Method for removing phosphorus and heavy metal elements in phosphate tailings and phosphogypsum by using duckweed

Abstract

The invention relates to the technical field of environmental restoration, in particular to a method for removing phosphorus and heavy metal elements in phosphate tailings and phosphogypsum by using duckweed, which comprises the following steps: pretreating and crushing; preparing an acid leaching solution; dynamic leaching and separation are carried out; screening and cleaning duckweed; carrying out gradient adaptive culture; constructing a light reaction system; the pollutant concentration and the duckweed growth state are monitored in real time; separating the dehydrated biomass; and pyrolysis and resource recovery are performed, the duckweed biomass is subjected to pyrolysis treatment, and heavy metal and energy resources are directionally recovered. According to the method, the uniformity of minerals is improved through multi-step synergism, pollutants are effectively dissolved, the tolerance and enrichment capacity of the duckweed to the pollutants are enhanced through adaptive culture, the contact efficiency and photosynthesis activity of the duckweed and the pollutants are improved, meanwhile, treatment parameters are dynamically adjusted, and finally, through dehydration and low-temperature pyrolysis of duckweed biomass, the content of the duckweed in the duckweed biomass is increased. And a complete'pollutant adsorption-enrichment-recycling 'closed-loop system is formed.

Description

Technical Field

[0001] The present invention relates to the technical field of environmental remediation, and specifically provides a method for removing phosphorus and heavy metal elements from phosphorus tailings and phosphogypsum using duckweed. Background Art

[0002] Phosphorus and heavy metal elements contained in phosphorus tailings, if not properly treated, will cause serious pollution to the surrounding soil and water environment, threatening ecological balance and human health. Traditional treatment methods often have problems such as high cost, complex treatment processes, and easy generation of secondary pollution. Currently, the methods for treating phosphorus and heavy metal elements in phosphorus tailings mainly include chemical precipitation method, ion exchange method, and adsorption method. The chemical precipitation method forms insoluble precipitates of phosphorus and heavy metals by adding chemical reagents. Although the treatment efficiency is relatively high, it will generate a large amount of sludge, and the subsequent sludge treatment cost is high, and there is also a risk of secondary pollution.

[0003] Generally, the traditional ion exchange method uses ion exchange resins to adsorb phosphorus and heavy metal ions, but it has strict requirements for operating conditions. Changes in temperature, pH value, etc. will affect the adsorption performance of the resin, and the resin regeneration process is complex and the cost is high. The adsorption method uses adsorption materials such as activated carbon and zeolite. Although it has a good adsorption effect on phosphorus and heavy metals, the cost of the adsorption materials is high, the adsorption capacity is limited, and the adsorbed materials are difficult to treat and regenerate, which limits its large-scale application. In recent years, the application of duckweed in the field of ecological remediation has become increasingly widespread. Research shows that duckweed has a high absorption capacity for nutrients such as nitrogen and phosphorus in sewage and can effectively reduce the eutrophication degree of water bodies. As a common aquatic plant, duckweed has the characteristics of rapid growth, easy access, and strong absorption capacity for nutrients. However, there is currently no mature method for using duckweed to treat pollutants in phosphorus tailings.

[0004] Based on this, the present invention provides a method for removing phosphorus and heavy metal elements from phosphorus tailings and phosphogypsum using duckweed to solve the above-mentioned technical problems. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for removing phosphorus and heavy metal elements from phosphorus tailings and phosphogypsum using duckweed to solve the problems mentioned in the above background art.

[0006] To achieve the above purpose, the present invention provides the following technical solutions:

[0007] The present invention proposes a method for removing phosphorus and heavy metal elements from phosphorus tailings and phosphogypsum using duckweed, which includes the following steps:

[0008] S1. Perform pretreatment and pulverization, physically break and sort the phosphorus tailings to improve the mineral uniformity;

[0009] S2. Prepare the acidic leaching solution, dissolve phosphorus and heavy metal elements with an acidic solution, and stabilize the reaction conditions;

[0010] S3. Implement dynamic leaching and separation, and obtain a clear contaminated leaching solution through stirring reaction and filtration process;

[0011] S4. Conduct duckweed screening and cleaning, screen duckweed varieties with strong tolerance and remove surface impurities;

[0012] S5. Conduct gradient adaptation culture, gradually increase the proportion of the leaching solution, and enhance the adaptability of duckweed to the polluted environment;

[0013] S6. Construct a light reaction system, and optimize the contact efficiency between duckweed and the leaching solution using a photobioreactor;

[0014] S7. Monitor the pollutant concentration and the growth status of duckweed in real time, and dynamically adjust the treatment parameters;

[0015] S8. Separate and dehydrate the biomass, separate duckweed through a combined process and reduce its water content;

[0016] S9. Conduct pyrolysis and resource recovery, pyrolyze the duckweed biomass, and directionally recover heavy metals and energy resources.

[0017] Preferably, the implementation process of step S1 is as follows: Physically crush the phosphate tailings, grind them to a particle size of 80 - 100 mesh using a ball mill, and remove impurities through magnetic separation or screening to improve the uniformity of the minerals.

[0018] Preferably, the implementation process of step S2 is as follows: Add deionized water according to a solid - liquid ratio of 1:8 - 12, add dilute sulfuric acid with a concentration of 0.1 - 0.5 mol / L, and adjust the pH to 4 - 6 using a pH automatic monitor to ensure stable acidic conditions.

[0019] Preferably, the implementation process of step S3 is as follows: Continuously stir in a constant - temperature stirring reactor at 200 r / min for 3 - 5 hours, and then filter through a plate - and - frame filter press to obtain a clear phosphate tailings leaching solution.

[0020] Preferably, the implementation process of step S4 is as follows: Collect local duckweed, including Wolffia arrhiza and Spirodela oligorrhiza, screen out varieties with strong tolerance to phosphorus and heavy metals through laboratory hydroponic experiments, and remove surface attachments using ultrasonic cleaning.

[0021] Preferably, the implementation process of step S5 is as follows: After pre - culturing in Hoagland nutrient solution for 3 - 5 days, gradually add the leaching solution using the gradient method, with an initial proportion of 5%, increasing by 2% daily, and accelerating the physiological adaptation of duckweed in combination with an LED light source, with the spectral optimization of red light: blue light = 3:1.

[0022] Preferably, the implementation process of step S6 is as follows: transfer the cultured duckweed to a photobioreactor equipped with a microbubble aeration device with a bubble diameter < 1 mm and a low-speed agitator with a rotation speed of 100 - 150 r / min, and use a PLC system to adjust the temperature to 20 - 30 °C, the light intensity to 4000 - 6000 lx, and the light cycle to 12 - 16 h of light in real time.

[0023] Preferably, the implementation process of step S7 is as follows: use the combined technology of ion-selective electrode and ICP-MS to on-line monitor the concentrations of phosphorus and heavy metals in the leachate, and combine the real-time feedback data of the duckweed biomass sensor. The duckweed biomass sensor is a chlorophyll fluorometer, which automatically adjusts the circulation rate of the leachate and the light parameters.

[0024] Preferably, the implementation process of step S8 is as follows: adopt the combined process of centrifugation and vacuum belt dewatering. First, centrifuge the duckweed and the treatment liquid at 3000 rpm to separate them, and then use a belt dewatering machine to reduce the water content of the duckweed to 60% - 70%, reducing the subsequent drying energy consumption.

[0025] Preferably, the implementation process of step S9 is as follows: pyrolyze the dewatered duckweed at 300 - 400 °C under nitrogen protection to generate biochar for adsorbent and pyrolysis gas for energy recovery. At the same time, collect the heavy metal enrichment phase through a condensation system to further extract valuable metals.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] The present invention improves the mineral uniformity through multi-step coordination, ensures the sufficiency of the subsequent leaching reaction, effectively dissolves pollutants, provides a high-concentration pollution source for duckweed absorption, and the adaptive cultivation strengthens its tolerance and enrichment ability to pollutants. Combining the optimized design of the photobioreactor improves the contact efficiency between duckweed and pollutants and the photosynthesis activity. At the same time, the treatment parameters are dynamically adjusted to ensure the stability and controllability of the treatment process. Finally, through the dehydration and low-temperature pyrolysis of duckweed biomass, the harmless treatment of pollutants and the directional recovery of resources are realized, which not only exerts the natural remediation ability of duckweed but also intelligently improves the process efficiency, forming a complete "pollutant adsorption - enrichment - resource utilization" closed-loop system. Detailed implementation manners

[0028] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0029] The present invention provides a method for removing phosphorus and heavy metal elements from phosphorus tailings and phosphogypsum using duckweed, comprising the following steps:

[0030] S1. Conduct pretreatment and crushing. Physically break and sort the phosphorus tailings to improve the mineral uniformity. Specifically, the steps are as follows:

[0031] The implementation process of step S1 is: Physically break the phosphorus tailings, crush them to a particle size of 80 - 100 mesh using a ball mill, and remove impurities through magnetic separation or screening to improve the mineral uniformity;

[0032] It should also be noted that in this step, the pretreatment and crushing ball mill uses a QM - WX4 planetary ball mill (particle size range 50 - 200 mesh, power 5.5 kW) to crush the phosphorus tailings to 80 - 100 mesh. The magnetic separator selects a CTB - 718 permanent magnet drum magnetic separator (magnetic field strength ≥ 1500 Gauss) to remove ferromagnetic impurities, and the vibrating screen is equipped with a ZSG - 1545 high - efficiency linear vibrating screen (screen mesh size 80 - 100 mesh) to ensure the mineral uniformity;

[0033] S2. Prepare the acidic leaching solution. Prepare an acidic solution to dissolve phosphorus and heavy metal elements and stabilize the reaction conditions. Specifically, the steps are as follows:

[0034] The implementation process of step S2 is: Add deionized water according to a solid - liquid ratio of 1:8 - 12, and add dilute sulfuric acid with a concentration of 0.1 - 0.5 mol / L. Adjust it to 4 - 6 through a pH automatic monitor to ensure stable acidic conditions;

[0035] It should also be noted that in this step, the pH automatic monitor for preparing the acidic leaching solution uses a METTLER TOLEDO Seven Excellence TM S400 (accuracy ±0.01 pH) to adjust the solution pH to 4 - 6 in real - time. The stirring reactor uses a GSA - 1000L stainless - steel reaction kettle (equipped with a variable - frequency speed - regulating stirrer) to ensure uniform solid - liquid mixing;

[0036] S3. Implement dynamic leaching and separation. Obtain a clear polluted leaching solution through stirring reaction and filtration processes. Specifically, the steps are as follows:

[0037] The implementation process of step S3 is: Continuously stir in a constant - temperature stirring reactor at 200 r / min for 3 - 5 hours, and then filter through a plate - and - frame filter press to obtain a clear phosphorus tailings leaching solution;

[0038] Among them, it should also be noted that in this step, the dynamic leaching and separation constant-temperature stirring reactor selects the Biobase BJS-50L constant-temperature magnetic stirring reactor (temperature control accuracy ±0.5°C, rotation speed 0-500 r / min), continuously stirs at 200 r / min for 3-5 hours, and the plate and frame filter press is configured with the XMZ-100 / 1250-U automatic plate and frame filter press (filter area 100m 2 , pressure 1.0 MPa) to achieve efficient solid-liquid separation;

[0039] S4. Conduct duckweed screening and cleaning, screen duckweed varieties with strong tolerance and remove surface impurities. Specifically, the steps are as follows:

[0040] The implementation process of step S4 is: collect local duckweed, including Wolffia arrhiza and Spirodela oligorrhiza, screen out varieties with strong tolerance to phosphorus and heavy metals through laboratory hydroponic experiments, and use ultrasonic cleaning to remove surface attachments;

[0041] Among them, it should also be noted that in this step, the duckweed screening and cleaning ultrasonic cleaner uses the KQ-500DE numerical control ultrasonic cleaner (frequency 40 kHz, power 500 W) to thoroughly remove surface attachments of duckweed, and the laboratory hydroponic system uses Delta hydroponic incubator (temperature control range 15-30°C, light intensity adjustable) to screen duckweed varieties with strong tolerance;

[0042] S5. Conduct gradient adaptability cultivation, gradually increase the proportion of leaching solution, and enhance the adaptability of duckweed to the polluted environment. Specifically, the steps are as follows:

[0043] The implementation process of step S5 is: after pre-culturing in Hoagland nutrient solution for 3-5 days, gradually add the leaching solution by the gradient method, with an initial proportion of 5%, increasing by 2% daily, and accelerating the physiological adaptation of duckweed in combination with the LED light source, and the spectral optimization is red light: blue light = 3:1;

[0044] Among them, it should also be noted that in this step, the gradient adaptability cultivation LED light source system is configured with the Photontek X600 LED plant growth lamp (spectral ratio red light 660 nm: blue light 450 nm = 3:1, light intensity 0-6000 lx adjustable) to accelerate the physiological adaptation of duckweed, and the nutrient solution circulation pump uses the IWAKI MD-30R magnetic drive pump (flow rate 30 L / min) to achieve gradient addition of the leaching solution;

[0045] S6. Construct a light reaction system and use a photobioreactor to optimize the contact efficiency between duckweed and the leaching solution. Specifically, the steps are as follows:

[0046] The implementation process of step S6 is as follows: Transfer the cultivated duckweed to a photobioreactor equipped with a microbubble aeration device with a bubble diameter < 1 mm and a low-speed stirring paddle with a rotation speed of 100 - 150 r / min. Use a PLC system to adjust the temperature to 20 - 30 °C, the light intensity to 4000 - 6000 lx, and the light cycle to 12 - 16 h of light in real time;

[0047] It should also be noted that in this step, for the construction of the photobioreactor in the photosynthesis reaction system, the AlgaeLinkPBR - 1000 photobioreactor (with a volume of 1000 L and equipped with a microbubble aeration device) is selected. The microbubble aeration device is configured with a NanobubbleNB - 200 generator (bubble diameter < 1 μm, gas - liquid ratio 1:10), and the low - speed stirring paddle uses an IKA RW20 digital stirrer (rotation speed 50 - 150 r / min) to ensure sufficient contact between the duckweed and the leachate. The PLC control system integrates a SIEMENS S7 - 1200 PLC to adjust the temperature (20 - 30 °C), light intensity (4000 - 6000 lx), and light cycle (12 - 16 h) in real time;

[0048] S7. Monitor the pollutant concentration and the growth status of duckweed in real time, and dynamically adjust the treatment parameters. Specifically, the steps are as follows:

[0049] The implementation process of step S7 is as follows: Use the combined technology of ion - selective electrode and ICP - MS for on - line monitoring of the phosphorus and heavy metal concentrations in the leachate, combined with the real - time feedback data of the duckweed biomass sensor. The duckweed biomass sensor is a chlorophyll fluorometer, and automatically adjust the leachate circulation rate and light parameters;

[0050] It should also be noted that in this step, for real - time monitoring and regulation, the ion - selective electrode uses a HACH HQd series multi - parameter electrode (phosphorus ion detection limit 0.01 mg / L), the ICP - MS combined instrument is configured with an Agilent 7900 ICP - MS (heavy metal detection limit at the ppb level), and the chlorophyll fluorometer selects the Walz Imaging - PAM M series to monitor the duckweed biomass in real time;

[0051] S8. Separate and dehydrate the biomass, and separate the duckweed and reduce its water content through a combined process. Specifically, the steps are as follows:

[0052] The implementation process of step S8 is as follows: Adopt a combined process of centrifugation - vacuum belt dehydration. First, centrifuge the duckweed and the treatment liquid at 3000 rpm to separate them, and then use a belt dehydrator to reduce the water content of the duckweed to 60% - 70%, reducing the subsequent drying energy consumption;

[0053] It should also be noted that in this step, a Thermo Scientific Sorvall LYNX 6000 high-speed centrifuge (rotation speed 3000 rpm, capacity 6 × 1 L) is used for the biomass separation and dehydration centrifuge to preliminarily separate duckweed from the treatment liquid, and an Andritz DDS series belt filter press is configured for the vacuum belt filter press (processing capacity 1 - 5 t / h, water content after dehydration ≤ 70%);

[0054] S9. Conduct pyrolysis and resource recovery, pyrolyze duckweed biomass, and directionally recover heavy metals and energy resources. Specifically, the steps are as follows:

[0055] The implementation process of step S9 is: pyrolyze the dehydrated duckweed at 300 - 400 °C under nitrogen protection to generate biochar for adsorbent and pyrolysis gas for energy recovery, and at the same time collect the heavy metal enrichment phase through a condensation system to further extract valuable metals.

[0056] It should also be noted that in this step, a Carbolite Gero PEF11 / 50 tubular pyrolysis furnace (temperature range 0 - 1000 °C, nitrogen protection) is selected for the low-temperature pyrolysis furnace of pyrolysis and resource recovery, pyrolyze duckweed at 300 - 400 °C, a Büchi B-295 condensation recovery device (condensation temperature -50 °C) is configured for the condensation system to collect the heavy metal enrichment phase, and a Siemens Ultramat 23 infrared gas analyzer is used for the gas analyzer to monitor the components of the pyrolysis gas (CO, CH4).

[0057] Example 1, in this example, a method for removing phosphorus and heavy metal elements from phosphorus tailings and phosphogypsum using duckweed includes the following steps:

[0058] Step S1: Crush the phosphorus tailings to 90 meshes with a ball mill and remove impurities by magnetic separation;

[0059] Step S2: Add deionized water according to a solid-liquid ratio of 1:10, add 0.3 mol / L dilute sulfuric acid, and adjust the pH to 5;

[0060] Step S3: Stir in a constant-temperature reactor at 200 r / min for 4 hours, and obtain the leachate after plate and frame filtration;

[0061] Step S4: Screen Wolffia arrhiza, ultrasonically clean it, and pre-culture it for 4 days;

[0062] Step S5: The initial addition ratio of the leachate is 5%, increasing by 2% daily, red light: blue light = 3:1;

[0063] Step S6: Set microbubble aeration (bubble diameter 0.8 mm) and a stirring paddle at 150 r / min in the photobioreactor, and use a PLC to control the temperature at 25 °C, the light intensity at 5000 lx, and the light cycle at 14 h;

[0064] Step S7: Online monitor the phosphorus concentration (ion electrode) and biomass (chlorophyll fluorometer), and automatically adjust the circulation rate;

[0065] Step S8: Centrifuge (3000 rpm) and then dehydrate with a belt until the water content reaches 65%;

[0066] Step S9: Pyrolyze at 350 °C under nitrogen protection, and collect the biochar and the heavy metal condensate phase;

[0067] Example 2: In this example, the crushing particle size in Step S1 is 80 mesh, and other parameters are the same as those in Example 1;

[0068] Example 3: In this example, the concentration of dilute sulfuric acid in Step S2 is 0.1 mol / L, and other parameters are the same as those in Example 1;

[0069] Example 4: In this example, the stirring speed in Step S3 is 150 r / min, and other parameters are the same as those in Example 1;

[0070] Example 5: In this example, the pre-cultivation time in Step S5 is 3 days, and other parameters are the same as those in Example 1.

[0071] The process parameters in Examples 1 to 5 are shown in Table 1:

[0072] Table 1 Process parameter table of Examples 1 to 5

[0073]

[0074]

[0075] To verify the scientificity of the process parameter ranges in Examples 1 to 5, comparative examples were designed for verification as follows:

[0076] Comparative Example 1: In this comparative example, the crushing particle size in Step S1 is 120 mesh, exceeding the scope of the claims, and other parameters are the same as those in Example 1;

[0077] Comparative Example 2: In this comparative example, the concentration of dilute sulfuric acid in Step S2 is 0.8 mol / L, exceeding the scope of the claims, and other parameters are the same as those in Example 1;

[0078] Comparative Example 3: In this comparative example, the stirring time in Step S3 is 2 hours, lower than the scope of the claims, and other parameters are the same as those in Example 1;

[0079] Comparative Example 4: In this comparative example, the initial proportion of the leaching solution in Step S5 is 10%, exceeding the gradient increasing rule, and other parameters are the same as those in Example 1;

[0080] Comparative Example 5. In this comparative example, the pyrolysis temperature in step S9 was 500 °C, exceeding the low-temperature pyrolysis range, and other parameters were the same as those in Example 1;

[0081] The process parameters in Comparative Examples 1 to 5 are shown in Table 2:

[0082] Table 2 Process parameter table for Comparative Examples 1 to 5

[0083]

[0084]

[0085] The methods for removing phosphorus and heavy metal elements from phosphorus tailings and phosphogypsum using duckweed in Examples 1 to 5 were verified for performance, and experiments were designed as follows:

[0086] a. Phosphorus removal rate: Refer to "Molybdate Ammonium Spectrophotometric Method for the Determination of Total Phosphorus in Water Quality" (GB11893-89);

[0087] a1. Sampling: Take leachate samples before treatment (initial solution) and after treatment (final solution) respectively;

[0088] a2. Digestion: Add potassium persulfate and digest under high pressure at 120 °C for 30 minutes to convert organic phosphorus into inorganic phosphate;

[0089] a3. Color development: Add a mixed solution of ammonium molybdate-potassium antimonyl tartrate and ascorbic acid to form a blue complex;

[0090] a4. Determination: Measure the absorbance at a wavelength of 700 nm with a spectrophotometer and calculate the phosphorus concentration through the standard curve;

[0091] a5. Calculation: Phosphorus removal rate (%) = (initial concentration - final concentration) / initial concentration × 100%;

[0092] b. Heavy metal removal rate: Refer to "Determination of Total Metal Elements in Soil and Sediments - Microwave Digestion - Inductively Coupled Plasma Mass Spectrometry" (HJ803-2016);

[0093] b1. Sampling and digestion: Take leachate samples, add a mixed solution of nitric acid-hydrofluoric acid, and microwave digest until clear;

[0094] b2. Dilution and volume determination: Dilute to 50 mL with ultrapure water and pass through a 0.45 μm filter membrane;

[0095] b3. Instrumental analysis: Use ICP-MS to determine the concentrations of heavy metals (such as Pb, Cd, As);

[0096] b4. Calculation: Heavy metal removal rate (%) = (initial concentration - final concentration) / initial concentration × 100%;

[0097] c. Duckweed growth rate: refer to the "Specifications for Determination of Aquatic Plant Biomass" (NY / T3969-2021);

[0098] c1. Sampling and weighing: Take duckweed samples regularly every day, dry the surface water with filter paper and weigh the fresh weight (g);

[0099] c2. Drying and weighing: Dry some samples at 105°C to constant weight and record the dry weight (g);

[0100] c3. Calculation:

[0101] Fresh weight growth rate (g / d) = (final fresh weight - initial fresh weight) / number of culture days;

[0102] Dry weight biomass (g / m 2 ) = dry weight / culture area;

[0103] d. Biochar yield: in accordance with the "Determination Method for Yield of Biomass Pyrolysis Products" (GB / T35818-2018);

[0104] d1. Raw material weighing: accurately weigh the mass of dehydrated duckweed (M1, g);

[0105] d2. Pyrolysis treatment: Pyrolysis at 300-400 °C for 1 hour under nitrogen protection, and weigh the mass of biochar after cooling (M2, g);

[0106] d3. Calculation: biochar yield (%) = (M2 / M1) × 100%;

[0107] Among them, it should be noted that in the performance test of the embodiments of the present invention and the comparative examples:

[0108] Before testing, the instrument needs to be calibrated with standard substances. Three parallel samples are set for each group of experiments, and the average value is taken to reduce the error;

[0109] The extract samples need to be acidified (pH < 2) and refrigerated at 4°C, and the test should be completed within 24 hours. The duckweed biomass needs to be freeze-dried and stored in a sealed container away from light.

[0110] The performance experimental data of the methods in Examples 1 to 5 are recorded, see Table 3:

[0111] Table 3 Performance data comparison table of the embodiments

[0112]

[0113]

[0114] The performance experimental data of the methods in Comparative Examples 1 to 5 are recorded, see Table 4:

[0115] Table 4 Comparison of performance data of comparative examples

[0116] Experimental group Phosphorus removal rate (%) Heavy metal removal rate (%) Duckweed survival rate (%) Pyrolysis gas yield (%) Control ratio 1 75.3 68.9 60 18.2 Control ratio 2 82.1 72.4 45 15.7 Control ratio 3 70.8 65.3 55 12.9 Control ratio 4 78.6 70.1 50 14.5 Control ratio 5 85.2 76.8 30 20.4

[0117] Analyze the methods of the examples and comparative examples in combination with the data in Tables 1 to 4:

[0118] For the different grinding particle sizes of Example 1 and Comparative Example 1, the mineral uniformity of 90 mesh particle size in Example 1 is better than that of 120 mesh in Comparative Example 1, and the leaching efficiency is increased by 17.2%. For the different acid concentrations of Example 1 and Comparative Example 2, 0.3 mol / L dilute sulfuric acid in Example 1 can not only effectively dissolve pollutants but also avoid acidification damage to duckweed, and the survival rate is 55% higher than that of Comparative Example 2. For the different stirring speeds of Example 1 and Example 4, 200 r / min in Example 1 is more conducive to solid-liquid mass transfer than 150 r / min in Example 4, and the phosphorus removal rate is increased by 3.6%. Moreover, each performance parameter in the examples is better than that in the comparative examples. Therefore, the rationality of each process parameter in the examples is verified;

[0119] At the same time, the parameter settings of Example 1 are balanced. The 90 mesh grinding particle size, 0.3 mol / L acid concentration, 200 r / min stirring speed, and 4-day pre-culture time comprehensively improve the pollutant dissolution efficiency and the adaptability of duckweed. The optimized light intensity of 5000 lx and the spectral ratio of red light:blue light = 3:1 in the photobioreactor significantly promote the photosynthesis of duckweed, and the biomass growth rate reaches 1.8 g / d. The pore structure of the biochar is better at 350 °C, with strong adsorption performance, while avoiding heavy metal volatilization, and the recovery rate is as high as 88.3%;

[0120] In summary, in the present invention, Example 1 is the best example.

[0121] Therefore, compared with the traditional chemical precipitation method that relies on chemical reagents and is prone to produce sludge and secondary pollution, and the ion exchange method and adsorption method that are difficult to be scaled up due to high material costs and complex regeneration, the present invention uses duckweed as a natural adsorption medium, without adding chemical reagents, avoiding sludge generation from the source. Duckweed grows rapidly and is easily obtained, greatly reducing the treatment cost. The biomass after enriching pollutants is converted into high-value products through low-temperature pyrolysis, realizing the resource utilization of pollutants and completely eliminating the risk of secondary pollution. At the same time, the intelligent monitoring and control technology simplifies the operation process and overcomes the defects of the traditional method that requires harsh operating conditions. The present invention takes ecological friendliness, low energy consumption, and high resource recovery rate as the core and solves the environmental pollution problem of phosphorus tailings.

[0122] In the description of this specification, the descriptions referring to the terms "one embodiment", "example", "specific example", etc. mean that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in a suitable manner in any one or more embodiments or examples.

[0123] The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific embodiments described. Obviously, many modifications and variations can be made according to the content of this specification. These embodiments are selected and specifically described in this specification in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can well understand and utilize the present invention. The present invention is only limited by the claims and their full scope and equivalents.

Claims

1. A method for removing phosphorus and heavy metal elements from phosphorus tailings and phosphogypsum by using duckweed, which is characterized in that, It includes the following steps: S1. Conduct pretreatment and crushing, physically break and separate the phosphorus tailings to improve the mineral uniformity; S2. Prepare the acidic leaching solution, prepare an acidic solution to dissolve phosphorus and heavy metal elements, and stabilize the reaction conditions; S3. Implement dynamic leaching and separation, and obtain a clear contaminated leaching solution through stirring reaction and filtration process; S4. Conduct duckweed screening and cleaning, screen duckweed varieties with strong tolerance and remove surface impurities; S5. Conduct gradient adaptation cultivation, gradually increase the proportion of the leaching solution, and enhance the adaptability of duckweed to the polluted environment; S6. Construct a photoreaction system, and use a photobioreactor to optimize the contact efficiency between duckweed and the leaching solution; S7. Real-time monitor the pollutant concentration and the growth status of duckweed, and dynamically adjust the treatment parameters; S8. Separate and dehydrate the biomass, separate duckweed through a combined process and reduce its water content; S9. Conduct pyrolysis and resource recovery, pyrolyze the duckweed biomass, and directionally recover heavy metals and energy resources.

2. The method for removing phosphorus and heavy metal elements from phosphorus tailings and phosphogypsum by using duckweed according to claim 1, wherein The implementation process of step S1 is as follows: Physically break the phosphorus tailings, crush them to a particle size of 80 - 100 mesh using a ball mill, and remove impurities through magnetic separation or screening to improve the mineral uniformity.

3. A method for removing phosphorus and heavy metal elements from phosphorus tailings and phosphogypsum by using duckweed according to claim 2, characterized in that, The implementation process of step S2 is as follows: Add deionized water according to a solid-liquid ratio of 1:8 - 12, add dilute sulfuric acid with a concentration of 0.1 - 0.5 mol / L, and adjust it to 4 - 6 through a pH automatic monitor to ensure stable acidic conditions.

4. A method for removing phosphorus and heavy metal elements from phosphorus tailings and phosphogypsum by using duckweed according to claim 1, characterized in that, The implementation process of step S3 is as follows: Continuously stir in a constant-temperature stirring reactor at 200 r / min for 3 - 5 hours, and then filter through a plate and frame filter press to obtain a clear phosphorus tailings leaching solution.

5. A method for removing phosphorus and heavy metal elements from phosphorus tailings and phosphogypsum by using duckweed, characterized in that, The implementation process of step S4 is as follows: Collect local duckweed, including Wolffia arrhiza and Spirodela oligorrhiza, screen out varieties with strong tolerance to phosphorus and heavy metals through laboratory hydroponic experiments, and use ultrasonic cleaning to remove surface attachments.

6. A method for removing phosphorus and heavy metal elements from phosphorus tailings and phosphogypsum using duckweed according to claim 4, characterized in that, The implementation process of step S5 is as follows: After pre-culturing in Hoagland nutrient solution for 3 - 5 days, gradually add the leaching solution using the gradient method, with an initial ratio of 5%, increasing by 2% daily, and accelerating the physiological adaptation of duckweed by combining with an LED light source, and optimizing the spectrum to red light: blue light = 3:

1.

7. A method for removing phosphorus and heavy metal elements from phosphorus tailings and phosphogypsum by using duckweed according to claim 1, characterized in that, The implementation process of step S6 is as follows: Transfer the cultured duckweed to a photobioreactor, which is equipped with a microbubble aeration device with a bubble diameter < 1 mm and a low-speed stirring paddle with a rotation speed of 100 - 150 r / min, and use a PLC system to continuously regulate the temperature to 20 - 30 °C, the light intensity to 4000 - 6000 lx, and the light cycle to 12 - 16 h of light.

8. A method for removing phosphorus and heavy metal elements from phosphorus tailings and phosphogypsum by using duckweed, characterized in that, The implementation process of step S7 is as follows: Use the combined technology of ion-selective electrode and ICP-MS to online monitor the phosphorus and heavy metal concentrations in the leaching solution, and combine with a duckweed biomass sensor to real-time feedback data. The duckweed biomass sensor is a chlorophyll fluorometer, and automatically adjust the leaching solution circulation rate and light parameters.

9. A method for removing phosphorus and heavy metal elements from phosphorus tailings and phosphogypsum by using duckweed, characterized in that, The implementation process of step S8 is as follows: Use a centrifugation-vacuum belt dehydration combined process, first centrifuge to separate duckweed and the treatment solution at 3000 rpm, and then reduce the water content of duckweed to 60% - 70% through a belt dehydrator to reduce the subsequent drying energy consumption.

10. A method for removing phosphorus and heavy metal elements from phosphorus tailings and phosphogypsum by using duckweed according to claim 9, characterized in that, The implementation process of step S9 is as follows: Under nitrogen protection, dewatered duckweed is pyrolyzed at a low temperature of 300 - 400 °C to generate biochar for adsorbent and pyrolysis gas for energy recovery. Meanwhile, the heavy metal enrichment phase is collected through a condensation system, and valuable metals are further extracted.

Images