CN113231012A

CN113231012A - Method for treating sludge sewage by using modified red mud and modified steel slag

Info

Publication number: CN113231012A
Application number: CN202110319117.6A
Authority: CN
Inventors: 周显; 韩毅; 陈霞; 庞波; 娄宗斌; 万沙; 彭子凌; 范泽宇; 高卓凡; 吕兴栋; 高志杨; 郭文康; 李明霞
Original assignee: Changjiang River Scientific Research Institute Changjiang Water Resources Commission
Current assignee: Changjiang River Scientific Research Institute Changjiang Water Resources Commission
Priority date: 2021-03-25
Filing date: 2021-03-25
Publication date: 2021-08-10
Anticipated expiration: 2041-03-25
Also published as: CN113231012B

Abstract

The invention discloses a method for treating sludge sewage by using modified red mud and modified steel slag. The method comprises the steps of performing modification pretreatment on red mud and steel slag, adding the red mud and the steel slag into sludge for dehydration treatment, drying dehydrated mud cakes, performing high-temperature pyrolysis treatment on the dried mud cakes and the modified red mud and the modified steel slag to prepare the biochar-based hercynite, and using the biochar-based hercynite to treat sewage. The invention realizes the cooperative treatment of the steel slag, the red mud and the sludge and the recycling of the final product, and has important significance for expanding the application range and the application range of wastes such as the steel slag, the red mud and the sludge and improving the recycling rate of iron and aluminum resources; and can be widely applied to the field of sewage treatment, and realizes the dual functions of degrading novel pollutants and adsorbing heavy metals. The method has the characteristics of simple production process, easily obtained raw materials, wide product application range, good economic benefit and social benefit and the like.

Description

Method for treating sludge sewage by using modified red mud and modified steel slag

Technical Field

The invention belongs to the field of treatment of wastewater, sewage or sludge, in particular to a technology for treating sludge and sewage by utilizing solid waste; in particular to a method for preparing biochar-based hercynite for treating sewage by using modified red mud and modified steel slag to condition the sludge dewatering performance and using sludge cakes, modified red mud and modified steel slag as raw materials.

Background

The sludge is produced along with the sewage treatment process, along with the deepening of the attention degree of China on the sewage treatment, the popularization of the construction of urban sewage treatment plants and the continuous improvement of treatment process technology, the sewage treatment efficiency is greatly improved, and the yield of the sludge is also rapidly increased. Therefore, the improvement of the dehydration performance of the sludge and the obvious reduction of the water content of the sludge are the premise of realizing sludge reduction, harmlessness and recycling, and have important research significance and social value.

The red mud is the most main solid waste residue generated in the industrial production process of alumina, at present, the annual emission amount of the domestic red mud exceeds 3000 million tons, except that a small part of the red mud is applied to cement production, brick making and other purposes, most of the red mud is stockpiled in an open dam by a wet method, and the accumulated stockpiling of the red mud exceeds 1 hundred million tons nowadays. The comprehensive utilization of the red mud is a worldwide problem and has become a problem which seriously restricts the sustainable development of the alumina industry in China.

The steel slag is high-alkalinity slag generated in steel making production, and about 0.12 ton of steel slag is discharged when 1 ton of steel is produced. At present, the comprehensive utilization rate of steel slag in China is only 50%, and the comprehensive utilization rate of steel slag is only 10%. The steel slag has more complex components, and the steel slag treatment is always a difficult problem which troubles the steel-making industry in China. In the past, most of the solid waste is used as roadbed backfill materials, the utilization rate is low all the time, a large amount of urban land is occupied, and the environment and air are seriously polluted. If the method can be deeply developed and utilized, not only can the environmental pollution be eliminated, but also great economic benefits can be created.

The technology of pretreating red mud by using hydrochloric acid and conditioning the sludge dewatering capacity by combining the red mud with steel slag is disclosed in the section of improving the sludge dewatering performance by combining the red mud with the steel slag. In the technology, only the red mud is modified, the steel slag is not modified, and the utilization rate of the steel slag is not high; and the sludge cake after the sludge dewatering is not treated, and the sludge cake still becomes a large amount of accumulated solid waste.

At present, no document or patent technology discloses a technology for preparing biochar-based hercynite from red mud, steel slag and sludge cakes and using the biochar-based hercynite for sewage treatment.

Disclosure of Invention

The invention provides a method for treating sludge sewage by using modified red mud and modified steel slag, aiming at the problems of low utilization rate of red mud and steel slag waste and difficult sludge treatment in the prior art, the method firstly performs modification pretreatment on the red mud and the steel slag, and jointly conditions the dehydration performance of the sludge by using the modified red mud and the modified steel slag, thereby improving the dehydration rate of the sludge; and the mud cake after sludge dehydration, the modified red mud and the modified steel slag are combined to prepare the biochar-based hercynite, and the biochar-based hercynite is used for treating sewage. In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

s1, adding the red mud into a salicylic acid solution, soaking for 6-12 hours, and adding 0.5-1.5 kg of red mud into 1.5-2.5L of the salicylic acid solution to obtain modified red mud; adding the steel slag into a citric acid solution, soaking for 6-12 hours, and adding 0.5-1.5 kg of steel slag into 1.5-2.5L of the citric acid solution to obtain modified steel slag;

s2, adding the modified red mud and the modified steel slag obtained in the step S1 into sludge, uniformly stirring, and filtering and dehydrating to obtain mud cakes and filtrate; detecting the filtrate, directly discharging if the filtrate meets the discharge standard, and reserving for subsequent treatment if the filtrate does not meet the discharge standard;

s3, drying the mud cakes in the step S2, adding the modified red mud and the modified steel slag in the step S1, and cracking the red mud-steel slag-mud cake system obtained after uniformly mixing at 550-1000 ℃ to obtain biochar-based hercynite; generally, drying the mud cakes until the water content is less than or equal to 5 percent;

s4, adding the biochar-based hercynite obtained in the step S3 into the sewage or the filtrate which does not meet the discharge standard in the step S2, adding hydrogen peroxide or persulfate, and uniformly stirring the obtained mixed solution to finish the treatment of the sewage or the filtrate which does not meet the discharge standard.

Salicylic acid modified red mud can provide activated Fe³⁺And Al³⁺Plays a role in flocculation; the citric acid modified steel slag can be combined with O-H, C-O, C-C, N-H bonds in protein and polysaccharide organic matters in sludge flocs, so that the surface charge of floc particles is reduced; meanwhile, the RO phase, quartz and other inert mineral phases in the steel slag and the red mud canCan destroy the EPS structure of the sludge, convert the combined water in the sludge into free water, destroy the protein structure and further achieve the effect of improving the sludge dewatering performance.

Al in red mud₂O₃And Fe₂O₃The content (calculated by oxide) is 20-40%; fe in steel slag₂O₃The content is more than 10 percent; al in sludge₂O₃And Fe₂O₃The content is generally below 5%. The red mud and the steel slag are added into the mud cake to effectively improve the Al content in the mud₂O₃And Fe₂O₃Content of Al is adjusted by₂O₃And Fe₂O₃The proper proportion of the iron-aluminum spinel can be beneficial to generating the hercynite (FeAl) in the pyrolysis of a steel slag-red mud-sludge system₂O₄) And more other iron or aluminum compounds are avoided.

The redundant organic acid is decomposed at high temperature to generate simple substance carbon to participate in the reduction reaction of the ferric oxide; iron oxide and aluminum oxide in the steel slag, the red mud and the mud cake react at high temperature to generate hercynite, organic matter in the mud cake is decomposed at high temperature to become biochar, and the prepared hercynite is dispersed in the biochar to become biochar-based hercynite. The reaction principle is as follows:

3Fe₂O₃+C＝2Fe₃O₄+CO

Fe₂O3+3C＝2Fe+3CO

fe + oxide → Fe₃O₄

The biochar-based hercynite can play a role in enhancing adsorption and advanced oxidation during sewage treatment. FeAl₂O₄The components can promote hydrogen peroxide and persulfate to decompose to generate hydroxyl free radical OH-and sulfate free radical SO₄ ^2-And the heterogeneous Fenton reaction is promoted during sewage treatment. The biochar is beneficial to simultaneous adsorption of pollutants and hydrogen peroxide, the heterogeneous Fenton reaction diffusion distance is shortened, and the reaction efficiency is improved.

Preferably, in the step S2, the adding amount of the modified red mud accounts for 5-20% of the mass ratio of the sludge dry basis, and the adding amount of the modified steel slag accounts for 2-10% of the mass ratio of the sludge dry basis.

Preferably, the amounts of the modified red mud, the modified steel slag and the mud cake in the red mud-steel slag-mud cake system in the step S3 satisfy the following formulas at the same time:

(1)

(2)

m₁is Fe₂O₃Mass of (c), m²Is Na₂Mass of O, m₃Is K₂Mass of O, m₄Is the mass of CaO, m₅Is the mass of MgO, m₆Is SiO₂Mass of (c), m₇Is Al₂O₃The quality of (c).

Preferably, the adding amount of the biochar-based hercynite in the sewage or filtrate system in the step S4 meets the condition that the concentration is 0.1-1.0 g/L.

Preferably, in the step S1, the red mud is added into the salicylic acid solution to be soaked for 6-12 hours, and 1.0kg of red mud is added into each 2L of the salicylic acid solution to obtain the modified red mud; adding the steel slag into a citric acid solution, soaking for 6-12 hours, and adding 1.0kg of steel slag into every 2L of the citric acid solution to obtain the modified steel slag.

Preferably, the concentration of salicylic acid in the salicylic acid solution in the step S1 is 0.034mol/L, and the concentration of citric acid in the citric acid solution is 0.034 mol/L.

Preferably, in the step S4, the concentration of hydrogen peroxide in the hydrogen peroxide solution in the mixed solution is 0.3 to 1.2 mmol/L; the concentration of the persulfate in the mixed solution is 2-4 mmol/L.

Preferably, before the modified red mud and the modified steel slag in the step S2 are added into the sludge, the modified red mud and the modified steel slag are respectively dried at 60-80 ℃, then mixed and ground by a ball mill, and then screened by a sieve with more than 100 meshes.

Through a mechanical mixed grinding mode, the difficult-to-grind mineral RO phase in the steel slag collides with free calcium oxide to generate excited calcium oxide, and aluminum ores containing hydroxyl groups, such as gibbsite, dickite and the like, preactivated in the salicylic acid modified red mud are deeply activated to generate an aluminoxy tetrahedron structure with high activity, and the reaction principle is as follows.

Preferably, the stirring speed in the step S3 is controlled to be 300-360 rpm, and the stirring is carried out for 15-20 min; reducing the stirring speed to 150-200 rpm, and continuing stirring for 10-15 min.

Preferably, the cracking process in step S3 is divided into two steps: A. heating to 550-650 ℃ from room temperature at the speed of 5 ℃/min, and preserving heat for 40-70 min; B. heating to 800-1000 ℃ at the speed of 10 ℃/min, and preserving heat for 2-3 h.

Preferably, step S4 is to treat the sewage containing tetracycline, methylene blue and sulfanilamide compounds, and adsorb heavy metals in the sewage.

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

(1) the invention carries out chemical and physical combined modification on the red mud and the steel slag, plays a role in enhancing excitation by chemical-physical method, can fully excite active components of the red mud and the steel slag, and is beneficial to sludge dehydration and generation of hercynite; the used modifying reagent is organic acid, and the redundant organic acid is changed into an effective component of the sludge biochar in the pyrolysis process; the prepared biochar-based hercynite can be applied to hydrogen peroxide and persulfate systems, so that organic pollutants in water are degraded and heavy metals are adsorbed, and efficient cooperative treatment of various pollutants is realized;

(2) the raw materials adopted by the invention are the red mud, the steel slag and the sludge which are solid wastes, and through reasonable component design and a specific process, the red mud, the steel slag and the sludge are harmless, and the high-efficiency recycling of resources such as iron, aluminum, carbon and the like in the wastes is realized; the technology for jointly conditioning the sludge by utilizing the modified red mud and the modified steel slag belongs to an in-situ treatment process, has no sludge transportation cost, is suitable for the process conditions of the existing urban sewage treatment plant, and does not need to add other process facilities;

(3) the method of the invention can realize the full chain treatment from the dehydration to the resource utilization of the sludge and is convenient to be linked with the existing mature process;

(4) the sludge filtrate conditioned by the modified red mud and the modified steel slag is neutral, and does not cause secondary pollution.

Drawings

FIG. 1 is a flow chart of the present invention for treating sludge and sewage by using modified red mud and modified steel slag;

FIG. 2 is a SEM image of sludge obtained by conditioning sludge and dewatering sludge in examples 1 and 2 with red mud and steel slag at 5000 times magnification; FIG. 2(a) is a microscopic morphology of raw sludge after filter pressing and dewatering by a plate-and-frame filter; FIG. 2(b) is a micro-topography of the sludge cake after #1 mixed-milling sample conditioning of example 1; FIG. 2(c) is the micro-topography of the sludge cake after #2 mixed-milling sample conditioning of example 2;

FIG. 3 is a graph showing the relationship between the absorption enhancement and the catalytic degradation effect of methylene blue of biochar-based hercynite prepared from different red mud-steel slag-sludge compositions in examples 2 to 5 and comparative examples 1 to 5 and time;

FIG. 4 is the X-ray diffraction pattern of the biochar-based Fe-Al spinel material prepared in example 2.

Detailed Description

The technical solution of the present invention is described in detail and fully with reference to the following examples, it is obvious that the described examples are only a part of the examples of the present invention, and not all of the examples. All other embodiments, which can be derived by a person skilled in the art from the embodiments of the present invention without any inventive step, are within the scope of the present invention. Any equivalent changes or substitutions by those skilled in the art according to the following embodiments are within the scope of the present invention.

Example 1

The embodiment provides a method for treating sewage by conditioning sludge with red mud and steel slag and preparing biochar-based hercynite, and as shown in fig. 1, the method specifically comprises the following steps:

s1, adding 500g of red mud into 1L of salicylic acid solution with the concentration of 0.034mol/L, and soaking for 8 hours. Drying the soaked red mud at 60-80 ℃; 500g of steel slag is added into 1L of citric acid solution with the concentration of 0.034mol/L and soaked for 8 hours. Drying the soaked red mud at 60-80 ℃;

s2, feeding the dried modified red mud and the modified steel slag into a ball mill according to the mass ratio of 2:1 for mixed milling for 1 hour. And (3) sieving the mixed and ground sample by using a 100-mesh screen, and marking the treated mixed and ground sample as a No. 1 mixed and ground sample. And adding the No. 1 mixed grinding sample into sludge with the water content of 95%, wherein the mass ratio of the adding amount to the dry basis of the sludge is 1: 9. Stirring at 300rpm for 15 minutes, then reducing the stirring speed, stirring at 150rpm for 10 minutes, sending the conditioned sludge to a plate and frame filter press for dehydration, and detecting that the water content of the dehydrated sludge cake is 64.21%. The micro-morphology of the sludge dewatered cake treated by #1 mixed grinding sample is analyzed by a scanning electron microscope, and the obtained SEM image is shown in FIG. 2 (b). And detecting the filtrate, and if the detection result meets the discharge standard specified by the state, discharging the filtrate into the environment, and if the detection result does not meet the discharge standard specified by the state, reserving the filtrate for subsequent treatment.

S3, drying the mud cake in the step S2 at 103 ℃ until the water content is 3%, weighing 10g of dried sample, and mixing with No. 1 mixed grinding sample to enable the dry basis weight of the sludge to account for 75% of the mass of the mixture system. Putting the mixture into a high-temperature tube furnace for pyrolysis in a nitrogen environment, wherein the pyrolysis process is divided into two stages, the pyrolysis temperature in the first stage is 550 ℃, the heating rate is 5 ℃/min, and the temperature is kept for 70 min; and in the second stage, the pyrolysis temperature is 1000 ℃, the heating rate is 10 ℃/min, the temperature is kept for 2h, and the product after pyrolysis is screened by a 200-mesh screen to obtain the biochar-based hercynite.

S4, weighing 0.1g of the biochar-based hercynite obtained in the step S3, adding the biochar-based hercynite into a beaker, accurately weighing 100mL of wastewater with the methylene blue concentration of 10mg/L, adding the wastewater into the beaker, adding 6.7 muL of 30% hydrogen peroxide, stirring for 55min, sampling, detecting by using a spectrophotometer, comparing the residual methylene blue concentration with the initial concentration, and calculating the removal rate of pollutants to be 98.5%.

Example 2

In this example, steps S1 to S2 are the same as in example 1, except that the mass ratio of the modified red mud to the modified steel slag in step S2 is 1:1, the obtained mixed ground sample is designated as #2 mixed ground sample, and the water content of the dewatered cake is 53.17%. The micro-morphology of the sludge dewatered cake treated by #2 mixed grinding sample is analyzed by a scanning electron microscope, and the obtained SEM image is shown in FIG. 2 (c). In fig. 2, a diagram (a) is raw sludge which is not processed, and as can be seen from fig. 2, after the sludge in fig. 2(b) and 2(c) is conditioned by the modified red mud and the modified steel slag, the flocculent structure of the raw sludge is destroyed, a large-particle structure is formed, and some irregular blocky structures appear, which serve as a skeleton structure in the extrusion dehydration process and are beneficial to moisture removal; FIG. 2(c) shows that the sludge particles after #2 mixed grinding sample conditioning are larger and easier to dewater.

S3, drying the mud cake in the step S2 at 103 ℃ until the water content is 3%, weighing 10g of dried sample, and mixing with No. 2 mixed grinding sample to enable the dry basis weight of the sludge to account for 80% of the mass of the mixture system. Putting the mixture into a high-temperature tube furnace for pyrolysis in a nitrogen environment, wherein the pyrolysis process is divided into two stages, the pyrolysis temperature in the first stage is 600 ℃, the heating rate is 5 ℃/min, and the temperature is kept for 60 min; and in the second stage, the pyrolysis temperature is 800 ℃, the heating rate is 10 ℃/min, the temperature is kept for 3h, and the product after pyrolysis is screened by a 200-mesh screen to obtain the biochar-based hercynite.

S4, weighing 0.1g of the biochar-based hercynite, adding the biochar-based hercynite into a beaker, accurately measuring 100mL of wastewater with 10mg/L of methylene blue, adding the wastewater into the beaker, adding 6.7 muL of 30% hydrogen peroxide, uniformly stirring, sampling every 5min, 10min, 15min, 20min, 25min, 30min, 35min, 45min and 55min, detecting by adopting a spectrophotometer, comparing the residual methylene blue concentration with the initial concentration, and calculating the removal rate of pollutants. The results are shown in FIG. 3.

Example 3

This example is the same as example 2 except that the mass percentage of the sludge dry basis in the mixture system in step S3 is 90%. The removal rate of contaminants is shown in fig. 3.

Example 4

Steps S1 to S3 of the present embodiment are the same as those of embodiment 2.

S4: weighing 0.1g of biochar-based hercynite, accurately measuring 100mL of wastewater with the tetracycline concentration of 20mg/L and the Pb (II) concentration of 100mg/L, adding into a beaker, adding 3.3 muL of 30% hydrogen peroxide, stirring for 20min, sampling, detecting the residual tetracycline concentration by a spectrophotometer, and detecting the residual Pb (II) concentration by an inductively coupled atomic emission spectrometer. The concentration of the organic pollutant tetracycline in the original sewage is reduced to 0.6mg/L, and 97 percent of tetracycline is degraded; the leaching concentration of the heavy metal Pb (II) is reduced to 0.08mg/L, and the limit value of the pollution concentration in the integrated wastewater discharge standard (GB 8978 & 1996) is met.

Example 5

The method for conditioning sludge and preparing biochar-based hercynite to treat sewage by utilizing red mud and steel slag comprises the following steps:

s1, 1000g of red mud is added into 2L of salicylic acid solution with the concentration of 0.034mol/L and soaked for 12 hours. Drying the soaked red mud at 60-80 ℃; 1000g of steel slag is added into 2L of citric acid solution with the concentration of 0.034mol/L and soaked for 12 hours. Drying the soaked red mud at 60-80 ℃;

s2, feeding the dried modified red mud and the modified steel slag into a ball mill according to the mass ratio of 1.85:1 for mixed milling for 2 hours. And (4) sieving the mixed and ground sample by using a 100-mesh sieve. Adding the mixed grinding sample into electroplating sludge with the water content of 97%, wherein the mass ratio of the added amount to the dry basis of the sludge is 2:8, stirring for 15 minutes at the stirring speed of 360rpm, then reducing the stirring speed, stirring for 15 minutes at 200rpm, feeding the conditioned sludge into a plate and frame filter press for dehydration, and the water content of a dehydrated mud cake is 56.31%. The concentration of heavy metal in the filtrate is tested, the concentration of total Cd is 0.54mg/L, the concentration of total Pb is 1.87mg/L, and the concentration of hexavalent Cr is 0.87mg/L, which exceeds the limit of pollution concentration in the Integrated wastewater discharge Standard (GB 8978-1996).

S3, drying the dehydrated mud cake at 103 ℃ until the water content is 5%. Weighing 20g of dried sample, continuously adding the dried sample mixed and ground in the step S2 until the mass of the dry basis of the sludge accounts for 70% of the total mass of the mixture, putting the mixture into a high-temperature tube furnace for pyrolysis in a nitrogen environment, wherein the pyrolysis process is divided into two stages, the pyrolysis temperature in the first stage is 650 ℃, the heating rate is 5 ℃/min, and the heat preservation time is 40 min; and in the second stage, the pyrolysis temperature is 900 ℃, the heating rate is 10 ℃/min, the temperature is kept for 2.5h, and the product after pyrolysis is sieved by a 200-mesh sieve to obtain the biochar-based hercynite.

S4, measuring 1L of the filtrate with the excessive heavy metal leaching concentration in the step S2, adding 0.5g of the biochar-based hercynite, adding 4mmol of potassium persulfate, stirring for 30min, sampling, and testing the concentration of the residual heavy metal by using an inductively coupled atomic emission spectrometer. Heavy metals Cd and Cr in the filtrate after the biochar-based hercynite treatment are not detected, and the leaching concentration of Pb is reduced to 0.04mg/L, so that the requirement of the pollution concentration limit value in the Integrated wastewater discharge Standard (GB 8978-1996) is met.

Comparative example 1

This comparative example is the same as example 2 except that the percentage of the dry mass of sludge to the mass of the mixture system in step S3 was 0. The removal rate of contaminants is shown in fig. 3.

Comparative example 2

This comparative example is the same as example 2 except that the mass percentage of the sludge dry basis in the mass of the mixture system in step S3 is 100%. The removal rate of contaminants is shown in fig. 3.

Comparative example 3

This comparative example is the same as example 2 except that the mass percentage of the sludge dry basis in the mass of the mixture system in step S3 was 33.3%. The removal rate of contaminants is shown in fig. 3.

Comparative example 4

This comparative example is the same as example 2 except that the mass percentage of the sludge dry basis in the mass of the mixture system in step S3 was 50%. The removal rate of contaminants is shown in fig. 3.

Comparative example 5

This comparative example is the same as example 2 except that the mass percentage of the sludge dry basis in the mass of the mixture system in step S3 was 60%. The removal rate of contaminants is shown in fig. 3.

According to the figure 3, the biochar-based hercynite prepared by the mixture system with the sludge dry basis mass fraction of 80% has the best effect of degrading methylene blue, and the removal rate of the methylene blue after 20min of degradation reaches 99%. XRD mineral phase analysis was performed on biochar-based hercynite prepared from a mixture system with 80% dry basis mass fraction of sludge, and the obtained results are shown in FIG. 4. As can be seen from fig. 4, the biocarbon-based hercynite obtained at 800 ℃ mainly contains iron oxide, ferroferric oxide and hercynite.

Comparative example 6

This comparative example is the same as the example, except that 1: step S1, adding 500g of red mud into 1L of acetic acid solution with the concentration of 0.034mol/L, and soaking for 8 hours; in the step S2, detecting that the water content of the dewatered mud cake is 78.24%; the removal rate of the contaminants in step S4 was 94.7%.

Comparative example 7

This comparative example is the same as the example, except that 1: step S1, adding 500g of red mud into 1L of citric acid solution with the concentration of 0.034mol/L, and soaking for 8 hours; in the step S2, detecting that the water content of the dewatered mud cake is 79.62%; the removal rate of the contaminants in step S4 was 93.9%.

As can be seen from the above comparative example, when other organic acids are used to modify the red mud in step S1, the acetic acid or citric acid can react with the metal oxide in the red mud, so that the metal elements in the compound become free metal ions and enter the solution, and the dewatering performance of the sludge is not significantly improved; the subsequent preparation of the biochar-based hercynite is also greatly influenced, so that the content of the hercynite is not high enough, and the sewage treatment efficiency is influenced. In step S3, when the amounts of the modified red mud, the modified steel slag and the mud cake in the red mud-steel slag-mud cake system are not within the limited range, the content of hercynite in the prepared product is low, resulting in a significant decrease in sewage treatment efficiency.

The above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. The present invention may be subject to various modifications and changes by any person skilled in the art. Any simple equivalent changes and modifications made in accordance with the protection scope of the present application and the content of the specification are intended to be included within the protection scope of the present invention.

Claims

1. The method for treating sludge sewage by using modified red mud and modified steel slag is characterized by comprising the following steps:

s3, drying the mud cakes in the step S2, adding the modified red mud and the modified steel slag in the step S1, and cracking the red mud-steel slag-mud cake system obtained after uniformly mixing at 550-1000 ℃ to obtain biochar-based hercynite;

s4, adding the biochar-based hercynite obtained in the step S3 into the sewage or the filtrate which does not meet the discharge standard in the step S2, adding hydrogen peroxide or persulfate, and uniformly stirring the obtained mixed solution to finish the treatment of the sewage or the filtrate.

2. The method for treating sludge sewage by using modified red mud and modified steel slag as claimed in claim 1, wherein in step S2, the adding amount of modified red mud is 5-20% of the mass ratio of the dry basis of the sludge, and the adding amount of modified steel slag is 2-10% of the mass ratio of the dry basis of the sludge.

3. The method for treating sludge sewage by using modified red mud and modified steel slag as claimed in claim 1, wherein the amounts of the modified red mud, the modified steel slag and the mud cake in the red mud-steel slag-mud cake system in step S3 satisfy the following formulas:

(1)

(2)

m₁is Fe₂O₃Mass of (c), m₂Is Na₂Mass of O, m₃Is K₂Mass of O, m₄Is the mass of CaO, m₅Is the mass of MgO, m₆Is SiO₂Mass of (c), m₇Is Al₂O₃The quality of (c).

4. The method for treating sludge sewage by using modified red mud and modified steel slag according to claim 1, wherein the adding amount of the biochar-based hercynite in the sewage or filtrate system in the step S4 meets the condition that the concentration is 0.1-1.0 g/L.

5. The method for treating sludge sewage by using the modified red mud and the modified steel slag according to any one of claims 1 to 4, wherein in the step S1, the red mud is added into a salicylic acid solution to be soaked for 6 to 12 hours, and 1.0kg of red mud is added into 2L of the salicylic acid solution to obtain the modified red mud; adding the steel slag into a citric acid solution, soaking for 6-12 hours, and adding 1.0kg of steel slag into every 2L of the citric acid solution to obtain the modified steel slag.

6. The method for treating sludge sewage by using modified red mud and modified steel slag as claimed in claim 1, wherein the salicylic acid concentration in the salicylic acid solution in the step S1 is 0.034mol/L, and the citric acid concentration in the citric acid solution is 0.034 mol/L.

7. The method for treating sludge sewage by using modified red mud and modified steel slag according to claim 1, wherein the concentration of hydrogen peroxide in the mixed solution in the step S4 is 0.3-1.2 mmol/L; the concentration of the persulfate in the mixed solution is 2-4 mmol/L.

8. The method as claimed in claim 1, wherein the modified red mud and the modified steel slag in step S2 are dried at 60-80 ℃ before being added to the sludge, and then mixed and ground by a ball mill and then sieved by a 100-mesh sieve.

9. The method according to claim 1, wherein the stirring speed in step S3 is controlled to be 300-360 rpm, and the stirring is carried out for 15-20 min; reducing the stirring speed to 150-200 rpm, and continuing stirring for 10-15 min.

10. The method according to claim 1, wherein step S4 is used for treating the sewage containing tetracycline, methylene blue and sulfanilamide compounds and adsorbing heavy metals in the sewage.