Continuous positive and negative flotation method for medium and low grade phosphate rock

Abstract

The present application relates to the technical field of phosphate ore dressing, and particularly relates to a continuous positive and reverse flotation method for medium and low grade phosphate ore. The preliminary separation of phosphate ore and gangue ore is realized through 'two-stage crushing-gradient magnetic separation-cyclone classification', then the tailings of magnetic separation and coarse-grained phosphate ore are re-ground by a tower mill, and then 'positive flotation-reverse flotation-reverse flotation again' is carried out on the coarse phosphate ore based on a micro-bubble flotation column. In the positive flotation stage, combined depressants are used to efficiently depress gangue minerals such as quartz and dolomite, in the reverse flotation I stage, carbonates are deeply removed, in the reverse flotation II stage, an activator is introduced to improve the adsorption activity of silicate impurities, and silicate minerals are deeply removed, so that the efficient flotation of medium and low grade phosphate ore is realized. The flotation method provided by the present application effectively improves the flotation efficiency of medium and low grade phosphate ore, improves the quality and recovery rate of the concentrate, and achieves good flotation effect.

Description

Technical Field

[0001] This invention relates to the field of phosphate rock beneficiation technology, specifically to a continuous forward and reverse flotation method for medium- and low-grade phosphate rock. Background Technology

[0002] my country has the world's second largest phosphate rock reserves, but the average grade is only 17%. With the increasing depletion of high-grade phosphate rock resources, medium and low-grade phosphate rock has become the main target of mining. However, medium and low-grade phosphate rock is often associated with gangue minerals such as magnesium, silicon, and iron, and generally has problems such as fine particle size and high clay content. It must be enriched through beneficiation before it can be used in the downstream phosphate chemical industry.

[0003] Currently, the processing of low-grade phosphate rock in China mainly employs flotation methods, including direct flotation, reverse flotation, direct-reverse flotation, and reverse-flotation. Direct flotation is primarily used for processing single-type siliceous phosphate rock; reverse flotation is mainly used for processing single-type magnesian or siliceous phosphate rock; and direct-reverse flotation and reverse-flotation are mainly used for processing mixed siliceous-magnesian phosphate rock. However, due to the fine particle size of low-grade phosphate minerals and the complex intergrowth relationship between phosphate rock and gangue minerals, single flotation methods are insufficient to obtain high-quality phosphate concentrate products. In particular, several problems still exist in the existing forward and reverse flotation processes. For example, the raw ore pretreatment is insufficient, and associated magnetic minerals, such as pyrrhotite, are not effectively separated in advance, resulting in high consumption of flotation reagents and high iron content in the concentrate. In the forward flotation stage, a single inorganic depressant, such as sodium silicate, is often used to suppress carbonate minerals, but its suppression effect is limited and it is easy to cause high magnesium content in the concentrate. In the reverse flotation stage, the collector selectivity for silicate minerals is insufficient, making it difficult to achieve deep desilication. In addition, the bubble distribution of traditional mechanical flotation equipment is uneven and the bubble size is large, which easily produces mechanical entrainment and the recovery effect of fine-grained disseminated phosphate rock is not ideal. Summary of the Invention

[0004] To address the technical problems of insufficient pretreatment, poor selectivity in gangue mineral separation, and low recovery rate of fine-grained phosphate rock in existing technologies for processing low- and medium-grade phosphate rock, this invention provides a continuous forward and reverse flotation method for low- and medium-grade phosphate rock. The method provided by this invention is applicable to the efficient flotation of low- and medium-grade phosphate rock and achieves good flotation results.

[0005] The technical solution of this invention is as follows: This invention provides a continuous flotation method for medium- and low-grade phosphate rock, comprising the following steps: S1. The medium- and low-grade phosphate ore is crushed in two stages using a jaw crusher and a cone crusher. The crushed ore is then subjected to magnetic separation to obtain magnetic separation products and tailings. The magnetic separation products are then classified by a hydrocyclone to obtain fine-grained minerals with a particle size of less than 0.074 mm and coarse-grained minerals with a particle size of more than 0.074 mm. The fine-grained minerals are then discharged. S2. Grind the coarse-grained minerals obtained in step S1 with the magnetic separation tailings into a tower mill until the proportion of particles smaller than 0.074mm is ≥80% to obtain phosphate rock powder; dilute the phosphate rock powder with water to make phosphate rock slurry. S3. Adjust the pH of the phosphate rock slurry obtained in step S2 to 9-10 with sodium carbonate, inject it into the top feed inlet of the microbubble packing flotation column, add inhibitors and positive flotation collectors, and at the same time introduce high-pressure gas from the bottom of the column. The gas is cut by multiple layers of corrugated packing to form uniform microbubbles. The phosphate rock adheres to the microbubbles and is scraped out from the top of the column to obtain positive flotation phosphate rock slurry. The inhibited carbonates and siliceous veins are discharged from the bottom of the column. S4. Add the positive flotation phosphate rock slurry obtained in step S3 to a thickener for concentration and de-reagenting until the phosphate rock slurry concentration reaches 17%-20%. The overflow water after de-reagenting is recycled into the S3 positive flotation process. S5. Add phosphoric acid to the phosphate rock slurry obtained in step S4 to adjust the pH value to 5-6. Inject the pH-adjusted phosphate rock slurry into the top feed port of the reverse flotation microbubble flotation column I. Then add reverse flotation collector I. At the same time, high-pressure gas is introduced from the bottom of the column. The gas is cut by multiple layers of corrugated packing to form uniform microbubbles. Carbonate minerals are attached to the microbubbles and scraped out from the top of the column. The reverse flotation phosphate rock slurry is discharged from the bottom. S6. The reverse flotation phosphate slurry obtained in step S5 is injected into the top feed inlet of the reverse flotation microbubble flotation column II. Then, reverse flotation collector II and activator are added. High-pressure gas is introduced from the bottom of the column. The gas is cut by multiple layers of corrugated packing to form uniform microbubbles. Silicate minerals are attached to the microbubbles and scraped out from the top of the column. Phosphate concentrate is discharged from the bottom.

[0006] This invention achieves efficient separation and full dissociation of magnetic minerals through a pretreatment process of "two-stage crushing-gradient magnetic separation-cyclone classification" combined with regrinding in a tower mill; and implements a three-stage continuous flotation process of forward flotation-reverse flotation I-reverse flotation II using a microbubble packed flotation column to remove carbonate and silicate impurities step by step.

[0007] Furthermore, in low- to medium-grade phosphate rock, w(P2O5) < 20%. The applicable ore range for this invention is low- to medium-grade phosphate rock with a grade below 20%. Phosphate rocks in this grade range have high gangue mineral content and complex mineral intergrowth relationships.

[0008] Furthermore, the particle size of the medium-to-low grade phosphate rock after two-stage crushing in step S1 is ≤2mm. Controlling the crushed particle size to ≤2mm ensures uniform feeding of the material in subsequent magnetic separation and grinding processes, avoiding reduced magnetic separation efficiency and uneven load on the tower mill due to excessively large particles. At the same time, an appropriate crushed particle size helps reduce the energy consumption of the tower mill and improve operational efficiency.

[0009] Furthermore, in step S1, the graded magnetic separation is a two-stage separation. The first stage uses a weak magnetic field of 900-1500 Gs to separate strongly magnetic minerals, and the second stage uses a strong magnetic field of 12000 Gs to separate weakly magnetic minerals. This two-stage gradient magnetic separation (weak-strong magnetic) can efficiently remove strongly magnetic minerals (such as magnetite) and weakly magnetic minerals (such as pyrrhotite and limonite) in a stepwise manner. Compared to single-stage magnetic separation, it achieves a higher iron removal rate while reducing the consumption and interference of ferromagnetic minerals with subsequent flotation reagents, thus improving flotation selectivity.

[0010] Furthermore, the phosphate rock slurry obtained in step S2 has a mass concentration of 30% ± 2%. Controlling the mass concentration of the phosphate rock slurry at 30% ± 2% ensures that the slurry has suitable fluidity and particle suspension in the microbubble packed flotation column: too low a concentration will reduce the probability of collision between particles and bubbles, affecting the recovery rate; too high a concentration will increase the viscosity of the slurry and intensify bubble co-optation, which is not conducive to the flotation of fine-grained phosphate rock.

[0011] Furthermore, in step S3, the inhibitor is a combination of corn starch and sodium silicate or a combination of sodium carboxymethyl cellulose and sodium silicate. The amount of inhibitor used in step S3 is 1.0-2.0 kg / t relative to the amount of low-grade phosphate rock used in step S1. Using a combination of organic polymer (corn starch or sodium carboxymethyl cellulose) and inorganic inhibitor (sodium silicate) as a positive flotation inhibitor can exert a synergistic inhibition effect: the organic polymer forms a hydrophilic protective layer through multi-point adsorption of macromolecular chains on the surface of carbonate minerals, effectively inhibiting carbonate minerals such as dolomite; sodium silicate inhibits siliceous gangue through the adsorption of silicate ions on the surface of silicate minerals.

[0012] Further, in step S3, the mass ratio of corn starch to sodium silicate in the composition of corn starch and sodium silicate is 1:3; and the mass ratio of sodium carboxymethyl cellulose to sodium silicate in the composition of sodium carboxymethyl cellulose and sodium silicate is 1:3.

[0013] Furthermore, in step S3, the positive flotation collector is one of fatty acid soap, oxidized paraffin soap, or tal oil. The amount of positive flotation collector used in step S3 relative to the low-grade phosphate rock in step S1 is 0.8-1.5 kg / t. Fatty acid soap, oxidized paraffin soap, or tal oil are all anionic collectors. Anionic collectors all contain polar groups such as carboxyl or hydroxyl groups, which can selectively chemically adsorb onto the calcium sites on the surface of apatite under alkaline conditions, mineralizing the phosphate rock particles on the bubble surface and achieving effective separation of phosphate rock from carbonate and silicate gangue.

[0014] Furthermore, in step S5, the reverse flotation collector I is sodium oleate, and the amount of reverse flotation collector I used in step S5 relative to the low-grade phosphate rock in step S1 is 0.3-1.5 kg / t. Under the weakly acidic conditions (pH=5-6) of reverse flotation I, sodium oleate acts as an anionic collector, and its oleate ions can react with Ca on the surface of carbonate minerals. 2+ Mg 2+ Strong chemisorption occurs, causing the hydrophobic carbonate minerals to float to the surface. At this pH value, the surface potential difference of apatite makes the adsorption of oleate weak, thus achieving selective separation of carbonate minerals and phosphate rock, and further reducing the MgO content of the concentrate.

[0015] Furthermore, in step S6, the reverse flotation collector II is either dodecylamine or benzyldimethyltetradecyl ammonium chloride, and the amount of reverse flotation collector II used in step S6 relative to the low-grade phosphate rock in step S1 is 0.4-0.8 kg / t. Both dodecylamine and benzyldimethyltetradecyl ammonium chloride are cationic collectors. The amino or quaternary ammonium groups in the collector can electrostatically adsorb onto the active sites on the surface of silicate minerals that are negatively charged due to the action of the activator, causing the silicate minerals to float hydrophobically.

[0016] Furthermore, in step S6, the activator is calcium chloride, and the amount of calcium chloride used in step S6 relative to the low-grade phosphate rock in step S1 is 0.1-0.4 kg / t. Calcium chloride, as an activator, has a Ca... 2+ It can be adsorbed on the surface of silicate minerals, enhancing their electrostatic attraction with cationic collectors, thereby improving the adsorption efficiency and collection selectivity of cationic collectors on silicate minerals; at the same time, calcium chloride has a weak activation effect on the surface of apatite, which is conducive to the separation of phosphate rock and silicate minerals, achieving deep desilication.

[0017] The beneficial effects of this invention are as follows: This invention pre-treats phosphate rock through a "two-stage crushing-gradient magnetic separation-cyclone classification" process, efficiently separating magnetic minerals such as pyrrhotite associated with low-grade phosphate rock. This effectively reduces the feed pressure on the subsequent flotation system and lowers unnecessary reagent consumption. A hydrocyclone is used to pre-classify the magnetic separation products, eliminating fine gangue particles that interfere with the separation and further improving beneficiation efficiency. In the grinding stage, a tower mill is used to grind the minerals to a particle size of -0.074mm with a proportion ≥80%, ensuring sufficient individual liberation of the phosphate rock and gangue minerals. In the flotation stage, this invention uses a microbubble-filled flotation column instead of a traditional trough flotation machine. Multiple layers of corrugated packing generate uniform microbubbles, significantly increasing the collision probability between bubbles and mineral particles and improving the separation kinetics. The forward flotation stage employs a combination of inhibitors to efficiently suppress gangue such as quartz and dolomite; the reverse flotation stage I deeply removes carbonates; and the crucial reverse flotation stage II introduces a specific activator, which significantly enhances the adsorption activity of silicate impurities, solving the technical problem of incomplete silicate removal in existing technologies.

[0018] The experimental results show that the flotation method provided by this invention, for medium and low grade phosphate rock (w(P2O5) < 20%), produces phosphate concentrate with P2O5 content of more than 30.5%, MgO content reduced to less than 0.8%, SiO2 content reduced to less than 10.2%, and Fe2O3 content reduced to less than 1.22%, thus achieving efficient and comprehensive utilization of medium and low grade phosphate rock resources. Detailed Implementation

[0019] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions in the embodiments of this invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0020] Example 1 A continuous forward and reverse flotation method for medium- and low-grade phosphate rock includes the following steps: S1. Medium- and low-grade phosphate rock (P2O5 15.24%, CaO 35.44%, MgO 7.85%, Fe2O3 3.97%, Al2O3 2.55%, SiO2 25.12%) is crushed in two stages using a jaw crusher and a cone crusher (phosphate rock particle size ≤ 2mm). The crushed raw ore is then subjected to graded magnetic separation to obtain magnetic separation products and magnetic separation tailings. Subsequently, the magnetic separation products are graded by a hydrocyclone to obtain fine-grained (-0.074mm) and coarse-grained minerals (+0.074mm). The fine-grained minerals are discharged. S2. Grind the coarse-grained minerals and magnetic separation tailings into the tower mill until the proportion of -0.074mm particles is ≥80%, and dilute with water until the phosphate rock slurry mass concentration reaches 30%±2%. S3. The phosphate rock slurry obtained in S2 is adjusted to pH 9-10 with sodium carbonate and injected into the top feed inlet of the microbubble packed flotation column. Corn starch, sodium silicate and fatty acid soap are added. The amount of corn starch and sodium silicate combination is 1.0 kg / t (the mass ratio of corn starch and sodium silicate is 1:3). The amount of fatty acid soap as the positive flotation collector is 0.8 kg / t. At the same time, high-pressure gas is introduced from the bottom of the column. It is cut by the multi-layer corrugated packing to form uniform microbubbles. The phosphate rock adheres to the microbubbles and is scraped out from the top of the column to obtain the positive flotation phosphate rock slurry. The suppressed carbonate and siliceous veins are discharged from the bottom of the column. S4. Add the phosphate rock slurry obtained from the direct flotation to the thickener for concentration and de-reagenting until the phosphate rock slurry concentration reaches 18%. The overflow water after de-reagenting is recycled into the S3 direct flotation. S5. Add phosphoric acid to the phosphate rock slurry obtained in S4 to adjust the pH value to 5-6. Inject the pH-adjusted phosphate rock slurry into the top feed port of the reverse flotation microbubble flotation column I. Then add 0.8 kg / t sodium oleate. At the same time, high-pressure gas is introduced from the bottom of the column. The gas is cut by multiple layers of corrugated packing to form uniform microbubbles. Carbonate minerals are attached to the microbubbles and scraped out from the top of the column. The reverse flotation phosphate rock slurry is discharged from the bottom. S6. The reverse flotation phosphate slurry obtained in S5 is injected into the top feed inlet of the reverse flotation microbubble flotation column II. Then, 0.5 kg / t of dodecylamine and 0.2 kg / t of calcium chloride are added. At the same time, high-pressure gas is introduced from the bottom of the column. The gas is cut by multiple layers of corrugated packing to form uniform microbubbles. Silicate minerals are attached to the microbubbles and scraped out from the top of the column. The phosphate concentrate is discharged from the bottom.

[0021] In step S1, the graded magnetic separation is a two-stage magnetic separation. The first stage uses a weak magnetic field of 1000 Gs to separate strong magnetic minerals, and the second stage uses a strong magnetic field of 12000 Gs to separate weak magnetic minerals.

[0022] Example 2 A continuous forward and reverse flotation method for medium- and low-grade phosphate rock includes the following steps: S1. Medium- and low-grade phosphate rock (P2O5 15.24%, CaO 35.44%, MgO 7.85%, Fe2O3 3.97%, Al2O3 2.55%, SiO2 25.12%) is crushed in two stages using a jaw crusher and a cone crusher (phosphate rock particle size ≤ 2mm). The crushed raw ore is then subjected to graded magnetic separation to obtain magnetic separation products and magnetic separation tailings. Subsequently, the magnetic separation products are graded by a hydrocyclone to obtain fine-grained (-0.074mm) and coarse-grained minerals (+0.074mm). The fine-grained minerals are discharged. S2. Grind the coarse-grained minerals and magnetic separation tailings into the tower mill until the proportion of -0.074mm particles is ≥80%, and dilute with water until the phosphate rock slurry mass concentration reaches 30%±2%. S3. Adjust the pH of the phosphate rock slurry obtained in S2 to 9-10 with sodium carbonate, inject it into the top feed inlet of the microbubble packed flotation column, and add carboxymethyl cellulose, sodium silicate and oxidized paraffin soap. The composition of sodium carboxymethyl cellulose and sodium silicate is 1.4 kg / t (the mass ratio of sodium carboxymethyl cellulose and sodium silicate is 1:3), and the positive flotation collector oxidized paraffin soap is 1.0 kg / t. At the same time, high-pressure gas is introduced from the bottom of the column, which is cut by the multi-layer corrugated packing to form uniform microbubbles. The phosphate rock adheres to the microbubbles and is scraped out from the top of the column to obtain the positive flotation phosphate rock slurry. The suppressed carbonate and siliceous veins are discharged from the bottom of the column. S4. Add the phosphate rock slurry obtained from the direct flotation to the thickener for concentration and de-reagenting until the phosphate rock slurry concentration reaches 18%. The overflow water after de-reagenting is recycled into the S3 direct flotation. S5. Add phosphoric acid to the phosphate rock slurry obtained in S4 to adjust the pH value to 5-6. Inject the pH-adjusted phosphate rock slurry into the top feed port of the reverse flotation microbubble flotation column I. Then add 1.2 kg / t sodium oleate. At the same time, high-pressure gas is introduced from the bottom of the column. The gas is cut by multiple layers of corrugated packing to form uniform microbubbles. Carbonate minerals are attached to the microbubbles and scraped out from the top of the column and discharged from the bottom. S6. The reverse flotation phosphate slurry obtained in S5 is injected into the top feed inlet of the reverse flotation microbubble flotation column II. Then, 0.6 kg / t dodecylamine and 0.3 kg / t calcium chloride are added. At the same time, high-pressure gas is introduced from the bottom of the column. The gas is cut by multiple layers of corrugated packing to form uniform microbubbles. Silicate minerals are attached to the microbubbles and scraped out from the top of the column. The phosphate concentrate is discharged from the bottom.

[0023] In step S1, the graded magnetic separation is a two-stage magnetic separation. The first stage uses a weak magnetic field of 1000 Gs to separate strong magnetic minerals, and the second stage uses a strong magnetic field of 12000 Gs to separate weak magnetic minerals.

[0024] Example 3 A continuous forward and reverse flotation method for medium- and low-grade phosphate rock includes the following steps: S1. Medium- and low-grade phosphate rock (P2O5 15.24%, CaO 35.44%, MgO 7.85%, Fe2O3 3.97%, Al2O3 2.55%, SiO2 25.12%) is crushed in two stages using a jaw crusher and a cone crusher (phosphate rock particle size ≤ 2mm). The crushed raw ore is then subjected to graded magnetic separation to obtain magnetic separation products and magnetic separation tailings. Subsequently, the magnetic separation products are graded by a hydrocyclone to obtain fine-grained (-0.074mm) and coarse-grained minerals (+0.074mm). The fine-grained minerals are discharged. S2. Grind the coarse-grained minerals and magnetic separation tailings into the tower mill until the proportion of -0.074mm particles is ≥80%, and dilute with water until the phosphate rock slurry mass concentration reaches 30%±2%. S3. Adjust the pH of the phosphate rock slurry obtained in S2 to 9-10 with sodium carbonate, inject it into the top feed inlet of the microbubble packed flotation column, and add carboxymethyl cellulose, sodium silicate and tal oil. The composition of sodium carboxymethyl cellulose and sodium silicate is 2.0 kg / t (the mass ratio of sodium carboxymethyl cellulose and sodium silicate is 1:3), and tal oil is 1.5 kg / t. At the same time, high-pressure gas is introduced from the bottom of the column, which is cut by the multi-layer corrugated packing to form uniform microbubbles. The phosphate rock adheres to the microbubbles and is scraped off from the top of the column to obtain positive flotation phosphate rock slurry. The suppressed carbonate and siliceous veins are discharged from the bottom of the column. S4. Add the phosphate rock slurry obtained from the direct flotation to the thickener for concentration and de-reagenting until the phosphate rock slurry concentration reaches 18%. The overflow water after de-reagenting is recycled into the S3 direct flotation. S5. Add phosphoric acid to the phosphate rock slurry obtained in S4 to adjust the pH value to 5-6. Inject the pH-adjusted phosphate rock slurry into the top feed port of the reverse flotation microbubble flotation column I. Then add 1.5 kg / t sodium oleate and simultaneously introduce high-pressure gas from the bottom of the column. The gas is cut by multiple layers of corrugated packing to form uniform microbubbles. Carbonate minerals adhere to the microbubbles and are scraped out from the top of the column and discharged from the bottom. S6. The reverse flotation phosphate slurry obtained in S5 is injected into the top feed inlet of the reverse flotation microbubble flotation column II. Then, 0.8 kg / t of benzyl dimethyl tetradecyl ammonium chloride and 0.4 kg / t of calcium chloride are added. At the same time, high-pressure gas is introduced from the bottom of the column. The gas is cut by multiple layers of corrugated packing to form uniform microbubbles. Silicate minerals are attached to the microbubbles and scraped out from the top of the column. The phosphate concentrate is discharged from the bottom.

[0025] In step S1, the graded magnetic separation is a two-stage magnetic separation. The first stage uses a weak magnetic field of 1000 Gs to separate strong magnetic minerals, and the second stage uses a strong magnetic field of 12000 Gs to separate weak magnetic minerals.

[0026] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that in step S1, the raw ore is directly fed into the tower mill after two-stage crushing, without gradient magnetic separation and hydrocyclone classification. Specifically: A continuous forward and reverse flotation method for medium- and low-grade phosphate rock includes the following steps: S1. Medium- and low-grade phosphate rock (P2O5 15.24%, CaO 35.44%, MgO 7.85%, Fe2O3 3.97%, Al2O3 2.55%, SiO2 25.12%) is subjected to two-stage crushing using a jaw crusher and a cone crusher (phosphate rock particle size ≤ 2mm). The crushed phosphate rock is then fed into a tower mill for grinding until the -0.074mm particle size accounts for ≥ 80%. Water is added to dilute the phosphate rock slurry to a mass concentration of 30% ± 2%. S2. The phosphate rock slurry obtained in S1 is adjusted to pH 9-10 with sodium carbonate and injected into the top feed inlet of the microbubble packed flotation column. Corn starch, sodium silicate and fatty acid soap are added. The amount of corn starch and sodium silicate combination is 1.0 kg / t (the mass ratio of corn starch and sodium silicate is 1:3). The positive flotation collector is 0.8 kg / t of oxidized paraffin soap. At the same time, high-pressure gas is introduced from the bottom of the column. It is cut by the multi-layer corrugated packing to form uniform microbubbles. The phosphate rock is attached to the microbubbles and scraped off from the top of the column to obtain the positive flotation phosphate rock slurry. The suppressed carbonate and siliceous veins are discharged from the bottom of the column. S3. Add the phosphate rock slurry obtained from the direct flotation to the thickener for concentration and de-reagenting until the phosphate rock slurry concentration reaches 18%. The overflow water after de-reagenting is recycled into the S2 direct flotation. S4. Add phosphoric acid to the phosphate rock slurry obtained in S2 to adjust the pH value to 5-6. Inject the pH-adjusted phosphate rock slurry into the top feed port of the reverse flotation microbubble flotation column I. Then add 0.8 kg / t sodium oleate and simultaneously introduce high-pressure gas from the bottom of the column. The gas is cut by multiple layers of corrugated packing to form uniform microbubbles. Carbonate minerals adhere to the microbubbles and are scraped out from the top of the column and discharged from the bottom. S5. The reverse flotation phosphate slurry obtained in S3 is injected into the top feed inlet of the reverse flotation microbubble flotation column II. Then, 0.5 kg / t of dodecylamine and 0.2 kg / t of calcium chloride are added. At the same time, high-pressure gas is introduced from the bottom of the column. The gas is cut by multiple layers of corrugated packing to form uniform microbubbles. Silicate minerals are attached to the microbubbles and scraped out from the top of the column. The phosphate concentrate is discharged from the bottom.

[0027] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that in step S3, only sodium silicate is used as a single inhibitor and corn starch is not added; the remaining steps are the same as in Example 1.

[0028] A continuous forward and reverse flotation method for medium- and low-grade phosphate rock includes the following steps: S1. Medium- and low-grade phosphate rock (P2O5 15.24%, CaO 35.44%, MgO 7.85%, Fe2O3 3.97%, Al2O3 2.55%, SiO2 25.12%) is crushed in two stages using a jaw crusher and a cone crusher (phosphate rock particle size ≤ 2mm). The crushed raw ore is then subjected to graded magnetic separation to obtain magnetic separation products and magnetic separation tailings. Subsequently, the magnetic separation products are graded by a hydrocyclone to obtain fine-grained (-0.074mm) and coarse-grained minerals (+0.074mm). The fine-grained minerals are discharged. S2. Grind the coarse-grained minerals and magnetic separation tailings into the tower mill until the proportion of -0.074mm particles is ≥80%, and dilute with water until the phosphate rock slurry mass concentration reaches 30%±2%. S3. The pH of the phosphate rock slurry obtained in S2 is adjusted to 9-10 with sodium carbonate and injected into the top feed inlet of the microbubble packing flotation column. Sodium silicate 1.0 kg / t and fatty acid soap 0.8 kg / t are added. At the same time, high-pressure gas is introduced from the bottom of the column. The gas is cut by the multi-layer corrugated packing to form uniform microbubbles. The phosphate rock adheres to the microbubbles and is scraped off from the top of the column to obtain positive flotation phosphate rock slurry. The suppressed carbonate and siliceous vein ore are discharged from the bottom of the column. S4. Add the phosphate rock slurry obtained from the direct flotation to the thickener for concentration and de-reagenting until the phosphate rock slurry concentration reaches 17%-20%. The overflow water after de-reagenting is recycled into the S3 direct flotation. S5. Add phosphoric acid to the phosphate rock slurry obtained in S4 to adjust the pH value to 5-6. Inject the pH-adjusted phosphate rock slurry into the top feed port of the reverse flotation microbubble flotation column I. Then add 0.8 kg / t of sodium oleate. At the same time, high-pressure gas is introduced from the bottom of the column. The gas is cut by multiple layers of corrugated packing to form uniform microbubbles. Carbonate minerals are attached to the microbubbles and scraped out from the top of the column. The reverse flotation phosphate rock slurry is discharged from the bottom. S6. The reverse flotation phosphate slurry obtained in S5 is injected into the top feed inlet of the reverse flotation microbubble flotation column II. Then, 0.5 kg / t of dodecylamine and 0.2 kg / t of calcium chloride are added. At the same time, high-pressure gas is introduced from the bottom of the column. The gas is cut by multiple layers of corrugated packing to form uniform microbubbles. Silicate minerals are attached to the microbubbles and scraped out from the top of the column. The phosphate concentrate is discharged from the bottom.

[0029] In step S1, the graded magnetic separation is a two-stage magnetic separation. The first stage uses a weak magnetic field of 1000 Gs to separate strong magnetic minerals, and the second stage uses a strong magnetic field of 12000 Gs to separate weak magnetic minerals.

[0030] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that in step S6, calcium chloride, the activator, is not added, and only dodecylamine is used as the reverse flotation collector II. The remaining steps are the same as in Example 1.

[0031] A continuous forward and reverse flotation method for medium- and low-grade phosphate rock includes the following steps: S1. Medium- and low-grade phosphate rock (P2O5 15.24%, CaO 35.44%, MgO 7.85%, Fe2O3 3.97%, Al2O3 2.55%, SiO2 25.12%) is crushed in two stages using a jaw crusher and a cone crusher (phosphate rock particle size ≤ 2mm). The crushed raw ore is then subjected to graded magnetic separation to obtain magnetic separation products and magnetic separation tailings. Subsequently, the magnetic separation products are graded by a hydrocyclone to obtain fine-grained (-0.074mm) and coarse-grained minerals (+0.074mm). The fine-grained minerals are discharged. S2. Grind the coarse-grained minerals and magnetic separation tailings into the tower mill until the proportion of -0.074mm particles is ≥80%, and dilute with water until the phosphate rock slurry mass concentration reaches 30%±2%. S3. The phosphate rock slurry obtained in S2 is adjusted to pH 9-10 with sodium carbonate and injected into the top feed inlet of the microbubble packed flotation column. Corn starch, sodium silicate and fatty acid soap are added. The composition of corn starch and sodium silicate is 1.0 kg / t (the mass ratio of corn starch to sodium silicate is 1:3), and fatty acid soap is 0.8 kg / t. At the same time, high-pressure gas is introduced from the bottom of the column. It is cut by the multi-layer corrugated packing to form uniform microbubbles. The phosphate rock adheres to the microbubbles and is scraped out from the top of the column to obtain positive flotation phosphate rock slurry. The suppressed carbonate and siliceous veins are discharged from the bottom of the column. S4. Add the phosphate rock slurry obtained from the direct flotation to the thickener for concentration and de-reagenting until the phosphate rock slurry concentration reaches 18%. The overflow water after de-reagenting is recycled into the S3 direct flotation. S5. Add phosphoric acid to the phosphate rock slurry obtained in S4 to adjust the pH value to 5-6. Inject the pH-adjusted phosphate rock slurry into the top feed port of the reverse flotation microbubble flotation column I. Then add 0.8 kg / t of sodium oleate. At the same time, high-pressure gas is introduced from the bottom of the column. The gas is cut by multiple layers of corrugated packing to form uniform microbubbles. Carbonate minerals are attached to the microbubbles and scraped out from the top of the column. The reverse flotation phosphate rock slurry is discharged from the bottom. S6. The reverse flotation phosphate slurry obtained in S5 is injected into the top feed inlet of the reverse flotation microbubble flotation column II. Then, 0.5 kg / t of dodecylamine is added, and high-pressure gas is introduced from the bottom of the column. The gas is cut by multiple layers of corrugated packing to form uniform microbubbles. Silicate minerals are attached to the microbubbles and scraped out from the top of the column, while the phosphate concentrate is discharged from the bottom.

[0032] In step S1, the graded magnetic separation is a two-stage magnetic separation. The first stage uses a weak magnetic field of 1000 Gs to separate strong magnetic minerals, and the second stage uses a strong magnetic field of 12000 Gs to separate weak magnetic minerals.

[0033] Test Result Analysis: Flotation was performed on samples of Fangmashan phosphate rock from Zhongxiang City, Jingmen City, Hubei Province, using Examples 1-3 and Comparative Examples 1-3. The elemental content of the phosphate rock samples was analyzed (w(P2O5) = 17.28%, w(MgO) = 6.22%, w(SiO2) = 27.85%, w(Fe2O3) = 3.54%). After flotation, the contents of P2O5, MgO, SiO2, and Fe2O3 in the phosphate concentrate were determined. The test results are shown in Table 1 below.

[0034] Table 1

[0035] As shown in Table 1, compared with the absence of graded magnetic separation in the pretreatment stage (Comparative Example 1), the continuous flotation method for medium and low grade phosphate rock of the present invention improves the grade of phosphate rock and reduces the iron content; compared with the use of a single depressant in the forward flotation stage (Comparative Example 2), the grade of phosphate rock improves and the magnesium content decreases; compared with the absence of the activator calcium chloride in the reverse flotation II stage (Comparative Example 3), the grade of phosphate rock improves and the silicon content decreases.

[0036] Although the present invention has been described in detail by way of preferred embodiments, the present invention is not limited thereto. Various equivalent modifications or substitutions can be made to the embodiments of the present invention by those skilled in the art without departing from the spirit and essence of the invention, and such modifications or substitutions should all be within the scope of the present invention. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should also be covered within the protection scope of the present invention.

Claims

1. A continuous direct reverse flotation process of a medium-low grade phosphate rock, characterized in that, Includes the following steps: S1. The medium- and low-grade phosphate ore is crushed in two stages using a jaw crusher and a cone crusher. The crushed ore is then subjected to magnetic separation to obtain magnetic separation products and tailings. The magnetic separation products are then classified by a hydrocyclone to obtain fine-grained minerals with a particle size of less than 0.074 mm and coarse-grained minerals with a particle size of more than 0.074 mm. The fine-grained minerals are then discharged. S2. Grind the coarse-grained minerals obtained in step S1 with the magnetic separation tailings into a tower mill until the proportion of particles smaller than 0.074mm is ≥80% to obtain phosphate rock powder; dilute the phosphate rock powder with water to make slurry to obtain phosphate rock slurry. S3. Adjust the pH of the phosphate rock slurry obtained in step S2 to 9-10 with sodium carbonate, inject it into the top feed inlet of the microbubble packing flotation column, add inhibitors and positive flotation collectors, and at the same time introduce high-pressure gas from the bottom of the column. The gas is cut by multiple layers of corrugated packing to form uniform microbubbles. The phosphate rock adheres to the microbubbles and is scraped out from the top of the column to obtain positive flotation phosphate rock slurry. The inhibited carbonates and siliceous veins are discharged from the bottom of the column. S4. Add the positive flotation phosphate rock slurry obtained in step S3 to a thickener for concentration and de-reagenting until the phosphate rock slurry concentration reaches 17%-20%. The overflow water after de-reagenting is recycled into the S3 positive flotation process. S5. Add phosphoric acid to the phosphate rock slurry obtained in step S4 to adjust the pH value to 5-6. Inject the pH-adjusted phosphate rock slurry into the top feed port of the reverse flotation microbubble flotation column I. Then add reverse flotation collector I. At the same time, high-pressure gas is introduced from the bottom of the column. The gas is cut by multiple layers of corrugated packing to form uniform microbubbles. Carbonate minerals are attached to the microbubbles and scraped out from the top of the column. The reverse flotation phosphate rock slurry is discharged from the bottom. S6. The reverse flotation phosphate slurry obtained in step S5 is injected into the top feed inlet of the reverse flotation microbubble flotation column II. Then, reverse flotation collector II and activator are added. High-pressure gas is introduced from the bottom of the column. The gas is cut by multiple layers of corrugated packing to form uniform microbubbles. Silicate minerals are attached to the microbubbles and scraped out from the top of the column. Phosphate concentrate is discharged from the bottom.

2. The flotation method as described in claim 1, characterized in that, In medium- and low-grade phosphate rock, w(P2O5) < 20%.

3. The flotation method as described in claim 2, characterized in that, The particle size of the medium- and low-grade phosphate rock after two-stage crushing in step S1 is ≤2mm.

4. The flotation method as described in claim 1, characterized in that, In step S1, the graded magnetic separation is a two-stage magnetic separation. The first stage uses a weak magnetic field of 900-1500 Gs to separate strong magnetic minerals, and the second stage uses a strong magnetic field of 12000 Gs to separate weak magnetic minerals.

5. The flotation method as described in claim 1, characterized in that, The mass concentration of the phosphate rock slurry obtained in step S2 is 30% ± 2%.

6. The flotation method as described in claim 1, characterized in that, In step S3, the inhibitor is a combination of corn starch and sodium silicate or a combination of sodium carboxymethyl cellulose and sodium silicate. The amount of inhibitor used in step S3 is 1.0-2.0 kg / t relative to the amount of medium- and low-grade phosphate rock used in step S1.

7. The flotation method as described in claim 1, characterized in that, In step S3, the positive flotation collector is one of fatty acid soap, oxidized paraffin soap, or tar oil. The amount of positive flotation collector used in step S3 relative to the amount of medium- and low-grade phosphate rock used in step S1 is 0.8-1.5 kg / t.

8. The flotation method as described in claim 1, characterized in that, In step S5, the reverse flotation collector I is sodium oleate, and the amount of reverse flotation collector I used in step S5 relative to the low-grade phosphate rock in step S1 is 0.3-1.5 kg / t.

9. The flotation method as described in claim 1, characterized in that, In step S6, the reverse flotation collector II is either dodecylamine or benzyl dimethyl tetradecyl ammonium chloride, and the amount of reverse flotation collector II used in step S6 relative to the low-grade phosphate rock in step S1 is 0.4-0.8 kg / t.

10. The flotation method as described in claim 1, characterized in that, The activator in step S6 is calcium chloride, and the amount of calcium chloride used in step S6 relative to the amount of medium- and low-grade phosphate rock in step S1 is 0.1-0.4 kg / t.

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