Water treatment agent produced from red mud of aluminum factory and preparation method therefor

Abstract

Disclosed in the present invention is a preparation method for a water treatment agent produced from red mud of an aluminum factory, comprising: first, dealkalizing red mud slurry by means of a filter pressing process; then drying same and crushing same into powder; adding to a stirring tank the dry red mud powder to be heated and dissolved, and adding an excess of hydrochloric acid to obtain a chlorine salt material; then adding alkali to the chlorine salt material to adjust the pH value to weak acid; and finally spray-drying the water treatment agent to obtain a powdery preparation. The water treatment agent prepared in the present invention has excellent effects of flocculation and COD and ammonia nitrogen removal, and can effectively solve the problem that red mud waste residues stacked in aluminum factories cause environment pollution.

Description

A water treatment agent produced by utilizing red mud from an aluminum plant and its preparation method Technical Field

[0001] The present invention relates to the technical field of water treatment, in particular to a water treatment agent produced by utilizing red mud from an aluminum plant and a preparation method thereof. Background Art

[0002] Water, as a non-renewable resource, must be recycled. During the treatment of industrial wastewater and domestic sewage, water treatment agents must be added to precipitate the large particles in them before subsequent processing can be carried out.

[0003] Red mud is a polluting waste residue discharged when the aluminum industry extracts alumina. Red mud has a high alkali content and a complex mineral composition. Its main components are calcium, aluminum, silicon, iron, etc. my country produces more than 30 million tons of red mud each year. The large amount of red mud produced cannot be fully and effectively utilized and can only be stored in large-scale stockpiles, which not only occupies a large amount of land but also pollutes the environment. How to effectively utilize red mud resources is a research focus in my country's scientific research and technology field. Application No. 202111123940.6 discloses a method for preparing a water treatment agent using red mud. The red mud is made into an algaecide through oxidation, dealkalization, mineral blending, and double saltization, thereby achieving effective utilization of the red mud. Although this technical solution makes full use of the useful components such as iron, aluminum, and silicon in the red mud, it only converts the red mud into an algaecide for algae removal and does not process it into a flocculant. At the same time, the processing steps are many, the process is complicated, and the cost is high. Therefore, how to develop the useful components such as iron, aluminum, and silicon in the red mud into water treatment flocculants and control the cost of the process steps to make it suitable for factory-scale mass production is a problem that needs to be solved. Summary of the Invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art that red mud from aluminum plants cannot be effectively utilized and easily causes environmental pollution, and to provide a water treatment agent produced using red mud from aluminum plants and a preparation method thereof.

[0005] One of the objects of the present invention is to provide a method for preparing a water treatment agent, which is achieved by the following technical solution, comprising the following steps:

[0006] S1. The red mud slurry is dealkalized by a filter press process to obtain dealkalized red mud and a filtrate;

[0007] S2. Drying and crushing the dealkalized red mud into powder to obtain dry red mud powder;

[0008] S3. The dry red mud powder was added to a pressure stirred tank and heated to dissolve to obtain a red mud solution;

[0009] S4. Adding excess hydrochloric acid to the red mud solution to obtain a chloride material;

[0010] S5. Adding alkali to the chloride material to adjust the pH value to a weakly acidic water treatment agent;

[0011] S6. spray-drying the water treatment agent to obtain a powdered preparation.

[0012] As a further improvement of the present invention, the temperature required for dissolution in step S3 is 80° C.-110° C., and the dissolution time is 5-6 hours.

[0013] As a further improvement of the present invention, in step S4, hydrochloric acid is added in excess according to a mass ratio of dry powdered red mud to 25% concentration hydrochloric acid of 1:3-5.

[0014] As a further improvement of the present invention, in step S5, the alkali is one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, and sodium bicarbonate.

[0015] As a further improvement of the present invention, in step S5, the alkali used is the filtrate after the red mud filter press in step S1.

[0016] As a further improvement of the present invention, in step S5, the pH value of the water treatment agent obtained is 1-2.

[0017] A second object of the present invention is to provide a water treatment agent prepared according to the above method.

[0018] The present invention has the following beneficial effects:

[0019] 1. The present invention uses polluting red mud from aluminum plants as raw materials, and prepares a water treatment agent with excellent performance through multiple steps such as dealkalization, monohydrochloration, and alkali polymerization. The water treatment agent can not only adsorb suspended particles in water to purify the water, but also has the excellent effects of removing COD, decolorizing and degrading ammonia nitrogen in the water, effectively solving the problem of environmental pollution caused by the accumulation of waste residue from aluminum plants; during the preparation process, a large amount of alkaline filtrate generated in the red mud dealkalization pretreatment step is used as the raw material in the alkali polymerization step, effectively avoiding the problem of treatment and discharge of alkaline pollutants during the red mud pretreatment process, and greatly reducing the processing and preparation costs; in the preparation process of traditional polyaluminum chloride and polyferric sulfate water treatment agents, technicians usually use hydrochloric acid and sulfuric acid as equivalent substitutes. In the process of preparing flocculants using red mud as raw material, the inventors overcame technical prejudice and determined through experiments that the water treatment agent obtained by salt treatment with monohydrochloric acid has better performance than that obtained by salt treatment with dihydrochloric acid, and has unexpected outstanding effects.

[0020] 2. The present invention provides a method for preparing a water treatment agent using red mud, a solid waste from an aluminum plant, as a raw material. The process steps and equipment are simple, and the recycling resource utilization of various components in the red mud can be achieved. The cost is low and it is suitable for factory-scale mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIG1 is a schematic flow chart of the method of the present invention. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with specific embodiments.

[0023] As shown in FIG1 , the method for preparing a water treatment agent using red mud from an aluminum plant provided by the present invention is implemented by the following technical solutions:

[0024] The red mud produced by the aluminum plant of China Aluminum Corporation Henan Branch was selected for component analysis, and the specific content (wt%) is shown in the following table.

[0025] Fe2O3AL2O3SiO2TiO2CaOMgONa2O15.922.714.34.64.524.2

[0026] S1. The red mud produced by the aluminum plant is filtered and separated, the purpose of which is to separate the alkaline liquid contained in the red mud, and the dealkalized red mud cake and alkaline filtrate are obtained after extrusion filtration. The solid-liquid separation can be one of various methods such as sedimentation clarification, centrifugal filtration, vacuum filtration, and pressure filtration;

[0027] S2. After the red mud cake is dried in a drum dryer, it is crushed into powder to facilitate subsequent dissolution;

[0028] S3. Dissolve the crushed red mud powder in a pressure stirring tank, increase the stirring temperature to 80°C-110°C, and the pressure to 0.5-0.6 MPa for 5-6 hours to promote the dissolution of the components in the red mud;

[0029] S4. Keeping the stirred tank temperature at 110 ° C, a mass concentration of 25% hydrochloric acid was added to the pressure stirred tank, and the hydrochloric acid was added in an excess amount according to the mass ratio of dry red mud to 25% hydrochloric acid concentration of 1:3-5. In this step, the hydrochloric acid was added in excess. The addition of hydrochloric acid not only neutralized the alkali in the red mud after solid-liquid separation, but also dissolved the insoluble oxidized matter to generate a chloride solution of calcium, magnesium, sodium, iron, aluminum, etc. In this step, sulfuric acid was not used instead of hydrochloric acid for acidification because the solubility of chlorides is generally higher than that of sulfates, which can avoid the formation of slightly soluble precipitates such as calcium sulfate that hinder the subsequent polymerization of iron and aluminum.

[0030] S5. Adding an alkali to the obtained chloride solution, wherein the alkali in this step can be one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, and sodium bicarbonate, and can also be preferably the filtrate obtained after the solid-liquid separation in step S1. Using the filtrate after solid-liquid separation can not only reduce costs, but also maximize the effective utilization of the components in the red mud of the aluminum plant and avoid the discharge of excess waste liquid; the addition of the alkali causes the aluminum and iron in the chloride solution to polymerize to form polyaluminum-iron compounds, which are the main components of the flocculation effect. The amount of alkali added is controlled so that the water treatment agent solution is weakly acidic as a whole, with a pH value of 1-2, which can keep the calcium and magnesium ions in the solution stable and avoid precipitation;

[0031] S6. Drying the obtained water treatment agent solution into a powdered preparation through a spray dryer.

[0032] In Example 1, the red mud from the aluminum plant was subjected to solid-liquid separation by a plate and frame filter press, the filtered red mud cake was dried by a drum dryer, and then crushed into 7-8 mm granules by a crusher. The granular red mud was added to a pressure stirring tank, water was added and continuously heated to 110° C., and then hydrochloric acid with a mass concentration of 25% was added to the pressure stirring tank in multiple times to react for 5 hours, wherein the hydrochloric acid was added in excess according to the mass ratio of dry powder red mud to 25% concentration hydrochloric acid of 1:3, and the pressure was adjusted to 0.5-0.6 MPa. Thereafter, the alkaline filtrate after solid-liquid separation was added to the solution in multiple times, and the pH value of the solution was adjusted to 1-2. Finally, the solution was spray-dried by a spray dryer to obtain the final product.

[0033] In Example 2, the red mud from the aluminum plant was subjected to solid-liquid separation by a plate and frame filter press, the filtered red mud cake was dried by a drum dryer, and then crushed into 7-8 mm granules by a crusher. The granular red mud was added to a pressure stirring tank, water was added and continuously heated to 80° C., and then hydrochloric acid with a mass concentration of 25% was added to the pressure stirring tank in multiple times to react for 6 hours. The hydrochloric acid was added in excess according to the mass ratio of dry powder red mud to 25% concentration hydrochloric acid of 1:5, and the pressure was adjusted to 0.5-0.6 MPa. Thereafter, the alkaline filtrate after solid-liquid separation was added to the solution in multiple times, and the pH value of the solution was adjusted to 1-2. Finally, the solution was spray-dried by a spray dryer to obtain the final product.

[0034] In Example 3, the red mud from the aluminum plant was separated into solid and liquid by a plate and frame filter press, the filtered red mud cake was dried by a drum dryer, and then crushed into 7-8 mm granules by a crusher. The granular red mud was added to a pressure stirring tank, water was added and continuously heated to 110° C., and then hydrochloric acid with a mass concentration of 25% was added to the pressure stirring tank in multiple times to react for 5 hours, wherein the hydrochloric acid was added in excess according to the mass ratio of dry powdered red mud to 25% concentration hydrochloric acid of 1:3, and the pressure was adjusted to 0.5-0.6 MPa. A sodium hydroxide solution with a mass concentration of 20% was added to the solution in multiple times, and the pH value of the solution was adjusted to 1-2. Finally, the solution was spray-dried by a spray dryer to obtain the final product.

[0035] In comparative example 1, the red mud from the aluminum plant was subjected to solid-liquid separation by a plate and frame filter press, the filtered red mud cake was dried by a drum dryer, and then crushed into 7-8 mm granules by a crusher. The granular red mud was added to a stirring tank, water was added and continuously heated to 110° C., and then 95% industrial sulfuric acid was added to the stirring tank in multiple times to react for 5 hours. Concentrated sulfuric acid was added in a mass ratio of 1:1 between dry powdered red mud and concentrated sulfuric acid, and the pressure was adjusted to 0.5-0.6 MPa. Thereafter, the alkaline filtrate after solid-liquid separation was added to the solution in multiple times, and the pH value of the solution was adjusted to 1-2. Finally, the solution was spray-dried by a spray dryer to obtain the final product.

[0036] In comparative example 2, the red mud from the aluminum plant was separated into solid and liquid by a plate and frame filter press, the filtered red mud cake was dried by a drum dryer, and then crushed into 7-8 mm granules by a crusher. The granular red mud was added to a stirring tank, water was added and continuously heated to 110°C, and then hydrochloric acid with a mass concentration of 15% was added to the pressure stirring tank in a 1:1 mass ratio with the dry powder red mud for multiple times to react for 2 hours. Then, 95% industrial sulfuric acid was added to the solution in a 1:1 mass ratio with the dry powder red mud for 3 hours, and the pressure was adjusted to 0.5-0.6 MPa. After that, the alkaline filtrate after solid-liquid separation was added to the solution in multiple times, and the pH value of the solution was adjusted to 1-2. Finally, it was spray-dried by a spray dryer to obtain the final product.

[0037] In comparative example 3, the red mud from the aluminum plant was separated into solid and liquid by a plate and frame filter press, the filtered red mud cake was dried by a drum dryer, and then crushed into 7-8 mm granules by a crusher. The granular red mud was added to a pressure stirring tank, water was added and continuously heated to 110°C, and then 95% industrial sulfuric acid was added to the solution at a mass ratio of 1:1 to the dry powdered red mud, and the reaction took place for 2 hours. Then, 15% hydrochloric acid was added to the pressure stirring tank in a mass ratio of 1:1 to the dry powdered red mud several times to react for 3 hours, and the pressure was adjusted to 0.5-0.6 MPa. After that, the alkaline filtrate after solid-liquid separation was added to the solution several times, and the pH value of the solution was adjusted to 1-2. Finally, the final product was spray-dried by a spray dryer to obtain the final product.

[0038] In comparative example 4, commercially available calcium aluminate powder was purchased and added to a pressure stirring tank. Water was added and the temperature was raised to 110° C. The pressure was adjusted to 0.5-0.6 MPa. Then, 25% hydrochloric acid was slowly added in multiple times, the pH value was adjusted to 2-3, and finally, the mixture was spray-dried using a spray dryer to obtain the final product.

[0039] In comparative example 5, the red mud from the aluminum plant was subjected to solid-liquid separation through a plate and frame filter press. The red mud cake after solid-liquid separation was directly placed in a pressure stirring tank, water was added, and the temperature was raised to 110°C for stirring and dissolution. The pressure was adjusted to 0.5-0.6 MPa. After 6 hours of heat preservation and dissolution, it was observed that the red mud cake was still in block form and had not dissolved. The obtained block red mud was different from general mixed mineral materials and was insoluble in water at high temperatures. The existing water treatment process was not suitable for treating dealkalized red mud.

[0040] The water treatment effect of the water treatment agent products prepared in Examples 1-3 and Comparative Examples 1-4 was tested. 800 ml of domestic sewage from a water plant was taken, and its COD was measured to be 370 mg / L and ammonia nitrogen was 45 mg / L. The solid water treatment agent was prepared into a 20% concentration solution, and 4 mL of the prepared liquid water treatment agent was added to the 800 ml water sample. After rapid mixing for 30 seconds, a slow flocculation reaction was performed for 3 minutes, and then the supernatant was taken for static sedimentation for 10 minutes for measurement. The measurement results are shown in the following table.

[0041] Group COD (mg / L) Ammonia nitrogen (mg / L) Example 1 12.3 0.24 Example 2 12.9 0.28 Example 3 12.5 0.26 Comparative Example 1 23.5 0.46 Comparative Example 2 21.1 0.39 Comparative Example 3 22.8 0.43 Comparative Example 4 26.4 0.52

[0042] According to the above table, after the water treatment agents prepared in Example 1, Example 2, and Example 3 were used to treat biological sewage, the COD content was less than 13 mg / L and the ammonia nitrogen content was less than 0.3 mg / L, which showed excellent flocculation effect. At the same time, the numerical values ​​of the measurement results of Example 1 and Example 3 were not much different. Therefore, the filtrate after solid-liquid separation of red mud can be used to replace the alkali solution to treat the chloride solution, greatly reducing the cost. The COD measurement data of Comparative Example 1, Comparative Example 2, and Comparative Example 3 were all around 22 mg / L, and the ammonia nitrogen content was around 0.4 mg / L, which was much greater than the COD measurement data of Example 1 of 12.3. mg / L, ammonia nitrogen content of 0.24 mg / L. It is inferred that the addition of sulfate ions can produce calcium sulfate insolubles with calcium ions in red mud, affecting the subsequent polymerization of iron and aluminum. The flocculation effect of the water treatment agent finally prepared by treating red mud with single hydrochloric acid is better than that of treating red mud with two acids together. The main components of commercially available calcium aluminate powder are calcium dialuminate and calcium monoaluminate. The COD and ammonia nitrogen content results of Comparative Example 4 are both greater than those of Examples 1-3 and Comparative Examples 1-3. It is inferred that the polyaluminum chloride water treatment agent prepared with calcium aluminate powder as raw material does not contain multiple components such as polyaluminum chloride iron and sodium silicate in the water treatment agent prepared with red mud as raw material, and has weak flocculation bridging ability. Therefore, the water treatment agent prepared with red mud as raw material has stronger COD and ammonia nitrogen removal capabilities than a single flocculant.

[0043] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a water treatment agent produced by using red mud from an aluminum plant, characterized in that: The steps include: S1. The red mud slurry is dealkalized by a filter press process to obtain dealkalized red mud and a filtrate; S2. Drying and crushing the dealkalized red mud into powder to obtain dry red mud powder; S3. The dry red mud powder was added to a pressure stirred tank and heated to dissolve to obtain a red mud solution; S4. Adding excess hydrochloric acid to the red mud solution to obtain a chloride material; S5. Adding alkali to the chloride material to adjust the pH value to a weakly acidic water treatment agent; S6. spray-drying the water treatment agent to obtain a powdered preparation.

2. The method for preparing a water treatment agent produced by using red mud from an aluminum plant according to claim 1, characterized in that: The temperature required for dissolution in step S3 is 80° C.-110° C., and the dissolution time is 5-6 hours.

3. The method for preparing a water treatment agent produced by using red mud from an aluminum plant according to claim 1, characterized in that: In step S4, hydrochloric acid is added in excess according to the ratio of dry powdered red mud to 25% concentration hydrochloric acid of 1:3-5.

4. The method for preparing a water treatment agent produced by using red mud from an aluminum plant according to claim 1, characterized in that: In step S5, the alkali is one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, and sodium bicarbonate.

5. The method for preparing a water treatment agent produced by using red mud from an aluminum plant according to claim 1, characterized in that: In step S5, the alkali used is the filtrate after the red mud filter press in step S1.

6. The method for preparing a water treatment agent produced by using red mud from an aluminum plant according to claim 1, characterized in that: In step S5, the pH value of the obtained water treatment agent is 1-2.

7. The water treatment agent obtained by the preparation method of a water treatment agent produced by utilizing red mud from an aluminum plant according to any one of claims 1 to 6.

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