A method of drying and solidifying a flowable silt based on phosphogypsum powder

Abstract

The application discloses a method for drying and curing flow plastic silt by using phosphogypsum-based powder, and belongs to the field of silt treatment. The method comprises the following steps: preparing a curing agent and phosphogypsum-based powder by using phosphogypsum, slag and cement respectively, and filling the phosphogypsum-based powder into non-woven fabric in a quantitative manner to form a strip-shaped component similar to lotus node; mixing the flow plastic silt with the curing agent uniformly to obtain cured silt, and then implanting the strip-shaped component containing the phosphogypsum-based powder into the cured silt for curing. The method separates the drying process and the curing process of the flow plastic silt, mixes the flow plastic silt with the curing agent first, and then implants the strip-shaped component containing the phosphogypsum-based powder immediately after mixing, so that the strip-shaped component can absorb free water, dry first and then cure. The method reduces the negative effects of high water content of the silt, absorbs a large amount of phosphogypsum, realizes in-situ curing of the silt with low energy consumption, improves the overall strength of the silt, and achieves the purpose of "waste treatment by waste".

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of environmental geotechnical-solid waste treatment, and particularly relates to a method for dryizing and solidifying phosphogypsum-based powder to flow-like silt. BACKGROUND

[0002] Dredged silt is a waste in the process of ecological environment governance of rivers, lakes and seas, which is black in color, stinks, and some of which contains heavy metal pollutants. For a long time, offshore filling and land piling are the main methods for treating silt, and the methods of piling and landfilling occupy a large amount of land resources and have potential risks of polluting the environment. In order to curb the deterioration of water environment and improve the flood control and storage capacity, scientific disposal of dredged silt and resource utilization of silt are key problems to be solved. At present, there are two measures for solidifying silt: ① separating mud and water by vacuum preloading and other methods; and ② solidifying silt by organic (inorganic) cementing materials.

[0003] Among them, the method of cement solidification is usually used for solidifying silt, but the method of hydraulic dredging is often used in China. The water content of the silt produced after the dredging construction is completed is as high as 2-3 times of the original mud liquid limit, or even higher. Therefore, the cost of using cement solidification to treat high-moisture dredged silt is too high, which seriously limits the popularization and application of the method of cement solidification.

[0004] Chinese patent CN102173695A discloses a new additive for composite solidification material of high-moisture dredged silt, which is composed of cement, quicklime and sodium polyacrylate. The additive solves the problem of rapid solidification and disposal of high-moisture dredged silt, and can significantly improve the strength of the soil. Chinese patent CN114149202A discloses a solidification agent for high-moisture dredged silt, a preparation method and application thereof. The solidification agent is prepared by mixing garbage incineration bottom slag and garbage incineration bottom slag fine powder to obtain a garbage incineration bottom slag mixture, mixing straw ash and industrial steel slag to obtain a mixture of straw ash fine powder and industrial steel slag fine powder, and finally mixing the raw materials according to the proportion. The solidification agent can effectively solidify dredged silt, reduce the water content of dredged silt, and improve the low strength characteristics of dredged silt. The solidified dredged silt can be used as a filling material, achieving the purpose of waste treatment and environmental protection.

[0005] Phosphogypsum is a solid waste produced in the process of wet-process phosphoric acid, and its main component is calcium sulfate dihydrate. The composition of phosphogypsum is relatively complex, in addition to calcium sulfate, there are also incomplete decomposition of phosphate rock, residual phosphoric acid, fluoride, acid-insoluble substances, organic matter, etc., among which the existence of fluoride and organic matter has the greatest impact on the resource utilization of phosphogypsum. The random discharge and accumulation of phosphogypsum have seriously damaged the ecological environment, not only polluting the groundwater resources, but also wasting the land resources. The random discharge and accumulation of phosphogypsum restricts the sustainable development of the wet-process phosphoric acid, phosphate fertilizer and other industries, so the treatment and recycling of phosphogypsum has become an urgent problem. Phosphogypsum is mainly used in agriculture, industry, construction and other fields. However, the storage of phosphogypsum in China is still high, and the comprehensive utilization is insufficient.

[0006] Chinese patent CN106478012A discloses a kind of sludge solidifying agent and its preparation method, using phosphogypsum, cement, quicklime, limestone, fly ash, hydroxypropyl methyl cellulose, cast stone powder, ceramic micro powder and other substances are mixed to obtain sludge solidifying agent, can significantly reduce the water content of sludge, reduce internal strain of solidified sludge, prevent cracking. Based on the traditional cement solidification treatment of sludge, Ding Jianwen et al. proposed a method of using cement-phosphogypsum double-doped solidification treatment of high-moisture dredged sludge (Ding Jianwen, Zhang Shuai, Hong Zhen-shun et al., cement-phosphogypsum double-doped solidification treatment of high-moisture dredged sludge. Rock and soil mechanics, 2010, 31 (9): 2817-2822.).

[0007] However, dredged sludge has high moisture content, and conventional solidifying agents cannot achieve good solidification effect, so it is often necessary to use drying technology, such as natural airing, mechanical dewatering, vacuum preloading dewatering, etc. However, the existing drying technology is slow, requires large-scale dewatering equipment or complex construction, and is difficult to meet the drying needs of large amounts of dredged sludge, and the heavy metal pollutants contained in the dredged sludge during the drying process have the risk of secondary environmental pollution. Therefore, it is necessary to develop a method that can not only reduce the moisture content of dredged sludge and improve the solidification effect, but also absorb a large amount of phosphogypsum. SUMMARY

[0008] In view of the above technical problems, the present application provides a method for drying and solidifying flowable sludge with phosphogypsum-based powder, which utilizes the strength growth law of phosphogypsum-based solidifying agent ("slow at first and fast later"), and ingeniously turns the disadvantages of phosphogypsum-based solidifying agent into advantages, providing sufficient time for the "lotus node" structure to absorb free water, realizing the mode of "water absorption first and solidification later" for phosphogypsum-based powder, avoiding the influence of high moisture content on the solidification effect of solidifying agent on sludge, thereby improving the strength of solidified sludge and realizing efficient and low-energy in-situ solidification of sludge.

[0009] In order to achieve the above purpose, the present application provides a method for drying and solidifying flowable sludge with phosphogypsum-based powder, comprising the following steps:

[0010] (1) preparing phosphogypsum-based powder and packing by section to make strip-shaped components;

[0011] (2) mixing phosphogypsum, slag and cement to prepare solidifying agent;

[0012] (3) mixing the solidifying agent with silt to obtain solidified silt;

[0013] (4) implanting the strip-shaped components into the solidified silt and curing the solidified silt.

[0014] Preferably, the phosphogypsum-based powder in step (1) is prepared from phosphogypsum, slag and cement in a mass ratio of 50-80:45-15:5, preferably 70:25:5.

[0015] Preferably, the strip-shaped components in step (1) are packed by section with non-woven fabric, and each section is approximately spherical.

[0016] Further preferably, the mass per unit area of the non-woven fabric is 15-25 g / m 2 , and the radius of each section is 1-3 cm.

[0017] Further, the distance between each section is 0-13 cm, and the mass of each section is 30-100 g; preferably, the distance between each section is 8-13 cm, and the mass of each section is 50 g.

[0018] Preferably, the mass ratio of phosphogypsum, slag and cement in step (2) is 15-35:65-80:5.

[0019] Preferably, the amount of the solidifying agent in step (3) is 20%-40% of the mass of the silt.

[0020] Further preferably, the water content of the silt is 120%-200%.

[0021] Preferably, the distance between the strip-shaped components in step (4) is 8-13 cm.

[0022] Further preferably, the distance between each strip-shaped component is 9.6 cm.

[0023] The present application has the following beneficial effects:

[0024] 1. The solidifying agent is mixed with the flowable silt, and the strip-shaped components containing phosphogypsum-based powder, which are similar to "lotus root sections", are implanted into the solidified silt in the early stage of solidification. The phosphogypsum-based solidifying agent absorbs free water in the solidified silt according to the strength growth rule of "slow at first and fast later", and then the silt is dried and solidified. This solves the problem of insufficient solidification strength of silt due to high water content, and reduces the negative effects of high water content of silt.

[0025] 2, the phosphogypsum-based powder is packaged into a strip-shaped member similar to "lotus node" by using non-woven fabric, the phosphogypsum-based powder forms a solidified body after absorbing free water, and the overall silt is solidified to improve the uplift resistance, thereby playing a role in improving the overall strength of the silt; at the same time, the free water in the silt absorbed by the phosphogypsum-based powder can fix the heavy metal pollutants in the silt and the phosphorus, fluorine and other pollutants in the phosphogypsum, thereby avoiding secondary pollution to the environment caused by the outflow of pollutants with water.

[0026] 3, the lower content of phosphogypsum is used to configure the solidifying agent, and the higher content of phosphogypsum is used to configure the phosphogypsum-based powder, so that a large amount of phosphogypsum is absorbed during the solidification of the fluid plastic silt, the solidification cost is reduced, the application scene of the phosphogypsum is expanded, and "waste treatment" is realized.

[0027] 4, the strip-shaped member is packaged by using non-woven fabric, which provides a channel for the free water in the silt to seep out to the outer surface, which is beneficial to the accelerated evaporation of the free water. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 It is a column chart of the curing age and compressive strength of the solidifying agent in Example 1.

[0029] Figure 2 It is a structure diagram of the strip-shaped member similar to "lotus node" in Example 2; 1 in the figure is non-woven fabric, 2 is a sleeve, and 3 is phosphogypsum-based powder.

[0030] Figure 3 It is a lacing diagram of the strip-shaped member in Example 2.

[0031] Figure 4 It is a parameter determination process and water absorption condition diagram of a single "lotus node" in Examples 2 and 3, A in the figure is the strip-shaped member prepared in Example 1, B is the water absorption experiment of "lotus node" with different radii in Example 1; C is the water absorption experiment diagram of a single "lotus node" in silt in Example 2, and D is the phosphogypsum-based powder in a gel body after water absorption.

[0032] Figure 5 It is a sectional view of the water absorption radius of the strip-shaped member in Example 4, 1 in the figure is a solid "lotus node" formed after the phosphogypsum-based powder absorbs water.

[0033] Figure 6 It is a shape diagram of the guide rod in Example 5. DETAILED DESCRIPTION

[0034] The technical solution of the present invention will be further explained and described below with reference to the accompanying drawings and specific embodiments. It is worth noting that the following embodiments are only preferred embodiments of the present invention and should not be construed as limiting the present invention. The scope of protection of the present invention should be determined by the contents of the claims. Modifications and substitutions made by those skilled in the art to the technical solution of the present invention without creative effort all fall within the scope of protection of the present invention.

[0035] In the following examples, the phosphogypsum (RPG) was purchased from Zhongfu Chemical Group Co., Ltd., with a particle size of 1.38-296 μm, and its chemical composition is shown in Table 1;

[0036] The slag (GBS) was purchased from Hubei Hongqian Environmental Protection Building Materials Co., Ltd., with a particle size of 0.97-25μm. Its chemical composition is shown in Table 1.

[0037] The cement is ordinary Portland cement (OPC) of PO42.5, and its chemical composition is shown in Table 1.

[0038] Table 1 Chemical composition of raw materials (wt%)

[0039]

[0040] Example 1: Investigation into the strength growth pattern after curing

[0041] (1) Mix phosphogypsum, slag and cement in different mass ratios to prepare curing agents with different proportions (Table 2).

[0042] (2) Mix the curing agent with the dredged sludge, stir evenly to obtain cured sludge, cure at room temperature, and test the compressive strength of the sludge after different curing times.

[0043] Table 2 Raw material ratio of curing agent

[0044]

[0045] The results are as follows Figure 1 As shown, the compressive strength of the sludge gradually increases with the extension of the curing time. When different curing agents are used for 7 days, the compressive strength of the sludge is about 14 MPa. After 28 days of curing, the compressive strength increases significantly, indicating that the compressive strength of dredged sludge and curing agent has a "fast at first and slow later" growth pattern.

[0046] Example 2: Determination of the radius and mass of a single "lotus root segment"

[0047] (1) Phosphogypsum, slag and cement are mixed evenly in a mass ratio of 70:25:5 to prepare phosphogypsum-based powder;

[0048] (2) The unit area mass is 20g / m².2 The non-woven fabric of the application is cut into a continuous long rectangle with a width of 4π cm, and the long edges are continuously heat-pressed and sealed to form a sleeve with a radius of 2 cm;

[0049] (3) The phosphogypsum-based powder is filled into the non-woven fabric sleeve by using a feeding machine, and every 2, 4, 6 cm is segmented by using a string to form a strip-shaped component similar to "lotus node" (Fig. 1) Figures 2-3 ), and then dispersed into single "lotus nodes", and the corresponding single "lotus nodes" have a radius of 1 cm, 2 cm and 3 cm, and a mass of 30 g, 50 g and 100 g, respectively;

[0050] (4) The single "lotus nodes" of different masses obtained in step (3) are respectively placed in 300 mL of water or flowable silt (moisture content is 125%), and stirred and mixed to completely immerse the single "lotus nodes", the time for the single "lotus nodes" to completely absorb water and soak is counted, and the moisture content of the single "lotus nodes" after absorbing water and soaking is calculated (A and B). Figure 4

[0051] Table 3 Mass and moisture content of "lotus nodes" before and after water absorption

[0052]

[0053] The results show that the mass of the single "lotus node" does not change after 30 min in the flowable silt, indicating that the phosphogypsum-based powder is uniformly and fully absorbed by water and soaked, and reaches a saturated state; when the radius of the single "lotus node" is 2 cm and the mass is 50 g, the mass after water absorption is the highest, which is 81.05 g, and the moisture content is the highest, which is 62.1%, indicating that the optimal radius of the single "lotus node" is 2 cm and the optimal mass is 50 g. It is shown that the phosphogypsum-based powder can absorb free water after being segmented and packaged into "lotus node" shape, and has the potential to dry the flowable silt.

[0054] Example 3

[0055] (1) The single "lotus node" with a radius of 2 cm and a mass of 50 g is prepared according to the method described in Example 1;

[0056] (2) The phosphogypsum, slag and cement are mixed uniformly according to a mass ratio of 25:75:5 to obtain a solidifying agent;

[0057] (3) The moisture content of the dredged silt is detected, the silt is mixed with the solidifying agent and stirred uniformly to obtain solidified silt (C); wherein the amount of the solidifying agent is 30% of the mass of the silt; Figure 4

[0058] ​​(4) The single "knot" obtained in step (1) and the solidified silt obtained in step (3) are mixed by means of a stirrer to make the single "knot" be distributed in the solidified silt in a point shape, and the free water in the solidified silt is absorbed by the phosphogypsum-based powder contained in the single "knot"; wherein the water absorption thickness of the "knot" is 4.8 cm, and the unit water absorption volume range is 58 cm 3 ;

[0059] (5) The solidified silt containing the single "knot" is cured at room temperature, and after 30 min, the gelling condition of the phosphogypsum-based powder is observed (D), and the compressive strength is detected after 28 d of curing. Figure 4 D), and the compressive strength is detected after 28 d of curing.

[0060] Results: The single "knot" is taken out after 30 min, the mass after water absorption is counted, and the average water absorption rate of the single "knot" is calculated to be 64.5%, and the solidification effect is shown in Table 3.

[0061] Table 4 Influence of whether "knots" are added on the solidification effect of silt

[0062]

[0063] Example 4 Water absorption area and thickness of "knot"

[0064] (1) Water absorption area of single "knot": taking a single "knot" with a mass of 50 g as an example, it is known through experiments that the water absorption mode of the single "knot" component is to spread water outward with the center as the center point on the plane; and the adsorption object of the phosphogypsum-based powder is the water in the silt, so it is assumed that ;

[0065] The volume of the dried silt is ;

[0066] The water absorption radius is ;

[0067] The water absorption area is ( Figure 5 );

[0068] (2) The sample solidified by the single "knot" in Example 3 is cut open to measure the water absorption thickness of the single "knot", and the water absorption thickness is measured to be 4.8 cm, which is the same as the calculation result in step (1). It is shown that the interval between the "knots" is 8-13 cm, and the optimal interval distance is 9.6 cm.

[0069] Example 5

[0070] (1) The strip-shaped components similar to "knots" are prepared according to the method described in Example 2, and the radius of each "knot" is 2 cm and the mass is 50 g, which are prepared for use; wherein the length of the strip-shaped component is 32 cm;

[0071] (2) mixing phosphogypsum, slag and cement uniformly according to the mass ratio of 25:70:5 to obtain a solidifying agent;

[0072] (3) mixing the dredged silt with the solidifying agent and stirring uniformly to obtain solidified silt; wherein the water content of the dredged silt is 125%; wherein the amount of the solidifying agent is 30% of the mass of the dredged silt;

[0073] (4) immediately implanting the strip-shaped member obtained in step (1) into the solidified silt layer by means of a guide rod (1) Figure 6 ) for adsorbing free water in the solidified silt and drying and solidifying for 28 days under room temperature; wherein the spacing of the strip-shaped member is 9.6 cm;

[0074] Results: the average water absorption rate of the strip-shaped member of a single "lotus node" is 63.8%, the water content of the silt after drying and solidifying for 28 days is 38.31%, and the unconfined compressive strength is 32.9 MPa.

[0075] Example 6

[0076] The method and steps are the same as those in Example 5, except that the dredged silt with a water content of 165.3% is used for solidification; the water content of the silt after drying and solidifying for 28 days is 39.21%, and the unconfined compressive strength is 30.15 MPa.

[0077] Example 7

[0078] The method and steps are the same as those in Example 5, except that the dredged silt with a water content of 198.3% is used for solidification; the water content of the silt after solidification for 28 days is 40.33%, and the unconfined compressive strength is 28.47 MPa.

[0079] Example 7

[0080] The method and steps are the same as those in Example 4, except that the spacing of the strip-shaped member is changed to 13 cm; the water content of the silt after drying and solidifying for 28 days is 45.47%, and the unconfined compressive strength is 24.17 MPa.

[0081] Example 8

[0082] The method and steps are the same as those in Example 4, except that the spacing of the strip-shaped member is changed to 8 cm; the water content of the silt after drying and solidifying for 28 days is 30.15%, and the unconfined compressive strength is 31.76 MPa.

[0083] Comparative Example 1

[0084] (1) mixing phosphogypsum, slag and cement uniformly according to the mass ratio of 25:70:5 to obtain a solidifying agent;

[0085] (2) The curing agent is mixed with the flow plastic silt, stirred uniformly, and cured at room temperature for 28 days; wherein the moisture content of the flow plastic silt is 125%.

[0086] The moisture content after drying and curing for 28 days is 78.42%, and the unconfined compressive strength is 5.63 MPa.

[0087] Comparative Example 2

[0088] (1) The non-woven fabric is cut into a continuous long rectangle with a width of 4π cm, and the long edges are continuously heat-pressed and sealed to form a sleeve with a radius of 2 cm;

[0089] (2) The phosphogypsum, slag and cement are mixed uniformly in a mass ratio of 70:25:5 to obtain a phosphogypsum-based powder;

[0090] (3) The phosphogypsum-based powder is filled into the sleeve prepared in step (1) using a filling section machine, and a line is tied every 4 cm to prepare a strip-shaped member similar to "lotus node", wherein the radius of each "lotus node" is 2 cm, and the mass of the phosphogypsum-based powder is about 50 g;

[0091] (4) The strip-shaped member obtained in step (3) is implanted into the flow plastic silt using a guide rod, and cured at room temperature for 28 days; wherein the moisture content of the flow plastic silt is 125%.

[0092] The moisture content after drying and curing for 28 days is 42.68%, and the unconfined compressive strength is 5.32 MPa.

[0093] Comparative Example 3

[0094] The method and steps are the same as those of Comparative Example 2, step (3) is omitted, and the sleeve is not tied with a line but directly cured in the flow plastic silt.

[0095] The moisture content after drying and curing for 28 days is 38.13%, and the unconfined compressive strength is 28.67 MPa, which shows that segmenting the strip-shaped member into "lotus node" shape can increase the contact area between the phosphogypsum-based powder and the cured silt, thereby improving the unconfined compressive strength.

[0096] Comparative Example 4

[0097] Since the phosphogypsum-based powder is composed of phosphogypsum, slag and cement, and contains pollutants such as "phosphorus" and "fluorine" in the phosphogypsum, and heavy metals and other pollutants in the slag, the phosphogypsum is easy to pollute the surrounding environment during transportation. The non-woven fabric not only plays a role in water diversion in water exchange, but also plays an important role in fixing pollutants such as "phosphorus" and "fluorine". Under the wrapping of the non-woven fabric, the phosphogypsum-based powder generates a cementitious product under the action of water in the silt, which fixes the pollutants in the phosphogypsum-based powder in the non-woven fabric under the premise of completing water absorption.

[0098] Comparative Example 5

[0099] The method and steps are the same as in Example 4, except that the non-woven fabric is replaced by cotton cloth. After curing for 28 days, the water content is 38.16%, and the unconfined compressive strength is 32.2 MPa. However, it is found during the experiment that after replacing the non-woven fabric with cotton cloth, a clogging phenomenon occurs during water absorption, resulting in poor water absorption effect.

Claims

1. A method for drying and solidifying phosphogypsum-based powder into fluidized sludge, characterized in that: Includes the following steps: (1) Prepare phosphogypsum base powder, and package it in sections to make strip-shaped components; (2) Mix phosphogypsum, slag and cement to prepare a curing agent; (3) Mix the curing agent with the fluidized sludge to obtain solidified sludge; (4) Insert the strip-shaped component into the solidified silt and allow it to absorb water and solidify; The phosphogypsum-based powder mentioned in step (1) is made by mixing phosphogypsum, slag, and cement in a mass ratio of 50-80:45-15:5; The strip-shaped component described in step (1) is made by packaging in sections with non-woven fabric, and each section is nearly spherical.

2. The method for drying and solidifying phosphogypsum-based powder into fluidized sludge according to claim 1, characterized in that: The nonwoven fabric has a unit area mass of 15-25 g / m². 2 Each section has a radius of 1-3cm.

3. The method for drying and solidifying phosphogypsum-based powder into fluidized sludge according to claim 2, characterized in that: The spacing between each segment is 0-13cm, and the weight of each segment is 30-100g.

4. The method for drying and solidifying phosphogypsum-based powder into fluidized sludge according to claim 1, characterized in that: The mass ratio of phosphogypsum, slag and cement in the curing agent described in step (2) is 15-35:65-80:

5.

5. The method for drying and solidifying phosphogypsum-based powder into fluidized sludge according to claim 1, characterized in that: The amount of curing agent used in step (3) is 20%-40% of the mass of the fluidized sludge.

6. The method for drying and solidifying phosphogypsum-based powder into fluidized sludge according to claim 5, characterized in that: The fluidized sludge has a water content of 120%-200%.

7. The method for drying and solidifying phosphogypsum-based powder into fluidized sludge according to claim 1, characterized in that: Step (4) The spacing between adjacent strip components is 8-13cm.

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