Method for water and heat reduction and heavy metal stabilization of river channel sediment

Abstract

The present application relates to the field of environmental science, in particular to a method for water-heat reduction and heavy metal stabilization of river channel sediment, which realizes the reduction and heavy metal stabilization of river channel sediment by water-heat treatment after adsorption and dewatering pretreatment of the river channel sediment. The present application studies the influence of water-heat treatment on the physicochemical properties of river channel sediment, reveals the main mechanism of water-heat reduction of river channel sediment, and explores the migration behavior and stabilization mechanism of heavy metals in the water-heat treatment process, so as to provide technical support for water-heat reduction and stabilization of sediment and basis for subsequent land use of sediment.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of environmental science, in particular to a method for reducing water and heat and stabilizing heavy metals in river sediment. BACKGROUND

[0002] The release of heavy metals from sediment into water is one of the key problems in water remediation. When the water environment changes, the heavy metals enriched in the sediment of the water body can pollute the overlying water body, causing secondary pollution of the water body. For example, the high-bio-toxicity heavy metals such as Zn, Cu, Cr, Cd, Ni, and Pb contained in the river sediment have great toxic risk to the ecological environment and human health when they migrate to water and soil. Therefore, reducing the amount of water and heat and stabilizing heavy metals in the sediment is an important measure to control the risk of heavy metals in the sediment. SUMMARY

[0003] Based on the above, the present application provides a method for reducing water and heat and stabilizing heavy metals in river sediment. The present application uses a hydrothermal method to reduce the amount of water and heat and stabilize heavy metals in the sediment. The treated sediment is first added with tannic acid and magnetic biochar for dehydration and adsorption pretreatment, and then subjected to hydrothermal treatment by stage heating. After the reaction is completed, the sediment is quickly cooled with a water bath cooling cycle machine, so as to achieve the purpose of high-speed and high-efficiency stabilization of heavy metals and realize the reduction of the amount of sediment.

[0004] To achieve the above purpose, the present application provides the following solutions:

[0005] The present application provides a method for reducing water and heat and stabilizing heavy metals in river sediment. After the adsorption and dehydration pretreatment of the river sediment, the river sediment is subjected to hydrothermal treatment.

[0006] Further, the adsorption and dehydration pretreatment is performed by adding tannic acid and magnetic biochar to the river sediment.

[0007] Further, the hydrothermal treatment is divided into two stages. The temperature of the first stage of hydrothermal treatment is 150-180℃, and the time is 20-30min. The temperature of the second stage of hydrothermal treatment is 240-280℃, and the time is 0.5h-7.5h.

[0008] Further, before the hydrothermal treatment of the river sediment, the adsorption and dehydration pretreated river sediment is subjected to centrifugal separation and freeze-drying.

[0009] Further, after the hydrothermal treatment, the method further comprises the steps of rapid cooling and suction filtration.

[0010] Further, after the suction filtration, the method further comprises the step of drying the solid product obtained by suction filtration.

[0011] Further, the drying temperature is 100-110 DEG C.

[0012] Further, the drying time is 10-12h.

[0013] The application also provides a method for reducing the bioavailability of heavy metal components in river sediment, which adopts the above-mentioned method for water heat reduction and heavy metal stabilization of river sediment.

[0014] The application discloses the following technical effects:

[0015] The application provides a method for reducing river sediment and stabilizing heavy metal in the sediment by using a hydrothermal method. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0017] Figure 1 The application also provides a method for reducing the bioavailability of heavy metal components in river sediment, which adopts the above-mentioned method for water heat reduction and heavy metal stabilization of river sediment.

[0018] Figure 2 The application also provides a method for reducing the bioavailability of heavy metal components in river sediment, which adopts the above-mentioned method for water heat reduction and heavy metal stabilization of river sediment.

[0019] Figure 3 The application also provides a method for reducing the bioavailability of heavy metal components in river sediment, which adopts the above-mentioned method for water heat reduction and heavy metal stabilization of river sediment. DETAILED DESCRIPTION

[0020] The following detailed description of various exemplary embodiments of the application should not be considered to place limitations on the present application, but should be understood to be a description of certain aspects, features, and embodiments of the application.

[0021] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. Additionally, for a range of values of, an intermediate value of is specifically contemplated. Each of these intermediate values is also encompassed within the scope of the present application. The upper and lower limits of these smaller ranges can independently be included or excluded in the ranges.

[0022] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Although preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application. All documents mentioned herein are incorporated by reference to disclose and describe in detail the methods and / or materials which are related to the present application. In the case of conflict between the present specification and any document incorporated herein by reference, the present specification will control.

[0023] Many modifications and variations of the present application described in the specification are possible without departing from the scope or spirit of the application. Other embodiments of the application will be apparent to those skilled in the art from consideration of the specification and practice of the application. The specification and examples are illustrative only.

[0024] As used herein, the terms "comprises", "comprising", "includes", "including", "has", "having", "contains", "containing", or variations thereof, are intended to be open-ended terms that mean including, but not limited to.

[0025] As used herein, the term "room temperature" means 20-30℃, unless otherwise specified.

[0026] The first aspect of the present application provides a method for water heat reduction and heavy metal stabilization of river sediment. The river sediment is subjected to adsorption and dewatering pretreatment, and then subjected to hydrothermal treatment.

[0027] In some embodiments of the present application, the adsorption and dewatering pretreatment is performed by adding tannic acid and magnetic biochar to the river sediment. The adsorption and dewatering pretreatment is performed at room temperature for 5 minutes.

[0028] In the present application, tannic acid and magnetic biochar are used as auxiliary means for dewatering and adsorbing the river sediment. The tannic acid assists in hydrothermal treatment and improves the dewatering effect. The magnetic biochar adsorbs part of the heavy metals in the sediment and supernatant.

[0029] In some embodiments of the present application, the hydrothermal treatment is carried out in two stages, the first stage of hydrothermal treatment is at a temperature of 150-180℃ for 20-30 minutes; the second stage of hydrothermal treatment is at a temperature of 240-280℃ for 0.5h-7.5h. The heating rate of the first stage and the second stage is 5℃ / min.

[0030] In the present application, the heating is carried out in two stages: in the first stage, i.e. the hydrolysis stage (150-180℃), the temperature is maintained for 20-30 minutes, mainly for the hydrolysis of the macromolecular substances, the secondary structure of the protein is destroyed, which is conducive to the enhancement of the hydrophobicity of the sludge and the release of the bound water of the sludge, thereby improving the dewatering property of the sludge; in the second stage, i.e. the carbonization stage (240-280℃), the temperature is maintained for 0.5h-7.5h (preferably 3-7.5h), the decarboxylation, deamination and dehydration reactions cause the polymerization and aromatization of the macromolecular substances in the high-temperature sludge, which can make the high-temperature sludge have a stable and smooth structure, thereby further reducing the water holding capacity of the sludge.

[0031] In some embodiments of the present application, before the hydrothermal treatment of the river channel sediment, the step of centrifugal separation and freeze-drying of the river channel sediment after the adsorption and dewatering pretreatment is further included. The parameters of freeze-drying are set as follows (temperature: -10℃ to -50℃, vacuum degree: 1.3-13Pa).

[0032] In some embodiments of the present application, after the hydrothermal treatment, the step of rapid cooling and suction filtration is further included.

[0033] In some embodiments of the present application, after the suction filtration, the step of drying the solid product obtained by suction filtration is further included.

[0034] In some embodiments of the present application, the drying temperature is 100-110℃.

[0035] In some embodiments of the present application, the drying time is 10-12h.

[0036] The second aspect of the present application provides a method for reducing the bioavailability of heavy metals in river channel sediment, which adopts the above-mentioned method for hydrothermal reduction and heavy metal stabilization of river channel sediment.

[0037] The hydrothermal method is a chemical reaction carried out in a closed container under relatively low temperature and high pressure conditions with water as the solvent. The hydrothermal treatment can change the form of heavy metals in the river channel sediment, promote the transformation from unstable state to stable state, and realize the stabilization and harmlessness of the heavy metals in the river channel sediment. After the hydrothermal treatment, the heavy metals such as Ni, Cr, Zn, Cu, Cd and Pb are transformed from weakly bound state to stable state, which greatly reduces the ecological risk.

[0038] The river channel sediment deposit has great difference from sludge, and the present application carries out the influence of hydrothermal treatment on the physical and chemical properties of river channel sediment, reveals the main mechanism of river channel sediment hydrothermal reduction, and explores the migration behavior and stabilization mechanism of heavy metals in the hydrothermal treatment process, so as to provide technical support for the hydrothermal reduction and stabilization of sediment, and provide basis for subsequent land use of sediment.

[0039] The tannic acid used in the embodiments of the present application is analytical grade from Sigma-Aldrich.

[0040] The magnetic biochar used in the embodiments of the present application is a biochar / hydro ferrite composite material, which is prepared by the following steps:

[0041] The original biochar (AB, from Zhejiang Ecological Environment Technology Co., Ltd.) is ground and sieved to a size of less than 0.2 mm. 4.48 g of AB is added to a 250 mL beaker, 80 mL of deionized water is added, and ultrasonic is applied for 10 minutes to disperse the particles. Then, 1.0 g of Na2SO4 is added to the mixture, and then 20 mL of 1 mol / L FeCl3 solution is added to the beaker, and incubated for 10 minutes, corresponding to the mass ratio of AB / Fe of 4.0. Sodium hydroxide solution (5.0 mol / L) is added dropwise to these mixtures to produce hydrated iron precipitate. The mixture is aged at room temperature with plastic wrap for 12 h, washed with deionized water, and filtered with a 0.1 μm membrane. The obtained ABF is dried at 40℃ for 24 h to obtain the biochar / hydro ferrite composite material. The magnetic biochar obtained by other ways such as purchase is also suitable for the present application.

[0042] The present application is further illustrated by the following examples.

[0043] Example 1

[0044] A method for hydrothermal reduction and heavy metal stabilization of river channel sediment, the steps are as follows:

[0045] Tannic acid and magnetic biochar were added to riverbed sediment for dehydration and adsorption pretreatment (tannic acid added at 0.15 mmol / g, magnetic biochar added at 5%–10% of the sludge dry weight, dehydration and adsorption pretreatment at room temperature for 5 min). The mixture was then centrifuged, freeze-dried, and placed in a hydrothermal reactor for staged heating. The first stage involved heating to 150–180℃ and holding for 20–30 min; the second stage involved heating to 240–280℃ and holding for 4.5–7.5 h (heating rate of 5℃ / min). After the holding period, the hydrothermal reactor was cooled to room temperature using a water bath refrigeration system. The reactor was then opened, and the solid-liquid mixture was removed and filtered. The filtered solid and liquid products were collected. The solid product was heated in a 105℃ oven for 12 h and then placed in a desiccator for later use. The liquid product, being a hydrothermal liquid, was refrigerated at 4℃ for analysis.

[0046] Experimental Example 1: Effects of hydrothermal temperature and time in the second stage on the physicochemical properties of bottom sediment

[0047] Figure 2 The effect of hydrothermal conditions on the reduction rate of organic matter in sediment and COD in hydrothermal fluid was investigated based on Example 1 (i.e., only the hydrothermal conditions in the second stage were changed, and the parameters of the other steps were the same as in Example 1); wherein, (a) the hydrothermal time was fixed at 3 h, and the hydrothermal temperatures were 180, 200, 220, 240, 260 and 280 °C respectively; (b) the hydrothermal temperature was fixed at 260 °C, and the hydrothermal time was 0.5, 1.5, 3, 4.5, 6 and 7.5 h respectively.

[0048] Depend on Figure 2 As shown in (a), the COD of the hydrothermal fluid increases continuously with the increase of hydrothermal temperature (based on Example 1, the hydrothermal time of the second stage was fixed at 3 hours, and the hydrothermal temperatures were 180, 200, 220, 240, 260, and 280℃). Its trend is basically the same as the organic matter reduction rate. When the hydrothermal temperature reaches 260℃, the change in organic matter content tends to level off, indicating that the optimal hydrothermal temperature is 260℃. Figure 2 As shown in (b), with the extension of hydrothermal time (based on Example 1, the hydrothermal temperature of the second stage was fixed at 260℃, and the hydrothermal time was 0.5, 1.5, 3, 4.5, 6 and 7.5 h respectively), the reduction rate of organic matter in the sediment and the COD of the hydrothermal liquid both increased continuously. After 3 h of hydrothermal treatment, the mass of organic matter in the sediment decreased by 31.1% compared with that before hydrothermal treatment, while the COD in the hydrothermal liquid phase of the sediment increased to 3093 mg / L. However, when the time was further extended, the changes of both tended to level off, indicating that the hydrolysis of organic matter in the sediment had reached an equilibrium state, and the reduction rate was difficult to increase. Considering energy consumption and cost issues, the optimal hydrothermal time was 3 h.

[0049] Test Example 2: Changes in the contents of chemical forms of heavy metals during the second-stage hydrothermal treatment process

[0050] Figure 3 The changes in the chemical forms of heavy metals Zn (a), Cu (b), Cr (c), Cd (d), Ni (e), and Pb (f) in the original bottom sludge and the hydrothermal solid products of the bottom sludge; in the figure, RS represents the original bottom sludge, HS represents the solid product after hydrothermal treatment, A in HS-A-B represents the hydrothermal temperature of the second stage, and B represents the hydrothermal time of the second stage, for example, HS-180-3 represents the solid product obtained under the condition of a hydrothermal temperature of 180°C and a hydrothermal time of 3h in Example 1, HS-220-3 represents the solid product obtained under the condition of a hydrothermal temperature of 220°C and a hydrothermal time of 3h in Example 1, and so on.

[0051] As shown in (a) of FIG. 6, Figure 3 As shown in (a) of FIG. 6,

[0052] As shown in (b) of FIG. 6, Figure 3 As shown in (b) of FIG. 6,

[0053] As shown in (c) of FIG. 6, Figure 3 As shown in (c) of FIG. 6,

[0054] As shown in (d) of FIG. 6, Figure 3 As shown in (d) of FIG. 6,

[0055] As shown in (e) of FIG. 6, Figure 3As shown in (e), for heavy metal Ni, the proportion of T4 state heavy metal, which is the largest, did not change significantly before and after hydrothermal treatment, and only a small amount of T1 state heavy metal was converted to T3 state heavy metal. This shows that the stabilization of Ni by hydrothermal treatment is not significant, and the effect of hydrothermal temperature and hydrothermal time on the change of state is small.

[0056] As shown in (e), for heavy metal Ni, the proportion of T4 state heavy metal, which is the largest, did not change significantly before and after hydrothermal treatment, and only a small amount of T1 state heavy metal was converted to T3 state heavy metal. This shows that the stabilization of Ni by hydrothermal treatment is not significant, and the effect of hydrothermal temperature and hydrothermal time on the change of state is small. Figure 3 As shown in (f), for heavy metal Pb, hydrothermal treatment resulted in a significant decrease in the proportion of T1, T2 and T3 state heavy metals, and a significant increase in the proportion of T4 state heavy metal. The higher the hydrothermal temperature and the longer the hydrothermal time, the greater the proportion of T4 state heavy metal, and the stronger the stability of Pb. This shows that hydrothermal treatment has a strong stabilizing effect on Pb in the sediment, which can significantly reduce its bioavailability.

[0057] Overall, the hydrothermal process resulted in a significant decrease in the proportion of bioavailable heavy metals (T1 and T2) in the sediment, and a significant increase in the proportion of stable heavy metals (T4). The results show that after hydrothermal treatment, the bioavailability of heavy metals decreases significantly, and the heavy metals in the sediment are more stable. Hydrothermal treatment has a significant effect on the conversion of unstable heavy metals (T1 and T2) to relatively stable heavy metals (T3) and stable heavy metals (T4), and the higher the temperature or the longer the time, the more obvious the stabilization.

[0058] Comparative Example 1

[0059] The difference between Example 1 and Comparative Example 1 is only that the step of adding tannin acid and magnetic biochar to the river sediment for dehydration and adsorption pretreatment is omitted; the rest of the steps and parameters are the same as Example 1.

[0060] Results: When the second stage hydrothermal temperature is fixed at 260℃ and the hydrothermal time is 3h, the mass of organic matter in the sediment decreases by 20.8% compared with before hydrothermal treatment.

[0061] Comparative Example 2

[0062] The difference between Example 1 and Comparative Example 2 is only that the step of heating in the first stage is omitted, i.e. after freeze-drying, directly heating in the second stage; the rest of the steps and parameters are the same as Example 1.

[0063] Results: When the second stage hydrothermal temperature is fixed at 260℃ and the hydrothermal time is 3h, the mass of organic matter in the sediment decreases by 25.3% compared with before hydrothermal treatment.

[0064] The application provides a method for water heat reduction and heavy metal stabilization of river channel sediment.

[0065] The above-described embodiments are only used to describe the preferred modes of the application, and do not limit the scope of the application. Without departing from the design spirit of the application, various modifications and improvements of the technical solutions of the application made by those skilled in the art shall fall within the protection scope of the claims of the application.

Claims

1. A method for reducing water heat and stabilizing heavy metals in riverbed sediment, characterized in that, After adding tannic acid and magnetic biochar to the riverbed sediment for adsorption and dehydration pretreatment, the sediment is centrifuged, freeze-dried, and then subjected to hydrothermal treatment; after hydrothermal treatment, it is cooled and filtered. The hydrothermal treatment is divided into two stages. The first stage of hydrothermal treatment is carried out at a temperature of 150~180℃ for 20~30 min. The second stage of hydrothermal treatment is carried out at a temperature of 240~280℃ for 0.5 h~7.5 h.

2. The method for reducing water and heat loss and stabilizing heavy metals in riverbed sediment according to claim 1, characterized in that, The process after filtration also includes a step of drying the solid product obtained by filtration.

3. The method for reducing water heat and stabilizing heavy metals in riverbed sediment according to claim 1, characterized in that, The drying temperature is 100~110℃.

4. The method for reducing water heat and stabilizing heavy metals in riverbed sediment according to claim 1, characterized in that, The drying time is 10-12 hours.

5. A method for reducing the bioavailable components of heavy metals in riverbed sediment, characterized in that, The method for reducing the hydrothermal load and stabilizing heavy metals in riverbed sediment as described in any one of claims 1 to 4 is adopted.

Images