Method for comprehensively utilizing red mud

Abstract

The invention relates to the technical field of environmental protection, in particular to a method for comprehensively utilizing red mud. The method comprises the following steps: mixing red mud, sodium carbonate, calcium oxide and coke powder, carrying out reduction roasting in a reducing atmosphere, cooling the obtained roasted material in water, and filtering to obtain filtrate and cooling slag; the filtrate contains sodium aluminate and is used for preparing aluminum oxide; the cooling slag is subjected to ore grinding and screening, and fine ore materials are obtained; the fine mineral aggregate is subjected to low-intensity magnetic separation, a strong magnetic material and first tailings are obtained, and the strong magnetic material is high-grade elemental iron; the first tailings are subjected to strong magnetic separation, weakly magnetic materials and second tailings are obtained, and the weakly magnetic materials are titaniferous magnetite; the second tailings are subjected to flotation, and titanium dioxide and third tailings are obtained; the third tailings comprise calcium silicate; and drying and finely grinding the third tailings to obtain the cement mixture. According to the method, Fe can be efficiently recycled, resource utilization of the Fe element is achieved, and resource utilization of other valuable elements in the red mud can be achieved.

Description

Technical Field

[0001] The invention relates to the technical field of environmental protection, and in particular to a method for comprehensive utilization of red mud. Background Art

[0002] Red mud is a solid waste produced by the preparation of alumina from bauxite. Red mud contains Fe2O3 and is red, so it is called red mud. The main components of red mud are Fe2O3, Al2O3, SiO2, TiO2, CaO, and NaOH. More than 100 million tons of red mud are produced in the country every year, but less than 10% is used, and the rest is stored in piles, which not only occupies a large amount of land resources, but also causes serious pollution to the environment. If red mud can be comprehensively utilized as a resource, the above problems can be effectively alleviated.

[0003] At present, a lot of research has been conducted at home and abroad on the comprehensive recycling of red mud. The main process is that red mud is used in the steel industry as a low-cost raw material after gravity separation or magnetic separation. There is also red mud reduction roasting, which converts Fe2O3 in red mud into magnetic Fe3O4 and then uses it in the steel industry. Although the total Fe content of iron products obtained by reduction roasting is higher than that obtained by direct gravity separation or magnetic separation, the iron grains in red mud are particularly small and most of them are wrapped by other minerals, which are difficult to dissociate and reduce during the roasting process. Therefore, the total iron content in the product after reduction roasting still needs to be improved.

[0004] In addition, the existing technology focuses mainly on how to extract iron and realize the resource utilization of Fe element. In addition to Fe, red mud also contains many other valuable metal elements, such as Ti, Al, etc. How to achieve the recycling of other valuable elements is rarely reported in the existing technology. Summary of the invention

[0005] In view of this, the object of the present invention is to provide a method for comprehensive utilization of red mud. The method provided by the present invention can not only efficiently recover Fe and realize resource utilization of Fe element, but also realize resource utilization of other valuable elements in red mud.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for comprehensive utilization of red mud, comprising the following steps:

[0008] Mix red mud, soda ash, calcium oxide and coke powder, and perform reduction roasting in a reducing atmosphere at a temperature of 1000-1200° C. Place the roasted material in water for cooling, filter, and obtain a filtrate and cooling slag; the filtrate contains sodium aluminate and is used for preparing alumina;

[0009] Grinding and screening the cooled slag to obtain fine ore;

[0010] The fine ore is subjected to weak magnetic separation to obtain a strong magnetic material and a first tailing; the strong magnetic material is high-grade elemental iron, wherein the total Fe content is above 85wt% and the metallization rate is above 90%;

[0011] The first tailings are subjected to strong magnetic separation to obtain weak magnetic material and second tailings; the weak magnetic material is titanium-containing magnetite;

[0012] flotation the second tailings to obtain titanium dioxide and third tailings; the third tailings comprising calcium silicate;

[0013] The third tailings are dried and finely ground to make cement admixture.

[0014] Preferably, based on dry weight, the mass ratio of the red mud, soda ash, calcium oxide and coke powder is (60-70):(15-20):(5-10):(10-15).

[0015] Preferably, the reduction roasting time is 60 to 90 minutes.

[0016] Preferably, the magnetic field strength of the weak magnetic separation is 800-1200 GS.

[0017] Preferably, the magnetic field strength of the strong magnetic separation is 5000-6000GS.

[0018] Preferably, the passing rate of the fine mineral material through a 200-mesh sieve is ≥90%.

[0019] Preferably, the red mud comprises Fe2O3, Al2O3, SiO2, TiO2, CaO and NaOH.

[0020] Preferably, the total Fe content in the red mud is 25-40wt%.

[0021] Preferably, the soda ash is spent soda ash.

[0022] Preferably, after obtaining the third tailings, the method further includes extracting precious metal elements from the third tailings.

[0023] The invention provides a method for comprehensive utilization of red mud, comprising the following steps: mixing red mud, soda ash, calcium oxide and coke powder, performing reduction roasting in a reducing atmosphere, wherein the temperature of the reduction roasting is 1000-1200 DEG C, placing the obtained roasted material in water for cooling, filtering, and obtaining a filtrate and cooling slag; the filtrate contains sodium aluminate and is used for preparing alumina; grinding and screening the cooling slag to obtain fine ore; performing weak magnetic separation on the fine ore to obtain a strong magnetic material and a first tailing; the strong magnetic material is high-grade elemental iron, wherein the total Fe content is above 85wt% and the metallization rate is above 90%; performing strong magnetic separation on the first tailing to obtain a weak magnetic material and a second tailing; the weak magnetic material is titanium-containing magnetite; performing flotation on the second tailing to obtain titanium dioxide and a third tailing; the third tailing contains calcium silicate; and drying and fine grinding the third tailing to make a cement admixture.

[0024] Compared with the prior art which cannot fully extract and utilize multiple elements in red mud, the present invention realizes the recycling of multiple valuable elements in red mud through the steps of reduction roasting, water cooling, weak magnetic separation, strong magnetic separation and flotation, wherein ferric oxide is converted into high-grade elemental iron (i.e., strong magnetic material); Al is converted into sodium aluminate and enters the filtrate for the preparation of alumina; Ti partially enters the titanium-containing magnetite, and the rest is recovered in the form of titanium dioxide and can be sold directly; Ca and Si finally enter the tailings after flotation (i.e., the third tailings), and are used as cement admixtures after fine grinding. The present invention makes full use of various valuable elements in red mud, not only solves the problem of red mud storage, but also achieves better economic benefits.

[0025] In addition, the present invention adds soda ash during reduction roasting, which can promote the dissociation of ferric oxide grains from the mineral, and then promote the reduction of ferric oxide to elemental iron, thereby increasing the total iron content and the yield of elemental iron in the ferromagnetic material, which is conducive to realizing the high value of iron.

[0026] Furthermore, the present invention uses waste soda ash as raw material. The waste soda ash is produced in large quantities and at a low price, which can reduce the cost of the process of the present invention and is more suitable for industrialization. DETAILED DESCRIPTION

[0027] The present invention provides a method for comprehensive utilization of red mud, comprising the following steps:

[0028] Mix red mud, soda ash, calcium oxide and coke powder, and perform reduction roasting in a reducing atmosphere at a temperature of 1000-1200° C. Place the roasted material in water for cooling, filter, and obtain a filtrate and cooling slag; the filtrate contains sodium aluminate and is used for preparing alumina;

[0029] Grinding and screening the cooled slag to obtain fine ore;

[0030] The fine ore is subjected to weak magnetic separation to obtain a strong magnetic material and a first tailing; the strong magnetic material is high-grade elemental iron, wherein the total Fe content is above 85wt% and the metallization rate is above 90%;

[0031] The first tailings are subjected to strong magnetic separation to obtain weak magnetic material and second tailings; the weak magnetic material is titanium-containing magnetite;

[0032] flotation the second tailings to obtain titanium dioxide and third tailings; the third tailings comprising calcium silicate;

[0033] The third tailings are dried and finely ground to make cement admixture.

[0034] The invention mixes red mud, soda ash, calcium oxide and coke powder, and performs reduction roasting in a reducing atmosphere to obtain roasted material.

[0035] In the present invention, the red mud preferably includes Fe2O3, Al2O3, SiO2, TiO2, CaO and NaOH; the total Fe content in the red mud is preferably 25-40wt%. In the present invention, the mass ratio of the red mud, soda ash, calcium oxide and coke powder is preferably (60-70):(15-20):(5-10):(10-15) on a dry weight basis, and in an embodiment of the present invention, specifically 70:15:5:15 or 60:18:10:12. In the present invention, the soda ash is preferably spent soda ash.

[0036] The present invention has no special requirements for the reducing atmosphere, and any reducing atmosphere known in the art can be used, such as a hydrogen atmosphere or an atmosphere containing CO. In an embodiment of the present invention, the reducing gas used in the reducing atmosphere is a mixed gas produced by carbon-containing materials in a low-oxygen environment, wherein the volume content of CO is 60%.

[0037] In the present invention, the temperature of the reduction roasting is 1000-1200° C., preferably 1010-1150° C.; the time of the reduction roasting is preferably 60-90 minutes.

[0038] In the present invention, most of the iron oxide grains in the red mud are wrapped by other minerals and are difficult to reduce. The present invention promotes mineral dissociation by adding soda ash, and then reduces under the action of coke powder. Specifically, the present invention uses reduction roasting to decompose sodium carbonate into Na2O, Al2O3 in the red mud and Na2O to generate sodium aluminate, SiO2 in the red mud and Na2O to generate sodium silicate, and most of the iron oxide is dissociated and reduced to elemental iron.

[0039] After obtaining the roasted material, the present invention places the roasted material in water for cooling, and filters it to obtain a filtrate and cooling slag; the filtrate contains sodium aluminate.

[0040] In the present invention, the cooling is preferably carried out under air-tight conditions to prevent Fe from being oxidized. The present invention preferably cools to below 100°C. In the present invention, after the roasted material is placed in water, the sodium silicate and sodium aluminate produced by roasting are dissolved in water, and the CaO in the red mud and the calcium oxide used in roasting react with water to generate calcium hydroxide, which then reacts with sodium silicate to generate calcium silicate calcium slag, which enters the cooling slag, while the reduced iron powder and TiO2 and some unreacted iron ore also enter the cooling slag, and the sodium aluminate enters the filtrate.

[0041] The present invention uses the filtrate for preparing alumina; and grinds and screens the cooled slag to obtain fine ore.

[0042] The present invention has no special requirements for the grinding, and the grinding method known in the art can be used. In the present invention, the water-slurry ratio of the grinding is 3:1. In the present invention, the mesh number of the screen used for screening is preferably 200 mesh. The present invention removes large particles remaining in the grinding process by screening. In the present invention, the passing rate of the 200 mesh screen of the fine ore is preferably ≥90%. The grinding of the present invention is beneficial to subsequent magnetic separation and flotation.

[0043] After obtaining the fine ore, the present invention performs weak magnetic separation on the fine ore to obtain strong magnetic material and first tailings; the strong magnetic material is high-grade elemental iron, wherein the total Fe content is above 85wt% and the metallization rate is above 90%.

[0044] In the present invention, the magnetic field strength of the weak magnetic separation is preferably 800-1200GS, specifically 800GS, 900GS, 1000GS, 1100GS or 1200GS, which are not exhaustively listed here. The present invention separates the elemental iron with strong magnetism through weak magnetic separation, and the obtained strong magnetic material is mainly reduced iron powder, wherein the total Fe content is above 85wt%, the metallization rate is above 90%, and it can be directly sold as a high-value product.

[0045] After obtaining the first tailings, the present invention performs strong magnetic separation on the first tailings to obtain weak magnetic materials and second tailings; the weak magnetic materials are titanium-containing magnetite.

[0046] In the present invention, the magnetic field strength of the strong magnetic separation is preferably 5000-6000GS, specifically 5000GS, 5500GS or 6000GS, which will not be listed here. Since titanium dioxide has weak magnetism, the present invention separates the weak magnetic material in the first tailings through strong magnetic separation, wherein the weak magnetic material is mainly titanium-containing magnetite. In the present invention, the titanium content in the titanium-containing magnetite is 30-40wt%, and the iron content is 30-40wt%, which can be sold directly. The remaining second tailings are mainly calcium slag and also contain a small amount of titanium dioxide.

[0047] After obtaining the second tailings, the present invention performs flotation on the second tailings to obtain titanium dioxide and third tailings; the third tailings include calcium silicate.

[0048] The present invention does not specifically limit the flotation conditions, as long as the titanium dioxide can be separated. In the present invention, the titanium dioxide can be directly sold as a product.

[0049] After obtaining the third tailings, the present invention can directly dry and finely grind the third tailings to make cement admixture, or extract precious metal elements (such as Sc) from the third tailings and then use them as cement admixture, or use them for other building materials.

[0050] In the present invention, the third tailings are active after being roasted, so they can be directly used as cement admixtures for preparing cement. The present invention does not specifically limit the method for preparing cement using the third tailings, and the preparation can be carried out using operations well known to those skilled in the art.

[0051] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0052] Example 1

[0053] 70 g of red mud (with a total Fe content of 40%), 15 g of soda ash, 5 g of calcium oxide and 15 g of coke powder were mixed, and reduction roasted (the reduction roasting temperature was 1100° C. and the roasting time was 1 h) under a reducing atmosphere (with a CO volume content of 60%) to obtain a roasted material;

[0054] The calcined material is placed in water and cooled to below 100° C. under air-tight conditions, and then ground and passed through a 200-mesh sieve to obtain fine ore, wherein the 200-mesh passing rate of the fine ore is 90%;

[0055] The fine ore is subjected to weak magnetic separation in 800GS to obtain reduced iron powder and first tailings, wherein the total Fe content in the reduced iron powder is 89.7% and the metallization rate is 92.5%;

[0056] The first tailings are subjected to strong magnetic separation at 5000GS to obtain titanium-containing magnetite and second tailings;

[0057] flotation the second tailings to obtain titanium dioxide and third tailings;

[0058] The third tailings are dried, finely ground and sent to a cement plant to prepare cement.

[0059] Example 2

[0060] 60 g of red mud (with a total Fe content of 35%), 18 g of soda ash, 10 g of calcium oxide and 12 g of coke powder were mixed, and reduction roasted (the reduction roasting temperature was 1050° C. and the roasting time was 1.5 h) in a reducing atmosphere (with a CO volume content of 60%) to obtain a roasted material;

[0061] The calcined material is placed in water and cooled to below 100° C. under air-tight conditions, and then ground and passed through a 200-mesh sieve to obtain fine ore, wherein the 200-mesh passing rate of the fine ore is 95%;

[0062] The fine ore is subjected to weak magnetic separation at 1000GS to obtain reduced iron powder and first tailings, wherein the total Fe content in the reduced iron powder is 85.2% and the metallization rate is 91.5%;

[0063] The first tailings are subjected to strong magnetic separation at 5500GS to obtain titanium-containing magnetite and second tailings;

[0064] flotation the second tailings to obtain titanium dioxide and third tailings;

[0065] The third tailings are dried, finely ground and sent to a cement plant to prepare cement.

[0066] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention, not all of the embodiments. Other embodiments can be obtained based on this embodiment without creativity, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for comprehensive utilization of red mud, characterized in that: The following steps are involved: Mix red mud, soda ash, calcium oxide and coke powder, and perform reduction roasting in a reducing atmosphere at a temperature of 1000-1200° C. Place the roasted material in water for cooling, filter, and obtain a filtrate and cooling slag; the filtrate contains sodium aluminate and is used for preparing alumina; Grinding and screening the cooled slag to obtain fine ore; The fine ore is subjected to weak magnetic separation to obtain a strong magnetic material and a first tailing; the strong magnetic material is high-grade elemental iron, wherein the total Fe content is above 85wt% and the metallization rate is above 90%; The first tailings are subjected to strong magnetic separation to obtain weak magnetic material and second tailings; the weak magnetic material is titanium-containing magnetite; flotation the second tailings to obtain titanium dioxide and third tailings; the third tailings comprising calcium silicate; The third tailings are dried and finely ground to make cement admixture.

2. The method according to claim 1, characterized in that Based on dry weight, the mass ratio of the red mud, soda ash, calcium oxide and coke powder is (60-70):(15-20):(5-10):(10-15).

3. The method according to claim 1 or 2, characterized in that: The reduction roasting time is 60 to 90 minutes.

4. The method according to claim 1, characterized in that: The magnetic field strength of the weak magnetic separation is 800-1200 GS.

5. The method according to claim 1, characterized in that The magnetic field strength of the strong magnetic separation is 5000-6000GS.

6. The method according to claim 1, characterized in that The passing rate of the fine mineral material through a 200-mesh sieve is ≥90%.

7. The method according to claim 1, characterized in that The red mud includes Fe2O3, Al2O3, SiO2, TiO2, CaO and NaOH.

8. The method according to claim 1 or 7, characterized in that: The total Fe content in the red mud is 25-40 wt%.

9. The method according to claim 1, characterized in that: The soda ash is waste soda ash.

10. The method according to claim 1, characterized in that After the third tailings are obtained, the method further includes extracting precious metal elements from the third tailings.