A method for extracting magnesium and phosphorus from high-magnesium phosphorus tailings by vacuum carbothermic reduction

Abstract

This invention discloses a method for extracting magnesium and phosphorus from high-magnesium phosphorus tailings through vacuum carbothermic reduction, relating to the field of high-magnesium phosphorus tailings reuse technology. The method involves uniformly mixing phosphorus tailings, silica, magnesite, and coke, pressing them into briquettes, calcining them to remove crystal water, and coking them to obtain pellets. The phosphorus tailings are high-magnesium phosphorus tailings with an MgO content of 16%–18%. The pellets are placed in a vacuum furnace, maintaining a vacuum of 10–100 Pa, and heated to 1200–1500°C, held for 30–60 minutes. The steam from the reaction is recovered, and the steam is condensed at 400–600°C to obtain crude magnesium. The partially cooled steam is then passed into a cold water tank to recover the precipitate, which is then filtered to obtain yellow phosphorus. This method effectively reuses high-magnesium phosphorus tailings and further recovers the difficult-to-refine phosphorus, allowing phosphorus and magnesium to be extracted and recovered in the same equipment and process. Simultaneously, it fully utilizes the calcium and fluorine as additives, lowering the reaction temperature and significantly reducing production costs.

Description

Technical Field

[0001] This invention relates to the field of high magnesium phosphorus tailings recycling technology, and in particular to a method for extracting magnesium phosphorus from high magnesium phosphorus tailings by vacuum carbothermal reduction. Background Technology

[0002] Currently, the most commonly used methods for smelting and producing metallic magnesium are electrolysis and thermal reduction. The silicothermic reduction method uses ferrosilicon to thermally reduce magnesium oxide produced from calcined dolomite ore. The reaction is completed under high temperature and high vacuum, but the use of ferrosilicon results in high costs. Carbon (C) is also used as a reducing agent, with the reduction reaction carried out at 1850℃ under normal pressure. Under these conditions, the reduction reaction is reversible, and the reaction products, magnesium and CO, are both gaseous and separated after condensation. To improve the reduction rate of carbothermic reduction, the paper "Process for Preparing Metallic Magnesium by Vacuum Carbothermic Reduction of Calcined White Metal" (Tian Yang et al.) discloses the use of calcined white metal, coking coal, and calcium fluoride to produce metallic magnesium. First, coking coal and magnesium oxide are ground finely. Then, 5% of the total mass of coking coal and magnesium oxide is weighed and mixed with calcium fluoride, pressed into lumps. In a vacuum furnace at 30-100 Pa, a reduction temperature above 1623 K, a reduction time exceeding 4 hours, and a carbon ratio of 1.6, the reduction rate of magnesium oxide significantly increases. Among them, the calcination and decomposition of dolomite consumes a lot of energy and has a high raw material cost.

[0003] Phosphate tailings are solid waste discarded after phosphate rock flotation, and are currently mostly disposed of through stockpiling. High-magnesium phosphate tailings contain approximately 16% MgO and also contain difficult-to-refine phosphorus, with a P2O5 content of 6%-10%. Recycling and reusing these tailings could significantly improve their utilization rate. On the other hand, phosphate tailings contain harmful elements such as fluorine and heavy metals. Over long-term stockpiling, these harmful elements can enter the soil with rainwater, causing environmental pollution.

[0004] If high-magnesium phosphorus tailings can be used for the smelting of metallic magnesium, and the difficult-to-process phosphorus can be recovered, the production cost can be greatly reduced. At the same time, consuming phosphorus tailings reduces their processing cost, and the magnesium and phosphorus produced can also generate significant economic benefits. Summary of the Invention

[0005] The purpose of this invention is to provide a method for extracting magnesium and phosphorus from high-magnesium-phosphorus tailings by vacuum carbothermal reduction, thereby solving the problems of low utilization rate of high-magnesium-phosphorus tailings and high cost of magnesium smelting raw materials.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a method for extracting magnesium and phosphorus from high-magnesium-phosphorus tailings by vacuum carbothermal reduction, characterized by comprising the following steps:

[0007] S1. Mix phosphorus tailings, silica, magnesite, and coke evenly, press them into lumps, calcine them, remove the water of crystallization, and coke them to obtain pellets; the phosphorus tailings are high-magnesium phosphorus tailings, in which the MgO content is 16% to 18%.

[0008] S2. Place the pellets into a vacuum furnace, maintain the vacuum level in the furnace at 10-100 Pa, raise the temperature to 1200-1500℃, hold for 30-60 min, recover the steam in the reaction, and obtain crude magnesium by passing the steam through a condenser at 400-600℃. The initially cooled steam is passed into a cold water tank to recover the precipitate in the cold water tank, and obtain yellow phosphorus after filtration.

[0009] A further technical solution is that the mass ratio of the phosphorus tailings to magnesite is 1.5 to 4:1, and the MgO content in the magnesite is ≥40%.

[0010] A further technical solution is that the SiO2 content in the silica is ≥90%, and the mass ratio of SiO2 to CaO in the pellet material is 0.75 to 0.85.

[0011] A further technical solution is that the carbon content in the coke is ≥80%, and the amount of carbon used is 1.1 to 1.5 times the theoretical amount.

[0012] A further technical solution is that in step S1, silica, magnesite, and coke are initially crushed and passed through a 60-80 mesh sieve.

[0013] A further technical solution is to press the mixture into blocks under a pressure of 15MPa after mixing in step S1, heat it to 600-700℃, and hold it for 20-60 minutes to obtain pellet material.

[0014] Reaction mechanism: MgO + C = Mg↑ + CO↑

[0015] 10C + 2P₂O₅ = P₄↑ + 10CO↑

[0016] Using coke as a reducing agent, a small amount of magnesite is mixed with high-magnesium phosphorus tailings to make the Mg content in the furnace feed about 20%. Under suitable vacuum conditions, magnesium and phosphorus are simultaneously reduced by carbon and recovered in gaseous state. Then, they are cooled at different temperatures to obtain crude magnesium and yellow phosphorus.

[0017] Compared with the prior art, the beneficial effects of the present invention are:

[0018] 1. Using a vacuum furnace can lower the reduction temperature of phosphorus and magnesium, increase the release rate of magnesium and phosphorus in the system, shorten the reaction time, and thus reduce energy consumption.

[0019] 2. Effectively reuse high-magnesium phosphorus tailings and further recover the difficult-to-process phosphorus, so that phosphorus and magnesium are extracted and recovered in the same equipment and process. At the same time, make full use of calcium and fluorine as additives to reduce the reaction temperature and greatly reduce production costs. Attached Figure Description

[0020] Figure 1This is a process flow diagram of the present invention.

[0021] Figure 2 The image shows the XRD pattern of crude magnesium in Example 1. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0023] Example 1

[0024] Chemical composition of high magnesium phosphate tailings:

[0025] Components <![CDATA[P2O5]]> <![CDATA[SiO2]]> CaO MgO <![CDATA[Fe2O3]]> <![CDATA[Al2O3]]> <![CDATA[K2O]]> Loss on ignition content% 6.30 4.39 30.08 16.60 0.76 0.59 0.08 36.22

[0026] The MgO content in magnesite is 42.28%, the SiO2 content in silica is 91.2%, and the fixed carbon content in coke is 85.66%. After crushing, the magnesite, silica, and coke are passed through a 60-mesh sieve, and the material passing through the sieve is collected.

[0027] Take 15.000g of phosphorus tailings, 7.118g of magnesite, 2.745g of silica, and 2.612g of coke. Mix the raw materials evenly, press them into blocks under 15MPa pressure, and then calcine them. Raise the temperature to 600℃ and hold for 50min to remove the crystal water and coke the material to obtain pellets.

[0028] The dried pellets were loaded into a vacuum furnace with a vacuum degree of 90 Pa. The furnace was kept at a vacuum degree and the temperature was raised to 1200℃ for 60 minutes before heating was stopped.

[0029] The reduced steam is collected and condensed in a condenser at 400-600℃ to obtain crude magnesium. The steam after preliminary heat exchange is continuously fed into a cold water tank to collect precipitates for yellow phosphorus enrichment.

[0030] After the furnace body cooled down, the vacuum furnace was opened, and the condensed metallic magnesium was removed from the condenser. X-ray analysis was performed, and the resulting spectrum is shown below. Figure 2 As shown, it was identified as metallic magnesium. Calculations showed that the escape rates of yellow phosphorus and magnesium were 83.49% and 77.26%, respectively.

[0031] Example 2

[0032] Chemical composition of high magnesium phosphate tailings:

[0033] Components <![CDATA[P2O5]]> <![CDATA[SiO2]]> CaO MgO Loss on ignition content% 9.35 11.59 28.90 18.07 22.24

[0034] The MgO content in magnesite is 46.44%, the SiO2 content in silica is 91.2%, and the fixed carbon content in coke is 85.66%. Magnesite, silica, and coke are crushed and passed through an 80-mesh sieve, and the material passing through the sieve is collected.

[0035] Take 15.000g of phosphorus tailings, 4.158g of magnesite, 1.425g of silica, and 2.549g of coke. Mix the raw materials evenly, press them into blocks under 15MPa pressure, and then calcine them. Raise the temperature to 700℃ and hold for 20 minutes to remove the water of crystallization and coke the material to obtain pellets.

[0036] The dried pellets were loaded into a vacuum furnace, with a vacuum level of 75-85 Pa. Maintaining the vacuum, the temperature was raised to 1500℃ and reacted for 30 minutes, after which heating was stopped. The reduced steam was collected and condensed in a condenser at 400-600℃ to obtain crude magnesium. The steam after initial heat exchange was continuously passed into a cold water tank, and the precipitate was collected for yellow phosphorus enrichment. Calculations showed that the escape rates of yellow phosphorus and magnesium were 90.55% and 82.75%, respectively.

[0037] Example 3

[0038] Chemical composition of high magnesium phosphate tailings:

[0039] Components <![CDATA[P2O5]]> <![CDATA[SiO2]]> CaO MgO Loss on ignition content% 7.79 3.85 31.29 18.64 35.09

[0040] The MgO content in magnesite is 44.73%, the SiO2 content in silica is 91.2%, and the fixed carbon content in coke is 85.66%. Magnesite, silica, and coke are crushed and passed through an 80-mesh sieve, and the material passing through the sieve is collected.

[0041] Take 15.000g of phosphate tailings, 3.907g of magnesite, 2.969g of coke, and 2.384g of coke. Mix the raw materials evenly, press them into blocks under 15MPa pressure, and then calcine them. Raise the temperature to 650℃ and hold for 40 minutes to remove the water of crystallization and coke the material. Obtain pellets.

[0042] The dried pellets were loaded into a vacuum furnace, with a vacuum level of 25-55 Pa. Maintaining this vacuum, the temperature was raised to 1400℃ and reacted for 40 minutes, after which heating was stopped. The reduced steam was collected and condensed in a condenser at 400-600℃ to obtain crude magnesium. The steam after initial heat exchange was continuously passed into a cold water tank, and the precipitate was collected, dried, and then used for yellow phosphorus enrichment. The calculated escape rates of yellow phosphorus and magnesium were 89.64% and 80.33%, respectively.

[0043] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for extracting magnesium and phosphorus from high-magnesium-phosphorus tailings by vacuum carbothermal reduction, characterized in that... The process includes the following steps: S1. Mixing phosphorus tailings, silica, magnesite, and coke evenly, pressing them into lumps, and calcining them to remove crystal water and coke, resulting in pellets; the phosphorus tailings are high-magnesium phosphorus tailings, with an MgO content of 16%–18%; S2. Placing the pellets into a vacuum furnace, maintaining a vacuum of 10–100 Pa, heating to 1200–1500℃, holding for 30–60 min, recovering the steam from the reaction, and passing the steam through a condenser at 400–600℃ to obtain crude magnesium. The initially cooled steam is passed into a cold water tank to recover the precipitate in the cold water tank, and after filtration, yellow phosphorus is obtained. The mass ratio of phosphorus tailings to magnesite is 1.5 to 4:1, and the MgO content in the magnesite is ≥40%. The silica contains ≥90% SiO2, and the mass ratio of SiO2 to CaO in the pellets is 0.75 to 0.

85. The coke contains ≥80% carbon, and the amount of carbon used is 1.1 to 1.5 times the theoretical amount. In step S1, silica, magnesite, and coke are initially crushed and passed through a 60-80 mesh sieve. After mixing in step S1, the mixture is pressed into blocks under a pressure of 15 MPa, heated to 600-700°C, and held for 20-60 minutes to obtain pellet material.

Images