A method for the resource recovery and full-component utilization of Bayer process red mud

Abstract

This invention discloses a method for the resource recovery and full utilization of Bayer process red mud. First, the red mud undergoes a hydrogen-based mineral phase conversion, causing thermal cracking. Then, iron is recovered from the red mud through magnetic separation. The magnetic separation tailings are leached with phosphoric acid to extract valuable metals, effectively improving the recovery of valuable metals from the red mud while minimizing equipment corrosion. The leaching tailings, due to the decomposition and removal of alkaline components and the formation of phosphates during the leaching process, can be used as a raw material for the production of slow-release mineral fertilizers. The method described in this invention enables the full recovery of valuable metals such as iron, aluminum, and gallium from Bayer process red mud, and allows the leaching residue to be fully utilized in the production of mineral fertilizers. Therefore, this invention, focusing on the resource recovery and full utilization of Bayer process red mud, is of great significance for improving resource security and the treatment of large-scale solid waste, and has promising application prospects.

Description

Technical Field

[0001] This invention discloses a method for the resource recovery and full-component utilization of Bayer process red mud, which belongs to the fields of hydrometallurgical technology and comprehensive solid waste treatment and recycling. Background Technology

[0002] Red mud, a solid waste generated during the Bayer process for alumina production, produces 1-1.5 tons of red mud for every ton of alumina produced. Due to its production process, red mud is highly alkaline and corrosive. Therefore, it is a large-scale solid waste posing a significant environmental hazard. During alumina production, valuable metals leached into the red mud become a potential secondary resource. The main metallic element in red mud is iron, often found as hematite. Recovery of iron-bearing minerals includes direct magnetic separation and magnetized roasting. Direct magnetic separation suffers from poor separation performance because the red mud has a fine particle size and the main iron-bearing minerals are weakly magnetic. During the magnetic separation process, magnetic inclusions occur in the strong magnetic field, leading to poor separation results. Other valuable metal components in red mud can also be extracted using hydrometallurgical and pyrometallurgical methods. However, hydrometallurgical processes often use strong acids that severely corrode equipment and react with silica to form polysilicic acid, which adsorbs the leached valuable metal ions, thus reducing the leaching rate. Pyrometallurgy suffers from high energy consumption. The recycling and utilization of red mud also includes the preparation of building materials and filler materials, and due to its large specific surface area, strong adsorption capacity, and porous structure, it can be used to prepare adsorbent materials for the treatment of waste gas and wastewater, and the remediation of contaminated soil. As a major alumina producer, my country currently has a very large stockpile of red mud. Therefore, developing a method for the complete utilization of all components of red mud through the Bayer process is of great significance for environmental protection and improving resource utilization efficiency. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the background art and to provide a method for the resource recovery and full-component utilization of Bayer process red mud, which aims to improve or solve the problems or key issues of red mud pollution and recycling.

[0004] To solve the above technical problems, the specific technical solution of the present invention is as follows:

[0005] Step 1: Feed the red mud into the hydrogen-based mineral phase conversion system for directional mineral phase conversion to obtain the material after mineral phase conversion;

[0006] Step 2: The material after mineral phase transformation is fed into a magnetic separator through stirring and slurry preparation for magnetic separation to recover iron-containing minerals from the red mud;

[0007] Step 3: The tailings obtained from magnetic separation are directly pumped into the leaching system for phosphoric acid leaching. After leaching, the leaching solution and leaching residue are separated by a pressure filter. The leaching residue is washed with water to enrich the valuable components extracted into the leaching solution.

[0008] Step 4: Mix the leached residue after washing with microbial inoculants and binders, and then air dry it to obtain phosphorus-rich mineral slow-release fertilizer.

[0009] In step 1, the mineral phase conversion temperature of the hydrogen-based mineral phase conversion system is 500-650℃, the conversion time is 10-30min, the reaction gases in the gas phase are hydrogen and carbon monoxide, the hydrogen content is ≥55%, and the gas flow rate is 600-1000mL / min.

[0010] In step 2, the magnetic separation equipment selected is a wet drum type weak magnetic separator with a magnetic field strength of 1500-3000Gs;

[0011] In step 3, the main component of the leaching system is the leaching tank, which is mainly connected by pipelines. Phosphoric acid is selected as the leaching agent, and the leaching time is 5-12 hours to obtain two products: leaching solution and leaching residue.

[0012] In step 4, the main raw material used in the phosphorus-rich mineral slow-release fertilizer preparation system is the leaching residue obtained after multiple washings to remove leached valuable metals. It is mixed with microbial agents and binders to prepare phosphorus-rich mineral slow-release fertilizer.

[0013] In step 4, the microbial agent is one or more combinations of Bacillus subtilis and yeast.

[0014] In step 4, the binder used in the preparation method of phosphorus-rich mineral slow-release fertilizer is one or more of cassava starch, corn starch and sweet potato starch.

[0015] In step 4, the mass ratio of leaching residue to cementing agent in the preparation of phosphorus-rich mineral slow-release fertilizer is 7:3-9:1; the mass ratio of cementing agent to microbial inoculant is 6:1-20:1.

[0016] The beneficial effects of this invention are:

[0017] In this invention, by employing hydrogen-based mineral phase conversion, the iron-bearing mineral phase in the material can be transformed from hematite / limonite to magnetite, which helps to fully recover and utilize the high iron content in red mud. At the same time, the iron content in the tailings obtained after magnetic separation is significantly reduced, which can also effectively reduce the impact of ion types and contents on the enrichment and recovery of valuable metals in the leachate. Phosphoric acid, as a mild acid, can avoid the formation of polysilicic acid with silica in the material, thereby avoiding secondary adsorption of valuable metal ions. Furthermore, phosphoric acid as a leaching agent has less corrosive effect on equipment. The phosphorus-rich leaching residue obtained by phosphoric acid leaching is a high-quality raw material for preparing mineral slow-release fertilizers, and can realize the resource recovery and harmless treatment of all components in red mud. Attached Figure Description

[0018] Figure 1 This is a diagram showing the equipment connections for the present invention. 1- Hydrogen-based mineral phase conversion system, 2- Weak magnetic separator, 3- Mechanically stirred leaching tank, 4- Filter press, 5- Mineral slow-release fertilizer preparation system. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0020] Example 1

[0021] like Figure 1 As shown, red mud was fed into a hydrogen-based mineral phase transformation system 1. The red mud had a TFe grade of 30.26%, an FeO content of 0.13%, an Al2O3 content of 13.57%, a TiO2 content of 2.14%, and a SiO2 content of 5.98%. The mineral phase transformation of the red mud was carried out at a mineral phase transformation temperature of 500℃, a transformation time of 10 min, with hydrogen and carbon monoxide as the reaction gases in the gas phase, a hydrogen content ≥55%, and a gas flow rate of 600 mL / min. The transformed red mud sample was then fed into a weak magnetic separator 2 for magnetic separation under a magnetic field strength of 1500 Gs. Iron concentrate and magnetic separation tailings were obtained separately. The magnetic separation tailings were pumped to a mechanically stirred leaching tank 3 for leaching. Leaching was carried out for 5 hours under the conditions of 10 mol / L phosphoric acid concentration, 100℃ leaching temperature, 400 rpm / min stirring speed, and a liquid-to-solid ratio of 7:3. The leached slurry was pumped to a plate and box filter press 4, and after multiple water washing, the leachate (rich in valuable metal ions) was collected and extracted. The leaching residue was fed into a mineral slow-release fertilizer preparation system 5, and stirred to produce fertilizer at a mass ratio of leaching residue: binder: microbial agent = 14:6:1. After natural air drying, it became a phosphorus-rich mineral slow-release fertilizer. This scheme can achieve the following indicators:

[0022] Table 1. Multi-element chemical analysis of different products

[0023] Element <![CDATA[Al2O3]]> TFe <![CDATA[SiO2]]> <![CDATA[TiO2]]> <![CDATA[Na2O]]> CaO <![CDATA[Ga2O3]]> raw ore 13.57％ 30.48％ 5.98％ 2.14％ 6.08％ 1.43％ 0.0141％ Iron concentrate 1.38％ 65.36％ 4.78％ 3.89％ 0.30％ 0.28％ 0.0045％ Leaching residue 4.34％ 2.69％ 53.29％ 8.96％ 2.92％ 0.98％ 0.0080％

[0024] Table 2. Multi-element chemical analysis of leachate

[0025] element Fe Al Si Ti Ca Na Ga leachate 3.68％ 11.7％ 0.039％ 1.41％ 1.04％ 3.45％ 0.092％

[0026] Table 3 Elemental Analysis of Mineral Slow-Release Fertilizers

[0027] element P Fe Cu Pb Hg K <![CDATA[SiO2]]> Slow-release fertilizer 6.78％ trace amounts trace amounts ＜0.0001％ ＜0.0001％ 4.32％ 55.75％

[0028] Example 2

[0029] like Figure 1 As shown, red mud was fed into a hydrogen-based mineral phase transformation system 1. The red mud had a TFe grade of 30.26%, an FeO content of 0.13%, an Al2O3 content of 13.57%, a TiO2 content of 2.14%, and a SiO2 content of 5.98%. The mineral phase transformation of the red mud was carried out at a mineral phase transformation temperature of 600℃, a transformation time of 18 min, with hydrogen and carbon monoxide as the reaction gases in the gas phase, a hydrogen content ≥55%, and a gas flow rate of 800 mL / min. The transformed red mud sample was then fed into a weak magnetic separator 2 for magnetic separation under a magnetic field strength of 2000 Gs. Iron concentrate and magnetic separation tailings were obtained separately. The magnetic separation tailings were pumped to a mechanically stirred leaching tank 3 for leaching. Leaching was carried out for 8 hours under the conditions of 10 mol / L phosphoric acid concentration, 100℃ leaching temperature, 400 rpm / min stirring speed, and a liquid-to-solid ratio of 8:2. The leached slurry was pumped to a plate and box filter press 4, and after multiple water washing, the leachate (rich in valuable metal ions) was collected and extracted. The leaching residue was fed into a mineral slow-release fertilizer preparation system 5, and stirred to produce fertilizer at a mass ratio of leaching residue: binder: microbial agent = 48:12:1. After natural air drying, it became a phosphorus-rich mineral slow-release fertilizer. This scheme can achieve the following indicators:

[0030] Table 4. Multi-element chemical analysis of different products

[0031] Element <![CDATA[Al2O3]]> TFe <![CDATA[SiO2]]> <![CDATA[TiO2]]> <![CDATA[Na2O]]> CaO <![CDATA[Ga2O3]]> raw ore 18.27％ 28.34％ 10.23％ 2.14％ 3.38％ 1.98％ 0.0091％ Iron concentrate 3.69％ 65.91％ 2.61％ 3.40％ 0.37％ 0.26％ 0.0035％ Leaching residue 6.96％ 4.83％ 56.10％ 7.04％ 2.96％ 0.66％ 0.0018％

[0032] Table 5. Multi-element chemical analysis of leachate

[0033] element Fe Al Si Ti Ca Na Ga leachate 2.62％ 12.8％ 0.021％ 1.39％ 1.39％ 3.51％ 0.099％

[0034] Table 6. Elemental Analysis of Mineral Slow-Release Fertilizers

[0035] element P Fe Cu Pb Hg K <![CDATA[SiO2]]> Slow-release fertilizer 7.69％ trace amounts trace amounts ＜0.0001％ ＜0.0001％ 2.12％ 59.73％

[0036] Example 3

[0037] like Figure 1As shown, red mud was fed into a hydrogen-based mineral phase transformation system 1. The red mud had a TFe grade of 38.01%, an FeO content of 0.24%, an Al2O3 content of 23.59%, a TiO2 content of 6.16%, and a SiO2 content of 7.52%. The mineral phase transformation of the red mud was carried out at a mineral phase transformation temperature of 650℃, a transformation time of 30 min, with hydrogen and carbon monoxide as the reaction gases in the gas phase, a hydrogen content ≥55%, and a gas flow rate of 1000 mL / min. The transformed red mud sample was then fed into a weak magnetic separator 2 for magnetic separation under a magnetic field strength of 3000 Gs. Iron concentrate and magnetic separation tailings were obtained separately. The magnetic separation tailings were pumped to a mechanically stirred leaching tank 3 for leaching. Leaching was carried out for 12 hours under the conditions of 10 mol / L phosphoric acid concentration, 100℃ leaching temperature, 400 rpm / min stirring speed, and a liquid-to-solid ratio of 9:1. The leached slurry was pumped to a plate and box filter press 4, and after multiple water washing, the leachate (rich in valuable metal ions) was collected and extracted. The leaching residue was fed into a mineral slow-release fertilizer preparation system 5, and stirred to produce fertilizer at a mass ratio of leaching residue: binder: microbial agent = 180:20:1. After natural air drying, it became a phosphorus-rich mineral slow-release fertilizer. This scheme can achieve the following indicators:

[0038] Table 7. Multi-element chemical analysis of different products

[0039] Element <![CDATA[Al2O3]]> TFe <![CDATA[SiO2]]> <![CDATA[TiO2]]> <![CDATA[Na2O]]> CaO <![CDATA[Ga2O3]]> raw ore 23.59％ 38.01％ 7.52％ 6.16％ 4.58％ 1.89％ 0.0167％ Iron concentrate 2.52％ 66.78％ 3.15％ 2.54％ 0.25％ 0.17％ 0.0032％ Leaching residue 7.37％ 1.86％ 54.29％ 9.74％ 3.88％ 0.79％ 0.0092％

[0040] Table 8. Multi-element chemical analysis of leachate

[0041] element Fe Al Si Ti Ca Na Ga leachate 1.10％ 19.34％ 0.047％ 5.26％ 1.35％ 4.95％ 0.101％

[0042] Table 9 Elemental Analysis of Mineral Slow-Release Fertilizers

[0043] element P Fe Cu Pb Hg K <![CDATA[SiO2]]> Slow-release fertilizer 7.67％ trace amounts trace amounts ＜0.0001％ ＜0.0001％ 5.42％ 53.67％

[0044] The above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A method for the resource recovery and full-component utilization of Bayer process red mud, characterized in that, Includes the following steps: Step 1: Feed the red mud into the hydrogen-based mineral phase conversion system for directional mineral phase conversion to obtain the material after mineral phase conversion; Step 2: The material after mineral phase transformation is fed into a magnetic separator through stirring and slurry preparation for magnetic separation to recover iron-containing minerals from the red mud; Step 3: The tailings obtained from magnetic separation are directly pumped into the leaching system for phosphoric acid leaching, and then separated into leaching solution and leaching residue by a pressure filter. The leaching residue is washed with water to enrich the valuable components extracted into the leachate; Step 4: Mix the leaching residue after washing with microbial inoculants and binders, stir, and air dry naturally to obtain phosphorus-rich mineral slow-release fertilizer; The mineral phase transformation temperature is 600-650 ℃, the transformation time is 10-30 min, the reaction gases in the gas phase are hydrogen and carbon monoxide, the hydrogen content is ≥55%, and the gas flow rate is 600-1000 mL / min; The microbial inoculant is one or more of Bacillus subtilis and yeast; The binder is one or more of tapioca starch, corn starch, and sweet potato starch; The mass ratio of leaching residue to cementing agent is 7:3-9:1; the mass ratio of cementing agent to microbial inoculant is 6:1-20:

1.

2. The method for resource recovery and full-component utilization of Bayer process red mud according to claim 1, characterized in that, The magnetic separation equipment is a wet drum-type weak magnetic separator; the magnetic field strength of the weak magnetic separator is 2000-3000Gs.

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