Magnesium-modified sludge-based phosphorus-rich biochar material and preparation method thereof

Abstract

The invention relates to a magnesium modified sludge-based phosphorus-rich biochar material and a preparation method thereof, and belongs to the technical field of harmless treatment and resource utilization of municipal sludge. The invention provides a magnesium-modified sludge-based phosphorus-rich biochar material and a preparation method thereof.The preparation method comprises the following steps that municipal sludge is heated and dried, and sludge particles are obtained after treatment; pyrolyzing the sludge particles, and cooling to obtain sludge semicoke; adding a magnesium-based additive into the sludge semi-coke, heating and calcining in a nitrogen atmosphere, and cooling to obtain the phosphorus-rich biochar. According to the phosphorus-rich biochar prepared by the method, the harm caused by mass production and accumulation of municipal sludge is solved, a large amount of phosphorus element is enriched, and the phosphorus-rich biochar prepared by the method can replace phosphate fertilizer to be applied to grassland gardens or replace phosphorite to be exploited as a phosphate ore source; and the environment damage and resource waste caused in the phosphorite mining and phosphate fertilizer production process are reduced on the whole.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of harmless treatment and resource utilization of municipal sludge, and particularly relates to a magnesium-modified sludge-based phosphorus-rich biochar material and a preparation method thereof. BACKGROUND

[0002] With the development of China's economy and the enhancement of environmental protection awareness, waste resource utilization is attracting much attention. Sludge, as a byproduct of wastewater treatment, is increasing in production. Municipal sludge is a complex aggregate containing a large amount of organic pollutants and various heavy metals, and is rich in nitrogen, phosphorus, potassium and other essential nutrients for plant growth, and has both pollution and resource dualities. If not properly treated, the emissions will cause secondary pollution, and the resources cannot be effectively utilized. How to achieve the "reduction, harmlessness and resource utilization" treatment of sludge has become a core problem to be solved in the field of environmental engineering.

[0003] Although the traditional thermal treatment of sludge can reduce the volume of sludge to a certain extent and kill pathogens, the fixation rate of phosphorus is low. Under the action of high temperature, the structure of part of the phosphorus-containing compounds is destroyed, and a large amount of phosphorus is volatilized and lost. The sludge is first pyrolyzed to remove part of the heavy metals and achieve phosphorus enrichment, and then calcined by adding a magnesium-based additive, which can further fix the phosphorus in the biochar and stabilize the heavy metals in the sludge. The phosphorus in the product has high biological availability, and the risk of pollutants such as heavy metals is lower than the national application standard.

[0004] From the existing research, the two-step thermal treatment of sludge process of pyrolysis and calcination has some related technical research on feasibility, but there are few studies on the inhibition of magnesium-based additives on the volatilization of phosphorus in the product and the residual of heavy metals during calcination.

[0005] In summary, it is an important problem to develop a municipal sludge thermal treatment technology that can inhibit the volatilization of phosphorus to improve the fixation rate of phosphorus and promote the removal or stabilization of heavy metals. SUMMARY

[0006] In view of the deficiencies of the prior art, the purpose of the present application is to provide a magnesium-based additive added on the basis of two-step thermal treatment to prepare phosphorus-rich biochar, which can not only inhibit the volatilization of phosphorus, but also promote the removal or safe and stable occurrence of heavy metals, and the prepared phosphorus-rich biochar has high biological availability and industrial utilization.

[0007] The present application provides a magnesium-modified sludge-based phosphorus-rich biochar material and a preparation method thereof, comprising the following steps:

[0008] (1) heating and drying municipal sludge, grinding, crushing and sieving to obtain sludge particles;

[0009] (2) the sludge particles are placed in a microwave pyrolysis device for pyrolysis, and sludge semi-coke is obtained after cooling;

[0010] (3) the sludge semi-coke of step (2) is added with a magnesium-based additive and heated and calcined in a nitrogen atmosphere, and phosphorus-enriched biochar is obtained after cooling.

[0011] Further, the heated and dried municipal sludge in step (1) is ground and crushed and then passed through a 100-mesh-200-mesh sieve.

[0012] Further, before pyrolysis in step (2), high-purity inert gas is introduced to replace the air atmosphere in the microwave pyrolysis device, and the gas flow rate is greater than 100 mL / min; the pyrolysis temperature is 300 DEG C-500 DEG C, the heating rate is 10 DEG C / min-20 DEG C / min, and the pyrolysis time is 60 min-90 min.

[0013] Further, the magnesium-based additive in step (3) is Mg(OH)2, and the addition amount is 10%-20% of the mass of the sludge semi-coke.

[0014] Further, the calcination in step (3) is performed using a tube furnace.

[0015] Further, the calcination temperature in step (3) is 700 DEG C-900 DEG C, the heating rate is 10 DEG C / min, the calcination time is 30 min, and the gas flow rate is greater than 100 mL / min.

[0016] Further, the phosphorus element fixation rate of the prepared phosphorus-enriched biochar reaches 90.2%-93.1%.

[0017] A magnesium-modified sludge-based phosphorus-enriched biochar material is prepared using the preparation method of the magnesium-modified sludge-based phosphorus-enriched biochar material.

[0018] The application further provides a novel magnesium-modified sludge-based phosphorus-enriched biochar in the application of phosphate ore or phosphate fertilizer.

[0019] Compared with the prior art, the application has the following advantages and effects:

[0020] 1. The magnesium-based additive inhibits phosphorus volatilization in the sludge two-step biochar preparation method, and the prepared phosphorus-enriched biochar solves the harm caused by the large-scale production and accumulation of municipal sludge and enriches a large amount of phosphorus elements.

[0021] 2. The phosphorus-enriched biochar is more practical, can be applied to grassland and gardens instead of phosphate fertilizer, or can be used as a source of phosphate ore instead of phosphate ore mining, thereby reducing environmental damage and resource waste in the process of phosphate ore mining and phosphate fertilizer production, and solving the problems of excessive production of municipal sludge, inefficient treatment, and low utilization rate. DETAILED DESCRIPTION

[0022] The application will be described in detail below with reference to examples. The embodiments described in the following exemplary examples do not represent all the embodiments consistent with the present application. Obviously, the described examples are only a part of the embodiments of the present application, rather than all the embodiments. The examples in the present application and the features in the examples can be combined with each other without conflict. Based on the examples in the present application, all other examples obtained by those of ordinary skill in the art without creative labor fall within the scope of the present application.

[0023] In view of the problems of large municipal sludge output, low recycling means, and large phosphorus loss in the treatment of sludge by the thermochemical method, the present application provides a two-step method for preparing biochar by inhibiting phosphorus volatilization of sludge by using a magnesium-based additive.

[0024] A method for inhibiting phosphorus volatilization of sludge semi-coke in the calcination process, comprising the following steps:

[0025] (1) heating and drying the residual sludge from a municipal sewage treatment plant, crushing and grinding the dried sludge, and passing it through a 200-mesh sieve;

[0026] (2) placing the sludge particles of (1) in a microwave pyrolysis device for pyrolysis, setting the pyrolysis conditions, the target pyrolysis temperature being 300-500℃, the heating rate being 10℃ / min, the pyrolysis time being kept for 60 min, high-purity inert gas being introduced to dilute the air atmosphere in the furnace chamber for replacement, the gas flow rate being greater than 100 mL / min, after the replacement is completed, starting the microwave oven for sludge pyrolysis, and cooling after the pyrolysis is completed to obtain sludge semi-coke;

[0027] (3) adding 10% magnesium-based additive (Mg(OH)2) to the sludge semi-coke of step (2) in the furnace chamber of a tube furnace, setting the calcination conditions, the target calcination temperature being 700-900℃, the heating rate being 10℃ / min, the calcination time being 30 min, nitrogen gas being introduced to replace the air in the furnace chamber before calcination, the gas flow rate being greater than 100 mL / min, maintaining the nitrogen atmosphere to start the calcination furnace to perform sludge semi-coke calcination; and obtaining phosphorus-rich biochar after cooling.

[0028] To better illustrate the technical means and product effects of the present application, the preferred embodiments of the present application are described below.

[0029] Example 1

[0030] A method for inhibiting phosphorus volatilization of sludge semi-coke in the calcination process, comprising the following steps:

[0031] (1) heating and drying the residual sludge from a municipal sewage treatment plant, crushing and grinding the dried sludge, and passing it through a 200-mesh sieve;

[0032] (2) The sludge particles of (1) are placed in a microwave pyrolysis device for pyrolysis, and the pyrolysis conditions are set, the target pyrolysis temperature is 500℃, the heating rate is 10℃ / min, the pyrolysis time is kept for 60min, high-purity inert gas is introduced to dilute the air atmosphere in the furnace chamber for replacement, the gas flow rate is greater than 100mL / min, after the replacement is completed, the microwave oven is started to pyrolyze the sludge, and after the pyrolysis is completed, cooling is performed to obtain sludge semicoke;

[0033] (3) The sludge semicoke of step (2) is placed in a tube furnace chamber, and the calcination conditions are set, the target calcination temperature is 700℃, the heating rate is 10℃ / min, the calcination time is 30min, before calcination, nitrogen is introduced into the furnace chamber to replace air, the gas flow rate is greater than 100mL / min, the calcination furnace is started to calcine the sludge semicoke under a nitrogen atmosphere; and after cooling, unmodified biochar is obtained.

[0034] Example 2

[0035] The operation steps of this example are the same as those of Example 1, except that the calcination temperature is adjusted, and the temperature is set to 800℃. After the experiment is completed, ICP is used to detect the heavy metal ion content of the unmodified biochar, and the SMT method is used to detect the fixation rate of phosphorus elements in the unmodified biochar.

[0036] Example 3

[0037] The operation steps of this example are the same as those of Example 1, except that the calcination temperature is adjusted, and the temperature is set to 900℃. After the experiment is completed, ICP is used to detect the heavy metal ion content of the unmodified biochar, and the SMT method is used to detect the fixation rate of phosphorus elements in the unmodified biochar.

[0038] Example 4

[0039] A method for inhibiting the volatilization of phosphorus in sludge semicoke during calcination, comprising the following steps:

[0040] (1) Heating and drying the residual sludge from a municipal sewage treatment plant, crushing and grinding the dried sludge, and passing it through a 200-mesh sieve;

[0041] (2) The sludge particles of (1) are placed in a microwave pyrolysis device for pyrolysis, and the pyrolysis conditions are set, the target pyrolysis temperature is 500℃, the heating rate is 10℃ / min, the pyrolysis time is kept for 60min, high-purity inert gas is introduced to dilute the air atmosphere in the furnace chamber for replacement, the gas flow rate is greater than 100mL / min, after the replacement is completed, the microwave oven is started to pyrolyze the sludge, and after the pyrolysis is completed, cooling is performed to obtain sludge semicoke;

[0042] (3) The sludge semi-coke of step (2) is added with 10% magnesium-based additive (Mg(OH)2) and placed in the tube furnace hearth, the calcination conditions are set, the target calcination temperature is 700°C, the temperature rising rate is 10°C / min, the calcination time is 30 min, before calcination, the furnace hearth is replaced with nitrogen gas to replace air, the gas flow rate is greater than 100 mL / min, the nitrogen atmosphere is maintained to start the calcination furnace, and the sludge semi-coke is calcined; after cooling, the phosphorus-rich biochar is obtained.

[0043] Example 5

[0044] The operation steps of this example are the same as those of example 4, except that the calcination temperature is adjusted, and the temperature is set to 800°C. After the experiment is completed, ICP is used to detect the reduction amount of heavy metal ions in the magnesium-modified biochar, and SMT method is used to detect the fixation rate of phosphorus elements in the phosphorus-rich biochar.

[0045] Example 6

[0046] The operation steps of this example are the same as those of example 4, except that the calcination temperature is adjusted, and the temperature is set to 900°C. After the experiment is completed, ICP is used to detect the reduction amount of heavy metal ions in the magnesium-modified biochar, and SMT method is used to detect the fixation rate of phosphorus elements in the phosphorus-rich biochar.

[0047] Performance analysis

[0048] 1. Analysis of heavy metal content of phosphorus-rich biochar

[0049] 0.1 g of sample is weighed and placed in a polytetrafluoroethylene digestion tank, 8 mL of 65% HNO3, 1 mL of 30% H2O2, and 2 mL of 30% HF are added to the sample, and then a microwave digestion instrument is used to control the temperature according to the method shown in Table 1:

[0050] Table 1 is a parameter table for setting the temperature of microwave digestion;

[0051]

[0052] Table 1

[0053] After digestion, the sample is cooled and taken out, filtered with a 0.45 micron filter head, and then ICP is used to detect the heavy metal concentration in the sample. Table 2 shows the heavy metal content (mg / kg) of unmodified sludge biochar and magnesium-modified phosphorus-rich sludge biochar.

[0054] Table 2 shows the heavy metal content of samples in examples 1-6;

[0055]

[0056] Table 2

[0057] From Table 2, it can be seen that the heavy metal content of the sludge-based biochar modified by magnesium is lower than that of the unmodified sludge-based biochar.

[0058] 2. Analysis of phosphorus yield and fixation rate in phosphorus-rich biochar

[0059] The SMT method was used to detect the fixation rate of phosphorus in the phosphorus-rich biochar. 20 ml of 3.5M hydrochloric acid was added to 0.2g of sample, and constant temperature oscillation extraction was performed for 16h. The supernatant was extracted using a 0.45 micron filter head, and then the molybdenum blue experiment was performed to analyze the phosphorus content in the sample. Table 3 shows the phosphorus fixation rate in the Fenton-modified sludge-based phosphorus-rich biochar at different calcination temperatures.

[0060] The yield calculation formula is as follows:

[0061] R yield = M2 / M1 x 100% (1)

[0062] In the formula, M1 and M2 are the masses of the biochar before and after heat treatment, respectively.

[0063] The sample phosphorus fixation rate is calculated as follows:

[0064] ψP = C2 / C1 x R yield x 100% (2)

[0065] In the formula, C1 and C2 are the concentrations of phosphorus in the sample before and after heat treatment, respectively.

[0066] Table 3 shows the phosphorus yield and fixation rate of the samples in Examples 1-6;

[0067]

[0068] Table 3

[0069] According to Table 3, the phosphorus fixation rate of the modified sludge-based semi-coke increases after calcination at different temperatures, and the fixation rate is between 90.2% and 93.1%.

[0070] 3. Analysis of phosphorus bioavailability of phosphorus-rich biochar

[0071] The 2% formic acid extraction method was used to analyze the bioavailable content and bioavailable proportion of phosphorus in the phosphorus-rich biochar prepared in Examples 1-8.

[0072] The 2% formic acid extraction method was used to extract the sample with a solid-liquid ratio of 1:100, and the supernatant was extracted after standing for 16h. The molybdenum blue colorimetric method was used to determine the phosphorus content of the sample, and the bioavailable proportion was calculated using the following formula:

[0073] θ p = C2 / C1 x 100%

[0074] Wherein, C1, C2 are total phosphorus concentration of the sample and the concentration of phosphorus element in the corresponding leaching solution respectively.

[0075] Table 4 is a table of the bioavailable content and bioavailable proportion of phosphorus element of the phosphorus-rich biochar samples of Examples 1-8.

[0076]

[0077]

[0078] Table 4

[0079] According to Table 4, compared with the unmodified sludge biochar, the phosphorus in the magnesium-modified sludge biochar has higher bioavailability, and the bioavailable proportion reaches 52.50%, which fully shows that the phosphorus in the phosphorus-rich biochar prepared in the application realizes efficient utilization.

[0080] From the above analysis, it can be seen that the method for preparing biochar with high bioavailability and industrial usability by inhibiting phosphorus volatilization through magnesium-based additives combined with pyrolysis-calcination process in the application not only inhibits the volatilization of phosphorus, obtains higher phosphorus yield and fixation rate, but also reduces the pollution risk of heavy metals during the resource utilization of sludge-based phosphorus-rich biochar, which shows that the preset goal of harmless and resourceful treatment and disposal of municipal sludge can be achieved.

Claims

1. A magnesium-modified sludge-based phosphorus-rich biochar material and a preparation method thereof, characterized in that: The following steps are involved: (1) heating and drying municipal sludge, grinding, crushing, and screening to obtain sludge particles; (2) placing the sludge particles in a microwave pyrolysis device for pyrolysis, and obtaining sludge semi-coke after cooling; (3) Adding a magnesium-based additive to the sludge semi-coke obtained in step (2) and heating and calcining the mixture in a nitrogen atmosphere, and cooling the mixture to obtain phosphorus-rich biochar.

2. A magnesium-modified sludge-based phosphorus-rich biochar material and a preparation method thereof according to claim 1, characterized in that: The heated and dried municipal sludge in step (1) is ground and crushed, and then passed through a 100-200 mesh sieve.

3. A magnesium-modified sludge-based phosphorus-rich biochar material and a preparation method thereof according to claim 1, characterized in that: Before step (2), high-purity inert gas is introduced to replace the air atmosphere in the microwave pyrolysis device, and the gas flow rate is greater than 100 mL / min; the pyrolysis temperature is 300°C-500°C, the heating rate is 10°C / min-20°C / min, and the pyrolysis time is 60min-90min.

4. A magnesium-modified sludge-based phosphorus-rich biochar material and a preparation method thereof according to claim 1, characterized in that: The magnesium-based additive in step (3) is Mg(OH)2, and the added amount is 10%-20% of the mass of the sludge semi-coke.

5. A magnesium-modified sludge-based phosphorus-rich biochar material and a preparation method thereof according to claim 1, characterized in that: The step (3) is calcined in a tubular furnace.

6. A magnesium-modified sludge-based phosphorus-rich biochar material and a preparation method thereof according to claim 1, characterized in that: The calcination temperature in step (3) is 700° C.-900° C., the heating rate is 10° C. / min, the calcination time is 30 min, and the gas flow rate is greater than 100 mL / min.

7. The magnesium-modified sludge-based phosphorus-rich biochar material and preparation method thereof according to claim 1, characterized in that: The phosphorus fixation rate in the prepared phosphorus-rich biochar reaches 90.2%-93.1%.

8. A magnesium-modified sludge-based phosphorus-rich biochar material, characterized in that: The biochar is prepared by using the method for preparing a magnesium-modified sludge-based phosphorus-rich biochar material according to any one of claims 1 to 7.

9. The magnesium-modified sludge-based phosphorus-rich biochar material according to claim 8, characterized in that: The magnesium-modified sludge-based phosphorus-rich biochar is used in phosphate rock or phosphate fertilizer.

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