Beneficiation method and system for phosphate ore

Abstract

The present invention relates to a process for producing a phosphate concentrate from an ore containing magnesium, iron and phosphate, and the process comprising the steps of reacting the ore with water and an amphoteric surfactant, thereby providing a first concentrate containing magnesium, iron and phosphorus; in the first low-gradient magnetic separation step, phosphorus and iron in the first concentrate are separated; and collecting a second concentrate comprising phosphorus and a third concentrate comprising iron from the first separation step. The method is characterized in that it further comprises the steps of: classifying the particles in the second concentrate according to a specified cut-off particle size; in a second high-gradient magnetic separation step, further separating phosphorus from magnesium and iron in the classified particles with the particle size smaller than the cut-off particle size; collecting a fourth concentrate comprising phosphorus and a fifth concentrate comprising magnesium and iron from the second separation step; and mixing the particles of the second concentrate, the particle size of which is equal to or higher than the cut-off particle size, with the fourth concentrate, thereby obtaining the phosphate concentrate. The present disclosure further relates to a system for performing the method of the present disclosure.

Description

Phosphate ore beneficiation methods and systems Technical Field

[0001] This disclosure relates to the field of phosphate ore beneficiation. Background Technology

[0002] Phosphate ore is an important raw material for the production of phosphoric acid and NPK fertilizers.

[0003] Phosphoric acid can be prepared by a wet process, in which an inorganic acid (usually sulfuric acid) reacts with calcium phosphate concentrate to form a precipitate of dilute phosphoric acid and calcium sulfate containing approximately 30% P2O5.

[0004] NPK fertilizers can be produced using the nitrate phosphate fertilizer process, which involves digesting phosphate powder with nitrate or with sulfuric acid, followed by the addition of nitrogen and potassium to achieve the target NPK melt (which can then be granulated).

[0005] For successful processing of phosphate powder in phosphoric acid and NPK production, the phosphate powder should be as pure as possible, i.e., as phosphorus-rich as possible. Furthermore, as much phosphorus as possible should be recovered from the ore into the phosphate powder.

[0006] Step a) is mentioned in US6814949B1 (Kemira Chemicals, 2000), in which the phosphate concentrate is directed to a high-intensity magnetic separation step after the froth flotation step to reduce the concentration of magnesium ions. It has thus been recognized that high concentrate quality and high yield can be obtained by adding a high-intensity magnetic separator at the end of the froth flotation cycle.

[0007] This disclosure aims to further improve the yield and quality of phosphate concentrates for ores with complex iron, magnesium and phosphorus mineral compositions. Summary of the Invention

[0008] In one aspect of this disclosure, a method for producing phosphate concentrate is disclosed. The method includes the following steps:

[0009] (a) React magnesium, iron and phosphate ore with water and amphoteric surfactant to separate a first concentrate containing magnesium, iron and phosphorus by flotation;

[0010] (b) In the first magnetic separation step, phosphorus in the first concentrate is separated from magnesium and iron. The first magnetic separation step is a low-gradient magnetic separation step carried out in a magnetic field not exceeding 0.2 T, particularly in the range of 0.1 to 0.2 T; and

[0011] (c) In the first collection step, a second concentrate containing phosphorus and a third concentrate containing magnesium and iron are collected from the first magnetic separation step.

[0012] The method is characterized by further including the following steps:

[0013] (d) The particles in the second concentrate with a diameter lower than the cutoff diameter are classified with a diameter equal to or higher than the cutoff diameter, wherein the cutoff diameter ranges from 30 to 175 µm, or 35 to 160 µm, or 37 to 150 µm.

[0014] (e) In the second magnetic separation step, phosphorus, magnesium and iron are separated from the classified particles with a particle size smaller than the cutoff particle size. The second magnetic separation step is a high-gradient magnetic separation step carried out in a magnetic field above 0.2 T, particularly in the range of 0.25 to 0.5 T, or 0.25 to 1 T, or 0.25 to 1.5 T, or 0.25 to 2 T.

[0015] (f) In the second collection step, a fourth concentrate containing phosphorus and a fifth concentrate containing magnesium and iron are collected from the second high-gradient magnetic separation step; and

[0016] (g) Particles with a diameter equal to or greater than the cutoff diameter of the second concentrate are blended with the fourth concentrate to obtain phosphate concentrate.

[0017] The inventors surprisingly discovered that all particles of a concentrate containing phosphorus, magnesium, and iron minerals can be subjected to a first low-gradient magnetic separation step to obtain phosphate and iron concentrates. Furthermore, by classifying the particles in the obtained phosphate concentrate, allowing particles with diameters below the cutoff size to undergo further processing in an additional high-gradient magnetic separation step, higher phosphorus recovery and a more concentrated phosphate concentrate can be obtained. In fact, this high-gradient magnetic separation step produces both phosphate concentrate and a magnesium concentrate containing iron, which was not separated from phosphorus in the first low-gradient magnetic separation step. By combining the phosphate concentrates obtained from the two magnetic separation steps, an even higher phosphorus recovery and a more concentrated phosphate concentrate are thus achieved.

[0018] In one embodiment of the method according to the present disclosure, the method further includes the following steps: (h) separating phosphorus from magnesium and iron in a third magnetic separation step (which is a high-gradient magnetic separation step) from the classified particles with a particle size equal to or greater than the cutoff particle size; (i) collecting a seventh concentrate containing phosphorus and an eighth concentrate containing magnesium and iron from the third magnetic separation step in a third collection step; and (j) blending the seventh concentrate with the fourth concentrate to produce the phosphate concentrate.

[0019] In one embodiment of the method according to this disclosure, the magnesium content in the fourth concentrated phosphate concentrate and / or (optionally) the seventh concentrated phosphate concentrate is measured, and the magnetic field and (optionally) rotation speed in the second magnetic separation step and / or (optionally) the third magnetic separation step are adjusted accordingly, such that the MgO content measured in the concentrate is 0.7 to 1.1 wt%.

[0020] In one embodiment of the method according to this disclosure, the magnetic field generated in the second and / or third magnetic separation steps is 0.9 to 1.1 T.

[0021] In one embodiment of the method according to this disclosure, in the first magnetic separation step, the second magnetic separation step, and / or the third magnetic separation step, the flow rate of the corresponding concentrate in the magnetic separator is 150 to 250 m³. 3 / h.

[0022] In one embodiment of the method according to this disclosure, the first magnetic separation step, the second magnetic separation step, and / or the third magnetic separation step are performed in a magnetic separator that rotates at a speed of 50 to 160 mm / s.

[0023] In one embodiment of the method according to this disclosure, the magnesium, iron and phosphate ore comprises 3.0 to 8.0 wt% P2O5, 5.0 to 19.0 wt% MgO and 6.0 to 15.0 wt% Fe2O3, particularly wherein the magnesium, iron and phosphate ore comprises 5.0 to 8.0 wt% P2O5, 5.0 to 8.0 wt% MgO and 10.0 to 15.0 wt% Fe2O3.

[0024] In one embodiment of the method according to this disclosure, the reaction step further includes the use of an emulsifier, particularly wherein the reaction step uses a fatty acid as an amphoteric surfactant and an ethoxylated alcohol as an emulsifier.

[0025] In one embodiment of the method according to this disclosure, the reaction step is carried out using 400 to 600 grams of surfactant per ton of ore.

[0026] In one embodiment of the method according to this disclosure, the temperature in the reaction step is 20 to 25°C, and / or the pH in the reaction step is pH 8 to pH 9.

[0027] In one aspect of this disclosure, a system for producing phosphate concentrate is disclosed. The system is adapted to perform the methods of this disclosure and includes:

[0028] * A reactor used to react ores containing magnesium, iron, and phosphate with water and amphoteric surfactants, such as to separate a first concentrate containing magnesium, iron, and phosphorus by flotation;

[0029] * A first magnetic separator, configured to perform low-gradient and optionally high-gradient magnetic separation downstream of the reactor, for separating phosphorus from magnesium and iron in the first concentrate at a low magnetic gradient.

[0030] * A first collector for collecting a second concentrate containing phosphorus and magnesium and a third concentrate containing iron from a first magnetic separator;

[0031] * A classifier, located downstream of the first collector, is used to classify particles in the second concentrate into particles with a diameter smaller than the cutoff diameter and particles with a diameter equal to or greater than the cutoff diameter.

[0032] * A second magnetic separator is configured to perform high-gradient magnetic separation downstream of the classifier to separate phosphorus from magnesium and iron in classified particles with a particle size smaller than the cutoff particle size under a high magnetic gradient.

[0033] * A second collector for collecting a fourth concentrate containing phosphorus and a fifth concentrate containing magnesium and iron from a second magnetic separator; and

[0034] * Blending unit, used to blend the fourth concentrate with classified particles of a size equal to or greater than the cutoff particle size.

[0035] In one embodiment of the system according to this disclosure, the system further includes:

[0036] * A third magnetic separator, configured to perform high-gradient magnetic separation downstream of the classifier, is used to separate phosphorus from magnesium and iron in classified particles with a diameter equal to or greater than the cutoff diameter under a high magnetic gradient; and

[0037] * The third collector is used to collect the seventh concentrate containing phosphorus and the eighth concentrate containing magnesium and iron from the third magnetic separator;

[0038] The blending unit is used to blend the fourth concentrate with the seventh concentrate.

[0039] In one embodiment of the system according to this disclosure, the first magnetic separator is configured for both low-gradient magnetic separation and high-gradient magnetic separation, the first magnetic separator being the same as the second magnetic separator and / or the third magnetic separator, the system further including means for transferring graded particles with a particle size below the cutoff particle size to the first magnetic separator, and optionally, the system further including means for transferring graded particles with a particle size equal to or above the cutoff particle size to the first magnetic separator; and / or the second collector and / or (optionally) the third collector being the same collector.

[0040] In one embodiment of the system according to the present disclosure, the system further includes a control loop comprising an analyzer adapted to analyze the magnesium content in the fourth concentrated phosphate concentrate and / or ...

[0041] In one aspect of this disclosure, the use of the system disclosed herein for carrying out the methods disclosed herein is disclosed.

[0042] Figure 1 is a schematic diagram depicting an embodiment of the system of this disclosure.

[0043] Figure 2 is a schematic diagram depicting an embodiment of the system of this disclosure.

[0044] List of figure marks / symbols used in the attached figures

[0045]

[0046] manual

[0047] Throughout the description and claims of this application, the word "comprising" and its variations mean "including but not limited to," and are not intended (and do not) exclude other parts, additions, components, integrals, or steps. Throughout the description and claims of this disclosure, unless the context requires otherwise, the singular reference includes the plural. In particular, where the indefinite article is used, unless the context requires otherwise, this disclosure will be understood to consider both the plural and the singular.

[0048] Features, integrals, properties, compounds, chemical portions, or groups described in conjunction with specific aspects, embodiments, or examples of this disclosure shall be understood to be applicable to any other aspect, embodiment, or example described herein, unless incompatible therewith. All features of the features disclosed in this disclosure (including the description, claims, abstract, and drawings) and / or all steps of any method or process disclosed herein may be combined in any combination, except for combinations in which at least some of the features and / or steps are mutually exclusive. This disclosure is not limited to the details of any of the foregoing embodiments. This disclosure extends to any novel feature or combination of novel features disclosed in the features disclosed in this disclosure (including the description, claims, abstract, and drawings), or to any novel step or combination of novel steps of any method or process disclosed herein.

[0049] The numerical values ​​listed with the aid of the accompanying figures include all values ​​and fractions within these ranges, as well as the referenced endpoint values. The terms “range from… to…” or “within the range of… to…” or “up to”, used when referring to a range of measurable values ​​(such as parameters, quantities, time periods, etc.), are intended to include the limits associated with the disclosed range.

[0050] Throughout this disclosure, the concentrations of phosphorus, magnesium, and iron are conveniently expressed as the concentrations of P2O5, MgO, and Fe2O3, respectively.

[0051] In one aspect of this disclosure, a method for producing phosphate concentrate is disclosed. The method includes the following steps:

[0052] (a) React magnesium, iron and phosphate ore with water and amphoteric surfactant to separate a first concentrate containing magnesium, iron and phosphorus by flotation;

[0053] (b) In the first magnetic separation step, phosphorus in the first concentrate is separated from magnesium and iron. The first magnetic separation step is a low-gradient magnetic separation step carried out in a magnetic field not exceeding 0.2 T, particularly in the range of 0.1 to 0.2 T; and

[0054] (c) In the first collection step, a second concentrate containing phosphorus and a third concentrate containing magnesium and iron are collected from the first magnetic separation step.

[0055] The method is characterized by further including the following steps:

[0056] (d) The particles in the second concentrate with a diameter lower than the cutoff diameter are classified with a diameter equal to or higher than the cutoff diameter, wherein the cutoff diameter ranges from 30 to 175 µm, or 35 to 160 µm, or 37 to 150 µm.

[0057] (e) In the second magnetic separation step, phosphorus, magnesium and iron are separated from the classified particles with a particle size smaller than the cutoff particle size. The second magnetic separation step is a high-gradient magnetic separation step carried out in a magnetic field above 0.2 T, particularly in the range of 0.25 to 0.5 T, or 0.25 to 1 T, or 0.25 to 1.5 T, or 0.25 to 2 T.

[0058] (f) In the second collection step, a fourth concentrate containing phosphorus and a fifth concentrate containing magnesium and iron are collected from the second high-gradient magnetic separation step; and

[0059] (g) Particles with a diameter equal to or greater than the cutoff diameter of the second concentrate are blended with the fourth concentrate to obtain phosphate concentrate.

[0060] Specifically, the ore contains phosphorus, iron, and magnesium in the form of phosphate minerals, iron minerals, and magnesium minerals, respectively.

[0061] Those skilled in the art can assess the optimal cutoff particle size based on the ore being processed for the production of phosphate concentrate. That is, based on the composition of the starting ore, those skilled in the art can routinely establish the cutoff particle size in the classification steps to obtain optimal second and third concentrates. This means that, for fixed parameters in the high-gradient magnetic separation step, the second high-gradient magnetic separation step produces the most phosphorus-enriched fourth concentrate, and the sixth concentrate (i.e., the final phosphate concentrate) provides the maximum phosphorus recovery from the starting ore. Specifically, this cutoff particle size is 30 to 175 μm. More specifically, the cutoff particle size is 35 to 160 μm. Even more specifically, the cutoff particle size is 37 to 150 μm.

[0062] The inventors surprisingly discovered that all particles of a concentrate containing phosphorus, magnesium, and iron minerals can be subjected to a first low-gradient magnetic separation step to obtain phosphorus and iron concentrates. Furthermore, by classifying the particles in the obtained phosphorus concentrate, allowing particles with diameters below the cutoff size to undergo further processing in an additional high-gradient magnetic separation step, higher phosphorus recovery and a more concentrated phosphorus concentrate can be obtained. In fact, this high-gradient magnetic separation step produces both phosphorus-containing concentrate and magnesium-containing concentrate containing iron, which was not separated from phosphorus in the first low-gradient magnetic separation step. By combining the phosphorus concentrates obtained from the two magnetic separation steps, an even higher phosphorus recovery and a more concentrated phosphorus concentrate are thus achieved.

[0063] In mining or extractive metallurgy, mineral processing is any process that increases the economic value of an ore by removing gangue minerals, resulting in a higher-grade product (ore concentrate) and a waste stream (tailings). There are many mineral processing methods, each step further increasing the concentration of the raw ore. The mineral processing process can include the following three steps: liberation, physical separation, and chemical separation.

[0064] Mineral processing can begin within the mine with a liberation step. Most mines have crushers within the mine, where the ore is separated from gangue minerals, and as a byproduct, becomes easier to transport. After crushing, the ore passes through a grinding mill or mill to become finer particles. Heavy media separation (DMS) is used to further separate the desired ore from the rock and gangue minerals. This stratifies the crushed material by density, making separation easier. The location of the DMS in the process can be important; if DMS is performed earlier, the grinding mill or mill will process significantly less waste rock. This reduces equipment wear and tear, and also lowers operating costs due to reduced throughput.

[0065] Following the liberation step and during the physical separation step, the ore can be further separated from the rock. One method to achieve this is to utilize the physical properties of the ore to separate it from other parts of the rock. These processes include gravity separation, flotation, and magnetic separation. Gravity separation uses centrifugal force and the specific gravity of the ore and gangue to separate them. Magnetic separation is used to separate magnetic gangue from the desired ore, or conversely, to remove the magnetic target ore from non-magnetic gangue. DMS is also considered a form of physical separation.

[0066] In this disclosure, physical separation is performed via magnetic separation. Magnetic separation is a process that uses magnets to attract magnetic materials to separate components of a mixture. The magnetic separation process separates non-magnetic materials from magnetic materials. This technique is applicable to a few specific minerals that exhibit both ferromagnetism (such as iron-, nickel-, and cobalt-containing minerals) and paramagnetism (such as magnesium-containing minerals). Ferromagnetism is a property of certain materials (such as iron) that results in significant, observable permeability and, in many cases, significant coercivity—the ability to resist demagnetization by an external magnetic field—allowing the material to form permanent magnets. Paramagnetism is a form of magnetism in which materials exhibit weak attraction to an externally applied magnetic field, creating an internal induced magnetic field in the direction of the applied field. Due to the presence of unpaired electrons in the material, these unpaired electrons have magnetic dipole moments on their spins, behaving like tiny magnets. The external magnetic field aligns the electron spins parallel to the direction of the magnetic field, resulting in a net attraction.

[0067] A variety of mechanical methods can be used to separate magnetic materials. In a particular embodiment, during magnetic separation, magnets are located inside two separator drums containing steel coils and a liquid such as water. Under the influence of the magnets, magnetic particles migrate due to the movement of the drums. An electric current passes through the coils to generate a magnetic field, which magnetizes an expanded steel matrix ring. The magnetic matrix material behaves like a magnet in the magnetic field, thereby attracting magnetic particles. The ring is rinsed while in the magnetic field, and all non-magnetic particles are carried away with the rinse water. Then, as the ring leaves the magnetic zone, it is rinsed and a vacuum of approximately -0.3 bar is applied to remove the magnetic particles attached to the matrix ring. This produces a concentrate (e.g., ore concentrate) and thus achieves the separation of non-magnetic concentrates (e.g., phosphate concentrate) from magnetic concentrates (e.g., iron concentrate).

[0068] Magnetic separators using permanent magnets can only generate low-intensity magnetic fields, i.e., low magnetic field strength gradients. In contrast, high-intensity magnetic separators can generate fields with high magnetic field strength. Low-gradient magnetic separation is effective at removing ferromagnetic particles, but it is not very effective at removing fine paramagnetic particles. High-intensity magnetic separators, on the other hand, are effective at collecting paramagnetic particles, and are particularly suitable for separating very fine paramagnetic particles. US6814949B1 teaches that for ores containing phosphorus, iron, and magnesium minerals, all particles of the ore should be processed together in a single high-gradient magnetic separation step.

[0069] However, contrary to the teachings of US6814949B1, the inventors surprisingly discovered that all particles of a concentrate containing phosphorus, magnesium, and iron minerals can be subjected to a first low-gradient magnetic separation step to obtain phosphate and iron concentrates. Furthermore, by classifying the particles in the obtained phosphate concentrate, allowing particles with a diameter below a specified cutoff size to be further processed through an additional high-gradient magnetic separation step, higher phosphorus recovery and a more enriched phosphate concentrate can be obtained. Optionally, the classified particles with a diameter equal to or greater than the specified cutoff size can also be further processed via a high-gradient magnetic separation step. In effect, this high-gradient magnetic separation step produces both phosphate concentrate and a magnesium concentrate containing iron, which was not separated from phosphorus in the first low-gradient magnetic separation step. By combining the phosphate concentrates obtained from the two magnetic separation steps, a higher phosphorus recovery and a more enriched phosphate concentrate are thus achieved.

[0070] However, in this disclosure, separation cannot rely solely on the physical properties of the ore; therefore, a further chemical process, namely a reactive flotation step, is performed prior to magnetic separation to separate the ore from the rock. In fact, this disclosure uses a flotation step prior to the magnetic separation step. Foam flotation utilizes hydrophobicity and hydrophilicity to separate ore from gangue. Hydrophobic particles rise to the top of the solution for skimming. Changes in the pH of the solution can affect which particles are hydrophilic. One way to separate the desired ore from the rock is to make the ore more hydrophobic than the rock particles, thereby achieving selective precipitation of the desired ore particles. Alternatively, the desired ore particles can be made more hydrophilic than the rock particles, causing unwanted solids to precipitate and the desired ore to be recovered after evaporation of the aqueous solution. The difference in hydrophobicity or hydrophilicity between ore and rock particles can be achieved by using chemical reagents that selectively aggregate on the ore or rock particles.

[0071] Choosing appropriate flotation chemicals, along with suitable temperature and pH, can improve the separation of ore particles from rock particles. In this disclosure, an amphoteric surfactant is used. An amphoteric surfactant is a molecule that simultaneously carries a positive and a negative charge, which can be permanent or pH-dependent, thereby increasing the flexibility of its interaction with the hydrophobic particles to be precipitated.

[0072] In one embodiment of the method according to this disclosure, the method includes the following steps:

[0073] (a) React magnesium, iron and phosphate ore with water and amphoteric surfactant to separate a first concentrate containing magnesium, iron and phosphorus by flotation;

[0074] (b) In the first magnetic separation step, phosphorus in the first concentrate is separated from magnesium and iron. The first magnetic separation step is a low-gradient magnetic separation step carried out in a magnetic field not exceeding 0.2 T, particularly in the range of 0.1 to 0.2 T; and

[0075] (c) In the first collection step, a second concentrate containing phosphorus and a third concentrate containing magnesium and iron are collected from the first magnetic separation step.

[0076] The method is characterized by further including the following steps:

[0077] (d) The particles in the second concentrate with a diameter lower than the cutoff diameter are classified with a diameter equal to or higher than the cutoff diameter, wherein the cutoff diameter ranges from 30 to 175 µm, or 35 to 160 µm, or 37 to 150 µm.

[0078] (e) In the second magnetic separation step, phosphorus, magnesium and iron are separated from the classified particles with a particle size smaller than the cutoff particle size. The second magnetic separation step is a high-gradient magnetic separation step carried out in a magnetic field above 0.2 T, particularly in the range of 0.25 to 0.5 T, or 0.25 to 1 T, or 0.25 to 1.5 T, or 0.25 to 2 T.

[0079] (f) In the second collection step, a fourth concentrate containing phosphorus and a fifth concentrate containing magnesium and iron are collected from the second high-gradient magnetic separation step.

[0080] (h) In the third magnetic separation step, phosphorus, magnesium and iron are separated from the particles whose particle size is equal to or greater than the cutoff particle size after classification. The third magnetic separation step is a high gradient magnetic separation step.

[0081] (i) In the third collection step, a seventh concentrate containing phosphorus and an eighth concentrate containing magnesium and iron are collected from the third magnetic separation step; and

[0082] (j) The seventh concentrate is blended with the fourth concentrate to obtain phosphate concentrate.

[0083] By processing fine and larger particles separately relative to a specified cutoff particle size (separated according to the grading steps) in a magnetic separator with a high gradient magnetic field, and then combining the phosphate concentrate obtained from each high gradient magnetic separation step, a more enriched phosphate concentrate was obtained compared to the case where fine particles were processed only by a high gradient magnetic separation step.

[0084] In one embodiment of the method according to this disclosure, the magnesium content in the fourth concentrated phosphate concentrate and / or (optionally) the seventh concentrated phosphate concentrate is measured, and the magnetic field and (optionally) rotation speed in the second magnetic separation step and / or (optionally) the third magnetic separation step are adjusted accordingly, such that the MgO content measured in the concentrate is 0.7 to 1.1 wt%.

[0085] In fact, the magnesium content in the fourth and (optionally) seventh concentrates can be used to improve the separation of phosphorus and magnesium in the second and (optionally) third magnetic separation steps, i.e., adjusting the magnetic field and rotation speed according to the measured magnesium content level.

[0086] In one embodiment of the method according to this disclosure, in the second magnetic separation step and / or the third magnetic separation step, the generated magnetic field is 0.9 to 1.1 T.

[0087] When the magnetic field is within this range, the separation of phosphorus during magnetic separation is improved.

[0088] In one embodiment of the method according to this disclosure, in the first magnetic separation step, the second magnetic separation step, and / or the third magnetic separation step, the flow rate of the corresponding concentrate in the magnetic separator is 150 to 250 m³. 3 / h.

[0089] At this flow rate of the magnetic separator, the concentration of the ore and its residence time in the magnetic separator improve the separation of phosphorus during the magnetic separation process.

[0090] In one embodiment of the method according to this disclosure, the first magnetic separation step, the second magnetic separation step, and / or the third magnetic separation step are performed in a magnetic separator that rotates at a speed of 50 to 160 mm / s.

[0091] At this rotational speed, the residence time of the ore within the magnetic separator improves the separation of phosphorus during the magnetic separation process.

[0092] In one embodiment of the method according to this disclosure, the magnesium, iron and phosphate ore comprises 3.0 to 8.0 wt% P2O5, 5.0 to 19.0 wt% MgO and 6.0 to 15.0 wt% Fe2O3, particularly wherein the magnesium, iron and phosphate ore comprises 5.0 to 8.0 wt% P2O5, 5.0 to 8.0 wt% MgO and 10.0 to 15.0 wt% Fe2O3.

[0093] It has been found that when the starting raw material ore contains such concentrations of phosphorus, magnesium and iron, the method of this disclosure can achieve particularly satisfactory phosphorus recovery and phosphorus enrichment of the produced phosphate concentrate.

[0094] In one embodiment of the method according to this disclosure, the reaction step further includes the use of an emulsifier, particularly wherein the reaction step uses a fatty acid as an amphoteric surfactant and an ethoxylated alcohol as an emulsifier.

[0095] By using emulsifiers, the precipitated particles are stabilized and become more homogeneous because they do not aggregate or agglomerate. Furthermore, it has been found that the combination of fatty acids as surfactants with ethoxylated alcohol emulsifiers can improve the reaction in the reactive flotation step.

[0096] In one embodiment of the method according to this disclosure, the reaction step is carried out using 400 to 600 grams of surfactant per ton of ore.

[0097] It has been found that the reactive flotation step requires an appropriate amount of surfactant to successfully separate the ore particles to be processed in the reaction step and then in the separation step. Once the addition of an additional surfactant results in stable ore separation (i.e., a change of no more than 5%, preferably 2%, or even more preferably 1%), it can be concluded that the correct amount of surfactant is being used.

[0098] In one embodiment of the method according to this disclosure, the temperature in the reaction step is 20 to 25°C, and / or the pH in the reaction step is pH 8 to pH 9.

[0099] It has been found that a temperature range of 20 to 25°C and / or a pH of 8 to 9 can improve the reaction in the reactive flotation step. NaOH, Na₂CO₃, or Na₂CO₃ can all be used to achieve pH control in the reactive flotation step.

[0100] Referring to Figure 1, in one aspect of this disclosure, a system for producing phosphate concentrate is disclosed. This system is adapted to perform the methods of this disclosure and includes:

[0101] * A reactor used to react ores containing magnesium, iron, and phosphate with water and amphoteric surfactants, such as to separate a first concentrate containing magnesium, iron, and phosphorus by flotation;

[0102] * A first magnetic separator, configured for low-gradient magnetic separation and optionally high-gradient magnetic separation, is located downstream of the reactor for separating phosphorus from the first concentrate, particularly from iron and optionally from some magnesium, at a low magnetic gradient.

[0103] * A first collector or collecting device for collecting a second concentrate containing phosphorus and magnesium and a third concentrate containing iron from the first magnetic separator;

[0104] * A classifier, downstream of the first collector or collecting device, for classifying particles in the second concentrate with a diameter smaller than a specified cutoff diameter from particles with a diameter equal to or greater than the cutoff diameter.

[0105] * A second magnetic separator is configured to perform high-gradient magnetic separation downstream of the classifier to separate phosphorus from magnesium and iron in classified particles with a particle size smaller than the cutoff particle size under a high magnetic gradient.

[0106] * A second collector or collecting device for collecting from the second magnetic separator a fourth concentrate containing phosphorus and a fifth concentrate containing magnesium and iron; and

[0107] * Blending unit, particularly for blending the fourth concentrate with graded particles of a diameter equal to or greater than the cutoff diameter.

[0108] The system disclosed herein is adapted to perform the methods of this disclosure. Therefore, the system disclosed herein contains all the necessary elements for performing the reaction, separation, and collection steps.

[0109] Specifically, and taking into account the aforementioned benefits of processing particles smaller than the cutoff particle size in an additional high-gradient magnetic separation step, the system includes a classifier for classifying particles in the second concentrate according to a specified cutoff particle size. Further, the system includes a magnetic separator suitable for low-gradient magnetic separation and a magnetic separator suitable for high-gradient magnetic separation. Moreover, the system includes collectors for collecting the second and third concentrates provided by the first low-gradient magnetic separation step, and collectors for collecting the fourth and fifth concentrates provided by the second high-gradient magnetic separation step, respectively. Additionally, the system includes a blending unit for blending the fourth concentrate with particles from the second concentrate that have been classified to have a particle size equal to or greater than the cutoff particle size.

[0110] Referring further to Figure 2. In one embodiment of the system according to the present disclosure, the system further includes a third magnetic separator configured for high-gradient magnetic separation, located downstream of the classifier, for separating phosphorus from both magnesium and iron in the classified particles with a particle size equal to or greater than the cutoff particle size under a high magnetic gradient; and a third collector for collecting a seventh concentrate containing phosphorus and an eighth concentrate containing magnesium and iron from the third magnetic separator, wherein the blending unit is used to blend the fourth concentrate and the seventh concentrate.

[0111] The system can be equipped with a third separation step of high-gradient magnetic separation to perform on the coarser particles obtained from the grading step. In addition, the system is equipped with collectors for collecting the seventh and eighth concentrates provided by the third magnetic separation step.

[0112] In one embodiment of the system according to this disclosure, the first magnetic separator is configured for both low-gradient magnetic separation and high-gradient magnetic separation, the first magnetic separator being the same as the second magnetic separator and / or the third magnetic separator, the system further including means for transferring graded particles with a particle size below the cutoff particle size to the first magnetic separator, and optionally, the system further including means for transferring graded particles with a particle size equal to or above the cutoff particle size to the first magnetic separator; and / or the second collector and / or (optionally) the third collector being the same collector.

[0113] If the magnetic separator used for the first magnetic separation step is also suitable for both low-gradient and high-gradient magnetic separation, then the same magnetic separator can be used to perform all the first, second, and third magnetic separation steps, respectively. Similarly, if the collectors used to collect the second and third concentrates are also suitable for collecting the fourth and fifth concentrates, as well as the seventh and eighth concentrates, then the same collector can be used to perform the first, second, and third collection steps, respectively.

[0114] In one embodiment of the system according to the present disclosure, the system further includes a control loop comprising an analyzer adapted to analyze the magnesium content in the fourth concentrated phosphate concentrate and / or ...

[0115] In view of the aforementioned benefits of determining the magnesium concentration in the fourth and (optionally) seventh concentrates, the system further includes an analyzer for analyzing the magnesium content in these concentrates, and a control loop that allows adjustment of the magnetic fields in the second and (optionally) third magnetic separators to produce fourth and (optionally) seventh concentrates with magnesium content below a set limit.

[0116] In one aspect of this disclosure, the use of the system disclosed herein for carrying out the methods disclosed herein is disclosed.

[0117] Example

[0118] Referring to Figure 1. In the first flotation step, 500 g of ore containing 6.4 wt% P2O5, 7.1 wt% MgO, and 11.4 wt% Fe2O3 was reacted with water and Nouryon's Atrac 1563 compound (containing 50-100% tall oil maleate, a fatty acid, and 1-5% maleic anhydride) in reactor (1) at 21°C and pH 8.7 for 45 minutes. This yielded a first concentrate (C1) containing 28.3 wt% P2O5, 2.2 wt% MgO, and 1.5 wt% Fe2O3. This first concentrate (C1) was then subjected to a low-gradient first magnetic separation step in a first magnetic separator (2). In this low-gradient magnetic separation step, the magnetic field was set to 0.2 T, the rotation speed was set to 110 mm / s, and the concentrate flow rate in the magnetic separator was set to 200 m³ / s. 3 / h. The second concentrate (C2) is collected at the bottom of the magnetic separator in the first collector (3), and the third concentrate (C3) is washed out from the magnet inside the first magnetic separator (2) and collected separately in the first collector (3). The second concentrate (C2) is then classified in the classifier (4) to separate particles with a diameter less than 37 μm. These classified particles are then subjected to a high-gradient second magnetic separation step in the second magnetic separator (5). In this high-gradient magnetic separation step, the magnetic field is set to 0.25 T, the rotation speed is set to 110 mm / s, and the concentrate flow rate in the magnetic separator is set to 200 m³ / s. 3 / h. The fourth concentrate (C4), containing 35.4 wt% P2O5, 0.9 wt% MgO, and 0.4 wt% Fe2O3, is collected at the bottom of the second magnetic separator (5) in the second collector (6); and the fifth concentrate (C5), containing 25.5 wt% P2O5, 4.1 wt% MgO, and 3.9 wt% Fe2O3, is washed out from the magnet inside the second magnetic separator (5) and collected separately in the second collector (6). Particles with a diameter of 37 μm or larger are separately subjected to a high-gradient third magnetic separation step in the third magnetic separator (8). In this subsequent high-gradient magnetic separation step, the magnetic field is set to 0.5 T, the rotation speed is set to 110 mm / s, and the concentrate flow rate in the magnetic separator is set to 200 m³ / s. 3 / h. The seventh concentrate (C7), containing 33.3 wt% P2O5, 0.8 wt% MgO, and 0.4 wt% Fe2O3, is collected at the bottom of the third magnetic separator (8) in the third collector (9); and the eighth concentrate (C8), containing 17.1 wt% P2O5, 4.3 wt% MgO, and 3.0 wt% Fe2O3, is washed out from the magnet inside the third magnetic separator (9) and collected separately in the third collector (9). The fourth concentrate (C4) and the seventh concentrate (C7) are blended in the blending unit (7) to produce the sixth concentrate, containing 34.4 wt% P2O5, 0.8 wt% MgO, and 0.4 wt% Fe2O3, referred to herein as the final phosphate concentrate (C6). The recovery rate of phosphorus in the ore in the phosphate concentrate is calculated to be 65.7%. Magnesium concentrations were measured in the fourth concentrate (C2) and the seventh concentrate (C4) to optimize the magnetic field strength, separator speed, and concentrate flow rate in the corresponding second and third high-gradient magnetic separation steps for supplying these concentrates, if needed. When no classification step was performed and high-gradient magnetic separation was not applied to unclassified particles, the resulting phosphate concentrate had a P2O5 concentration of 32.9% and a P2O5 recovery of 65.5%.

[0119] It was also found that when the magnetic field in the second and third magnetic separation steps was in the range of 0.9 to 1.1 T, the P2O5 concentration in the phosphate concentrate and the recovery rate of phosphorus in the ore were improved.

Claims

1. A method for producing phosphate concentrate, comprising the following steps: (a) reacting a magnesium, iron, and phosphate-containing ore with water and an amphoteric surfactant to separate a first concentrate containing magnesium, iron, and phosphorus by flotation; (b) in a first magnetic separation step, separating phosphorus from magnesium and iron in the first concentrate, the first magnetic separation step being a low-gradient magnetic separation step performed in a magnetic field not exceeding 0.2 T, particularly in the range of 0.1 to 0.2 T; and (c) in a first collection step, collecting a second concentrate containing phosphorus and a third concentrate containing magnesium and iron from the first magnetic separation step; wherein the method further comprises the steps of: (d) classifying particles in the second concentrate with a particle size below a cutoff particle size from particles with a particle size equal to or higher than the cutoff particle size, wherein the cutoff particle size ranges from 30 to 175 µm, or 35 to 160 µm, or 37 to 150 µm; (e) in a second magnetic separation step, separating phosphorus from magnesium and iron in the classified particles with a particle size smaller than the cutoff particle size, the second magnetic separation step being performed in a magnetic field higher than 0.2 T. (f) a high-gradient magnetic separation step performed under a magnetic field in the range of 0.25 to 0.5 T, or 0.25 to 1 T, or 0.25 to 1.5 T, or 0.25 to 2 T; and (g) in a second collection step, collecting a fourth concentrate containing phosphorus and a fifth concentrate containing magnesium and iron from the second high-gradient magnetic separation step; and (g) blending particles of the second concentrate with a particle size equal to or greater than the cutoff particle size with the fourth concentrate to obtain the phosphate concentrate.

2. The method according to claim 1, further comprising the following steps: (h) In the third magnetic separation step, phosphorus, magnesium, and iron are separated from the classified particles with a particle size equal to or greater than the cutoff particle size, the third magnetic separation step being a high-gradient magnetic separation step; (i) In the third collection step, a seventh concentrate containing phosphorus and an eighth concentrate containing magnesium and iron are collected from the third magnetic separation step; and (j) The seventh concentrate is blended with the fourth concentrate to obtain the phosphate concentrate.

3. The method according to claim 1 or 2, wherein, The magnesium content in the fourth concentrated phosphate concentrate and / or optionally the seventh concentrated phosphate concentrate is measured, and the magnetic field and optional rotation speed in the second magnetic separation step and / or optionally the third magnetic separation step are adjusted respectively, so that the measured MgO content in the concentrate is in the range of 0.7 to 1.1% by weight.

4. The method according to any one of claims 1 to 3, wherein the magnetic field generated in the second magnetic separation step and / or the third magnetic separation step is in the range of 0.9 to 1.1 T.

5. The method according to any one of claims 1 to 4, wherein in the first magnetic separation step, the second magnetic separation step, and / or the third magnetic separation step, the flow rate of the corresponding concentrate in the separator is between 150 and 250 m³. 3 Within the range of / h.

6. The method according to any one of claims 1 to 5, wherein the first magnetic separation step, the second magnetic separation step and / or the third magnetic separation step are performed in a magnetic separator that rotates at a speed in the range of 50 to 160 mm / s.

7. The method according to any one of claims 1 to 6, wherein the magnesium, iron and phosphate-containing ore comprises 3.0 to 8.0 wt% P2O5, 5.0 to 19.0 wt% MgO and 6.0 to 15.0 wt% Fe2O3, particularly wherein the magnesium, iron and phosphate-containing ore comprises 5.0 to 8.0 wt% P2O5, 5.0 to 8.0 wt% MgO and 10.0 to 15.0 wt% Fe2O3.

8. The method according to any one of claims 1 to 7, wherein the reaction step further comprises using an emulsifier, particularly wherein the reaction step is carried out using a fatty acid as the amphoteric surfactant and an ethoxylated alcohol as the emulsifier.

9. The method of claim 8, wherein the reaction step is carried out using 400 to 600 grams of surfactant per ton of ore.

10. The method according to any one of claims 1 to 9, wherein the temperature in the reaction step is in the range of 20°C to 25°C, and / or the pH in the reaction step is in the range of pH 8 to pH 9.

11. A system for producing phosphate concentrate and suitable for carrying out the method according to any one of claims 1 to 10, comprising: * A reactor for reacting magnesium, iron, and phosphate-containing ores with water and an amphoteric surfactant, such as to separate the first concentrate containing magnesium, iron, and phosphorus by flotation; * A first magnetic separator configured downstream of the reactor to perform low-gradient and optionally high-gradient magnetic separation for separating phosphorus from both magnesium and iron in the first concentrate at a low magnetic gradient; * A first collector for collecting the second concentrate containing phosphorus and magnesium and the third concentrate containing iron from the first magnetic separator; * A classifier downstream of the first collector for classifying particles in the second concentrate into particles with a diameter smaller than the cutoff diameter and particles with a diameter equal to or greater than the cutoff diameter. * A second magnetic separator configured to perform high-gradient magnetic separation downstream of the classifier for separating phosphorus from magnesium and iron in classified particles with a particle size smaller than the cutoff particle size under a high magnetic gradient; * A second collector for collecting the fourth concentrate containing phosphorus and the fifth concentrate containing magnesium and iron from the second magnetic separator. And a blending unit for blending the fourth concentrate with particles of graded size equal to or greater than the cutoff size.

12. The system of claim 11, further comprising: * A third magnetic separator configured to perform high-gradient magnetic separation downstream of the classifier for separating phosphorus from magnesium and iron in classified particles with a diameter equal to or greater than the cutoff diameter under a high magnetic gradient; and * a third collector for collecting the seventh concentrate containing phosphorus and the eighth concentrate containing magnesium and iron from the third magnetic separator; wherein the blending unit is for blending the fourth concentrate with the seventh concentrate.

13. The system according to claim 11 or 12, wherein: * The first magnetic separator is configured for both low-level and high-level magnetic separation, wherein the first magnetic separator and the second magnetic separator and / or the third magnetic separator are the same magnetic separator, wherein the system further includes a component for transferring classified particles with a diameter below the cutoff diameter to the first magnetic separator, and optionally wherein the system further includes a component for transferring classified particles with a diameter equal to or greater than the cutoff diameter to the first separator; and / or * the second collector and / or optionally the third collector are the same collector.

14. The system according to any one of claims 11 to 13, further comprising a control loop including an analyzer adapted to analyze the magnesium content in the fourth concentrated phosphate concentrate and / or optionally the seventh concentrated phosphate concentrate, respectively downstream of the second magnetic separator and / or the third magnetic separator, wherein the result of the analyzer is used to adjust the magnetic field in the second magnetic separator and / or optionally the third magnetic separator in the control loop.

15. The system according to any one of claims 11 to 14 is used for performing the method according to any one of claims 1 to 10.

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