Method for preparing flocculating agent and adsorbent from red mud in quality-divided manner and method for treating arsenic-containing wastewater by using flocculating agent and adsorbent

Abstract

The invention aims to provide a method for preparing a flocculating agent and an adsorbent from red mud in a quality-divided manner and a method for treating arsenic-containing wastewater by using the flocculating agent and the adsorbent, and belongs to the technical field of solid waste recycling and water treatment.The red mud is used as a raw material, and the flocculating agent and the adsorbent are prepared through a hydrothermal alkaline leaching-low-temperature acid leaching-alkalization polymerization process. The directional dissolution of iron, aluminum, silicon and other elements in the red mud is realized, and the iron-based adsorbent and the polysilicate aluminum ferric flocculant are prepared in a quality-divided manner for efficient treatment of arsenic-containing wastewater. The raw materials are cheap and easy to obtain, the preparation process is simple, no secondary waste is generated, and resource high-value utilization of the red mud is realized; an iron-based adsorbent and a polysilicate aluminum ferric flocculant are used as water treatment functional materials, arsenic-containing wastewater is treated through a pre-oxidation-flocculation-adsorption grading combined process, and efficient removal of arsenic in the wastewater is achieved. The method has both economic benefits and environmental protection benefits, achieves the purpose of treating waste with waste, and provides a feasible scheme for resource utilization of red mud and deep treatment of arsenic-containing wastewater.

Description

Technical Field

[0001] The invention belongs to the technical field of solid waste resource utilization and water treatment, and specifically relates to a method for preparing flocculants and adsorbents by fractionating red mud and a method for using the flocculants and adsorbents for treating arsenic-containing wastewater. Background Art

[0002] Red mud is an alkaline solid waste generated in the process of producing alumina, which is highly alkaline. Every ton of alumina produces 0.8-1.5 tons of red mud. In recent years, my country's alumina industry has developed rapidly, and the amount of red mud produced is very large. At present, the stock of red mud in my country is as high as 600 million tons, and it is still growing at a rate of 70 million tons per year. However, the resource utilization efficiency of red mud in my country is less than 20%, resulting in a large amount of red mud stockpiling. In this process, a series of environmental problems will arise, such as dust pollution, groundwater pollution and soil pollution. These environmental problems restrict the development of the alumina industry. Therefore, there is an urgent need to utilize red mud as a resource without environmental burden.

[0003] Red mud can be used in many ways. For example, the existing patent CN112093870A discloses a method for preparing a high-efficiency composite flocculant using red mud as raw material. Red mud is used as raw material, and red mud is sequentially acid-leached and alkaline-leached in a reactor. The obtained acid leaching solution and alkaline leaching solution are mixed in proportion and the pH is adjusted for alkalization to obtain a high-efficiency composite flocculant. Regarding the treatment effect of red mud-based flocculants on wastewater, CN107140718A discloses a method for preparing an iron-aluminum flocculant by treating red mud with a coupled external field. The excess iron in the red mud is enriched by microwave carbon thermal reduction-magnetic separation for smelting pig iron. The remaining red mud is acid-leached under the action of ultrasound, and the acid leaching solution is polymerized with alkali to obtain an iron-aluminum flocculant, which has a turbidity and COD removal rate for sewage at about 95% and 97%, respectively. Although the above method successfully prepares red mud as flocculant, a large amount of waste residue is generated during the preparation process, and the prepared flocculant is mainly used to treat turbidity and COD in domestic sewage, and is not used for the treatment of arsenic-containing industrial wastewater.

[0004] Red mud is also often used to prepare adsorbents. For example, the existing patent CN109107524B discloses a red mud adsorbent and its preparation method and application method. Red mud is used as raw material, and the red mud is de-alkalized by washing and precipitation of seawater. The iron oxide content in the red mud is increased by ferric chloride modification, thereby improving its adsorption capacity. The prepared red mud adsorbent has good adsorption capacity for arsenic. When the dosage is 5g / L and the adsorption time is 2h, the concentration of arsenic-containing wastewater with an initial concentration of 2mg / L can be reduced to below 0.005mg / L. Patent CN114832788A discloses a method for preparing a red mud-based porous microbead adsorbent for arsenic-containing wastewater treatment. Red mud is added to a mixed solution of NaCl and sodium alginate, and FeCl3 solution is used to cross-link it into beads. The wet microbeads are soaked in FeCl3 solution for 12h and dried in an oven to obtain a red mud agent porous microbead adsorbent. The removal rate of the adsorbent for arsenic solution (5mg / L) is 90.71%. The above method has a certain adsorption effect on arsenic-containing wastewater, but the preparation process is relatively complicated, and the waste liquid or waste residue generated in the preparation process is not fully utilized as a resource. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing flocculants and adsorbents by fractionating red mud and a method for treating arsenic-containing wastewater, which has simple process and low preparation cost, and no waste liquid or waste is generated during the preparation process, thus realizing high added value utilization of red mud. At the same time, the prepared products are used for treating high-concentration arsenic-containing wastewater through a graded combined process, thus achieving the purpose of treating waste with waste, and having both economic and environmental benefits.

[0006] The present invention adopts the following technical solution: The present invention uses red mud as raw material, and realizes the directional dissolution of elements such as iron, aluminum, and silicon in red mud through hydrothermal alkaline leaching-low-temperature acid leaching-alkalinization polymerization process, and prepares iron-based adsorbents and polysilicate aluminum iron flocculants by separation for efficient treatment of arsenic-containing wastewater. The present invention uses industrial solid waste to prepare iron-based adsorbents and polysilicate aluminum iron flocculants. The raw materials are cheap and easy to obtain, the preparation process is simple, and no secondary waste is generated, thereby realizing the resource-based and high-value utilization of red mud; iron-based adsorbents and polysilicate aluminum iron flocculants are used as water treatment functional materials, and arsenic-containing wastewater is treated through a graded combined process of "pre-oxidation-flocculation-adsorption", thereby realizing efficient removal of arsenic from wastewater. The specific steps are as follows.

[0007] A method for preparing flocculants and adsorbents by fractionating red mud comprises the following steps: In the first step, the red mud raw material and the sodium hydroxide solution are subjected to alkali leaching reaction in a hydrothermal kettle, and the product after alkali leaching is subjected to solid-liquid separation to obtain alkali leaching liquid and alkali leaching residue, and the alkali leaching residue is washed and dried for standby use; The second step is to carry out an acid leaching reaction between the alkaline leaching residue obtained in the first step and an acid in a reactor, and to separate the product after the acid leaching into solid and liquid to obtain the acid leaching residue and the acid leaching liquid, and to obtain the adsorbent after washing and drying the acid leaching residue; The third step is to drop the alkaline leaching solution in the first step into the acid leaching solution in the second step to adjust the pH, perform mixing and polymerization to obtain a liquid flocculant, and dry the liquid flocculant to obtain a solid flocculant.

[0008] Furthermore, in the first step, the mass concentration of the sodium hydroxide solution is 15-25%, the ratio of the red mud mass to the volume of the sodium hydroxide solution is 150-350:1 g / L; the temperature of the alkali leaching reaction is 120-220°C, and the alkali leaching time is 1.5-2h.

[0009] Furthermore, the acid in the second step includes any one of hydrochloric acid and nitric acid, the mass concentration of the acid is 10-20%, the ratio of the mass of the alkali leaching residue to the volume of the acid is 150-250:1 g / L; the temperature of the acid leaching reaction is 20-30°C, and the acid leaching time is 1.5-2h; the washing liquid used for washing is distilled water.

[0010] Furthermore, in the third step, the dropping speed of the alkaline leaching solution is 10-20 ml / min; the pH of the acid leaching solution is adjusted to 3.5-4.5; the drying method is drum drying or spray drying, and the drying temperature is 120-180°C.

[0011] The present invention also provides an application of the polysilicate aluminum iron flocculant and the iron-based adsorbent prepared by the method in treating arsenic-containing wastewater. Specifically, H2O2 is first used for pre-oxidation to convert the difficult-to-treat As(III) into As(V), and then the polysilicate aluminum iron flocculant prepared by the present invention is used for flocculation pretreatment of the arsenic-containing wastewater, and finally the iron-based adsorbent prepared by the present invention is used for deep treatment so that the arsenic concentration in the wastewater reaches the current emission standard. The specific steps are as follows: In the first step, H2O2 is added to the high-concentration arsenic-containing wastewater for pre-oxidation; The second step is to add the prepared flocculant into the arsenic-containing wastewater after pre-oxidation in the first step to perform flocculation pretreatment; The third step is to add the prepared adsorbent to the arsenic-containing wastewater that has been flocculated in the second step, so that the arsenic-containing wastewater meets the discharge standards.

[0012] Furthermore, the mass concentration of H2O2 in the first step is 15%, the amount of H2O2 added is 5-9 ml per liter of arsenic-containing wastewater, and the oxidation time is 1-3 min.

[0013] Furthermore, the dosage of the flocculant in the second step is 5-15 g per liter of arsenic-containing wastewater; the flocculation conditions are: rapid stirring speed of 180-220 r / min, rapid stirring time of 2.5-3.5 min, then slow stirring speed of 35-50 r / min, slow stirring time of 10-20 min, sedimentation time of 30 min, flocculation pH of 3, and flocculation temperature of 25-45 ° C.

[0014] Furthermore, in the third step, the dosage of the adsorbent is 2-5 g per liter of arsenic-containing wastewater, the adsorption pH is 3, the adsorption temperature is 25-45° C., and the adsorption time is 20-24 h.

[0015] The beneficial effects of the present invention are as follows: 1. Red mud is often accompanied by the generation of secondary waste in the traditional resource utilization process. The present invention provides a method for preparing flocculants and adsorbents by fractionating red mud, thereby achieving full utilization of red mud.

[0016] 2. The iron-based adsorbent and polysilicate aluminum iron flocculant prepared by red mud hydrothermal alkali leaching-low temperature acid leaching-alkalization polymerization can be used to treat arsenic-containing wastewater. Not only is the process simple and the preparation cost low, but no secondary waste is generated during the preparation process, and high added value utilization of red mud is achieved. 3. The graded combination of polysilicate aluminum iron flocculant and iron-based adsorbent not only has a good removal effect on low-concentration arsenic-containing wastewater, but also can make high-concentration arsenic-containing wastewater meet the discharge standard. The present invention achieves the purpose of treating waste with waste, and has both economic and environmental benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The figure is a flow chart of the method of the present invention.

[0018] Figure 2 This is a diagram of the red mud raw materials and products of the present invention. DETAILED DESCRIPTION

[0019] 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, but the protection scope of the present invention is not limited to the following embodiments.

[0020] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs, and the disclosure and materials cited therein are hereby incorporated by reference.

[0021] Technical equivalents to the specific embodiments described that are apparent to those skilled in the art using no more than routine experimentation are intended to be encompassed by this application.

[0022] In a specific embodiment of the present invention, the mass fraction of Al2O3 in the red mud is 20.8%, the mass fraction of SiO2 is 16.3%, the mass fraction of Fe2O3 is 24.3%, the mass fraction of CaO is 10.9%, and the remainder is unnecessary impurities. The specific surface area of ​​the red mud is 8-20 m 2 / g.

[0023] Example 1 A method for preparing flocculants and adsorbents by fractionating red mud, comprising the following steps: (1) alkali leaching the red mud raw material and 20% sodium hydroxide in a hydrothermal kettle at 140° C. for 2 h at a ratio of red mud mass to sodium hydroxide solution volume of 250:1 g / L, and performing solid-liquid separation on the alkali leaching product to obtain an alkali leaching solution and an alkali leaching residue; (2) the alkali leaching residue obtained in step (1) is acid-leached in a reactor at 20° C. for 2 h with 15% hydrochloric acid at a volume ratio of 160:1 g / L of the alkali leaching residue mass to the hydrochloric acid solution, the product after acid leaching is subjected to solid-liquid separation, and the acid leaching residue is washed with distilled water and dried to obtain the iron-based adsorbent; (3) The alkaline leaching solution in step (1) is added dropwise to the acid leaching solution obtained in step (2) at a rate of 15 ml / min to adjust the pH of the acid leaching solution to 4, and then spray-dried at 140° C. to obtain a solid flocculant.

[0024] Example 2 A method for preparing flocculants and adsorbents by fractionating red mud, comprising the following steps: (1) alkali leaching the red mud raw material and 25% sodium hydroxide in a hydrothermal kettle at 140° C. for 2 h at a ratio of red mud mass to sodium hydroxide solution volume of 250:1 g / L, and performing solid-liquid separation on the alkali leaching product to obtain an alkali leaching solution and an alkali leaching residue; (2) the alkali leaching residue obtained in step (1) is acid-leached in a reactor at 20° C. for 2 h with 20% hydrochloric acid at a ratio of 160:1 g / L by volume of the alkali leaching residue to the hydrochloric acid solution, the product after acid leaching is subjected to solid-liquid separation, and the acid leaching residue is washed with distilled water and dried to obtain the iron-based adsorbent; (3) The alkaline leaching solution in step (1) is added dropwise to the acid leaching solution obtained in step (2) at a rate of 15 ml / min to adjust the pH of the acid leaching solution to 4, and then spray-dried at 140° C. to obtain a solid flocculant.

[0025] Comparative Example 1 A method for preparing flocculants and adsorbents by fractionating red mud, the steps are the same as those in Example 1, except that hydrothermal alkaline leaching is not performed, and the remaining steps are the same as those in Example 1.

[0026] Comparative Example 2 A method for preparing flocculants and adsorbents by fractionating red mud, the steps are the same as those in Example 2, except that hydrothermal alkaline leaching is not performed, and the remaining steps are the same as those in Example 2.

[0027] Comparative Example 3 A method for preparing flocculants and adsorbents by fractionating red mud, the steps are the same as those in Example 1, except that low-temperature acid leaching is not performed, and the remaining steps are the same as those in Example 1.

[0028] Comparative Example 4 A method for preparing flocculants and adsorbents by fractionating red mud, the steps are the same as those in Example 2, except that low-temperature acid leaching is not performed, and the remaining steps are the same as those in Example 2.

[0029] Comparative Example 5 A method for preparing flocculants and adsorbents by fractionating red mud, the steps are the same as those in Example 1, except that the polymerization pH in step (4) is 5.0, and the remaining steps are the same as those in Example 1.

[0030] Comparative Example 6 A method for preparing flocculants and adsorbents by fractionating red mud, the steps are the same as those in Example 2, except that the polymerization pH in step (4) is 5.0, and the remaining steps are the same as those in Example 2.

[0031] The performance of the adsorbents prepared in Examples 1-2 and Comparative Examples 1-6 was tested, and the results are shown in Table 1.

[0032] Table 1 Properties of adsorbents The chemical compositions (mass fraction / %) of red mud and the iron-based adsorbents prepared in Examples 1-2 and Comparative Examples 1-6 are shown in Table 2.

[0033] Table 2 Chemical composition of red mud and iron-based adsorbents prepared in Examples 1-2 and Comparative Examples 1-6 (mass fraction / %) Example 3 The flocculants prepared in Examples 1 to 2 and Comparative Examples 1 to 6 were used for application experiments, and the specific method was as follows: 5 ml / L of H2O2 was added to the wastewater with an arsenic content of 100 mg / L for pre-oxidation, and then 10 g / L of flocculant was added. The rapid stirring speed was 200 r / min, the rapid stirring time was 3.0 min, the slow stirring speed was 30 r / min, the slow stirring time was 15 min, the sedimentation time was 30 min, the flocculation pH was 3, the flocculation temperature was 25 °C, and the arsenic concentration before and after the treatment with the above flocculants was tested by sampling. The arsenic removal rate of the flocculant was calculated and recorded in Table 3.

[0034] Table 3 Effects of different flocculants in treating arsenic-containing wastewater Example 4 The adsorbents prepared in Examples 1-2 and Comparative Examples 1-6 were subjected to application experiments, and the specific method was as follows: 4 g / L of adsorbent was added to wastewater with an arsenic content of 12 mg / L. The adsorption pH was 3, the adsorption temperature was 25°C, and the adsorption time was 24 h. Samples were taken to test the arsenic concentration before and after treatment with the above adsorbent. The arsenic removal rate of the adsorbent was calculated and recorded in Table 4.

[0035] Table 4 Effects of different adsorbents on treating arsenic-containing wastewater Example 5 The flocculants and adsorbents prepared in Examples 1 to 2 and Comparative Examples 1 to 6 were used to carry out application experiments, and the specific method was as follows: First, 5 ml / L of H2O2 was added to the wastewater with an arsenic content of 100 mg / L to pre-oxidize the arsenic-containing wastewater; then the high-concentration arsenic-containing wastewater was pretreated, specifically, 15 g / L of flocculant was added to the arsenic-containing wastewater, the rapid stirring speed was 200 r / min, the rapid stirring time was 3.0 min, the slow stirring speed was 30 r / min, the slow stirring time was 15 min, the sedimentation time was 30 min, the flocculation pH was 3, and the flocculation temperature was 25°C; subsequently, 4 g / L of adsorbent was added to the arsenic-containing wastewater that had been pretreated by flocculation, the adsorption pH was 3, the adsorption temperature was 25°C, and the adsorption time was 24 h.

[0036] The effect of red mud-prepared flocculants and adsorbents in graded combination for treating arsenic-containing wastewater is shown in Table 5.

[0037] Table 5 Effect of different flocculants and adsorbents combined in the treatment of arsenic-containing wastewater Combined with the above test data, it can be seen that the graded combination of the flocculant and the adsorbent provided by the present invention has a good effect in treating high-concentration arsenic-containing wastewater.

[0038] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing flocculants and adsorbents by fractionating red mud, characterized in that: The steps include: In the first step, the red mud raw material and the sodium hydroxide solution are subjected to alkali leaching reaction in a hydrothermal kettle, and the product after alkali leaching is subjected to solid-liquid separation to obtain alkali leaching liquid and alkali leaching residue, and the alkali leaching residue is washed and dried for standby use; The second step is to carry out an acid leaching reaction between the alkaline leaching residue obtained in the first step and an acid in a reactor, and to separate the product after the acid leaching into solid and liquid to obtain the acid leaching residue and the acid leaching liquid, and to obtain the adsorbent after washing and drying the acid leaching residue; The third step is to drop the alkaline leaching solution in the first step into the acid leaching solution in the second step to adjust the pH, perform mixing and polymerization to obtain a liquid flocculant, and dry the liquid flocculant to obtain a solid flocculant.

2. The method for preparing flocculants and adsorbents by fractionating red mud according to claim 1, characterized in that: The mass concentration of the sodium hydroxide solution in the first step is 15-25%, and the ratio of the mass of red mud to the volume of the sodium hydroxide solution is 150-350:1 g / L; The temperature of the alkali leaching reaction is 120-220° C., and the alkali leaching time is 1.5-2 hours.

3. The method for preparing flocculants and adsorbents by fractionating red mud according to claim 1, characterized in that: The acid in the second step includes any one of hydrochloric acid and nitric acid, the mass concentration of the acid is 10-20%, and the ratio of the mass of the alkali leaching residue to the volume of the acid is 150-250:1 g / L; The temperature of the acid leaching reaction is 20-30° C., and the acid leaching time is 1.5-2 hours; the washing liquid used for washing is distilled water.

4. The method for preparing flocculants and adsorbents by fractionating red mud according to claim 1, characterized in that: In the third step, the dropping speed of the alkaline leaching solution is 10-20 ml / min; the pH of the acid leaching solution is adjusted to 3.5-4.5; the drying method is drum drying or spray drying, and the drying temperature is 120-180°C.

5. A method for treating arsenic-containing wastewater using the flocculant and adsorbent prepared by the method of claim 1, characterized in that: The steps include: In the first step, H2O2 is added to the high-concentration arsenic-containing wastewater for pre-oxidation; The second step is to add the prepared flocculant into the arsenic-containing wastewater after pre-oxidation in the first step to perform flocculation pretreatment; The third step is to add the prepared adsorbent to the arsenic-containing wastewater that has been flocculated in the second step, so that the arsenic-containing wastewater meets the discharge standards.

6. The method for treating arsenic-containing wastewater according to claim 5, characterized in that: The mass concentration of H2O2 in the first step is 15%, the amount of H2O2 added is 5-9 ml per liter of arsenic-containing wastewater, and the oxidation time is 1-3 minutes.

7. The method for treating arsenic-containing wastewater according to claim 5, characterized in that: The dosage of the flocculant in the second step is 5-15 g per liter of arsenic-containing wastewater; the flocculation conditions are: rapid stirring speed of 180-220 r / min, rapid stirring time of 2.5-3.5 min, then slow stirring speed of 35-50 r / min, slow stirring time of 10-20 min, sedimentation time of 30 min, flocculation pH of 3, and flocculation temperature of 25-45 ° C.

8. The method for treating arsenic-containing wastewater according to claim 5, characterized in that: In the third step, the dosage of the adsorbent is 2-5 g per liter of arsenic-containing wastewater, the adsorption pH is 3, the adsorption temperature is 25-45° C., and the adsorption time is 20-24 h.

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