A method for comprehensively treating high-iron and low-silica red mud by alkali magnetization roasting

Abstract

A method for comprehensively treating high-iron and low-silica red mud by alkali magnetization roasting belongs to the field of metallurgical technology and includes the following steps: Step (1): Mix high-iron and low-silica red mud, liquid alkali, and solid reducing agent and granulate to obtain green pellets; Step (2): Dry the green pellets through kiln tail gas to remove adsorbed water and part of the crystal water to obtain dried pellets; Step (3): Under the atmosphere of inert protective gas, adopt the dry roasting method to carry out reduction roasting to obtain calcined pellets; Step (4): Wet grind and leach the calcined pellets with dilute alkali solution, etc. By supplementing liquid alkali and solid reducing agents such as coal or sawdust organic matter to high-iron and low-silica red mud and roasting, the present invention realizes the directional regulation of the red mud mineral phase, recovers iron and aluminum resources in the form of magnetite and sodium aluminate, and significantly reduces the dosage of the reducing agent and the reaction temperature.

Description

Technical Field

[0001] The present invention belongs to the field of metallurgical technology, and particularly relates to a method for comprehensively treating high-iron and low-silica red mud by alkali magnetization roasting. Background Art

[0002] High-iron and low-silica red mud is a strongly alkaline industrial waste generated from extracting alumina using bauxite of the gibbsite type as raw material. Since its Fe2O3 content is relatively high, generally between 10% - 50%, it appears red. Also, because it contains 15% - 25% of Al2O3, it is regarded as a potential iron-aluminum symbiotic resource. Currently, the global stockpile of red mud has exceeded 4 billion tons and continues to grow at a rate of 180 million tons per year. As of 2023, the annual output of red mud in China has exceeded 100 million tons, and the stockpile of red mud has exceeded 1 billion tons, causing huge environmental safety hazards and resource waste. Efficiently recovering iron and aluminum resources from high-iron and low-silica red mud and achieving effective reduction has always been a pain point problem faced by the alumina and even the entire metallurgical industry. Reduction smelting and reduction sintering usually introduce reducing agents and calcium carbonate or sodium carbonate additives to achieve the reduction and aggregation of iron and the co-generation of calcium aluminate or sodium aluminate, and then recover aluminum resources through atmospheric leaching. However, these methods all require adding calcium to the remaining components in the red mud, thus significantly increasing the slag volume. Additionally, the reduction temperature is usually higher than 1200°C, which makes the above methods have low treatment efficiency, high energy consumption, large slag volume, and poor economy. Excessive use of reducing agents and additives also causes disadvantages such as large carbon dioxide emissions, complex mixing, high cost, and poor homogeneity of raw materials.

[0003] Chinese Patent Application CN112442565A proposed making carbon-containing pellets by mixing red mud with a carbon-based reducing agent, and mixing it with calcium oxide and placing it in a rotary kiln and a submerged arc furnace, so as to achieve the gradient reduction of iron oxides in high-iron red mud and recover them in the form of metallic iron particles. The molten slag is calcium aluminate slag that is easy to leach and recover alumina. The sodium aluminate solution obtained from the leaching product is further processed to obtain alumina products. Although this method solves the problem of difficult separation of iron and aluminum isomorphs and realizes the co-recovery of valuable elements, the reduction temperature is too high, the energy consumption is too high, and the slag volume of the leaching product of calcium aluminate slag is large.

[0004] Chinese Patent Applications CN113604663A, CN107083467A, and CN112609074A proposed adding reducing agents, sodium-based, calcium-based, or magnesium-based additives to red mud, and converting iron oxide and alumina in the red mud into metallic iron and soluble sodium aluminate respectively through roasting. Subsequently, valuable metals are recovered through weak magnetic separation and leaching. These methods target sodium aluminate as the product, effectively reducing the reaction temperature required, but the energy consumption for generating metallic iron, calcium silicate, and magnesium silicate is relatively high, and the slag volume discharged is still large. Summary of the Invention

[0005] In view of the above disadvantages and deficiencies of the prior art, the present invention provides a method for comprehensively treating high-iron and low-silica red mud by alkali magnetization roasting. By adding liquid alkali and solid reducing agents such as coal or sawdust organic matter to the high-iron and low-silica red mud and roasting, the directional regulation of the red mud mineral phase is realized, and iron and aluminum resources are recovered in the form of magnetite and sodium aluminate, significantly reducing the dosage of the reducing agent and the reaction temperature.

[0006] To achieve the above object, the main technical solutions adopted by the present invention include:

[0007] A method for comprehensively treating high-iron and low-silica red mud by alkali magnetization roasting, comprising the following steps:

[0008] Step (1): Mix the high-iron and low-silica red mud, liquid alkali, and solid reducing agent raw materials and granulate them to obtain raw material pellets. The addition amount of liquid alkali is in accordance with the molar ratio of Na2O / Al2O3 = 1.0 - 2.5, and the addition amount of solid reducing agent is in accordance with the molar ratio of C / O = 0.1 - 0.5, where O is the molar content of oxygen atoms in Fe2O3 in the red mud.

[0009] Step (2): Dry the raw material pellets through kiln tail gas to remove adsorbed water and part of the crystal water to obtain dried pellets; removing adsorbed water and part of the crystal water by drying can reduce the heat required for reduction roasting. The dried pellets have relatively high compressive strength (the strength of a single pellet is greater than 50 N), which can effectively avoid the phenomenon of fragmentation and pulverization during transportation and roasting.

[0010] Step (3): Under the atmosphere of inert protective gas, adopt the dry roasting method to carry out reduction roasting on the dried pellets, and the roasting temperature is 500 - 800 °C; after roasting is completed, continue to cool down to 300 °C and below under the atmosphere of inert protective gas to prevent the magnetite in the reduction product from being oxidized to hematite, and obtain clinker pellets. The main chemical reaction formulas in this stage are as follows:

[0011] ;

[0012] ;

[0013] ;

[0014] ;

[0015] .

[0016] Step (4): Wet grind and leach the clinker pellets with dilute alkali solution, and control the liquid-solid ratio to be 5 - 10.

[0017] Step (5): Carry out liquid-solid separation on the leached slurry, and the obtained liquid phase is sodium aluminate solution, and the solid phase is aluminum extraction residue.

[0018] Step (6): The sodium aluminate solution is transported to the alumina production system through pipelines to recover the batching liquid caustic soda and alumina.

[0019] Step (7): Ultrasonic pretreatment is used to separate magnetite and gangue components in the aluminum-extracted slag, thereby improving the monomer dissociation degree of iron minerals and promoting the magnetic separation enrichment of iron concentrate.

[0020] Step (8): The aluminum-extracted slag is subjected to low-intensity wet magnetic separation with the magnetic field intensity set at 1000 - 3000 Oe. The strongly magnetic magnetite is enriched and separated from non-magnetic minerals to obtain iron concentrate and iron-separation tailings.

[0021] Furthermore, in the said step (1), the amount of particles with a particle size less than 0.074 mm (i.e., 200 mesh) in the high-iron low-silica red mud accounts for more than 85% of the total mass.

[0022] Furthermore, in the said step (1), the high-iron low-silica red mud is a by-product discharged from the extraction of alumina from diaspore-type bauxite. By mass percentage, it contains 40 - 60% Fe₂O₃, 10 - 25% Al₂O₃, 3 - 6% SiO₂, 4 - 8% TiO₂, 1 - 3% CaO, and 1 - 3% Na₂O.

[0023] Furthermore, in the said step (1), the solid reducing agent is pulverized coal and wood chip organic matter solid reducing agent. By mass percentage, the pulverized coal contains 55 - 75% fixed carbon, 25 - 35% volatile matter, 6 - 8% moisture, and 3 - 6% ash; the wood chip organic matter contains 15 - 25% fixed carbon, 65 - 80% volatile matter, 2 - 4% moisture, and 1 - 3% ash.

[0024] Furthermore, in the said step (1), the liquid caustic soda is a high-concentration caustic solution, containing 540 - 600 g / L NaOH (calculated as Na₂O), 12 - 20 g / L Na₂CO₃ (calculated as Na₂O), and 5 - 10 g / L Al₂O₃ by mass concentration.

[0025] Furthermore, in the said step (1), a mixer is used for raw material mixing, and the mixing time is 2 - 3 h.

[0026] Furthermore, in the said step (1), granulation is carried out by a disk granulator, and the obtained raw material pellets have a particle size of 1 - 5 cm and a moisture content of 15 - 25%.

[0027] Furthermore, in the said step (2), a dryer is used for preheating and drying the raw material pellets. The drying temperature is 200 - 400 °C, the drying time is 12 - 36 h, and the heat source is the tail gas generated from the dry roasting in step (3).

[0028] Furthermore, in the said step (3), the inert protective gas is nitrogen or argon.

[0029] Further, in the step (3), the roasting time is 0.5 - 3.0 h.

[0030] Further, in the step (3), the dry roasting is carried out by a grate-kiln, a tunnel kiln or a rotary kiln.

[0031] Further, in the step (3), the main components of the roasted clinker are iron tetroxide, sodium aluminate, silicon dioxide, titanium dioxide and calcium titanate.

[0032] Further, in the step (4), the dilute alkali solution is 10 - 20 g / L of NaOH and 3 - 10 g / L of Na2CO3.

[0033] Further, in the step (4), the wet grinding and leaching is carried out by a lattice type abrasive crusher with a grading liner, filled with steel ball grinding media inside, and the rotation speed is 15 - 30 r / min.

[0034] Further, in the step (4), the leaching reaction temperature is 70 - 85 °C and the leaching reaction time is 5 - 30 min.

[0035] Further, in the step (4), the leaching rates of alumina and sodium oxide in the clinker pellets are respectively higher than 88% and 95%.

[0036] Further, in the step (5), the liquid-solid separation is carried out by a settling tank, a filter press or a plate and frame filter press.

[0037] Further, in the step (7), the ultrasonic treatment is carried out by a tank type ultrasonic instrument, the ultrasonic power is 100 - 300 W, and the ultrasonic time is 1 - 5 min.

[0038] Further, in the step (8), the grade and iron recovery rate of the magnetic separation iron concentrate are respectively higher than 55% and 90%.

[0039] The beneficial effects of the present invention are as follows:

[0040] (1) The present invention adopts the alkali-magnetic roasting method with iron tetroxide as the target iron ore phase, effectively solving the problems of high energy consumption and high carbon emissions caused by the traditional reduction sintering method for recovering iron resources from red mud, which is beneficial to improving the roasting performance of the clinker and further improving the recovery efficiency of valuable elements.

[0041] (2) In the magnetic roasting process of the present invention, the alumina is simultaneously sodiumized and leached in the form of sodium aluminate, solving the drawback that the traditional magnetic roasting cannot recover the alumina in the red mud and realizing the efficient collaborative recovery of iron and aluminum resources from high-iron and low-silica red mud.

[0042] (3) Since the roasting temperature of the present invention is relatively low, the silica in the quartz phase of the red mud does not participate in the reaction, and there is no need to proportion it. Compared with the traditional lime sintering method or the alkali-lime sintering method for extracting alumina from red mud, the slag volume is extremely small, and the reduction rate of red mud is higher than 90%.

[0043] (4) The batching and roasting processes of the method of the present invention are simple, and the efficiency of treating unit volume of red mud is higher.

[0044] (5) The present invention adopts pellet dry roasting, which can effectively solve problems such as poor roasting uniformity caused by wet spraying into the kiln. By recycling the kiln tail gas twice, the energy consumption is significantly reduced by more than 30%.

[0045] (6) The iron-extracted tailings obtained by magnetic separation of the present invention are roasted and activated, and have certain cementitious activity, and can be used as raw materials in the preparation of low-carbon building materials, thereby realizing the full utilization of high-iron and low-silica red mud. Description of the Drawings

[0046] Figure 1 It is a schematic flow chart of the method for comprehensively treating high-iron and low-silica red mud by alkali magnetization roasting of the present invention. Specific Embodiments

[0047] In order to better explain the present invention for easy understanding, the present invention will be described in detail below in conjunction with the drawings through specific embodiments.

[0048] The present invention provides a method for comprehensively treating high-iron and low-silica red mud by alkali magnetization roasting, as Figure 1 shown, including the following steps:

[0049] Step (1): Granulate the high-iron and low-silica red mud, liquid caustic soda, and solid reducing agent to obtain raw material pellets. The addition amount of liquid caustic soda is in accordance with the molar ratio Na2O / Al2O3 = 1.0 - 2.5, and the addition amount of solid reducing agent is in accordance with the molar ratio C / O = 0.1 - 0.5, where O is the molar content of oxygen atoms in Fe2O3 in the red mud. The solid reducing agent is a pulverized coal or wood chip organic solid reducing agent. The liquid caustic soda is a high-concentration caustic solution, containing 540 - 600 g / L of NaOH by mass concentration, calculated as Na2O; 12 - 20 g / L of Na2CO3, calculated as Na2O; and 5 - 10 g / L of Al2O3.

[0050] Step (2): Dry the raw material pellets with the kiln tail gas to remove the adsorbed water and part of the crystal water to obtain dried pellets.

[0051] Step (3): Under the atmosphere of inert protective gas, adopt the dry roasting method to carry out reduction roasting on the dried pellets. The roasting temperature is 500 - 800 °C, and the roasting time is 0.5 - 3.0 h. After roasting is completed, continue to cool down to below 300 °C under the atmosphere of inert protective gas to obtain clinker pellets.

[0052] Step (4): Wet-grind and leach the clinker pellets with the dilute alkali solution, controlling the liquid-solid ratio to be 5 - 10; the dilute alkali solution is 10 - 20 g / L of NaOH and 3 - 10 g / L of Na2CO3.

[0053] Step (5): Perform liquid-solid separation on the leached slurry to obtain the sodium aluminate solution as the liquid phase and the aluminum-extracted residue as the solid phase.

[0054] Step (6): Transport the sodium aluminate solution to the alumina production system through a pipeline to recover the batching liquid alkali and alumina.

[0055] Step (7): Use ultrasonic pretreatment to separate the magnetite and gangue components in the aluminum-extracted residue, with the ultrasonic power being 100 - 300 W and the ultrasonic time being 1 - 5 min.

[0056] Step (8): Perform low-intensity wet magnetic separation on the aluminum-extracted residue, set the magnetic field intensity to 1000 - 3000 Oe, and obtain iron concentrate and iron-separation tailings.

[0057] In the embodiment of the present invention, the caustic soda concentration (N K ) is the mass-volume concentration of NaOH (calculated as Na2O), and the carbonate soda concentration (N C ) is the mass-volume concentration of Na2CO3 (calculated as Na2O), and the liquid-solid ratio (L / S) is the ratio of the volume of the leaching alkali solution to the mass of the clinker.

[0058] In the embodiment of the present invention, a mixer is used for raw material mixing, a briquetting press is used for pelletizing, and a dryer is used for preheating and drying.

[0059] In the embodiment of the present invention, a rotary kiln with a protective gas is used for dry roasting, and it is cooled to below 300 °C in a protective atmosphere cooling tank.

[0060] In the embodiment of the present invention, a lattice-type abrasive crusher is used for wet-grind leaching, and a sedimentation tank, a filter press or a plate-and-frame filter press is used for liquid-solid separation.

[0061] Example 1

[0062] The main chemical components of the high-iron and low-silica red mud (by mass percentage): Fe2O3 55.66%, Al2O3 17.90%, SiO2 4.80%, CaO 2.40%, TiO2 5.38%, Na2O 1.89%, and the aluminum-silicon ratio is 3.7.

[0063] The main chemical components of the pulverized coal (by mass percentage): fixed carbon 60.40%, volatile matter 27.04%, moisture 6.72%, ash 5.84%.

[0064] Main chemical components of wood chips (by mass percentage): fixed carbon 19.28%, volatile matter 72.80%, moisture 3.43%, ash 4.49%.

[0065] Main chemical components of liquid caustic soda (by mass percentage): N K 570 g / L, N C 15.26 g / L, C AO 8.69 g / L.

[0066] Add pulverized coal and liquid caustic soda solution according to the molar ratios C / O = 0.2 and Na2O / Al2O3 = 2.0. The moisture content of the raw material pellets is 16.5%.

[0067] Preheat and dry the raw material pellets and heat them to 700 o °C for dry roasting. The roasting time is 0.5 h, and then cool to 300 o °C in a protective atmosphere.

[0068] Main chemical components of the leached dilute caustic soda solution (by mass concentration): N K 15 g / L, N c 5 g / L.

[0069] Wet grinding and leaching ensure full mixing and reaction of the clinker and caustic liquor. Control the leaching temperature at 85 o °C, leaching time at 15 min, and liquid-solid ratio at 10.

[0070] The magnetic field intensity used for low-intensity wet magnetic separation is 2200 Oe.

[0071] The ultrasonic treatment power is 150 W and the ultrasonic time is 2 min.

[0072] The recovery rate of Al2O3 in the roasted clinker is 90.17%, and the recovery rate of Na2O is 96.17%; the grade of iron concentrate is 57.21%, and the iron recovery rate is 90.72%.

[0073] Example 2

[0074] The method is the same as that in Example 1, the differences are as follows:

[0075] (1) Add wood chips and liquid caustic soda solution according to the molar ratios C / O = 0.2 and Na2O / Al2O3 = 1.6. The moisture content of the raw material pellets is 14.5%;

[0076] (2) Preheat and dry the raw material pellets and heat them to 700 o °C for dry roasting. The roasting time is 1 h, and then cool to 300 o °C;

[0077] (3) The recovery rate of Al2O3 in the calcined clinker is 88.48%, and the recovery rate of Na2O is 94.82%; the grade of iron concentrate is 56.42%, and the recovery rate of iron is 90.24%.

[0078] Example 3

[0079] The method is the same as that of Example 1, and the differences are as follows:

[0080] (1) Sawdust and liquid caustic soda solution are added according to the molar ratios of C / O = 0.2 and Na2O / Al2O3 = 1.6, and the moisture content of the raw material pellets is 14.3%;

[0081] (2) The preheated and dried raw material pellets are heated to 800 o °C for dry calcination, and the calcination time is 1 h, and then cooled to 250 o °C in a protective atmosphere;

[0082] (3) The recovery rate of Al2O3 in the calcined clinker is 88.07%, and the recovery rate of Na2O is 95.25%; the grade of iron concentrate is 55.98%, and the recovery rate of iron is 90.58%.

[0083] Example 4

[0084] The method is the same as that of Example 1, and the differences are as follows:

[0085] (1) The main chemical components of the high-iron and low-silica red mud (by mass percentage): Fe2O3 57.52%, Al2O3 16.01%, SiO2 3.88%, CaO 2.16%, TiO2 6.02%, Na2O 1.55%, and the aluminum-silica ratio is 4.1;

[0086] (2) The main chemical components of the liquid caustic soda (by mass percentage): N K 558.17 g / L, N C 17.21 g / L, C AO 7.45 g / L;

[0087] (3) Coal powder and liquid caustic soda solution are added according to the molar ratios of C / O = 0.22 and Na2O / Al2O3 = 1.95, and the moisture content of the raw material pellets is 15.8%;

[0088] (4) The raw material pellets are heated to 750 o °C for dry calcination, and the calcination time is 0.5 h, and then cooled to 200 o °C in a protective atmosphere;

[0089] (5) The recovery rate of Al2O3 in the calcined clinker is 89.90%, and the recovery rate of Na2O is 96.47%; the grade of iron concentrate is 56.21%, and the recovery rate of iron is 90.95%.

[0090] Example 5

[0091] The method is the same as that in Example 1, except that:

[0092] (1) The main chemical components of high-iron and low-silica red mud (by mass percentage): Fe2O3 53.96%, Al2O3 16.16%, SiO2 7.07%, CaO 1.06%, TiO2 6.12%, Na2O 3.38%, and the aluminum-silica ratio is 2.3;

[0093] (2) The main chemical components of liquid caustic soda (by mass percentage): N K 558.17 g / L, N C 17.21 g / L, C AO 7.45 g / L;

[0094] (3) Sawdust and liquid caustic soda solution are added according to the molar ratios of C / O = 0.2 and Na2O / Al2O3 = 2.2, and the moisture content of the green pellet is 16.6%;

[0095] (4) The green pellet is heated to 750 o °C for dry roasting, the roasting time is 0.5 h, and then it is cooled to 300 o °C in a protective atmosphere;

[0096] (5) The recovery rate of Al2O3 in the roasted clinker is 90.21%, and the recovery rate of Na2O is 96.69%; the grade of iron concentrate is 56.34%, and the iron recovery rate is 91.35%.

[0097] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any modifications, alterations, substitutions, and variations made by those of ordinary skill in the art to the above embodiments fall within the scope of the present invention.

Claims

1. A method for comprehensively treating high-iron and low-silica red mud by alkali magnetization roasting, characterized in that, It includes the following steps: Step (1): Granulate the high-iron low-silica red mud, liquid caustic soda, and solid reducing agent to obtain green pellet balls. The addition amount of liquid caustic soda is based on the molar ratio of Na2O / Al2O3 = 1.0 - 2.5, and the addition amount of solid reducing agent is based on the molar ratio of C / O = 0.1 - 0.5, where O is the molar content of oxygen atoms in Fe2O3 in the red mud; Step (2): Dry the green pellet balls with kiln tail gas to remove adsorbed water and part of the crystal water to obtain dried pellet balls; Step (3): Under the atmosphere of inert protective gas, use the dry roasting method for reduction roasting. The roasting temperature is 500 - 800 °C; after roasting is completed, continue to cool down to 300 °C and below under the atmosphere of inert protective gas to obtain clinker pellet balls; Step (4): Wet grind and leach the clinker pellet balls with dilute caustic soda solution, and control the liquid-solid ratio to be 5 - 10; Step (5): Perform liquid-solid separation on the leached slurry. The obtained liquid phase is sodium aluminate solution, and the solid phase is aluminum-extracted slag; Step (6): Transport the sodium aluminate solution to the alumina production system through pipelines to recover the batching liquid caustic soda and alumina; Step (7): Use ultrasonic pretreatment to separate the magnetite and gangue components in the aluminum-extracted slag; Step (8): Perform low-intensity wet magnetic separation on the aluminum-extracted slag, and set the magnetic field intensity to 1000 - 3000 Oe to obtain iron concentrate and iron-separation tailings; 2. The method for comprehensively treating high-iron and low-silica red mud by alkali magnetization roasting according to claim 1, wherein: In the said step (1), the amount of particles with a particle size less than 0.074 mm in the high-iron low-silica red mud accounts for more than 85% of the total mass.

3. The method for comprehensively treating high-iron and low-silica red mud by alkali magnetization roasting according to claim 1, characterized in that: In the said step (1), the solid reducing agent is pulverized coal or wood chip organic matter solid reducing agent.

4. A method for comprehensively treating high-iron and low-silica red mud by alkali magnetization roasting according to claim 1, characterized in that: In the said step (1), the liquid caustic soda is a high-concentration caustic solution, containing 540 - 600 g / L of NaOH by mass concentration, calculated as Na2O; 12 - 20 g / L of Na2CO3, calculated as Na2O; and 5 - 10 g / L of Al2O3.

5. A method for comprehensively treating high-iron and low-silica red mud by alkali magnetization roasting according to claim 1, characterized in that: In the said step (1), granulation is carried out by a disc granulator, and the obtained green pellet balls have a particle size of 1 - 5 cm.

6. The method for comprehensively treating high-iron and low-silica red mud by alkali magnetization roasting according to claim 1, characterized in that: In the said step (3), the inert protective gas is nitrogen or argon.

7. A method for comprehensively treating high-iron and low-silica red mud by alkali magnetization roasting according to claim 1, characterized in that: In the said step (3), the roasting time is 0.5 - 3.0 h.

8. A method for comprehensively treating high-iron and low-silica red mud by alkali magnetization roasting according to claim 1, characterized in that: In the said step (4), the dilute caustic soda solution is 10 - 20 g / L of NaOH and 3 - 10 g / L of Na2CO3.

9. A method for comprehensively treating high-iron and low-silica red mud by alkali magnetization roasting according to claim 1, characterized in that: In the said step (4), wet grinding and leaching are carried out using a lattice-type abrasive crusher with a grading lining plate, filled with steel ball grinding media inside, and the rotation speed is 15 - 30 r / min.

10. A method for comprehensively treating high-iron and low-silica red mud by alkali magnetization roasting according to claim 1, characterized in that: In the said step (7), the ultrasonic power is 100 - 300 W, and the ultrasonic time is 1 - 5 min.

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