CN109665534B - A method for preparing mesoporous silica by using fly ash acid leaching slag - Google Patents

Abstract

The invention discloses a method for preparing mesoporous silicon oxide by using fly ash acid leaching residue, which comprises the following steps: 1) performing acid leaching on the fly ash and sulfuric acid or hydrochloric acid at 120-140 ℃, and filtering and separating to obtain fly ash acid leaching residue; 2) mixing the acid leaching residue of the fly ash with a sodium hydroxide solution according to a solid-to-liquid ratio of 1: 2-1: 4, dissolving and reacting for 0.5-2 h at 60-90 ℃, and filtering while hot to obtain high-modulus water glass; 3) adjusting the concentration of silicon in the water glass, adjusting the pH value of the solution to 4-5 by using sulfuric acid, and reacting for 5-10 min; 4) adjusting the pH value of the sol to 7-9 by using ammonia water, adding sodium hexametaphosphate, and aging at 30-60 ℃ for 0.5-2 h; 5) carrying out solid-liquid separation on the aged mixture to obtain a filter cake; 6) and drying the filter cake at 100-110 ℃ for 1-2 h, roasting at 300-400 ℃ for 1.5-3 h, and cooling to obtain the mesoporous silicon oxide.

Description

A method for preparing mesoporous silica by using fly ash acid leaching slag

technical field

The invention belongs to the technical field of resource utilization of industrial solid waste fly ash and synthesis of mesoporous silica, in particular to a method for preparing mesoporous silica by using fly ash acid leaching slag.

Background technique

Fly ash is one of the main solid wastes produced by coal-fired power plants, with a huge annual output. At present, fly ash is widely used in the fields of building materials and construction, and the utilization rate reaches 70%. serious impact on the environment.

The main components of fly ash are silicon oxide and alumina (60-85%), so the utilization of silicon and aluminum in fly ash is an important direction of fly ash. Acid leaching of fly ash under mild conditions, and then separation and purification can obtain a series of high value-added aluminum products such as polyaluminum chloride, metallurgical grade alumina, etc. At the same time as the preparation of the aluminum product, the silica is separated out in the form of an acid leaching residue. The main component of the acid leaching residue is silicon oxide (>85%), which is a good source of silicon; but the silicon oxide in the acid leaching residue cannot be used directly, it must be converted into sodium silicate solution, or through sodium silicate Solution-prepared silicon material. Therefore, the efficient preparation of sodium silicate solution from acid leaching residue is the primary problem of silicon utilization in acid leaching residue. In addition, the market demand for sodium silicate solution is large. In industry, quartz sand is used as raw material to be prepared by alkali dissolution under high temperature and high pressure conditions. In this process, not only a large amount of quartz sand is mined, causing environmental damage, but also the process energy consumption is high. Since the silicon in the acid leaching residue is mainly amorphous silicon oxide with high activity, the sodium silicate solution can be obtained by alkali dissolution at low temperature. Using low-cost fly ash-based sodium silicate solution as raw material, the ordered mesoporous silica material with higher added value can be further prepared through process optimization.

Mesoporous silica has a wide range of applications in catalysis, adsorption and separation due to its suitable specific surface area and pore size. At present, most of the mesoporous silica materials prepared from fly ash are prepared by using fly ash-based sodium silicate as a precursor, and with the aid of a template agent, they are prepared by a hydrothermal method or a sol-gel method. However, the cost of preparing mesoporous silica is high and the production efficiency is low due to the expensive templating agent and low silicon concentration. In addition, the low modulus sodium silicate solution produces a large amount of sodium salt in the material preparation process, which is difficult to post-process and is difficult to popularize and apply in industry. Therefore, it is urgent to develop an efficient and large-scale method for the production of fly ash-based mesoporous silica, so as to meet the demand for the continuous growth of mesoporous silica, and at the same time, the fly ash can be fully absorbed to truly solve the problem of fly ash. handling issues.

To sum up, the present invention uses fly ash acid leaching slag as raw material to prepare high modulus sodium silicate solution, and then uses this as raw material, adopts simple sol-gel process, and controls silicic acid by controlling chemical reaction process The hydrolysis and polymerization rates of sodium enable the large-scale controllable synthesis of mesoporous silica, which has good economic, environmental and social benefits.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a method for preparing mesoporous silica by using fly ash acid leaching residue, the method has the advantages of simple process flow, low raw material price, low synthesis cost, simple industrial synthesis process and low energy consumption . The mesoporous silica material synthesized by the method of the present invention has large specific surface area and pore volume, and has broad prospects in the field of adsorption.

In order to achieve the above object, a method for preparing mesoporous silica by utilizing fly ash acid leaching slag designed by the present invention comprises the following steps:

1) After acid leaching of fly ash and sulfuric acid or hydrochloric acid solution at 120～140℃ for 100～140min, filter and separate to obtain fly ash acid leaching slag;

2) Mix the fly ash acid leaching residue obtained in step 1) with the sodium hydroxide solution according to the solid-liquid ratio of 1:2 to 1:4, dissolve and react at 60 to 90° C. for 0.5 to 2 hours, and after the reaction is completed, keep it hot. Filtration to obtain high modulus water glass;

3) adjusting the concentration of silicon in the water glass to be 20-60 g/L, adjusting the pH value of the high-modulus sodium silicate solution with sulfuric acid to be 4-5, and performing a sol-gel reaction for 5-10 min to obtain a sol;

4) Adjust the pH of the sol with ammonia water to 7-9, then add sodium hexametaphosphate, and age at 30-60°C for 0.5-2 hours, wherein the mass ratio of sodium hexametaphosphate to water glass is 0.05-0.2%;

5) carrying out solid-liquid separation on the aged solid-liquid mixture in step 4), by filtering and washing with water until the pH value is close to neutral, to obtain a filter cake;

6) Drying the filter cake obtained in step 5) at 100-110°C for 1-2h, then calcining at 300-400°C for 1.5-3h, and cooling to obtain mesoporous silica.

As a preferred solution, the concentration of the hydrochloric acid solution in the step 1) is 20-37%, and the concentration of the sulfuric acid solution is 20-40%.

As a preferred solution, the concentration of the sodium hydroxide solution in the step 2) is 5-15%, and the liquid-solid ratio of the sodium hydroxide solution to the acid leaching residue is 1:3.

As a preferred solution, in the step 3), the concentration of silicon in the water glass is adjusted to be 40-60 g/L, and the concentration of the sulfuric acid is 5-20%.

As a preferred solution, in the step 4), the concentration of ammonia water is 5-25%, the aging temperature is 40-50°C, and the aging time is 1-2h; the mass ratio of the sodium hexametaphosphate to water glass is 0.05-0.15 %.

As a preferred solution, in the step 5), the drying temperature is 105°C, and the calcination temperature is 350°C.

As a preferred solution, the mesoporous silica obtained in the step 6) has a specific surface area of 452 m ² /g and an average pore diameter of 13.22 nm.

The beneficial effects of the present invention are:

First, the scheme of the present invention uses the industrial waste fly ash acid leaching slag as the raw material, the reaction conditions are mild, and the obtained water glass has high purity, which not only realizes the resource utilization of fly ash, but also synthesizes mesoporous silica with a wide range of uses. , to achieve the rational use of resources.

Second, the high modulus and high concentration sodium silicate solution is used to synthesize mesoporous silica, which improves the production efficiency of mesoporous silica and reduces the cost of post-processing.

Third, the solution of the present invention does not add a template agent, and controls the hydrolysis and condensation rates of the sodium silicate solution by adding a small amount of sodium hexametaphosphate, and synthesizes mesoporous silica with a controllable pore structure, and the average pore size is between 10 and 20 nm. The specific surface area is as high as 452m ² /g.

Description of drawings

Fig. 1 is a process flow diagram of the method of the present invention.

Fig. 2 is the nitrogen adsorption curve diagram of the product mesoporous silica in the present invention.

specific embodiment

The present invention will be further described below through specific embodiments, but the content of the present invention is not limited to these embodiments.

The fly ash acid leaching slag raw material used in the following specific examples is to obtain fly ash acid leaching slag by leaching industrial waste fly ash with sulfuric acid or hydrochloric acid solution at 120-140° C. for 100-140 min, filtering and separating. The composition and content of fly ash acid leaching residue are shown in Table 1;

Example 1

A certain amount of acid leaching residue was weighed and mixed with 10wt.% sodium hydroxide solution according to a solid-liquid ratio of 1:2.5, dissolved at 80°C for 1 hour, the reaction was completed, and filtered while hot to obtain high modulus water glass. The concentration of silicon in the water glass was adjusted to 40 g/L, the pH value was adjusted to 2.0 with 10 wt.% sulfuric acid solution, and the reaction was carried out at room temperature for 30 min; the pH value of the mixed system was adjusted to 7.0 with 20 wt. Sodium metaphosphate, aged at 40°C for 2h; after the reaction, the solid-liquid mixture was subjected to solid-liquid separation, the separated solid powder was dried at 105°C for 1.5h, and then calcined at 400°C for 1.5h to obtain mesoporous Silicon oxide products.

Example 2

A certain amount of acid leaching residue was weighed and mixed with 15wt.% sodium hydroxide solution according to a solid-liquid ratio of 1:3, dissolved at 90°C for 0.5h, the reaction was completed, and filtered while hot to obtain high modulus water glass. The concentration of silicon in the water glass was adjusted to 50g/L, the pH value was adjusted to 2.5 with 20wt.% sulfuric acid, and the reaction was carried out at room temperature for 30min; the pH value of the mixed system was adjusted to 8.0 with 15wt% ammonia water, and 0.10% hexametaphosphoric acid was added. Sodium, aged at 50°C for 2h; after the reaction, the solid-liquid mixture was subjected to solid-liquid separation, and the solid powder obtained by separation was dried at 105°C for 1h; then calcined at 350°C for 3h, and cooled to obtain mesoporous silica .

Example 3

A certain amount of acid leaching residue was weighed and mixed with 10wt.% sodium hydroxide solution according to a solid-liquid ratio of 1:4, dissolved at 90°C for 1.5h, the reaction was completed, and filtered while hot to obtain high modulus water glass. The concentration of silicon in the water glass was adjusted to 60g/L, the pH value was adjusted to 3.0 with 30wt.% sulfuric acid, and the reaction was carried out at room temperature for 30min; the pH value of the mixed system was adjusted to 9.0 with 25wt.% ammonia water, and 0.05% hexagonal Sodium phosphate, aged at 60°C for 2h; after the reaction, the solid-liquid mixture was subjected to solid-liquid separation, and the separated solid powder was dried at 100°C for 2h, then calcined at 300°C for 2h, and cooled to obtain mesoporous oxidation silicon.

From the nitrogen adsorption curve of mesoporous silica shown in Figure ² , it can be seen that the adsorption curve is an IV curve, indicating that silica has a typical mesoporous structure. is 13.22nm.

Table 1

Composition and content table of fly ash acid leaching residue

The specific embodiments of the present invention described above do not limit the protection scope of the present invention. Any other corresponding changes and modifications made according to the technical concept of the present invention shall be included in the protection scope of the claims of the present invention.

Claims (5)

1. a method utilizing fly ash acid leaching slag to prepare mesoporous silica, is characterized in that: comprise the following steps: 1) After acid leaching of fly ash and sulfuric acid or hydrochloric acid solution for 100 to 140 min at 120 to 140° C., filter separation to obtain fly ash acid leaching residue; the concentration of the hydrochloric acid solution is 20 to 37%, and the concentration of the sulfuric acid solution is 20 ~40%, 2) Mix the fly ash acid leaching residue obtained in step 1) with the sodium hydroxide solution according to the solid-liquid ratio of 1:2 to 1:4, dissolve and react at 60 to 90° C. for 0.5 to 2 hours, and after the reaction is completed, keep it hot. Filtration to obtain high modulus water glass; the concentration of the sodium hydroxide solution is 5-15%, and the liquid-solid ratio of the sodium hydroxide solution to the acid leaching residue is 1:3, 3) adjusting the concentration of silicon in the water glass to be 20-60 g/L, adjusting the pH value of the high-modulus sodium silicate solution with sulfuric acid to be 4-5, and performing a sol-gel reaction for 5-10 min to obtain a sol; 4) Adjust the pH of the sol with ammonia water to 7-9, then add sodium hexametaphosphate, and age at 30-60°C for 0.5-2 hours, wherein the mass ratio of sodium hexametaphosphate to water glass is 0.05-0.2%; 5) carrying out solid-liquid separation on the aged solid-liquid mixture in step 4), by filtering and washing with water until the pH value is close to neutral, to obtain a filter cake; 6) The filter cake obtained in step 5) is dried at 100-110° C. for 1-2 hours, then calcined at 300-400° C. for 1.5-3 hours, and cooled to obtain mesoporous silica. 2. A method for preparing mesoporous silica by utilizing fly ash acid leaching slag according to claim 1, characterized in that: in the step 3), the concentration of silicon in the water glass is adjusted to be 40-60 g/L, The concentration of the sulfuric acid is 5-20%. 3. A method for preparing mesoporous silica by utilizing fly ash acid leaching slag according to claim 1, wherein the concentration of ammonia water in the step 4) is 5～25%, and the aging temperature is 40～25%. 50° C., the aging time is 1-2 hours; the mass ratio of the sodium hexametaphosphate to water glass is 0.05-0.15%. 4 . The method for preparing mesoporous silica by using fly ash acid leaching slag according to claim 1 , wherein the drying temperature in the step 5) is 105° C., and the roasting temperature is 350° C. 5 . 5. a kind of method utilizing fly ash acid leaching slag to prepare mesoporous silica according to claim 1, is characterized in that: the mesoporous silica specific surface area obtained in described step 6) reaches 452m ² /g, The average pore size is 13.22 nm.

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