Method for purifying magnetite concentrate

Abstract

The invention discloses a purification method of magnetite concentrate, and belongs to the technical field of extreme purification of magnetite concentrate. The purification method comprises the following steps: carrying out ultrafine grinding on a magnetite concentrate raw material, adding alkali metal hexametaphosphate and alkali metal silicate, carrying out flocculation desliming to obtain primarily purified magnetite, and adding a magnetite inhibitor, a composite collector and an activator into ore pulp containing the primarily purified magnetite for reverse flotation, the composite collecting agent comprises fatty amine and a zwitterionic surfactant, and the activating agent comprises a calcium compound and a rare earth compound. The separation and removal effects of gangue minerals and impurity metal elements are greatly improved through flocculation desliming and a specific flotation reagent system, the yield and recovery rate of the high-purity magnetite concentrate are improved while the grade of the magnetite concentrate is improved, and the method is simple, low in cost, small in reagent dosage in the flotation process, environmentally friendly and suitable for industrial application.

Description

Technical Field

[0001] This invention relates to a method for purifying magnetite concentrate, belonging to the field of extreme purification technology for magnetite concentrate. Background Technology

[0002] Magnetite is not only an important component of iron ore resources but also a crucial raw material for the steel industry, with abundant global reserves. However, natural magnetite is often associated with gangue minerals (such as quartz and mica), requiring beneficiation for enrichment. Efficient beneficiation technologies can improve concentrate grade and reduce impurity content, which is vital for resource utilization and economic benefits. Magnetic separation, as a key technology in magnetite beneficiation, is widely used in magnetite purification and upgrading processes. However, with the increasing mining of magnetite, the grade of magnetic separation feed is continuously decreasing, the particle size of the feed is gradually becoming finer, and the ore properties are becoming more complex and variable, resulting in increasingly poor ore beneficiation. It is difficult to obtain high-quality iron concentrate through magnetic separation alone. Reverse flotation, as a beneficiation process that can also effectively remove silicon, is gradually becoming another breakthrough for iron enrichment and silicon reduction. Currently existing magnetite beneficiation processes include combined magnetic-flotation processes, single magnetic separation processes, and combined magnetic-gravity-flotation processes. In recent years, researchers have employed specific process flows for the purification and upgrading of magnetite, including "high-pressure roller mill ultrafine crushing - dry pre-selection - staged grinding - single-magnetic separation, magnetized roasting - weak magnetic separation, magnetic roughing - grinding - magnetic re-selection - magnetic column cleaning - one roughing and three scavenging reverse flotation, grinding - one roughing and one cleaning, classification - grinding - weak magnetic roughing - magnetic column cleaning." While existing beneficiation processes can improve concentrate grade and recovery rate to some extent, increase iron ore beneficiation efficiency, reduce beneficiation plant costs, and improve concentrate quality, some problems remain. Traditional coarse grinding processes do not adequately liberate finely disseminated minerals, resulting in low metal recovery rates. Ultrafine grinding can significantly increase the degree of mineral liberation, allowing for sufficient individual liberation of target minerals from gangue. However, ultrafine grinding processes are energy-intensive and prone to producing slime interference. Submicron-sized secondary slime is generated during ultrafine grinding, and its high specific surface area adsorbs a large amount of flotation reagents, interfering with the separation process. Single mineral processing reagents lack sufficient selective adsorption capacity for ultrafine minerals. Using combined collectors offers higher selectivity and can improve flotation recovery. For example, Chinese patent CN118663424A describes the use of combined collectors—octanoyl salicylic acid and benzoyl hydroxamic acid in a 1:1 mass ratio, and octanoyl salicylic acid and hexyl hydroxamic acid in a 1:1 mass ratio—to significantly improve the flotation recovery of oxide ores. However, publicly reported methods using combined collectors for magnetite flotation still suffer from insufficient selectivity for aluminosilicate gangue minerals, poor separation of target minerals from gangue minerals, and low concentrate yield.

[0003] Therefore, it is crucial to develop a magnetite purification method that is highly selective for aluminosilicate gangue minerals, while improving the separation of the target mineral from the gangue minerals and increasing the concentrate yield. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a method for purifying magnetite concentrate. This method significantly improves purification efficiency, increases mineral recovery rate, and achieves high concentrate yield. Furthermore, the method is simple, has a short process flow, and is low in cost, making it suitable for industrial applications.

[0005] To achieve the above-mentioned technical objectives, the present invention provides a method for purifying magnetite concentrate. This method involves ultra-fine grinding of the magnetite concentrate raw material, followed by flocculation and desliming with alkali metal hexametaphosphate and alkali metal silicate to obtain pre-purified magnetite. Then, magnetite inhibitors, a composite collector, and an activator are added to the slurry containing the pre-purified magnetite for reverse flotation. The composite collector includes aliphatic amines and zwitterionic surfactants, and the activator includes calcium compounds and rare earth compounds.

[0006] First, this invention uses ultrafine grinding and flocculation desliming to initially remove gangue minerals and some impurity metal elements from magnetite concentrate. The specific principle is as follows:

[0007] Ultrafine grinding of magnetite concentrate raw materials allows for the complete dissociation of fine-grained gangue minerals (quartz, orthoclase, amphibole, apatite, etc.) from the target minerals. By adding a combination of dispersants, alkali metal hexametaphosphate and alkali metal silicates, the target mineral particles are enriched at the magnetic poles, while the fine-grained gangue minerals remain suspended and negatively charged. Specifically, alkali metal hexametaphosphates (such as sodium hexametaphosphate (NaPO3)6) can hydrolyze to generate hydrogen phosphate (H2PO4). - and HPO4 2- The negatively charged hydrogen phosphate ions repel the negatively charged gangue minerals (quartz, muscovite, etc.), which facilitates the full dispersion and suspension of the gangue mineral fines, and then enables effective separation from the target minerals. Simultaneously, alkali metal hexametaphosphates undergo a complexation reaction with impurity metal ions (M representing Ca, Mg, Al, Ti, Mn, etc.) dissolved from the mineral surface, forming complex metal salts. This pre-removes some of the impurity metal ions. The complexation reaction formula is as follows:

[0008] (NaPO3)6+M 2+ =[MNa2P6O 18 ] 2- +4Na + ;

[0009] (NaPO3)6+M 3+ =[MNa2P6O 18 ] - +4Na + .

[0010] Alkali metal silicates (SiO3) 2- Sodium hexametaphosphate (SHP) acts as a highly efficient flocculant and can also effectively react with impurity metal ions (M representing Ca, Mg, Al, Ti, Mn, etc.) dissolved from the mineral surface to form silicate substances. Therefore, under the synergistic effect of SHP and sodium silicate, impurity metal ions in fine-grained gangue mineral mud are selectively and efficiently flocculated and removed, significantly reducing the difficulty of flotation purification.

[0011] Secondly, in the reverse flotation process, this invention further improves flotation efficiency through a specific flotation reagent system consisting of a composite collector, activator, and inhibitor. The specific principle is as follows:

[0012] In the composite collectors used in this invention, aliphatic amine collectors have strong hydrophobic carbon chains, which can provide good bubble mineralization ability and have good selectivity for silicate minerals such as quartz. However, their pH applicable range is relatively narrow. Amphoteric surfactants can make up for the narrow pH applicable range of aliphatic amines. They can still effectively collect aluminosilicate gangue minerals in pulps with a wide pH range, such as acidic and alkaline, thus improving the flotation separation effect.

[0013] Meanwhile, this invention uses an activator as an auxiliary agent to transform traditional Ca... 2+ With emerging rare earth ions (RE) 3+ , such as La 3+ Ce 3+ 、Nd 3+ Combined with RE 3+ Its unique 4f electron layer structure and strong complexing ability overcome the limitations of single Caa. 2+ To address the issue of insufficient selectivity of activators, a stable bimetallic composite activation layer is constructed to achieve more efficient and selective flotation of aluminum-containing gangue minerals, wherein Ca... 2+ +RE 3+ The synergistic activation mechanism of rare earth ions is as follows:

[0014] ;

[0015] ;

[0016] Ca 2+ First, it coordinates internally with hydroxyl groups on the mineral surface to form a positively charged ≡MO-Ca + Activation layer, followed by RE 3+ With ≡MO-Ca + The activated layer and adjacent hydroxyl groups further coordinate internally to form a bimetallic oxide bridge ≡MO-Ca-O-RE. 3+ Compared to ≡MO-Ca + Activation layer, ≡MO-Ca-O-RE 3+With higher surface positive charge density, greater coordination saturation, and stronger dehydration ability, it can significantly improve the adsorption energy and film stability of cationic and amphoteric collectors, thereby achieving stronger activation and better selectivity for gangue minerals.

[0017] This invention utilizes the synergistic effect of a special composite collector, activator, and inhibitor to significantly reduce the total reagent usage in the flotation process while effectively improving the separation effect, thereby significantly enhancing the quality and yield of flotation concentrate and increasing the flotation recovery rate.

[0018] As a preferred embodiment, the total iron content in the magnetite concentrate raw material is 62-69%.

[0019] As a preferred embodiment, the magnetite concentrate raw material is ultrafine ground to a particle size of no more than 10 μm, more preferably 0.5~5 μm. This invention employs a nano-sand mill to ultrafine grind the magnetite concentrate raw material, wherein the main mill speed is 500~1000 rpm, the stirring rotor speed is 10~200 rpm, and the circulating cooling water temperature is 10±1℃. This invention uses a nano-sand mill as the grinding equipment. Compared to traditional ball mills, the sand mill can achieve rapid material crushing through strong shearing and collision actions, fully dissociating the fine-grained gangue minerals from the target minerals. Since submicron-sized secondary slime is generated during ultrafine grinding, its high specific surface area adsorbs a large amount of flotation reagents, interfering with the separation process. This invention efficiently removes this secondary slime by combining dispersants and electromagnetic stirring, avoiding its negative impact on flotation while pre-removing some impurity metal ions.

[0020] As a preferred embodiment, the mass ratio of the alkali metal hexametaphosphate to the alkali metal silicate is 5~20:1. The alkali metal hexametaphosphate is preferably sodium hexametaphosphate. The alkali metal silicate is preferably sodium silicate.

[0021] As a preferred embodiment, the amount of alkali metal hexametaphosphate added is 0.05~0.5wt% of the magnetite concentrate raw material.

[0022] As a preferred embodiment, the flocculation and desliming conditions are: a magnetic field strength of 200~2000 Gs, more preferably 800~1200 Gs, and a time of 20min~120min, more preferably 30min~60min. This invention employs an electromagnetic washing machine for the flocculation and desliming process.

[0023] As a preferred embodiment, the slurry containing the pre-purified magnetite has a mass concentration of 30-75%, more preferably 45-65%.

[0024] As a preferred embodiment, the reverse flotation process includes a roughing process and three or more cleaning processes. The amounts of magnetite inhibitor, composite collector, and activator added during the cleaning process are all halved with each subsequent cleaning process, wherein the amount of magnetite inhibitor, composite collector, and activator added during the first cleaning process is half the amount added during the roughing process.

[0025] As a preferred embodiment, in the roughing process, relative to the initial purification of magnetite, the addition amount of the composite collector is 50-500 g / t, the addition amount of the activator is 5-200 g / t, and the addition amount of the magnetite depressant is 200-2000 g / t. Controlling the addition amounts of the composite collector, activator, and magnetite depressant within appropriate ranges is beneficial to improving flotation efficiency. However, if the addition amount of the activator is too low, a good synergistic effect cannot be achieved; if the addition amount is too high, Ca... 2+ Residual substances remain in the slurry, thus affecting the slurry pH and flotation efficiency.

[0026] As a preferred embodiment, the mass ratio of fatty amine to zwitterionic surfactant in the composite collector is 1 to 10:1.

[0027] As a preferred embodiment, the fatty amine includes at least one of dodecylamine, hexadecamine, and octadecamine. That is, the fatty amine can be a long-chain fatty amine.

[0028] As a preferred embodiment, the zwitterionic surfactant includes at least one of betaine compounds, amino acid compounds, and imidazoline compounds.

[0029] As a preferred embodiment, the betaine compound includes at least one of sulfobetaine, cocobetaine, and phosphate betaine.

[0030] As a preferred embodiment, the amino acid compound includes at least one of sodium lauroyl methyl aminopropionate and potassium cocoyl glycinate.

[0031] As a preferred embodiment, the imidazoline compound includes alkyl hydroxyethyl imidazoline.

[0032] As a preferred embodiment, the molar ratio of calcium to rare earth elements in the calcium compound and rare earth compound is 5-50:1. Controlling the molar ratio of calcium to rare earth elements within a suitable range is beneficial for improving flotation efficiency.

[0033] As a preferred embodiment, the calcium compound includes at least one of calcium oxide, calcium chloride, calcium hydroxide, and calcium carbonate.

[0034] As a preferred embodiment, the rare earth compound is a lanthanide compound. Lanthanide compounds include at least one of lanthanum compounds, cerium compounds, and neodymium compounds, wherein the lanthanum compound includes lanthanum oxide, the cerium compound includes cerium oxide, and the neodymium compound includes neodymium oxide.

[0035] As a preferred embodiment, the magnetite inhibitor comprises at least one of caustic starch, dextrin, and carboxymethyl cellulose. Caustic corn starch is the most preferred.

[0036] As a preferred embodiment, the total iron content in the purified magnetite concentrate is not less than 72%.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0038] (1) The specific combination of composite collectors, activators and inhibitors in the flocculation and desliming process and the flotation process greatly improves the separation and removal of gangue minerals and impurity metal elements, improves the grade of magnetite concentrate, and at the same time improves the yield and recovery rate of ultrapure magnetite concentrate.

[0039] (2) The method is simple, low-cost, and requires a small amount of reagents in the flotation process. It is green and environmentally friendly and suitable for industrial application. Detailed Implementation

[0040] The present invention will be further described below with reference to embodiments. The described embodiments and their results are for illustrative purposes only and should not, and will not, limit the technical invention described in detail in the claims.

[0041] Example 1

[0042] A method for purifying magnetite concentrate includes the following steps:

[0043] (1) Take 40g of magnetite concentrate (ordinary ore) and place it in a nano-sand mill for ultrafine grinding until the particle size is 0.5~5μm. The main speed of the sand mill is 800rpm, the stirring rotor speed is 100rpm, and the circulating cooling water temperature is 10℃.

[0044] (2) Then the finely ground slurry is transferred to an electromagnetic washing machine. Under stirring (200 r / min), 0.2wt% sodium hexametaphosphate and 0.02wt% sodium silicate are added to carry out full flocculation and desliming. Mechanical stirring is used to keep the fine mud particles in a dispersed state, so that the target mineral particles are enriched at the magnetic pole, while the gangue mineral mud remains suspended. After washing, the filtrate is separated to obtain the preliminary purified magnetite.

[0045] (3) The above-mentioned pre-purified magnetite is mixed with water to prepare a slurry with a mass concentration of 60%, and then the slurry is placed in a flotation cell for reverse flotation, including a roughing and a cleaning process: magnetite inhibitor, composite collector and activator are added to the slurry in sequence. The magnetite inhibitor is caustic starch, and the amount added in the roughing process is 1000 g / t relative to the pre-purified magnetite; the composite collector is dodecylamine and dodecyl sulfobetaine, and the total amount added in the roughing process is 200 g / t, with a mass ratio of 10:1; the activator is a mixture of CaO and La2O3 in a mass ratio of 20:1, and the amount of activator added in the roughing process is 20 g / t. In the cleaning process, the amount of magnetite inhibitor, composite collector and activator in the first cleaning process is controlled to be half of that in the roughing process, and the amount of each reagent in the subsequent cleaning process is half of that in the previous cleaning process.

[0046] Comparative Example 1

[0047] Magnetite was purified using the method of Example 1, except that the flocculation and desliming steps were not performed, and the finely ground slurry was directly subjected to reverse flotation.

[0048] Comparative Example 2

[0049] Magnetite was purified using the method of Example 1, except that the flocculation and desliming process in step (2) was controlled as ordinary magnetic separation, i.e. no combined dispersant was added.

[0050] The iron concentrate obtained from the sorting in Example 1 was compared with the products obtained from Comparative Example 1 and Comparative Example 2. The results are shown in Table 1.

[0051]

[0052] As can be seen from Table 1, the grade of the concentrate purified by this invention is better than that of Comparative Example 1 and Comparative Example 2, indicating that single flotation and ordinary magnetic separation + flotation cannot achieve the effect of the magnetite purification method in this application, demonstrating that ultrafine grinding plus flocculation desliming can play a unique role in the purification of magnetite.

[0053] Example 2

[0054] A method for purifying magnetite concentrate includes the following steps:

[0055] (1) Take 50g of magnetite concentrate (ordinary ore) and place it in a nano-sand mill for ultrafine grinding until the particle size is 0.5~5μm. The main speed of the sand mill is 1000rpm, the stirring rotor speed is 200rpm, and the circulating cooling water temperature is 10℃.

[0056] (2) Then the finely ground slurry is transferred to an electromagnetic washing machine. Under stirring (300 r / min), 0.1 wt% sodium hexametaphosphate and 0.05 wt% sodium silicate are added to carry out full flocculation and desliming. Mechanical stirring is used to keep the fine mud particles in a dispersed state, so that the target mineral particles are enriched at the magnetic pole, while the gangue mineral mud remains suspended. After washing, the filtrate is separated to obtain the preliminary purified magnetite.

[0057] (3) The above-mentioned pre-purified magnetite is mixed with water to prepare a slurry with a mass concentration of 45%, and then the slurry is placed in a flotation cell for reverse flotation, including one roughing and four cleaning: magnetite inhibitor, composite collector and activator are added to the pre-purified magnetite in sequence. The magnetite inhibitor is caustic starch, and the amount added in the roughing process is 1500g / t relative to the pre-purified magnetite; the composite collector is hexadecylamine and lauramide propyl hydroxysulfonate betaine, and the total amount added in the roughing process is 300g / t, with a mass ratio of 5:1; the activator is a mixture of CaCl2 and Ce2O3 in a mass ratio of 30:1, and the amount of activator added in the roughing process is 15g / t. In the cleaning process, the amount of magnetite inhibitor, composite collector and activator in the first cleaning process is controlled to be half of that in the roughing process, and the amount of each reagent in the subsequent cleaning process is half of that in the previous cleaning process.

[0058] Comparative Example 3

[0059] Magnetite was purified using the method of Example 2, except that the combined dispersant used in the flocculation and desliming process of step (2) was 0.1 wt% sodium polyacrylate and 0.1 wt% sodium hexametaphosphate.

[0060] Comparative Example 4

[0061] Magnetite was purified using the method of Example 2, except that the combined dispersant used in step (2) during the flocculation and desliming process was 0.1 wt% sodium polyacrylate and 0.05 wt% sodium silicate.

[0062] Comparative Example 5

[0063] The method of Example 2 was used to purify magnetite, except that the combined dispersant used in step (2) during the flocculation and desliming process was 0.1 wt% sodium lignosulfonate and 0.1 wt% sodium hexametaphosphate.

[0064] Comparative Example 6

[0065] Magnetite was purified using the method of Example 2, except that the combined dispersant used in the flocculation and desliming process of step (2) was 0.1 wt% sodium lignosulfonate and 0.05 wt% sodium silicate.

[0066] Comparative Example 7

[0067] Magnetite was purified using the method of Example 2, except that the combined dispersant used in step (2) during the flocculation and desliming process was 0.1 wt% sodium polyacrylate and 0.1 wt% sodium lignosulfonate.

[0068] The flotation concentrate obtained from Example 2 was compared with the products obtained from Comparative Examples 3-7, and the results are shown in Table 2.

[0069]

[0070] As can be seen from Table 2, the grade of the concentrate purified by this invention is better than that of comparative examples 3-7. It is evident that only by using the specific combination of dispersants alkali metal hexametaphosphate and alkali metal silicate of this invention can a good purification effect be obtained. Other conventional dispersants cannot achieve the technical effect of this invention.

[0071] Example 3

[0072] A method for purifying magnetite concentrate includes the following steps:

[0073] (1) Take 30g of magnetite concentrate (ordinary ore) and place it in a nano sand mill for ultrafine grinding until the particle size is 5~10μm. The main speed of the sand mill is 500rpm, the stirring rotor speed is 50rpm, and the temperature of the circulating cooling water is 10℃.

[0074] (2) Then the finely ground slurry is transferred to an electromagnetic washing machine. Under stirring (400 r / min), 0.5 wt% sodium hexametaphosphate and 0.1 wt% sodium silicate are added to carry out full flocculation and desliming. Mechanical stirring is used to keep the fine mud particles in a dispersed state, so that the target mineral particles are enriched at the magnetic pole, while the gangue mineral mud remains suspended. After washing, the filtrate is separated to obtain the preliminary purified magnetite.

[0075] (3) The above-mentioned pre-purified magnetite is mixed with water to prepare a slurry with a mass concentration of 55%, and then the slurry is placed in a flotation cell for reverse flotation, including a roughing and a cleaning process: magnetite inhibitor, composite collector and activator are added to the pre-purified magnetite in sequence. The magnetite inhibitor is caustic starch, and the amount added in the roughing process is 200 g / t relative to the pre-purified magnetite; the composite collector is dodecylamine and dodecyl sulfobetaine, and the total amount added in the roughing process is 50 g / t, with a mass ratio of 3:1; the activator is a mixture of CaO and Nd2O3 in a mass ratio of 40:1, and the amount of activator added in the roughing process is 10 g / t. In the cleaning process, the amount of magnetite inhibitor, composite collector and activator in the first cleaning process is controlled to be half of that in the roughing process, and the amount of each reagent in the subsequent cleaning process is half of that in the previous cleaning process.

[0076] Comparative Example 8

[0077] Magnetite was purified using the method of Example 3, the difference being that in the flotation process of step (3), the combined collector was controlled to be dodecylamine and sodium oleate (cationic reagent + anionic reagent), the total amount added was 50g / t, and the mass ratio of the two was 3:1.

[0078] Comparative Example 9

[0079] Magnetite was purified using the method of Example 3, the difference being that in the flotation process of step (3), the combined collector was controlled to be dodecylamine + hexadecylamine (dual cationic reagent), the total amount added was 50g / t, and the mass ratio of the two was 3:1.

[0080] Comparative Example 10

[0081] Magnetite was purified using the method of Example 3, except that in the flotation process of step (3), the combined collector was controlled to be dodecyl sulfobetaine (a single amphoteric agent), and the addition amount was 50g / t.

[0082] Comparative Example 11

[0083] Magnetite was purified using the method of Example 3, except that in the flotation process of step (3), the mass ratio of dodecylamine and dodecyl sulfobetaine in the combined collector was controlled to be 15:1.

[0084] Comparative Example 12

[0085] Magnetite was purified using the method of Example 3, except that in the flotation process of step (3), the mass ratio of dodecylamine and dodecyl sulfobetaine in the combined collector was controlled to be 0.5:1.

[0086] Comparative Example 13

[0087] Magnetite was purified using the method of Example 3, except that no activator was added during the flotation process in step (3).

[0088] Comparative Example 14

[0089] Patent CN 113617513 A discloses a method for preparing ultrapure iron concentrate from iron concentrate. In this patent, dodecylamine is used for reverse flotation to obtain ultrapure iron concentrate with 72.14% total iron. In Example 1, the amount of dodecylamine as the rougher collector is 50 g / t, and the amount of caustic starch as the inhibitor is 500 g / t.

[0090] The iron concentrate obtained from the sorting in Example 3 was compared with the products obtained in Comparative Examples 8-14. The results are shown in Table 3.

[0091]

[0092] As shown in Table 3, the concentrate grade of this invention is superior to that of the comparative examples. Comparative examples 8-10 demonstrate that replacing any one of the composite collectors would adversely affect the purification of magnetite, indicating that the composite collector formed by the aliphatic amine and zwitterionic surfactant in this invention can improve the flotation purification effect. Comparative examples 11-12 show that an excessively high or low ratio of dodecylamine to dodecyl sulfobetaine would inhibit the purification of magnetite, indicating that the ratio of the composite collector affects the flotation effect. Comparative example 13 shows that without an activator as an aid, the flotation effect is significantly reduced. In this Example 3, the total amount of rougher collector used is 50 g / t, the amount of caustic starch inhibitor is as low as 200 g / t, and the activator is 10 g / t. The total amount of reagents used is significantly lower than that of comparative example 14. The purity, yield, and iron recovery rate of the ultrapure iron concentrate obtained in Example 3 of this invention are also superior to those of comparative example 14, indicating that this invention can greatly reduce the amount of flotation reagents used while improving the purity of the iron concentrate.

Claims

1. A method for purifying magnetite concentrate, characterized in that: Magnetite concentrate raw material is ultra-fine ground and then alkali metal hexametaphosphate and alkali metal silicate are added for flocculation and desliming to obtain pre-purified magnetite. Then, magnetite inhibitor, composite collector and activator are added to the slurry containing the pre-purified magnetite for reverse flotation. The composite collector includes fatty amine and zwitterionic surfactant, and the activator includes calcium compound and rare earth compound.

2. The method for purifying magnetite concentrate according to claim 1, characterized in that: The magnetite concentrate raw material is ultra-fine ground to a particle size of no more than 10 μm.

3. A method for purifying magnetite concentrate according to claim 1 or 2, characterized in that: The mass ratio of the alkali metal hexametaphosphate to the alkali metal silicate is 5~20:1; The amount of alkali metal hexametaphosphate added is 0.05~0.5wt% of the magnetite concentrate raw material.

4. The method for purifying magnetite concentrate according to claim 1, characterized in that: The conditions for flocculation and desliming are: magnetic field strength of 200~2000Gs and time of 20min~120min.

5. The method for purifying magnetite concentrate according to claim 1, characterized in that: The reverse flotation process includes a roughing process and three or more cleaning processes; wherein, the amount of magnetite inhibitor, composite collector and activator added in each cleaning process is half of the amount used in the previous cleaning process, and the amount of magnetite inhibitor, composite collector and activator added in the first cleaning process is half of the amount used in the roughing process.

6. The method for purifying magnetite concentrate according to claim 5, characterized in that: In the roughing process, relative to the initial purification of magnetite, the amount of compound collector added is 50~500g / t, the amount of activator added is 5~200g / t, and the amount of magnetite inhibitor added is 200~2000g / t.

7. The method for purifying magnetite concentrate according to claim 1, characterized in that: The mass ratio of fatty amine to zwitterionic surfactant in the composite collector is 1~10:1; The fatty amine includes at least one of dodecylamine, hexadecylamine, and octadecylamine; The zwitterionic surfactant includes at least one of betaine compounds, amino acid compounds, and imidazoline compounds.

8. The method for purifying magnetite concentrate according to claim 1, characterized in that: The molar ratio of calcium to rare earth elements in the calcium compound and rare earth compound is 5~50:

1.

9. A method for purifying magnetite concentrate according to claim 1 or 8, characterized in that: The calcium compound includes at least one of calcium oxide, calcium chloride, calcium hydroxide, and calcium carbonate; The rare earth compounds are lanthanide compounds.

10. The method for purifying magnetite concentrate according to claim 1, characterized in that: The magnetite inhibitor includes at least one of caustic starch, dextrin, and carboxymethyl cellulose.

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