A method of separating a low intensity magnetic separation concentrate containing pseudomorphed hematite

Abstract

The present application belongs to the technical field of mineral processing, and discloses a method for sorting weak magnetic separation concentrate containing pseudomorphic hematite. In the treatment of complex and refractory iron ore containing pseudomorphic hematite, how to accurately control the key process parameters, while achieving the full dissociation of the target mineral, inhibit the overgrinding and mudification of pseudomorphic hematite in the grinding process and the loss in the separation, and reduce the mechanical inclusion of gangue minerals, so as to provide the subsequent separation with stable properties and excellent grade in the front-end physical separation stage. On this basis, by constructing an efficient and undisturbed sequential flotation reagent system, the problems of poor selectivity of reagents, unstable foam properties and mutual interference of multi-stage reagent residues in the traditional flotation process are solved, and finally qualified iron concentrate products with TFe grade not less than 66% are obtained.

Description

Technical Field

[0001] This invention relates to the field of mineral processing technology, and in particular to a method for separating weak magnetic concentrate containing pseudomorphic hematite. Background Technology

[0002] my country has abundant Anshan-type iron ore reserves, but they are generally characterized by being "poor, fine-grained, and complex," with iron minerals and gangue such as quartz intercalated into extremely fine grains and exhibiting complex intergrowth relationships. As easily beneficiated, high-quality resources become increasingly depleted, the efficient development and utilization of fine-grained, complex, and difficult-to-beneficiate iron ore has become a major requirement for the sustainable development of the steel industry. The Guanbaoshan iron mine is a typical representative of Anshan-type difficult-to-beneficiate iron ore. Its first-stage weak magnetic separation concentrate contains approximately 46%–47% TFe and 31% SiO2, classifying it as a high-silica weak magnetic concentrate. Mineralogical studies indicate that it contains approximately 10% pseudomorphic and semi-pseudomorphic hematite. These minerals are brittle and prone to mud formation, making it difficult to synergistically improve the grade and recovery rate in the weak magnetic separation stage.

[0003] In industrial production, a combined process of "two-stage grinding-weak magnetic separation-strong magnetic separation-reverse flotation" is commonly used for Anshan-type lean ore. The two-stage weak magnetic separation not only undertakes the task of further liberating individual particles and discarding tailings from the rough concentrate, but also directly determines the processing load and reagent consumption of the subsequent strong magnetic separation and reverse flotation. In the actual operation of weak magnetic separation, there is always a contradiction between concentrate grade and recovery rate: to improve the liberation degree of the target mineral, finer grinding is required, but excessive fine grinding will lead to selective over-grinding of pseudomorphic and semi-pseudomorphic hematite, producing a large amount of fine-grained strong magnetic iron ore slime, which is easily lost with the tailings under the drag force of fluid in the weak magnetic field, causing a significant decrease in recovery rate; although increasing the magnetic field strength is beneficial for capturing weak magnetic intergrowths and semi-pseudomorphic hematite containing residual magnetite cores, excessively high field strength will significantly enhance the magnetic agglomeration effect, allowing fine-grained gangue such as quartz to enter the concentrate through mechanical inclusions and mud covering, resulting in a decrease in concentrate grade.

[0004] Regarding the efficient separation of fine-grained lean magnetite, Yuan Gaige et al., in their article "Key Technologies and Research Progress of Efficient Separation of Fine-Grained Lean Magnetite" published in *Metal Mines*, systematically reviewed the progress of pre-selection and cleaning technologies both domestically and internationally. They pointed out that while optimizing the crushing-grinding-magnetic separation process can alleviate the problems of "lean, fine, and impurity" to some extent, a bottleneck remains for difficult-to-process ores containing complex iron phases and brittle minerals, where grade and recovery are difficult to balance. Tu Jixian et al., in *Mining Research and Development*, conducted pre-selection experiments on semi-autogenous grinding and high-pressure roller mill products of Anshan-type low-grade iron ore, utilizing different crushing and grinding methods to improve the particle size composition of the feed and increase the efficiency of subsequent magnetic separation. However, their main focus was on low-grade iron ore dominated by magnetite, with less attention paid to a weakly magnetic concentrate containing pseudomorphic / semi-pseudomorphic hematite. Jiang Yaxiong et al. proposed a "fluidized magnetized roasting-weak magnetic separation" process for difficult-to-process limonite, which improved the recovery rate of weak magnetic separation by changing the magnetic properties of the mineral through roasting. However, the process focused on oxidative roasting modification and did not systematically discuss the problem of synergistic optimization of grinding-magnetic separation parameters within the existing weak magnetic concentrate.

[0005] In the flotation stage, reverse flotation desilication is typically employed for iron ore, especially for strongly magnetic concentrates containing siliceous gangue. Traditional reverse flotation systems (e.g., using cationic collectors such as dodecylamine) often suffer from poor selectivity, high froth viscosity, easy entrainment of target minerals, and difficulty in effectively removing siliceous gangue. Furthermore, the adsorption and residue of reagents on the mineral surface during preceding flotation significantly interfere with subsequent cleaning operations (such as direct flotation for iron extraction), leading to increased reagent consumption and affecting the final concentrate grade and recovery rate. Therefore, developing efficient and highly selective flotation reagent systems and addressing the interference of reagent residues on the overall process is one of the key challenges in achieving high-grade concentrate preparation from fine-grained, complex, and difficult-to-process iron ores.

[0006] In terms of process parameter optimization methods, while traditional orthogonal experiments can reduce experimental workload, they are essentially discrete-level combinatorial screening methods, making it difficult to reveal the continuous functional relationship between parameters and indicators across the entire value range, and especially unable to accurately and quantitatively characterize the nonlinear interactions between process parameters. In recent years, statistical optimization methods, represented by response surface methodology, have begun to be introduced into the field of mineral processing. For example, Zou Cuncun et al. used Box-Behnken design to optimize ball milling processes; Zhang Jinxia et al. used response surface methodology to optimize the flotation behavior of hematite flocs; and Li Chen et al. established a ball mill energy consumption prediction model based on this method. The applications of these studies are mostly concentrated on the optimization of relatively conventional material systems or relatively well-defined individual process steps. For the complex mineral system involving a large amount of brittle and fragile pseudomorphic / semi-pseudomorphic hematite involved in this invention, the coupling effect between its grinding behavior (over-grinding and mud formation) and magnetic separation behavior (competition between magnetic force and fluid drag) is particularly complex and sensitive, and the interaction between parameters far exceeds that of conventional ore systems, making its optimization results highly unpredictable.

[0007] Despite the significant progress made in the pre-selection of low-grade iron ore, efficient grinding, and the application of statistical optimization methods, substantial technological gaps remain. First, existing research has not yet published any studies systematically applying response surface methodology to analyze the highly nonlinear interaction between the two key parameters of "grinding fineness" and "weak magnetic field strength" in addressing the challenge of "a single-stage weak magnetic separation concentrate containing a significant proportion of pseudomorphic / semi-pseudomorphic hematite." This approach aims to establish a mathematical model capable of accurately predicting grade and recovery, thereby identifying and providing an optimal process parameter window with engineering feasibility. Second, current technologies for treating weak magnetic separation tailings lack a systematic process design that organically integrates front-end weak magnetic separation optimization with high-gradient strong magnetic re-selection of the tailings from a holistic perspective. This results in the underutilization of the overall recovery potential of fine-grained iron minerals. Finally, in the flotation stage, how to develop novel reagent systems that can overcome the limitations of traditional reagents (such as the poor selectivity and foaming problem of dodecylamine) and fundamentally solve the problem of reagent cross-interference between multiple flotation stages remains a key technical bottleneck restricting the final concentrate quality of such refractory ores. Therefore, a grinding-weak magnetic-strong magnetic synergistic separation method for weak magnetic separation concentrates of Anshan-type iron ore containing pseudomorphic hematite is still needed. Based on full consideration of mineralogical characteristics, the nonlinear influence of grinding fineness and magnetic field strength on concentrate grade and recovery rate should be analyzed through response surface methodology to determine a reasonable engineering operation range. This should be combined with high-gradient strong magnetic re-separation of weak magnetic tailings, supplemented by a novel composite flotation reagent system that achieves selectivity breakthrough through synergistic enhancement mechanisms, and combined with effective reagent desorption strategies to achieve a synergistic improvement in concentrate grade and recovery rate. Summary of the Invention

[0008] To address the problems existing in the prior art, this invention provides a method for separating concentrate containing pseudomorphic hematite using weak magnetic separation. The aim is to effectively balance the contradiction between grade and recovery rate by controlling grinding fineness, optimizing the parameters of weak and strong magnetic separation, and combining fine flotation purification, thereby obtaining high-grade iron concentrate.

[0009] The technical problem solved by this invention is: when processing complex and refractory iron ore concentrate containing pseudomorphic hematite using weak magnetic separation, how to precisely control key process parameters to achieve full liberation of the target mineral while suppressing over-grinding and mud formation of pseudomorphic hematite during grinding and its loss during separation, and reducing mechanical inclusions of gangue minerals, thereby providing stable and high-grade feed for subsequent separations at the front-end physical separation stage. Based on this, by constructing an efficient and undisturbed sequential flotation reagent system, the problems of poor reagent selectivity, unstable froth properties, and mutual interference of reagent residues in multiple stages of traditional flotation processes are solved, ultimately obtaining a qualified iron concentrate product with a TFe grade of not less than 66%.

[0010] The technical solution of the present invention is as follows: A method for separating weak magnetic concentrate containing pseudomorphic hematite, comprising the following steps: Step 1: Feed the first-stage weak magnetic separation rough concentrate into a grinding mill for selective liberation grinding to obtain the grinding product; the content of -0.045 mm particles in the grinding product is 68% to 72% by weight. Step 2: The grinding product from Step 1 is made into a slurry and fed into a weak magnetic separator for weak magnetic separation to obtain a two-stage weak magnetic concentrate and weak magnetic tailings; the magnetic field strength of the weak magnetic separation operation is 115 kA / m to 125 kA / m. Step 3: Feed the weak magnetic separation tailings obtained in Step 2 into a high gradient magnetic separator for strong magnetic separation to obtain strong magnetic separation concentrate and strong magnetic separation tailings. Step 4: The strong magnetic separation concentrate obtained in Step 3 is subjected to slurry conditioning. Under stirring conditions, inhibitors and cationic collectors are added to carry out reverse flotation desilication operation, selectively collecting and removing siliceous gangue to obtain reverse flotation underflow product and reverse flotation froth product. Step 5: Adjust the pH of the reverse flotation underflow product and perform enhanced decanting under stirring conditions to obtain decanted slurry; Step 6: Add anionic collector to the de-treated slurry and perform direct flotation to selectively collect iron minerals and obtain direct flotation concentrate and direct flotation tailings; Step 7: Combine the two-stage weak magnetic concentrate obtained in Step 2 with the positive flotation concentrate to obtain the final iron concentrate product.

[0011] The grinding product contains 69% to 70% by weight of -0.045 mm particle size.

[0012] The magnetic field strength of the weak magnetic separation operation is 120 kA / m to 122 kA / m.

[0013] The high gradient magnetic separator is a vertical ring pulsating high gradient magnetic separator with a background magnetic field strength of 477 kA / m to 637 kA / m.

[0014] The background magnetic field strength is 477 kA / m.

[0015] In step 4, the slurry mass concentration after conditioning of the strong magnetic concentrate is 28% to 32%, and the amount of inhibitor added is 450 g / t to 550 g / t.

[0016] The slurry concentration after conditioning the strong magnetic concentrate is 30%.

[0017] The cationic collector is composed of the main collector methyl ammonium oleate imidazoline sulfate and the auxiliary collector propylenediamine; the mass ratio of the main collector to the auxiliary collector is (8.5-9.5):1, and the amount of cationic collector added is 500 g / t to 600 g / t.

[0018] In step 5, the enhanced decanting treatment involves adjusting the pH of the slurry to 5.5–6.5 by adding an acidic regulator; the stirring speed of the enhanced decanting treatment is 3000 r / min–4000 r / min.

[0019] The amount of anionic collector added is 550 g / t to 650 g / t; the anionic collector is one or more of TD-7, sodium oleate or talc oil.

[0020] Furthermore, the grinding equipment is a ball mill or a tower mill.

[0021] Furthermore, the inhibitor is causticized starch.

[0022] Furthermore, an acid regulator is used to adjust the pH of the pulp to 6.0.

[0023] Compared with the prior art, the present invention has the following significant advantages: This invention addresses the mineralogical characteristics of hematite containing pseudomorphs and semi-pseudomorphs. Through systematic experimental research using the response surface methodology, a quadratic polynomial model capable of accurately predicting concentrate grade Y1 and concentrate recovery Y2 is obtained. This quadratic polynomial model is: Y1 = 66.67 + 1.31A - 0.11B + 0.24AB - 0.85A 2 - 0.23B 2 ;Y2= 72.03 - 2.98A +2.73B - 0.75AB - 0.88A 2 - 1.19B 2 In the formula, A represents the grinding fineness (content of particles in the -0.045 mm size, %), and B represents the magnetic field strength (kA / m) of the weak magnetic separation operation. This model enables precise control of grinding and weak magnetic separation parameters. These synergistically optimized parameters effectively balance the magnetic force and fluid drag in the separation flow field, suppressing the loss of fine-grained iron minerals through mud formation, particularly the selective over-grinding of pseudomorphic and semi-pseudomorphic hematite, while significantly mitigating the problem of non-selective mechanical inclusions of gangue minerals.

[0024] The overall separation process of this invention exhibits good compatibility with grinding processes in the high-intensity magnetic separation stage, and can be effectively adapted to different types of grinding equipment such as ball mills and tower mills. Under a specific magnetic field strength of 477 kA / m, high-grade feed can be obtained from high-intensity magnetic separation concentrates processed by both ball mills and tower mills, thus providing more stable and higher-quality feed ore for subsequent fine flotation operations.

[0025] This invention integrates a sequential flotation strategy of "reverse flotation desilication - enhanced deretting - direct flotation iron extraction" into the process flow. In particular, by applying an enhanced deretting step between reverse and direct flotation, it effectively solves the problem of flotation environment deterioration caused by reagent residue, ensuring that subsequent flotation reagents (especially the novel composite collector proposed in this invention) can exert their optimal efficiency, laying the foundation for achieving high grade and high purity of the final concentrate. Specifically, the pH value is precisely adjusted to 6.0 to ensure that the residual cationic collector (amines) is fully protonated (-NH3). + This increases its water solubility, making it easier to desorb from the mineral surface under ultra-high mechanical shear force, thus achieving synergistic detoxification by chemical and physical means.

[0026] The core innovation of this invention lies in the creative proposal and application of a composite cationic collector system. It is this innovative reagent system based on a synergistic mechanism that makes the highly efficient sorting process described in this invention possible. Unlike existing technologies, this invention discovers a synergistic mechanism between the main collector (methyl oleate imidazoline sulfate ammonium) and the auxiliary collector (propylenediamine) at a specific ratio. Its working principle is as follows: at the molecular level, the diamine structure of propylenediamine plays a crucial role in "molecular bridging" and "adsorption enhancement." It can adsorb onto the negative potential point on the quartz surface at one end, while at the other end, it strongly "anchors" the main collector molecule through electrostatic or hydrogen bonding forces. This anchoring effect greatly improves the adsorption density and stability of the main collector on the quartz surface, forming a hydrophobic layer that is much denser and stronger than that of a single reagent, thereby achieving unprecedented selective collection of silica gangue. At the macroscopic level, this ordered and robust adsorption layer directly improves the properties of the flotation foam. Unlike traditional dodecylamine-induced foams or foams that are too brittle due to single-agent formulations, the foam system of this invention exhibits moderate stability and good toughness. This effectively inhibits the mechanical entrainment of fine iron minerals in the foam, fundamentally solving the problems of "foam runoff" and "foam entrainment." This synergistic system based on a specific molecular structure design is the key technological innovation of this invention, enabling the production of high-quality concentrates with a TFe grade of over 66%. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the process flow for the weak magnetic separation concentrate separation method containing pseudomorphic hematite as described in this invention.

[0028] Figure 2 (a) is a schematic diagram of the synergistic mechanism of the composite cationic collector; (b) is a schematic diagram of bubble adhesion at the macro level; (c) is a schematic diagram of the macro level foaming structure of traditional amines; (d) is a schematic diagram of the macro level foaming structure of the system of the present invention. Detailed Implementation

[0029] The inventiveness of this invention lies not in isolated parameter optimization, but in a systematic solution to a series of key mechanisms in the beneficiation process of specific refractory ores. It reveals the nonlinear interaction between grinding and magnetic separation, and creatively applies response curves to quantitatively characterize a quadratic polynomial model, thereby locking in the globally optimal process window that conventional experiments cannot discover. It confirms that excessively high magnetic field strength can induce a large number of inclusions in gangue, leading to a "grade cliff" effect. This invention proves the necessity and inventiveness of the selected optimization point of 477 kA / m by precisely avoiding this failure range. To overcome the problem of poor selectivity of traditional collectors, this invention creatively proposes a novel reagent system that achieves "synergistic enhancement" of collectors through specific components (the main collector, methyl oleate imidazoline sulfate ammonium, and the auxiliary collector, propylenediamine) in a specific ratio. To ensure that the above-mentioned novel synergistic reagent system is not interfered with by preceding reagents in the sequential process, this invention integrates an ultra-high intensity stirring de-removal step, achieving "forced desorption" of residual reagents, clearing obstacles for the core reagent system to function, and solving the problem of cross-contamination between anion and cation systems.

[0030] Example 1 The ore sample used in this embodiment is a weak magnetic separation rough concentrate containing pseudomorphic hematite from an iron mine in Liaoning Province. The total iron grade of the ore sample is 46.87%, which contains 10.15% pseudomorphic and semi-pseudomorphic hematite by mass. The main gangue mineral is quartz, which belongs to the typical Anshan-type high-silica refractory iron ore.

[0031] First, the weak magnetic separation concentrate is fed into a grinding mill for fine grinding. A ZQM-Φ250×100 ball mill can be used for regrinding, with the following operating parameters: media filling rate of 42%, feed-to-ball ratio of 0.064, and rotational speed of 77.3%. Alternatively, a tower mill can be used for regrinding, with the following operating parameters: slurry concentration of 58%, media filling rate of 70%, feed-to-ball ratio of 0.19, and rotational speed of 75%. The fineness of the grinding product is adjusted by controlling the grinding time, with the -0.045 mm particle size content used as the evaluation index for grinding fineness. Ultimately, the -0.045 mm particle size content in the grinding fineness is controlled to reach 69.33%.

[0032] The regrinded slurry was fed into a DTCXG-ZN50 weak magnetic separator and separated under a magnetic field strength of 120.74 kA / m to obtain a two-stage weak magnetic concentrate and weak magnetic tailings. The TFe grade of the two-stage weak magnetic concentrate was 66.62%, and the recovery rate was 72.80%. The obtained weak magnetic tailings were used as feed for subsequent strong magnetic separation.

[0033] A central composite design optimization experiment was conducted using response surface methodology, with grinding fineness (-0.045 mm content) and magnetic field strength as independent variables, and concentrate grade and recovery rate as response values. The theoretically optimal process parameters were determined to be: grinding fineness (-0.045 mm content) 69.33%, and magnetic field strength 120.74 kA / m. Three parallel verification experiments were conducted under these theoretically optimal conditions.

[0034] Using the above method, the average grade of the re-selected weak magnetic separation concentrate was 66.62% by weight, and the average recovery rate was 72.80% by weight.

[0035] Example 2 The feed used in this embodiment is the weak magnetic separation tailings produced in Example 1, processed by a ball mill and a tower mill under the optimal conditions of grinding fineness (-0.045 mm particle size content of 69.33%) and weak magnetic field strength of 120.74 kA / m. The strong magnetic separation test used a feed rate of 1000 g per treatment, with a slurry mass fraction of 30%. This embodiment employs a vertical ring pulse high-gradient magnetic separator for strong magnetic separation.

[0036] First, strong magnetic separation tests were conducted on the weak magnetic separation tailings generated from the ball mill path under different magnetic field intensities. When the magnetic field intensity was 318 kA / m, the yield of the strong magnetic concentrate was 17.38%, the TFe grade was 38.45%, and the operating recovery rate was 25.51%; at this time, the yield of the strong magnetic tailings was 82.62%, the TFe grade was 23.62%, and the operating recovery rate was 74.49%. When the magnetic field intensity was increased to the 477 kA / m recommended in this invention, the yield of the strong magnetic concentrate was 36.25%, the TFe grade significantly increased to 42.88%, and the operating recovery rate was 59.71%; at this time, the yield of the strong magnetic tailings was 63.75%, the TFe grade was 16.45%, and the operating recovery rate was 40.29%. As the magnetic field strength further increases to 637 kA / m, the yield of the strong magnetic concentrate is 55.80%, but the TFe grade decreases to 35.92%, and the operational recovery rate is 76.99%. At this point, the yield of the strong magnetic tailings is 44.20%, the TFe grade is 13.55%, and the operational recovery rate is 23.01%. When the magnetic field strength reaches 796 kA / m, the yield of the strong magnetic concentrate is 72.50%, the TFe grade further decreases to 30.85%, and the operational recovery rate is 85.23%. At this point, the yield of the strong magnetic tailings is 27.50%, the TFe grade is 14.10%, and the operational recovery rate is 14.77%.

[0037] Strong magnetic separation tests were conducted on the weak magnetic separation tailings generated in the tower mill path under different magnetic field intensities. When the magnetic field intensity was 318 kA / m, the strong magnetic concentrate yield was 16.85%, the TFe grade was 39.05%, and the operating recovery rate was 25.31%; at this time, the strong magnetic tailings yield was 83.15%, the TFe grade was 23.35%, and the operating recovery rate was 74.69%. When the magnetic field intensity was increased to the 477 kA / m recommended in this invention, the strong magnetic concentrate yield was 35.10%, the TFe grade significantly increased to 43.72%, and the operating recovery rate was 58.39%; at this time, the strong magnetic tailings yield was 64.90%, the TFe grade was 16.85%, and the operating recovery rate was 41.61%. When the magnetic field strength further increases to 637 kA / m, the yield of the strong magnetic concentrate is 54.40%, but the TFe grade decreases to 36.85%, and the operational recovery rate is 76.37%. At this point, the yield of the strong magnetic tailings is 45.60%, the TFe grade is 13.62%, and the operational recovery rate is 23.63%. When the magnetic field strength reaches 796 kA / m, the yield of the strong magnetic concentrate is 71.80%, the TFe grade further decreases to 31.35%, and the operational recovery rate is 86.41%. At this point, the yield of the strong magnetic tailings is 28.20%, the TFe grade is 12.55%, and the operational recovery rate is 13.59%.

[0038] Based on the analysis of the above experimental data, it can be seen that regardless of whether a ball mill or a tower mill is used as the regrinding equipment, the TFe grade of the strong magnetic concentrate reaches its peak at a background magnetic field strength of 477 kA / m. For example, the grade of the strong magnetic concentrate in the ball mill path is 42.88%, and the grade in the tower mill path is 43.72%. Under this magnetic field strength, while obtaining a high-grade concentrate, a good recovery rate is also maintained (59.71% in the ball mill path and 58.39% in the tower mill path). This indicates that a magnetic field strength of 477 kA / m can effectively enrich iron minerals and maximally suppress the mechanical inclusions of gangue, achieving an optimal balance between grade and recovery rate, and providing high-quality feed for subsequent flotation. When the magnetic field strength is below 477 kA / m (e.g., 318 kA / m), the grade of the strong magnetic concentrate (38.45% in the ball mill path, 39.05% in the tower mill path) and the operating recovery rate (25.51% in the ball mill path, 25.31% in the tower mill path) are both unsatisfactory. However, when the magnetic field strength is above 477 kA / m (e.g., 637 kA / m and 796 kA / m), although the operating recovery rate improves, the TFe grade of the strong magnetic concentrate decreases significantly. For example, at a magnetic field strength of 796 kA / m, the grade of the strong magnetic concentrate has dropped to 30.85% (ball mill path) and 31.35% (tower mill path), respectively. This will result in a large amount of gangue entering the concentrate, severely affecting subsequent flotation efficiency and the quality of the final product. Furthermore, a comparison of results at 477 kA / m revealed that, when achieving the same fineness, the tower milling process yielded a slightly higher grade of the strong magnetic concentrate (43.72%) than the ball-milled sample (42.88%). This indicates that tower milling has an advantage in protecting the integrity of the pseudomorphic hematite lattice, thereby improving separation selectivity. Therefore, the preferred background magnetic field strength for strong magnetic separation in this invention is 477 kA / m, a parameter that optimally balances grade and recovery, providing high-quality feed for subsequent flotation.

[0039] Example 3 This embodiment aims to illustrate the best practice of the method of the present invention by flotation purification of the strong magnetic concentrate (TFe grade 42.88%) obtained in Example 2 using a ball milling path and a magnetic field strength of 477 kA / m. The flotation equipment used is an RK / FD type single-cell flotation machine.

[0040] First, reverse flotation desilication is performed: the strong magnetic concentrate slurry is adjusted to a mass concentration of 30%, and 500 g / t of causticized starch inhibitor is added under stirring conditions; simultaneously, a composite cationic collector, composed of the main collector methyl oleate imidazoline sulfate ammonium and the auxiliary collector propylenediamine in a mass ratio of 9:1, is added, with a total dosage of 550 g / t. After reverse flotation, reverse flotation underflow product and reverse flotation froth product are obtained.

[0041] Subsequently, the underflow product was subjected to enhanced agitation and decanting: the pH of the slurry was adjusted to 6.0 using hydrochloric acid, and decanting was carried out for 10 minutes at an enhanced agitation speed of 4000 r / min to obtain the decanted slurry.

[0042] Finally, iron extraction was carried out by direct flotation: 600 g / t of anionic collector TD-7 was added to the de-reagented slurry, and direct flotation was performed to obtain direct flotation concentrate and tailings. This direct flotation concentrate was combined with the two-stage weak magnetic concentrate obtained in Example 1 (grade 66.62%, recovery rate 72.80%). The calculated TFe grade of the final composite concentrate was 66.58%, and the final overall recovery rate was 88.5%.

[0043] Example 4 To determine the optimal dosage range of the causticizing starch inhibitor, conditional experiments were conducted by varying only the inhibitor dosage, based on the process parameters of Example 3. When the inhibitor dosage was reduced to 400 g / t, the final overall concentrate TFe grade was 66.15%, and the overall recovery rate was 88.2%. When the inhibitor dosage was increased to 600 g / t, the final overall concentrate TFe grade was 66.32%, and the overall recovery rate was 87.6%. Comparing this to the 66.58% grade and 88.5% recovery rate obtained in Example 3 with a dosage of 500 g / t, it can be seen that when the dosage is too low, insufficient inhibition of iron minerals leads to their loss during reverse flotation, affecting the grade and recovery rate; when the dosage is too high, it may adversely affect subsequent forward flotation, leading to a decrease in recovery rate. The experimental results show that the overall effect is best when the inhibitor dosage is around 500 g / t; therefore, the suitable dosage range is 450 g / t to 550 g / t.

[0044] Example 5 To determine the optimal dosage range of the composite cationic collector, conditional experiments were conducted by varying only the total dosage of the composite cationic collector, based on the process parameters of Example 3. When the total collector dosage was reduced to 450 g / t, the final overall concentrate TFe grade was 66.21%, and the overall recovery rate was 87.9%. When the total collector dosage was increased to 650 g / t, the final overall concentrate TFe grade was 66.45%, and the overall recovery rate was 87.1%. Compared with the 66.58% grade and 88.5% recovery rate obtained in Example 3 with a dosage of 550 g / t, it is evident that when the dosage is too low, the collection capacity for siliceous gangue is insufficient, affecting the final concentrate grade; when the dosage is too high, excessive collector will reduce selectivity and place a greater burden on subsequent dewatering and positive flotation, leading to a decrease in recovery rate. Experimental results show that the effect is best when the total dosage of the composite cationic collector is around 550 g / t. Therefore, the suitable total dosage range is 500 g / t to 600 g / t.

[0045] Comparative Example 1[1][2] This study aims to emphasize the crucial importance of magnetic field strength control during the high-intensity magnetic separation stage. Using the same ore sample and grinding conditions as in Example 1 (ball milling process, -0.045 mm particle size content 69.33%), the background magnetic field strength was significantly increased to 796 kA / m during the high-intensity magnetic separation stage. Experimental results showed that at a strong magnetic field strength of 796 kA / m, the grade of the obtained high-intensity magnetic concentrate was only 30.85%. Although the iron recovery rate was as high as 85.23%, the grade was severely diluted, mainly because the excessively high magnetic field strength captured a large amount of non-magnetic gangue minerals. This low-grade high-intensity magnetic concentrate directly resulted in an excessively low feed grade entering the subsequent flotation process. This not only increased the reagent consumption of the subsequent flotation process by an estimated 40% or more, but more importantly, the final concentrate quality was unlikely to meet the industrial requirement of a TFe grade of over 65%. For example, when the TFe grade of the magnetically separated concentrate is 30.85%, even with an optimized flotation process, the final iron concentrate grade can only reach 64.33%, failing to meet industrial standards. This result strongly demonstrates the criticality and superiority of the 477 kA / m to 637 kA / m, especially 477 kA / m, strong magnetic field strength control proposed in this invention, clearly indicating that excessively high magnetic field strength leads to a large number of gangue mineral mechanical inclusions, seriously affecting the concentrate grade and the quality of the final product.

[0046] Comparative Example 2 To demonstrate the superiority of the composite cationic collector system and its specific ratio proposed in this invention, a series of comparative experiments were conducted. In the experiments, except for the cationic collector system, all other process parameters were consistent with those in Example 3.

[0047] First, as a benchmark, Example 3 of the present invention used a collector composed of ammonium methyl oleate and propylene diamine in a mass ratio of 9:1 to obtain a final comprehensive concentrate TFe grade of 66.58%.

[0048] In a comparative experiment, the aforementioned composite collector was replaced with an equal amount of the traditional cationic collector, dodecylamine. The results showed that the final overall concentrate TFe grade was only 64.37%, far lower than the result of this invention. Furthermore, the experiment revealed viscous foam, easy overflow from the tank, and poor operational stability.

[0049] In another comparative experiment, only the main collector component of the composite collector of this invention, namely methyl ammonium oleate imidazoline sulfate, was used without the addition of propylenediamine. The results were improved, with the obtained overall concentrate TFe grade being 65.13%, but still significantly lower than the results of Example 3 of this invention, which preliminarily proves the necessity of compounding.

[0050] To further verify the criticality of the compounding ratio, two sets of comparative experiments were set up. When the mass ratio of the main collector, methyl ammonium oleate imidazoline sulfate, to the auxiliary collector, propylenediamine, was 5:1, the final comprehensive concentrate TFe grade was 65.88%; when the mass ratio was 12:1, the final comprehensive concentrate TFe grade was 66.05%.

[0051] The results of the comparative experiments described above demonstrate that the composite collector system employed in this invention exhibits a significant synergistic effect. Oleic acid-based imidazoline methyl sulfate ammonium, as the primary collector, possesses a long carbon chain in its molecular structure that provides strong hydrophobicity, while the imidazoline ring provides a basic affinity for the quartz surface. However, its selectivity is limited when used alone (65.13% purity). The ingenuity of this invention lies in the introduction of a small amount of a specific structural auxiliary agent, propylenediamine. While propylenediamine molecules themselves have weak collecting ability, their unique diamine structure plays a crucial role in this system: it adsorbs at one end onto the negative potential point of the quartz surface, while the amine group at the other end strongly "anchors" the primary collector molecule through hydrogen bonding or electrostatic forces, thereby significantly increasing the adsorption density and stability of the primary agent on the quartz surface, forming a denser and more robust hydrophobic layer.

[0052] This synergistic effect is highly sensitive and dependent on the ratio, exhibiting a significant performance peak within a narrow range of (8.5–9.5):1 (9:1 in this example). As shown in the comparative experiment, when the ratio of excipients is too low (e.g., 12:1), the number of "molecular bridges" is insufficient, and the synergistic effect is not fully realized; when the ratio of excipients is too high (e.g., 5:1), excessive propylenediamine molecules will compete with the main agent for active sites on the quartz surface, and may even produce a certain inhibitory effect, destroying the optimal adsorption layer configuration.

[0053] Therefore, the technical solution proposed in this invention, which combines the main collector and the auxiliary collector in a mass ratio of (8.5 to 9.5):1, is based on a profound understanding and scientific verification of the above-mentioned synergistic effect mechanism. The technical effect obtained (grade 66.58%) has outstanding substantive characteristics and significant progress.

[0054] Comparative Example 3 This study aims to illustrate the negative impact of excessively coarse grinding fineness on the separation effect. The same ore sample as in Example 1 was used, and a similar magnetic field strength (111.40 kA / m, the recommended range of this invention is 115 kA / m to 125 kA / m, and 120.74 kA / m in Example 1) was employed in the weak magnetic separation operation. However, the content of -0.045 mm particles in the grinding product was controlled at 60.53% (i.e., below the lower limit of the preferred range of 68%).

[0055] Under these excessively coarse grinding conditions, weak magnetic separation was performed. Experimental results showed that the obtained two-stage weak magnetic concentrate had a TFe grade of 62.81% and an operating recovery rate of 76.04%. Comparing this with the two-stage weak magnetic concentrate obtained in Example 1 under optimized grinding fineness (69.33%) and magnetic field strength (120.74 kA / m) (TFe grade 66.62%, operating recovery rate 72.80%), it can be seen that excessively coarse grinding fineness leads to a significant decrease in concentrate grade (62.81% vs 66.62%). This is mainly because insufficient mineral liberation results in a large amount of gangue minerals and iron mineral intergrowths entering the concentrate, thus diluting the concentrate grade. Although the recovery rate is slightly improved, this is often at the expense of concentrate grade, and a synergistic improvement in grade and recovery rate is not achieved.

[0056] Using this low-grade secondary weak magnetic concentrate as feed for subsequent separation will significantly increase the load and reagent consumption of subsequent strong magnetic separation and flotation purification. If processed according to the subsequent process of Example 3 and combined with the positive flotation concentrate, it is expected that the final overall concentrate grade will be difficult to meet the industrial requirement of TFe not less than 66%. This strongly demonstrates the importance of controlling the content of -0.045 mm particle size in the grinding product within the range of 68% to 72% proposed in this invention; that is, excessively coarse grinding fineness will lead to incomplete liberation of iron minerals, affecting the concentrate quality.

[0057] Comparative Example 4 The purpose is to illustrate the negative impact of excessively fine grinding on the separation effect. The same ore sample as in Example 1 was used, and a magnetic field strength (111.40 kA / m) similar to that in Example 1 was used in the weak magnetic separation operation, but the content of -0.045 mm particles in the grinding product was controlled at 77.53% (i.e., higher than the upper limit of 72% of the preferred range of the present invention).

[0058] Under these excessively fine grinding conditions, weak magnetic separation was performed. Experimental results showed that the obtained two-stage weak magnetic concentrate had a TFe grade of 66.80% and an operational recovery rate of 66.50%. Comparing this with the two-stage weak magnetic concentrate obtained in Example 1 under optimized grinding fineness (69.33%) and magnetic field strength (120.74 kA / m) (TFe grade 66.62%, operational recovery rate 72.80%), it can be seen that while excessively fine grinding slightly increased the concentrate grade (66.80% vs 66.62%), it significantly decreased the operational recovery rate (66.50% vs 72.80%). This verifies the problem mentioned in the background section, namely, that excessively fine grinding leads to selective over-grinding of pseudomorphic and semi-pseudomorphic hematite, producing a large amount of fine-grained strongly magnetic iron ore slime. These fine-grained iron minerals are easily lost with the tailings due to fluid drag in a weak magnetic field, thus causing a significant decrease in iron recovery rate.

[0059] The significantly reduced recovery rate of the second-stage weak magnetic concentrate leads to a substantial decrease in the overall iron metal recovery rate of the entire beneficiation process, failing to fully exploit the recovery potential of fine-grained iron minerals. If processed according to the subsequent process of Example 3 and combined with the positive flotation concentrate, the final overall recovery rate is expected to be far lower than the optimal level achievable by this invention. This result strongly demonstrates the criticality and superiority of controlling the -0.045 mm particle size content in the grinding product within the range of 68% to 72% proposed in this invention, clearly indicating that excessive fine grinding will cause the target minerals to be over-crushed and muddy, resulting in a loss of recovery rate and affecting the comprehensive utilization of iron ore resources.

Claims

1. A method for separating weak magnetic concentrate containing pseudomorphous hematite, characterized in that, Includes the following steps: Step 1: Feed the first-stage weak magnetic separation rough concentrate into a grinding mill for selective liberation grinding to obtain the grinding product; the content of -0.045 mm particles in the grinding product is 68% to 72% by weight. Step 2: The grinding product from Step 1 is made into a slurry and fed into a weak magnetic separator for weak magnetic separation to obtain a two-stage weak magnetic concentrate and weak magnetic tailings; the magnetic field strength of the weak magnetic separation operation is 115 kA / m to 125 kA / m. Step 3: Feed the weak magnetic separation tailings obtained in Step 2 into a high gradient magnetic separator for strong magnetic separation to obtain strong magnetic separation concentrate and strong magnetic separation tailings. Step 4: The strong magnetic separation concentrate obtained in Step 3 is subjected to slurry conditioning. Under stirring conditions, inhibitors and cationic collectors are added sequentially to carry out reverse flotation desilication operation, selectively collecting and removing siliceous gangue to obtain reverse flotation underflow product and reverse flotation froth product. Step 5: Adjust the pH of the reverse flotation underflow product and perform enhanced decanting under stirring conditions to obtain decanted slurry; Step 6: Add anionic collector to the de-treated slurry and perform direct flotation to selectively collect iron minerals and obtain direct flotation concentrate and direct flotation tailings; Step 7: Combine the two-stage weak magnetic concentrate obtained in Step 2 with the positive flotation concentrate to obtain the final iron concentrate product.

2. The method for separating weak magnetic concentrate containing pseudomorphic hematite according to claim 1, characterized in that, The grinding product contains 69% to 70% by weight of -0.045 mm particle size.

3. The method for separating weak magnetic concentrate containing pseudomorphic hematite according to claim 1, characterized in that, The magnetic field strength of the weak magnetic separation operation is 120 kA / m to 122 kA / m.

4. The method for separating weak magnetic concentrate containing pseudomorphic hematite according to claim 1, characterized in that, The high gradient magnetic separator is a vertical ring pulsating high gradient magnetic separator with a background magnetic field strength of 477 kA / m to 637 kA / m.

5. The method for separating weak magnetic concentrate containing pseudomorphic hematite according to claim 4, characterized in that, The background magnetic field strength is 477 kA / m.

6. The method for separating weak magnetic concentrate containing pseudomorphic hematite according to claim 1, characterized in that, In step 4, the slurry concentration after conditioning with strong magnetic concentrate is 28% to 32%, and the amount of inhibitor added is 450 g / t to 550 g / t.

7. The method for separating weak magnetic concentrate containing pseudomorphic hematite according to claim 6, characterized in that, The slurry concentration after conditioning the strong magnetic concentrate is 30%.

8. The method for separating weak magnetic concentrate containing pseudomorphic hematite according to claim 1, characterized in that, In step 4, the cationic collector is composed of the main collector methyl ammonium oleate imidazoline sulfate and the auxiliary collector propylenediamine; the mass ratio of the main collector to the auxiliary collector is (8.5-9.5):1, and the amount of cationic collector added is 500 g / t to 600 g / t.

9. The method for separating weak magnetic concentrate containing pseudomorphic hematite according to claim 1, characterized in that, In step 5, the enhanced decanting treatment involves adjusting the pH of the slurry to 5.5–6.5 by adding an acidic regulator; the stirring speed of the enhanced decanting treatment is 3000 r / min–4000 r / min.

10. The method for separating weak magnetic concentrate containing pseudomorphic hematite according to claim 1, characterized in that, The amount of anionic collector added is 550 g / t to 650 g / t; the anionic collector is one or more of TD-7, sodium oleate or talc oil.

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