阅读说明：本技术 一种从磷石膏中提取二氧化硅的方法 (Method for extracting silicon dioxide from phosphogypsum ) 是由 张婧 孟醒 唐永波 刘丽娟 万建东 于 2021-02-01 设计创作，主要内容包括：本发明提供了一种从磷石膏中提取二氧化硅的方法,所述方法包括以下步骤：将磷石膏配制成浆体后进行机械搅拌,再经筛分处理,得到预处理后的磷石膏；将预处理后的磷石膏采用酸溶液进行洗涤,洗涤结束后固液分离,得到一次酸洗磷石膏,重复上述洗涤操作,洗涤次数至少为3次,最终得到二氧化硅产品。本发明所述方法通过对磷石膏的预处理以及多次酸洗,在脱除杂质后将硫酸钙组分充分溶解,从而提纯得到高纯度的二氧化硅产品,实现了磷石膏有价组分的分离与回收,有效提高其利用价值；所述方法操作简便,处理效率高,能够大量处理磷石膏,具有广泛的应用前景。(The invention provides a method for extracting silicon dioxide from phosphogypsum, which comprises the following steps: preparing phosphogypsum into slurry, mechanically stirring, and screening to obtain pretreated phosphogypsum; and (3) washing the pretreated phosphogypsum by using an acid solution, carrying out solid-liquid separation after washing to obtain the acid-washed phosphogypsum for one time, repeating the washing operation for at least 3 times, and finally obtaining the silicon dioxide product. According to the method, through pretreatment and multiple acid washing of the phosphogypsum, the calcium sulfate component is fully dissolved after impurities are removed, so that a high-purity silicon dioxide product is obtained through purification, separation and recovery of valuable components of the phosphogypsum are realized, and the utilization value of the phosphogypsum is effectively improved; the method is simple and convenient to operate, high in treatment efficiency, capable of treating a large amount of phosphogypsum and wide in application prospect.)

1. A method for extracting silica from phosphogypsum, characterized in that it comprises the following steps:

(1) preparing phosphogypsum into slurry, mechanically stirring, and screening to obtain pretreated phosphogypsum;

(2) and (2) washing the pretreated phosphogypsum obtained in the step (1) by using an acid solution, carrying out solid-liquid separation after washing to obtain the acid-washed phosphogypsum for one time, repeating the washing operation for at least 3 times, and finally obtaining the silicon dioxide product.

2. The method according to claim 1, wherein the phosphogypsum of step (1) is a by-product of a wet process phosphoric acid production process;

preferably, the phosphogypsum obtained in the step (1) is mixed with water to prepare phosphogypsum slurry;

preferably, the solid-liquid mass ratio of the mixed phosphogypsum and water is 1 (25-75).

3. The method according to claim 1 or 2, wherein the temperature of the mechanical stirring in the step (1) is 20-40 ℃;

preferably, the mechanical stirring time in the step (1) is 15-60 min;

preferably, the speed of the mechanical stirring in the step (1) is 300-800 r/min;

preferably, air is introduced during the mechanical stirring in the step (1);

preferably, the flow rate of the introduced air is 0.004-0.4 mL/s;

preferably, after the mechanical stirring in the step (1) is finished, the organic components floating on the surface layer of the slurry are scraped.

4. The method according to any one of claims 1 to 3, wherein the sieving treatment of step (1) is a wet sieving treatment;

preferably, the aperture of the screen used for the screening treatment in the step (1) is 0.3-0.4 mm;

preferably, the screened substances obtained in the screening treatment in the step (1) are sequentially washed, filtered and dried to obtain the pretreated phosphogypsum;

preferably, the screenings of the screening process of step (1) comprise calcium sulphate dihydrate for preparing the cementitious material.

5. The method according to any one of claims 1 to 4, wherein the acid solution of step (2) comprises a nitric acid solution;

preferably, the concentration of the acid solution in the step (2) is 0.025-0.25 mol/L.

6. The method according to any one of claims 1 to 5, wherein the solid-liquid mass ratio of the washing in the step (2) is 1 (25-75);

preferably, the time of the single washing in the step (2) is independently 15-60 min;

preferably, stirring is carried out in the washing process of the step (2);

preferably, the stirring speed is 300-800 r/min.

7. The method according to any one of claims 1 to 6, wherein step (2) is filtered, dried and then washed again after each washing;

preferably, the number of washing in the step (2) is 3-8.

8. The process according to any one of claims 1 to 7, wherein the washing liquid obtained after the solid-liquid separation in step (2) is returned to reuse or the washing liquids are combined and subjected to a recovery treatment.

9. The process of any one of claims 1-8, wherein the silica product of step (2) has a purity of 90 wt.% or greater.

10. Method according to any of claims 1-9, characterized in that the method comprises the steps of:

(1) preparing phosphogypsum slurry from phosphogypsum and water according to a solid-liquid mass ratio of 1 (25-75), then mechanically stirring at the temperature of 20-40 ℃ for 15-60 min at the speed of 300-800 r/min, introducing air at the flow rate of 0.004-0.4 mL/s during the mechanical stirring, scraping organic components floating on the surface layer of the slurry after the mechanical stirring is finished, and then carrying out screening treatment, wherein the aperture of a screen used for the screening treatment is 0.3-0.4 mm, and the screened substances are sequentially washed, filtered and dried to obtain the pretreated phosphogypsum;

(2) washing the pretreated phosphogypsum obtained in the step (1) by using a nitric acid solution, wherein the concentration of the nitric acid solution is 0.025-0.25 mol/L, the solid-liquid mass ratio of washing is 1 (25-75), the washing time is 15-60 min, stirring is carried out in the washing process, solid-liquid separation and drying are carried out after washing is finished to obtain the acid-washed phosphogypsum for one time, the washing operation is repeated for 3-8 times, the washing liquid obtained after solid-liquid separation is returned for reuse, or the washing liquids are combined and then recycled, and the phosphogypsum is subjected to acid washing for multiple times to finally obtain a silicon dioxide product.

Technical Field

The invention belongs to the technical field of solid waste utilization, and relates to a method for extracting silicon dioxide from phosphogypsum.

Background

The phosphogypsum is mainly derived from a wet-process phosphoric acid production process, belongs to one of industrial byproduct gypsums, has larger yield, and most of the phosphogypsum is mainly stockpiled, thereby occupying a large amount of storage space, causing serious pollution to the surrounding environment and influencing the ecological environment and human life, and therefore, the phosphogypsum is necessary to be recycled and recycled. The main and side reactions in the production process of phosphoric acid and the addition of various additives cause the impurities in the byproduct phosphogypsum to be complex in type and wide in concentration range, and the comprehensive utilization of the phosphogypsum has the defects of high impurity removal difficulty, complex process flow, high investment, poor economic feasibility and the like, so that the overall utilization rate is not high, and the main utilization direction is still used for preparing sulfuric acid, cement retarder, gypsum plasterboard and the like.

At present, the impurity removal mode of the phosphogypsum mainly comprises a water washing method, a neutralization method, a flotation method, an acid leaching method or the combination of the methods, but generally only can remove soluble impurities, the impurity removal is insufficient, the water consumption is large, and the generated wastewater is easy to cause secondary pollution; moreover, the impurity removal of the phosphogypsum only removes soluble impurities and organic matters, insoluble components such as silicon dioxide are not treated and still exist in the phosphogypsum, and the performance of the components is influenced, so that a new impurity removal and utilization mode of the phosphogypsum needs to be found, and the problem of low utilization rate at present is solved.

CN 107381512A discloses a method for simultaneously preparing sulfuric acid and potassium sulfate by using potassium feldspar, phosphogypsum and silica, which comprises the following steps: uniformly mixing potassium feldspar, phosphogypsum and silica which are finely ground to be less than 150 mu m according to a certain proportion, mixing the mixture with a binder for pelletizing, and roasting the pellets for a certain time at a certain temperature to obtain a solid reduction product and SO-containing products₂Tail gas; leaching the obtained solid reduction product with water at a certain temperature and a certain liquid-solid ratio for a period of time to obtain a potassium-rich solution; the obtained SO-containing₂And (4) dedusting and purifying the tail gas, and then sending the tail gas into a sulfuric acid system to prepare a sulfuric acid finished product. The method still belongs to the traditional utilization direction of the phosphogypsum, the phosphogypsum is not fully separated but directly utilized by multiple components, the utilization effect is limited, other components are required to be matched for use, the utilization amount of the phosphogypsum is limited, and SO is contained₂The tail gas is easy to cause secondary pollution.

CN 109553372A discloses a preparation and use method of a recyclable phosphogypsum roadbed material, which comprises the steps of adding phosphogypsum with the free water content of 7-20% into a saturated calcium hydroxide solution for neutralization reaction to obtain phosphogypsum with the soluble phosphate radical and fluoride ions removed, then carrying out high-temperature calcination at the temperature of 170-350 ℃ to convert dihydrate gypsum into III-type anhydrous gypsum, mixing the prepared III-type anhydrous gypsum with water, a water reducing agent and a waterproof agent to obtain the phosphogypsum roadbed material, wherein the treatment of the phosphogypsum only removes the soluble impurities, even if the phosphogypsum is calcined, components such as silicon dioxide and the like cannot be removed, the obtained product has limited performance, the anhydrous gypsum is easy to hydrate, the water reducing agent and the waterproof agent are not required to be added, and the cost of the raw materials is high.

In conclusion, for the comprehensive utilization of the phosphogypsum, on the basis of removing impurities, valuable components need to be separated so as to be respectively utilized, the product performance of each product is improved, and the high-value utilization of the phosphogypsum is realized.

Disclosure of Invention

Aiming at the problems in the prior art, the invention aims to provide a method for extracting silicon dioxide from phosphogypsum, which is characterized in that the phosphogypsum is pretreated and pickled for multiple times, and calcium sulfate components are dissolved after impurities are removed, so that high-purity silicon dioxide is obtained by purification, the separation and recovery of valuable components of the phosphogypsum are realized, and the utilization value of the phosphogypsum is effectively improved.

In order to achieve the purpose, the invention adopts the following technical scheme:

the invention provides a method for extracting silicon dioxide from phosphogypsum, which comprises the following steps:

(1) preparing phosphogypsum into slurry, mechanically stirring, and screening to obtain pretreated phosphogypsum;

(2) and (2) washing the pretreated phosphogypsum obtained in the step (1) by using an acid solution, carrying out solid-liquid separation after washing to obtain the acid-washed phosphogypsum for one time, repeating the washing operation for at least 3 times, and finally obtaining the silicon dioxide product.

In the invention, the comprehensive utilization of the phosphogypsum is an effective way for solving the problem of stockpiling, firstly, pretreatment operation is adopted to remove soluble impurities and organic matters in the phosphogypsum, the utilization difficulty of the phosphogypsum is reduced, and the influence on the performance of a subsequent preparation product is avoided, then, the characteristic of inorganic strong acid is utilized, repeated washing is carried out, the main component calcium sulfate of the phosphogypsum is dissolved, the high-purity silicon dioxide component is mainly remained, the purification of the silicon dioxide component is realized, the influence of the calcium sulfate and the silicon dioxide on the performance of the product taking the calcium sulfate as the main component is avoided by separating the calcium sulfate and the silicon dioxide, and the utilization value of the phosphogypsum is; the method is simple and convenient to operate, high in treatment efficiency, capable of treating a large amount of phosphogypsum and wide in application prospect.

The following technical solutions are preferred technical solutions of the present invention, but not limited to the technical solutions provided by the present invention, and technical objects and advantageous effects of the present invention can be better achieved and achieved by the following technical solutions.

As a preferable technical scheme of the invention, the phosphogypsum in the step (1) is a byproduct of a wet-process phosphoric acid production process.

Preferably, the phosphogypsum in the step (1) is mixed with water to prepare phosphogypsum slurry.

Preferably, the solid-liquid mass ratio of the phosphogypsum mixed with water is 1 (25-75), such as 1:25, 1:30, 1:40, 1:50, 1:60, 1:70 or 1:75, but not limited to the recited values, and other values not recited in the range of the values are also applicable.

In a preferred embodiment of the present invention, the temperature of the mechanical stirring in the step (1) is 20 to 40 ℃, for example, 20 ℃, 25 ℃, 30 ℃, 35 ℃ or 40 ℃, but the mechanical stirring is not limited to the above-mentioned values, and other values not shown in the above-mentioned range of values are also applicable.

Preferably, the mechanical stirring time in step (1) is 15-60 min, such as 15min, 20min, 30min, 40min, 50min or 60min, but not limited to the recited values, and other values not recited in the range of the values are also applicable.

Preferably, the mechanical stirring rate in step (1) is 300-800 r/min, such as 300r/min, 400r/min, 500r/min, 600r/min, 700r/min or 800r/min, but not limited to the recited values, and other values not recited in the range of values are also applicable.

Preferably, air is introduced during the mechanical stirring in the step (1).

Preferably, the air is introduced at a flow rate of 0.004 to 0.4mL/s, for example, 0.004mL/s, 0.01mL/s, 0.05mL/s, 0.1mL/s, 0.2mL/s, 0.3 mL/s, or 0.4mL/s, but not limited to the values listed, and other values not listed in the range of values are also applicable.

In the invention, as the composition of the phosphogypsum is more complex and the impurities are more in variety, the soluble components are dissolved by adopting a mode of preparing the phosphogypsum, the process is promoted by mechanical stirring, and air is introduced to bring organic components out of the phosphogypsum, so that the impurities floating on the surface of the slurry are scraped better, and the impurities in the phosphogypsum can be effectively removed.

Preferably, after the mechanical stirring in the step (1) is finished, the organic components floating on the surface layer of the slurry are scraped.

In the invention, due to the use of organic components in the wet-process phosphoric acid production process, the obtained byproduct phosphogypsum inevitably has residual organic components, and due to the difference of density and property with a water phase, the components float on the surface of slurry after pretreatment.

As a preferable technical scheme of the invention, the screening treatment in the step (1) is wet screening treatment.

Preferably, the screen used for the sieving treatment in step (1) has a pore size of 0.3 to 0.4mm, such as 0.3mm, 0.32mm, 0.34mm, 0.35mm, 0.36mm, 0.38mm, or 0.4mm, but not limited to the recited values, and other values not recited in the range of values are also applicable.

Preferably, the screened material obtained by the screening treatment in the step (1) is washed, filtered and dried in sequence to obtain the pretreated phosphogypsum.

Preferably, the screenings of the screening process of step (1) comprise calcium sulphate dihydrate for preparing the cementitious material.

In the invention, the phosphogypsum after being dissolved and stirred is sieved again, large particle components are separated out, and the phosphogypsum is further subjected to impurity removal.

As a preferred technical scheme of the invention, the acid solution in the step (2) comprises a nitric acid solution.

Preferably, the concentration of the acid solution in step (2) is 0.025-0.25 mol/L, such as 0.025mol/L, 0.05mol/L, 0.075mol/L, 0.1mol/L, 0.15mol/L, 0.2mol/L, or 0.25mol/L, but not limited to the recited values, and other values in the range are also applicable.

In the invention, the use of the high-concentration nitric acid solution can improve the solubility of slightly soluble calcium sulfate, and in order to fully dissolve the calcium sulfate, the phosphogypsum is repeatedly washed for many times, so that only the silicon dioxide component which is difficult to dissolve in acid is remained. If the concentration of the acid solution is too low, the dissolution amount of calcium sulfate is insufficient, the purity of the silicon dioxide product is reduced, and if the concentration of the acid solution is too high, the crystal lattice of calcium sulfate can be damaged, the loss of calcium sulfate is caused, and the recovery is not facilitated.

In a preferred embodiment of the present invention, the solid-liquid mass ratio of the washing in step (2) is 1 (25) to 75, for example, 1:25, 1:30, 1:40, 1:50, 1:60, 1:70, or 1:75, but the present invention is not limited to the above-mentioned values, and other values not listed in the above-mentioned range are also applicable.

Preferably, the time of the single washing in step (2) is independently 15-60 min, such as 15min, 20min, 30min, 40min, 50min or 60min, but not limited to the recited values, and other values not recited in the range of the values are also applicable.

Preferably, stirring is performed during the washing process in the step (2).

Preferably, the stirring rate is 300 to 800r/min, such as 300r/min, 400r/min, 500r/min, 600r/min, 700r/min, 800r/min, etc., but not limited to the recited values, and other values not recited within the range of values are equally applicable.

As a preferable embodiment of the present invention, the step (2) is carried out by filtering, drying and then washing again after each washing.

Preferably, the number of washing in step (2) is 3-8, such as 3, 4, 5, 6, 7 or 8.

As a preferable embodiment of the present invention, the washing liquid obtained after the solid-liquid separation in the step (2) is returned to reuse, or the washing liquids are combined and then subjected to a recovery treatment.

As a preferred embodiment of the present invention, the silica product of step (2) has a purity of 90 wt% or more, for example, 90 wt%, 91 wt%, 92 wt%, 93 wt%, 94 wt%, 95 wt%, or 96 wt%, but is not limited to the recited values, and other values not recited within the range of the recited values are also applicable.

As a preferred technical scheme of the invention, the method comprises the following steps:

(1) preparing phosphogypsum slurry from phosphogypsum and water according to a solid-liquid mass ratio of 1 (25-75), then mechanically stirring at the temperature of 20-40 ℃ for 15-60 min at the speed of 300-800 r/min, introducing air at the flow rate of 0.004-0.4 mL/s during the mechanical stirring, scraping organic components floating on the surface layer of the slurry after the mechanical stirring is finished, and then carrying out screening treatment, wherein the aperture of a screen used for the screening treatment is 0.3-0.4 mm, and the screened substances are sequentially washed, filtered and dried to obtain the pretreated phosphogypsum;

(2) washing the pretreated phosphogypsum obtained in the step (1) by using a nitric acid solution, wherein the concentration of the nitric acid solution is 0.025-0.25 mol/L, the solid-liquid mass ratio of washing is 1 (25-75), the washing time is 15-60 min, stirring is carried out in the washing process, solid-liquid separation and drying are carried out after washing is finished to obtain the acid-washed phosphogypsum for one time, the washing operation is repeated for 3-8 times, the washing liquid obtained after solid-liquid separation is returned for reuse, or the washing liquids are combined and then recycled, and the phosphogypsum is subjected to acid washing for multiple times to finally obtain a silicon dioxide product.

Compared with the prior art, the invention has the following beneficial effects:

(1) according to the method, through pretreatment and multiple acid washing of the phosphogypsum, the calcium sulfate component is fully dissolved after impurities are removed, so that a high-purity silicon dioxide product is obtained through purification, the purity of the silicon dioxide product can reach over 90 wt%, separation and recovery of valuable components of the phosphogypsum are realized, and the utilization value of the silicon dioxide product is effectively improved;

(2) the method disclosed by the invention is simple and convenient to operate, high in treatment efficiency, capable of treating a large amount of phosphogypsum and wide in application prospect.

Detailed Description

In order to better illustrate the present invention and facilitate the understanding of the technical solutions of the present invention, the present invention is further described in detail below. However, the following examples are only simple examples of the present invention and do not represent or limit the scope of the present invention, which is defined by the claims.

The invention provides in part a method of extracting silica from phosphogypsum, the method comprising the steps of:

(1) preparing phosphogypsum into slurry, mechanically stirring, and screening to obtain pretreated phosphogypsum;

(2) and (2) washing the pretreated phosphogypsum obtained in the step (1) by adopting an acid solution, carrying out solid-liquid separation after washing to obtain the acid-washed phosphogypsum for one time, repeating the washing operation for at least 3 times, and finally obtaining the silicon dioxide product.

The following are typical but non-limiting examples of the invention:

example 1:

this example provides a process for extracting silica from phosphogypsum, comprising the steps of:

(1) preparing phosphogypsum slurry from phosphogypsum and water according to the solid-liquid mass ratio of 1:50, then mechanically stirring, wherein the temperature of mechanical stirring is 25 ℃, the time is 30min, the speed of mechanical stirring is 800r/min, air is introduced during the mechanical stirring process, the flow rate is 0.04mL/s, after the mechanical stirring is finished, the organic components floating on the surface layer of the slurry are scraped and then screened, the aperture of a screen used for screening is 0.315mm, and screened substances are sequentially washed, filtered and dried to obtain the pretreated phosphogypsum;

(2) washing the pretreated phosphogypsum obtained in the step (1) by using a 0.1mol/L nitric acid solution, wherein the solid-liquid mass ratio of washing is 1:50, the washing time is 30min, stirring is carried out in the washing process, the stirring speed is 800r/min, filtering and drying are carried out after the washing is finished to obtain the acid-washed phosphogypsum for one time, the washing liquid obtained after filtering and separating is returned for reuse, the washing operation is repeated for 5 times, the washing is finally carried out, the recycling treatment is carried out on the washing liquid finally obtained, and the silicon dioxide product is finally obtained after the phosphogypsum is subjected to acid washing for multiple times.

In the embodiment, through pretreatment and repeated washing of the phosphogypsum, the silicon dioxide component in the phosphogypsum is effectively purified, the purity of the silicon dioxide product reaches 95.43 wt%, and the full separation and recovery of valuable components in the phosphogypsum are realized.

Example 2:

this example provides a process for extracting silica from phosphogypsum, comprising the steps of:

(1) preparing phosphogypsum slurry from phosphogypsum and water according to the solid-liquid mass ratio of 1:25, then mechanically stirring, wherein the temperature of the mechanical stirring is 30 ℃, the time is 45min, the speed of the mechanical stirring is 450r/min, air is introduced during the mechanical stirring, the flow rate is 0.2mL/s, after the mechanical stirring is finished, the organic components floating on the surface layer of the slurry are scraped, and then screening treatment is carried out, the aperture of a screen used for screening treatment is 0.35mm, and screened objects after the screening treatment are sequentially washed, filtered and dried to obtain the pretreated phosphogypsum;

(2) washing the pretreated phosphogypsum obtained in the step (1) by using a 0.03mol/L nitric acid solution, wherein the solid-liquid mass ratio of washing is 1:25, the washing time is 45min, stirring is carried out in the washing process, the stirring speed is 450r/min, filtering and drying are carried out after the washing is finished to obtain the acid-washed phosphogypsum for one time, the washing operation is repeated for 6 times, finally the obtained washing liquid is recycled, and finally the silicon dioxide product is obtained after the phosphogypsum is subjected to acid washing for multiple times.

In the embodiment, through pretreatment and repeated washing of the phosphogypsum, the silicon dioxide component in the phosphogypsum is effectively purified, the purity of the silicon dioxide product reaches 90.22 wt%, and the full separation and recovery of valuable components in the phosphogypsum are realized.

Example 3:

this example provides a process for extracting silica from phosphogypsum, comprising the steps of:

(1) preparing phosphogypsum slurry from phosphogypsum and water according to the solid-liquid mass ratio of 1:75, then mechanically stirring, wherein the temperature of mechanical stirring is 40 ℃, the time is 15min, the speed of mechanical stirring is 700r/min, air is introduced during the mechanical stirring process, the flow rate is 0.4mL/s, after the mechanical stirring is finished, the organic components floating on the surface layer of the slurry are scraped and then screened, the aperture of a screen used for screening is 0.3mm, and screened substances are sequentially washed, filtered and dried to obtain the pretreated phosphogypsum;

(2) washing the pretreated phosphogypsum obtained in the step (1) by using a 0.25mol/L nitric acid solution, wherein the solid-liquid mass ratio of washing is 1:75, the washing time is 15min, stirring is carried out in the washing process, the stirring speed is 700r/min, filtering and drying are carried out after the washing is finished to obtain the acid-washed phosphogypsum for one time, the washing liquid obtained after filtering and separating is returned for reuse, the washing operation is repeated for 3 times, the washing liquid obtained finally is recycled, and the silicon dioxide product is finally obtained after the phosphogypsum is subjected to acid washing for multiple times.

In the embodiment, through pretreatment and repeated washing of the phosphogypsum, the silicon dioxide component in the phosphogypsum is effectively purified, the purity of the silicon dioxide product reaches 93.56 wt%, and the full separation and recovery of valuable components in the phosphogypsum are realized.

Example 4:

this example provides a process for extracting silica from phosphogypsum, comprising the steps of:

(1) preparing phosphogypsum slurry from phosphogypsum and water according to the solid-liquid mass ratio of 1:60, then mechanically stirring, wherein the temperature of mechanical stirring is 20 ℃, the time is 60min, the speed of mechanical stirring is 300r/min, air is introduced during the mechanical stirring process, the flow rate is 0.006mL/s, after the mechanical stirring is finished, the organic components floating on the surface layer of the slurry are scraped and then screened, the aperture of a screen used for screening is 0.4mm, and screened objects are sequentially washed, filtered and dried to obtain the pretreated phosphogypsum;

(2) washing the pretreated phosphogypsum obtained in the step (1) by using a 0.15mol/L nitric acid solution, wherein the solid-liquid mass ratio of washing is 1:60, the washing time is 60min, stirring is carried out in the washing process, the stirring speed is 300r/min, filtering and drying are carried out after the washing is finished to obtain the acid-washed phosphogypsum for one time, the washing liquid obtained after filtering and separating is returned for reuse, the washing operation is repeated for 8 times, the washing is carried out for the final time, the finally obtained washing liquid is recycled, and the phosphogypsum is subjected to acid washing for multiple times to obtain the silicon dioxide product.

In the embodiment, through pretreatment and repeated washing of the phosphogypsum, the silicon dioxide component in the phosphogypsum is effectively purified, the purity of the silicon dioxide product reaches 92.14 wt%, and the full separation and recovery of valuable components in the phosphogypsum are realized.

Example 5:

this example provides a process for extracting silica from phosphogypsum, comprising the steps of:

(1) preparing phosphogypsum slurry from phosphogypsum and water according to the solid-liquid mass ratio of 1:40, then mechanically stirring at the temperature of 35 ℃ for 40min at the speed of 600r/min, scraping organic components floating on the surface layer of the slurry after the mechanical stirring is finished, and then carrying out screening treatment, wherein the aperture of a screen used for the screening treatment is 0.38mm, and sequentially washing, filtering and drying screened substances subjected to the screening treatment to obtain the pretreated phosphogypsum;

(2) washing the pretreated phosphogypsum obtained in the step (1) by using a 0.2mol/L nitric acid solution, wherein the solid-liquid mass ratio of washing is 1:40, the washing time is 40min, stirring is carried out in the washing process, the stirring speed is 600r/min, filtering and drying are carried out after the washing is finished to obtain the acid-washed phosphogypsum for one time, the washing liquid obtained after filtering and separating is returned for reuse, the washing operation is repeated for 4 times, the washing liquid obtained finally is recycled, and the silicon dioxide product is finally obtained after the phosphogypsum is subjected to acid washing for multiple times.

In the embodiment, through pretreatment and repeated washing of the phosphogypsum, the silicon dioxide component in the phosphogypsum is effectively purified, the purity of the silicon dioxide product reaches 90.58 wt%, and the full separation and recovery of valuable components in the phosphogypsum are realized.

Example 6:

this example provides a process for extracting silica from phosphogypsum, which is referred to the process of example 2, except that: the concentration of the nitric acid used in the step (2) is 0.02 mol/L.

Example 7:

this example provides a process for extracting silica from phosphogypsum, which is referred to the process of example 3, except that: the concentration of the nitric acid used in the step (2) is 0.3 mol/L.

In both of the above examples, the lower concentration of nitric acid used in example 6 reduced the dissolution of the calcium sulphate component in phosphogypsum, resulting in a reduction of the purity of the silica in the final product of 75 wt%; on the other hand, the concentration of the nitric acid used in example 7 is too high, which may cause the crystal lattice of calcium sulfate to be damaged, resulting in the loss of calcium sulfate and difficult recovery.

The method has the advantages that through the pretreatment and multiple acid washing of the phosphogypsum, the calcium sulfate component is fully dissolved after impurities are removed, so that a high-purity silicon dioxide product is obtained through purification, the purity of the silicon dioxide product can reach over 90 wt%, the separation and recovery of valuable components of the phosphogypsum are realized, and the utilization value of the silicon dioxide product is effectively improved; the method is simple and convenient to operate, high in treatment efficiency, capable of treating a large amount of phosphogypsum and wide in application prospect.

The applicant states that the present invention is illustrated in detail by the above examples, but the present invention is not limited to the above detailed methods, i.e. it is not meant that the present invention must rely on the above detailed methods for its implementation. It will be apparent to those skilled in the art that any modification, equivalent substitution of the process of the invention and addition of ancillary operations, selection of specific means, etc., of the present invention are within the scope and disclosure of the invention.