A method of purifying a magnetite concentrate

Abstract

The application discloses a kind of magnetite concentrate purification methods, belong to magnetite concentrate extreme purification technical field.The purification method is to carry out superfine grinding after magnetite concentrate raw materials are added alkali metal hexametaphosphate and alkali metal silicate and flocculation desliming, obtain preliminary purification magnetite, again to the ore pulp containing preliminary purification magnetite is added magnetite inhibitor, composite collector and activator and carries out reverse flotation, namely, wherein, the composite collector includes fatty amine and zwitterionic surfactant, and the activator includes calcium compound and rare earth compound.The application greatly improves the separation and removal effect of gangue mineral and impurity metal element by flocculation desliming and specific flotation reagent system, improves the grade of magnetite concentrate while improving the yield and recovery rate of high-purity magnetite concentrate, the method is simple, low in cost, small in dosage of reagent in flotation process, green and environmentally friendly, suitable for industrial application.

Description

TECHNICAL FIELD

[0001] The application relates to a magnetite concentrate purification method and belongs to the technical field of magnetite concentrate purification. BACKGROUND

[0002] Magnetite is not only an important component of iron ore resources, but also an important raw material for the steel industry, and is rich in reserves worldwide. However, natural magnetite is often associated with gangue minerals (such as quartz, mica, etc.), and needs to be enriched through beneficiation. Efficient beneficiation technology can improve the concentrate grade and reduce impurity content, which is crucial for resource utilization and economic benefits. As an important technology for magnetite beneficiation, magnetic separation is widely used in the purification and upgrading process of magnetite. However, with the year-by-year exploitation of magnetite, the feed grade of magnetic separation is continuously decreasing, the embedded particle size is gradually becoming finer, and the ore properties are becoming more complex and variable. The ore selectivity is getting worse and worse. It is difficult to obtain high-quality iron concentrate through single magnetic separation. As an effective beneficiation process that can also effectively remove silicon, reverse flotation has gradually become another breakthrough in iron removal and silicon reduction. The existing beneficiation flowsheet of magnetite includes magnetic-flotation combined process, single magnetic separation process, and magnetic-gravity-flotation combined process, etc. In recent years, researchers have adopted specific process flowsheet in the purification and upgrading of magnetite, such as "high-pressure roller mill superfine crushing-dry pre-concentration-stage grinding-single-magnetic separation, magnetization roasting-weak magnetic separation, magnetic separation roughing-grinding-magnetic separation re-concentration-magnetic separation column concentration-one roughing-three scavenging reverse flotation, grinding-one roughing-one cleaning, classification-grinding-weak magnetic roughing-magnetic separation column concentration", etc. Although the existing beneficiation flowsheet can improve the concentrate grade and recovery rate, improve the efficiency of iron ore beneficiation, reduce the cost of the beneficiation plant, and improve the quality of the concentrate, there are still some problems. The traditional coarse grinding process is not sufficient for the dissociation of fine-grained embedded minerals, resulting in low metal recovery. Ultrafine grinding can significantly increase the degree of mineral monomer dissociation, making the target mineral and gangue fully dissociated. However, the ultrafine grinding process has high energy consumption and is prone to produce slurry interference. Submicron secondary slurry is produced during ultrafine grinding, which has a high specific surface area and can adsorb a large amount of flotation reagents, interfering with the separation process. Single beneficiation reagent has insufficient selectivity for ultrafine particles, and the use of combined collectors has higher selectivity, which can improve the flotation recovery rate. For example, the Chinese patent with publication number CN118663424A uses a combination of capryl acyl salicylic acid and benzohydroxamic acid with a mass ratio of 1:1, and a combination of capryl acyl salicylic acid and hexyl hydroxamic acid with a mass ratio of 1:1 as the combined collector for the flotation of oxidized ore, which greatly improves the flotation recovery rate. However, the existing reports on the use of combined collectors for magnetite flotation still have problems such as insufficient selectivity for aluminum silicate gangue minerals, poor separation effect of target minerals and gangue minerals, and low concentrate yield.

[0003] Therefore, it is crucial to develop a magnetite purification method that has strong selectivity for aluminum silicate gangue minerals, improves the separation effect of target minerals and gangue minerals, and improves the concentrate yield. SUMMARY

[0004] In view of the deficiencies of the prior art, the purpose of the present application is to provide a method for purifying magnetite concentrate. The method greatly improves the purification efficiency, increases the mineral recovery rate, and has high yield of purified concentrate. The method is simple, short in process flow, low in cost, and suitable for industrial application.

[0005] To achieve the above technical purpose, the present application provides a method for purifying magnetite concentrate. The method is to add alkali metal hexametaphosphate and alkali metal silicate to the superfine ground magnetite concentrate to remove the gangue minerals and part of the impurity metal elements, and then add magnetite depressant, composite collector and activator to the slurry containing the preliminary purified magnetite to perform reverse flotation.

[0006] Firstly, the present application preliminarily removes the gangue minerals and part of the impurity metal elements in the magnetite concentrate through superfine grinding and flocculation desliming treatment. The specific principle is as follows:

[0007] The superfine grinding of the magnetite concentrate raw material makes the fine particle size gangue minerals (quartz, orthoclase, amphibole, apatite, etc.) and the target mineral fully dissociate. By adding the combined dispersant alkali metal hexametaphosphate and alkali metal silicate, the target mineral particles are enriched at the magnetic pole, while the fine particle size gangue mineral fine mud remains suspended and the surface is negatively charged. The alkali metal hexametaphosphate (such as sodium hexametaphosphate (NaPO3)6) can hydrolyze to generate hydrogen phosphate H2PO4 - and HPO4 2- The negatively charged hydrogen phosphate ions and the negatively charged gangue minerals (quartz, muscovite, etc.) repel each other, which is beneficial to the full dispersion and suspension of the gangue mineral fine mud, and then effectively separates the target mineral. At the same time, the alkali metal hexametaphosphate reacts with the impurity metal ions (M represents Ca, Mg, Al, Ti, Mn, etc.) dissolved on the surface of the mineral to generate complex metal salt, thereby removing part of the impurity metal ions in advance. The complex 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 silicate (SiO3 2- ) as a high-efficiency flocculant can also effectively react with impurity metal ions (M represents Ca, Mg, Al, Ti, Mn, etc.) dissolved from the mineral surface to generate silicate substances. Therefore, under the synergistic effect of sodium hexametaphosphate and sodium silicate, the impurity metal ions in the fine particle size gangue mineral fine mud are selectively and efficiently flocculated and removed, greatly reducing the difficulty of flotation purification.

[0011] Secondly, in the reverse flotation process, the flotation reagent system of the specific composite collector, activator and depressant is used to further improve the flotation efficiency, and the specific principle is as follows:

[0012] In the composite collector used in the present application, the fatty amine collector has a strong hydrophobic carbon chain, can provide good bubble mineralization capacity, and has good selectivity to silicate minerals such as quartz, but its pH applicable range is relatively narrow, and the zwitterionic surfactant can compensate for the defect of narrow pH applicable range of the fatty amine collector, and can still effectively collect aluminosilicate gangue minerals in the slurry with wide pH range fluctuations such as acid and alkali, and improve the flotation separation effect.

[0013] Meanwhile, the activator is used as an additive in the present application, and the traditional Ca 2+ is combined with emerging rare earth ions (RE 3+ , such as La 3+ , Ce 3+ , Nd 3+ , etc.), which overcomes the problem of insufficient selectivity of single Ca 2+ activator by means of the special 4f electron layer structure and strong complexing ability of RE 3+ , constructs a stable double-metal composite activation layer, and realizes more efficient and more selective flotation of aluminum-containing gangue minerals. The synergistic activation mechanism of Ca 2+ + RE 3+ is as follows:

[0014] ;

[0015] ;

[0016] Firstly, Ca 2+ is coordinated with the hydroxyl group on the mineral surface to form a positively charged ≡M-O-Ca + activation layer, and then RE 3+ is further coordinated with the ≡M-O-Ca + activation layer and the adjacent hydroxyl group to form a double-metal oxidation bridge ≡M-O-Ca-O-RE 3+ . Compared with the ≡M-O-Ca + activation layer, the ≡M-O-Ca-O-RE 3+The higher surface positive charge density, greater coordination saturation and stronger dehydrating ability can significantly improve the adsorption energy of cationic and amphoteric collectors and the stability of the membrane layer, thereby achieving stronger activation and better selectivity to gangue minerals.

[0017] The present application greatly reduces the total reagent dosage in the flotation process while effectively improving the separation effect, significantly improving the flotation concentrate quality and yield and improving the flotation recovery rate through the synergistic effect of the special composite collector, activator and inhibitor.

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

[0019] As a preferred scheme, the magnetite concentrate raw material is superfine ground to a particle size of not more than 10 μm, and further preferably 0.5-5 μm. The present application uses a nano sand mill to superfine grind the magnetite concentrate raw material, wherein the sand mill main machine speed is 500-1000 rpm, the stirring rotor speed is 10-200 rpm, and the circulating cooling water temperature is 10±1℃. Compared with the traditional ball mill, the sand mill can realize rapid crushing of materials through strong shearing and collision, and fully dissociate the fine particle gangue minerals and target minerals. Due to the generation of submicron secondary slimes in the superfine grinding process, the high specific surface area will adsorb a large amount of flotation reagents, which will interfere with the separation process. The present application combines dispersants and electromagnetic stirring to efficiently remove this part of secondary slimes, avoiding the negative impact on flotation while pre-removing part of impurity metal ions.

[0020] As a preferred scheme, the mass ratio of the alkali metal hexametaphosphate and 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 scheme, the addition amount of the alkali metal hexametaphosphate is 0.05-0.5 wt% of the magnetite concentrate raw material.

[0022] As a preferred scheme, the flocculation desliming conditions are: magnetic field strength of 200-2000Gs, further preferably 800-1200Gs, and time of 20 min-120 min, further preferably 30 min-60 min. The present application uses an electromagnetic elutriation machine to carry out the flocculation desliming process.

[0023] As a preferred scheme, the mass concentration of the ore slurry containing the preliminarily purified magnetite is 30-75%, further preferably 45-65%.

[0024] As a preferred solution, the reverse flotation process comprises one roughing and 3 or more cleaning. The addition amount of the magnetite inhibitor, composite collector and activator in the cleaning process is halved successively, wherein the addition amount of the magnetite inhibitor, composite collector and activator in the first cleaning is half of the amount used in the roughing.

[0025] As a preferred solution, in the roughing process, 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 inhibitor is 200-2000 g / t, relative to the preliminary purified magnetite. Controlling the addition amount of the composite collector, activator and magnetite inhibitor in a suitable range is conducive to improving the flotation efficiency, wherein the addition amount of the activator is too low to achieve good synergistic effect, and the addition amount is too high to cause Ca 2+ The residual calcium compound and rare earth compound in the slurry affect the pH of the slurry and the flotation effect.

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

[0027] As a preferred solution, the fatty amine comprises at least one of dodecylamine, hexadecylamine and octadecylamine. That is, the fatty amine can be selected from long-chain fatty amines.

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

[0029] As a preferred solution, the betaine compounds comprise at least one of sulfobetaine, cocobetaine and phosphate betaine.

[0030] As a preferred solution, the amino acid compounds comprise at least one of sodium lauroyl methyl amino propionate and potassium cocoyl glycinate.

[0031] As a preferred solution, the imidazoline compounds comprise alkyl hydroxyethyl imidazoline.

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

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

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

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

[0036] As a preferred solution, the purified magnetite concentrate has a total iron grade of not less than 72%.

[0037] Compared with the prior art, the present application has the following beneficial effects:

[0038] (1) The specific composite collector, activator, and inhibitor combination reagent system in the flocculation desliming process and the flotation process greatly improves the separation and removal effect of gangue minerals and impurity metal elements, improves the magnetite concentrate grade, and improves the yield and recovery rate of the ultra-pure magnetite concentrate;

[0039] (2) The method is simple, low in cost, small in reagent dosage in the flotation process, green and environmentally friendly, and suitable for industrial application. DETAILED DESCRIPTION

[0040] The present application will be further described below in conjunction with examples. The described examples and their results are only for illustration of the present application and should not and will not limit the technical invention described in detail in the claims.

[0041] Example 1

[0042] A purification method of a magnetite concentrate includes the following steps:

[0043] (1) 40 g of magnetite concentrate raw material (common ore) is placed in a nano sand mill for superfine grinding to a particle size of 0.5-5 μm, wherein the sand mill main machine rotates at 800 rpm, the stirring rotor rotates at 100 rpm, and the circulating cooling water temperature is 10°C.

[0044] (2) Then, the fine grinding slurry is transferred into an electromagnetic elutriator, and a combined dispersant of 0.2 wt% sodium hexametaphosphate and 0.02 wt% sodium silicate is added under stirring (200 r / min) to perform sufficient flocculation desliming. The fine mud particles are kept in a dispersed state by mechanical stirring, the target mineral particles are enriched at the magnetic pole, and the gangue mineral fine mud is kept suspended. After the elutriation is completed, the filtrate is separated to obtain a preliminary purified magnetite.

[0045] (3) The preliminary purified magnetite is configured into a slurry with a mass concentration of 60% by adding water, and the slurry is placed in a flotation tank for reverse flotation, including one roughing and three times of cleaning: the magnetite depressant, the composite collector and the activator are sequentially added to the slurry, wherein the magnetite depressant is caustic starch, the addition amount of the caustic starch in the roughing process is 1000 g / t relative to the preliminary purified magnetite; the composite collector is dodecylamine and dodecyl sulfobetaine, the total addition amount of the composite collector in the roughing process is 200 g / t, and the mass ratio of the dodecylamine to the dodecyl sulfobetaine is 10:1; the activator is a mixture of CaO and La2O3 in a mass ratio of 20:1, and the addition amount of the activator in the roughing process is 20 g / t; in the cleaning process, the addition amounts of the magnetite depressant, the composite collector and the activator in the first cleaning are all half of those in the roughing process, and the addition amounts of the reagents in the subsequent cleaning processes are all half of those in the previous cleaning process.

[0046] Comparative Example 1

[0047] The magnetite is purified by the method of Example 1, except that the flocculation and desliming step is not performed, and the fine grinding slurry is directly subjected to the reverse flotation process.

[0048] Comparative Example 2

[0049] The magnetite is purified by the method of Example 1, except that the flocculation and desliming process in step (2) is controlled to be ordinary magnetic separation, that is, no combined dispersant is added.

[0050] The iron concentrate obtained by Example 1 is compared with the products obtained by Comparative Examples 1 and 2, and the results are shown in Table 1.

[0051]

[0052] As can be seen from Table 1, the concentrate grade after purification of the present application is better than that of Comparative Examples 1 and 2, which shows that single flotation and ordinary magnetic separation + flotation cannot achieve the effect of the magnetite purification method in the present application, indicating that ultra-fine grinding and flocculation and desliming can play a unique role in the purification of magnetite.

[0053] Example 2

[0054] A magnetite concentrate purification method, comprising the following steps:

[0055] (1) 50 g of magnetite concentrate raw material (common ore) is placed in a nano sand mill for ultra-fine grinding to a particle size of 0.5-5 μm, wherein the sand mill main machine rotates at 1000 rpm, the stirring rotor rotates at 200 rpm, and the circulating cooling water temperature is 10℃.

[0056] (2) Then the fine grinding slurry is transferred into the electromagnetic elutriator, and the flocculation desliming is carried out under stirring (300 r / min) and adding 0.1wt% sodium hexametaphosphate and 0.05wt% sodium silicate, the fine mud particles are kept in a dispersed state by mechanical stirring, the target mineral particles are enriched at the magnetic pole, and the gangue mineral fine mud is kept suspended, and the elutriation is ended to carry out the filtrate separation, and the preliminary purified magnetite is obtained.

[0057] (3) The preliminary purified magnetite is configured into a slurry with a mass concentration of 45% by adding water, and the slurry is placed in a flotation tank for reverse flotation, including one roughing and four times of cleaning: the magnetite depressant, the composite collector and the activator are sequentially added to the preliminary purified magnetite, wherein the magnetite depressant is caustic starch, the addition amount of the roughing process is 1500g / t relative to the preliminary purified magnetite; the composite collector is hexadecylamine and lauryl amide propyl hydroxyl sulfobetaine, the total addition amount of the roughing process is 300g / t, and the mass ratio of the two is 5:1, the activator is a mixture of CaCl2 and Ce2O3 in a mass ratio of 30:1, and the addition amount of the activator in the roughing process is 15g / t, and in the cleaning process, the amounts of the magnetite depressant, the composite collector and the activator in the first cleaning are all half of those in the roughing process, and the amounts of the reagents in the subsequent cleaning processes are all half of those in the previous cleaning process.

[0058] Comparative Example 3

[0059] The method of Example 2 is used to purify magnetite, except that in the flocculation desliming process of step (2), the combined dispersant used is 0.1wt% sodium polyacrylate and 0.1wt% sodium hexametaphosphate.

[0060] Comparative Example 4

[0061] The method of Example 2 is used to purify magnetite, except that in the flocculation desliming process of step (2), the combined dispersant used is 0.1wt% sodium polyacrylate and 0.05wt% sodium silicate.

[0062] Comparative Example 5

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

[0064] Comparative Example 6

[0065] The method of Example 2 is used to purify magnetite, except that in the flocculation desliming process of step (2), the combined dispersant used is 0.1wt% sodium lignosulfonate and 0.05wt% sodium silicate.

[0066] Comparative Example 7

[0067] The method of Example 2 was used to purify magnetite, except that in the flocculation desliming process of step (2), the combined dispersant used was 0.1wt% sodium polyacrylate and 0.1wt% sodium lignosulfonate.

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

[0069]

[0070] As can be seen from Table 2, the concentrate after purification according to the present application is superior to that of Comparative Examples 3-7, and it can be seen that only the specific combined dispersant alkali metal hexametaphosphate and alkali metal silicate according to the present application can achieve good purification effect, and other conventional dispersants cannot achieve the technical effect of the present application.

[0071] Example 3

[0072] A method for purifying a magnetite concentrate, comprising the following steps:

[0073] (1) 30g of magnetite concentrate raw material (bulk ore) was placed in a nano sand mill for superfine grinding to a particle size of 5-10μm, wherein the sand mill main machine speed was 500rpm, the stirring rotor speed was 50rpm, and the circulating cooling water temperature was 10℃.

[0074] (2) Then the fine grinding slurry was transferred into an electromagnetic elutriator, and a combined dispersant of 0.5wt% sodium hexametaphosphate and 0.1wt% sodium silicate was added under stirring (400 r / min) to carry out sufficient flocculation desliming. The fine mud particles were kept in a dispersed state by mechanical stirring, and the target mineral particles were enriched at the magnetic pole, while the gangue mineral fine mud was kept in suspension. After elutriation, the filtrate was separated to obtain a preliminary purified magnetite.

[0075] (3) The above preliminary purified magnetite was configured into a slurry with a mass concentration of 55% by adding water, and the slurry was placed in a flotation tank for reverse flotation, including one roughing and three times of cleaning. A magnetite depressant, a composite collector and an activator were sequentially added to the preliminary purified magnetite, wherein the magnetite depressant was caustic starch, the addition amount in the roughing process was 200g / t relative to the preliminary purified magnetite; the composite collector was dodecylamine and dodecyl sulfobetaine, the total addition amount in the roughing process was 50g / t, and the mass ratio of the two was 3:1; the activator was a mixture of CaO and Nd2O3 in a mass ratio of 40:1, and the addition amount in the roughing process was 10g / t. In the cleaning process, the amounts of the magnetite depressant, the composite collector and the activator in the first cleaning were all half of those in the roughing process, and the amounts of the reagents in the subsequent cleaning processes were all half of those in the previous cleaning process.

[0076] Comparative Example 8

[0077] The method of Example 3 was used to purify magnetite, except that in the flotation process of step (3), the combined collector was controlled to be dodecylamine and sodium oleate (cationic agent + anionic agent), and the total amount of addition was 50 g / t, and the mass ratio of the two was 3:1.

[0078] Comparative Example 9

[0079] The method of Example 3 was used to purify magnetite, except that in the flotation process of step (3), the combined collector was controlled to be dodecylamine + hexadecylamine (double cationic agent), and the total amount of addition was 50 g / t, and the mass ratio of the two was 3:1.

[0080] Comparative Example 10

[0081] The method of Example 3 was used to purify magnetite, except that in the flotation process of step (3), the combined collector was controlled to be dodecylamine and sodium oleate (cationic agent + anionic agent), and the total amount of addition was 50 g / t, and the mass ratio of the two was 3:1.

[0082] Comparative Example 11

[0083] The method of Example 3 was used to purify magnetite, 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] The method of Example 3 was used to purify magnetite, 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] The method of Example 3 was used to purify magnetite, except that in the flotation process of step (3), no activator was added.

[0088] Comparative Example 14

[0089] Patent CN 113617513 A discloses a method for preparing ultra-pure iron concentrate powder from iron concentrate. In the patent, dodecylamine is used for reverse flotation to obtain an ultra-pure iron concentrate with a total iron content of 72.14%, wherein the dosage of the roughing collector dodecylamine in Example 1 is 50 g / t, and the dosage of the depressant caustic starch is 500 g / t.

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

[0091]

[0092] As can be seen from Table 3, the concentrate grade of the present application is better than each of the comparative examples, wherein comparative examples 8-10 show that replacing any one of the composite collector will have an adverse effect on the purification of magnetite, indicating that the composite collector formed by the fatty amine and the zwitterionic surfactant can improve the flotation purification effect; Comparative examples 11-12 show that too high or too low ratio of dodecylamine and dodecyl sulfobetaine will have an inhibitory effect on the purification of magnetite, indicating that the ratio of the composite collector has an effect on the flotation effect; Comparative example 13 shows that without the activator as an additive, the flotation effect is obviously reduced. In this embodiment 3, the total dosage of the roughing collector is 50 g / t, the dosage of the depressor caustic starch is as low as 200 g / t, the dosage of the activator is 10 g / t, and the total dosage of the reagent is significantly lower than that of comparative example 14. The purity, yield and iron recovery of the super-pure iron concentrate obtained in embodiment 3 of the present application are also better than those of comparative example 14, indicating that the present application can greatly reduce the dosage of the flotation reagent while improving the purity of the iron concentrate.

Claims

1. A method of purifying a magnetite concentrate, characterized by: The magnetite concentrate raw material is superfine ground, and then alkali metal hexametaphosphate and alkali metal silicate are added for flocculation desliming to obtain a preliminary purified magnetite, and then a magnetite depressant, a composite collector and an activator are added to the slurry containing the preliminary purified magnetite for reverse flotation, wherein the composite collector comprises a fatty amine and a zwitterionic surfactant, and the activator comprises a calcium compound and a rare earth compound.

2. A method of purifying a magnetite concentrate according to claim 1, characterised in that: The magnetite concentrate raw material is superfine ground to a particle size of not more than 10 μm.

3. The method according to claim 1 or 2, characterized in that: The mass ratio of the alkali metal hexametaphosphate and the alkali metal silicate is 5-20:

1. The addition amount of the alkali metal hexametaphosphate is 0.05-0.5 wt% of the magnetite concentrate raw material.

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

5. A method of purifying a magnetite concentrate according to claim 1, characterised in that: The reverse flotation process comprises one roughing and three or more than three cleaning; wherein the addition amount of the magnetite depressant, the composite collector and the activator in each cleaning is half of that in the previous cleaning, and the addition amount of the magnetite depressant, the composite collector and the activator in the first cleaning is half of that in the roughing.

6. A method of purifying a magnetite concentrate according to claim 5, characterised in that: In the roughing process, 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, relative to the preliminary purified magnetite.

7. The method according to claim 1, characterized in that: The mass ratio of the fatty amine and the zwitterionic surfactant in the composite collector is 1-10:

1. The fatty amine comprises at least one of dodecylamine, hexadecylamine and octadecylamine. The zwitterionic surfactant comprises at least one of betaine compounds, amino acid compounds and imidazoline compounds.

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

1.

9. The method according to claim 1 or 8, characterized in that: The calcium compound comprises at least one of calcium oxide, calcium chloride, calcium hydroxide and calcium carbonate. The rare earth compound is a lanthanide compound.

10. A method of purifying a magnetite concentrate according to claim 1, characterised in that: The magnetite depressant comprises at least one of caustic starch, dextrin and carboxymethyl cellulose.

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