Method for directly dissolving out high-sulfur bauxite to produce aluminum oxide by regulating and controlling oxidation-reduction potential

Abstract

The invention provides a method for producing aluminum oxide by directly dissolving out high-sulfur bauxite by regulating and controlling oxidation-reduction potential, and relates to the technical field of aluminum oxide production. According to the method, on the basis of the potentials of S < 2->, S < 2->, Fe < 2 + > and Fe < 3 + > in the bauxite, an oxidizing agent is used as a potential regulation and control means, a weak reduction environment is constructed, the existence forms of sulfur and iron are regulated and controlled through the potentials in pre-desiliconization and high-temperature dissolution, the reaction of pyrite is inhibited, dissolved iron and sulfur are directionally converted into magnetite and S2O3 < 2->, sodium silicon slag is embedded into the S2O3 < 2-> in desiliconization, efficient desulfurization is achieved, and high-efficiency desulfurization is achieved. Iron ore concentrate is recycled in magnetic separation, so that red mud is reduced, and high-sulfur bauxite is efficiently and economically utilized. The method synchronously achieves the goals of pyrite reaction inhibition, efficient desulfurization and reinforced iron ore concentrate recovery, is suitable for high-sulfur high-iron ore, has the characteristics of small oxidizing agent amount, short process, easiness in industrialization, red mud process reduction, low cost and the like, is beneficial to economically and green processing of high-sulfur bauxite, and promotes sustainable development of the aluminum oxide industry.

Description

Technical Field

[0001] The present invention relates to the technical field of alumina production, and particularly relates to a method for directly dissolving high-sulfur bauxite to produce alumina by regulating the redox potential. Background Art

[0002] In the Bayer process, sulfur in high-sulfur bauxite mainly exists in the form of pyrite (FeS2). After high-temperature digestion, sulfur mainly enters the sodium aluminate solution in the form of S 2- , corroding equipment, deteriorating the red mud settlement, increasing the alkali consumption, and exceeding the iron content standard of the product, seriously endangering the alumina production. This restricts the development and utilization of high-sulfur bauxite with a reserve of more than 1.5 billion tons in China. In addition, after the traditional high-temperature digestion process, iron in the red mud mainly exists in the forms of goethite (FeOOH) and hematite (Fe2O3), with weak magnetism and difficult magnetic separation recovery, resulting in low iron grade (TFe < 56%) and low iron recovery rate from the red mud. Therefore, inhibiting the reaction of pyrite, directing the formation of magnetite (Fe3O4), and self-purifying desulfurization are the keys to the green production of alumina from high-sulfur bauxite.

[0003] At present, the relatively mature method for controlling the sulfur concentration in the circulating mother liquor is mainly the pretreatment of high-sulfur bauxite. This includes two desulfurization processes: roasting (CN 102897812 B, CN 106269470 A) and flotation (CN 119186819 A, CN 118874700 A). By the above mineral pretreatment, the sulfur content in the bauxite is reduced to less than 0.3%, initially meeting the safety production requirements. However, the pretreatment process is complex, and roasting desulfurization has high energy consumption and large flue gas emissions, while flotation desulfurization has a large amount of washing water and expensive flotation reagents, etc., which all limit the popularization of the pretreatment technology. In addition, since sulfur (<0.3%) in the bauxite concentrate will still continuously accumulate in the Bayer process mother liquor circulation, it is still necessary to remove sulfur from the solution. Solution desulfurization mainly includes methods such as adding iron salts, adding oxidants (sodium nitrate, hydrogen peroxide, O3, O2), and cooling precipitation. Currently, the oxidation method is the main industrial application method. For example: introducing oxygen or oxygen-enriched air to oxidize S 2- to SO4 2- (CN 102502746 A, CN 102616821 A), or adding sodium nitrate, sodium nitrite, and hydrogen peroxide, etc. to oxidize sulfur to the high-valent SO4 2- , and then SO4 2- is removed by evaporation and salt discharge. Although the oxidation method has high desulfurization efficiency, the amount of oxidant used for complete oxidation is large, the cost of caustic soda recovery for the generated sodium sulfate is high, the steam consumption for evaporation and salt discharge is large, and it has a great impact on production organization. There is an urgent need to develop a new process to economically treat high-sulfur bauxite, especially high-sulfur and high-silica bauxite in China.

[0004] To reduce the consumption of oxidants and improve the iron selection from red mud, a method for synchronously removing sulfur, iron, and silicon from sodium aluminate solution by controlled oxidation (CN 115594208 B) and a method for the directional conversion of sulfur and iron in high-iron and high-sulfur bauxite by self-oxidation-reduction (CN118579817 A) oxidize sulfur directionally to S2O3 2- , while magnetite is generated; S2O3 2- enters the sodium silicate slag, realizing short-process desulfurization and directionally generating Fe3O4 with strong magnetism. Although the above methods consider redox reactions, these methods do not quantitatively regulate the potential during the digestion process from the perspective of potential regulation, and do not associate the inhibition of the reaction of pyrite, the directional conversion of S2O3 2- , and the generation of Fe3O4, resulting in relatively high costs for the production of alumina from high-sulfur bauxite at present.

[0005] Based on this, the present invention designs a method for directly digesting high-sulfur bauxite to produce alumina by regulating the redox potential. Summary of the Invention

[0006] The present invention provides a method for directly digesting high-sulfur bauxite to produce alumina by regulating the redox potential, aiming to solve the above problems in the background technology.

[0007] To achieve the above object, an embodiment of the present invention provides a method for directly digesting high-sulfur bauxite to produce alumina by regulating the redox potential. Based on the requirement of a weak reducing atmosphere, by regulating the sulfur ions and the form of iron minerals (iron ions) in the solution, the redox potential of the system is quantitatively regulated. By inhibiting the dissolution of sulfur in pyrite, the directional conversion of S2O3 2- and the generation of Fe3O4, the consumption of oxidants is significantly reduced, sulfur is efficiently removed, and iron is selected from red mud, achieving the goal of economically producing alumina.

[0008] An embodiment of the present invention provides a method for directly digesting high-sulfur bauxite to produce alumina by regulating the redox potential, including the following steps:

[0009] S1: Prepare the original ore pulp by mixing high-sulfur bauxite, calcium-containing compounds, and recycled mother liquor. Add an appropriate amount of oxidant I to the recycled mother liquor and perform pre-desilication under normal pressure to obtain the pre-desilicated slurry;

[0010] S2: Add oxidant II to the pre-desilicated slurry and digest at high temperature. Pyrite is directionally converted to obtain the digested slurry, and sulfur-containing cancrinite-type sodium silicate slag is simultaneously generated;

[0011] S3: Stir and mix the digested slurry with the red mud washing liquid, and dilute and desilicate under normal pressure to generate sulfur-containing sodalite-type sodium silicate slag and obtain the desilicated slurry;

[0012] S4: Filter the desilication slurry, wash the filter cake with hot water to obtain red mud washing liquid and red mud, and recover iron concentrate from the red mud.

[0013] Preferably, in step S1, the high-sulfur bauxite has a sulfur content of less than 2.0%, and sulfur mainly exists in the form of pyrite.

[0014] Preferably, in step S1, the calcium-containing compound is lime, calcium aluminate hydrate or hydrogarnet, with a particle size of less than 10 μm. The addition amount is calculated as CaO and is 1% - 5% of the dry ore amount in the high-sulfur bauxite or the molar ratio of CaO / SiO2 is less than 0.5.

[0015] Preferably, in step S1, the first oxidant is at least one of hydrogen peroxide, sodium peroxide, and sodium persulfate, and the addition amount is added according to 0 - 70% of the stoichiometric coefficient of S 2- converted to S2O3 2- in the solution.

[0016] Preferably, in step S1, the pre-desilication temperature is 90 - 105 °C and the time is 3 - 10 h.

[0017] Preferably, in step S2, the second oxidant is at least one of sodium nitrate, potassium nitrate, and sodium nitrite. The addition amount is controlled according to the weak reduction potential regulation principle to add at a potential between -0.5 V and -1.3 V. The potential calculation method is that the sum of the potentials of S 2- 、S2O3 2- 、SO3 2- 、Fe 2+ 、Fe 3+ and the oxidant in the slurry is ∑xiφ; or it is added according to the contents of reducing pyrite, siderite, oxidizing hematite, and goethite. It is added according to less than 70% of the stoichiometric coefficient of FeS2 oxidized to Fe3O4 and S2O3 2- More preferably, it is added according to 20 - 70% of the stoichiometric coefficient of FeS2 oxidized to Fe3O4 and S2O3 2- .

[0018] Preferably, in step S2, when the digestion temperature is 250 - 280 °C, the pyrite digestion rate is less than 50%.

[0019] Preferably, in step S2, the proportion of high-valent sulfur ions (S2O3 2- 、SO3 2- and SO4 2- ) in the digestion slurry is greater than 80%, and the S 2- concentration in the refined liquid is less than 0.25 g / L.

[0020] Preferably, in step S3, the dilution desilication temperature is 90 - 110 °C, the time is 3 - 10 h, and the S 2-The concentration is less than 0.25 g / L.

[0021] Preferably, in step S4, the red mud contains unreacted pyrite, directionally transformed magnetite and hematite, and the sulfur content is greater than 0.4%.

[0022] The present invention combines the inventors' detailed research on the directional transformation process of pyrite in sodium aluminate solution, desilication and iron removal, and specifically finds that:

[0023] (1) By using the formula calculate the potentials for the transformation of pyrite into different forms of iron and sulfur, and draw the Fe-S-H2O system diagram (such as Figure 1 ).

[0024] (2) Based on various ions (S 2- , S2O3 2- , Fe 2+ , Fe 3+ ) in the solution, calculate the solution potential (xi is the mole fraction or mass percentage, and Φ is the standard potential) Based on the weak reduction potential of -0.5 to -1.3 V, the addition amount of the oxidant can be determined.

[0025] (3) It is also possible to determine the addition amount of the oxidant (less than 70% of the theoretical amount) based on the following redox reaction, based on the presence of a certain concentration of sulfide ions and iron ions in the solution, so as to achieve the directional transformation of pyrite. Taking sodium nitrate as the oxidant as an example, the chemical reaction equation for the directional transformation of sulfide ions is:

[0026] 2S 2- +NO3 - +3H2O = S2O3 2- +NH3↑ + 3OH -

[0027] Among them, the electron transfer equation involving sulfide ions is:

[0028]

[0029] The chemical equation for the directional transformation of pyrite into magnetite and S2O3 2- is:

[0030] 6FeS2 + 5NO3 - +4H2O + 7OH - =2Fe3O4 + 6S2O3 2- +5NH3↑

[0031] 6FeS2 + 22OH - =2Fe3O4 + 10S2- +S2O3 2- +11H2O

[0032] Among them, the electron transfer equations involving pyrite are as follows:

[0033] 6FeS2 + 5NO3 - + 4H2O + 7OH - =2Fe3O4 + 6S2O3 2- + 5NH3↑

[0034] Based on the above reaction equations, the addition amount of the oxidant (sodium nitrate) can regulate the redox potential of the system, thereby directionally regulating the transformation forms of pyrite and sulfide ions, achieving the purpose of inhibiting the reaction of pyrite (such as Figure 2 , 3 ).

[0035] Under atmospheric pressure, in an alkaline system, S 2- reacts with the oxidant to form S2O3 2- . For example, adding hydrogen peroxide

[0036] 2S 2- + 4H2O2 = S2O3 2- + 2OH - + 3H2O

[0037] (4) Compared with the traditional method of completely oxidizing S 2- to SO4 2- , regulating the leaching process to a weak reduction environment can not only reduce the addition amount of the oxidant, but also be more conducive to the formation of magnetite and S2O3 2- .

[0038] (5) During the high-temperature leaching process, sodium nitrate directionally converts the sulfur in pyrite and S 2- in the solution into S2O3 2- which can be embedded in the sodium silicate residue for synchronous removal.

[0039] (6) At high temperature, the magnetization of the pyrite surface can help the subsequent recovery of iron concentrate in red mud by magnetic separation, thereby promoting the reduction of red mud.

[0040] The above-mentioned scheme of the present invention has the following beneficial effects:

[0041] (1) It fits the Bayer leaching process and has a simple process. In the present invention, a measured amount of oxidant is added during leaching, without the need for bauxite pretreatment, additional bypass processes, or large-scale equipment.

[0042] (2) Two-step regulation of potential shows good effect in inhibiting pyrite reaction. By adding oxidants into the circulating mother liquor and the pre-desilication slurry to regulate the sulfur ion form and the sulfur-iron form in the dissolution, two-step coupled regulation of potential is achieved, so as to inhibit the pyrite reaction and achieve the directional conversion into Fe3O4 and S2O3 2- .

[0043] (3) Simultaneous achievement of multiple objectives. Under weak reduction potential, the pyrite reaction is inhibited, and a small amount of pyrite is directionally converted into S2O3 2- and Fe3O4, enabling the simultaneous achievement of multiple objectives such as reducing the amount of oxidant, simultaneous desilication of sulfur, recovering iron minerals and reducing the amount of red mud.

[0044] (4) Good economy and easy production organization. The cost of the oxidant is reduced. By precisely regulating the redox potential in the present invention, it is only necessary to directionally convert the surface of pyrite into magnetite S2O3 2- only, without the need to completely oxidize S into SO3 2- and SO4 2- . The amount of oxidant required is significantly reduced, and the operating cost is low.

[0045] (5) Reduction of red mud, facilitating comprehensive utilization. The directionally generated magnetite covers the surface of hematite, significantly improving the grade and recovery rate of iron concentrate. This not only promotes the sales of iron concentrate, is conducive to the reduction of red mud, but also facilitates the subsequent comprehensive utilization of red mud.

[0046] (6) Easy to industrialize. Based on the existing Bayer process, only by adjusting the process parameters, the present invention can be embedded into the process flow without additional investment. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0048] Figure 1 is the Fe-S-H2O system diagram of the present invention diagram;

[0049] Figure 2 is the solution ion distribution diagram of the reaction between pyrite and sodium nitrate of the present invention;

[0050] Figure 3 is the XRD spectrum diagram of the slag sample after the reaction between pyrite and sodium nitrate of the present invention;

[0051] Figure 4It is the surface scanning electron microscope image of pyrite after passivation with sodium nitrate in the present invention; after adjusting the potential and high-temperature leaching of pyrite, the surface is densely covered with magnetite and a small amount of hematite, inhibiting the reaction of pyrite. Detailed implementation manners

[0052] To make the technical problems, technical solutions and advantages to be solved by the present invention clearer, the following will be described in detail with reference to the accompanying drawings and specific embodiments.

[0053] Unless otherwise defined, all professional terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention.

[0054] Unless otherwise specifically stated, various raw materials, reagents, instruments and equipment used in the present invention can be obtained through market purchase or can be prepared by existing methods.

[0055] In view of the existing problems, an embodiment of the present invention provides a method for directly leaching high-sulfur bauxite to produce alumina by regulating the redox potential, including the following steps:

[0056] S1: Prepare the raw ore pulp by mixing high-sulfur bauxite, calcium-containing compound and recycled mother liquor, add an appropriate amount of oxidant I to the recycled mother liquor, and perform pre-desilication under normal pressure to obtain the pre-desilicated slurry;

[0057] S2: Add oxidant II to the pre-desilicated slurry, leach at high temperature, and pyrite is directionally converted to obtain the leached slurry, and at the same time, calcium sulfide nepheline-type sodium silicate slag is generated;

[0058] S3: Stir and mix the leached slurry with the red mud washing liquid, dilute and desilicate under normal pressure to generate sulfur-containing sodalite-type sodium silicate slag, and obtain the desilicated slurry;

[0059] S4: Filter the desilicated slurry, wash the filter cake with hot water to obtain the red mud washing liquid and red mud, and recover iron concentrate from the red mud.

[0060] Preferably, in step S1, the high-sulfur bauxite has a sulfur content of less than 2.0%, and sulfur mainly exists in the form of pyrite.

[0061] Preferably, in step S1, the calcium-containing compound is lime, calcium aluminate hydrate or hydrogarnet, with a particle size of less than 10 μm, and the addition amount is calculated as CaO, which is 1% - 5% of the dry ore amount in the high-sulfur bauxite or the molar ratio of CaO / SiO2 is less than 0.5.

[0062] Preferably, in step S1, the oxidant I is at least one of hydrogen peroxide, sodium peroxide, and sodium persulfate, and the addition amount is based on S in the solution 2- converted to S2O3 2-Add 0 to 70% of the stoichiometric coefficient.

[0063] Preferably, in step S1, the pre-desilication temperature is 90 to 105 °C and the time is 3 to 10 h.

[0064] Preferably, in step S2, the oxidant II is at least one of sodium nitrate, potassium nitrate, and sodium nitrite, and the addition amount is controlled according to the weak reduction potential regulation principle to add at a potential between -0.5 and -1.3 V. The potential calculation method is that the sum of the potentials of S 2- , S2O3 2- , SO3 2- , Fe 2+ , Fe 3+ and the oxidant is ∑xiΦ; or add according to the contents of reducing pyrite, siderite, oxidizing hematite, and goethite, and add less than 70% of the stoichiometric coefficient according to the FeS2 oxidation reaction to generate Fe3O4 and S2O3 2- . More preferably, add 20 to 70% of the stoichiometric coefficient of FeS2 oxidation reaction to generate Fe3O4 and S2O3 2- .

[0065] Preferably, in step S2, when the leaching temperature is 250 to 280 °C, the pyrite leaching rate is less than 50%.

[0066] Preferably, in step S2, the proportion of high-valence sulfur ions (S2O3 2- , SO3 2- and SO4 2- ) in the leaching slurry is greater than 80%, and the S 2- concentration in the refined liquid is less than 0.25 g / L.

[0067] Preferably, in step S3, the dilution desilication temperature is 90 to 110 °C, the time is 3 to 10 h, and the S 2- concentration in the solution is less than 0.25 g / L.

[0068] Preferably, in step S4, the red mud contains unreacted pyrite, directionally transformed magnetite and hematite, and the sulfur content is greater than 0.4%.

[0069] The following is illustrated by specific examples.

[0070] Example 1

[0071] This example provides a method for regulating the redox potential to inhibit the reaction of pyrite and the directional transformation of iron and sulfur in the dissolved pyrite.

[0072] The method of this example includes the following steps:

[0073] S1. Prepare 0.75 g of pyrite (49.47% S, 42.95% Fe) and 100 mL of recycled mother liquor (Na2O 230.0 g / L, Al2O3 128.5 g / L, α k 2.95) into the original ore pulp, and obtain the pre-desilication slurry after pre-desilication at 93 °C for 4 h.

[0074] S2. Add 0.1 g of sodium nitrate (23% of the theoretical amount for the directional conversion of FeS2 to S2O3 2- , with a potential of -0.61 V, as Figure 2 shown) to the pre-desilication slurry, and carry out high-temperature digestion at 260 °C for 40 min to obtain the digested slurry.

[0075] S3. Stir and mix the digested slurry with the red mud washing liquid at 100 °C for dilution desilication for 3 h to obtain the desilicated slurry. The S 2- concentration in the desilicated slurry is 0.06 g / L, the S2O3 2- concentration is 0.28 g / L, the SO4 2- concentration is 0.10 g / L, the SO3 2- concentration is 0.08 g / L, and the Fe2O3 concentration is 0.024 g / L. The sulfur digestion rate is about 10%.

[0076] S4. Filter the desilicated slurry and wash the filter cake (red mud) with hot water; the S content in the red mud is 47.63%; the main components in the red mud are pyrite (93.6%) and a small amount of magnetite (6.4%); the reaction rate of pyrite is as Figure 3 shown.

[0077] Figure 2 is the solution ion distribution diagram of the reaction between pyrite and sodium nitrate. Pyrite undergoes a very complex redox reaction during digestion. After adding different amounts of sodium nitrate, the distributions of S 2- , S2O3 2- , SO3 2- and SO4 2- in the solution will change significantly. By adding an appropriate amount of sodium nitrate and regulating the potential to -0.5 to -1.3 V, not only can the reaction of pyrite be significantly inhibited, but also the concentrations of S 2- , S2O3 2- , SO3 2- , and SO4 2- in the solution can be reduced.

[0078] Figure 3It is the XRD pattern of the slag sample after the reaction of pyrite with sodium nitrate. Specifically, it shows the distribution of reaction products after adjusting the potential to -0.53V (0.5g / L), -0.61V (1g / L), -0.43V (3g / L), and -0.23V (5g / L). When 0.5g / L and 1g / L of sodium nitrate are added, a large amount of unreacted pyrite and magnetite are contained in the reaction products; while when an excessive amount of sodium nitrate (>3g / L) is added, the main reaction product is hematite.

[0079] Example 2

[0080] This example provides a method for directly dissolving high-sulfur bauxite to produce alumina by regulating the redox potential.

[0081] The method of this example includes the following steps:

[0082] S1. According to the batch molecular ratio of 1.42, 28.41g of high-sulfur bauxite (Al2O3 56.74%, SiO2 10.89%, Fe2O3 10.61%, S 0.53%, containing 10.6% hematite), 100mL of recycled mother liquor (Na2O 230.0g / L, Al2O3 128.5g / L, α k 2.95), and 1.16g of lime (4.1% of dry ore, CaO / SiO2 = 0.4, lime milk particle size d50 7.9μm) are formulated into the original ore pulp, and after pre-desilication at 100°C for 6h, the pre-desilicated slurry is obtained.

[0083] S2. 0.034g of sodium nitrate (20% of the theoretical amount for the directional conversion of FeS2 to S2O3 2- , with a potential of -0.78V) is added to the pre-desilicated slurry, and high-temperature dissolution is carried out at 260°C for 60min to obtain the dissolved slurry.

[0084] S3. The dissolved slurry and the red mud washing liquid are stirred and mixed at 102°C for dilution desilication, and the desilication time is 3h to obtain the desilicated slurry. The S 2- concentration in the desilicated slurry is 0.10g / L, the S2O3 2- concentration is 0.37g / L, the SO4 2- concentration is 0.13g / L, the Fe2O3 concentration is 0.020g / L, and the SiO2 concentration is 0.70g / L; the sulfur dissolution rate of pyrite is about 27%.

[0085] S4. The desilicated slurry is filtered, and the filter cake (red mud) is washed with hot water; the alumina dissolution rate is 75.47%, and the S content in the red mud is 1.24%; the red mud has magnetite phase, pyrite phase, and hematite phase, as well as cancrinite-type sodium silicate slag; under a magnetic field of 0.6 - 0.8T, the iron concentrate grade TFe is 53.5%, and the iron recovery rate is 54.8%.

[0086] Example 3

[0087] This embodiment provides a method for directly dissolving high-sulfur bauxite to produce alumina by regulating the redox potential.

[0088] The method of this embodiment includes the following steps:

[0089] S1, in the circulating mother liquor (Na2O 230.0g / L, Al2O3 128.5g / L, α k 2.95, S 2- 0.1g / L) was added with 0.35mL of 30% H2O2 (converted into S2O3 2- Then, according to the molecular ratio of 1.42, 28.41g of high-sulfur bauxite (Al2O3 56.74%, SiO2 10.89%, Fe2O3 10.61%, S 0.53%, containing 10.2% hematite and 1.5% siderite), 100mL of circulating mother liquor, and 1.16g of lime (3.5% of dry ore CaO / SiO2=0.35, lime milk particle size d50 7.9μm) were prepared into raw ore slurry, and pre-desiliconized at 105℃ for 3h to obtain pre-desiliconized slurry.

[0090] S2, 0.02g sodium nitrate and 0.01g sodium nitrite (potential of -0.73V) were added to the pre-desiliconization slurry, and high-temperature dissolution was carried out at 268°C for 60 minutes to obtain a dissolution slurry.

[0091] S3, the dissolved slurry and the red mud washing liquid were stirred and mixed at 102 ° C for dilution and desiliconization. The desiliconization time was 5 hours to obtain a desiliconized slurry. The S in the desiliconized slurry was 2- The concentration is 0.11g / L, S2O3 2- The concentration is 0.39g / L, SO4 2- The concentration is 0.18g / L, the Fe2O3 concentration is 0.018g / L, and the SiO2 concentration is 0.67g / L; the sulfur dissolution rate in pyrite is about 20%.

[0092] S4. Filter the desiliconized slurry and wash the filter cake (red mud) with hot water; the alumina dissolution rate is 80.63%, and the S content of the red mud is 1.57%; there are magnetite, hematite and cancrinite-type sodium silicate slag in the red mud; under a magnetic field of 0.6-0.8T, the iron concentrate grade TFe is 55.2%, and the iron recovery rate is 57.1%.

[0093] Example 4

[0094] This embodiment provides a method for directly dissolving high-sulfur bauxite to produce alumina by regulating the redox potential.

[0095] The method of this embodiment includes the following steps:

[0096] S1. According to the ingredient molecular ratio of 1.42, 28.41 g of high-sulfur bauxite (Al2O3 56.74%, SiO2 10.89%, Fe2O3 10.61%, S 0.53%), 100 mL of recycled mother liquor (Na2O 230.0 g / L, Al2O3 128.5 g / L, S2O3 2- 0.3 g / L α k 2.95), and 2.61 g of calcium aluminate hydrate (3CaO·Al2O3·6H2O) (4.0% of dry ore, CaO / SiO2 ratio is 0.4, particle size of calcium aluminate hydrate d50 4.8 μm) are formulated into the original ore pulp, and pre-desilication is carried out at 95 °C for 7 h to obtain the pre-desilicated slurry.

[0097] S2. 0.05 g of sodium nitrate (equivalent to 30% of the theoretical amount, potential is -0.81 V) is added to the pre-desilicated slurry, and high-temperature digestion is carried out at 263 °C for 60 min to obtain the digested slurry.

[0098] S3. The digested slurry and the red mud washing liquid are stirred and mixed at 103 °C for dilution desilication, and the desilication time is 6 h to obtain the desilicated slurry. The S 2- concentration in the desilicated slurry is 0.10 g / L, the S2O3 2- concentration is 0.37 g / L, the SO4 2- concentration is 0.12 g / L, and the Fe2O3 concentration is 0.022 g / L; the dissolution rate of pyrite sulfur is about 25%.

[0099] S4. The desilicated slurry is filtered, and the filter cake (red mud) is washed with hot water; the alumina dissolution rate is 80.79%, and the S content in the red mud is 1.25%; the red mud contains magnetite, hematite and cancrinite-type sodium silicate slag.

[0100] Example 5

[0101] This embodiment provides a method for directly dissolving high-sulfur bauxite to produce alumina by regulating the redox potential.

[0102] The method of this embodiment includes the following steps:

[0103] S1. According to the ingredient molecular ratio of 1.42, 26.88 g of high-sulfur bauxite (Al2O3 56.74%, SiO2 10.89%, Fe2O3 10.61%, S 0.53%), 100 mL of recycled mother liquor (Na2O 230.0 g / L, Al2O3 128.5 g / L, α k 2.95, S 2-Prepare the original ore pulp by mixing 28.41 g of high-sulfur bauxite (Al2O3 56.74%, SiO2 10.89%, Fe2O3 11.12%, S 1.63%, containing 3% siderite), 100 mL of recycled mother liquor (Na2O 230.0 g / L, Al2O3 128.5 g / L, α 2.95), and 1.51 g of hydrogarnet (3CaO·Al2O3·0.6SiO2·4.8H2O) (5.0% of dry ore, CaO / SiO2 = 0.45, hydrogarnet particle size d50 5.5 μm) according to the ingredient molar ratio of 1.42. After pre-desilication at 98 °C for 4 h, obtain the pre-desilicated slurry. Then add 0.5 mL of 30% H2O2 (35% of the theoretical amount) to the pre-desilicated slurry and carry out pre-desilication at 96 °C for 5 h to obtain the pre-desilicated slurry.

[0104] S2. Add 0.03 g of sodium nitrite (with a potential of -0.85 V) to the pre-desilicated slurry and carry out high-temperature digestion at 263 °C for 55 min to obtain the digested slurry.

[0105] S3. Mix the digested slurry and the red mud washing liquid with stirring at 100 °C for dilution and desilication for 4 h to obtain the desilicated slurry. The S concentration in the desilicated slurry is 0.09 g / L, the S2O3 concentration is 0.29 g / L, the SO4 concentration is 0.14 g / L, and the Fe2O3 concentration is 0.016 g / L; the sulfur dissolution rate of pyrite is about 24%. 2- concentration is 0.09 g / L, S2O3 2- concentration is 0.29 g / L, SO4 2- concentration is 0.14 g / L, and the Fe2O3 concentration is 0.016 g / L; the sulfur dissolution rate of pyrite is about 24%.

[0106] S4. Filter the desilicated slurry and wash the filter cake (red mud) with hot water; the alumina digestion rate is 81.29%, and the S content in the red mud is 2.48%; the red mud contains magnetite, hematite, and sodium silicate slag containing sulfur; under a magnetic field of 0.6 - 0.8 T, the grade of iron concentrate TFe is 53.2%, and the iron recovery rate is 50.1%.

[0107] Example 6

[0108] This example provides a method for directly digesting high-sulfur bauxite to produce alumina by regulating the redox potential.

[0109] The method of this example includes the following steps:

[0110] S1. According to the ingredient molar ratio of 1.42, mix 28.41 g of high-sulfur bauxite (Al2O3 56.74%, SiO2 10.89%, Fe2O3 11.12%, S 1.63%, containing 3% siderite), 100 mL of recycled mother liquor (Na2O 230.0 g / L, Al2O3 128.5 g / L, α k 2.95), and 1.51 g of hydrogarnet (3CaO·Al2O3·0.6SiO2·4.8H2O) (5.0% of dry ore, CaO / SiO2 = 0.45, hydrogarnet particle size d50 5.5 μm) to prepare the original ore pulp. After pre-desilication at 98 °C for 4 h, obtain the pre-desilicated slurry.

[0111] S2. Add 0.085 g of sodium nitrate (50% of the theoretical amount, with a potential of -0.67 V) to the pre-desilicated slurry and carry out high-temperature digestion at 273 °C for 45 min to obtain the digested slurry.

[0112] S3. The digestion slurry and the red mud washing liquid are stirred and mixed at 103 °C for dilution and desilication for 3 h to obtain a desilicated slurry. The S content in the desilicated slurry is 2- 0.15 g / L, the S2O3 content is 2- 0.57 g / L, the SO4 content is 2- 0.26 g / L, and the Fe2O3 content is 0.021 g / L; the sulfur dissolution rate in pyrite is about 15%.

[0113] S4. The desilicated slurry is filtered, and the filter cake (red mud) is washed with hot water; the alumina digestion rate is 80.15%, and the S content in the red mud is 2.98%; there are obvious magnetite mineral phases and cancrinite-type sodium silicate slag phases in the red mud, and there is also hematite.

[0114] Example 7

[0115] This example provides a method for directly digesting high-sulfur bauxite to produce alumina by regulating the redox potential.

[0116] The method of this example includes the following steps:

[0117] S1. First, 0.04 g of sodium persulfate is added to 100 mL of circulating mother liquor (Na2O 200.0 g / L, Al2O3 111.5 g / L, α k 2.95, S 2- 0.14 g / L), and the mixture is stirred at 90 °C for 2 h; then, according to the ingredient molar ratio of 1.42, 24.67 g of high-sulfur bauxite (Al2O3 56.74%, SiO2 10.89%, Fe2O3 10.61%, S 0.53%) and 0.74 g of lime (3% of the dry ore, CaO / SiO2 = 0.29) are added to the above circulating mother liquor to prepare a raw ore slurry, which is pre-desilicated at 95 °C for 4 h to obtain a pre-desilicated slurry.

[0118] S2. 0.03 g of sodium nitrate and 0.02 g of potassium nitrate (potential -0.75 V) are added to the pre-desilicated slurry, and high-temperature digestion is carried out at 270 °C for 50 min to obtain a digestion slurry.

[0119] S3. The digestion slurry and the red mud washing liquid are stirred and mixed at 106 °C for dilution and desilication for 3 h to obtain a desilicated slurry. The S content in the desilicated slurry is 2- 0.14 g / L, the S2O3 content is 2- 0.27 g / L, the SO4 content is 2- 0.27 g / L, and the Fe2O3 content is 0.022 g / L; the sulfur dissolution rate in pyrite is about 14%.

[0120] S4. Filter the desilication slurry and wash the filter cake (red mud) with hot water; the alumina digestion rate is 80.88%, and the S content in the red mud is 2.01%; there are magnetite, hematite and cancrinite-type sodium silicate slag in the red mud.

[0121] Example 8

[0122] S1. According to the batching molecular ratio of 1.42, mix 24.67 g of high-sulfur bauxite (Al2O3 56.74%, SiO2 10.89%, Fe2O3 10.61%, S 0.53%, containing 10% hematite and 3.2% siderite), 100 mL of circulating mother liquor (Na2O 200.0 g / L, Al2O3 111.5 g / L, α k 2.95), and 1.76 g of hydrogarnet (equivalent to 3% of the ore in terms of CaO, CaO / SiO2 = 0.26, and the particle size of hydrogarnet d50 is 5.5 μm) to prepare the original ore pulp, and obtain the pre-desilication slurry after pre-desilication at 96 °C for 5 h.

[0123] S2. Add 0.03 g of the mixture of sodium nitrate and potassium nitrate (with a potential of -0.69 V) to the pre-desilication slurry, and carry out high-temperature digestion at 270 °C for 40 min to obtain the digestion slurry.

[0124] S3. Mix the digestion slurry and the red mud washing liquid at 95 °C with stirring for dilution desilication. The desilication time is 5 h to obtain the desilication slurry. The S 2- concentration in the desilication slurry is 0.16 g / L, the S2O3 2- concentration is 0.36 g / L, the SO4 2- concentration is 0.28 g / L, and the Fe2O3 concentration is 0.021 g / L; the sulfur digestion rate in pyrite is about 34%.

[0125] S4. Filter the desilication slurry and wash the filter cake (red mud) with hot water; the alumina digestion rate is 79.39%, and the S content in the red mud is 2.01%; there are magnetite, hematite and sulfur-containing sodium silicate slag in the red mud.

[0126] Comparative Example 1

[0127] A method for producing alumina from high-sulfur bauxite, comprising the following steps:

[0128] S1. According to the batching molecular ratio of 1.42, mix 28.41 g of high-silicon and high-sulfur bauxite (Al2O3 56.74%, SiO2 10.89%, Fe2O3 10.61%, S 0.53%), 100 mL of circulating mother liquor (Na2O 230.0 g / L, Al2O3 128.5 g / L, α k2.95), 2.88 g of lime (10.14% of the dry ore, CaO / SiO2 = 1.0) were formulated into the original ore pulp, and after pre-desilication at 95 °C for 6 h, the pre-desilicated pulp was obtained.

[0129] S2, 0.36 g of sodium nitrate (S 2- was oxidized to SO4 2- 110% of the theoretical amount, with a potential of -0.34 V) was added to the pre-desilicated pulp, and high-temperature digestion was carried out at 265 °C for 40 min to obtain the digested pulp.

[0130] S3, the digested pulp and the red mud washing liquid were stirred and mixed at 105 °C for dilution desilication, and the desilication time was 4 h to obtain the desilicated pulp. The S 2- concentration in the desilicated pulp was 0.27 g / L, the S2O3 2- concentration was 0.32 g / L, the SO3 2- was 0.59 g / L, the SO4 2- concentration was 1.18 g / L, and the Fe2O3 concentration was 0.021 g / L; the sulfur dissolution rate in pyrite was about 77%.

[0131] S4, the desilicated pulp was filtered, and the filter cake (red mud) was washed with hot water. The S content in the red mud was 0.08%, and there was no magnetite phase in the red mud, mainly hematite phase; under a magnetic field of 0.6 - 0.8 T, the grade of the iron concentrate TFe was 45.89%, and the iron recovery rate was 30.02%.

[0132] The above is the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art of this technology, without departing from the principle described in the present invention, several improvements and retouches can be made, and these improvements and retouches should also be regarded as the protection scope of the present invention.

Claims

1. A method for producing alumina by directly dissolving high-sulfur bauxite by regulating redox potential, characterized in that: The steps include: S1: preparing raw ore slurry with high-sulfur bauxite, calcium-containing compounds and circulating mother liquor, adding an appropriate amount of oxidant 1 to the circulating mother liquor, and performing pre-desiliconization under normal pressure to obtain pre-desiliconization slurry; S2: adding oxidant 2 to the pre-desiliconization slurry, dissolving at high temperature, directionally converting pyrite to obtain dissolution slurry, and simultaneously generating sulfur-containing cancrinite-type sodium silicate slag; S3: stirring and mixing the leached slurry and the red mud washing liquid, diluting and desiliconizing under normal pressure to generate sulfur-containing sodalite-type sodium silicate slag, and obtaining desiliconized slurry; S4: filtering the desiliconized slurry, washing the filter cake with hot water to obtain red mud washing liquid and red mud, and recovering iron concentrate from the red mud.

2. The method for producing alumina by directly dissolving high-sulfur bauxite by regulating redox potential according to claim 1, characterized in that: In step S1, the high-sulfur bauxite has a sulfur content of less than 2.0%, and the sulfur mainly exists in the form of pyrite.

3. The method for producing alumina by directly dissolving high-sulfur bauxite by regulating redox potential according to claim 2, characterized in that: In step S1, the calcium-containing compound is lime, hydrated calcium aluminate or hydrated garnet, with a particle size of less than 10 μm, and the added amount is 1% to 5% of the dry ore amount in the high-sulfur bauxite in terms of CaO or a CaO / SiO2 molar ratio of less than 0.

5.

4. The method for producing alumina by directly dissolving high-sulfur bauxite by regulating redox potential according to claim 1, characterized in that: In step S1, the oxidant 1 is at least one of hydrogen peroxide, sodium peroxide, and sodium persulfate, and the amount added is 2- Converted to S2O3 2- 0 to 70% of the theoretical amount.

5. The method for producing alumina by directly dissolving high-sulfur bauxite by regulating redox potential according to claim 1, characterized in that: The pre-desiliconization temperature is 90-105°C and the time is 3-10 hours.

6. The method for producing alumina by directly dissolving high-sulfur bauxite by regulating redox potential according to claim 1, characterized in that: In step S2, the second oxidant is at least one of sodium nitrate, potassium nitrate and sodium nitrite, and the amount added is controlled to be between -0.5 and -1.3 V according to the weak reduction potential regulation principle. The potential calculation method is: 2- 、S2O3 2- 、SO3 2- , Fe 2+ , Fe 3+ The potential of the oxidant is summed to ∑xiφ; or depending on the content of reduced pyrite and siderite and oxidized hematite and goethite, FeS2 is oxidized to generate Fe3O4 and S2O3 2- Less than 70% of the stoichiometric amount was added.

7. The method for producing alumina by directly dissolving high-sulfur bauxite by regulating redox potential according to claim 1, characterized in that: In step S2, when the dissolution temperature is 250-280°C, the pyrite dissolution rate is less than 50%.

8. The method for producing alumina by directly dissolving high-sulfur bauxite by regulating redox potential according to claim 1, characterized in that: In step S3, the dilution desiliconization temperature is 90-110°C, the time is 3-10 hours, and the S in the solution is 2- The concentration is less than 0.25g / L.

9. The method for producing alumina by directly dissolving high-sulfur bauxite by regulating redox potential according to claim 1, characterized in that: In step S4, the red mud contains pyrite, magnetite and hematite, and the sulfur content is greater than 0.4%.

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