Method for comprehensively treating high-iron low-silicon red mud through alkali magnetization roasting

Abstract

A method for comprehensive treatment of high-iron and low-silicon red mud through alkali magnetization roasting belongs to the technical field of metallurgy and comprises the following steps: (1) mixing the high-iron and low-silicon red mud, liquid caustic soda and a solid reducing agent, and granulating to obtain raw material pellets; (2) the raw material pellets are dried through kiln tail gas to remove adsorbed water and part of crystal water, and dried pellets are obtained; (3) the dried pellets are subjected to reduction roasting in an inert protective gas atmosphere in a dry roasting mode, and clinker pellets are obtained; and (4) the clinker pellets and a dilute alkali solution are subjected to wet grinding leaching and the like. According to the method, the high-iron and low-silicon red mud is supplemented with liquid caustic soda and solid reducing agents such as coal or sawdust organic matter and roasted, directional regulation and control of a red mud mineral phase are achieved, iron and aluminum resources are recycled in the form of magnetite and sodium aluminate, and the using amount of the reducing agents and the reaction temperature are remarkably reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy, and in particular relates to a method for comprehensively treating high-iron and low-silicon red mud by alkali magnetization roasting. Background Art

[0002] High iron and low silicon red mud is a strong alkaline industrial waste produced by extracting alumina from gibbsite bauxite. 2 O 3 The content is relatively high, generally between 10%-50%, so it is red. Because it contains 15%-25% Al 2 O 3 , and is also regarded as a potential symbiotic resource of iron and aluminum. At present, 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, my country's annual red mud production has exceeded 100 million tons, and the stockpile of red mud has exceeded 1 billion tons, causing huge environmental safety hazards and resource waste. Efficient recovery of iron and aluminum resources from high-iron and low-silicon red mud and effective reduction have always been the pain points faced by alumina and the entire metallurgical industry. Reduction smelting and reduction sintering usually introduce reducing agents and calcium carbonate or sodium carbonate additives to achieve iron reduction aggregation and synergistic generation of calcium aluminate or sodium aluminate, and then recover aluminum resources by atmospheric leaching. However, these methods require calcium distribution to the remaining components in the red mud, thereby significantly increasing the slag volume. In addition, the reduction temperature is usually higher than 1200°C, which makes the above methods low in efficiency, high in energy consumption, large in slag volume, and poor in economy. Excessive use of reducing agents and additives also results in large carbon dioxide emissions, complex and high cost mixing, and poor uniformity of raw materials.

[0003] Chinese patent application CN112442565A proposes mixing red mud with a carbon-based reducing agent to form carbon-containing pellets, which are mixed with calcium oxide and placed in a rotary kiln and an ore-fired furnace, thereby achieving gradient reduction of iron oxides in high-iron red mud and recovering them in the form of metallic iron particles. The slag is calcium aluminate slag that is easy to leach and recover alumina, and the leached product sodium aluminate solution is subsequently treated to obtain an alumina product. Although this method solves the problem of the difficulty in separating the isomorphous iron and aluminum and realizes the coordinated recovery of valuable elements, the reduction temperature is too high, the energy consumption is too high, and the amount of slag produced by the calcium aluminate slag leaching product is large.

[0004] Chinese patent applications CN113604663A, CN107083467A and CN112609074A proposed adding reducing agents, sodium and calcium or magnesium additives to red mud, converting iron oxide and aluminum oxide in red mud into metallic iron and soluble sodium aluminate respectively by roasting, and then recovering valuable metals by weak magnetic separation and leaching. These methods use sodium aluminate as the target product and effectively reduce the temperature required for the reaction, but the energy consumption required to generate metallic iron, calcium silicate and magnesium silicate is high, and the amount of slag discharged is still large. Summary of the invention

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

[0006] In order to achieve the above object, the main technical solutions adopted by the present invention include: A method for comprehensively treating high-iron and low-silicon red mud by alkali magnetization roasting comprises the following steps: Step (1), mixing high iron and low silicon red mud, liquid caustic soda, and solid reducing agent raw material and granulating them to obtain raw material pellets, the amount of liquid caustic soda added is according to the molar ratio of Na 2 O / Al 2 O 3 =1.0-2.5, the amount of solid reducing agent added is based on the molar ratio C / O=0.1-0.5, where O is Fe in red mud 2 O 3 The molar content of oxygen atoms.

[0007] Step (2), drying the raw material pellets through kiln exhaust gas to remove adsorbed water and part of the crystallized water, and obtaining dried pellets; drying to remove adsorbed water and part of the crystallized water can reduce the heat required for reduction roasting. The dried pellets have a relatively high compressive strength (the strength of the single pellet is greater than 50N), which can effectively avoid the phenomenon of fragmentation and pulverization during transportation and roasting.

[0008] Step (3), dry roasting the dried pellets in an inert protective gas atmosphere, reduction roasting, the roasting temperature is 500-800°C; after roasting, continue to cool down to 300°C or below in an inert protective gas atmosphere to prevent the magnetite in the reduction product from being oxidized to hematite, and obtain clinker pellets. The main chemical reaction formula of this stage is as follows: ; ; ; ; .

[0009] Step (4), wet grinding and leaching the clinker pellets with a dilute alkali solution, and controlling the liquid-to-solid ratio to be 5-10.

[0010] Step (5), separating the leached slurry into liquid and solid, and obtaining a liquid phase of sodium aluminate solution and a solid phase of aluminum extraction slag.

[0011] Step (6), the sodium aluminate solution is transported to the alumina production system through a pipeline to recover the batching liquid alkali and alumina.

[0012] Step (7), using ultrasonic pretreatment to separate the magnetite and gangue components in the aluminum extraction slag, thereby improving the monomer dissociation degree of iron minerals and promoting magnetic separation enrichment of iron concentrate.

[0013] Step (8), subjecting the aluminum extraction slag to low-intensity wet magnetic separation, with the magnetic field strength set to 1000-3000 Oe, so that the strongly magnetic magnetite is enriched and separated from the non-magnetic minerals, thereby obtaining iron concentrate and iron ore tailings.

[0014] Furthermore, in step (1), the amount of particles with a particle size of less than 0.074 mm, i.e., 200 mesh, in the high-iron and low-silicon red mud accounts for more than 85% of the total mass.

[0015] Furthermore, in step (1), the high-iron and low-silicon red mud is a byproduct discharged from the extraction of alumina from gibbsite-type bauxite, and contains Fe 2 O 3 40-60%, Al 2 O 3 10-25%, SiO 2 3-6%, TiO 2 4-8%, CaO 1-3%, Na 2 O 1-3%.

[0016] Furthermore, in step (1), the solid reducing agent is coal powder or sawdust organic solid reducing agent. In terms of mass percentage, the coal powder contains 55-75% fixed carbon, 25-35% volatile matter, 6-8% moisture, and 3-6% ash; the sawdust organic matter contains 15-25% fixed carbon, 65-80% volatile matter, 2-4% moisture, and 1-3% ash.

[0017] Furthermore, in step (1), the liquid caustic soda is a high concentration caustic soda solution, which contains 540-600 g / L of NaOH and 100 g / L of NaOH. 2 O meter; Na 2 CO 3 12-20g / L, Na 2 O meter; Al 2 O 3 5-10g / L.

[0018] Furthermore, in the step (1), the raw materials are mixed using a mixer for a mixing time of 2-3 hours.

[0019] Furthermore, in the step (1), the granulation is performed by a disc granulator, and the obtained raw material pellets have a particle size of 1-5 cm and a moisture content of 15-25%.

[0020] Furthermore, in step (2), the raw material pellets are preheated and dried using a dryer, the drying temperature is 200-400° C., the drying time is 12-36 hours, and the heat source is the tail gas generated by the dry roasting in step (3).

[0021] Furthermore, in step (3), the inert protective gas is nitrogen or argon.

[0022] Furthermore, in the step (3), the calcination time is 0.5-3.0h.

[0023] Furthermore, in the step (3), the dry roasting is carried out using a chain grate, a tunnel kiln or a rotary kiln.

[0024] Furthermore, in step (3), the main components of the roasted clinker are ferroferric oxide, sodium aluminate, silicon dioxide, titanium dioxide and calcium titanate.

[0025] Furthermore, in step (4), the dilute alkaline solution is 10-20 g / L NaOH, 2 CO 3 3-10g / L.

[0026] Furthermore, in step (4), the wet grinding and leaching adopts a grid-type abrasive crusher with a graded liner, which is filled with steel ball grinding media and has a rotation speed of 15-30 r / min.

[0027] Furthermore, in the step (4), the leaching reaction temperature is 70-85°C and the leaching reaction time is 5-30 min.

[0028] Furthermore, in step (4), the leaching rates of alumina and sodium oxide from the clinker pellets are higher than 88% and 95%, respectively.

[0029] Furthermore, in step (5), liquid-solid separation is performed using a sedimentation tank, a filter or a filter press.

[0030] Furthermore, in step (7), the ultrasonic treatment is performed using a tank ultrasonicator with an ultrasonic power of 100-300 W and an ultrasonic time of 1-5 min.

[0031] Furthermore, in step (8), the grade and iron recovery rate of the magnetically separated iron concentrate are higher than 55% and 90%, respectively.

[0032] The beneficial effects of the present invention are: (1) The present invention adopts an alkali-magnetic roasting method with ferroferric oxide as the target iron ore phase, which effectively solves the problems of high energy consumption and high carbon emissions caused by the traditional reduction sintering method for recovering iron resources in red mud, and is beneficial to improving the clinker roasting performance and thus improving the recovery efficiency of valuable elements.

[0033] (2) The present invention simultaneously converts aluminum into sodium during the magnetizing roasting process and leaches it in the form of sodium aluminate, thereby solving the problem that the conventional magnetizing roasting cannot recover aluminum oxide in red mud and realizing the efficient and coordinated recovery of iron and aluminum resources in high-iron and low-silicon red mud.

[0034] (3) Since the roasting temperature of the present invention is relatively low, the quartz phase silicon dioxide in the red mud does not participate in the reaction and does not need to be added. Compared with the traditional lime sintering method or the soda lime sintering method for extracting alumina from red mud, the amount of slag is extremely small, and the reduction rate of red mud is higher than 90%.

[0035] (4) The batching and roasting process of the method of the present invention are simple, and the efficiency of treating unit volume of red mud is higher.

[0036] (5) The present invention adopts the dry roasting method of pellets, which can effectively solve the problems such as poor roasting uniformity caused by wet spraying into the kiln, and the energy consumption is significantly reduced by more than 30% through the secondary utilization of the kiln exhaust gas.

[0037] (6) The iron-extracting tailings obtained by magnetic separation of the present invention are activated by roasting and have a certain gelling activity, and can be used as a raw material for the preparation of low-carbon building materials, thereby realizing the full quantitative utilization of high-iron and low-silicon red mud. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 The present invention is a schematic flow chart of the method for comprehensive treatment of high-iron and low-silicon red mud by alkali magnetization roasting. DETAILED DESCRIPTION

[0039] In order to better explain the present invention and facilitate understanding, the present invention is described in detail below through specific implementation modes in conjunction with the accompanying drawings.

[0040] The present invention provides a method for comprehensively treating high-iron and low-silicon red mud by alkali magnetization roasting. Figure 1 As shown, the following steps are included: Step (1), mixing high iron and low silicon red mud, liquid caustic soda and solid reducing agent and granulating to obtain raw material pellets, the amount of liquid caustic soda added is according to the molar ratio of Na 2 O / Al 2 O 3 =1.0-2.5, the amount of solid reducing agent added is based on the molar ratio C / O=0.1-0.5, where O is Fe in red mud 2 O 3 The molar content of oxygen atoms. The solid reducing agent is coal powder or sawdust organic solid reducing agent. The liquid caustic soda is a high concentration caustic soda solution, containing 540-600g / L NaOH and 100g / L NaOH. 2 O meter; Na 2 CO 3 12-20g / L, Na 2 O meter; Al2 O 3 5-10g / L.

[0041] Step (2), drying the raw material pellets with kiln exhaust gas to remove adsorbed water and part of crystallized water, thereby obtaining dried pellets.

[0042] Step (3), dry calcining the dried pellets in an inert protective gas atmosphere, reduction calcining, the calcining temperature is 500-800°C, and the calcining time is 0.5-3.0h. After the calcining is completed, continue to cool down to below 300°C in an inert protective gas atmosphere to obtain clinker pellets.

[0043] Step (4), wet grinding and leaching the clinker pellets with a dilute alkali solution, controlling the liquid-to-solid ratio to be 5-10; the dilute alkali solution is 10-20 g / L NaOH, 2 CO 3 3-10g / L.

[0044] Step (5), separating the leached slurry into liquid and solid, and obtaining a liquid phase of sodium aluminate solution and a solid phase of aluminum extraction slag.

[0045] Step (6), the sodium aluminate solution is transported to the alumina production system through a pipeline to recover the batching liquid alkali and alumina.

[0046] Step (7), using ultrasonic pretreatment to separate the magnetite and gangue components in the aluminum slag, the ultrasonic power is 100-300W, and the ultrasonic time is 1-5min.

[0047] Step (8), subjecting the aluminum extraction slag to low-intensity wet magnetic separation, with the magnetic field strength set to 1000-3000 Oe, to obtain iron concentrate and iron ore tailings.

[0048] In the embodiment of the present invention, the concentration of caustic soda (N K ) is NaOH (Na 2 O) mass volume concentration, carbon alkali concentration (N C ) for Na 2 CO 3 (With Na 2 The liquid-to-solid ratio (L / S) is the ratio of the volume of leached alkali solution to the mass of clinker.

[0049] In the embodiment of the present invention, a mixer is used for mixing raw materials, a ball press is used for making balls, and a dryer is used for preheating and drying.

[0050] In the embodiment of the present invention, the dry roasting adopts a rotary kiln with protective gas, and is placed in a protective atmosphere cooling tank to cool to below 300°C.

[0051] In the embodiment of the present invention, a lattice-type abrasive mill is used for wet grinding and leaching, and a sedimentation tank, a filter or a filter press is used for liquid-solid separation.

[0052] Example 1 The main chemical components of high iron and low silicon red mud (by mass percentage): Fe 2 O 3 55.66%, Al 2 O 3 17.90%, SiO 2 4.80%, CaO 2.40%, TiO 2 5.38%, Na 2 O 1.89%, aluminum silicon ratio is 3.7.

[0053] The main chemical components of coal powder (by mass percentage) are: fixed carbon 60.40%, volatile matter 27.04%, moisture 6.72%, and ash 5.84%.

[0054] The main chemical components of sawdust (by mass percentage) are: fixed carbon 19.28%, volatile matter 72.80%, moisture 3.43%, and ash 4.49%.

[0055] The main chemical components of liquid caustic soda (by mass percentage): N K 570g / L, N C 15.26g / L, C AO 8.69g / L.

[0056] According to the molar ratio of C / O=0.2, Na 2 O / Al 2 O 3 =2.0, adding coal powder and liquid alkali solution, the moisture content of raw meal pellets is 16.5%.

[0057] Preheat the dried raw material pellets to 700 o C for 0.5 h, and then cooled to 300 °C in a protective atmosphere. o C.

[0058] The main chemical components of the leached dilute alkaline solution (by mass concentration): N K 15g / L, N c 5g / L.

[0059] Wet grinding leaching ensures that the clinker and alkali solution are fully mixed and reacted, and the leaching temperature is controlled at 85 o C. The leaching time is 15 minutes and the liquid-to-solid ratio is 10.

[0060] The magnetic field strength used for low-intensity wet magnetic separation is 2200Oe.

[0061] The ultrasonic treatment power was 150 W and the ultrasonic time was 2 min.

[0062] Al in roasted clinker 2 O 3 The recovery rate of Na 2 The recovery rate of O is 96.17%; the iron concentrate grade is 57.21%, and the iron recovery rate is 90.72%.

[0063] Example 2 The method is the same as in Example 1, except that: (1) According to the molar ratio of C / O = 0.2, Na 2 O / Al 2 O 3 =1.6 Add sawdust and liquid alkali solution, the moisture content of raw material pellets is 14.5%; (2) Preheat the dried raw material pellets to 700 o C for 1 h and then cooled to 300°C in a protective atmosphere. o C; (3) Al in roasted clinker 2 O 3 The recovery rate of Na 2 The recovery rate of O is 94.82%; the iron concentrate grade is 56.42%, and the iron recovery rate is 90.24%.

[0064] Example 3 The method is the same as in Example 1, except that: (1) According to the molar ratio of C / O = 0.2, Na 2 O / Al 2 O 3 =1.6 Add sawdust and liquid alkali solution, the moisture content of raw pellets is 14.3%; (2) Preheat the dried raw material pellets to 800 o C for 1 h, and then cooled to 250°C in a protective atmosphere. o C; (3) Al in roasted clinker 2 O 3 The recovery rate of Na 2 The recovery rate of O is 95.25%; the iron concentrate grade is 55.98%, and the iron recovery rate is 90.58%.

[0065] Example 4 The method is the same as in Example 1, except that: (1) The main chemical components of high-iron and low-silicon red mud (by mass percentage): Fe 2 O 357.52%, Al 2 O 3 16.01%, SiO 2 3.88%, CaO 2.16%, TiO 2 6.02%, Na 2 O 1.55%, aluminum-silicon ratio 4.1; (2) Main chemical components of liquid caustic soda (by mass percentage): N K 558.17g / L, N C 17.21g / L, C AO 7.45g / L; (3) According to the molar ratio of C / O = 0.22, Na 2 O / Al 2 O 3 =1.95Add coal powder and liquid alkali solution, the moisture content of raw material pellets is 15.8%; (4) Heating the raw material pellets to 750 o C for 0.5 h, and then cooled to 200 °C in a protective atmosphere. o C; (5) Al in roasted clinker 2 O 3 The recovery rate of Na 2 The recovery rate of O is 96.47%; the iron concentrate grade is 56.21%, and the iron recovery rate is 90.95%.

[0066] Example 5 The method is the same as in Example 1, except that: (1) The main chemical components of high-iron and low-silicon red mud (by mass percentage): Fe 2 O 3 53.96%, Al 2 O 3 16.16%, SiO 2 7.07%, CaO 1.06%, TiO 2 6.12%, Na 2 O 3.38%, aluminum-silicon ratio 2.3; (2) Main chemical components of liquid caustic soda (by mass percentage): N K 558.17g / L, N C 17.21g / L, C AO 7.45g / L; (3) According to the molar ratio of C / O = 0.2, Na 2 O / Al 2 O 3 =2.2 Add sawdust and liquid alkali solution, the moisture content of raw pellets is 16.6%; (4) Heating the raw material pellets to 750 o C for 0.5 h, and then cooled to 300 °C in a protective atmosphere. o C; (5) Al in roasted clinker 2 O 3 The recovery rate of Na 2 The recovery rate of O is 96.69%; the iron concentrate grade is 56.34%, and the iron recovery rate is 91.35%.

[0067] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. Alterations, modifications, substitutions and variations of the above embodiments by a person skilled in the art are all within the scope of the present invention.

Claims

1. A method for comprehensive treatment of high iron and low silicon red mud by alkali magnetization roasting, characterized in that: The steps include: Step (1), mixing high iron and low silicon red mud, liquid caustic soda and solid reducing agent and granulating to obtain raw material pellets, wherein the amount of liquid caustic soda added is according to the molar ratio of Na2O / Al2O3=1.0-2.5, and the amount of solid reducing agent added is according to the molar ratio of C / O=0.1-0.5, wherein O is the molar content of oxygen atoms in Fe2O3 in red mud; Step (2), drying the raw material pellets with kiln tail gas to remove adsorbed water and part of crystallized water, to obtain dried pellets; Step (3), dry roasting the dried pellets in an inert protective gas atmosphere, reducing roasting, and the roasting temperature is 500-800°C; after the roasting is completed, continue to cool down to 300°C or below in the inert protective gas atmosphere to obtain clinker pellets; Step (4), wet grinding and leaching the clinker pellets with a dilute alkali solution, controlling the liquid-to-solid ratio to be 5-10; Step (5), separating the leached slurry into liquid and solid, and obtaining a liquid phase of sodium aluminate solution and a solid phase of aluminum extraction slag; Step (6), the sodium aluminate solution is transported to the alumina production system through a pipeline to recover the batching liquid alkali and alumina; Step (7), using ultrasonic pretreatment to separate the magnetite and gangue components in the aluminum extraction slag; Step (8), subjecting the aluminum extraction slag to low-intensity wet magnetic separation, with the magnetic field strength set to 1000-3000 Oe, to obtain iron concentrate and iron ore tailings.

2. The method for comprehensive treatment of high-iron and low-silicon red mud by alkali magnetization roasting according to claim 1, characterized in that: In the step (1), the amount of particles with a particle size of less than 0.074 mm in the high-iron and low-silicon red mud accounts for more than 85% of the total mass.

3. The method for comprehensive treatment of high-iron and low-silicon red mud by alkali magnetization roasting according to claim 1, characterized in that: In the step (1), the solid reducing agent is a coal powder or sawdust organic solid reducing agent.

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

5. The method for comprehensive treatment of high iron and low silicon red mud by alkali magnetization roasting according to claim 1, characterized in that: In the step (1), granulation is performed by a disc granulator, and the particle size of the obtained raw material pellets is 1-5 cm.

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

7. The method for comprehensive treatment of high iron and low silicon red mud by alkali magnetization roasting according to claim 1, characterized in that: In the step (3), the calcination time is 0.5-3.0h.

8. The method for comprehensive treatment of high iron and low silicon red mud by alkali magnetization roasting according to claim 1, characterized in that: In step (4), the dilute alkaline solution is 10-20 g / L NaOH and 3-10 g / L Na2CO3.

9. The method for comprehensive treatment of high iron and low silicon red mud by alkali magnetization roasting according to claim 1, characterized in that: In the step (4), the wet grinding and leaching adopts a grid-type abrasive crusher with a graded liner, which is filled with steel ball grinding media and has a rotation speed of 15-30 r / min.

10. The method for comprehensive treatment of high iron and low silicon red mud by alkali magnetization roasting according to claim 1, characterized in that: In the step (7), the ultrasonic power is 100-300 W, and the ultrasonic time is 1-5 min.

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