Method for enriching phosphate ores

Abstract

The present invention relates to a method for enriching phosphate ores, most particularly by means of a method that comprises steps of washing, grinding and flotation, helping to increase the yield of the method.

Description

[0001] Phosphate ore enrichment process.

[0002] TECHNICAL FIELD OF THE INVENTION

[0003] The present invention relates to a process for enriching phosphate ores, particularly by a process comprising washing, grinding and flotation steps, allowing the process yield to be increased.

[0004] STATE OF THE ART

[0005] Global phosphate consumption, primarily for the production of phosphoric acid and fertilizers (95%), exceeded 47 million tons in 2019 and is projected to reach over 50 million tons in 2023 (USGS). Phosphates are produced by extracting phosphate rock from marine sediment deposits (75%), igneous and metamorphic deposits (15–20%), or biogenetic deposits (2–3%). The main source of phosphates is calcium phosphate from apatite ores (Ca5(PO4)3)(F, Cl, OH), whose global reserves are mainly located in North Africa (Morocco), the United States (Florida), Russia, and China. These ores account for approximately 80% of total global phosphate rock production and typically contain between 18% and 35% P2O5.The predominant types of apatite in these ores are Francolite or Collophane, which in addition to calcium phosphate contain varying amounts of carbonates (such as calcite, dolomite or magnesite), silicates, clays (illite, kaolinite, smectite, etc.) or even organic residues.

[0006] Mineral processing techniques for enrichment depend primarily on the type of gangue minerals present in the ore being mined. Flotation remains one of the most widely used processes for mineral enrichment. In such processes, the ore is first crushed and then suspended in water. A collector is then added, often in combination with other additives such as foaming agents, pH regulators, dispersants, depressants, and / or stimulants (activators), which help separate the valuable minerals from the gangue minerals. After a conditioning period, the flotation process begins. This involves injecting air into the suspension to break up the fine ore particles and produce foam on the surface.One of the major challenges of this process is the difficulty in flotating particles smaller than 40 µm. These particles form the washing and grinding sludge (fine granular fraction). Due to their low probability of collision and adhesion with an air bubble, these particles lead to excessive reagent consumption and a loss of selectivity. Removing this fine granular fraction results in significant losses in treatment processes that include a grinding stage, as these particles contain valuable minerals.

[0007] From the 1970s onwards, extensive research was undertaken to valorize fine granular wafers, leading to the development of new, so-called intensive flotation techniques. These technologies have proven their effectiveness and are used industrially, particularly for the valorization of coal, base metals, and industrial minerals. The fact that certain intensive flotation techniques allow for more efficient processing of fine granular fractions can benefit existing operations. However, the application of these techniques requires modifications to the flotation mechanisms and a change in the flotation reagents typically used for larger, coarser wafers (greater than 40 microns).

[0008] Therefore, a need remains for a process to limit losses during phosphate ore beneficiation and thus increase process yield. Advantageously, the process will allow the use of conventional flotation agents and reduce the amount of washing and grinding sludge produced.

[0009] SUMMARY OF THE INVENTION

[0010] The present invention thus relates to a process for enriching a phosphate ore comprising the following steps:

[0011] - pulping and settling of the ore;

[0012] - a succession of particle size separations of the cleaned ore so as to separate at least one fraction having a particle size of less than 40 microns and a fraction having a particle size ranging from 40 to 125 microns or from 40 to 160 microns or from 40 to 200 microns or from 40 to 400 microns;

[0013] - particle size separation of the fraction having a particle size less than 40 microns so as to separate a fraction having a particle size less than 20 microns or less than 10 microns and a fraction having a particle size ranging from 20 to 40 microns or from 10 to 40 microns;

[0014] - flotation of the fraction having a particle size ranging from 20 to 40 microns or from 10 to 40 microns and of the fraction having a particle size ranging from 40 to 125 microns, or from 40 to 160 microns, or from 40 to 200 microns, or from 40 to 400 microns, leading to the obtaining of an ore enriched in phosphates.

[0015] Other aspects of the invention are as described below.

[0016] DETAILED DESCRIPTION OF THE INVENTION Surprisingly, the inventors have discovered a process for enriching phosphate ores that allows for the recovery of a portion of the fine granular fraction during flotation. The process according to the invention increases the yield of BPL (Bone Phosphorus of Lime; tricalcium phosphate) and reduces the amount of sludge produced.

[0017] The present invention therefore relates to a process for enriching a phosphate ore comprising the following steps:

[0018] - pulping and settling of the ore;

[0019] - a succession of particle size separations of the cleaned ore so as to separate at least one fraction having a particle size of less than 40 microns and a fraction having a particle size ranging from 40 to 125 microns or from 40 to 160 microns or from 40 to 200 microns or from 40 to 400 microns;

[0020] - particle size separation of the fraction having a particle size less than 40 microns so as to separate a fraction having a particle size less than 20 microns or less than 10 microns and a fraction having a particle size ranging from 20 to 40 microns or from 10 to 40 microns;

[0021] - flotation of the fraction having a particle size of 20 to 40 microns or 10 to 40 microns and of the fraction having a particle size of 40 to 125 microns or 40 to 160 microns or 40 to 200 microns or 40 to 400 microns leading to the obtaining of an ore enriched in phosphates.

[0022] The process according to the invention makes it possible to obtain efficient enrichment of phosphate ore by flotation while limiting the quantities of washing and grinding sludge produced. In this description, washing and grinding sludge corresponds to the fine fraction, that is, the fraction with a particle size of less than 40 µm. Washing and grinding sludge is typically removed in conventional phosphate ore enrichment processes. The process according to the invention makes it possible to reduce the quantities of fine washing and grinding waste by approximately 27 to 29%.

[0023] Advantageously, the process of the present invention can be implemented on existing phosphate ore beneficiation plants. Financial investments are therefore minimized.

[0024] Advantageously, the enrichment process according to the invention also makes it possible to remove heavy metals such as cadmium, lead, nickel, chromium and / or zinc from phosphate ore.

[0025] The enrichment process according to the invention improves production capacity (by approximately 10 to 12%) and increases metal yield (by approximately 8 to 10%). In particular, when the process is implemented using an ore such as that used in the examples, the process according to the invention removes at least 59% by weight of the cadmium in mg / kP2O5 present in the phosphate ore; advantageously, at least 59% by weight of the cadmium in mg / kP2O5 is removed.

[0026] In particular, when the process is implemented using an ore such as that used in the examples, the process according to the invention makes it possible to remove at least 47% by weight of the lead in mg / kP2O5 present in the phosphate ore, advantageously at least 47% by weight of the lead is removed.

[0027] In particular, when the process is implemented using an ore such as that used in the examples, the process according to the invention makes it possible to remove at least 82% by weight of the nickel in mg / kP2O5 present in the phosphate ore, advantageously at least 82% by weight of the nickel in mg / kP2O5 is removed.

[0028] In particular, when the process is implemented using an ore such as that used in the examples, the process according to the invention makes it possible to remove at least 70% by weight of the chromium in mg / kP2O5 present in the phosphate ore, advantageously at least 70% by weight of the chromium in mg / kP2O5 is removed.

[0029] In particular, when the process is implemented using an ore such as that used in the examples, the process according to the invention makes it possible to remove at least 50% by weight of the zinc in mg / kP2O5 present in the phosphate ore, advantageously at least 50% by weight of the zinc in mg / kP2O5 is removed.

[0030] It is understood that the reductions indicated above will vary depending on the percentage of BPL in the ore entering the process. However, the process according to the invention remains optimal for any concentration of BPL in the incoming ore.

[0031] Advantageously, the process according to the invention makes it possible to enrich phosphate ore with rare earths.

[0032] Advantageously, the process according to the invention makes it possible to extract clay (silica) from the fine tailings (particle size less than 10 or 20 microns). The silica obtained is much more concentrated (20% vs. approximately 4% in the raw ore).

[0033] Phosphate Ore The phosphate ore useful in the context of the invention is typically a phosphate ore having a BPL content less than or equal to 65% by weight relative to the total weight of the ore. The ores commonly have a particle size less than or equal to 10 millimeters (mm).

[0034] Generally, phosphate ore has a D90 of 650 mm or less, typically 1000 mm or less, or ranging from 160 to 2500 µm, for example, 650 µm. "D90" means that 90% by mass of the ore in question has a size less than or equal to D90, and 10% by mass has a size greater than D90.

[0035] Phosphate ore may also exhibit one or more of the following characteristics: a cadmium content of 35 ppm or less, typically ranging from 5 to 35 ppm or from 7 to 30 ppm; a chromium content of 510 ppm or less, typically ranging from 119 to 510 ppm; a lead content of 16 ppm or less, typically ranging from 4 to 16 ppm; a nickel content of 99 ppm or less, typically ranging from 19 to 99 ppm; a rare earth content of 600 ppm or less, typically ranging from 230 to 600 ppm; and / or a MgO content of 5.3% or less by weight relative to the total weight of the raw feed, typically ranging from 0.6 to 5.3% by weight.

[0036] Phosphate ore may also contain silicates and carbonates from dolomite. Table 1 describes an example of the composition of a phosphate ore from a deposit in the Ouald Abdoun basin in Morocco.

[0037] [Table 1]

[0038] Table 1: Chemical analyses of the composition of a phosphate ore, percentages are expressed by weight.

[0039] Table 1 shows primarily that the raw phosphate ore has a low BPL content, corresponding to a low-phosphate cut. It also appears desirable to reduce the magnesium (MgO), silica, CO2, and cadmium content of the ore. Pulping and settling

[0040] Pulping involves suspending the ore in water. Pulping breaks down the ore and typically allows for subsequent wet separation to obtain different fractions of specific particle sizes.

[0041] The pulp typically comprises 28 to 35% by weight of solids, preferably 40 to 60% by weight of solids.

[0042] Pulping is typically carried out at room temperature (20-30°C).

[0043] The settling process breaks down agglomerates attached to the ore and cleans it, making it suitable for subsequent operations such as cutting and flotation. Settling is ideally carried out at a solids content between 28 and 35%.

[0044] The desliming process is typically carried out for 10 to 15 minutes.

[0045] qranulometric separations

[0046] A series of particle size separations of the cleaned ore is then carried out. This allows the separation of at least one fraction with a particle size of less than 40 microns and a fraction with a particle size ranging from 40 to 160 microns (or from 40 to 125 microns or from 40 to 200 microns or from 40 to 400 microns, depending on the cut chosen).

[0047] Typically, the series of particle size separations is carried out in such a way as to lead to the following particle size fractions:

[0048] A coarse fraction with a particle size greater than 2,500 pm corresponding to coarse waste which can be removed for example by a belt conveyor for disposal on a spoil heap; in some embodiments the coarse fraction has a particle size greater than 3,150 pm;

[0049] A fraction with a particle size ranging from 160 pm to 2,500 pm (or 3150 pm) corresponding to a washing concentrate which may possibly be ground and reintroduced into the present process; in some embodiments this fraction has a particle size ranging from 125 pm to 2,500 pm (or 3150 pm) or from 200 pm to 2,500 pm (or 3150 pm) or even from 400 pm to 2,500 pm (or 3150 pm);

[0050] A fraction with a particle size ranging from 40 pm to 160 pm corresponding to a fraction intended to be enriched by flotation; in some embodiments this fraction has a particle size ranging from 40 pm to 125 pm or from 40 pm to 200 pm or from 40 pm to 400 pm;

[0051] A fraction with a particle size ranging from 10 pm to 40 pm or from 20 pm to 40 pm intended to be enriched by flotation; A fraction with a particle size less than 20 pm or less than 10 pm corresponding to washing and grinding sludge, which can be treated for example in settling tanks to recover a maximum of water.

[0052] Particle size separation steps are carried out using all methods known to those skilled in the art that allow for the separation of grains according to their particle size distribution. Typically, particle size separation steps are carried out by screening, centrifugation (centrifugal decanter), hydrocycloning (hydrocyclone, micro-hydrocyclone) or by means of a gravity separator such as the Hydrosizer™.

[0053] Typically, the particle size separation of coarse fractions (> 2500 microns) is carried out by screening, the particle size separation of intermediate fractions (between 200 and 800 microns) is carried out by means of a Hydrosizer™ type gravity separator, the particle size separation of fine fractions (between 40 and 160 microns) is carried out by a hydrocyclone and the particle size separation of ultrafine fractions (< 20 microns) by a micro-hydrocyclone or a centrifugal decanter (typically without flocculants).

[0054] The process of the present invention is characterized by a screening step of the fraction passing through a 40-micron cut-off. In known enrichment processes, this fraction is typically discarded (washing and grinding sludge). The particle size separation performed on this fraction makes it possible to separate an ultrafine fraction with a particle size of less than 20 microns from a fraction with a particle size ranging from 20 to 40 microns, or, depending on the chosen cut-off threshold, to separate an ultrafine fraction with a particle size of less than 10 microns from a fraction with a particle size ranging from 10 to 40 microns.

[0055] The particle size separation of the fraction with a particle size less than 40 microns is typically carried out using centrifugal decanters (typically without flocculants) or micro-hydrocyclones. The two-stage separation process, performed at 40 microns followed by further separation at 10 or 20 microns, prevents clogging of the micro-hydrocyclones. Indeed, a direct separation at 10 or 20 microns without first separating at 40 microns leads to systematic clogging of the micro-hydrocyclones.

[0056] The fraction with a particle size ranging from 20 to 40 microns or from 10 to 40 microns is then subjected to the flotation step. It is mixed with the fraction having a particle size ranging from 40 to 160 microns (or 40 µm to 125 µm, 40 µm to 200 µm, or 40 µm to 400 µm, depending on the cut-off size used). The mixture is then subjected to the flotation step after attrition and deliming. It should be noted that the process of the invention does not require the use of intensive flotation. The fraction with a particle size less than 20 µm or less than 10 µm, corresponding to the washing and grinding sludge produced by the process, can be sent to settling tanks for a thickening step to recover the water from the washing sludge. The fraction with a particle size of less than 20 pm or less than 10 pm can prove useful for chemical industries producing sulfuric acid because it is rich in reactive silicas.

[0057] Before flotation, attrition and desliming are typically carried out. The attrition stage is generally performed in an attritioner and allows the phosphate grains to be released from the silicate and carbonate gangue. Desliming removes the finest suspended particles. Following attrition and desliming, the fraction with a particle size ranging from 40 to 160 microns (or 40 µm to 125 µm, 40 µm to 200 µm, or 40 µm to 400 µm, depending on the cut size used) is subjected to flotation, while the fraction not retained at the 40-micron cut size may undergo further particle size separation with a cut size of 10 or 20 microns.The fraction with a particle size of less than 20 microns or less than 10 microns is set aside and typically sent to settling tanks, while the fraction with a particle size of 20 to 40 microns or 10 to 40 microns is directed to flotation (it will be pre-mixed with the fraction of 40 to 160 microns (or 40 pm to 125 pm or 40 pm to 200 pm or 40 pm to 400 pm depending on the cut implemented)).

[0058] The fraction with a particle size ranging from 160 µm to 2,500 µm (or from 125 µm to 2,500 µm (or 3,150 µm), or from 200 µm to 2,500 µm (or 3,150 µm), or even from 400 µm to 2,500 µm (or 3,150 µm), depending on the cut-off used), corresponding to a washing concentrate, may undergo one or more grinding stages. Particle size separation is carried out with a cut-off at 160 microns (or 125 microns, 200 microns, or 400 microns) and then at 40 microns, typically using a hydrocyclone. The fraction with a particle size ranging from 40 microns to 160 microns (or 40 µm to 125 µm, 40 µm to 200 µm, or 40 µm to 400 µm, depending on the cut size used) is intended for flotation. It is typically subjected to attrition / delamination with a 40-micron cut size.The fraction with a particle size ranging from 40 to 160 microns (or 40 µm to 125 µm, 40 µm to 200 µm, or 40 µm to 400 µm, depending on the cut-off size used) is subjected to flotation, while the fraction not retained at 40 microns can undergo further particle size separation with a cut-off size of 20 microns or 10 microns. The fraction with a particle size smaller than 20 microns or 10 microns is discarded and typically sent to settling tanks, while the fraction with a particle size ranging from 20 to 40 microns or 10 to 40 microns is directed to flotation. Generally, in the process of the present invention, the fractions not retained at the 20-micron or 10-micron cut-off size are discarded (constitute waste).

[0059] Flotation

[0060] Flotation of the fraction or fractions having a particle size ranging from 40 to 160 microns (or 40 pm to 125 pm or 40 pm to 200 pm or 40 pm to 400 pm depending on the cut implemented) and of the fraction or fractions having a particle size ranging from 20 to 40 microns or from 10 to 40 microns leads to an ore enriched in phosphates.

[0061] Flotation removes carbonates, dolomite, and silicates from phosphate ore. The non-floating portion is the flotation concentrate. The floated tailings, consisting mainly of carbonates, dolomite, and silicates, can be sent to settling tanks for a thickening process to recover the water.

[0062] Flotation can be carried out conventionally, in particular using agents other than those used for intensive flotation.

[0063] The fraction or fractions having a particle size ranging from 40 to 160 microns (or 40 pm to 125 pm or 40 pm to 200 pm or 40 pm to 400 pm depending on the cut implemented) and the fraction or fractions having a particle size ranging from 20 to 40 microns or from 10 to 40 microns are, in the first instance, conditioned with the flotation reagents and then flotation is implemented.

[0064] Enrichment by flotation can be carried out either by direct flotation, or by reverse flotation in one or more stages.

[0065] Flotation reagents are conventional flotation agents. They can be chosen from the group consisting of an amine, a phosphoric ester, a fatty acid, a fatty amine, a salt of a fatty amine, and mixtures thereof.

[0066] Phosphoric esters may be as described in European application 23305204.2 filed on 15 February 2023. Such esters correspond to the following formula: Ri - O - P(=O) - (OH)2(I) in which Ri is an alkyl group, linear or branched, saturated or unsaturated, comprising 6 to 18 carbon atoms.

[0067] The fatty acids may be as described in application WO2015 / 042735. This includes, in particular, fatty acids derived from oleic acid.

[0068] Fatty amines and their salts typically correspond to the following formulas:

[0069] R — O — (CH2)3— NH3, where R is an alkyl group with 10-14 carbon atoms,

[0070] R — O — (CH2)3— NH — (CH2)3— NH3, where R is an alkyl group with 10 or more carbon atoms. Flotation reagents can be used in combination with foaming and antifoaming agents to adjust the foaming effect.

[0071] Flotation is generally carried out in the presence of an acid, for example sulfuric acid, which acts as a pH regulator in the case of flotation in an acidic medium using fatty acids.

[0072] Flotation is also carried out in the presence of phosphoric acid, which acts as an apatite depressant.

[0073] Phosphate-enriched ore

[0074] The process according to the invention allows the production of an ore enriched in phosphates.

[0075] Typically, the ore has a quantity of BPL that is at least 65% higher than the quantity of BPL in the ore subjected to the process, or even 65 to 66% higher or 66 to 70% higher.

[0076] Generally, the ore obtained by the process according to the invention also has a reduced quantity of heavy metals.

[0077] The enriched ore may exhibit one or more of the following characteristics: a cadmium content of 11.26 ppm or less, typically ranging from 11.26 to 11 ppm or from 11 to 8.8 ppm; a lead content of 6 ppm or less, typically ranging from 5.5 to 6 ppm or from 4.71 to 5.5 ppm; a nickel content of 31 ppm or less, typically ranging from 20 to 31 ppm or from 10 to 16 ppm; a chromium content of 120 ppm or less, typically ranging from 100 to 120 ppm or from 78 to 120 ppm; a zinc content of 217 ppm or less, typically ranging from 190 to 217 ppm or from 170 to 217 ppm; and / an amount of MgO less than or equal to 0.88% by weight relative to the total weight of the raw charge, typically ranging from 0.5 to 0.88% by weight or from 0.22 to 0.5% by weight.

[0078] Figure 1 describes a first preferred embodiment of the process of the invention comprising the following steps: i. Particle size separation with a cut-off at 2,500 µm of the degreased fraction leading to the formation of a fraction having a particle size less than or equal to 2,500 µm; ii. Particle size separation with a cut-off at 160 µm of the fraction having a particle size less than or equal to 2,500 µm leading to the formation of a fraction having a particle size greater than 160 µm and less than or equal to 2,500 µm and a fraction having a particle size less than or equal to 160 µm; iii. Particle size separation with a cut at 40 pm of the fraction having a particle size less than or equal to 160 pm leading to the formation of a fraction having a particle size ranging from 40 pm to 160 pm (intended for flotation) and a fraction having a particle size less than 40 pm; iv.Particle size separation with a cut-off at 20 µm of the fraction with a particle size less than 40 µm, leading to the formation of a fraction with a particle size ranging from 20 µm to 40 µm (intended for flotation after attrition and desliming) and a fraction with a particle size less than 20 µm (rejects); v. Attrition of the fractions with a particle size ranging from 40 µm to 160 µm, and of the fraction with a particle size ranging from 20 µm to 40 µm, leading to the formation of an attrited fraction; vi. Particle size separation with a cut-off at 40 µm of the attrited fraction, leading to the formation of an attrited fraction with a particle size ranging from 40 µm to 160 µm (intended for flotation) and an attrited fraction with a particle size less than 40 µm; vii.Particle size separation with a cut at 20 pm of the attrited fraction having a particle size less than 40 pm leading to the formation of an attrited fraction with a particle size ranging from 20 pm to 40 pm (intended for flotation) and a fraction with a particle size less than 20 pm (rejects); viii. Flotation of the fractions having a particle size ranging from 40 pm to 160 pm and of the fractions having a particle size ranging from 20 pm to 40 pm leading to the obtaining of a phosphate-enriched ore concentrate.

[0079] In some embodiments, step i. is carried out with a cut-off at 3150 pm.

[0080] In some embodiments, step ii. is carried out with a cut at 125, 160, 200, 300 and / or 400 microns.

[0081] In some embodiments, steps iv. and vii. are carried out with a cut-off at 10 µm. The particle size fraction having a particle size greater than 160 µm and less than or equal to 2,500 µm constitutes the washing concentrate. Figure 2 shows a second preferred embodiment of the process of the invention comprising, in addition to the steps described in Figure 1, the following steps: i') grinding the fraction having a particle size less than or equal to 2,500 µm leading to the formation of a ground fraction; ii') particle size separation with a cut-off at 160 µm of the ground fraction leading to the formation of a fraction having a particle size greater than 160 µm and a fraction having a particle size less than or equal to 160 µm;iii') particle size separation with a cut at 40 pm, fraction having a particle size less than or equal to 160 pm leading to the formation of a fraction having a particle size ranging from 40 pm to 160 pm (intended for flotation with prior attrition) and a fraction having a particle size less than 40 pm; iv') attrition of the fraction having a particle size ranging from 40 pm to 160 pm; v') particle size separation of the attritiated fraction having a particle size ranging from 40 pm to 160 pm with a cut at 40 pm leading to the formation of an attritiated fraction having a particle size ranging from 40 pm to 160 pm (intended for flotation) and an attritiated fraction having a particle size less than 40 pm;vi') particle size separation with a cut at 20 pm of the fraction having a particle size less than 40 pm leading to the formation of a fraction having a particle size ranging from 20 pm to 40 pm (intended for flotation) and a fraction having a particle size less than 20 pm (rejects), the fraction having a particle size ranging from 20 pm to 40 pm obtained being subjected to the flotation step (after attrition and desliming; steps iv' and v'); vii') particle size separation with a cut at 20 pm of the attritioned fraction having a particle size less than 40 pm leading to the formation of a fraction having a particle size ranging from 20 pm to 40 pm (subjected to flotation) and a fraction having a particle size less than 20 pm (rejects);viii') flotation of the attrited fraction having a particle size ranging from 40 pm to 160 pm and of the fraction having a particle size ranging from 20 pm to 40 pm leading to the obtaining of a phosphate-enriched ore concentrate.;

[0082] The fractions subjected to flotation according to step viii') join the fractions subjected to flotation according to step viii) described in relation to figure 1.

[0083] In some embodiments, step i') is performed with a cut at 3150 µm. In some embodiments, step ii') is performed with a cut at 125, 160, 200, 300 and / or 400 microns. In some embodiments, steps vi') and vii') are performed with a cut at 10 µm.

[0084] FIGURES [Fig. 1]: Diagram of an embodiment of the process of the invention (washing and flotation) [Fig. 2]: Diagram of an embodiment of the process of the invention (washing, grinding and flotation)

[0085] EXAMPLES

[0086] Example 1: Comparison of the invention's process with a conventional process

[0087] The process of enriching a phosphate ore was carried out in accordance with the process illustrated in Figure 1.

[0088] The results are presented in Table 2 below.

[0089] [Table 2] Table 2

[0090] For comparison, a phosphate ore enrichment process was carried out without screening the washing sludge (fraction with a particle size less than 40 microns). The results are presented in Table 3.

[0091] [Table 3]

[0092] Table 3

[0093] It can be observed that the washing-flotation treatment process including the 20-40pm tranche from the washing sludge (process of the invention) makes it possible to have a treatment concentrate having chemical characteristics comparable to those of the concentrate obtained by the process outside the invention but with a better weight yield (66.48% versus 63.91%).

[0094] Example 2: Comparison of the process of the invention with a conventional process The process of enriching a phosphate ore was carried out in accordance with the process illustrated in Figure 2.

[0095] The results are presented in Table 4 below.

[0096] [Table 4]

[0097] Table 4 For comparison, a phosphate ore enrichment process was carried out without screening the washing and grinding sludge (fraction having a particle size less than 40 microns).

[0098] The results are presented in Table 5. [Table 5]

[0099] Table 5 II can be observed that the process of the present invention makes it possible to improve the weight yield by 4.83% (52.84 versus 48.01%) without impacting the chemical quality of the concentrate, in particular the content of BPL and MgO which is reduced to 0.5%.

Claims

DEMANDS 1. Process for enriching a phosphate ore comprising the following steps: - pulping and settling of the ore; - a succession of particle size separations of the cleaned ore so as to separate at least one fraction having a particle size of less than 40 microns and a fraction having a particle size ranging from 40 to 125 microns or from 40 to 160 microns or from 40 to 200 microns or from 40 to 400 microns; - particle size separation of the fraction having a particle size less than 40 microns so as to separate a fraction having a particle size less than 20 microns or less than 10 microns and a fraction having a particle size ranging from 20 to 40 microns or from 10 to 40 microns; - flotation of the fraction having a particle size ranging from 20 to 40 microns or from 10 to 40 microns and of the fraction having a particle size ranging from 40 to 125 microns, or from 40 to 160 microns, or from 40 to 200 microns, or from 40 to 400 microns, leading to the obtaining of an ore enriched in phosphates.

2. A method according to claim 1, wherein the particle size separation steps are carried out by screening, centrifugation, hydrocycloning or by means of a gravity separator.

3. A method according to claim 1 or 2 wherein the succession of particle size separations comprises a particle size separation with a cut-off at 2,500 pm leading to a fraction having a particle size less than or equal to 2,500 pm and to a fraction having a particle size greater than 2,500 pm.

4. A process according to claim 3 wherein the succession of particle size separations comprises a particle size separation with a cut at 160 pm of the fraction having a particle size less than or equal to 2,500 pm leading to the formation of a fraction having a particle size greater than 160 pm and less than or equal to 2,500 pm and a fraction having a particle size less than or equal to 160 pm.

5. A method according to claim 4 wherein the succession of particle size separations comprises a particle size separation with a cut at 40 pm of the fraction having a particle size less than or equal to 160 pm leading to the formation of a fraction having a particle size ranging from 40 pm to 160 pm and a fraction having a particle size less than 40 pm.

6. A process according to any one of claims 1 to 5 comprising, prior to the flotation step, an attrition of the fraction having a particle size ranging from 40 pm to 160 pm followed by a delamination at 40 microns leading to the formation of a fraction having a particle size ranging from 40 pm to 160 pm and a fraction having a particle size less than 40 pm, the fraction having a particle size ranging from 40 pm to 160 pm obtained being subjected to the flotation step.

7. A process according to any one of claims 4 to 6 wherein the fraction having a particle size ranging from 160 µm to 2,500 µm is subjected to a grinding step and then to a series of particle size separations leading to a fraction having a particle size ranging from 40 microns to 160 microns and a fraction having a particle size less than 40 microns, the fraction having a particle size ranging from 40 microns to 160 microns obtained being subjected to the flotation step.

8. A process according to claim 7 wherein the fraction having a particle size of less than 40 microns obtained after grinding and screening is subjected to particle size separation with a cut at 20 microns or 10 microns leading to a fraction having a particle size ranging from 20 microns to 40 microns or from 10 to 20 microns and a fraction having a particle size of less than 20 microns or less than 10 microns, the fraction having a particle size ranging from 20 microns to 40 microns or from 10 to 40 microns obtained being subjected to the flotation step after attrition and desliming.

9. A method according to any one of claims 1 to 8 wherein the fractions having a particle size of less than 20 microns are rejected.

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