A microporous foamed pyrite material and a method for preparing and applying the same

Abstract

The application discloses a kind of microporous foamed pyrite material and its preparation and application method, belong to environmental protection material and sewage treatment technical field.The application first proposes that carbon dioxide foaming technology under high pressure or even supercritical pressure condition is used for modifying inorganic material foaming process, CO2 fluid is pumped into reaction kettle, and then pressure relief obtains microporous foamed light material, the material has a large number of uniform micron-sized microporous structure, not only can greatly increase the compressive strength of material, porosity and sewage contact area, but also can independently control pH, attach more biomass, to realize stable and rapid denitrification and phosphorus removal capacity.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of microporous materials and sewage treatment, and more particularly relates to a microporous foamed pyrite material and a preparation and application method thereof. BACKGROUND

[0002] In recent years, due to frequent human activities, a large amount of nitrogen and phosphorus nutrients is discharged, causing serious eutrophication of water bodies. In order to control the eutrophication of water bodies, very strict sewage nitrogen and phosphorus discharge standards have been introduced in many places in China. Denitrification, as one of the key processes for removing nitrogen elements in water bodies in sewage treatment, has always been the focus of research on wastewater treatment. Among them, sulfur autotrophic denitrification technology, as a representative autotrophic denitrification technology, has gradually become a low-cost and efficient technology for removing nutrients in water due to its advantages of no need for external organic carbon source, low sludge production, and low treatment cost, and has become a research hotspot in the current denitrification field.

[0003] With the deepening of the research on sulfur autotrophic denitrification technology, some widely distributed but not yet reasonably utilized minerals have also been developed. For example, in recent years, more and more research results have confirmed that autotrophic denitrification using pyrite and pyrrhotite as sulfur source can achieve simultaneous nitrogen and phosphorus removal. For example, the Chinese invention patent application with the patent name of: Method for removing nitrogen and phosphorus by using pyrite as biochemical filler, application number: 201010524339.3, and application date: October 29, 2010 discloses that denitrifying bacteria utilize sulfur in pyrite as energy for autotrophic denitrification to remove nitrate nitrogen, and ferrous ions and iron ions generated during the denitrification process form a precipitate with phosphate ions to achieve the purpose of phosphorus removal. However, the denitrification rate of this technology is slow, and the hydraulic retention time reaches 5 days, and the nitrate nitrogen removal rate can reach more than 90%. For example, the Chinese invention patent application with the patent name of: Natural pyrrhotite biological filter and method for simultaneously removing nitrate nitrogen and phosphorus in water by using the same, application number: 201310695460.6, and application date: December 17, 2013 proposes to construct a biological filter by using natural pyrrhotite, and to use sulfur autotrophic denitrifying bacteria to reduce nitrate in water to nitrogen gas to remove nitrate nitrogen in water by using pyrrhotite as an electron donor; and to remove phosphorus by adsorption, chemical precipitation, etc. through the use of pyrrhotite and its oxidation products, thereby achieving simultaneous nitrogen and phosphorus removal of contaminated water bodies. However, the hydraulic retention time of this technology is 12 hours, and the highest nitrate nitrogen removal rate is 74%. Therefore, it is necessary to develop a technology that can quickly achieve nitrogen and phosphorus removal to meet the engineering requirements of wastewater treatment.

[0004] According to the search, the patent name is: a coupling filler autotrophic denitrification biofilter and application, application number: 201811034113.8, application date: September 5, 2018 Chinese invention patent application puts forward to mix pyrrhotite, sulfur, carbon source particles according to certain proportion, place in the reactor, inoculate the membrane, form autotrophic denitrification biofilter, used for removing nitrogen and phosphorus in sewage. Although this method is low in cost, but due to the simple mixing of granular material, there are defects such as uneven mixing of components, small specific surface area, etc., resulting in low denitrification rate of biological filter and unstable performance. At the same time, the method also has poor adhesion to microorganisms. In view of the above problems, the patent name is: a method for preparing and applying a lightweight material for simultaneous denitrification and phosphorus removal, application number: 201910329881.4, application date: April 23, 2019 Chinese invention patent application mixes sulfur, pyrite and calcium / magnesium carbonate powder, melts under high temperature conditions, and then foams the molten mixture under normal pressure. Then the molten mixture is cooled and shaped to obtain a lightweight material. The product has a lot of pore structure, which is beneficial to the adhesion of denitrifying microorganisms; at the same time, foaming also improves the specific surface area of the filler, which can well improve the denitrification and phosphorus removal capacity. However, since this method only disperses the gas in the material by physical or chemical methods under normal pressure, the solubility of the gas in the filler is low and the distribution is uneven, resulting in uneven pore structure of the material and large pore size (millimeter level) of the foam structure, which affects the performance in all aspects. SUMMARY

[0005] 1. Problems to be solved

[0006] In view of the problems of low denitrification rate, uneven filler components and poor performance stability in existing autotrophic denitrification technology, the present application provides a microporous foamed lightweight pyrite material and a preparation and application method thereof. The present application first proposes to use carbon dioxide foaming technology under high pressure or even supercritical pressure conditions to modify the foaming process of inorganic materials. CO2 fluid is pumped into the reaction kettle, and then the self-nourishing denitrification pyrite lightweight material is obtained by pressure relief. The material has a large number of uniform micron-level micropore structure, which can greatly increase the compressive strength, porosity and contact area with sewage of the material, and can also independently control pH and attach more biomass to improve the removal rate of pollutants.

[0007] 2. Technical scheme

[0008] In order to solve the above problems, the technical scheme adopted by the present application is as follows:

[0009] The application discloses a preparation method of a microporous foamed pyrite material, and belongs to the technical field of the preparation of the microporous foamed pyrite material.

[0010] Preferably, the mass ratio of the pyrite, sulfur and calcium-magnesium carbonate mineral is (1-10):10:(1-5).

[0011] More preferably, the mass ratio of the pyrite, sulfur and calcium-magnesium carbonate mineral is (1-5):10:(1-3).

[0012] Preferably, the particle size of the pyrite and calcium-magnesium carbonate mineral is less than or equal to 0.038 mm.

[0013] Preferably, the mass ratio of the carbon dioxide and sulfur is 0.0029-0.6400.

[0014] More preferably, the mass ratio of the carbon dioxide and sulfur is 0.244-0.640.

[0015] Preferably, the carbon dioxide is dissolved in the molten body under the pressure of 7.5-15 MPa.

[0016] Preferably, the contact time of the carbon dioxide and the molten body is less than 40 min, and the pressure releasing and cooling time is less than 3 min.

[0017] Preferably, the pyrite comprises one or both of pyrite and pyrrhotite; and the calcium-magnesium carbonate mineral comprises one or more of limestone, magnesite, dolomite and shell.

[0018] The application further discloses a microporous foamed pyrite material prepared by the preparation method. 3 The microporous foamed pyrite material has a bubble pore size less than 100 microns, a density of 0.8-2.0 g / cm 2 , a porosity of 10%-60% and a specific surface area of 30-180 cm

[0019] The application further discloses a sewage treatment method using the microporous foamed pyrite material.

[0020] Preferably, the biofilm includes sulfur autotrophic denitrifying bacteria, the sulfur autotrophic denitrifying bacteria include one or both of Thiobacillus denitrificans and Sulfuroximans, and the amount of the sulfur autotrophic denitrifying bacteria attached on the microporous foamed lightweight pyrite material is 2.454*10 7 -4.909*10 7 cfu / mm 3 .

[0021] 3. Beneficial effects

[0022] Compared with the prior art, the beneficial effects of the present application are:

[0023] (1) The preparation method of the microporous foamed lightweight pyrite material of the present application creatively proposes to melt and mix pyrite, sulfur and calcium-magnesium carbonate minerals under high-temperature conditions, and then to foam the mixture in high-pressure or supercritical carbon dioxide fluid to obtain a microporous foamed lightweight pyrite material with a pore size <100 μm, which has small pores, large specific surface area, good microbial adhesion, and high denitrification rate;

[0024] (2) The microporous foamed lightweight pyrite material of the present application has a density of 0.8-2.0 g / cm 3 , a porosity of 10%-60%, and a specific surface area of 30-180 cm 2 / g, and simultaneously has good compression resistance, light weight, self-regulation of water quality pH, high reaction activity, easy microbial adhesion, and slow-release electron donor denitrification, etc., and can be used as a filler for fluidized bed and fixed bed reactors for wastewater treatment.

[0025] (3) The biological filter constructed by using the microporous foamed lightweight pyrite material of the present application has a denitrification volumetric load of 1-3 kg NO3 - -N / (m 3 d), and under the condition of a hydraulic retention time of 0.5 h, the simulated wastewater containing 45.5±0.5 mg / L NO3 - -N and 12.4±0.2 mg / L PO4 3- -P can be treated, and the final effluent NO3 - -N and PO4 3- -P concentrations are 0.18±0.04 mg / L and 0.40±0.10 mg / L, respectively, and the stable and rapid denitrification and phosphorus removal capacity can be achieved. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 FIG. 1 is a schematic structural diagram of an apparatus for preparing the microporous foamed lightweight pyrite material of the present application;

[0027] Figure 2a is a diagram showing the microbial denitrification effect of the microporous foamed lightweight pyrite material prepared in Example 1 of the present invention in a batch reactor; Figure 2 b is a SEM image of microorganisms attached to the surface of the microporous foamed lightweight pyrite material prepared in Example 1 of the present invention;

[0028] In the picture:

[0029] 101. Carbon dioxide storage tank; 102. Plunger pump control panel; 103. Pressure monitoring instrument;

[0030] 104. Plunger pump; 201. High-pressure melting vessel; 202. High-pressure melting vessel rotor;

[0031] 203. High-pressure melting vessel venting valve; 300. Computer control system; 310. Computer data transmission pipeline;

[0032] 410. Carbon dioxide transmission pipeline. Detailed Implementation

[0033] The present invention will be further described below with reference to specific embodiments.

[0034] The following detailed description of exemplary embodiments of the invention is taken with reference to the accompanying drawings. Although these exemplary embodiments have been described in sufficient detail to enable those skilled in the art to practice the invention, it should be understood that other embodiments may be implemented and various changes may be made to the invention without departing from the spirit and scope thereof. The more detailed description of embodiments of the invention below is not intended to limit the scope of the claimed invention, but is merely illustrative and does not limit the description of the features and characteristics of the invention, in order to suggest the best mode for carrying out the invention and sufficient to enable those skilled in the art to practice the invention. Therefore, the scope of the invention is defined only by the appended claims.

[0035] like Figure 1 As shown, the preparation method of a microporous foamed lightweight pyrite material of the present invention includes the following steps: pyrite, sulfur, and calcium magnesium carbonate minerals in a mass ratio of (1-10):10:(1-5), preferably (1-5):10:(1-3), are placed into a high-pressure melting reactor 201. Carbon dioxide fluid is pumped from a carbon dioxide storage tank 101 into the high-pressure melting reactor 201 through a carbon dioxide delivery pipeline 410 at a pressure of 0.5-15 MPa using a plunger pump 104, so that the material inside the reactor is in a high-pressure carbon dioxide or supercritical carbon dioxide fluid atmosphere. A plunger pump control panel 102 is used to adjust and control the plunger pump body, and a pressure monitor 103 is used to monitor the carbon dioxide pressure in the carbon dioxide delivery pipeline 410. Preferably, the pressure in the high-pressure melting reactor 201 is controlled at 7.5-15 MPa, so that the carbon dioxide is in a supercritical state.

[0036] The computer control system 300 controls the high-pressure melting kettle 201 to melt and mix the material in the kettle at a temperature of 115-180°C to obtain a melt, and the mixing time is 10-60 min; and the carbon dioxide is dissolved in the melt by stirring of the high-pressure melting kettle rotor 202. The mass ratio of the amount of the carbon dioxide to the sulfur is 0.0029-0.6400, preferably, the mass ratio of the supercritical state carbon dioxide to the sulfur is 0.244-0.640. The carbon dioxide is contacted with the melt for less than 40 min, and then depressurized via the high-pressure melting kettle gas release valve 203, and cooled and formed to obtain the microcellular foamed lightweight pyrite material. The depressurizing and cooling forming time is less than 3 min. The cell size and number per unit of material are adjusted by controlling the pressure parameters, the contact time, and the depressurizing and cooling time. The modified microcellular foamed material prepared in the embodiment has a controllable density, the density is 0.8-2.0 g / cm 3 , the porosity is 10%-60%, and the specific surface area is 30-180 cm 2 / g.

[0037] It should be noted that no nucleating agent is additionally added in the melt of the present application, and the pyrite and calcium-magnesium carbonate mineral can be used as the nucleating agent, and the particle size d of the pyrite and calcium-magnesium carbonate mineral is ≤0.15 mm, preferably ≤0.038 mm. The pyrite includes one or both of pyrite and pyrrhotite; and the calcium-magnesium carbonate mineral includes one or more of limestone, magnesite, dolomite, and shell. In addition, the cooling and forming of the present application includes wet granulation, steel belt granulation, or post-solidification crushing granulation; wherein the wet granulation is to drop the foamed microcellular melt into water to cool and form the melt mixture in the water; the steel belt granulation is to drop the foamed microcellular melt on a steel belt, and the melt is cooled and formed on the surface of the steel belt by running of the steel belt and contacting with air, so as to realize the granulation and forming; and the post-solidification crushing granulation is to cool and solidify the foamed microcellular melt, and crush the solidified melt into particles. The present application first proposes to use the supercritical carbon dioxide foaming technology in the foaming process of the modified inorganic material. The CO2 fluid is pumped into the reaction kettle under high pressure or even supercritical state, and then the microcellular lightweight product is obtained by depressurization, and the present application provides a new idea for preparing the microcellular material.

[0038] A method for wastewater treatment using a microporous foamed lightweight pyrite material according to the present invention includes filling the prepared microporous foamed material into a reactor after sieving, and inoculating it with anaerobic sludge to treat the wastewater. The specific operation process is as follows: the microporous foamed lightweight pyrite material is placed in a wastewater treatment reactor or constructed wetland, and then microorganisms are inoculated to form a biofilm on the surface of the microporous foamed lightweight pyrite material. Nitrogen in the water is removed through the autotrophic denitrification of the microorganisms. The wastewater treatment reactor includes a fluidized bed or fixed bed reactor; the biofilm contains sulfur-autotrophic denitrifying bacteria, including one or two of *Thiobacillus denitrifyingus* and *Thiobolus sulfadiazine*. The amount of sulfur-autotrophic denitrifying bacteria attached to the microporous foamed lightweight pyrite material is 2.454 × 10⁻⁶. 7 -4.909×10 7 cfu / mm 3 .

[0039] This invention uses calcium magnesium carbonate minerals as the inorganic carbon source and sulfur and pyrite as electron donors to complete the denitrification process, while simultaneously utilizing the Fe released from the pyrite. 2+ The phosphorus is removed by chemical precipitation with phosphate ions. The specific reaction formula is as follows:

[0040] 2FeS2+6NO3 - +4H₂O→4SO₄ 2- +3N2+2H + +2Fe(OH)3

[0041] 10FeS + 18NO3 - +16H2O→10SO4 2- +9N2↑+2H + +10Fe(OH)3

[0042] Fe 3+ +PO4 3- →FePO4↓

[0043] H + +CaCO3→Ca 2+ +HCO3 -

[0044] The microporous foamed material prepared by this invention has the characteristics of small pore size (micrometer level), large specific surface area, good compressive strength, light weight, ability to autonomously regulate water pH, high reactivity, easy microbial attachment, slow-release electron donor denitrification, and effective improvement of carbon source utilization in inorganic minerals. It can be used as packing material for fluidized bed and fixed bed reactors in wastewater treatment. Under the denitrification action of microorganisms, the packing material has a good purification effect on pollutants in water, especially total nitrogen. Furthermore, the preparation method of this invention is simple and low in cost.

[0045] Example 1

[0046] The method for preparing the microcellular foamed pyrite material in this example specifically includes the following steps:

[0047] The pyrrhotite, sulfur and light calcium carbonate are uniformly mixed in a mass ratio of 1:5:1, and then the mixture is subjected to high-temperature melting at a high temperature of 160°C to obtain a molten body. CO2 is introduced into the molten body under a pressure of 0.5 MPa, and the CO2 bubbles are uniformly dispersed and dissolved in the molten body by fully mixing for 20 min. Finally, the target microcellular foamed material is obtained by crushing and granulating after cooling and molding. It is measured that the density of the microcellular foamed material obtained in this example is about 1.9 g / cm 3 , the porosity is 24.8%, and the specific surface area is about 43.2 cm 2 / g.

[0048] After the microcellular foamed material prepared in this example is crushed, 5 cm 3 of the above microcellular foamed material to be used is placed in a batch reaction container, 50 mL of simulated wastewater containing 28 mg / L of NO3 - -N and 12 mg / L of PO4 3- -P is added to the batch reaction container. Then, 3.5 mL of sulfur autotrophic denitrification bacteria liquid (the volume of the bacteria liquid accounts for 7% of the volume of the wastewater) is added to the batch reaction container, the above mixed solution is deoxygenated by nitrogen blowing, and then the denitrification reaction process is carried out in a sealed state. The denitrification reaction is carried out at a constant temperature of 28°C in the dark for 7 days. The adhesion of microorganisms on the surface of the carrier on the 7th day is observed by SEM, and the concentrations of NO3 - -N and PO4 3- -P in the wastewater are detected. The detection results are shown in Figs. Figure 2 a and Figure 2 b.

[0049] Example 2

[0050] The basic content of this example is the same as that of Example 1, except that the method for preparing the microcellular foamed pyrite material in this example specifically includes the following steps:

[0051] The pyrrhotite, sulfur and light calcium carbonate are uniformly mixed in a mass ratio of 3:5:1, and then the mixture is subjected to high-temperature melting at a high temperature of 160°C to obtain a molten body. Supercritical CO2 fluid is introduced into the molten body under a pressure of 7.5 MPa, and the CO2 bubbles are uniformly dispersed and dissolved in the molten body by fully mixing for 30 min. Finally, the target microcellular foamed material is obtained by crushing and granulating after cooling and molding. It is measured that the density of the microcellular foamed material obtained in this example is about 1.6 g / cm 3, porosity is 43.6%, specific surface area is about 90.9cm 2 / g.

[0052] The micro-porous foamed pyrite material of the present example is loaded into a fixed bed reactor, inoculated with anaerobic sludge to carry out denitrification simulation experiment, under the condition of hydraulic retention time 1h, the simulated wastewater containing 45.5±0.5mg / L NO3 - -N, 12.4±0.2mg / L PO4 3- -P, the final effluent NO3 - -N and PO4 3- -P concentrations are 0.15±0.04mg / L and 0.5±0.10mg / L respectively.

[0053] Example 3

[0054] The basic content of the present example is the same as example 1, the difference is that the preparation method of a micro-porous foamed pyrite material of the present example, specifically comprising the following steps:

[0055] The pyrrhotite, sulfur and light calcium carbonate are uniformly mixed according to the mass ratio of 3:5:1, and then the mixture is high-temperature melted at 180℃, to obtain a melt; the supercritical CO2 fluid is introduced into the melt under the condition of 15MPa, and mixed for 40min, so that the CO2 bubbles are uniformly dispersed and dissolved in the melt, and finally cooled and formed, and then broken and granulated to obtain the target micro-porous foaming material. It is measured that the micro-porous foaming material obtained in the present example has a density of about 1.2g / cm 3 , porosity is 60%, specific surface area is about 175cm 2 / g.

[0056] The micro-porous foamed pyrite material of the present example is loaded into a fixed bed reactor, inoculated with anaerobic sludge to carry out denitrification simulation experiment, under the condition of hydraulic retention time 0.5h, the simulated wastewater containing 45.5±0.5mg / L NO3 - -N, 12.4±0.2mg / L PO4 3- -P, the final effluent NO3 - -N and PO4 3- -P concentrations are 0.18±0.04mg / L and 0.40±0.10mg / L respectively.

[0057] Example 4

[0058] The basic content of the present example is the same as example 1, the difference is that the preparation method of a micro-porous foamed pyrite material of the present example, specifically comprising the following steps:

[0059] Pyrrhotite, sulfur and light calcium carbonate are mixed uniformly in a mass ratio of 1:10:5, and then the mixture is high-temperature melted at 180°C to obtain a melt; supercritical CO2 fluid is introduced into the melt at a pressure of 0.5 MPa, and mixed for 30 min to dissolve CO2 in the melt, and finally cooled and shaped, and then broken and granulated to obtain a target microporous foaming material. The microporous foaming material obtained in the embodiment has a density of about 1.7 g / cm 3 , a porosity of 26.5%, and a specific surface area of about 48.5 cm 2 / g.

[0060] The microporous foaming light pyrite material of the embodiment is loaded into a fixed bed reactor, inoculated with anaerobic sludge to perform a denitrification simulation experiment, and under the condition of a hydraulic retention time of 2 h, simulated wastewater containing 30±0.5 mg / L NO3 - -N, 3.1±0.2 mg / L PO4 3- -P is treated, and the final effluent NO3 - -N and PO4 3- -P concentrations are 0.5±0.04 mg / L and 0.5±0.10 mg / L, respectively.

Claims

1. A process for the production of a microcellular foamed lightweight pyrite material, characterized in that: The method comprises the following steps: melting pyrite, sulfur and calcium-magnesium carbonate minerals at 115-180 DEG C to obtain a melt, wherein the mass ratio of the pyrite, sulfur and calcium-magnesium carbonate minerals is (1-10):10:(1-5); then dissolving carbon dioxide in the melt under a pressure of 0.5-15 MPa, wherein the mass ratio of the carbon dioxide and sulfur is 0.0029-0.6400; releasing pressure, cooling and shaping to obtain a microporous foamed light pyrite material; wherein the melt does not need to be added with a nucleating agent, the pyrite and calcium-magnesium carbonate minerals are used as the nucleating agent, the contact time of the carbon dioxide and the melt is less than 40 min, and the time for releasing pressure and cooling is less than 3 min.

2. A process for the production of a microcellular foamed lightweight pyrite material according to claim 1, characterized in that: The particle size of the pyrite and calcium-magnesium carbonate minerals is less than or equal to 0.038 mm.

3. A process for the production of a microcellular foamed lightweight pyrite material according to claim 1, characterized in that: The carbon dioxide is dissolved in the melt under a pressure of 7.5-15 MPa.

4. A process for the production of a microcellular foamed lightweight pyrite material according to any one of claims 1 to 3, characterized in that: The pyrite comprises one or both of pyrite and pyrrhotite; and the calcium-magnesium carbonate minerals comprise one or more of limestone, magnesite, dolomite and shells.

5. A microcellular foamed lightweight pyrite material characterized by: The microporous foamed pyrite material prepared by the method according to any one of claims 1-4, wherein the bubble pore size in the microporous foamed pyrite material is less than 100 μm, the density is 0.8-2.0 g / cm 3 , the porosity is 10%-60%, and the specific surface area is 30-180 cm 2 / g.

6. A method of wastewater treatment using a microcellular foamed lightweight pyrite material according to claim 5, characterized in that: The microporous foamed light pyrite material is placed in a sewage treatment reactor or a constructed wetland, so that the microporous foamed light pyrite material is loaded with a biofilm on the surface, and nitrogen, phosphorus and arsenic, antimony, chromium and cadmium pollutants in water are removed through autotrophic denitrification, chemical precipitation and adsorption of microorganisms.

7. The method of sewage treatment according to claim 6, characterized in that: The biofilm includes sulfur autotrophic denitrifying bacteria, the sulfur autotrophic denitrifying bacteria including one or both of Thiobacillus denitrificans and Sulfuroximans; and the amount of the sulfur autotrophic denitrifying bacteria attached on the microporous foamed lightweight pyrite material is 2.454 x 10 7 -4.909 x 10 7 cfu / mm 3 .

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