A heavy metal ion blocking agent for desulfurization sludge, its preparation method and application

Abstract

This invention relates to the field of heavy metal ion treatment technology, and more particularly to a heavy metal ion blocking agent for desulfurization sludge, its preparation method, and its application. The invention provides a heavy metal ion blocking agent for desulfurization sludge, comprising the following raw materials in parts by weight: 20-40 parts chitosan; 1-3 parts metal oxide; 1-3 parts curing agent; 0.5-1 part seaweed extract; and 100-150 parts water; wherein the seaweed extract is selected from red algae extract and / or brown algae extract. The blocking agent of this invention, using chitosan, metal oxide, curing agent, seaweed extract, and water as raw materials, can effectively block heavy metal ions in desulfurization sludge, preventing them from leaching into the soil when the desulfurization sludge is used as a soil conditioner. Furthermore, the raw materials are inexpensive and readily available, and will not cause secondary pollution to the soil.

Description

Technical Field

[0001] This invention relates to the field of heavy metal ion treatment technology, and in particular to a heavy metal ion blocking agent for desulfurization sludge, its preparation method and application. Background Technology

[0002] The lime-gypsum process is a commonly used wet desulfurization method that can significantly reduce sulfur dioxide in emissions from coal-fired power plants. However, this process requires the discharge of desulfurization wastewater, which generates a large amount of desulfurization sludge during treatment.

[0003] The main components of desulfurization sludge are ash, gypsum, chloride ions, and heavy metals. It can be used as a cement retarder, to produce desulfurized gypsum insulation blocks, as building gypsum powder, and as a soil conditioner. Desulfurization sludge is used as a soil conditioner because it contains a large amount of desulfurized gypsum, which contains calcium sulfate, calcium sulfite, and essential or beneficial minerals for plants such as strontium, calcium, and silicon. The improvement of acidic soils by desulfurization sludge is mainly reflected in its ability to promote plant growth. It contains a large number of nutrients, providing essential mineral nutrition for plant growth. Simultaneously, the application of desulfurization sludge significantly increases soil pH and reduces the toxicity of Al and Mn in acidic soils. Furthermore, it enhances the ion adsorption capacity of acidic soils, improves soil water retention and cation exchange capacity, and promotes nutrient absorption by plants. Desulfurization sludge can also significantly reduce the alkalinity, sodium adsorption ratio, and pH value of alkaline soils. Calcium ions in desulfurization sludge can react chemically with sodium bicarbonate and sodium carbonate in saline-alkali soil to produce sodium bicarbonate and sodium sulfate, significantly reducing the alkalinity of the soil and eliminating its toxicity to crops. Simultaneously, the free calcium ions replace sodium ions, increasing the soil's resistance to alkali and replenishing its active calcium, thus promoting plant growth. However, desulfurization sludge also contains large amounts of heavy metal ions, such as Hg, As, Cd, Cr, Pb, Ni, and Zn. Directly adding desulfurization sludge containing heavy metal ions to the soil can cause serious pollution. Therefore, it is generally necessary to modify the desulfurization sludge to passivate and stabilize the heavy metals before it can be used as a soil conditioner.

[0004] For example, a prior art sludge heavy metal blocking agent is disclosed, composed of polysaccharide polymers, polysaccharides, glycerol, tributyl citrate, dimethyl phthalate, and water. This sludge heavy metal blocking agent encapsulates heavy metals within sludge particles, preventing their transfer or leakage into soil and groundwater during sludge land application. However, this blocking agent is expensive to manufacture and uses costly raw materials, making it unsuitable for large-scale promotion. Furthermore, dimethyl phthalate can pollute the soil and pose a health hazard. Summary of the Invention

[0005] To address the above technical problems, this invention provides a heavy metal ion blocking agent for desulfurization sludge, its preparation method, and its application. This blocking agent can block heavy metal ions in desulfurization sludge within the sludge particles, preventing the transfer of heavy metal ions into the soil. Furthermore, the raw materials are inexpensive and readily available, and will not cause secondary pollution to the soil, making it suitable for large-scale promotion.

[0006] To solve the above-mentioned technical problems, the embodiments of the present invention adopt the following technical solutions:

[0007] In a first aspect, embodiments of the present invention provide a heavy metal ion blocking agent for desulfurized sludge, comprising the following raw materials in parts by weight: 20-40 parts chitosan; 1-3 parts metal oxide; 1-3 parts curing agent; 0.5-1 part seaweed extract; and 100-150 parts water; wherein the seaweed extract is selected from red algae extract and / or brown algae extract.

[0008] In this invention, chitosan contains a large number of free amino and hydroxyl groups, which can form stable chelates with heavy metal ions. Metal oxides are widely present in soil and sediments and have the characteristics of high capacity, fast speed, and strong targeting in adsorbing heavy metals. They are environmentally friendly and high-performance adsorbent materials. The solidifying agent can change the existence form of heavy metals in desulfurization sludge, reducing their leaching toxicity and bioavailability. However, after preparing a blocking agent from chitosan, metal oxides, and solidifying agent, the blocking effect on heavy metal ions in desulfurization sludge is not good. The inventors creatively added seaweed extract to the blocking agent and found that it can effectively block heavy metal ions in desulfurization sludge, trapping heavy metal ions in the desulfurization sludge and preventing heavy metal ions in the sludge from leaching into the soil when the desulfurization sludge is used as a soil conditioner. In addition, the seaweed extract is selected from red algae extract and / or brown algae extract. Red algae and brown algae are abundant in the ocean, inexpensive and readily available, and will not cause secondary pollution to the soil.

[0009] Preferably, the metal oxide is selected from one or more of calcium oxide, magnesium oxide, or sodium oxide; and / or, the curing agent is selected from one or more of sodium sulfide, sodium thiosulfide, or metaphosphate, wherein the metaphosphate is selected from one or more of sodium metaphosphate, potassium metaphosphate, or calcium metaphosphate. Both the seaweed extract and the metal oxide are in powder form.

[0010] In this invention, the metal oxide and curing agent are inexpensive and readily available, and will not cause secondary pollution to the environment or the soil.

[0011] Preferably, the blocking agent is composed of 25-35 parts chitosan, 1.5-2.5 parts metal oxide, 1.5-2.5 parts curing agent, 0.6-0.8 parts seaweed extract, and 110-130 parts water. More specifically, the blocking agent is composed of 30 parts chitosan, 2 parts calcium oxide, 2 parts potassium metaphosphate, 0.8 parts red algae extract, and 120 parts water.

[0012] Secondly, embodiments of the present invention provide a method for preparing the above-mentioned heavy metal ion blocking agent for desulfurization sludge, characterized by comprising the following steps:

[0013] Chitosan, metal oxide, curing agent, and seaweed extract are dissolved in water and stirred at 60-80°C to obtain the blocking agent. Preferably, the stirring speed is 1000-1500 r / min; and / or the stirring time is 60-100 min.

[0014] Thirdly, embodiments of the present invention provide a method for preparing a soil conditioner, comprising the following steps:

[0015] After drying and crushing, the desulfurization sludge is added to the aforementioned desulfurization sludge heavy metal ion blocking agent, followed by stirring, filtration, and drying. Preferably, a pH adjuster is added during stirring to adjust the pH of the mixed solution to 6-8; and / or, the mass ratio of the heavy metal ions in the desulfurization sludge to the desulfurization sludge is 1:3-5.

[0016] In this invention, the pH adjuster is an acid solution, which can be acetic acid, hydrochloric acid, etc.

[0017] Fourthly, embodiments of the present invention provide a soil conditioner, which is prepared by the above-described preparation method.

[0018] Compared with the prior art, the present invention has one of the following beneficial effects:

[0019] The blocking agent of the present invention uses chitosan, metal oxide, curing agent, seaweed extract and water as raw materials. It can effectively block heavy metal ions in desulfurization sludge, and prevent heavy metal ions from leaching into the soil when the desulfurization sludge is used as a soil conditioner. Moreover, the raw materials are cheap and readily available, and will not cause secondary pollution to the soil. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0021] Desulfurization sludge is a residue formed from desulfurization wastewater with high suspended solids. The main components of desulfurization sludge include ash, gypsum, chloride ions, and heavy metals. It can be used as a soil conditioner. However, if desulfurization sludge is directly applied to the soil, it will cause the soil to be polluted by heavy metal ions. Therefore, this invention provides a desulfurization sludge heavy metal ion blocking agent. The raw materials include chitosan, metal oxides, solidifying agents, seaweed extracts, and water. The blocking agent can block heavy metal ions in desulfurization sludge within the sludge particles and prevent heavy metal ions from transferring into the soil.

[0022] Chitosan is obtained from chitin through deacetylation. The chitosan macromolecule contains active hydroxyl and amino groups, exhibiting strong chemical reactivity. Chitosan can form stable chelates with heavy metal ions through its amino and hydroxyl groups, thus finding wide applications in precious metal recovery and industrial wastewater treatment. High-viscosity soluble chitosan can be prepared using chitosan, resulting in a high-viscosity, high-quality product with excellent effects in activated sludge treatment. Furthermore, its non-toxicity and biodegradability mean that its use in wastewater treatment and metal extraction will not cause secondary pollution. While metal oxides also have adsorption properties for heavy metal ions, and solidifying agents can solidify heavy metal ions in activated sludge, the blocking effect of preparing an agent using chitosan, metal oxides, solidifying agents, and water is limited. Some heavy metal ions still transfer to the soil, causing secondary pollution. To address this, the inventors creatively added seaweed extract to the blocking agent, which effectively enhances the blocking effect of the blocking agent, trapping heavy metal ions in the desulfurization sludge and preventing heavy metal ions in the sludge from leaching into the soil when the desulfurization sludge is used as a soil conditioner.

[0023] In the raw materials of the aforementioned inhibitor, seaweed extract is a natural active substance extracted from seaweed. Seaweed is abundant in the ocean, inexpensive, and readily available. Seaweed has complex and diverse active components, including a large number of mineral elements, polysaccharides, sugar alcohols, amino acids, vitamins, cytochromes, betaine, and phenolic compounds. It also includes natural hormones such as auxins, cytokinins, gibberellins, and abscisic acid. As a raw material, it will not pollute the soil environment. In this invention, seaweed extract mainly refers to red algae extract and brown algae extract, which can be purchased commercially.

[0024] The metal oxide used in this invention can be selected from one or more of calcium oxide, magnesium oxide, or sodium oxide. Preferably, the metal oxide can be any combination of two of calcium oxide, magnesium oxide, or sodium oxide. This invention does not impose any particular limitation on the quantitative relationship between any two of the metal oxides; for example, the weight ratio can be 0.5-2:1, but this invention is not limited thereto.

[0025] The curing agent of this invention can be selected from one or more of sodium sulfide, sodium thiosulfide, or metaphosphate, and the metaphosphate can be selected from one or more of sodium metaphosphate, potassium metaphosphate, or calcium metaphosphate. Preferably, the curing agent can be any combination of two of sodium sulfide, sodium thiosulfide, sodium metaphosphate, potassium metaphosphate, or calcium metaphosphate. This invention does not particularly limit the amount of any two of the curing agents used; for example, the weight ratio can be 0.5-2:1, but this invention is not limited thereto.

[0026] The desulfurization sludge used in the following examples and comparative examples was taken from the desulfurization sludge of a coal-fired power plant in Shijiazhuang. The heavy metal ion content in the desulfurization sludge was determined according to the "Test Methods for Sludge from Urban Wastewater Treatment Plants" (CJ / T221-2005), using inductively coupled plasma atomic emission spectrometry (ICP-AES) after atmospheric pressure digestion. The heavy metal ion content in the desulfurization sludge is shown in Table 1.

[0027] Table 1. Heavy metal ion content in desulfurization sludge

[0028] Hg As Cd Cr Pb Ni Zn Cu Heavy metal ion content (mg / kg) 53.8 301.3 1.5 562.3 156.7 54.9 102.1 14.8

[0029] In the following examples and comparative examples, chitosan was purchased from Qingdao Hehai Biotechnology Co., Ltd., with a degree of deacetylation of ≥85%; red algae extract was purchased from Shaanxi Sinote Biotechnology Co., Ltd.; and brown algae extract was purchased from Shaanxi Xintianyu Biotechnology Co., Ltd.

[0030] The technical solution of the present invention will be described below with reference to specific embodiments.

[0031] Example 1

[0032] This embodiment provides a heavy metal ion blocking agent for desulfurized sludge. 30 kg of chitosan, 2 kg of calcium oxide, 2 kg of potassium metaphosphate and 0.8 kg of red algae extract are weighed, dissolved in 120 kg of water, and stirred at 1200 r / min for 80 min at 70 °C to obtain the blocking agent.

[0033] Examples 2-7

[0034] The preparation methods of the blocking agents provided in Examples 2-7 are the same as those in Example 1, and the components and their proportions are shown in Table 2.

[0035] Table 2. Raw materials and weights in the blocking agents of Examples 2-7

[0036]

[0037] In the table, "-" indicates that the raw materials do not contain that substance.

[0038] Example 8

[0039] This embodiment provides a soil conditioner. 40 kg of desulfurization sludge is weighed, dried, crushed, and set aside. It is then added to 10 kg of the blocking agent prepared in Example 1 and stirred. During the stirring process, 1 mol / L acetic acid is added to adjust the pH to about 7. The mixture is then filtered and dried to obtain the soil conditioner.

[0040] Examples 9-16

[0041] Examples 9-16 provide a soil conditioner, the preparation method, raw materials and weight parameters of which are shown in Table 3.

[0042] Table 3. Preparation methods, raw materials, and weights of soil conditioners in Examples 9-16

[0043] Blocker / weight (kg) Desulfurization sludge (kg) pH adjuster pH Example 9 Example 2 / 10 40 1 mol / L acetic acid 7 Example 10 Example 3 / 10 40 1 mol / L acetic acid 7 Example 11 Example 4 / 10 40 1 mol / L acetic acid 7 Example 12 Example 5 / 10 40 1 mol / L acetic acid 7 Example 13 Example 6 / 10 40 1 mol / L acetic acid 7 Example 14 Example 7 / 10 40 1 mol / L acetic acid 7 Example 15 Example 1 / 10 30 1 mol / L hydrochloric acid 6 Example 16 Example 1 / 10 50 1 mol / L hydrochloric acid 8

[0044] Comparative Example 1

[0045] This comparative example provides a heavy metal ion blocking agent for desulfurized sludge, which, compared to Example 1, does not contain red algae extract.

[0046] Comparative Example 2

[0047] This comparative example provides a soil conditioner. 40 kg of desulfurization sludge is weighed, dried, crushed, and set aside. It is then added to 10 kg of the blocking agent prepared in Comparative Example 1 and stirred. During the stirring process, 1 mol / L acetic acid is added to adjust the pH to about 7. The mixture is then filtered and dried to obtain the soil conditioner.

[0048] Test Case

[0049] The heavy metal content in the soil conditioners obtained in Examples 8-16 and Comparative Example 2 was determined according to the "Test Methods for Sludge from Urban Wastewater Treatment Plants" (CJ / T 221-2005), using inductively coupled plasma atomic emission spectrometry (ICP-AES) after atmospheric pressure digestion. The test results are shown in Table 4.

[0050] Table 4. Heavy metal content in soil conditioners of Examples 8-16 and Comparative Example 2.

[0051] Hg As Cd Cr Pb Ni Zn Cu Example 8 (mg / kg) 53.79 301.28 1.49 562.25 156.69 54.88 102.06 14.77 Example 9 (mg / kg) 53.77 301.23 1.48 562.18 156.67 54.87 102.09 14.76 Example 10 (mg / kg) 53.74 301.19 1.47 562.15 156.65 54.88 102.07 14.78 Example 11 (mg / kg) 53.72 301.11 1.47 562.14 156.66 54.82 102.05 14.79 Example 12 (mg / kg) 53.76 301.22 1.48 562.23 156.68 54.89 102.07 14.75 Example 13 (mg / kg) 53.76 301.25 1.48 562.22 156.62 54.87 102.04 14.72 Example 14 (mg / kg) 53.75 301.23 1.48 562.20 156.65 54.85 102.06 14.75 Example 15 (mg / kg) 53.78 301.26 1.49 562.24 156.67 54.86 102.08 14.78 Example 16 (mg / kg) 53.77 301.24 1.49 562.23 156.68 54.84 102.08 14.73 Comparative Example 2 (mg / kg) 50.14 285.17 1.30 540.13 148.31 51.16 98.47 12.65

[0052] As shown in Table 4, the addition of algae extract to the blocking agent resulted in changes in the heavy metal ion content in both the soil conditioner and the desulfurization sludge within the measurement error range. Therefore, it can be concluded that the heavy metal ion content in both the soil conditioner and the desulfurization sludge remained unchanged. Without the addition of algae extract to the blocking agent, the heavy metal ion content in the soil conditioner was significantly lower than that in the desulfurization sludge. This demonstrates that the addition of algae extract to the blocking agent can prevent the transfer of heavy metal ions from the desulfurization sludge to the water.

[0053] 100 kg of soil uncontaminated by heavy metals was collected from a site in Shijiazhuang. The soil was mixed thoroughly and divided into 10 portions of 10 kg each, labeled S8, S9, S10, S11, S12, S13, S14, S15, S16, and D2. The heavy metal content in the soil was determined using inductively coupled plasma atomic emission spectrometry (ICP-AES) after atmospheric pressure digestion. The results are shown in Table 5.

[0054] Table 5. Heavy metal content in soils not contaminated with heavy metals

[0055] Hg As Cd Cr Pb Ni Zn Cu Soil (mg / kg) 0.12 3.28 0.53 15.83 11.65 16.32 25.17 13.28

[0056] Then, 1 kg of the soil conditioner from Example 8 was buried in soil S8, 1 kg of the soil conditioner from Example 9 was buried in soil S9, 1 kg of the soil conditioner from Example 10 was buried in soil S10, 1 kg of the soil conditioner from Example 11 was buried in soil S11, 1 kg of the soil conditioner from Example 12 was buried in soil S12, 1 kg of the soil conditioner from Example 13 was buried in soil S13, 1 kg of the soil conditioner from Example 14 was buried in soil S14, 1 kg of the soil conditioner from Example 15 was buried in soil S15, 1 kg of the soil conditioner from Example 16 was buried in soil S16, and 1 kg of the soil conditioner from Comparative Example 2 was buried in soil D2. After 30 days of burial, the heavy metal content in the soil and the heavy metal content in the soil conditioner were determined by inductively coupled plasma atomic emission spectrometry (ICP-AES) after digestion under normal pressure. The test results are shown in Table 6.

[0057] Table 6. Heavy metal content in soil and soil conditioner 30 days after burial.

[0058]

[0059]

[0060] Table 6 shows that when algae extract was added to the blocking agent, the changes in heavy metal content in the soil with the embedded soil conditioner and in the uncontaminated soil were both within the measurement error range. Similarly, the changes in heavy metal ion content in the embedded soil conditioner and the uncontaminated soil conditioner were also within the measurement error range. Therefore, it can be concluded that the heavy metal content in the soil and the soil conditioner did not change before and after embedding. Without the addition of algae extract to the blocking agent, the heavy metal content in the soil with the embedded soil conditioner was significantly higher than that in the uncontaminated soil, while the heavy metal ion content in the embedded soil conditioner was significantly lower than that in the uncontaminated soil conditioner. This demonstrates that adding algae extract to the blocking agent can prevent the transfer of heavy metal ions from desulfurization sludge into the soil.

[0061] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. The application of a heavy metal ion blocking agent from desulfurization sludge in the preparation of soil conditioners from desulfurization sludge, characterized in that, The desulfurization sludge heavy metal ion blocking agent comprises the following raw materials in parts by weight: 20-40 parts chitosan; 1-3 parts of metal oxide; 1-3 parts of curing agent; 0.5-1 part seaweed extract; and 100-150 parts water; The seaweed extract is selected from red algae extract and / or brown algae extract; The metal oxide is selected from one or more of calcium oxide, magnesium oxide, or sodium oxide; The curing agent includes at least one of sodium sulfide or metaphosphate, wherein the metaphosphate is selected from at least one of sodium metaphosphate, potassium metaphosphate or calcium metaphosphate. The mass ratio of the heavy metal ion blocking agent to the desulfurized sludge is 1:3-5.

2. The application of the heavy metal ion blocking agent of desulfurization sludge according to claim 1 in the preparation of soil conditioner from desulfurization sludge, characterized in that, Both the seaweed extract and the metal oxide are in powder form.

3. The application of the heavy metal ion blocking agent of desulfurization sludge according to claim 1 in the preparation of soil conditioner from desulfurization sludge, characterized in that, The desulfurization sludge heavy metal ion blocking agent is composed of 25-35 parts chitosan, 1.5-2.5 parts metal oxide, 1.5-2.5 parts curing agent, 0.6-0.8 parts seaweed extract and 110-130 parts water.

4. The application of the heavy metal ion blocking agent of desulfurization sludge according to claim 1 in the preparation of soil conditioner from desulfurization sludge, characterized in that, The heavy metal ion blocking agent for desulfurized sludge is composed of 30 parts chitosan, 2 parts calcium oxide, 2 parts potassium metaphosphate, 0.8 parts red algae extract and 120 parts water.

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