodiment of the invention. As will be clear to anyone skilled in the art, the invention is not limited to such an embodiment. EXAMPLES

[0066] All examples presented in this report were obtained in the laboratory by treating several commercially available phosphate concentrates. The concentrates generally had the following average composition: 33.21 wt.% P2O5, 46.04 wt.% CaO, 3.69 wt.% Fe2O3, 0.36 wt.% Al2O3, 0.35 wt.% MgO, 4.74 wt.% SiO2, and 0.69 wt.% BaO.

[0067] Leaching tests were prepared with this type of phosphate concentrate on a laboratory scale, through acidity-controlled leaching under pre-established conditions of time, temperature, and solid / liquid ratio. After the leaching process, the suspension formed was filtered through a laboratory vacuum filter. The sampled filtrate was used for chemical analysis, and the cake, or purified concentrate, was washed and oven-dried at 110°C for one hour and analyzed. EXAMPLE 1

[0068] A 500 g sample of phosphate concentrate containing the following chemical composition: 35.18 wt% P2O5, 3.716 wt% FeiOs, 0.339 wt% AI2O3 and 0.342 wt% MgO, was subjected to a two-stage acid leaching process. In the first stage, the test was carried out at 80°C for 60 minutes, with a pH controlled between 0.5 and 1, in a pulp containing 20 wt% solids, with 151 grams of HCl (32%) and 70 grams of a sodium dithionite reducing solution (20%). In the second stage, the pulp obtained in the previous stage was subjected to leaching under the same conditions as before and with a controlled pH between 1 and 5, but with 125 grams of a hydrochloric acid solution (32%) and 124 grams of a sodium dithionite reducing solution (20%).The pulp was filtered and the cake obtained, after washing with water to remove acidity, was analyzed, obtaining the following impurity removal results: 41.0% by weight of F 626)3, 34.25% by weight of AI2O3 and 84% by weight of MgO. Considering the fraction of iron soluble in phosphoric acid, the removal of Fe2Ü3 was 67%. EXAMPLE 2

[0069] A concentrate sample containing 42 grams of the same concentrate as in Example 1 was subjected to a two-stage leaching process under the conditions of Example 1. In the first stage, 6.5 grams of 32% HCl solution and 1.60 grams of 20% sodium dithionite reducing solution were added, and in the second stage, only 6.5 grams of 32% HCl and 1.0 grams of ethylenediaminetetraacetic acid (EDTA) were added for the complexation of iron, calcium, and other impurities. The pulp was filtered and washed with an alkaline milk solution. of lime. After filtration of the pulp, the cake obtained was dried and sent for chemical analysis, obtaining the following impurity removal results: 37% by weight of Fe2C>3, 95% by weight of AhCh and 98% by weight of MgO. The content of Fe2C>3 soluble in phosphoric acid was approximately 60% removed. EXAMPLE 3

[0070] In another test, a concentrate sample, approximately 41 grams, was taken and the leaching process was carried out under the same solids, temperature, and time conditions as in Example 1. In this experiment, the HCl / concentrate ratios were increased by using 12.9 grams of HCl and 8.4 grams of a 20% sodium dithionite reducing solution. Thus, the pH control during the test, with only one reaction step, was 0.50, generating a more acidic leaching. The pulp was filtered and washed with milk of lime solution. After filtration, the resulting cake was dried and sent for chemical analysis, yielding the following impurity removal results: 52.6% by weight of Fe2C>3, 95% by weight of Al2Os, and 98% by weight of MgO. The soluble Fe2Ü3 content removed from the rock, considering solubilization in phosphoric acid, was approximately 80%.

[0071] Therefore, from the examples and tests described here, it is possible to prove that the present invention surprisingly and advantageously provides for obtaining a high purity phosphate concentrate obtained from highly contaminated phosphates.

[0072] Consequently, with the method claimed here, it is possible to increase the mineable reserves of phosphate ores, reduce the volume of material in waste, remove toxic and radioactive elements such as cadmium, arsenic, thorium, uranium, among others, from the food chain, and also reduce the loss of phosphorus that forms insoluble compounds with some metals and is discarded in the phosphogypsum.

[0073] Numerous variations affecting the scope of protection of this application are permitted. This reinforces the fact that the present invention is not limited to the particular configurations / embodiments described above.

Claims

CLAIMS 1. Method for removing impurities from phosphate concentrate, characterized by the fact that it comprises the following steps: - leaching the phosphate concentrate, in which the phosphate concentrate is mixed with an acid and a reducing solution at a temperature ranging from about 55 to about 95°C for a period of about 40 to about 80 minutes to form a pulp; - filter the pulp to form a cake; - wash and dry the cake to obtain a phosphate concentrate with a high degree of purity.

2. Method according to claim 1, characterized in that the acid is a dilute solution of hydrochloric acid, nitric acid, sulfuric acid or fluorosilicic acid or combinations thereof, preferably wherein the acid is a dilute solution of hydrochloric acid.

3. The method of claim 1, wherein the reducing solution is a sodium dithionite solution containing from about 5 to about 50% concentration.

4. Method according to claim 1, characterized in that the reducing solution comprises sodium hydrosulfite in the form of a crystalline powder or in the form of a solution.

5. Method according to any one of claims 1 to 4, characterized in that it additionally comprises a second leaching step after obtaining the pulp.

6. The method of claim 5, wherein the second leaching step comprises mixing the pulp with an acid and a reducing solution at a temperature ranging from about 55 to about 95°C for a period of about 40 to about 80 minutes.

7. Method according to any one of claims 1 to 6, characterized in that the leaching steps occur under a temperature ranging from about 70 to 85 °C, even more preferably about 80 °C, for a period of about 50 to 70 minutes, even more preferably about 60 minutes.

8. Method according to claim 6, characterized in that the acid used in the second leaching step is a dilute solution of hydrochloric acid, nitric acid, sulfuric acid or fluorosilicic acid or combinations thereof.

9. Method according to claim 5, characterized in that the second leaching step comprises mixing the pulp obtained in the first leaching step with an acid and an organic chelating agent.

10. Method according to claim 9, characterized in that the organic chelating agent is selected from citric acid, oxalic acid, ethylenediaminetetraacetic acid (EDTA), dimercaptosuccinic acid, tartaric acid, sodium citrate or a combination thereof.

11. Method according to any one of claims 1 to 10, characterized in that the impurities removed from the phosphate concentrate are oxides of iron, aluminum, magnesium, calcium and rare earth elements.

12. The method of claim 11, wherein from about 35 to about 55 wt.% FeiCh, from about 30 to about 100 wt.% AI2O3, and from about 80 to about 100 wt.% MgO are removed.

13. Method according to any one of claims 1 to 12, characterized in that the removal content of phosphoric acid-soluble FeiCh is from about 60% to about 85%.

14. Method according to any one of claims 1 to 13, characterized in that the phosphate concentrate is a phosphate rock or waste produced in phosphate industries.

15. Method according to any one of claims 1 to 14, characterized in that the dilute acid solution has a concentration of about 1 to about 7 molar, preferably about 1 to about 5 molar.

16. Method according to any one of claims 1 to 15, characterized in that in the step of mixing the phosphate concentrate with an acid and a reducing solution the pH varies in the range of about 0.2 to about 6, preferably from about 0.5 to about 5.

17. Phosphate concentrate with a high degree of purity, characterized by the fact that it is produced from the method as defined in any one of claims 1 to 16.

18. Phosphate concentrate according to claim 17, characterized in that it has a P2O5 concentration equal to or greater than about 32% by weight and an impurity concentration equal to or less than about 0.2% by weight.

19. Use of a high-purity phosphate concentrate prepared from the method as defined in any one of claims 1 to 16, characterized in that it is for the manufacture of phosphoric acid or phosphate products.

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