Treatment method of sludge containing heavy metals

Abstract

The invention discloses a heavy metal-containing sludge treatment method, which comprises: adding an activated iron source to heavy metal-containing sludge, introducing micro-nano bubbles, and carrying out homogeneous mixing to obtain a mixed slurry; adjusting the pH value of the mixed slurry to 9-11, adding ferrite, introducing micro-nano bubbles, and carrying out reaction and solid-liquid separation to obtain a solid product and filtrate; and carrying out magnetic separation on the solid product to obtain ferrite and treated sludge. According to the treatment method, heavy metals in the sludge can be stabilized, the dewatering performance of the sludge can be improved and the resource utilization rate can be increased under the combined action of the working procedures of mechanical activation, micro-nano bubble introduction and the like, and the treatment method has the advantages of simplicity and convenience in operation, low energy consumption, low cost, environmental friendliness, wide applicability, small iron source dosage, high reaction rate, good stability and the like; and high-efficiency treatment and resource utilization of the sludge containing heavy metals can be realized.

Description

Technical Field

[0001] The invention belongs to the field of sludge treatment and disposal, and specifically relates to a method for treating sludge containing heavy metals. Background Art

[0002] With the increase in the output of industrial sludge, these sludges have complex components, high content of toxic and harmful substances such as heavy metals and toxic organic matter, scattered sources and large output. If not handled properly, these substances will cause great harm to the environment and human health. Therefore, how to effectively treat these industrial sludges and reduce their harm to the environment is an urgent problem to be solved.

[0003] At present, the main methods for industrial sludge treatment and disposal are landfill or incineration after dehydration, but these methods have certain limitations, such as high disposal cost, complicated process, low treatment efficiency, easy to cause secondary pollution, low resource utilization rate, etc. Therefore, it is necessary to find a more efficient, environmentally friendly and economical industrial sludge treatment method.

[0004] As a new treatment method, the ferrite method is based on the principle of using ferrous salts to generate metal hydroxide colloids under alkaline conditions, and then dehydrating them under heating conditions to generate ferrites. Existing research on the ferrite method is mostly focused on the treatment of heavy metal wastewater. The core is to remove heavy metal ions in sewage under heating or room temperature conditions through the ferrite method. The focus is on improving sewage treatment efficiency and effluent water quality, and the stabilization of heavy metals is not considered. Unlike the ferrite method for treating heavy metal wastewater, the focus of the ferrite method for treating sludge is: how to convert heavy metals in the sludge into precipitates with good stabilization effects. At present, when treating sludge based on the ferrite method, there are problems such as large iron source addition, high reaction temperature, slow reaction rate, poor dehydration effect, poor heavy metal stabilization effect, and serious secondary pollution risk. For example, the existing patent document CN104692787B discloses a method for comprehensive recovery of electroplating sludge ferrite solidification, and the patented process route is to first acid-leach the metal ions in the sludge, adjust the pH to 9.2, stir at 80°C, and then recover the ferrite sediment; the process chain of this method is long, the acid consumption is large, and a high reaction temperature needs to be maintained. For example, the existing patent document CN103397193B discloses a method for extracting nickel-containing ferrite from stainless steel sludge, and the patented process is to first acidify the sludge, add an iron source and adjust the pH, and then recover the ferrite; the acid and alkali consumption of this process is large and the cost is high. For example, the existing patent document CN100431722C discloses a method for hydrothermal ferritization of electroplating sludge, which is to add high iron oxide and distilled water to the electroplating sludge to make a raw material slurry, then add ammonia water as a precipitant to adjust the pH value of the slurry to 9, and hydrothermally react at 200°C for 4 hours to obtain ferrite sediment; the reaction temperature of this method is high, and the pH adjustment of ammonia water will increase the ammonia nitrogen in the filtrate, and the energy consumption and rotation speed are high. The existing papers "Experimental Study on Stabilization of Heavy Metals in Sludge by Concentrated Slurry Ferrite Method" and "Experimental Study on Stabilization of Heavy Metals in Sludge by Ferrite Method" systematically studied the stabilization effect of the ferrite method on heavy metals in sludge, but this method has the problems of large iron source addition, the temperature needs to be controlled at 65-85°C during the process, and the subsequent resource utilization of ferrite sediment is not involved. Therefore, it is necessary to find a method for treating heavy metal-containing sludge with simple operation, low energy consumption, low cost, environmental friendliness, wide applicability, small amount of iron source, fast reaction rate and good stability, which is of great significance for achieving efficient treatment and resource utilization of industrial sludge. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a method for treating heavy metal-containing sludge which is simple to operate, has low energy consumption, low cost, is environmentally friendly, has wide applicability, uses a small amount of iron source, has a fast reaction rate and has good stability.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions.

[0007] A method for treating heavy metal-containing sludge comprises the following steps:

[0008] S1, mechanically activating the iron source to obtain an activated iron source;

[0009] S2, adding the activated iron source obtained in step S1 to the heavy metal-containing sludge, introducing micro-nano bubbles, and homogenously mixing under stirring conditions to obtain a mixed slurry;

[0010] S3, adjusting the pH value of the mixed slurry obtained in step S2 to 9-11, adding ferrite, introducing micro-nano bubbles, reacting under stirring conditions, and separating the solid and liquid to obtain a solid product and a filtrate;

[0011] S4. The solid product obtained in step S3 is subjected to magnetic separation to obtain ferrite and treated sludge.

[0012] The above treatment method is further improved, in step S2, the mass of iron in the activated iron source is 3 to 5 times the mass of heavy metals in the heavy metal-containing sludge.

[0013] The above treatment method is further improved in that in step S3, the amount of ferrite added is 0.5% to 2% of the mass of the heavy metal-containing sludge.

[0014] The above treatment method is further improved, in step S1, the iron source is at least one of ferrous chloride, ferrous sulfate and ferrous nitrate, and the mechanical activation is performed using a ball mill.

[0015] The above treatment method is further improved. In step S2, the micro-nano bubbles are prepared by a micro-nano bubble generating device, and the micro-nano bubbles are prepared using air as a gas source; the stirring speed is 100rpm to 300rpm, and the homogenizing mixing time is 5min to 10min.

[0016] The above treatment method is further improved, in step S3, an alkaline compound is used to adjust the pH value of the mixed slurry obtained in step S2, and the alkaline compound is sodium hydroxide.

[0017] The above-mentioned treatment method is further improved. In step S3, the micro-nano bubbles are prepared by a micro-nano bubble generating device, and the preparation of the micro-nano bubbles uses an oxygen-deficient gas as a gas source, and the oxygen-deficient gas is nitrogen or an inert gas; the stirring speed is 100rpm to 300rpm, and the reaction time is 30min to 120min.

[0018] The above treatment method is further improved, in step S4, the ferrite is returned to the reaction system of step S3 to continue to participate in the reaction.

[0019] The above treatment method is further improved, in step S2, the heavy metal-containing sludge further includes the following treatment before use: adding water to the heavy metal-containing sludge until the water content of the heavy metal-containing sludge is 90%; the heavy metal-containing sludge is industrial sludge.

[0020] The above treatment method is further improved in that in step S3, the filtrate is used to adjust the moisture content of the heavy metal-containing sludge.

[0021] The specific principle of the method for treating heavy metal-containing sludge of the present invention is as follows:

[0022] First, under the action of mechanical force, the crystal structure of the iron source is distorted and partially destroyed, thereby forming a variety of defects. These defects not only increase the internal energy of the iron salt, but also significantly enhance its reactivity. At the same time, the mechanical activation process will also change the physicochemical properties of the iron salt, increase its specific surface area and porosity, thereby increasing the reactive sites of the iron source. These changes promote the full contact between the reactant (iron source) and the reaction medium (heavy metal), further increasing the reaction rate; secondly, in the two stages of mixing the activated iron source and the heavy metal-containing sludge, adjusting the pH value to 9-11 and adding ferrite for reaction, micro-nano bubbles are introduced for aeration. The micro-nano bubbles can dissolve oxygen in the air into the slurry, promote the uniform dispersion of dissolved oxygen, sludge and activated iron source, thereby accelerating the reaction rate of the iron source and the heavy metal ions in the sludge; further, the introduction of ferrite into the reaction system as a seed can promote the synthesis of ferrite and further improve the reaction efficiency of the overall reaction system. The treatment method of the present invention can stabilize heavy metals in sludge, improve sludge dewatering performance and increase resource utilization rate through the combined action of "mechanical activation + micro-nano bubbles + ferrite introduction" and other processes. Specifically, after activation, the iron source quickly generates metal hydroxide colloid under alkaline conditions, and then adheres and grows on the surface of ferrite seed crystals to promote ferrite generation. At the same time, the heavy metal ions in the sludge quickly replace Fe in the ferrite lattice through multiple actions such as adsorption, entrainment and encapsulation. 2+ , Fe 3+ position, forming a heavy metal composite precipitate with good stability, thereby avoiding the re-dissolution of heavy metals and causing secondary pollution to the environment, and facilitating the disposal and resource utilization of sludge.

[0023] Compared with the prior art, the advantages of the present invention are:

[0024] In the treatment method of heavy metal-containing sludge of the present invention, the iron source is first mechanically activated to increase the reactive sites of the iron source and improve the reactive activity of the iron salt, so that the iron salt exhibits higher reactive activity at a lower temperature and a smaller dosage; then, the activated iron source is added to the heavy metal-containing sludge, and micro-nano bubbles are introduced for homogeneous mixing to obtain a mixed slurry. In this step, the micro-nano bubble technology is used to promote the full and uniform dispersion of dissolved oxygen, sludge and the activated iron salt to form a homogeneous slurry, thereby accelerating the subsequent reaction rate of the iron source and the heavy metal ions in the sludge; on this basis, the pH value of the mixed slurry is adjusted to 9-11, ferrite is added, and micro-nano bubbles are introduced again for reaction to obtain a solid product and a filtrate. The ferrite is introduced into the reaction system as a seed crystal, which is beneficial to the synthesis of the reaction product and promotes the rapid progress of the reaction, thereby improving the reaction efficiency of the overall system; finally, the solid product is magnetically separated to obtain ferrite and treated sludge, the filtrate and part of the ferrite can be returned to the treatment system for reuse, and the remaining ferrite and treated sludge can be recycled. The treatment method of the present invention does not generate harmful gases and liquids during the treatment process, has the advantages of simple operation, low energy consumption, low cost, environmental friendliness, wide applicability, small amount of iron source, fast reaction rate, good stability, etc., and can achieve efficient treatment and resource utilization of heavy metal-containing sludge. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the process flow of the heavy metal sludge treatment method in Example 1 of the present invention DETAILED DESCRIPTION

[0026] The present invention is further described below in conjunction with the accompanying drawings and specific preferred embodiments, but the protection scope of the present invention is not limited thereby. The materials and instruments used in the following embodiments are all commercially available.

[0027] Embodiment 1:

[0028] A method for treating heavy metal-containing sludge of the present invention has a process flow chart as shown in Figure 1 As shown, the following steps are included:

[0029] S1. Activate ferrous sulfate heptahydrate (FeSO4·7H2O) by ball milling to obtain activated ferrous sulfate heptahydrate.

[0030] S2. Take 1 kg of industrial sludge, add 1.5 kg of water to make the water content of the sludge 90%; then add 4.23 kg of activated ferrous sulfate heptahydrate, that is, the mass of iron in ferrous sulfate heptahydrate is 3.04 times the mass of heavy metals in the sludge, and introduce micro-nano bubble aeration, wherein the air source of the micro-nano bubble generating device is air, and homogenize and mix for 10 minutes under mechanical stirring at a speed of 200 rpm to obtain a mixed slurry.

[0031] In this step, the industrial sludge is taken from an industrial sewage treatment station in a certain industrial park, and its water content is 75% and its pH is weakly alkaline; the mass percentage of heavy metals in the industrial sludge is: Cr 4.6%, Ni 11.2%, Cu 5.4%, Zn6.24%, Pb0.45%, and Cd 0.11%.

[0032] S3. The mixed slurry is transported to a reaction tank, and liquid alkali (NaOH) is added to adjust the pH to 10.2. 10 g of ferrite is added, and micro-nano bubble aeration is introduced, wherein the gas source of the micro-nano bubble generator is nitrogen. The reaction is carried out for 90 minutes under stirring at a speed of 160 rpm, and the reaction product is subjected to solid-liquid separation to obtain a solid phase product and a filtrate, and the filtrate is refluxed to the homogeneous mixing stage.

[0033] The filtrate is refluxed into the industrial sludge in step S2 to replace water, so that the water content of the sludge is 90%.

[0034] S4, magnetic separation of the solid phase products to obtain ferrite and treated sludge. Part of the ferrite is reused, that is, it is returned to the system of the reaction in step S3 to participate in the reaction as a seed crystal, and the remaining ferrite is washed and dried, and after passing the test, it is recycled; after passing the test, the treated sludge is recycled.

[0035] Comparative Example 1:

[0036] A method for treating heavy metal-containing sludge is basically the same as Example 1, except that the ferrous sulfate heptahydrate is not subjected to ball milling activation, and the reaction time in step S3 is 180 min.

[0037] Comparative Example 2:

[0038] A method for treating heavy metal-containing sludge is basically the same as Example 1, except that: in step S2 and step S3, micro-nano bubble aeration is not introduced, but conventional stirring and mixing is performed, and the reaction time in step S3 is 180 minutes.

[0039] Comparative Example 3:

[0040] A method for treating heavy metal-containing sludge is basically the same as Example 1, except that: in step S2, ferrite is not added, and the reaction time in step S3 is 180 minutes.

[0041] Comparative Example 4:

[0042] A method for treating heavy metal-containing sludge is basically the same as Example 1, except that: ferrous sulfate heptahydrate is not subjected to ball milling activation, conventional stirring and mixing is used instead of micro-nano bubble aeration, and the reaction time in step S3 is 180 minutes.

[0043] The dehydration conditions and heavy metal leaching concentrations of the treated sludge in Example 1 and the treated sludge in Comparative Examples 1 to 4 were tested respectively. The heavy metal leaching concentrations in the treated sludge were tested according to the National Standard of the People's Republic of China "Identification Standards for Hazardous Wastes - Identification of Leaching Toxicity" (GB 5085.3-2007). The results are shown in Table 1.

[0044] Table 1 Water content data and heavy metal leaching concentration data (mg / L) of treated sludge (mud cake) under different treatment methods

[0045]

[0046] As shown in Table 1, the iron source was not activated in Comparative Example 1, so that the activity of ferrous sulfate heptahydrate was poor, thereby affecting its reaction rate with heavy metals. Although a stable heavy metal composite precipitate can be obtained after 180 minutes of reaction, and the leaching concentration of each heavy metal meets the requirements, when the reaction time is 90 minutes, the method in Comparative Document 1 is still difficult to solidify the heavy metals in the sludge well, and the leaching concentrations of multiple heavy metals in the formed heavy metal composite precipitate do not meet the relevant requirements. Similarly, micro-nano bubble aeration was not performed in Comparative Document 2, and ferrite was not introduced in Comparative Example 3, and the same problem also exists, that is, a longer reaction time is required to obtain a stable heavy metal composite precipitate, but when the reaction time is too short, it is difficult to achieve the stabilization of heavy metals in the sludge. In addition, it can be seen from Table 1 that in Comparative Example 4, when unactivated ferrous salt is directly used and treated under conventional stirring conditions, even after 180 minutes of reaction, it is difficult to achieve effective stabilization of heavy metals in sludge, such as chromium and zinc leaching concentrations are still excessive, and the dehydration effect of sludge is not ideal, and the moisture content of mud cake is still as high as 50.4%, which shows that the conventional stirring and mixing instead of micro-nano bubble aeration cannot improve the activity of ferrous sulfate heptahydrate, resulting in a slow reaction rate and poor dehydration performance, which is not only difficult to stabilize heavy metals in sludge, but also difficult to improve the dehydration effect of sludge. Completely different from them, in Example 1 of the present invention, the combined treatment process of "mechanical activation + micro-nano bubble + ferrite introduction" is adopted, which can not only make the heavy metals in the sludge quickly form heavy metal composite precipitates with good stability, but also can effectively improve the dehydration performance of sludge, and the result is that the leaching concentration of heavy metals in the mud cake is lower than the relevant standard threshold, and the moisture content of the mud cake is as low as 40.5%. It can be seen that in the treatment method of heavy metal-containing sludge of the present invention, through the combined action of the processes such as "mechanical activation + micro-nano bubbles + ferrite introduction", the heavy metals in the sludge can be effectively stabilized and the sludge dewatering performance can be improved. It has the advantages of fast reaction rate, good stability, good dehydration effect, etc., which is convenient for achieving sludge reduction and harmless treatment.

[0047] In this example, the effects of different ferrite addition amounts on the treatment of industrial sludge were also investigated. Except for the different ferrite addition amounts, other conditions were the same as in Example 1. The results are shown in Table 2.

[0048] Table 2 Water content data and heavy metal leaching concentration data (mg / L) of treated sludge (mud cake) at different ferrite addition amounts

[0049]

[0050] It can be seen from Table 2 that when the added amount of ferrite is 0.5%, 1%, 1.5% and 2% of the mass of the heavy metal-containing sludge, the treatment method of the heavy metal-containing sludge of the present invention has a good stabilization effect on the heavy metals in the sludge, and the sludge (mud cake) after treatment can meet the heavy metal leaching limit standards specified in the "Hazardous Waste Identification Standards - Leaching Toxicity Identification" (GB 5085.3-2007).

[0051] In summary, compared with the existing conventional ferrite-based sludge treatment method, the treatment method of heavy metal-containing sludge of the present invention has the following advantages: a) improving the utilization rate of iron source and accelerating the reaction rate, thereby improving the efficiency of the entire treatment process; b) being able to efficiently treat a variety of industrial sludges and convert them into stable ferrite complexes, reducing the risk of secondary pollution and having broad application prospects; c) the ferrite obtained after treating the heavy metal-containing sludge and the treated sludge can be reused as resources such as building materials, fertilizers or soil conditioners, which not only solves the disposal problem of industrial sludge, but also realizes the recycling of resources; d) low energy consumption, heavy metals in the sludge can be converted into stable precipitates without heating treatment, reducing industrial production costs and achieving the purpose of energy conservation and emission reduction; e) the treatment method of heavy metal-containing sludge has a simple process flow and is easy to operate. It can complete the treatment of heavy metal-containing sludge in a relatively short time, is easy to realize automatic control, improves treatment efficiency, and reduces treatment time; f) the entire treatment process is green and environmentally friendly, and the treated ferrite complex is harmless, environmentally friendly, and meets the requirements of sustainable development.

[0052] The above is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as above in the preferred embodiment, it is not used to limit the present invention. Any technician familiar with the art can make many possible changes and modifications to the technical solution of the present invention by using the methods and technical contents disclosed above without departing from the spirit and technical solution of the present invention, or modify it into an equivalent embodiment of equivalent changes. Therefore, any simple modification, equivalent replacement, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention, still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for treating heavy metal-containing sludge, characterized in that: The following steps are involved: S1, mechanically activating the iron source to obtain an activated iron source; S2, adding the activated iron source obtained in step S1 to the heavy metal-containing sludge, introducing micro-nano bubbles, and homogenously mixing under stirring conditions to obtain a mixed slurry; S3, adjusting the pH value of the mixed slurry obtained in step S2 to 9-11, adding ferrite, introducing micro-nano bubbles, reacting under stirring conditions, and separating the solid and liquid to obtain a solid product and a filtrate; S4. The solid product obtained in step S3 is subjected to magnetic separation to obtain ferrite and treated sludge.

2. The method for treating heavy metal-containing sludge according to claim 1, characterized in that: In step S2, the mass of iron in the activated iron source is 3 to 5 times the mass of heavy metals in the heavy metal-containing sludge.

3. The method for treating heavy metal-containing sludge according to claim 2, characterized in that: In step S3, the amount of ferrite added is 0.5% to 2% of the mass of the heavy metal-containing sludge.

4. The method for treating heavy metal-containing sludge according to any one of claims 1 to 3, characterized in that: In step S1, the iron source is at least one of ferrous chloride, ferrous sulfate and ferrous nitrate, and the mechanical activation is performed using a ball mill.

5. The method for treating heavy metal-containing sludge according to any one of claims 1 to 3, characterized in that: In step S2, the micro-nano bubbles are prepared by a micro-nano bubble generating device, and the micro-nano bubbles are prepared using air as a gas source; the stirring speed is 100 rpm to 300 rpm, and the homogenizing mixing time is 5 min to 10 min.

6. The method for treating heavy metal-containing sludge according to any one of claims 1 to 3, characterized in that: In step S3, an alkaline compound is used to adjust the pH value of the mixed slurry obtained in step S2, and the alkaline compound is sodium hydroxide.

7. The method for treating heavy metal-containing sludge according to any one of claims 1 to 3, characterized in that: In step S3, the micro-nano bubbles are prepared by a micro-nano bubble generating device, and the micro-nano bubbles are prepared using an oxygen-deficient gas as a gas source, and the oxygen-deficient gas is nitrogen or an inert gas; the stirring speed is 100rpm to 300rpm, and the reaction time is 30min to 120min.

8. The method for treating heavy metal-containing sludge according to any one of claims 1 to 3, characterized in that: In step S4, the ferrite is returned to the reaction system of step S3 to continue to participate in the reaction.

9. The method for treating heavy metal-containing sludge according to any one of claims 1 to 3, characterized in that: In step S2, the heavy metal-containing sludge further includes the following treatment before use: adding water to the heavy metal-containing sludge until the water content of the heavy metal-containing sludge is 90%; the heavy metal-containing sludge is industrial sludge.

10. The method for treating heavy metal-containing sludge according to any one of claims 1 to 3, characterized in that: In step S3, the filtrate is used to adjust the moisture content of the heavy metal-containing sludge.

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