Method for separating magnetite and pyrrhotite through combination of magnetic separation and flotation

Abstract

The invention relates to the technical field of mineral processing, and discloses a magnetic separation-flotation combined magnetite and pyrrhotite separation method which comprises the following steps: crushing and grinding high-sulfur magnetite ore to obtain ore pulp; carrying out ultrasonic treatment on the ore pulp, and carrying out magnetic separation and roughing to obtain a rough concentrate product; the rough concentrate product is subjected to pulsed electric field pretreatment; preparing a modifier aqueous solution with the concentration of 5%-10%, and mixing and blending the pretreated rough concentrate product and the modifier aqueous solution into ore pulp; performing magnetic separation on the ore pulp under a gradient magnetic field to obtain magnetic separation concentrate; and the magnetic concentrate is subjected to flotation treatment, and final pyrrhotite concentrate and high-quality iron concentrate are obtained. Through the synergistic effect of pulsed electric field pretreatment, modifier chemical modification and gradient magnetic field magnetic separation, the separation selectivity and separation efficiency of magnetite and pyrrhotite are remarkably improved, deep desulfurization of iron ore concentrate is achieved, the grade is greatly improved, and meanwhile the method has the advantages of being low in agent consumption and environmentally friendly.

Description

Technical Field

[0001] This invention relates to the field of mineral processing technology, and in particular to a method for the combined magnetic separation-flotation separation of magnetite and pyrrhotite. Background Technology

[0002] Magnetite is an important iron mineral resource, while pyrrhotite is a sulfur-containing iron mineral. They often coexist in nature, and the separation of magnetite and pyrrhotite is a crucial research direction in mineral processing. Magnetite and pyrrhotite share similar magnetic and physical properties, with similar magnetic susceptibility. During magnetic separation, they easily form strong magnetic agglomerates, leading to severe cross-contamination in the concentrate, a decrease in iron concentrate grade, and excessive sulfur content. Currently, the separation of magnetite and pyrrhotite mainly employs magnetic separation or a combined magnetic separation-flotation process. Traditional single magnetic separation or "magnetic separation-flotation" processes primarily rely on chemical reagents to adjust the mineral surface properties, which has the following inherent drawbacks:

[0003] Limited separation precision: magnetic agglomeration leads to incomplete physical separation of minerals; chemical reagents lack selectivity and are not effective in separating minerals with similar surface properties.

[0004] High dependence on chemicals: To achieve effective separation, large amounts of activators, inhibitors and collectors are often required, which not only results in high subsequent treatment costs, but also brings a serious environmental burden.

[0005] Severe interference from fine mud: Fine-grained minerals easily cover the surface of the target mineral (fine mud cover) or agglomerate themselves, which seriously affects the sorting efficiency.

[0006] For example, CN113019684A discloses a method for separating pyrite and pyrrhotite, employing a combined magnetic separation-flotation method. First, the symbiotic pyrite and pyrrhotite materials are magnetically separated to obtain magnetic concentrate and tailings. Then, the magnetic tailings are mixed with FeCl3 for flotation separation. The depth-inhibiting effect of FeCl3 on pyrrhotite reduces its floatability, thus achieving efficient separation. While this method can separate pyrite and pyrrhotite, its effectiveness is limited when separating magnetite and pyrrhotite. Summary of the Invention

[0007] In view of this, the purpose of the present invention is to provide a method for the combined magnetic separation-flotation separation of magnetite and pyrrhotite, which improves the separation efficiency of magnetite and pyrrhotite.

[0008] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0009] A method for combining magnetic separation and flotation to separate magnetite and pyrrhotite, characterized by comprising the following steps:

[0010] S1: The high-sulfur magnetite ore is crushed and ground to obtain a slurry;

[0011] S2: The slurry is subjected to ultrasonic treatment, and then rough concentrate is obtained by magnetic separation.

[0012] S3: Perform pulsed electric field pretreatment on the crude concentrate product described in S2;

[0013] S4: Prepare a 5%–10% aqueous solution of the modifier, and mix the crude concentrate product after ultrasonic treatment in S3 with the aqueous solution of the modifier to form a slurry; the modifier, by mass percentage, includes the following components: 60%–65% starch phosphate, 20%–25% polyacrylamide, 10%–15% sodium silicate, and 1%–5% rare earth chloride;

[0014] S5: The slurry described in S4 is subjected to magnetic separation under a gradient magnetic field to obtain magnetic concentrate;

[0015] S6: The magnetic concentrate described in S5 is subjected to flotation treatment, which includes one roughing, two cleaning and two scavenging processes; the froth product from the two cleaning processes is the final pyrrhotite concentrate, and the remaining product in the flotation cell after the two scavenging processes is the desulfurized magnetite rough concentrate; after the desulfurized magnetite rough concentrate is subjected to magnetic separation and cleaning, the final high-quality iron concentrate is obtained.

[0016] Preferably, in step S1, the proportion of grinding fineness of -0.074mm is ≥58%.

[0017] Preferably, the frequency of the ultrasonic treatment in step S2 is 25–30 kHz, and the ultrasonic power density is 0.5–0.8 W / cm². 2 The processing time is 2 to 5 minutes.

[0018] Preferably, the magnetic field strength in the coarse magnetic separation in step S2 is 0.1 to 0.3 T.

[0019] Preferably, the pulse electric field parameters in step S3 are set as follows: peak voltage 18kV, pulse width 100ns, repetition frequency 250Hz; and the pulse electric field processing time is 10-30S.

[0020] Preferably, in step S4, the starch phosphate ester is prepared by a phosphate-urea composite esterification method, and the preparation method includes the following steps:

[0021] Mix 100 parts by weight of cassava starch (purity >98%) with 15-25 parts by weight of sodium dihydrogen phosphate, 8-12 parts by weight of urea and deionized water to prepare a suspension slurry with a solid content of 40%-50%.

[0022] The above slurry was subjected to esterification reaction at pH 5.5–6.5 and temperature 150–160℃ for 2–3 hours;

[0023] After the reaction was completed, the product was cooled to room temperature and washed three times with 70% ethanol solution to remove unreacted phosphate and byproducts. The washed product was then vacuum dried at 60-70°C to constant weight to obtain starch phosphate.

[0024] Preferably, the rare earth chlorides include one or more of lanthanum chloride, cerium chloride, praseodymium chloride, neodymium chloride, samarium chloride, europium chloride, gadolinium chloride, and yttrium chloride.

[0025] Preferably, the slurry concentration in step S4 is 30% to 40%.

[0026] Preferably, in step S5, the gradient magnetic field strength increases step by step: 0.1T→0.12T→0.14T→0.16T→0.18T→0.2T, and the duration of each magnetic field is 30 to 60 seconds.

[0027] Preferably, the flotation process in step S6 includes a first roughing → a first roughing froth followed by a first cleaning → a first cleaning froth followed by a second cleaning; the tailings from the first roughing are then subjected to a first scavenging → the tailings from the first scavenging are then subjected to a second scavenging.

[0028] Preferably, the collectors used in the flotation process in step S6 include sodium butyl xanthate and pine oil.

[0029] Preferably, in step S6, the magnetic field strength for magnetic separation of the desulfurized magnetite rough concentrate is 0.1 to 0.2 T.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] 1. This invention utilizes ultrasonic treatment to powerfully clean the oxide layer and impurities on the mineral surface, effectively peeling off and removing the thin film of impurities and fine mud covering the mineral surface, exposing a relatively clean and fresh mineral interface. Then, the rough concentrate product is pretreated using a pulsed electric field. The strong electric field generated by the high-energy pulses utilizes the instantaneous Joule heating effect to effectively weaken and disperse the heterogeneous magnetic agglomerates between magnetite and pyrrhotite, improving the surface lattice of pyrrhotite and exposing more hydrophobic sites. The ultrasonic treatment and pulsed electric field pretreatment create a synergistic effect of "cleaning first, then activating," laying the foundation for the selective adsorption of subsequent modifiers. This allows the modifiers to act more precisely on the target mineral surface, improving the selective separation accuracy of magnetic separation-flotation.

[0032] 2. In this invention, starch phosphate and polyacrylamide are selected as modifiers. The phosphate groups (-PO3) introduced by starch phosphate are... 2-It has strong negative charge and selective adsorption capacity on the surface of different minerals in the ore. Because pyrrhotite contains sulfur, the sulfur atoms exposed on the surface are more likely to adsorb or coordinate with phosphate groups. In contrast, the surface of magnetite is mainly composed of iron and oxygen structures, and the adsorption effect is weak. This difference in selective adsorption enables precise treatment of the pyrrhotite surface, which lays the foundation for subsequent flotation separation. This allows pyrrhotite to be efficiently separated by flotation, thereby ensuring the deep desulfurization of magnetite.

[0033] 3. This invention employs a gradient magnetic field for magnetic separation, achieving a gradual separation process. In the lower magnetic field strength stage, it primarily captures the strongest individual magnetite particles and some strongly magnetic intergrowths. As the magnetic field strength gradually increases, weaker pyrrhotite particles and those affected by the modifier are gradually captured. This step-by-step, precise capture mechanism effectively reduces the chance of pyrrhotite being "co-opted" into the magnetite concentrate during the strong magnetic field stage, thus lowering the sulfur content of the concentrate from the physical separation stage. Furthermore, considering that the "heterogeneous magnetic agglomerates" of magnetite and pyrrhotite are the core issue causing separation difficulties, the magnetic force applied to the minerals during the progressively increasing gradient magnetic field changes dynamically. This changing magnetic force generates a periodic shearing and stretching effect on the agglomerates, acting like a "magnetic sieve," which helps to peel away loosely bound pyrrhotite particles, achieving high separation accuracy.

[0034] 4. This invention enhances the selective action on the surface of target minerals through the synergistic effect of ultrasonic treatment, pulsed electric field pretreatment and chemical modification by modifiers, significantly reducing the demand for traditional activators, inhibitors and collectors, and greatly reducing the use of activators. This not only reduces production costs, but also alleviates the environmental pressure of subsequent wastewater treatment.

[0035] 5. The iron concentrate obtained by the magnetic separation-flotation combined separation method of the present invention has an iron grade of up to 69.12%, a sulfur content as low as 0.07%, an iron recovery rate of 86.54%, and a pyrrhotite concentrate yield of 4.82% with a grade of up to 45.33%. The separation efficiency of magnetite and pyrrhotite is significantly improved. Detailed Implementation

[0036] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0037] Example 1

[0038] Using high-sulfur magnetite ore from the Qinghai mining area as the processing target, the main chemical composition of the ore is shown in the table below:

[0039] Elements / Components TFe S <![CDATA[SiO2]]> <![CDATA[Al2O3]]> CaO MgO Content (wt%) 48.43 1.45 18.56 4.32 2.11 1.89

[0040] The main metallic minerals in this ore are magnetite and pyrrhotite, which have a complex intergrowth relationship and uneven grain size distribution. Some pyrrhotite exists in the magnetite as fine-grained inclusions.

[0041] This embodiment provides a method for the combined magnetic separation-flotation separation of magnetite and pyrrhotite, the steps of which are as follows:

[0042] S1: The high-sulfur magnetite ore is crushed to a particle size of <20mm by a jaw crusher and a cone crusher; the crushed product is then ground in a grinding mill to obtain a slurry, with the grinding fineness controlled to be ≥58% of -0.074mm and the slurry concentration between 30% and 60%.

[0043] S2: Place the slurry obtained in S1 into the ultrasonic processor, turn on the ultrasonic processor, set the working frequency to 28kHz, and the power density to 0.7W / cm³. 2 The processing time is 5 minutes; this step aims to clean the mineral surface using the ultrasonic cavitation effect; the pretreated slurry is then subjected to magnetic separation using a permanent magnet drum magnetic separator to obtain a rough concentrate product, with the magnetic field strength set to 0.3T; the yield of the magnetic product (mixed concentrate of magnetite and pyrrhotite) is 65.2%, the iron grade is 62.15%, and the sulfur grade is 1.98%, which enters the subsequent slurry conditioning process, while the non-magnetic product is treated as tailings 1;

[0044] S3: The crude concentrate product obtained in S2 is prepared into a slurry with a concentration of 35%, and pretreated using a pulsed electric field. The pulsed electric field adopts a parallel plate electrode structure, and the parameters are set as follows: peak voltage 18kV, pulse width 100ns, repetition frequency 250Hz; the slurry flows through the treatment area between the electrode plates, and the treatment time is 20s.

[0045] S4: Prepare a 5% aqueous solution of the modifier, wherein the modifier components, by mass percentage, are as follows: 63% starch phosphate, 22% polyacrylamide, 12% sodium silicate, and 3% lanthanum chloride; the starch phosphate is prepared by a phosphate-urea composite esterification method, including the following steps:

[0046] 100 parts by weight of cassava starch (purity >98%) was mixed with 20 parts by weight of sodium dihydrogen phosphate, 10 parts by weight of urea and deionized water to prepare a suspension slurry with a solid content of 40%. The slurry was subjected to esterification reaction at pH 6 and temperature of 150°C for 2 hours. After the reaction was completed, the product was cooled to room temperature and the precipitate was washed three times with 70% ethanol solution to remove unreacted phosphate and byproducts. The washed product was vacuum dried at 60°C to constant weight to obtain starch phosphate ester.

[0047] The crude concentrate product after ultrasonic treatment in step S3 is mixed with the modifier aqueous solution and stirred at 1200 rpm for 5 minutes to prepare a slurry with a concentration of 40%.

[0048] S5: The prepared slurry is pumped into a gradient magnetic field for magnetic separation. First, the gradient magnetic field system is turned on, and the gradient magnetic field strength is set to increase step by step: 0.1T→0.12T→0.14T→0.16T→0.18T→0.2T, with each magnetic field acting for 60 seconds. During this process, the gradient magnetic field can produce a periodic shearing and stretching effect on the agglomerates, which helps to further disperse the remaining magnetic agglomerates and achieve preliminary enrichment and separation based on the differences in mineral magnetic properties, thus obtaining magnetic concentrate.

[0049] S6: Adjust the magnetically separated slurry to a concentration of 30%, adjust the pH to 9.2 with NaOH, introduce it into an XFD single-cell flotation machine, add 65g / t of sodium butyl xanthate as collector and 8g / t of pine oil as frother, and carry out flotation in the flotation machine; the flotation process includes one roughing, two cleaning, and two scavenging, including roughing (4min) → roughing froth undergoing one cleaning (3min) → one cleaning froth undergoing two cleaning (2min); roughing tailings undergo one scavenging (3min) → one scavenging tailings undergo two scavenging (2min); combine the froth products from the two cleaning processes as the final pyrrhotite concentrate, and the product in the flotation cell is the desulfurized magnetite rough concentrate;

[0050] After desulfurization, the magnetite rough concentrate is finely separated and treated in a permanent magnet drum separator with a magnetic field strength of 0.15T to obtain the final high-quality iron concentrate. The non-magnetic product is discharged as tailings 2.

[0051] Comparative Example 1

[0052] In this comparative example, no modifier was added in the "slurry preparation" step S4, and the remaining steps and process parameters were the same as in Example 1.

[0053] Comparative Example 2

[0054] In this comparative example, magnetic separation was not performed under gradient magnetic field conditions in step S5. Instead, magnetic separation was performed under a fixed magnetic field of 0.3 T / m. The remaining steps and process parameters were the same as in Example 1.

[0055] Comparative Example 3

[0056] In this comparative example, pulsed electric field treatment was not performed in step S2. Instead, 200 g / t of copper sulfate, a traditional activator, was added to activate the pyrrhotite before the flotation operation, and 130 g / t of sodium butyl xanthate, a collector, was added. The remaining steps and process parameters were the same as in Example 1.

[0057] Performance characterization:

[0058] The sulfur grade was determined by chemical analysis of the S element content. The separation effect of pyrite and pyrrhotite was judged based on the sulfur content of the final pyrite. The higher the sulfur grade of the pyrite, the better the separation effect.

[0059] Pyrite yield = Pyrite mass / (Pyrite mass + Pyrrhotite mass) × 100%;

[0060] Pyrrhotite yield = 100% - pyrite yield;

[0061] Sulfur recovery rate = (Product sulfur grade × Product yield) / Initial feed sulfur grade × 100%

[0062] Example 1 and Comparative Examples 1-3

[0063]

[0064] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for combined magnetic separation and flotation to separate magnetite and pyrrhotite, characterized in that, Includes the following steps: S1: The high-sulfur magnetite ore is crushed and ground to obtain a slurry; S2: The slurry is subjected to ultrasonic treatment, and then rough concentrate is obtained by magnetic separation. S3: Perform pulsed electric field pretreatment on the crude concentrate product described in S2; S4: Prepare a 5%–10% aqueous solution of the modifier, and mix the crude concentrate product after ultrasonic treatment in S3 with the aqueous solution of the modifier to form a slurry; the modifier, by mass percentage, includes the following components: 60%–65% starch phosphate, 20%–25% polyacrylamide, 10%–15% sodium silicate, and 1%–5% rare earth chloride; S5: The slurry described in S4 is subjected to magnetic separation under a gradient magnetic field to obtain magnetic concentrate; S6: The magnetic concentrate described in S5 is subjected to flotation treatment, which includes one roughing, two cleaning and two scavenging processes; the froth product from the two cleaning processes is the final pyrrhotite concentrate, and the remaining product in the flotation cell after the two scavenging processes is the desulfurized magnetite rough concentrate; after the desulfurized magnetite rough concentrate is subjected to magnetic separation and cleaning, the final high-quality iron concentrate is obtained.

2. The method for combined magnetic separation and flotation of magnetite and pyrrhotite according to claim 1, characterized in that, In step S1, the proportion of grinding fineness of -0.074mm is ≥58%.

3. The method for combined magnetic separation and flotation of magnetite and pyrrhotite according to claim 1, characterized in that, In step S2, the magnetic field strength during the roughing selection of magnetic separation is 0.1 to 0.3 T.

4. The method for combined magnetic separation and flotation of magnetite and pyrrhotite according to claim 1, characterized in that, In step S3, the pulse electric field parameters are set as follows: peak voltage 18kV, pulse width 100ns, repetition frequency 250Hz; the pulse electric field processing time is 10-30S.

5. The method for combined magnetic separation and flotation of magnetite and pyrrhotite according to claim 1, characterized in that, In step S4, starch phosphate is prepared by phosphate-urea composite esterification.

6. The method for combined magnetic separation and flotation of magnetite and pyrrhotite according to claim 1, characterized in that, In step S4, the slurry concentration is 30% to 40%.

7. The method for combined magnetic separation and flotation of magnetite and pyrrhotite according to claim 1, characterized in that, In step S5, the gradient magnetic field strength increases step by step: 0.1T→0.12T→0.14T→0.16T→0.18T→0.2T, and the duration of each magnetic field is 30 to 60 seconds.

8. The method for combined magnetic separation and flotation of magnetite and pyrrhotite according to claim 1, characterized in that, The flotation process in step S6 includes a first roughing → a first roughing froth followed by a first cleaning → a first cleaning froth followed by a second cleaning, and a first roughing tailings followed by a first scavenging → a first scavenging tailings followed by a second scavenging.

9. The method for combined magnetic separation and flotation of magnetite and pyrrhotite according to claim 1, characterized in that, The collectors used in the flotation process in step S6 include sodium butyl xanthate and pine oil.

10. The method for combined magnetic separation and flotation of magnetite and pyrrhotite according to claim 1, characterized in that, In step S6, the magnetic field strength for magnetic separation and fine selection of the desulfurized magnetite rough concentrate is 0.1 to 0.2 T.

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