Method for recovering titanium nitride by reducing red mud with aluminum ash

Abstract

The invention relates to the field of solid waste recycling, and discloses a method for recovering titanium nitride by reducing red mud with aluminum ash. The method comprises the following steps: mixing aluminum ash with red mud and waste glass, roasting in an inert atmosphere by taking aluminum nitride in the aluminum ash as a reducing agent and the waste glass as a reaction accelerant, and reducing titanium dioxide and ferric oxide in the red mud into titanium nitride and metallic iron; carrying out crushing and magnetic separation on the roasted material to separate out a magnetic material and non-magnetic slag; and melting the magnetic material, and casting by a filter screen to obtain titanium nitride and iron alloy. According to the invention, aluminum nitride in the aluminum ash is used as a reducing agent, ammonia pollution caused by hydrolysis of aluminum nitride is avoided, and carbon emission of reduced titanium and iron is reduced at the same time; titanium and iron in the red mud are reduced into titanium nitride and iron alloy, and titanium and iron resources in the red mud are recycled. According to the method, the red mud is co-processed by the aluminum ash, low-carbon high-value utilization of the solid waste is realized, and the method has the advantages of short process, no pollution and easiness in industrialization.

Description

Technical Field

[0001] The invention relates to the field of solid waste resource utilization, and in particular to a method for recovering titanium nitride by reducing red mud with aluminum ash slag. Background Art

[0002] With the development of the aluminum industry, the amount of aluminum ash and red mud has increased rapidly. Aluminum ash contains aluminum oxide (40-60 wt.%), aluminum nitride (20-40 wt.%), salt refining agent (10-20 wt.%) and a small amount of metallic aluminum. Because it contains a large amount of aluminum oxide, aluminum ash is a valuable aluminum resource; but aluminum nitride is easily hydrolyzed to produce ammonia pollution, and salt refining agents are easily dissolved with rainwater to pollute surface water and groundwater. Red mud contains iron oxide (20-60 wt.%), titanium dioxide (5-10 wt.%), aluminum oxide (20-40 wt.%), sodium hydroxide (10-20 wt.%) and other oxides. Because it contains a large amount of iron oxide and titanium dioxide, red mud is a valuable iron and titanium resource, but it also contains a large amount of alkali, which is easily dissolved with rainwater to pollute surface water and groundwater when landfilled. Therefore, the problem of harmless disposal and resource utilization of aluminum ash and red mud needs to be solved urgently.

[0003] At present, the resource utilization of aluminum ash slag is divided into wet method and pyrolysis. The wet process is as follows: the aluminum ash slag is washed with water, evaporated and desalted, and absorbs ammonia produced by the hydrolysis of aluminum nitride; the aluminum is leached out by acid or alkali dissolution to obtain a leachate; the leachate is precipitated, roasted and other processes to obtain an alumina product. The aluminum ash slag is recycled into building materials and refractory materials by pyrolysis. The process is as follows: the aluminum ash slag is washed with water, evaporated and desalted, and absorbs ammonia produced by the hydrolysis of aluminum nitride; the desalted and denitrified aluminum ash slag is evenly mixed with other raw materials, and is prepared into building materials and refractory materials through heat treatment such as molding, sintering or melting. At present, the methods for recycling red mud include recovering iron and producing building materials. The methods for recovering iron include: reduction roasting, magnetic separation to recover iron; reduction smelting to produce pig iron. The building materials for recycling red mud include cement, unfired bricks and ceramic materials.

[0004] The Chinese invention patent (CN106830030B) discloses a method for safely and efficiently producing sand-like alumina from aluminum ash. By adjusting the Bayer process, the aluminum element in the aluminum ash is used to produce sand-like alumina, and the ammonia and hydrogen in the production are reused. However, the impurity content of the recovered ammonia is high, and it is difficult to use.

[0005] China's invention patent (CN108516688A) discloses a method for producing spinel glass-ceramics using aluminum ash as the main raw material. The product has a compressive strength of 400-500 MPa and a flexural strength of 70-90 MPa. However, aluminum nitride is oxidized to aluminum oxide by oxygen, and its high reducibility is not realized.

[0006] The Chinese invention patent (CN112958584A) discloses a method for reducing hazardous solid waste heavy metals with secondary aluminum ash and utilizing slag, using aluminum nitride from secondary aluminum ash to reduce hazardous solid waste heavy metals, and utilizing slag in building materials. However, due to the small amount of heavy metals in hazardous solid waste, the utilization rate of aluminum nitride is low, and most of the aluminum nitride is still oxidized to aluminum oxide by oxygen, and its high reducibility value is not realized; at the same time, the heavy metals obtained by reduction are fused into alloys, which are difficult to separate and reuse.

[0007] A Chinese invention patent (CN102912067A) discloses a method for producing red mud sponge iron steelmaking coolant, which uses low-sulfur coal powder to directly reduce red mud iron to obtain sponge iron. However, coal resources are scarce and non-renewable, and it does not respond to the country's dual carbon policy.

[0008] A Chinese invention patent (CN108502907B) discloses a method for simultaneous treatment of aluminum ash and high-iron red mud, using aluminum ash as a reducing agent to reduce hematite in red mud to magnetite by hydrothermal reaction, and then obtaining iron concentrate by physical separation. However, the hydrothermal reaction process is prone to ammonia pollution, and because aluminum ash contains salt, saline wastewater is difficult to treat.

[0009] The Chinese invention patent (CN101429582A) discloses a method for preparing ferrosilicon alloy and calcium aluminate materials using red mud and aluminum ash. The metal in the aluminum ash is used as the main reducing agent, and ferrosilicon alloy and calcium aluminate are obtained by high-temperature melting (1400-1800°C). However, the aluminum ash used has a high aluminum content of 10-40 wt.%, which can be recovered through processes such as ash frying and ball milling. However, aluminum is more valuable than ferrosilicon alloy, so the process cost is high and industrialization is difficult. At the same time, titanium resources enter the calcium aluminate slag and are not recycled.

[0010] The existing aluminum ash and red mud resource utilization technologies have problems such as large amount of wastewater, high carbon emissions, and waste of aluminum nitride and titanium resources. There is an urgent need for aluminum ash and red mud resource utilization technology to realize the resource utilization of aluminum ash and aluminum nitride, as well as the low-carbon recovery of titanium and iron resources in red mud. Summary of the invention

[0011] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for recovering titanium nitride from red mud by reducing aluminum ash slag. The aluminum ash slag is mixed with red mud and waste glass. The aluminum nitride in the aluminum ash slag is used as a reducing agent and the waste glass is used as a reaction accelerator. The titanium dioxide and iron oxide in the red mud are reduced to titanium nitride and metallic iron by roasting in an inert atmosphere. The roasted material is crushed and magnetically separated to separate the magnetic material and non-magnetic slag. The magnetic material is melted and cast to obtain titanium nitride and ferroalloy. The problem of resource utilization of aluminum ash slag and red mud is completely solved.

[0012] The present invention adopts the following technical solution:

[0013] A method for recovering titanium nitride from red mud by reducing aluminum ash slag is characterized in that aluminum ash slag is mixed with red mud and waste glass, aluminum nitride in the aluminum ash slag is used as a reducing agent, and waste glass is used as a reaction accelerator, and titanium dioxide and iron oxide in the red mud are reduced to titanium nitride and metallic iron through roasting in an inert atmosphere; the roasted material is crushed and magnetically separated to separate magnetic materials and non-magnetic slag; the magnetic material is melted and cast through a filter screen to obtain titanium nitride and ferroalloy.

[0014] Furthermore, the ratio of aluminum ash slag to red mud and waste glass is: aluminum ash slag 30-60 wt.%, red mud 20-60 wt.%, waste glass 10-20 wt.%, totaling 100 wt.%.

[0015] Furthermore, the inert atmosphere is one of nitrogen, argon and helium.

[0016] Furthermore, the calcination process is carried out at 1000-1400° C. for 1.0-4.0 h.

[0017] Furthermore, the magnetic material melting process is to maintain the temperature at 1550-1650° C. for 1.0-2.0 h.

[0018] Furthermore, the method specifically comprises:

[0019] S1. Mixing: mixing aluminum ash slag, red mud and waste glass uniformly to obtain a mixture;

[0020] S2, calcination: the mixed material is heated to 1000-1400° C. in an inert atmosphere and kept at this temperature for 1.0-4.0 h to reduce titanium dioxide and iron oxide to titanium nitride and iron alloy to obtain a calcined material;

[0021] S3, crushing and magnetic separation: the roasted material is crushed and magnetically separated to separate the magnetic material and the non-magnetic slag;

[0022] S4, melting and filter casting: the magnetic material is heated to 1550-1650° C. and kept warm for 1.0-2.0 h to separate the titanium nitride and the ferroalloy, and then the titanium nitride and the ferroalloy are obtained by filter casting.

[0023] The principle of the present invention is:

[0024] (1) The Gibbs free energy of the reaction of aluminum nitride (AlN) reducing TiO2 and Fe2O3 to TiN and Fe is less than zero, and is lower than the Gibbs free energy of the carbon reduction reaction, that is, the reduction reaction is thermodynamically feasible, and the reducing ability of aluminum nitride is stronger than that of carbon. During the sintering process, the waste glass in the mixture melts to form a silicate melt; AlN, TiO2, and Fe2O3 can undergo a solid solution reaction with silicon dioxide and calcium oxide and enter the silicate melt; AlN, TiO2, and Fe2O3 entering the silicate melt can contact at the atomic level, and thus the reaction kinetics are feasible.

[0025] (2) Using the magnetic difference between the ferroalloy, titanium nitride and slag phases generated by reduction, magnetic ferroalloy and titanium nitride are separated from non-magnetic slag by magnetic separation;

[0026] (3) The melting points of ferroalloy and titanium nitride are approximately 1500°C and 2900°C, respectively. By utilizing the difference in melting points, the ferroalloy and titanium nitride in the magnetic material can be separated by melting.

[0027] The beneficial effects of the present invention are:

[0028] (1) The existing treatment technologies for aluminum nitride in aluminum ash are divided into wet method and pyrolysis method. The wet method uses hydrolysis to remove aluminum nitride, which has the problem of ammonia pollution; the pyrolysis method uses oxygen to oxidize aluminum nitride, which does not realize the high reducibility of aluminum nitride. The present invention solves the pollution problem of aluminum nitride and increases the value of reducing red mud titanium and iron, thus realizing the high-value utilization of aluminum nitride in aluminum ash.

[0029] (2) Existing red mud iron recovery methods include carbon reduction and metallic aluminum reduction. However, coal resources are scarce and non-renewable, with high emissions. The metallic aluminum in aluminum ash is of high value and can be recovered through processes such as ash roasting and ball milling. Iron reduction is not economically beneficial. The present invention uses aluminum nitride in aluminum ash as a reducing agent, and the oxidation product of aluminum nitride is nitrogen, which reduces the cost and carbon emissions of reducing red mud iron and has significant economic and environmental benefits.

[0030] (3) Currently, titanium resources in red mud are all recovered by wet methods, which has a long process flow and generates a large amount of wastewater. The present invention uses aluminum nitride in aluminum ash to reduce titanium dioxide to titanium nitride, which can be used as a high-temperature structural material and wear-resistant material, thus realizing the short process, green and high-value recovery of titanium resources in red mud. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Shown is a process flow chart of the present invention.

[0032] Figure 2 Shown is the SEM morphology and element distribution diagram of the magnetic material obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0034] On the contrary, the present invention covers any substitution, modification, equivalent method and scheme made on the essence and scope of the present invention as defined by the claims. Further, in order to make the public have a better understanding of the present invention, some specific details are described in detail in the detailed description of the present invention below. Those skilled in the art can fully understand the present invention without the description of these details.

[0035] Example 1

[0036] 30 wt.% aluminum ash slag, 60 wt.% red mud and 10 wt.% waste glass were uniformly mixed to obtain a mixture; the mixture was heated to 1000°C in a nitrogen atmosphere and kept at this temperature for 1.0 h to reduce titanium dioxide and iron oxide to titanium nitride and ferroalloy to obtain a roasted material; the roasted material was crushed and magnetically separated to separate the magnetic material and non-magnetic slag, and the morphology and element distribution of the obtained magnetic material were shown in Fig. Figure 2 The magnetic material is heated to 1550°C and kept for 1.0 h to separate titanium nitride from the iron alloy; titanium nitride and the iron alloy are obtained by casting. The composition of the obtained titanium nitride product is shown in Table 1, and the titanium nitride content is about 80 wt.%.

[0037] Table 1 Titanium nitride product composition in Example 1

[0038]

[0039] Example 2

[0040] 33 wt.% aluminum ash slag, 56 wt.% red mud and 11 wt.% waste glass are uniformly mixed to obtain a mixture; the mixture is heated to 1040°C in an argon atmosphere and kept warm for 1.3 h to reduce titanium dioxide and iron oxide to titanium nitride and ferroalloy to obtain a calcined material; the calcined material is crushed and magnetically separated to separate the magnetic material and non-magnetic slag; the magnetic material is heated to 1560°C and kept warm for 1.1 h to separate the titanium nitride and ferroalloy; titanium nitride and ferroalloy are obtained by casting.

[0041] Example 3

[0042] 36 wt.% aluminum ash slag, 52 wt.% red mud and 12 wt.% waste glass are uniformly mixed to obtain a mixture; the mixture is heated to 1080°C in a helium atmosphere and kept warm for 1.6 h to reduce titanium dioxide and iron oxide to titanium nitride and ferroalloy to obtain a calcined material; the calcined material is crushed and magnetically separated to separate the magnetic material and non-magnetic slag; the magnetic material is heated to 1570°C and kept warm for 1.2 h to separate the titanium nitride and ferroalloy; titanium nitride and ferroalloy are obtained by casting.

[0043] Example 4

[0044] 39 wt.% aluminum ash slag, 48 wt.% red mud and 13 wt.% waste glass are uniformly mixed to obtain a mixture; the mixture is heated to 1120°C in a nitrogen atmosphere and kept warm for 1.9 h to reduce titanium dioxide and iron oxide to titanium nitride and ferroalloy to obtain a calcined material; the calcined material is crushed and magnetically separated to separate the magnetic material and non-magnetic slag; the magnetic material is heated to 1580°C and kept warm for 1.3 h to separate the titanium nitride and ferroalloy; titanium nitride and ferroalloy are obtained by casting.

[0045] Example 5

[0046] 42 wt.% aluminum ash slag, 44 wt.% red mud, and 14 wt.% waste glass were uniformly mixed to obtain a mixture; the mixture was heated to 1160°C in an argon atmosphere for 2.2 h to reduce titanium dioxide and iron oxide to titanium nitride and ferroalloy to obtain a roasted material; the roasted material was crushed and magnetically separated to separate the magnetic material and non-magnetic slag; the magnetic material was heated to 1590°C for 1.4 h to separate titanium nitride and ferroalloy; titanium nitride and ferroalloy were obtained by casting. The composition of the obtained titanium nitride product is shown in Table 2, and the titanium nitride content is about 85 wt.%.

[0047] Table 2 Composition of titanium nitride product in Example 5

[0048]

[0049] Example 6

[0050] 45 wt.% aluminum ash slag, 40 wt.% red mud and 15 wt.% waste glass are uniformly mixed to obtain a mixture; the mixture is heated to 1200°C in a helium atmosphere and kept warm for 2.5 hours to reduce titanium dioxide and iron oxide to titanium nitride and ferroalloy to obtain a calcined material; the calcined material is crushed and magnetically separated to separate the magnetic material and non-magnetic slag; the magnetic material is heated to 1600°C and kept warm for 1.5 hours to separate the titanium nitride and ferroalloy; titanium nitride and ferroalloy are obtained by casting.

[0051] Example 7

[0052] 48 wt.% aluminum ash slag, 36 wt.% red mud and 16 wt.% waste glass are uniformly mixed to obtain a mixture; the mixture is heated to 1240°C in a nitrogen atmosphere and kept warm for 2.8 h to reduce titanium dioxide and iron oxide to titanium nitride and ferroalloy to obtain a calcined material; the calcined material is crushed and magnetically separated to separate the magnetic material and non-magnetic slag; the magnetic material is heated to 1610°C and kept warm for 1.6 h to separate the titanium nitride and ferroalloy; titanium nitride and ferroalloy are obtained by casting.

[0053] Example 8

[0054] 51 wt.% aluminum ash slag, 32 wt.% red mud and 17 wt.% waste glass are uniformly mixed to obtain a mixture; the mixture is heated to 1280°C in an argon atmosphere and kept warm for 3.1 h to reduce titanium dioxide and iron oxide to titanium nitride and ferroalloy to obtain a calcined material; the calcined material is crushed and magnetically separated to separate the magnetic material and non-magnetic slag; the magnetic material is heated to 1620°C and kept warm for 1.7 h to separate the titanium nitride and ferroalloy; titanium nitride and ferroalloy are obtained by casting.

[0055] Example 9

[0056] 54 wt.% aluminum ash slag, 28 wt.% red mud, and 18 wt.% waste glass were uniformly mixed to obtain a mixture; the mixture was heated to 1320°C in a helium atmosphere for 3.4 h to reduce titanium dioxide and iron oxide to titanium nitride and ferroalloy to obtain a roasted material; the roasted material was crushed and magnetically separated to separate the magnetic material and non-magnetic slag; the magnetic material was heated to 1630°C for 1.8 h to separate titanium nitride and ferroalloy; titanium nitride and ferroalloy were obtained by casting. The composition of the obtained titanium nitride product is shown in Table 3, and the titanium nitride content is about 85 wt.%.

[0057] Table 3 Composition of titanium nitride product in Example 9

[0058]

[0059] Example 10

[0060] 57 wt.% aluminum ash slag, 24 wt.% red mud and 19 wt.% waste glass are uniformly mixed to obtain a mixture; the mixture is heated to 1360°C in a nitrogen atmosphere and kept warm for 3.7 h to reduce titanium dioxide and iron oxide to titanium nitride and ferroalloy to obtain a calcined material; the calcined material is crushed and magnetically separated to separate the magnetic material and non-magnetic slag; the magnetic material is heated to 1640°C and kept warm for 1.9 h to separate the titanium nitride and ferroalloy; titanium nitride and ferroalloy are obtained by casting.

[0061] Embodiment 11

[0062] 60 wt.% aluminum ash slag, 20 wt.% red mud and 20 wt.% waste glass are uniformly mixed to obtain a mixture; the mixture is heated to 1400°C in an argon atmosphere and kept warm for 4.0 h to reduce titanium dioxide and iron oxide to titanium nitride and ferroalloy to obtain a calcined material; the calcined material is crushed and magnetically separated to separate the magnetic material and non-magnetic slag; the magnetic material is heated to 1650°C and kept warm for 2.0 h to separate the titanium nitride and ferroalloy; titanium nitride and ferroalloy are obtained by casting.

[0063] Aluminum ash slag has a high alumina content and is relatively refractory, so the higher the aluminum ash content, the higher the roasting temperature and the longer the time;

[0064] At the same time, the present invention utilizes aluminum nitride in aluminum ash to reduce iron and titanium in red mud. The higher the aluminum ash content, the higher the titanium reduction rate, and the higher the titanium content in the obtained titanium nitride product.

Claims

1. A method for recovering titanium nitride by reducing red mud with aluminum ash, characterized in that: Aluminum ash slag is mixed with red mud and waste glass. Aluminum nitride in the aluminum ash slag is used as a reducing agent and waste glass is used as a reaction accelerator. Titanium dioxide and iron oxide in the red mud are reduced to titanium nitride and metallic iron through roasting in an inert atmosphere. The roasted material is crushed and magnetically separated to separate the magnetic material and non-magnetic slag. The magnetic material is melted and cast through a filter to obtain titanium nitride and ferroalloy.

2. The method for recovering titanium nitride by reducing red mud with aluminum ash as claimed in claim 1, characterized in that: The ratio of aluminum ash slag to red mud and waste glass is: aluminum ash slag 30-60 wt.%, red mud 20-60 wt.%, waste glass 10-20 wt.%, totaling 100 wt.%.

3. The method for recovering titanium nitride by reducing red mud with aluminum ash slag as claimed in claim 1, characterized in that: The inert atmosphere is one of nitrogen, argon and helium.

4. The method for recovering titanium nitride by reducing red mud with aluminum ash slag as claimed in claim 1, characterized in that: The calcination process is to keep the temperature at 1000-1400° C. for 1.0-4.0 h.

5. The method for recovering titanium nitride by reducing red mud with aluminum ash slag as claimed in claim 1, characterized in that: The magnetic material melting process is to maintain the temperature at 1550-1650° C. for 1.0-2.0 h.

6. The method for recovering titanium nitride by reducing red mud with aluminum ash slag as claimed in claim 1, characterized in that: The method specifically comprises: S1. Mixing: mixing aluminum ash slag, red mud and waste glass uniformly to obtain a mixture; S2, calcination: the mixed material is heated to 1000-1400° C. in an inert atmosphere and kept at this temperature for 1.0-4.0 h to reduce titanium dioxide and iron oxide to titanium nitride and iron alloy to obtain a calcined material; S3, crushing and magnetic separation: the roasted material is crushed and magnetically separated to separate the magnetic material and the non-magnetic slag; S4, melting and filter casting: the magnetic material is heated to 1550-1650° C. and kept warm for 1.0-2.0 h to separate the titanium nitride and the ferroalloy, and then the titanium nitride and the ferroalloy are obtained by filter casting.

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