Method for removing inorganic salt in aluminum oxide mother liquor based on gradient crystallization and graphene adsorption

Abstract

The invention discloses a method for removing inorganic salt in aluminum oxide mother liquor based on gradient crystallization and graphene adsorption, and relates to the technical field of environment-friendly water treatment. The method comprises the following steps: heating the aluminum oxide mother liquor to 90 DEG C, and evaporating and concentrating the mother liquor; carrying out gradient cooling on the concentrated mother liquor for crystallization to obtain primary aluminum oxide mother liquor; the gradient cooling mode comprises the following steps: cooling to 45 DEG C in advance, standing for 5 days, continuously cooling to room temperature, and standing for 10 days; inorganic salt separated out by crystallization is separated and removed in the two gradient cooling processes; and adding graphene into the primary aluminum oxide mother liquor, and stirring and adsorbing at room temperature to obtain the purified target aluminum oxide mother liquor. The method comprises the following steps: firstly evaporating and concentrating the aluminum oxide mother liquor, then cooling the mother liquor to room temperature by a gradient cooling method, and then adsorbing by adopting graphene with the mass ratio of 0.1% to reduce scale generation; according to the combined process, the salt content in the mother liquor is effectively reduced, the scaling rate is slowed down, and the service life of instruments and equipment is prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of environmentally friendly water treatment, and in particular to a method for removing inorganic salts from an alumina mother liquor based on gradient crystallization and graphene adsorption. Background Art

[0002] An alumina refinery is an industrial facility dedicated to the production of alumina. Its core mission is to extract alumina from aluminum-containing raw materials such as bauxite. Alumina is a vital industrial raw material, serving not only as a key intermediate in the production of metallic aluminum but also as a widely used material in a variety of fields, including refractories, ceramics, electronics, and chemicals.

[0003] Alumina mother liquor is an intermediate product in the alumina production process. Alumina production is primarily based on the Bayer process, whose core technology relies on recyclable alumina mother liquor (sodium hydroxide solution) to dissolve alumina from bauxite.

[0004] However, after multiple cycles, alumina mother liquor will accumulate a large amount of inorganic salt and organic scale, which seriously affects the operating efficiency of the evaporator. At present, there is no complete solution for the major domestic alumina plants, and they can only temporarily solve the problem through simple methods such as boiling in water.

[0005] In this regard, the inventors believe that how to effectively remove inorganic salt impurities in alumina mother liquor, slow down the scaling rate in the evaporator, and increase the service life of instruments and equipment is a technical problem that generally needs to be solved by technicians in this field.

[0006] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art. Summary of the Invention

[0007] In response to the above technical problems, an embodiment of the present invention provides a method for removing inorganic salts from alumina mother liquor based on gradient crystallization and graphene adsorption to solve the problems raised in the above background technology.

[0008] 1. To address the problem of inorganic salt scaling caused by the recycling of alumina mother liquor, the present invention proposes a composite treatment scheme of "gradient crystallization pre-removal of impurities + graphene deep adsorption" by combining the solubility characteristics of inorganic salts with the adsorption characteristics of materials. The core ideas are as follows: (1) Theoretical basis: Utilizing the temperature dependence of the solubility of inorganic salts: Alumina mother liquor mainly includes inorganic salts such as sodium vanadate, sodium phosphate, and sodium fluoride, with sodium salt being the main one; these inorganic salts have relatively large solubility in sodium aluminate solution, but when these inorganic salts exist at the same time, their solubility is much smaller than when each salt exists alone.

[0009] The solubility of a single inorganic salt (such as sodium vanadate, sodium phosphate, sodium fluoride, etc.) in sodium aluminate solution increases with increasing temperature and is easily precipitated at low temperatures; when multiple inorganic salts coexist, the solubility is significantly lower than when they exist alone (synergistic inhibition effect), providing the possibility for staged impurity removal by gradient cooling crystallization.

[0010] (II) The first stage: evaporation and concentration at 90°C; the salt concentration in the mother liquor is increased by evaporation to approach or exceed the solubility threshold at low temperature: this stage is mainly based on evaporation, the temperature is relatively high, the solubility of inorganic salts is large, and usually no obvious crystallization is produced, which only creates supersaturation conditions for subsequent cooling and crystallization.

[0011] (III) The second stage: Gradual cooling to 45°C and standing for 5 days; 45°C is close to the solubility inflection point of most sodium salts. At this temperature, fluoride and phosphate are precipitated first due to their lower solubility, while sodium vanadate and the like may not be precipitated in large quantities due to their relatively high solubility.

[0012] (IV) The third stage: continue to cool to room temperature and let it stand for 10 days; during this stage, inorganic salts such as sodium vanadate are mainly precipitated.

[0013] (V) The fourth stage: graphene adsorption (room temperature); graphene has a high porosity and a high specific surface area, and can adsorb invisible impurities such as suspended matter and particles in the water, as well as salt-free molecules in the water; with the help of graphene, impurities in the water are effectively removed through physical adsorption, thereby achieving the purpose of desalting the mother liquor of alumina production and reducing scaling time.

[0014] 2. A method for removing inorganic salts from alumina mother liquor based on gradient crystallization and graphene adsorption, comprising the following steps: The alumina mother liquor is heated to 90° C. to evaporate and concentrate the mother liquor; The concentrated mother liquor is subjected to a gradient cooling process for crystallization to obtain a primary alumina mother liquor; the gradient cooling process includes: Pre-cool to 45°C and let stand for 5 days, then continue to cool to room temperature and let stand for 10 days; The inorganic salts precipitated by crystallization are separated and removed during the two gradient cooling processes; Graphene is added to the primary alumina mother liquor, and the mixture is stirred and adsorbed at room temperature to obtain a purified target alumina mother liquor.

[0015] Preferably, the alumina mother liquor is heated to 90° C. and maintained at this temperature for 30 minutes.

[0016] Preferably, during the process of gradually cooling the alumina mother liquor to 45° C. and cooling it to room temperature, the cooling method is natural cooling.

[0017] Preferably, the amount of graphene added to the primary alumina mother liquor satisfies: the mass ratio of graphene to primary alumina mother liquor is 0.01-1:100.

[0018] Preferably, the amount of graphene added to the primary alumina mother liquor satisfies: the mass ratio of graphene to primary alumina mother liquor is 0.01:100.

[0019] Preferably, the adsorption time of graphene in the primary alumina mother liquor is 0.5-1.5h.

[0020] Preferably, the adsorption time of graphene in the primary alumina mother liquor is 0.5h.

[0021] Preferably, the room temperature is 20°C; the room temperature condition in this patent is 20°C.

[0022] A method for removing inorganic salts from an alumina mother liquor based on gradient crystallization and graphene adsorption provided in an embodiment of the present invention has the following beneficial effects: the present invention first evaporates and concentrates the alumina mother liquor, then cools the mother liquor to room temperature by a gradient cooling method, and then uses graphene with a mass ratio of 0.1% to desorb and reduce scaling; this combined process effectively reduces the salt content in the mother liquor, slows down the scaling rate, and increases the service life of the instrument and equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The figure is a schematic flow chart of the method for removing inorganic salts from alumina mother liquor in the present invention. DETAILED DESCRIPTION

[0024] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making any creative efforts shall fall within the scope of protection of the present invention.

[0025] In response to the above technical problems, an embodiment of the present invention provides a method for removing inorganic salts from alumina mother liquor based on gradient crystallization and graphene adsorption to solve the problems raised in the above background technology.

[0026] Example 1: Gradient cooling crystallization process optimization test Conductivity unit (us / cm); the conductivity of the mother liquor is tested by a conductivity meter. The lower the conductivity, the lower the inorganic salt content and the better the gradient crystallization effect.

[0027] Mother solution 1: 131.7 μs / cm, pH: 12.99; Mother solution 2: 131.3 μs / cm, pH: 12.97; There are 12 cases in total for gradient crystallization. Six samples of mother liquor 1 and mother liquor 2 were taken, each with 150 ml. The samples used in the following cases 1-6 are mother liquor 1; the samples used in cases 7-12 are mother liquor 2.

[0028] In case 1, 200 ml of alumina mother liquor was added to a 250 mL round-bottom flask, heated to 90°C for 30 minutes, then naturally cooled to 25°C and allowed to stand for 5 days. The conductivity was 121.9. After naturally cooling to room temperature and standing for 10 days, the conductivity was 113.8.

[0029] In case 2, 200 ml of alumina mother liquor was added to a 250 mL round-bottom flask, heated to 90°C for 30 minutes, then naturally cooled to 25°C and allowed to stand for 5 days. The conductivity was 119.4. Then, the conductivity was 115.5 after naturally cooling to room temperature and standing for 10 days.

[0030] In case 3, 200 ml of alumina mother liquor was added to a 250 mL round-bottom flask, heated to 90°C for 30 minutes, then naturally cooled to 35°C and allowed to stand for 5 days. The conductivity was 124.3. Then, the conductivity was 109.5 after naturally cooling to room temperature and standing for 10 days.

[0031] In case 4, 200 ml of alumina mother liquor was added to a 250 mL round-bottom flask, heated to 90°C for 30 minutes, then naturally cooled to 35°C and allowed to stand for 5 days. The conductivity was 126.5. Then, the conductivity was 114.1 after naturally cooling to room temperature and standing for 10 days.

[0032] In case 5, 200 ml of alumina mother liquor was added to a 250 mL round-bottom flask, heated to 90°C for 30 minutes, then naturally cooled to 45°C and allowed to stand for 5 days. The conductivity was 127.2. After naturally cooling to room temperature and standing for 10 days, the conductivity was 109.3.

[0033] In case 6, 200 ml of alumina mother liquor was added to a 250 mL round-bottom flask, heated to 90°C for 30 minutes, then naturally cooled to 45°C and allowed to stand for 5 days. The conductivity was 127.3. Then, the conductivity was 108.3 after naturally cooling to room temperature and standing for 10 days.

[0034] In case 7, 200 ml of alumina mother liquor was added to a 250 mL round-bottom flask, heated to 90°C for 30 minutes, then naturally cooled to 25°C and allowed to stand for 5 days. The conductivity was 126.3. Then, the conductivity was 108.9 after naturally cooling to room temperature and standing for 10 days.

[0035] In Case 8, 200 ml of alumina mother liquor was added to a 250 mL round-bottom flask, heated to 90°C for 30 minutes, then naturally cooled to 25°C and allowed to stand for 5 days. The conductivity was 127.4. Then, the conductivity was 111.1 after naturally cooling to room temperature and standing for 10 days.

[0036] In Case 9, 200 ml of alumina mother liquor was added to a 250 mL round-bottom flask, heated to 90°C for 30 minutes, then naturally cooled to 35°C and allowed to stand for 5 days. The conductivity was 129.9, and then naturally cooled to room temperature and allowed to stand for 10 days. The conductivity was 111.8.

[0037] In case 10, 200 ml of alumina mother liquor was added to a 250 mL round-bottom flask, heated to 90°C for 30 minutes, then naturally cooled to 35°C and allowed to stand for 5 days. The conductivity was 128.9. After naturally cooling to room temperature and standing for 10 days, the conductivity was 106.4.

[0038] In case 11, 200 ml of alumina mother liquor was added to a 250 mL round-bottom flask, heated to 90 ° C for 30 minutes, then naturally cooled to 45 ° C and allowed to stand for 5 days. The conductivity was 130.0. Then, it was naturally cooled to room temperature and allowed to stand for 10 days. The conductivity was 107.6.

[0039] In Case 12, 200 ml of alumina mother liquor was added to a 250 mL round-bottom flask, heated to 90°C for 30 minutes, then naturally cooled to 45°C and allowed to stand for 5 days. The conductivity was 130.1. Then, the conductivity was 105.9 after naturally cooling to room temperature and standing for 10 days.

[0040] In gradient crystallization process optimization experiments, different cooling gradient conditions were explored with the core goal of reducing the mother liquor's electrical conductivity (indicating the effectiveness of inorganic salt removal). The 12 cases described above systematically examined the desalination effect of gradient crystallization on alumina mother liquor by controlling variables such as the mother liquor's initial state, concentration temperature, staged cooling temperatures, and rest time.

[0041] The above results show that Case 12 exhibits the optimal process conditions: after heating 200ml of mother liquor (mother liquor 2, initial conductivity 131.3μs / cm) to 90°C and concentrating for 30 minutes, it was naturally cooled to 45°C and allowed to stand for 5 days, and then further cooled to room temperature and allowed to stand for 10 days. The final conductivity dropped to 105.9μs / cm, which is significantly better than other cases.

[0042] Under the process optimization conditions of Case 12, the characteristic that the solubility of inorganic salts decreases with decreasing temperature was utilized to achieve efficient step-by-step crystallization and precipitation of salts, minimizing the residual scale-causing ions in the mother liquor. This laid a good foundation for subsequent deep desalination by graphene adsorption and verified the significant advantages of the gradient crystallization scheme with 45°C as the intermediate cooling node combined with room temperature standing in terms of desalination efficiency and energy consumption balance.

[0043] Example 2: Graphene adsorption temperature comparison test In the temperature comparison experiment, three experimental groups were set up at 20°C (room temperature), 30°C, and 45°C. Each temperature group was subjected to three time points: 0.5 hours, 1 hour, and 1.5 hours. The mother liquor after gradient crystallization in Case 12 was used, with an initial conductivity of 105.9. The graphene addition rate in each experimental group was 1% of the mother liquor mass. The experimental results are shown in Table 1 below.

[0044] Table 1 In a comparative graphene adsorption temperature experiment, focusing on exploring the impact of temperature on the desalination performance of alumina mother liquor, three experimental temperature groups were set up: 20°C, 30°C, and 45°C. The mother liquor with a conductivity of 105.9 μs / cm after gradient crystallization, as described in Case 12, was used. The graphene addition rate was uniformly set at 1% of the mother liquor mass. Data was collected at 0.5 hours, 1 hour, and 1.5 hours. The results showed that the 20°C experimental group exhibited the best adsorption performance.

[0045] In the 20°C experimental group, the conductivity of the mother liquor after graphene adsorption remained essentially stable at 0.5, 1, and 1.5 hours, and was significantly higher than that of the other temperature groups. This experiment confirmed that a low temperature environment (20°C) is more conducive to the physical adsorption properties of graphene, effectively reducing the salt content of the mother liquor and providing key temperature parameter support for optimizing the alumina mother liquor purification process. For the 30°C and 45°C experimental groups, after heating and adsorption, the temperature was lowered to 20°C for conductivity testing.

[0046] Example 3: Graphene Dosage Room Temperature Adsorption Test For the room-temperature adsorption test of graphene dosage, the mother liquor from Case 12, after gradient crystallization, was selected, with an initial conductivity of 105.9 μs / cm. The experimental temperature was fixed at room temperature, with uniform ambient temperature conditions. Three experimental groups with different graphene addition amounts were set: 0.1%, 0.5%, and 1% of the mother liquor mass. During the adsorption process, three time points were set uniformly: 0.5 hour, 1 hour, and 1.5 hours. The mother liquor was sampled at each time point and its conductivity measured. The experimental results are shown in Table 2 below.

[0047] Table 2 In a room-temperature adsorption test using graphene dosage, a mother liquor with a conductivity of 105.9 μs / cm after gradient crystallization was used as the test sample. Three graphene dosage gradients (0.1%, 0.5%, and 1%) were set to systematically study the effect of different addition ratios on desalination. The results showed that the 0.1% dosage group exhibited the best overall performance.

[0048] In summary, multiple alumina mother liquors were preheated to 90°C and then cooled to room temperature by different methods. The inorganic salts in the mother liquors were filtered out in batches to obtain a mother liquor with a minimum conductivity of 105.9 μS / cm. Graphene was then used for adsorption studies at different temperatures. Finally, different amounts of graphene were used for adsorption studies at room temperature to obtain an alumina mother liquor with a conductivity of 99.2 μS / cm.

[0049] The above experiments demonstrate that the present invention achieves the best results in reducing scaling by using a gradient cooling method: first evaporating and concentrating the alumina mother liquor, cooling it to 45°C, then cooling it to 20°C (room temperature), and then adding 1% graphene for desorption. This combined process effectively reduces the salt content in the mother liquor, slows scaling, and extends the service life of equipment.

[0050] The embodiments described above are merely descriptions of preferred implementations of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should fall within the scope of protection determined by the claims of the present invention.

Claims

1. A method for removing inorganic salts from alumina mother liquor based on gradient crystallization and graphene adsorption, characterized in that: The following steps are involved: The alumina mother liquor is heated to 90° C. to evaporate and concentrate the mother liquor; The concentrated mother liquor is subjected to gradient cooling for crystallization to obtain a primary alumina mother liquor; The gradient cooling method includes: pre-cooling to 45°C and standing for 5 days, then continuing to cool to room temperature and standing for 10 days; The inorganic salts precipitated by crystallization are separated and removed during the two gradient cooling processes; Graphene is added to the primary alumina mother liquor, and the mixture is stirred and adsorbed at room temperature to obtain a purified target alumina mother liquor.

2. The method for removing inorganic salts from alumina mother liquor based on gradient crystallization and graphene adsorption according to claim 1, wherein: The alumina mother liquor was heated to 90°C and maintained for 30 minutes.

3. The method for removing inorganic salts from alumina mother liquor based on gradient crystallization and graphene adsorption according to claim 1, wherein: The cooling method during the gradient cooling of the alumina mother liquor to 45°C and to room temperature was natural cooling.

4. The method for removing inorganic salts from alumina mother liquor based on gradient crystallization and graphene adsorption according to claim 1, wherein: The amount of graphene added to the primary alumina mother liquor satisfies: the mass ratio of graphene to the primary alumina mother liquor is 0.01-1:

100.

5. The method for removing inorganic salts from alumina mother liquor based on gradient crystallization and graphene adsorption according to claim 1, wherein: The amount of graphene added to the primary alumina mother liquor satisfies: the mass ratio of graphene to primary alumina mother liquor is 0.01:

100.

6. The method for removing inorganic salts from alumina mother liquor based on gradient crystallization and graphene adsorption according to claim 1, characterized in that: The adsorption time of graphene in the primary alumina mother liquor is 0.5-1.5h.

7. The method for removing inorganic salts from alumina mother liquor based on gradient crystallization and graphene adsorption according to claim 1, characterized in that: The adsorption time of graphene in the primary alumina mother liquor is 0.5h.

8. The method for removing inorganic salts from alumina mother liquor based on gradient crystallization and graphene adsorption according to claim 1, characterized in that: The room temperature is 20℃.

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