Method for treating phosphate ores containing heavy metals by reverse flotation

Abstract

The present disclosure relates to a method for treating phosphate ores containing heavy metals by reverse flotation. The method comprises adding, to an aqueous suspension of phosphate ore, a monophosphoric ester A of formula (I), R1 – O – P(=O) – (OH)2 (I), wherein R1 is a saturated or unsaturated, linear or branched hydrocarbon chain comprising 6 to 10 carbon atoms, preferably an alkyl group, alone or mixed with a compound B chosen from the group consisting of a monophosphoric ester of formula (II), R2 – O – P(=O) – (OH)2 (II), wherein R2 is a saturated or unsaturated, linear or branched hydrocarbon chain comprising 6 to 18 carbon atoms, preferably an alkyl group, different from the group R1 of the monophosphoric ester A of formula (I), an alcohol, a fatty acid, a fixed oil, a sulphate, a sulphonate, an ether and mixtures thereof.

Description

[0001] PROCESS FOR TREATING PHOSPHATE ORES CONTAINING METALS

[0002] HEAVY BY REVERSE FLOTATION

[0003] TECHNICAL FIELD OF THE INVENTION

[0004] The present invention relates to a process for treating phosphate ores containing heavy metals by reverse flotation in which a monophosphoric ester is used as a collector for the flotation of carbonates. The process according to the invention makes it possible to reduce the heavy metal content of phosphate ores.

[0005] STATE OF THE ART

[0006] Global consumption of phosphates, mainly for the production of phosphoric acid and fertilizers (95%), exceeded 47 million tonnes in 2019 and is expected to reach more than 50 million tonnes in 2023 (USGS). Phosphates are produced by mining phosphoric rocks collected from marine sediment deposits (75%), igneous and metamorphic deposits (15 to 20%), or biogenetic deposits (2 to 3%). The main source of phosphates comes from calcium phosphate apatite ores (Ca5(PO4)3j(F, Cl, OH), whose global reserves are mainly present in North Africa (Morocco), the United States (Florida), Russia, and China. These ores represent approximately 80% of the total global production of phosphate rocks and generally contain between 18% and 35% P2O5.The predominant types of apatites in these ores are Francolite or Colophane, which contain, in addition to calcium phosphate, variable amounts of carbonates (such as calcite, dolomite or magnesite), silicates, clays (illite, kaolinite, smectite, etc.) or even organic residues.

[0007] Phosphate ore processing techniques depend primarily on the type of associated gangue minerals present in the extracted rock. The historical beneficiation method used for half a century has been froth flotation. Sedimentary phosphate ore may contain either carbonate gangue or siliceous and / or silico-carbonate gangue. Silica and phosphates have significantly different physicochemical properties and can be easily separated by flotation. On the other hand, carbonates and phosphates have similar physicochemical properties and behave similarly during flotation operations; they are both found either as floated or depressed products. Usually, the ore is first crushed and suspended in water.Next, the collector is added, often in combination with other additives, such as frothers, pH regulators, dispersants, depressants, and / or stimulants (activators), to separate the valuable minerals from the gangue minerals in the ore. After a conditioning period, the flotation process then begins, which involves blowing air into the suspension to break up the fine ore particles and produce a froth on the surface. Three types of phosphate flotation processes have been developed in the industry to enhance the value of ores: direct flotation, reverse flotation, and the Crago process. In a direct flotation process, the collector makes the surface of the minerals more hydrophobic, while the hydrophilic gangue minerals do not adhere to the gas bubbles and remain in solution. The froth from the mineral collector is then removed and processed.In a reverse flotation process, the valuable minerals in the ore remain in solution and the gangues are carried away in the froth, which is then removed. The Crago process, on the other hand, uses coarse flotation with fatty acids followed by flotation by deoiling and cleaning with amines.

[0008] The objective of these flotation processes is to enrich the mixture with valuable minerals with the highest possible yield. To meet the growing demand for phosphate rock and the gradual depletion of global high-grade phosphate reserves, industries are therefore encouraged to improve enrichment technologies to valorize phosphate ores with lower P2O5 contents.

[0009] The removal of carbonates from phosphate ore has proven particularly difficult, and various nonionic, anionic, and cationic surfactants have been proposed as collectors.

[0010] Fatty acid-based collector systems are generally used to increase the hydrophobicity differences between the material to be retained and the material to be removed. The main primary collectors are based on partially unsaturated fatty acids (C12-C18), which are used at pH 4-5, with phosphoric acid as a depressant. Since fatty acids are poorly soluble in water at this pH, secondary collectors, usually anionic or non-ionic surfactants, are used to improve selectivity and recovery.

[0011] Application WO2018197476 thus describes a mixture of unsaturated fatty acids, pegylated alcohol and a sulfide-based surfactant used at a dose of 500g / t and in a pH range of 4.9 to 5.2.

[0012] A mixture of a fatty acid and an aromatic sulfonic acid used at a dose of 806g / t and in a pH range of 5.0 to 5.2 is described in application WO210162344. US 8,657,118B2 describes a reverse flotation process using mixtures of phosphoric monoester and phosphoric diester at contents of 340g / t and 500g / tonnes in order to enrich ores in P2O5.

[0013] Prior art reverse flotation processes have many disadvantages. They may involve the use of frothing agents, pH regulating agents, or activating agents. In particular, these processes require large quantities of collectors and involve operating in an acidic pH range.

[0014] Furthermore, the ores to be processed may contain elements that can pollute the soil or water tables, such as cadmium (Cd), copper (Cu), arsenic (As), lead (Pb), nickel (Ni) or chromium (Cr).

[0015] Cadmium levels in fertilizers are under particular scrutiny by the European Parliament and other institutions, which require limits on cadmium in phosphate fertilizers. Hence the importance of reducing the concentration of Cd, as well as other heavy metals, such as arsenic.

[0016] Overall, reverse flotation of siliceous and calcareous sedimentary phosphates remains an ongoing industrial challenge. Therefore, finding a suitable collector and / or formulation combining efficient silico-carbonate removal, good flotation yields, and manageable froth properties remains an important priority in this field.

[0017] Calcite increases sulfuric acid consumption in the manufacture of phosphoric acid and fertilizers, and significant levels of toxic impurities have been identified in dolomite ores. Therefore, despite several advances made in recent years to address these issues, improvements are still needed in the phosphoric rock flotation process.

[0018] There is therefore a need for new, simpler and less expensive processes for treating phosphate ores, enabling their P2O5 content to be enriched but also their content of heavy metals, such as cadmium and arsenic, to be reduced.

[0019] SUMMARY OF THE INVENTION

[0020] The present invention relates to a process for treating phosphate ores containing heavy metals by reverse flotation, the process comprising the following steps: - (i) adding to an aqueous suspension of phosphate ore a monophosphoric ester A of formula (I):

[0021] RI- O - P(=O) - (OH)2(I) in which Ri is a hydrocarbon chain, linear or branched, saturated or not, comprising 6 to 10 carbon atoms, preferably an alkyl group, alone or in a mixture with a compound B selected from the group consisting of: a monophosphoric ester of formula (II)

[0022] R2— O — P(=O) — (OH)2(II) in which R2 is a hydrocarbon chain, linear or branched, saturated or not, comprising 6 to 18 carbon atoms, preferably an alkyl group, different from the group Ri of the monophosphoric ester A of formula (I), an alcohol, a fatty acid, a fixed oil, a sulfate, a sulfonate, an ether, and their mixtures;

[0023] - (ii) injection of gas into the aqueous suspension to form foams; and

[0024] - (iii) removal of foams and recovery of the aqueous suspension of treated ore.

[0025] The present invention also relates to the use of such a monophosphoric ester A, alone or in combination with compound B as described herein, for the treatment of phosphate ores containing heavy metals.

[0026] Other aspects of the invention are as described below and in the claims.

[0027] FIGURES

[0028] Figure 1: Example of a laboratory-scale flotation column

[0029] DETAILED DESCRIPTION OF THE INVENTION

[0030] The inventors have developed a process that meets the expressed needs. The proposed process does not have the drawbacks of the prior art. It makes it possible to increase the P2O5 content of the ore by using a smaller quantity of collector. It also makes it possible to reduce the heavy metal content of the ore, in particular cadmium and arsenic. The various embodiments presented throughout the description can be used alone or in combination with each other, without limitation of combination.

[0031] Thus, the invention relates to a method for treating phosphate ores containing heavy metals by reverse flotation, the method comprising the following steps:

[0032] - (i) addition to an aqueous suspension of phosphate ore of a monophosphoric ester A of formula (I):

[0033] RI - O - P(=O) - (OH)2(I) in which Ri is a hydrocarbon chain, linear or branched, saturated or not, comprising 6 to 10 carbon atoms, preferably an alkyl group, alone or in a mixture with a compound B selected from the group consisting of: a monophosphoric ester of formula (II):

[0034] R2— O — P(=O) — (OH)2(II) in which R2 is a hydrocarbon chain, linear or branched, saturated or not, comprising 6 to 18 carbon atoms, preferably an alkyl group, different from the group Ri of the monophosphoric ester A of formula (I), an alcohol, a fatty acid, a fixed oil, a sulfate, a sulfonate, an ether, and their mixtures;

[0035] - (ii) injection of gas into the aqueous suspension to form foams; and

[0036] - (iii) removal of foams and recovery of the aqueous suspension of treated ore.

[0037] Advantageously, the treatment method according to the invention makes it possible to reduce the content of heavy metals present in phosphate ores such as Cadmium, Arsenic, Lead, Nickel, Chromium, Copper and Zinc, in particular Cadmium and Arsenic.

[0038] In particular, the method according to the invention can make it possible to eliminate at least 60% by weight of the heavy metals present in the phosphate ore. Advantageously at least 70% by weight of the heavy metals are eliminated, particularly advantageously at least 80% of the heavy metals are eliminated.

[0039] In particular, the method according to the invention makes it possible to eliminate at least 60% by weight of the cadmium and arsenic present in the phosphate ore, advantageously at least 70% by weight of the cadmium and arsenic are eliminated, particularly advantageously, at least 80% of the cadmium and arsenic are eliminated.

[0040] The advantages of the process according to the invention make it particularly applicable to the treatment of phosphate ores on an industrial scale.

[0041] Step (i)

[0042] Step (i) comprises adding to an aqueous suspension of phosphate ore a monophosphoric ester A of formula (I):

[0043] RI - O - P(=O) - (OH)2(I) in which Ri is a hydrocarbon chain, linear or branched, saturated or not, comprising 6 to 10 carbon atoms, preferably an alkyl group, alone or in a mixture with a compound B selected from the group consisting of: a monophosphoric ester of formula (II):

[0044] R2— O — P(=O) — (OH)2(II) in which R2 is a hydrocarbon chain, linear or branched, saturated or unsaturated, comprising 6 to 18 carbon atoms, preferably 6 to 10 carbon atoms, preferentially an alkyl group, different from the group Ri of the monophosphoric ester A of formula (I), an alcohol, a fatty acid, a fixed oil, a sulfate, a sulfonate, an ether and their mixtures.

[0045] Aqueous suspension of phosphate ore

[0046] Phosphate ore, also called “phosphate rock”, refers to an exogenous rock containing phosphate. The phosphate ore useful in the present invention can be taken from the Khouribga site (Bni-Amir), Morocco.

[0047] Typically, phosphate ore has a P2O5 content ranging from 18 to 35% by weight, relative to the total weight of the phosphate ore. The aqueous suspension is typically prepared by mixing phosphate ore with water. The phosphate ore is in the form of particles. Advantageously, the ore particles have a size ranging from 40 pm to 125 pm, or from 40 pm to 160 pm. The particle size is determined by sieving. Thus, before mixing with water, the phosphate ore is typically pre-ground and sized.

[0048] The mass percentage of phosphate ore in the aqueous suspension, also called pulp, typically varies from 10% to 30%, preferably from 10% to 20%, the percentage being expressed as a % by weight relative to the total weight of the phosphate ore suspension.

[0049] Monophosphoric ester A of formula (I), alone or in mixture with compound B, acts as a “collector” for the flotation of carbonates.

[0050] The "collector" has the ability to adsorb on the surface of the carbonate particles present in the phosphate ore, allowing their separation and elimination during subsequent stages of the process.

[0051] The “collector” will also form a complex with the heavy metals present in the ore, said complex then being at least partially eliminated during the subsequent stages of the process.

[0052] Monophosphoric ester A

[0053] The nature of the hydrocarbon chain, preferably of the alkyl group, in particular the length of the hydrocarbon chain, preferably of the alkyl chain and the presence of branches, can influence the ability of the monophosphoric ester to interact with the carbonates and heavy metals present in the phosphate ore.

[0054] The Ri group of the monophosphoric ester A of formula (I) is a hydrocarbon chain, linear or branched, saturated or not comprising 6 to 10 carbon atoms, preferably an alkyl group.

[0055] Advantageously, the group Ri of the monophosphoric ester A of formula (I) is a linear alkyl group comprising 6 to 10 carbon atoms, preferably 7 to 10 carbon atoms, preferably 8 to 9 carbon atoms, particularly preferably comprising 8 carbon atoms. Advantageously, the group Ri of the monophosphoric ester A of formula (I) is a branched alkyl group comprising 6 to 10 carbon atoms, preferably 8 to 9 carbon atoms.

[0056] Preferred branched Ri groups include 2-ethylhexyl, 2-4-4 trimethylpentyl and 3-5-5 trimethylhexyl.

[0057] Advantageously, the group Ri of the monophosphoric ester A of formula (I) is a linear alkyl group comprising 8 or 9 carbon atoms or a branched alkyl group comprising 8 or 9 carbon atoms.

[0058] In some embodiments, the collector is comprised of the monophosphoric ester A of formula (I) as described above.

[0059] At an equivalent number of carbons, the presence of branches on the hydrocarbon chain, preferentially of the alkyl group, of the Ri group of the monophosphoric ester A can then make it possible to minimize the quantity of foam (also called float) which is eliminated during step (iv) of the process while making it possible to enrich the ore in P2O5 and to eliminate heavy metals.

[0060] The combination of monophosphoric ester A and compound B can also influence the amount of foam formed and the enrichment of the ore in P2O5.

[0061] When compound B is present, it is selected from the group consisting of: a monophosphoric ester of formula (II):

[0062] R2— O — P(=O) — (OH)2(II) in which R2 is a hydrocarbon chain, linear or branched, saturated or unsaturated, having from 6 to 18 carbon atoms, preferably from 6 to 10 carbon atoms, preferentially an alkyl group, different from the group Ri of the monophosphoric ester A of formula (I) as described above, an alcohol, a fatty acid, a fixed oil, a sulfate, a sulfonate, an ether and their mixtures.

[0063] The combination of monophosphoric ester A and compound B can minimize the amount of foam (float) that is removed in step (iv) of the process while enriching the ore in P2O5 and removing heavy metals, compared to the use of monophosphoric ester A alone. In addition, the cost of the composition comprising monophosphoric ester A and compound B can also be reduced.

[0064] Combination of monophosphoric ester A and monophosphoric ester of formula (II)

[0065] According to embodiments, compound B is a monophosphoric ester of formula (II):

[0066] R2— O — P(=O) — (OH)2(II) in which the group R2, different from Ri, is a hydrocarbon chain, linear or branched, saturated or unsaturated, comprising 6 to 18 carbon atoms, preferably 6 to 14 carbon atoms, particularly preferably 6 to 10 carbon atoms, preferably an alkyl group.

[0067] In certain embodiments, the group R 1 of the monophosphoric ester A of formula (I) is a linear alkyl group comprising 6 to 10 carbon atoms and the group R 2 of the monophosphoric ester B of formula (II), different from R 1 , is a linear or branched, saturated or unsaturated hydrocarbon chain comprising 6 to 10 carbon atoms, preferably a linear alkyl group comprising 6 to 10 carbon atoms.

[0068] In certain embodiments, the group R 1 of the monophosphoric ester A of formula (I) is a linear alkyl group comprising 6 to 10 carbon atoms and the group R 2 of the monophosphoric ester B of formula (II), different from R 1 , is a branched alkyl group comprising 6 to 10 carbon atoms.

[0069] Preferably, the group R 1 of the monophosphoric ester A of formula (I) is a linear alkyl group comprising 7 to 10 carbon atoms, preferably 8 to 9 carbon atoms, particularly preferably comprising 8 carbon atoms and the group R 2 of the monophosphoric ester B of formula (II), different from R 1, is a branched alkyl group comprising 8 or 9 carbon atoms.

[0070] A synergistic effect linked to the combination of the two monophosphoric esters can be observed, in particular concerning the enrichment of the ore in P2O5.

[0071] According to certain embodiments, compound B is an alcohol of formula R3-OH (III), R3 being a linear or branched, saturated or unsaturated hydrocarbon chain comprising 2 to 20 carbon atoms, preferably 6 to 10 carbon atoms, particularly preferably 8 to 10 carbon atoms, preferably an alkyl group.

[0072] Preferably, the group R 1 of the monophosphoric ester A of formula (I) is a linear alkyl group comprising 7 to 10 carbon atoms, preferably 8 to 9 carbon atoms, particularly preferably comprising 8 carbon atoms and the group R 3 of the alcohol of formula (III) is a linear alkyl group comprising from 6 to 10 carbon atoms, preferably from 8 to 10 carbon atoms.

[0073] Advantageously, the mass percentage of alcohol is less than 70%, preferably less than 50%, preferably less than 40%, preferably less than 30% relative to the mass of the monophosphoric ester A and the alcohol.

[0074] Combination of monophosphoric ester A and sulfate or sulfonate

[0075] According to certain embodiments, compound B is a salt of a hydrocarbon chain sulfonic acid, or a salt of an aromatic sulfonic acid substituted by a hydrocarbon chain, the hydrocarbon chain being linear or branched, saturated or unsaturated, comprising 2 to 20 carbon atoms, preferably an alkyl group. Preferably, compound B is a salt of an alkylated aromatic sulfonic acid, the alkyl group being linear and comprising 10 to 14 carbon atoms, the sodium salt of dodecyl benzene sulfonic acid being particularly preferred.

[0076] Compound B may be a sulfate with a hydrocarbon chain, linear or branched, saturated or not, comprising 2 to 20 carbon atoms, preferably an alkyl sulfate.

[0077] Preferably, the alkyl group is linear and comprises 10 to 14 carbon atoms, sodium dodecyl sulfate being particularly preferred.

[0078] Preferably, the group R 1 of the monophosphoric ester A of formula (I) is a linear alkyl group comprising 7 to 10 carbon atoms, preferably 8 to 9 carbon atoms, particularly preferably comprising 8 carbon atoms and the compound B is a salt of an alkylated aromatic sulfonic acid, the alkyl group being linear and comprising 10 to 14 carbon atoms. Preferably, the group R 1 of the monophosphoric ester A of formula (I) is a linear alkyl group comprising 7 to 10 carbon atoms, preferably 8 to 9 carbon atoms, particularly preferably comprising 8 carbon atoms and the compound B is an alkyl sulfate, the alkyl group being linear and comprising 10 to 14 carbon atoms.

[0079] Advantageously, the mass percentage of the alkylated sulfonic acid salt or the alkylated aromatic sulfonic acid salt is less than or equal to 40% relative to the mass of the monophosphoric ester A and the alkylated sulfonic acid salt or the alkylated aromatic sulfonic acid salt.

[0080] Advantageously, the mass percentage of the alkyl sulfate is less than 70%, preferably less than 50%, preferably 40%, preferably 30%, preferably 20% relative to the mass of the monophosphoric ester A and the alkyl sulfate.

[0081] Combination of monophosphoric ester A and ether

[0082] According to certain embodiments, compound B is an ether, pegylated or not, of formula R5- (OCîF jnO-Rg (IV) with R5 being an alkyl or aromatic or alkylated aromatic group and Rg being an alkyl group or a hydrogen atom and n represents an integer ranging from 0 to 10.

[0083] The term “alkylated aromatic” means an aromatic group substituted by a linear or branched alkyl group comprising from 2 to 20 carbon atoms.

[0084] Preferably, R5 is an alkylated aromatic group, Rg is a hydrogen atom and n is different from zero.

[0085] Preferably, R5 is an aromatic group substituted by a branched alkyl group carrying 6 to 10 carbon atoms, Rg is a hydrogen atom and n is different from zero.

[0086] According to certain embodiments, compound B is an ether, pegylated or not, of formula R5- (OCîP jnO-Rg (IV) with R5 being an unsaturated hydrocarbon chain or an aromatic group substituted by an unsaturated hydrocarbon chain and Rg being an unsaturated hydrocarbon chain or a hydrogen atom and n represents an integer ranging from 0 to 10.

[0087] Preferably, the group R 1 of the monophosphoric ester A of formula (I) is a linear alkyl group comprising 7 to 10 carbon atoms, preferably 8 to 9 carbon atoms, particularly preferably comprising 8 carbon atoms and the compound B is a compound of formula (IV) with R 5 being an alkylated aromatic group, preferably carrying 6 to 10 carbon atoms, R 6 being a hydrogen atom and n being different from zero.

[0088] Advantageously, the mass percentage of the ether is less than 40% relative to the mass of the monophosphoric ester A and the ether.

[0089] Combination of monophosphoric ester A and aras acid or fixed oil

[0090] In some embodiments, compound B is a fatty acid or a fixed oil.

[0091] Preferably, component B is a saturated or unsaturated fatty acid having at least 12 carbon atoms. Preferably, the fatty acid comprises from 12 to 22 carbon atoms, more preferably from 14 to 20 carbon atoms and most preferably from 16 to 18 carbon atoms.

[0092] Advantageously, the mass percentage of fatty acid is less than 60%, preferably less than 40%, preferably less than 20% relative to the mass of the monophosphoric ester A and the fatty acid.

[0093] When compound B is a fixed oil, it can be rapeseed oil or sunflower oil.

[0094] Advantageously, the mass percentage of the fixed oil is less than 50%, preferably less than 30%, preferably less than 10% relative to the mass of the monophosphoric ester A and the fixed oil.

[0095] According to embodiments, the collector consists of the monophosphoric ester A of formula (I) and the compound B as described above.

[0096] The combination of a monophosphoric ester A of formula (I) and a diphosphoric ester leads to a significant reduction in the efficiency of the collector compared to a collector consisting of only the monophosphoric ester A of formula (I).

[0097] The collector according to the invention is more efficient than the collectors of the prior art and can be used in smaller quantities. Advantageously, the quantity of monophosphoric ester A and compound B added during step (i) varies from 100 g to 500 g per tonne of phosphate ores, preferably from 100 g to 300 g, particularly preferably from 120 g / tonne to 260 g / tonne of phosphate ores.

[0098] Advantageously, the collectors according to the invention allow their own foam to be developed without it being necessary to add an additional foaming agent, such as methyl isobutyl carbinol (MIBC) or pine oil.

[0099] Preferably, the process of the present invention does not require the use of an additional frothing agent, pH regulating agent or activating agent during the flotation process.

[0100] The suspensions of ores and collectors according to the invention are pH neutral and do not require the addition of a pH regulator. For example, a pH regulating agent is used when fatty acid-based collectors are used.

[0101] Furthermore, the use of flotation activators, which can also act as pH regulators, such as sodium hydroxide or sulfuric acid, is not necessary.

[0102] According to embodiments, the treatment method according to the invention further comprises a step i') before step i) of adding a depressant such as phosphoric acid and / or a step i") between step i) and step ii) of adding an amine compound for the flotation of silicates

[0103] Depressant agents such as phosphoric acid and its derivatives, diphosphonic acid [DPA] and orthophosphoric acid [OPA] may be used. amine for silicate flotation

[0104] In order to remove silicates from the phosphate ore to be treated, an amine collector such as the products in the FLOTINOR™ and FLOTIGAM™ ranges can be added to the aqueous suspension from step i).

[0105] Step (ii) of gas injection allows the foams comprising carbonates and heavy metals to float to the surface of the suspension. To do this, the gas is injected so as to form homogeneous gas bubbles which, after adsorption with the foams, will transport the foams by flotation to the surface of the suspension.

[0106] The gas bubbles can be formed by any means known to those skilled in the art, for example by a porous base, sintered glass or by one or more injection nozzles.

[0107] The gas injected in step (ii) may be air, nitrogen, or any other gas inert to the species present.

[0108] The gas injection in step (ii) can be carried out at a constant flow rate. A person skilled in the art will know how to adapt the flow rate of the gas injection.

[0109] Step (ii) is carried out with stirring in order to have a homogeneous distribution of the gas bubbles in the aqueous suspension. Stirring can be ensured by any means known to those skilled in the art, such as for example mechanical stirring such as a rotor or magnetic stirring.

[0110] Generally step (ii) can be carried out for a time ranging from 5 seconds to 30 minutes, typically from 5 seconds to 5 minutes.

[0111] The treatment process comprises a step (iii) of separating the foams containing carbonates and heavy metals from the ore suspension.

[0112] The recovered foams can eventually be reprocessed in order to separate and recover the extracted heavy metals.

[0113] The treated ore suspension obtained at the end of step (iii) is recovered after removal of the foams.

[0114] Typically, the foams are recovered in step (iii) from the upper part of the treated phosphoric acid solution by any means known to those skilled in the art. For example, the flotation foams may be discharged into a recovery tank.

[0115] The efficiency of the process according to the invention is expressed in terms of: mass percentage of floated product (rejected) expressed in relation to the total mass of floated product and dried concentrate recovered mass percentages of magnesium oxide (MgO), tricalcium phosphate (BPL or bone phosphate of lime) or P2O5 expressed in relation to the total mass of dried concentrate, as well as the cadmium and arsenic content in the concentrate. The BPL content is obtained by multiplying the P2O5 content by a correction factor of 2.185.

[0116] Typically, the process according to the invention makes it possible to obtain a mass percentage of floated product (rejected) expressed in relation to the total mass of floated product and dried concentrate recovered of less than 25%.

[0117] After treatment, the percentage of tricalcium phosphate (BPL or bone phosphate of lime) or P2O5 expressed in relation to the total mass of dried concentrate, as well as the cadmium and arsenic content in the concentrate are respectively increased and decreased compared to the untreated ore.

[0118] Advantageously, the percentage of tricalcium phosphate (BPL or bone phosphate of lime) is greater than or equal to 65% after implementing the method according to the invention. Advantageously, the percentage of P2O5 is greater than or equal to 30% after implementing the method according to the invention.

[0119] Advantageously, the percentage of tricalcium phosphate (BPL or bone phosphate of lime) is greater than or equal to 70% after implementing the method according to the invention. Advantageously, the percentage of P2O5 is greater than or equal to 32% after implementing the method according to the invention.

[0120] Figure 1 illustrates in a non-limiting manner devices capable of implementing the flotation treatment method according to the invention.

[0121] In certain embodiments, the method according to the invention is implemented in a flotation device, such as a flotation column combined with a froth recovery tank in the upper part of the column, as shown schematically in Figure 1.

[0122] Part I, called the treatment part, comprises the flotation column which consists of a glass column 1 filled with the phosphate ore pulp conditioned with the flotation collector according to the invention. The gas is introduced into the bottom of the column, the gas bubbles are formed by the passage of the gas through the sintered glass 2. The gas is generated by a gas generator 3 and its flow rate is controlled by a flow meter 4. The medium is stirred by a magnetic bar 5 with a magnetic stirrer 6 which makes it possible to obtain a good distribution of the gas bubbles 7. The foams 8 are formed on contact with the gas bubbles. The foams are then entrained at the top of the column in a foam discharge zone 9 corresponding to part II, called the separation part. The foams 8 then flow into a foam recovery tank 10.

[0123] The residence time in the flotation device is generally less than 30 minutes, preferably between 5 seconds and 5 minutes.

[0124] The ion flotation treatment process can be carried out at a temperature ranging from 15 to 90°C or from 20 to 80°C.

[0125] Use of monophosphoric ester A, alone or in combination with compound B

[0126] Another subject of the invention relates to the use of monophosphoric ester A, alone or in combination with compound B as described above for the treatment of phosphate ores containing heavy metals.

[0127] The use of monophosphoric ester A and compound B as described above as collector according to the invention makes it possible to have new processes for treating phosphate ores, which are simpler and less expensive, making it possible to enrich their P2O5 content but also to reduce their content of heavy metals, such as cadmium and arsenic.

[0128] The collector according to the invention is more effective than the compositions of the prior art and can be used in smaller quantities.

[0129] EXAMPLES

[0130] The following non-restrictive examples illustrate exemplary embodiments of the invention.

[0131] Phosphate ore samples were collected from the Khouribga mining site (Bni-Amir). They were crushed, mixed, homogenized and divided into quarters using a riffle sampler. They were then processed and analyzed. 1. Mineralogical characterization of phosphate ore

[0132] Characterization and quantification of these samples were performed using different analytical techniques, including atomic absorption and ICP-MS. The results are shown in Table 1.

[0133] Table 1: Characterization of a sample of phosphate ore from Khouribga

[0134] Phosphate ore contains heavy metals, particularly cadmium at 27 ppm and arsenic at 13 ppm.

[0135] 2. Synthesis of monophosphoric esters

[0136] All organic solvents were purchased and used as is, without purification. Chemicals were purchased from Aldrich, Merck and used without any purification. NMR spectra were recorded in deuterated solvent on a Bruker AC 400 spectrometer at 400 MHz for NMR. 1 H and at 50 MHz or 101 MHz for NMR 13 C; 6 is expressed in ppm relative to TMS (0 ppm) as an internal standard for 1 H and 13 C, H3PO4 for Phosphorus NMR. The fractionation schemes are designated as follows: s (singlet), d (doublet), t (triplet), m (multiplet), br (broad). The coupling constants (J values) are indicated in Hertz (Hz).

[0137] Alcohol (1 eq) is added dropwise to phosphorus (V) oxychloride (1.5 eq) with vigorous stirring at 0°C for one hour under an inert atmosphere, the reaction mixture is stirred continuously for a period of about 4 to 5 hours at room temperature. The obtained monoalkylphosphoryl dichloride is poured dropwise into ice water and stirring is maintained for a few hours (4-16 hours). Then, the mixture is extracted with diethyl ether, and the combined organic phases were dried with magnesium sulfate (MgSCh) and concentrated under reduced pressure, to obtain the appropriate product.

[0138] NMR analyses of the reaction product do not allow the presence of the phosphoric acid diester to be detected.

[0139] The reaction scheme for the synthesis of monophosphoric ester is illustrated in Scheme 1.

[0140] Scheme 1: General Procedure for the Preparation of Monophosphoric Esters

[0141] 3. Ore processing method

[0142] 3.1. Operating mode

[0143] A Denver D-12 flotation cell is used.

[0144] 200 g of dry sedimentary phosphate ore, ground and sized between 40 pm and 160 pm, are suspended in 1.5 L of water. The pulp is conditioned with 500 g per tonne (g / t) of phosphoric acid (H3PO4) as a depressant for 3 min at 1200 rpm, then the collector for carbonate flotation is added at 250 g / t. After 2 min of conditioning, the amine collector "FLOTINOR" for silicate flotation is added at 200 g / t, followed by 30 seconds of conditioning. The flotation process is started immediately after the air injection. The frothed product (floated product) and the concentrate are filtered, dried, weighed and analyzed.

[0145] Unless otherwise stated, the processing method is as described above.

[0146] 3.2. Evaluation of the different collectors

[0147] The processes preceded by a “C” correspond to comparative examples.

[0148] Unless otherwise stated, the percentages given below are mass percentages.

[0149] Example 1: Evaluation of monophosphoric esters

[0150] Table 2 below shows the results obtained for each collector in terms of: mass percentage of floated product (rejected) expressed in relation to the total mass of floated product and dried concentrate recovered mass percentages of magnesium oxide (MgO), tricalcium phosphate (BPL or bone phosphate of lime) or P2O5 expressed in relation to the total mass of dried concentrate, as well as the cadmium and arsenic content in the concentrate. The BPL content is obtained by multiplying the P2O5 content by a correction factor of 2.185. The Mono-Octylphosphoric ester collector at a concentration of 250 g / t allows to obtain a BPL content of 71.24 (32.59% P2O5) with a loss of 24.74% by weight. The Mono-Nonylphosphoric ester collector allows to obtain a BPL content of 69.56 (31.83% P2O5) with a loss of 17.27% by weight for a concentration of only 125 g / t.

[0151] Long-chain alkyl collectors are ineffective for flotation (process outside the invention). After treatment, the cadmium content is reduced by 75% and the arsenic content is reduced by 70%.

[0152] Example 2: Evaluation of the combination of monophosphoric esters

[0153] As illustrated in Tables 3 to 6 below, the combination of two monophosphoric esters makes it possible to optimize the amount of float discharged while obtaining a concentrate enriched in P2O5. Tables 3 to 6 illustrate the effect of the combination of the ester with a linear C8 chain and an ester with a branched chain.

[0154] Table 3

[0155] Table 4

[0156] Table 5

[0157] Table 6 Example 3: Evaluation of the combination of a monophosphoric ester and an alcohol

[0158] Table 7 illustrates the effect of combining a monophosphoric ester and an alcohol.

[0159] Table 7

[0160] For compositions comprising less than 30% by mass of octanol, a P2O5 content greater than or equal to 32% is obtained for the treated ore.

[0161] Example 4: Evaluation of the combination of a monophosphoric ester and a sulfate

[0162] Table 8 illustrates the effect of combining a monophosphoric ester and a sulfate.

[0163] Table 8

[0164] For compositions comprising less than 20% by mass of sulfate, a BPL content greater than or equal to 32% is obtained for the treated ore.

[0165] Example 5: Evaluation of the combination of a monophosphoric ester and a fatty acid

[0166] Table 9 illustrates the effect of combining a monophosphoric ester and a fatty acid.

[0167] Table 9 Example 6: Evaluation of the combination of a monophosphoric ester and an oil

[0168] Table 10 illustrates the effect of combining a monophosphoric ester and an oil.

[0169] Table 10 Example 7: Evaluation of the combination of a monophosphoric ester and a sulfonate

[0170] Table 11 illustrates the effect of combining a monophosphoric ester and a sulfonate.

[0171] Table 11 Example 8: Evaluation of the combination of a monophosphoric ester and a pegylated ether

[0172] Table 12 illustrates the effect of combining a monophosphoric ester and a pegylated ether.

[0173] Table 12 Example 9: Evaluation of the combination of a monophosphoric ester and a diphosphoric ester

[0174] Characterization and quantification of the phosphate ore samples used for Example 9 were performed using the techniques described above, including atomic absorption and ICP-MS. The results are shown in Table 13 below.

[0175] Table 13: Characterization of the ore sample used for Example 9 The phosphate ore contains heavy metals, in particular cadmium at a level of 15 ppm.

[0176] The monoester of phosphoric acid is octylphosphate (mono-octylphosphoric ester). The diester of phosphoric acid is dioctylphosphate (dio-octylphosphoric ester).

[0177] The phosphate ore is treated as described in section 3.1. Table 14 shows the effect of the combination of the monoester with a linear C8 chain and a diester with linear C8 chains.

[0178] Table 14

[0179] The presence of diester in the collector leads to a decrease in efficiency.

Claims

Tl CLAIMS 1. A method of treating phosphate ores containing heavy metals by reverse flotation, the method comprising the following steps: - (i) addition to an aqueous suspension of phosphate ore of a monophosphoric ester A of formula (I): RI - O - P(=O) - (OH)2(I) in which Ri is a hydrocarbon chain, linear or branched, saturated or not, comprising 6 to 10 carbon atoms, preferably an alkyl group, alone or in a mixture with a compound B selected from the group consisting of: a monophosphoric ester of formula (II) R2— O — P(=O) — (OH)2(II) in which R2 is a hydrocarbon chain, linear or branched, saturated or unsaturated, comprising 6 to 18 carbon atoms, preferably an alkyl group, different from the group Ri of the monophosphoric ester A of formula (I), an alcohol, a fatty acid, a fixed oil, a sulfate, a sulfonate, an ether, and mixtures thereof; - (ii) injection of gas into the aqueous suspension to form foams; and - (iii) removal of foams and recovery of the aqueous suspension of treated ore.

2. Treatment method according to claim 1, characterized in that the group Ri of the monophosphoric ester A of formula (I) is a linear alkyl group comprising 8 or 9 carbon atoms or a branched alkyl group comprising 8 or 9 carbon atoms.

3. Treatment method according to claim 1 or claim 2, characterized in that compound B, when present, is an alcohol of formula R3-OH (III), R3 being a chain hydrocarbon, linear or branched, saturated or unsaturated, comprising 2 to 20 carbon atoms, preferably 6 to 10 carbon atoms, preferably an alkyl group.

4. Treatment method according to claim 1 or claim 2, characterized in that compound B, when present, is: a salt of a hydrocarbon chain sulfonic acid or a salt of an aromatic sulfonic acid substituted by a hydrocarbon chain, the hydrocarbon chain being linear or branched, saturated or unsaturated, comprising 2 to 20 carbon atoms, preferably an alkyl group, compound B preferably being the sodium salt of dodecyl benzene sulfonic acid; or is a hydrocarbon chain sulfate, the hydrocarbon chain being linear or branched, saturated or unsaturated, comprising 2 to 20 carbon atoms, preferably an alkyl sulfate, preferably sodium dodecyl sulfate.

5. Treatment method according to claim 1 or claim 2, characterized in that compound B, when present, is an ether, pegylated or not, of formula Rs-fOCîH^nO-Rg (IV) with R5 being an alkyl or aromatic or alkylated aromatic group and Rg being an alkyl group or a hydrogen atom and n represents an integer ranging from 0 to 10.

6. Treatment method according to any one of the preceding claims, characterized in that the quantity of monophosphoric ester A and compound B added during step (i) ranges from 100 g to 500 g per tonne of phosphate ores, preferably from 100 g to 300 g.

7. Treatment method according to any one of the preceding claims, characterized in that it further comprises a step i') before step i) of adding a depressant such as phosphoric acid and / or a step i") between step i) and step ii) of adding an amine compound for the flotation of silicates.

8. Use of monophosphoric ester A alone or in combination with compound B as described in any one of claims 1 to 6 for the treatment of phosphate ores containing heavy metals.

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