Treatment method of sulfate-containing high-sulfur bauxite flotation desulfurization circulating water

Abstract

The invention discloses a treatment method of sulfate-containing high-sulfur bauxite flotation desulfurization circulating water. The treatment method comprises the following steps: step 1, putting the circulating water into a container, and uniformly stirring; 2, calcium nitrate tetrahydrate is added into the stirred circulating water for a chemical precipitation reaction; 3, calcium sulfate is added into the circulating water subjected to the chemical precipitation reaction to serve as a crystallization seed crystal; 4, a flocculant aqueous solution is added into the solution obtained after the chemical precipitation reaction is completed, solid-liquid separation is carried out, obtained filter residues are mainly calcium sulfate, and obtained filtrate is circulating water. The treatment method is simple and convenient in process and high in separation efficiency, the removal rate of sulfate radicals exceeds 87%, circulating water can be recycled and is environmentally friendly, the problem that the content of sulfate in the circulating water is too high is effectively solved, and stable operation of a flotation desulfurization production line and the quality of aluminum concentrate are guaranteed.

Description

Technical Field

[0001] The present invention relates to the technical field of water treatment, and in particular to a method for treating sulfate-containing high-sulfur bauxite flotation desulfurization circulating water. Background Art

[0002] In the Bayer process for alumina production, high-sulfur bauxite cannot be directly used industrially due to its high sulfur content. It must undergo desulfurization before it can be used in the alumina production system. Currently, flotation desulfurization of high-sulfur bauxite typically utilizes a circulating water process, where the water is sequentially recycled through the following steps: grinding the high-sulfur bauxite, flotation desulfurization in flotation tanks, concentration and sedimentation in settling tanks, and filtration in filter presses. However, a serious problem has gradually emerged during this recycling process. As the number of cycles increases, sulfate levels in the water accumulate, reaching as high as 16,420 mg / l.

[0003] Such high sulfate concentrations have a significant negative impact on flotation desulfurization production. For one thing, it causes the sulfur content of aluminum concentrate produced by flotation desulfurization to be excessively high. Aluminum concentrate is a key raw material for alumina production. Excessive sulfur content in aluminum concentrate can severely impact the quality of subsequent alumina products, making it unsuitable for large-scale use in alumina production. To ensure product quality, companies are often forced to reduce production; in severe cases, even suspend operations. This not only results in significant financial losses but also severely impacts the continuity and stability of production.

[0004] To address the issue of excessively high sulfate concentrations in circulating water, existing technologies typically discharge circulating water directly into the alumina production system and then replace it with secondary water for flotation desulfurization production. This is done to dilute the sulfate concentration in the circulating water and ensure the normal operation of the flotation desulfurization production line. However, this method has significant limitations. The alumina production system itself has a limited capacity to accommodate sulfates and cannot accept large quantities of circulating water containing high sulfate concentrations. If discharged in large quantities, it will interfere with the normal operation of the alumina production system and lead to a series of production process problems, such as affecting the balance of chemical reactions and reducing product quality. Therefore, this simple replacement method cannot fundamentally solve the problem of excessive sulfate in circulating water, nor can it meet the needs of enterprises for stable production.

[0005] In the water treatment sector, the main chemical treatment methods for sulfate in water include the lime-aluminum salt method and the barium salt precipitation method. When treating circulating water with the lime-aluminum salt method, the lime's poor solubility prevents most of the lime from dissolving, resulting in a high pH value in the treated circulating water, such as 9-10. This not only poses a corrosion risk to subsequent equipment but can also impact other production processes. While the barium salt precipitation method can remove sulfate, it is costly because it cannot use barium salts containing chlorine (which may have other adverse effects on the production system). Furthermore, the poor solubility of barium salts makes practical application difficult and requires significant labor and material resources. Overall, chemical precipitation methods must balance technical feasibility, economic rationality, and compatibility with the alumina production process. Therefore, developing a new and more effective chemical precipitation method to treat sulfate-containing, high-sulfur bauxite flotation desulfurization circulating water has significant research significance and broad application prospects. Summary of the Invention

[0006] The present invention aims to provide a method for treating circulating water from flotation desulfurization of high-sulfur bauxite containing sulfate, so as to solve the problems of difficult operation, low efficiency and low economic and environmental performance of the existing circulating water desulfurization process.

[0007] A method for treating sulfate-containing high-sulfur bauxite flotation desulfurization circulating water in this scheme comprises the following steps:

[0008] Step 1: Place the circulating water into a container and stir evenly;

[0009] Step 2: Adding calcium nitrate tetrahydrate to the stirred circulating water to perform a chemical precipitation reaction;

[0010] Step 3: adding calcium sulfate as crystal seeds to the circulating water for chemical precipitation reaction;

[0011] Step 4: Add flocculant aqueous solution to perform solid-liquid separation. The resulting filter residue is mainly calcium sulfate, and the resulting filtrate is circulating water.

[0012] Furthermore, after adding calcium sulfate crystal seeds in step 3, heating reaction is carried out, and then solid-liquid separation is carried out.

[0013] Furthermore, the heating reaction is carried out at a temperature of 10°C-50°C under normal pressure.

[0014] Preferably, the heating reaction temperature is 20°C-40°C.

[0015] Furthermore, in step 3, 0.2%-1% calcium sulfate crystal seeds are added according to the mass of the circulating water.

[0016] Preferably, 0.5% to 1% calcium sulfate crystal seeds are added based on the mass of the circulating water.

[0017] Furthermore, in step 2, the molar mass ratio of sulfate ions contained in the circulating water to calcium ions contained in calcium nitrate tetrahydrate is 1:1.

[0018] Furthermore, the flocculant aqueous solution in step 4 is a polyacrylamide aqueous solution with a mass concentration of 1‰.

[0019] Furthermore, the solid-liquid separation in step 4 is performed using a filter.

[0020] Furthermore, the calcium sulfate separated in step 4 can be used as crystal seeds and recycled for circulating water treatment.

[0021] The working principle and beneficial effects of this solution: The purpose of stirring in step 1 is to evenly distribute the components of the circulating water, create good conditions for subsequent chemical reactions, and ensure that the reactions can proceed more fully and evenly. In step 2, the sulfate ions contained in the circulating water and the calcium ions contained in calcium nitrate tetrahydrate are added in a molar mass ratio of 1:1. Calcium nitrate tetrahydrate is easily soluble in water, and after dissolving in water, all calcium is in the form of calcium ions. After calcium nitrate tetrahydrate is used for circulating water treatment, the circulating water is neutral and can be recycled. This ratio has been verified to ensure that sulfate ions and calcium ions fully react, generate calcium sulfate precipitates to the greatest extent, and improve the removal efficiency of sulfate ions. Adding crystal seeds in step 3 can provide a core for the formation of calcium sulfate crystals, accelerate the precipitation process, and improve the precipitation effect; in this step, heating reaction is more conducive to the generation of calcium sulfate; the temperature of the heating reaction is controlled at 10°C-50°C and carried out under normal pressure; considering economic factors, the reaction temperature is further preferably 20°C-40°C; heating is conducive to the generation of calcium sulfate. Within this temperature range, it can not only ensure that the reaction has a higher rate and precipitation effect, but also reduce energy consumption and improve the economic benefits of production. In step 4, the polyacrylamide flocculant can cause calcium sulfate to flocculate into agglomerates, which is convenient for precipitation and filtration separation; solid-liquid separation is preferably carried out using a filter, and the solid particles are effectively separated from the liquid phase through the physical filtration effect of the filter; after solid-liquid separation, the obtained filter residue is mainly calcium sulfate, and the obtained filtrate is the treated circulating water. The separated calcium sulfate can be used as crystal seeds and circulated in the circulating water treatment link to achieve the recycling of resources and reduce production costs.

[0022] The core of the present invention in treating the flotation desulfurization circulating water of high-sulfur bauxite containing sulfate is to remove sulfate ions. After adding calcium nitrate tetrahydrate, it reacts chemically with the sulfate ions in the circulating water to generate calcium sulfate according to the principle of double decomposition reaction. Calcium sulfate has limited solubility in aqueous solution. In the reaction system, as the reaction proceeds, when the ion product of calcium sulfate exceeds its solubility product constant, it will begin to crystallize. Under heating and stirring conditions, the movement of ions in the solution intensifies, providing an energy and material exchange basis for the formation of calcium sulfate crystal nuclei. The addition of seed crystals provides growth sites for the growth of calcium sulfate crystals, reduces the energy barrier required for nucleation, and enables calcium sulfate crystals to continue to grow on the surface of the seed crystals. As the reaction continues, the crystals gradually grow. Because their density is greater than that of water, under the action of gravity, the crystals begin to precipitate, achieving solid-liquid separation from the treated circulating water, thereby achieving the purpose of removing sulfate ions.

[0023] Compared with the prior art of directly discharging circulating water into the alumina production system and then replacing secondary water for flotation desulfurization production, the present invention has the following significant beneficial effects:

[0024] The process is simple and efficient: The treatment method provided by the present invention can be carried out at a temperature slightly above ambient temperature (10°C-50°C, preferably 20°C-40°C), eliminating the need for complex high-temperature and high-pressure equipment. The process is simple and easy to operate. Through rational step design and controlled reaction conditions, sulfate ions can be efficiently separated from circulating water with high separation efficiency, effectively solving the problem of excessive sulfate content in circulating water.

[0025] High removal rate: The treatment method of the present invention is highly effective in removing sulfate from circulating water. The higher the sulfate content in the circulating water, the higher the removal rate, reaching over 87%. This ensures that the treated circulating water meets the requirements of flotation desulfurization production, effectively improving the quality of aluminum concentrate and ensuring smooth alumina production.

[0026] Green and recyclable: The circulating water used in this invention is recyclable, and the entire process produces no harmful pollutants, reducing water waste and environmental pollution, in line with the development concept of green environmental protection. Furthermore, calcium sulfate can be recycled as crystal seeds, further improving resource utilization and reducing production costs.

[0027] Excellent circulating water properties: Calcium nitrate tetrahydrate, when used in circulating water treatment, renders the water neutral, with a pH between 7 and 8. This will not adversely affect subsequent production equipment and processes, contributing to the stable operation of the production system. Furthermore, the addition of a polyacrylamide flocculant solution causes calcium sulfate to form flocculent precipitates, resulting in excellent circulating water clarity that can be directly reused in flotation desulfurization production without further treatment. DETAILED DESCRIPTION

[0028] The following is a further detailed description through specific implementation methods:

[0029] Example 1

[0030] A method for treating sulfate-containing high-sulfur bauxite flotation desulfurization circulating water, step 1: taking 100L of sulfate-containing high-sulfur bauxite flotation desulfurization circulating water, placing it in a container with a stirring device, and stirring at a speed of 200r / min for 10 minutes to mix the circulating water evenly.

[0031] Step 2: According to the content of sulfate ions in the circulating water, calculate and weigh an appropriate amount of calcium nitrate tetrahydrate, and add it to the circulating water in a ratio of 1:1 between the molar mass ratio of sulfate ions and the calcium ions contained in calcium nitrate tetrahydrate. Continue stirring for 30 minutes to allow the chemical precipitation reaction to proceed fully.

[0032] Step 3: Add 0.5% of calcium sulfate by mass of the circulating water to the circulating water as crystal seeds, control the reaction temperature at 25° C., and the reaction time is 2 h.

[0033] Step 4: After the reaction is completed, add a polyacrylamide flocculant aqueous solution prepared at a mass ratio of 1‰ and stir for 15 minutes to allow the calcium sulfate to flocculate into agglomerates. Then use a filter to separate the solid and liquid to obtain filter residue and filtrate.

[0034] The sulfate ion content in the filtrate was tested to be 2134 mg / L, with a sulfate ion removal rate of 87.0%. The separated calcium sulfate residue was dried and stored as crystal seeds for the next batch of circulating water treatment, with the pH value of the circulating water being 7-8.

[0035] Example 2

[0036] A method for treating sulfate-containing high-sulfur bauxite flotation desulfurization circulating water, step 1: taking 200L of sulfate-containing high-sulfur bauxite flotation desulfurization circulating water, putting it into a stirring container, and stirring it at a speed of 250r / min for 15 minutes.

[0037] Step 2: Add calcium nitrate tetrahydrate to ensure that the molar mass ratio of sulfate ion to calcium ion is 1:1 and stir for 40 minutes.

[0038] Step 3: Add 1% of the mass of the circulating water as a crystallization seed, increase the reaction temperature to 40°C, and react for 1.5 hours.

[0039] Step 4: Add a 1‰ (by weight) aqueous solution of polyacrylamide flocculant, stir for 20 minutes, and filter to separate the solid and liquid. The filtrate is tested for sulfate ion content of 1970 mg / l, with a removal rate of 88.0%. The separated calcium sulfate residue is recycled for subsequent circulating water treatment.

[0040] Example 3

[0041] Step 1: Take 50L of sulfate-containing high-sulfur bauxite flotation desulfurization circulating water and stir it evenly at a stirring speed of 150r / min and a stirring time of 8min.

[0042] Step 2: Add calcium nitrate tetrahydrate in proportion and stir for 25 minutes.

[0043] Step 3: Add 0.8% of the mass of the circulating water as calcium sulfate as crystal seeds and react at 30°C for 2.5 hours.

[0044] Step 4: Add the polyacrylamide aqueous solution as a flocculant and stir for 12 minutes to separate the solid and liquid. Testing revealed a sulfate ion content of 2050 mg / l in the filtrate, representing a removal rate of 87.5%. The calcium sulfate residue was recycled as crystallization seed.

[0045] Comparative Example:

[0046] Experiment on treating circulating water using existing technology

[0047] Take 100L of sulfate-containing high-sulfur bauxite flotation desulfurization circulating water and prepare instruments and equipment for detecting sulfate ion content, such as ion chromatograph.

[0048] According to the existing technology, the circulating water is directly discharged into the alumina production system, and then the same volume of secondary water is replaced from the alumina production system to simulate flotation desulfurization production. The replaced "circulating water" is simply stirred without adding any other treatment agents.

[0049] An ion chromatograph was used to measure the sulfate ion content in the treated "circulating water." Simultaneously, a simulated flotation desulfurization experiment was conducted using this "circulating water," producing a small amount of aluminum concentrate sample to measure the sulfur content.

[0050] Experimental results: The test found that the sulfate ion content in the "circulating water" after replacement only dropped slightly from the initial 16420 mg / l to 15850 mg / l, with almost no obvious change.

[0051] Results Analysis: The comparative example results demonstrate that the prior art method of directly discharging circulating water into the alumina production system and replacing secondary water fails to effectively reduce the sulfate ion content in the circulating water. Sulfate ions continue to accumulate in the circulating water, resulting in the sulfur content of the aluminum concentrate produced by flotation desulfurization exceeding the standard and failing to meet the quality requirements for alumina production. This further demonstrates the superiority and necessity of the present method for treating sulfate-containing, high-sulfur bauxite flotation desulfurization circulating water.

[0052] It can be seen from the above examples that the treatment method of the present invention can achieve good results in circulating water treatment of different scales, with a high sulfate ion removal rate. The treated circulating water can meet production requirements, and calcium sulfate can be recycled as crystal seeds, which has significant economic and environmental benefits.

[0053] The above is only an embodiment of the present invention, and the common knowledge such as the specific structure and characteristics of the scheme is not described in detail here. It should be pointed out that for those skilled in the art, without departing from the structure of the present invention, several variations and improvements can be made, which should also be regarded as the scope of protection of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for treating sulfate-containing high-sulfur bauxite flotation desulfurization circulating water, characterized by: The steps include: Step 1: Place the circulating water into a container and stir evenly; Step 2: Adding calcium nitrate tetrahydrate to the stirred circulating water to perform a chemical precipitation reaction; Step 3: adding calcium sulfate as crystal seeds to the circulating water for chemical precipitation reaction; Step 4: Add flocculant aqueous solution to perform solid-liquid separation. The resulting filter residue is mainly calcium sulfate, and the resulting filtrate is circulating water.

2. The method for treating sulfate-containing high-sulfur bauxite flotation desulfurization circulating water according to claim 1, characterized in that: After adding calcium sulfate crystal seeds in step 3, heating reaction is carried out, and then solid-liquid separation is carried out.

3. The method for treating sulfate-containing high-sulfur bauxite flotation desulfurization circulating water according to claim 2, characterized in that: The heating reaction is carried out at a temperature of 10° C. to 50° C. under normal pressure.

4. The method for treating sulfate-containing high-sulfur bauxite flotation desulfurization circulating water according to claim 3, characterized in that: The amount of calcium sulfate crystal seeds added in step 3 is 0.2% to 1% of the mass of the circulating water.

5. The method for treating sulfate-containing high-sulfur bauxite flotation desulfurization circulating water according to claim 4, characterized in that: The molar mass ratio of sulfate ions contained in the circulating water in step 2 to calcium ions contained in calcium nitrate tetrahydrate is 1:

1.

6. The method for treating sulfate-containing high-sulfur bauxite flotation desulfurization circulating water according to claim 5, characterized in that: The flocculant aqueous solution in step 4 is a polyacrylamide aqueous solution with a mass concentration of 1‰.

7. The method for treating sulfate-containing high-sulfur bauxite flotation desulfurization circulating water according to claim 6, characterized in that: The solid-liquid separation in step 4 is performed using a filter.

8. The method for treating sulfate-containing high-sulfur bauxite flotation desulfurization circulating water according to claim 7, characterized in that: The calcium sulfate separated in step 4 is used as crystal seeds and circulated for circulating water treatment.