Method for enriching very lean dolomitic silico-carbonate phosphate ores

Abstract

The present invention relates to a method for enriching very lean dolomitic silico-carbonate phosphate ores, very particularly to a method comprising steps of washing, milling and two-stage flotation making it possible to obtain a rich concentrate with good mineral recovery.

Description

PROCESS FOR ENRICHEDITY OF PHOSPHATE ORE WITH VERY POOR DOLOMITIC SILICO-CARBONATE TECHNICAL FIELD OF THE INVENTION

[0001] The present invention reveals a new process for enriching very poor dolomitic silico-carbonate phosphate ores, particularly said process comprising the steps of degreasing, screening, grinding, attrition and flotation in two stages allowing to increase the P2O5 grade with good recovery of the ore. STATE OF THE ART

[0002] 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 rocks from marine sediment deposits (75%), igneous and metamorphic deposits (15-20%), or biogenetic deposits (2-3%).

[0003] The main source of phosphates comes from calcium phosphate from apatite ores (Cas(PO4)3)(F, Cl, OH), the world's reserves of which are mainly found in North Africa (Morocco), the United States (Florida), Russia and China.

[0004] These ores represent about 80% of the total world production of phosphate rocks and generally 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.

[0005] Mineral processing techniques aimed at enrichment depend primarily on the type of gangue minerals present in the extracted rock. Flotation remains one of the most widely used methods for mineral enrichment.

[0006] In such processes, the ore is first crushed and then suspended in water. A collector is then added, often in association with other additives, such as foaming agents, pH regulators, dispersants, depressants and / or stimulants (activators), allowing the valuable minerals to be separated from the gangue minerals of the ore.

[0007] After a certain conditioning period, the flotation process is initiated. 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 of enriching ores with very low P2O5 content. Enriching this type of ore results in significant P2O5 losses in the processing tailings. Due to their very low content, these ores lead to excessive reagent consumption and a loss of selectivity. Rejecting this type of ore at the mine results in high costs and resource losses.

[0008] Therefore, a need remains for a process to treat very low-grade dolomitic silico-carbonate ores with good selectivity, thereby increasing mine yields. Advantageously, the process will allow the use of very low-grade phosphate layers, reducing the cost per ton at the mine and decreasing the amount of washing, crushing, and flotation sludge produced. SUMMARY OF THE INVENTION

[0009] The invention aims to provide a device for enriching very poor dolomitic silico-carbonate phosphate ores, particularly by a process that improves the selectivity of the treatment of this type of ore while reducing losses and the amount of waste from the treatment of this type of ore.

[0010] The present invention reveals a process for enriching very low-grade dolomitic silico-carbonate ores, thereby improving the selectivity of the enrichment of this type of ore. The process comprises several steps, including: - pulping and settling of the ore; - grinding to a mesh size varying from approximately 160 to approximately 200 pm; - 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 about 40 pm and a fraction having a particle size ranging from about 40 to about 125 pm, or from about 40 to about 160 pm, or from about 40 to about 200 pm, or from about 40 to about 400 pm; - particle size separation of the fraction having a particle size of less than about 40 pm so as to separate a fraction having a particle size of less than about 20 pm, or less than about 10 pm and a fraction having a particle size ranging from about 20 to about 40 pm, or from about 10 to about 40 pm; - flotation of the fraction having a particle size ranging from approximately 20 to approximately 40 µm or from approximately 10 to approximately 40 µm and of the fraction having a particle size ranging from approximately 40 to approximately 125 µm, or from approximately 40 to approximately 160 µm, or from approximately 40 to approximately 200 µm, or from approximately 40 to approximately 400 µm, leading to the obtaining of an ore enriched in phosphates by the removal of calcite and dolomite; - flotation of the fraction having a particle size ranging from approximately 20 to approximately 40 µm or from approximately 10 to approximately 40 µm and of the fraction having a particle size ranging from approximately 40 to approximately 125 µm, or from approximately 40 to approximately 160 µm, or from approximately 40 to approximately 200 µm , or from about 40 to about 400 pm, leading to the obtaining of an ore enriched in phosphates by the elimination of silicates. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Exemplary embodiments of the present invention will be more fully understood and appreciated from the following detailed description, taken together with the drawings in which,

[0012] FIG. 1 presents an embodiment of the process of the invention in question. DETAILED DESCRIPTION OF THE INVENTION

[0013] The following detailed description includes references to the accompanying drawings, which form part of the detailed description. The drawings show illustrations conforming to exemplary embodiments. The figures represent similar elements across different views; exemplary embodiments of this disclosure are described. For convenience, only certain elements within a single group may be labeled with numbers. The purpose of the drawings is to describe exemplary embodiments and not to produce. Therefore, the features shown in the drawings are chosen solely for convenience and clarity of presentation.Furthermore, the language used in this description has been chosen primarily for readability and instruction and may not have been chosen to delimit or circumscribe the inventive subject matter, as recourse to the claims is necessary to determine this inventive subject matter. These examples of embodiments are described in sufficient detail to enable a person skilled in the art to carry out the present subject matter. However, it will be obvious to a person with average skill in the art that the present invention can be implemented without these specific details. The embodiments can be combined, other embodiments can be used, or structural and logical modifications can be made without departing from the scope of the invention. The detailed description that follows should therefore not be taken in a restrictive sense.

[0014] The process according to the invention allows for the efficient enrichment of very poor dolomitic silico-carbonate ores by two-stage flotation. The process according to the invention increases the P2O5 content from approximately 15.28% to approximately 30.67%, effectively doubling the yield.

[0015] The process according to the invention comprises several steps including: - pulping and degreasing of the ore; - grinding to a mesh size varying from approximately 160 to approximately 200 pm; - 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 about 40 pm and a fraction having a particle size ranging from about 40 to about 125 pm, or from about 40 to about 160 pm, or from about 40 to about 200 pm, or from about 40 to about 400 pm; - particle size separation of the fraction having a particle size of less than about 40 pm so as to separate a fraction having a particle size of less than about 20 pm, or less than about 10 pm and a fraction having a particle size ranging from about 20 to about 40 pm, or from about 10 to about 40 pm; - flotation of the fraction having a particle size ranging from about 20 to about 40 pm or from about 10 to about 40 pm and of the fraction having a particle size ranging from about 40 to about 125 pm, or from about 40 to about 160 pm, or from about 40 to about 200 pm, or from about 40 to about 400 pm, leading to the obtaining of an ore enriched in phosphates by elimination of calcite and dolomite; - flotation of the fraction having a particle size ranging from about 20 to about 40 pm or from about 10 to about 40 pm and of the fraction having a particle size ranging from about 40 to about 125 pm, or from about 40 to about 160 pm, or from about 40 to about 200 pm, or from about 40 to about 400 pm, leading to the obtaining of an ore enriched in phosphates by the elimination of silicates.

[0016] Advantageously, the process of the present invention allows the mine to extract more phosphate layer, thereby increasing extraction yield and reducing costs at the mine level.

[0017] Advantageously, the enrichment process according to the invention also makes it possible to increase the processing capacity by about 131% compared to a low-grade ore processing process.

[0018] Advantageously, the enrichment process according to the invention also makes it possible to remove heavy metals such as cadmium, nickel, chromium and / or zinc from phosphate ore.

[0019] In a preferred embodiment, when the process is implemented from an ore such as that used in the examples, the process according to the invention makes it possible to remove at least 80% by weight of the cadmium in mg / k P2O5 present in the phosphate ore, advantageously at least 80% by weight of the cadmium in mg / k P2O5 is removed.

[0020] In a preferred embodiment, when the process is implemented from an ore such as that used in the examples, the process according to the invention makes it possible to remove at least 81% by weight of the nickel in mg / k P2O5 present in the phosphate ore, advantageously at least 81% by weight of the nickel in mg / k P2O5 is removed.

[0021] In a preferred embodiment, when the process is implemented from an ore such as that used in the examples, the process according to the invention makes it possible to remove at least 64% by weight of the chromium in mg / k P2O5 present in the phosphate ore, advantageously at least 64% by weight of the chromium in mg / k P2O5 is removed.

[0022] In a preferred embodiment, when the process is implemented from an ore such as that used in the examples, the process according to the invention makes it possible to remove at least 61% by weight of the zinc in mg / k P2O5 present in the phosphate ore, advantageously at least 61% by weight of the zinc in mg / k P2O5 is removed.

[0023] Advantageously, the process according to the invention allows the extraction of 67% silica.

[0024] Advantageously, the process according to the invention allows for the extraction of 80% CaCCL.

[0025] It is understood that the reductions indicated above will vary depending on the percentage of BPL (Bone Phosphate Lime or tricalcium phosphate) in the ore entering the process. However, the process according to the invention remains optimal for any concentration of BPL in the incoming ore.

[0026] The phosphate ore useful in the context of the invention is typically a phosphate ore having a BPL content less than or equal to 45% by weight relative to the total weight of the ore. The ores commonly have a particle size less than or equal to approximately 10 millimeters (mm).

[0027] Generally, phosphate ore has a DI 00 less than or equal to approximately 10 mm, typically less than or equal to approximately 10 mm. "D100" means that 100% by mass of the ore in question has a size less than or equal to DI 00.

[0028] Phosphate ore may also exhibit one or more of the following characteristics: - an amount of cadmium less than or equal to about 11 ppm, typically ranging from about 5 to about 11 ppm, or from about 7 to about 30 ppm; - a quantity of chromium less than or equal to about 197 ppm, typically ranging from about 119 to about 200 ppm; - a nickel content less than or equal to approximately 65 ppm, typically ranging from approximately 19 to approximately 70 ppm; and - an amount of MgO less than or equal to about 4.3% by weight relative to the total weight of the gross charge, typically ranging from about 0.6 to about 5% by weight.

[0029] Phosphate ore may also contain silicates and carbonates from dolomite.

[0030] Table 1 describes an example of the composition of a phosphate ore from a deposit in the Gantour basin in Morocco: Table 1: Chemical analyses of the composition of a phosphate ore (% expressed by weight)

[0031] Table 1 shows primarily that the raw phosphate ore has a very low BPL content, corresponding to a low-phosphate cut. It also appears that it is desirable to reduce the magnesium (MgO), silica, CO2, and cadmium content of the ore.

[0032] In a preferred embodiment, the steps of the process are defined in the following paragraphs.

[0033] Pulping involves suspending the ore in water. This process breaks down the ore and typically allows for subsequent wet separation to obtain different particle size fractions. The pulp typically contains 28 to 35% solids by weight, preferably 40 to 60% by weight. Pulping is typically carried out at ambient temperature (20-30°C).

[0034] Degreasing breaks down agglomerates attached to the ore and cleans it, making it suitable for subsequent operations such as cutting and flotation. Ideally, degreasing is carried out at a solids content between 28 and 35%. It typically lasts 10 to 15 minutes.

[0035] A series of particle size separations of the cleaned ore is then carried out. This allows for the separation of at least one fraction with a particle size less than approximately 40 µm and a fraction with a particle size ranging from approximately 40 to approximately 400 µm. Typically, the series of particle size separations is performed in such a way as to produce the following particle size fractions: - A coarse fraction with a particle size greater than 1000 pm corresponding to the vegetation removed in the case where discharges from spreading basins are treated, which can be evacuated for example by a belt conveyor for disposal on a spoil heap; - A fraction with a particle size ranging from about 40 pm to about 400 pm corresponding to a fraction intended to be enriched by flotation; - A fraction with a particle size ranging from about 10 pm to about 40 pm or from about 20 pm to about 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 with the discharges from the first stage of flotation for example in settling tanks to recover a maximum of water.

[0036] 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 using a hydrosizer.

[0037] Typically, the particle size separation of coarse fractions (> 1000 pm) is carried out by screening, the particle size separation of intermediate fractions (between 400 and 200 pm) is carried out by means of a hydrosizer, the particle size separation of fine fractions (between 40 and 160 pm) is carried out by a hydrocyclone and the particle size separation of ultrafine fractions (< 20 pm) by a micro-hydrocyclone or a centrifugal decanter (typically without flocculants).

[0038] The process of the present invention is characterized by a screening step of the fraction passing through a 40 µm cutoff. 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 µm from a fraction with a particle size ranging from 20 to 40 µm, or, depending on the chosen cutoff threshold, to separate an ultrafine fraction with a particle size of less than 10 µm from a fraction with a particle size ranging from 10 to 40 µm.

[0039] The particle size separation of the fraction with a particle size less than 40 µm is typically carried out using centrifugal clarifiers (typically without flocculants) or micro-hydrocyclones. Cutting the material at 40 µm and then at 10 or 20 µm (i.e., in two stages) prevents clogging of the micro-hydrocyclones. Indeed, cutting directly at 10 or 20 µm without first cutting at 40 µm leads to systematic clogging of the micro-hydrocyclones.

[0040] The fraction with a particle size ranging from 20 to 40 µm or from 10 to 40 µm is then subjected to the flotation stage. It is mixed with the fraction having a particle size ranging from 40 to 400 µm. The mixture is then subjected to the first stage of calcite and dolomite flotation after attrition and desliming. It should be noted that the process of the invention does not require the use of intensive flotation.

[0041] The fraction with a particle size of less than 20 µm or less than 10 µm, corresponding to the washing and grinding sludge produced by the conventional process, can be sent to settling tanks and mixed with the first-stage flotation waste for a thickening step to recover water from the washing and grinding sludge. This fraction can be useful for chemical industries producing sulfuric acid because it is rich in reactive silica.

[0042] Before flotation, attrition and desliming are typically performed. The attrition stage is generally carried out 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 400 µm is subjected to the first flotation stage of calcite and dolomite, while the fraction not retained at the 40 µm cut can undergo further fine particle size separation with a cut at 10 or 20 µm.The fraction with a particle size less than 20 pm or less than 10 pm is discarded and typically sent mixed with the first stage flotation rejects to settling tanks, while the fraction with a particle size ranging from 20 to 40 pm or from 10 to 40 pm is directed to flotation (it will be pre-mixed with the fraction ranging from 40 to 400 pm).

[0043] 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 µm (or 125 µm or 200 µm or 400 µm) and then at 40 µm, typically using a hydrocyclone. The fraction with a particle size ranging from 40 µm to 160 µm (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 / desliming with a 40 µm cut size.The fraction with a particle size ranging from 40 to 160 µm (or 40 to 125 µm, 40 to 200 µm, or 40 to 400 µm, depending on the cut-off implemented) is subjected to flotation, while the fraction not retained at 40 µm may undergo further particle size separation with a cut-off at 20 µm or 10 µm. The fraction with a particle size smaller than 20 µm or 10 µm is discarded and typically sent to settling tanks and mixed with the tailings from the first flotation stage, while the fraction with a particle size ranging from 20 to 40 µm or 10 to 40 µm is directed to flotation.

[0044] In general, in the process of the present invention, the fractions not retained at the 20 pm or 10 pm cut are eliminated (constitute waste).

[0045] Flotation of the fraction or fractions having a particle size ranging from 40 to 400 pm and of the fraction or fractions having a particle size ranging from 20 to 40 pm or from 10 to 40 pm leads to an ore enriched in phosphates.

[0046] First stage flotation allows the removal by flotation of carbonates, dolomite present in the washing, grinding and flotation tailings, the non-floating part corresponds to the concentrate of the first flotation stage constituting the feed of the second stage dedicated to the removal of silicates in this feed, the non-floating part of the second stage corresponds to the flotation concentrate.

[0047] The floated tailings, consisting mainly of carbonates and dolomite, must be mixed with wash tailings of less than 10 pm or 20 pm before being sent to settling tanks to undergo a thickening stage to recover the water; this water can only be recycled at the stage preceding the thickening of the first stage flotation concentrate.

[0048] The floating silicate discharge can be sent to other settling tanks to undergo a thickening stage allowing the water to be recovered without this water being mixed with the recycled water from the first stage or the water from the preceding stages.

[0049] The fraction or fractions having a particle size ranging from 40 to 400 pm and the fraction or fractions having a particle size ranging from 20 to 40 pm or from 10 to 40 pm are, in the first instance, conditioned with flotation reagents and then flotation is carried out.

[0050] The fraction or fractions having a particle size ranging from 40 to 400 pm and the fraction or fractions having a particle size ranging from 20 to 40 pm or from 10 to 40 pm are obtained from the non-flotation of the first stage of flotation are conditioned with the flotation reagents and then a second flotation is carried out.

[0051] Flotation enrichment can be achieved by reverse flotation in two stages.

[0052] First-stage flotation is generally carried out in the presence of an acid, for example sulfuric acid, which acts as a pH regulator "4.5 to 5".

[0053] Flotation is also carried out in the presence of phosphoric acid which acts as a depressant of apatite.

[0054] The carbonate collector can be chosen from the following list of fatty acids or a mixture of the constituents in this list: Oleic Acid and Sodium Dodecyl Sulfate (SDS), Tall Oil and Anionic Phospholane, Linoleic Acid (LA), Linolenic Acid (LNA), Monocarboxylic Fatty Acid, Tall Oil, Dodecanedioic Acid, Sebacic and Adipic Acid, Sodium Oleate, Carboxymethylcellulose, Ethylene Glycol, Sodium Palmitate, Pataua Oil, Andiroba Oil, Sodium Potassium Double Tartrate, Non-ionic Polymers Containing Polyethylene Oxide (PEO), Cetyl Potassium Phosphate. This list does not in any way limit the choice of fatty acids.

[0055] Flotation reagents can be used in combination with foaming and antifoaming agents to adjust the foaming effect.

[0056] The flotation reagents in the second stage are: - phosphoric esters corresponding 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; - Amines and their salts typically correspond to the following formulas: R — O — (CFLjs — NH3 , where R is an alkyl group with 10-14 carbon atoms, or R — O — (CH2)3 — NH — (CH2)3 — NH3 , where R is an alkyl group with 10 or more carbon atoms. Examples include dodecylamine (Cl 2), tetradecylamine (Cl 4), and hexadecylamine (Cl 6).

[0057] Flotation reagents can be used in combination with foaming and antifoaming agents to adjust the foaming effect.

[0058] The process according to the invention allows the production of an ore enriched in phosphates.

[0059] Typically, the ore has a quantity of BPL that is at least 67% higher than the quantity of BPL in the ore subjected to the process, or even 63 to 65% higher or 66 to 67% higher.

[0060] Generally, the ore obtained by the process according to the invention also has a reduced quantity of heavy metals.

[0061] The enriched ore may exhibit one or more of the following characteristics: - a quantity of cadmium less than or equal to 4.5 ppm, typically ranging from 6 to 7 ppm or even from 6 to 7 ppm; - a quantity of nickel less than or equal to 23 ppm, typically ranging from 30 to 35 ppm or even from 23 to 30 ppm; - a quantity of chromium less than or equal to 107 ppm, typically ranging from 107 to 120 ppm or even from 107 to 120 ppm; - a quantity of zinc less than or equal to 170 ppm, typically ranging from 170 to 200 ppm or even from 170 to 200 ppm; - an amount of MgO less than or equal to 0.81% by weight relative to the total weight of the raw charge, typically ranging from 0.81 to 0.88% by weight or from 0.81 to 0.88% by weight.

[0062] The present invention will be better understood by studying a particular embodiment taken by way of non-limiting example and illustrated by the attached drawings.

[0063] Drawing 1 describes a first preferred embodiment of the process of the invention for discharges stored at the level of spreading dikes 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 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 after attrition and desliming) and a fraction having a particle size less than 20 pm (rejects); v. Attrition of the fractions 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 formation of an attrited fraction; vi. Particle size separation with a cut-off at 40 pm of the attrited fraction leading to the formation of an attrited fraction with a particle size ranging from 40 pm to 160 pm (intended for flotation) and an attrited fraction with a particle size less than 40 pm; vii. Particle size separation with a cut-off at 20 pm of the attrited fraction with 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. First stage flotation of fractions with a particle size ranging from 40 pm to 160 pm and of fractions with a particle size ranging from 20 pm to 40 pm leading to the obtaining of a phosphate-enriched ore concentrate free of calcite and dolomite; ix. grinding of the fraction having a particle size less than or equal to 2,500 pm leading to the formation of a ground fraction; x. particle size separation with a cut at 160 pm of the ground fraction leading to the formation of a fraction having a particle size greater than 160 pm and a fraction having a particle size less than or equal to 160 pm; xi. particle size separation with a cut-off 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; xii. attrition of the fraction having a particle size ranging from 40 pm to 160 pm; xiii. narrow particle size separation of the attritioned fraction having a particle size ranging from 40 pm to 160 pm with a cut-off at 40 pm, leading to the formation of an attritioned fraction having a particle size ranging from 40 pm to 160 pm (intended for flotation) and an attritioned fraction having a particle size less than 40 pm; xiv. 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 step 1 of flotation (after attrition and desliming; steps xii and xiii); xv. 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 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); xvi. 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 free of calcite and dolomite.

[0065] The fractions subjected to flotation according to step xvi) join the fractions subjected to flotation according to step viii) described in relation to drawing 1.

[0066] In some embodiments, step i') is carried out with a cut-off at 3150 pm.

[0067] In some embodiments, steps ii and x are carried out with a cut-off at 125, 160, 200, 300 and / or 400 pm.

[0068] In some embodiments, steps vi, vii, xi and xiv are carried out with a break at 10 pm.

[0069] Second-stage flotation of the enriched ore leading to the production of a phosphate-enriched ore concentrate free of calcite, dolomite and silicates.

Claims

DEMANDS 1. Process for enriching a very poor dolomitic silico-carbonate phosphate ore comprising the following steps: - pulping and settling of the ore; - grinding to a mesh size varying from approximately 160 to approximately 200 pm; - 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 about 40 pm and a fraction having a particle size ranging from about 40 to about 125 pm, or from about 40 to about 160 pm, or from about 40 to about 200 pm, or from about 40 to about 400 pm; - particle size separation of the fraction having a particle size less than about 40 pm so as to separate a fraction having a particle size less than about 20 pm, or less than about 10 pm and a fraction having a particle size ranging from about 20 to about 40 pm, or from about 10 to about 40 pm; - flotation of the fraction having a particle size ranging from about 20 to about 40 pm or from about 10 to about 40 pm and of the fraction having a particle size ranging from about 40 to about 125 pm, or from about 40 to about 160 pm, or from about 40 to about 200 pm, or from about 40 to about 400 pm, leading to the obtaining of an ore enriched in phosphates by elimination of calcite and dolomite; - flotation of the fraction having a particle size ranging from about 20 to about 40 pm or from about 10 to about 40 pm and of the fraction having a particle size ranging from about 40 to about 125 pm, or from about 40 to about 160 pm, or from about 40 to about 200 pm, or from about 40 to about 400 pm, leading to the obtaining of an ore enriched in phosphates by the elimination of silicates.

2. The process according to claim 1, wherein the particle size separation steps are carried out by screening, centrifugation, hydrocycloning or by means of a hydrosizer.

3. The process according to claim 1, wherein the succession of particle size separations comprises a particle size separation with a cut-off at approximately 2500 µm leading to a fraction having a particle size less than or equal to approximately 2500 µm and a fraction having a particle size greater than approximately 2500 µm.

4. The process according to claim 3, wherein the succession of narrow particle size separations comprises a narrow particle size separation with a cut-off at approximately 160 µm of the fraction having a particle size less than or equal to approximately 2500 µm leading to the formation of a fraction having a particle size greater than approximately 160 µm and less than or equal to approximately 2500 µm and a fraction having a particle size less than or equal to approximately 160 µm.

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

6. The process according to claim 1 wherein prior to the flotation step, an attrition of the fraction having a particle size ranging from about 40 pm to about 160 pm followed by desliming at about 40 pm leading to the formation of a fraction having a particle size ranging from about 40 pm to about 160 pm and a fraction having a particle size less than about 40 pm, the fraction having a particle size ranging from about 40 pm to about 160 pm obtained being subjected to the flotation step.

7. The process according to claim 4 wherein the fraction having a particle size ranging from about 160 pm to about 2500 pm 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 about 40 pm to about 160 pm and a fraction having a particle size less than about 40 pm, the fraction having a particle size ranging from about 40 pm to about 160 pm obtained being subjected to the flotation step.

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

9. The process according to claim 8 in which the conditioning for flotation is carried out as follows: - flotation in the first stage is carried out in the presence of an acid, preferably sulfuric acid and / or phosphoric acid, which plays the role of regulator of pH 4.5 to 5; - flotation is also carried out in the presence of phosphoric acid which plays the role of depressant of the apatite; - the carbonate collector may be chosen from the following list or from a mixture of the constituents in this list: oleic acid and sodium dodecyl sulfate (SDS), tall oil fatty acids and anionic phospholane, linoleic acid (LA), linolenic acid (LNA), monocarboxylic fatty acid, tall oil, dodecanedioic acid, sebacic and adipic acid, sodium oleate, carboxymethylcellulose, ethylene glycol, sodium palmitate, pataua oil, andiroba oil, sodium potassium double tartrate, non-ionic polymers containing polyethylene oxide (PEO), cetyl potassium phosphate; and in which flotation reagents can be used in combination with foaming and antifoaming agents to adjust the foaming effect.

10. The process according to claim 9 wherein the flotation concentrate "non-floated product" undergoes thickening, giving rise to an Overflow and an Underflow.

11. The process according to any one of claims 1 to 10 wherein the fractions having a particle size less than about 20 pm and the flotation rejects (greater than 20 pm) and the Overflow are rejected at the level of a first settling tank and spreading basin.

12. The process according to claim 11, wherein the return of water from the first settling tank, the first spreading basin and any addition of fresh water at this stage can only be used upstream of the first flotation stage.

13. The process according to claim 1, wherein the conditioning of the Underflow for the second flotation is carried out as follows: - the flotation reagents at the second stage are: phosphoric esters corresponding 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; amines and their salts typically corresponding to the following formulas: R — O — (CH2)3 — NH3, where R is an alkyl group with 10-14 carbon atoms, R — O — (CH2)3 — NH — (CH2)3 — NH3, where R is an alkyl group with 10 or more carbon atoms, optionally dodecylamine (C12), tetradecylamine (C14), and hexadecylamine (C16); and where Flotation reagents can be used in combination with foaming and antifoaming agents to adjust the foaming effect.

14. The process according to claim 13, wherein the floated product "reject from the second flotation" is sent to the level of the second settling tank and spreading basin.

15. The process according to claims 10 and 14, wherein recycled water or any fresh water supplement can only be used downstream of the thickening step.

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