Microbial phosphogypsum mineralization method based on electric field induction

Abstract

The invention discloses a microbial ardealite mineralization method based on electric field induction. The method comprises the following steps: S1, mixing a mineralized dry material, a microbial bacterial liquid and a curing agent containing calcium and magnesium ions, and dispersing to prepare ardealite mineralized primary pulp; s2, applying an electric field in the mineralization process of the phosphogypsum mineralization primary pulp, inducing ions to directionally migrate under the action of the electric field, and promoting the sediment to cure harmful substances; an electric field is applied to the microbial phosphogypsum mineralization process to induce directional movement of anions and cations in phosphogypsum mineralization primary pulp, under the tendency of relative movement of the anions and cations, the anions and cations are promoted to be combined to generate hydroxyapatite, struvite and calcium carbonate precipitates, and the purpose of promoting generation of phosphogypsum mineralization products is achieved; when the phosphogypsum slurry is solidified, cations move towards the cathode, and heavy metal ions are mostly high-valence cations, large in radius and prone to being complexed by SO4 < 2-> in the phosphogypsum slurry, so that compared with calcium and magnesium ions, the heavy metal ions move slowly and are easily solidified by precipitates, and the solidification efficiency of the heavy metal cations is improved.

Description

Technical Field

[0001] This invention relates to the field of microbial phosphogypsum mineralization preparation technology, specifically to a microbial phosphogypsum mineralization method based on electric field induction. Background Technology

[0002] Microbial mineralization of phosphogypsum technology mainly utilizes the metabolic activities of specific microorganisms to increase the pH of phosphogypsum and release PO4. 3- Microbial induction of free phosphate and carbonate ions in phosphogypsum leads to the precipitation of minerals such as calcium phosphate and magnesium phosphate. This process induces the formation of inert minerals like hydroxyapatite in phosphogypsum, achieving long-term stabilization of pollutants and recovery of resources such as phosphorus and calcium. Currently, in the preparation of microbial phosphogypsum mineralization, calcium and magnesium salt solutions are added to promote the combination of calcium and magnesium ions, resulting in the production of ammonium ions by urease hydrolysis by microorganisms, generating mineral products such as calcium carbonate, hydroxyapatite, and struvite. However, the mineralization efficiency is low simply by combining microbial solutions with phosphogypsum slurry. Although existing technologies use chemical additives to promote ion combination and precipitate formation, which has a certain effect on the solidification of heavy metal ions, there is an upper limit to the solidification of heavy metal ions in phosphogypsum by precipitates, making it difficult to improve the solidification efficiency of heavy metals. Patent application number CN202310422561 discloses a method for preparing a modified phosphogypsum-microbial cement filler, comprising: 1) preparation of a bio-gelling agent: Bacillus pasteurellii is activated and cultured in a liquid culture medium to obtain a bacterial solution; urea and the bacterial solution are mixed evenly according to a certain ratio to obtain a bio-gelling agent; 2) preparation of a phosphogypsum pretreatment slurry: phosphogypsum and ammonium acetate solution are mixed evenly according to a set ratio and reacted under constant temperature and shaking conditions. After the reaction is completed, a phosphogypsum pretreatment slurry is obtained; 3) preparation of a modified phosphogypsum slurry: the bio-gelling agent in step 1) is mixed evenly with the phosphogypsum pretreatment slurry in step 2), and reacted under constant temperature conditions, with stirring and aeration at set intervals. After the reaction is completed, a modified phosphogypsum slurry is obtained; 4) preparation of a modified phosphogypsum-microbial cement filler: the modified phosphogypsum slurry in step 3) is filled into a test block, and after curing, a modified phosphogypsum-microbial cement filler is obtained. This method also suffers from insufficient absorption of harmful substances by phosphogypsum mineralization. Furthermore, it only enhances mechanical properties by improving phosphogypsum mineralization without considering environmental safety issues and lacks effective means to adsorb and fix harmful substances such as heavy metal ions.

[0003] Therefore, it is necessary to solve the problem of solidification of heavy metal ions in phosphogypsum. Summary of the Invention

[0004] The purpose of this invention is to provide a microbial phosphogypsum mineralization method based on electric field induction, which improves the efficiency of phosphogypsum mineralization in solidifying heavy metal ions.

[0005] The electric field-induced microbial phosphogypsum mineralization method of the present invention includes the following steps:

[0006] S1, prepare phosphogypsum mineralization slurry by mixing and dispersing mineralized dry materials with microbial inoculum and a solidifying agent containing calcium and magnesium ions;

[0007] S2, an electric field is applied during the mineralization process of phosphogypsum mineralization slurry, and the electric field induces the directional migration of ions, promoting the solidification of harmful substances in the precipitate;

[0008] Furthermore, in step S2, the applied electric field strength is 80–200 V / m, and the average current density is 0.04–0.06 mA / cm².

[0009] Furthermore, in step S2, the electric field is applied and maintained for more than 12 hours by means of continuous or intermittent energization. When the electric field is applied intermittently, at least one of the following methods is used: energizing for 15-25 minutes and then cutting off for 8-10 minutes, energizing for 25-35 minutes and then cutting off for 12-15 minutes, or energizing for 35-45 minutes and then cutting off for 15-20 minutes.

[0010] Further, in step S2, after applying an electric field, pH buffer solution is added and the mixture is allowed to stand to obtain mineralized phosphogypsum.

[0011] Furthermore, in step S2, the pH buffer solution is a mixture of urea solution and NaHCO3 solution with a concentration of 20% to 30%, and after adding the pH buffer solution, it is left to stand for more than 6 hours in an environment with a temperature of 28 to 30°C.

[0012] Furthermore, in step S1, the curing agent comprises the following components: a 20-30 mM calcium salt solution, a 6-8 mM magnesium salt solution, and a 1-2 M urea solution;

[0013] Furthermore, in step S1, the calcium salt solution is at least one of calcium chloride, calcium oxide, calcium acetate, and calcium lactate; the magnesium salt solution is at least one of magnesium chloride, magnesium acetate, and magnesium sulfate.

[0014] Further, in step S1, the preparation of the microbial culture includes the following steps: inoculating Bacillus pasteurellii onto a culture medium for activation, and culturing it in a constant temperature shaker at 28℃~30℃ until the OD600 of the Bacillus pasteurellii culture is 1.8~1.9 and the urease activity is 7.6~7.7 mmol / (L∙min), thus obtaining the microbial culture;

[0015] Furthermore, the dispersion treatment step includes: adjusting the pH of the mixture to alkaline, and then performing mechanical stirring dispersion and high-frequency vibration dispersion treatment;

[0016] Furthermore, the mineralized dry material comprises 35-45 parts by weight of phosphogypsum and 2-5 parts of ordinary silicate cement, and the mass ratio of the curing agent, mineralized dry material, and bacterial solution is 1:1.5-2:1-1.5.

[0017] The beneficial effects of this invention are as follows: The electric field-induced microbial phosphogypsum mineralization method of this invention has the following beneficial effects:

[0018] 1. Promote the formation of phosphogypsum mineralization products: By applying an electric field to the microbial phosphogypsum mineralization process, the directional movement of anions and cations in the phosphogypsum mineralization slurry is induced. Under the trend of relative movement of anions and cations, the combination of anions and cations is promoted to form hydroxyapatite, struvite, and calcium carbonate precipitates.

[0019] 2. Improve the solidification efficiency of heavy metal ions: Under the action of an external electric field, cations move towards the cathode. Heavy metal ions are mostly high-valence cations with large radii and are easily affected by SO4 in the phosphogypsum slurry. 2- Because they are complexed, they move more slowly than calcium and magnesium ions and are more easily solidified by precipitates, thus improving the solidification efficiency of heavy metal cations.

[0020] 3. Expand the application range of phosphogypsum preforms. By setting different electrode shapes and positions and different electric field application methods, the electric field strength and current density can be controlled to adapt the applied electric field to different mineralization reaction vessels, thereby improving the production efficiency of phosphogypsum preforms and expanding their application range. Attached Figure Description

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0022] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0023] The electric field-induced microbial phosphogypsum mineralization method of this embodiment includes the following steps:

[0024] S1, prepare phosphogypsum mineralization slurry by mixing and dispersing mineralized dry materials with microbial inoculum and a solidifying agent containing calcium and magnesium ions;

[0025] S2, by applying an electric field during the mineralization process of phosphogypsum slurry, induces the directional migration of ions through the electric field, promoting the solidification of harmful substances in the precipitate. By applying an electric field to the microbial phosphogypsum mineralization process, the directional movement of cations and anions in the phosphogypsum slurry is induced. Under the trend of relative movement of cations and anions, the combination of cations and anions is promoted to form hydroxyapatite, struvite, and calcium carbonate precipitates, thus promoting the formation of phosphogypsum mineralization products. Furthermore, under the action of the applied electric field, cations move towards the cathode. Heavy metal ions are mostly high-valence cations with large radii and are easily affected by SO4 in the phosphogypsum slurry.2- Complexation, therefore, compared to calcium and magnesium ions, they move more slowly and are easily solidified by precipitates, thus improving the solidification efficiency of heavy metal cations. "Cure agent containing calcium and magnesium ions" refers to the curing agent used that contains both calcium and magnesium ions. The curing agent plays a core role in phosphogypsum mineralization, transforming loose, unbinding phosphogypsum particles into a solid material with specific strength and stability through physical filling and chemical reactions. In this embodiment, the role of the microbial inoculum is to induce the conversion of free phosphate and carbonate ions in phosphogypsum into stable mineral precipitates. The mineralization dry material includes phosphogypsum and ordinary silicate cement, with 35-45 parts by weight of phosphogypsum and 2-5 parts by weight of ordinary silicate cement.

[0026] In this embodiment, in step S2, an electric field is arranged on the mineralization reaction vessel to obtain an electric reaction vessel. The electric field arrangement includes:

[0027] A1. Adjust the electrode shape and position, and connect the electrodes in parallel to the DC regulated power supply;

[0028] A2. Inert electrodes are fixed insulated to the mineralization reaction container, and a voltage is applied to the mineralization reaction container so that the electric field strength inside the mineralization reaction container is 80-200V / m.

[0029] The phosphogypsum mineralization slurry is poured into the electrochemical reaction vessel until completely filled, ensuring full contact between the slurry and the electrodes. After settling, air bubbles are eliminated. The mineralization reaction vessel is a semi-enclosed or fully enclosed insulator used to contain the phosphogypsum mineralization slurry for mineralization within a regional electric field. The electric field application method and frequency are adjusted according to the shape of the electrochemical reaction vessel and maintained for at least 12 hours, with an average current density of 0.04–0.06 mA / cm². After the reaction, the electric field is turned off, and 10%–20% (by volume) of the curing agent in a pH buffer solution (1–2 M urea solution and 20%–30% 8–12 mM NaHCO3 solution, preferably 1.5 M urea solution and 10 mM NaHCO3 solution) is added to the electrochemical reaction vessel. The mixture is then allowed to stand at 28–30°C for at least 6 hours to obtain mineralized phosphogypsum. Due to partial electrolysis of water in the slurry under the influence of the electric field, H₂ is released. + and OH — This leads to pH differences within the slurry. After the electric field is stopped, these pH differences are detrimental to the subsequent mineralization of phosphogypsum. Therefore, NaHCO3 solution is used to balance the pH of the slurry.

[0030] The electric field is applied in at least one of the following methods: continuous application and intermittent application. The electric field application frequency is: continuous energization, energization for 15-25 minutes followed by an 8-10 minute interruption, energization for 25-35 minutes followed by a 12-15 minute interruption, or energization for 35-45 minutes followed by a 15-20 minute interruption. When intermittent energization is used, the preferred methods are: energization for 20 minutes followed by an 8-10 minute interruption, energization for 30 minutes followed by a 12-15 minute interruption, or energization for 40 minutes followed by a 15-20 minute interruption. The electrode shape is: rigid electrode, flexible electrode, integral electrode, segmented electrode, matrix electrode, or at least one of the following. The electrode position is: edge position, center position, symmetrical position, or asymmetrical position, or at least one of the following.

[0031] In this embodiment, in step S1, the curing agent includes the following components: a 20-30 mM calcium salt solution, a 6-8 mM magnesium salt solution, and a 1-2 M urea solution; the calcium salt solution is at least one of calcium chloride, calcium oxide, calcium acetate, and calcium lactate; the magnesium salt solution is at least one of magnesium chloride, magnesium acetate, and magnesium sulfate; the preparation of the microbial culture includes the following steps: inoculating Bacillus pasteurellii on a culture medium for activation, and culturing it in a constant temperature shaker at 28℃-30℃ until the OD600 of the Bacillus pasteurellii culture is 1.8-1.9 and the urease activity is 7.6-7.7 mmol / (L∙min), thus obtaining the microbial culture.

[0032] In this embodiment, the dispersion treatment step includes: adjusting the pH of the mixture to alkaline, preferably using NaHCO3 solution, adjusting the pH to 8~9, then continuously stirring at 250~300 rpm for 4~8 min, and then placing it on a vibration table and continuously vibrating at 50 Hz and an amplitude of 2 mm for 1 min.

[0033] In this embodiment, the mineralized dry material comprises 35-45 parts by weight of phosphogypsum and 2-5 parts by weight of ordinary silicate cement, and the mass ratio of the curing agent, mineralized dry material, and bacterial solution is 1:1.5-2:1-1.5.

[0034] Example 1

[0035] Prepare bacterial culture.

[0036] Weigh 1.0 g of tryptone, 0.5 g of yeast powder, 0.5 g of NaCl, 2.0 g of urea, and 100 mL of deionized water. Dissolve by stirring, then adjust the pH to neutral with 0.1 mol / L NaOH. Autoclave the culture medium and cool it for later use. Inject 1 mL of *Bacillus pasteurellii* into the culture medium and incubate at 29±1℃ for 12 h using a shaker at 150 rpm to activate the bacteria. Detect the bacterial concentration and urease activity; if the OD600 of the bacterial solution is 1.8–1.9 and the urease activity is 7.6–7.7 mmol / (L∙min), then proceed with the culture.

[0037] Raw material pretreatment.

[0038] Weigh 3000g of phosphogypsum and place it in a drying oven at 60℃±2℃. Dry for 4 hours, cool to room temperature, and pass through an 80-mesh standard sieve. Weigh 170g of cement for later use. Weigh 19g of calcium chloride, 13g of magnesium chloride, and 770g of urea and place them separately in a drying oven at 60℃±2℃. Dry for 2 hours, cool, and grind until they are in powder form with no obvious lumps. Add 1280g of water to the mixed powder of calcium chloride, magnesium chloride, and urea, and stir until the solids are completely dissolved to prepare the curing agent.

[0039] Mixed dispersion treatment.

[0040] Place phosphogypsum and cement powder in a mixer and stir at 150 rpm for 5 minutes. Mix the bacterial solution and curing agent, then add 10 mM NaHCO3 solution until the liquid pH is 8-9. Mix the solution with the solid powder, stir continuously at 250 rpm for 5 minutes, then place on a vibrating table and vibrate continuously at 50 Hz and 2 mm amplitude for 1 minute to obtain phosphogypsum mineralization slurry.

[0041] Electric field setup.

[0042] Because polytetrafluoroethylene (PTFE) has strong insulation and good biocompatibility, it was chosen as the mineralization reaction vessel to prepare a standard 1500mm×600mm×9.5mm paper-faced gypsum board. The mold was rectangular, with a fixed lower mold and an openable upper mold. Graphite electrodes, measuring 1500mm×600mm×3mm, were used. The anode was fixed to the upper surface of the mold cavity with insulating adhesive, and the cathode was fixed to the lower surface. This is because metal cations move towards the cathode under the influence of the electric field and need to be adsorbed and solidified by the precipitate generated during mineralization. Therefore, to accommodate the location of the mineralization precipitate, the cathode was placed on the lower surface of the mold cavity. In this embodiment, a rigid, integral, symmetrical electrode was used. To adapt to the rectangular shape of the mold, the integral rigid electrode could effectively apply the electric field. The fixing method could be either insulating adhesive or insulating rope, as long as the fixing method met the insulation requirements; no restriction was placed here. A copper terminal was welded to each end of the cathode and anode along their length, with a 10mm insulating sleeve fitted at the base to prevent contact between the terminal and the phosphogypsum mineralization slurry. The wires are connected to the power supply after being connected in parallel with the two terminals of the cathode and the two terminals of the anode. A DC regulated power supply (0-5V / 0-500mA) is selected, with a preset total current of 450mA and a voltage fluctuation stabilized between 0.25 and 0.35V. The preset voltage is 0.5–1V. After the voltage stabilizes, the input voltage is adjusted, and the electric field strength at the four edges and center of the mold is measured to be 80–100V / m, thus completing the electric field setup.

[0043] Apply an electric field.

[0044] Slowly add the phosphogypsum mineralization slurry into the mold, pouring it towards the center and spreading it throughout the entire mold until it is completely filled and the electrode is fully submerged. Let it stand for 5 minutes to allow the slurry to self-level, while observing for any adverse effects on the electrode. Gently vibrate the mold or use a vibrating tool to remove air bubbles from the slurry. The method of removing air bubbles should not affect the activity of microorganisms in the slurry or the normal use of the electrode; the method is not limited here. Removing air bubbles prevents local electric field interruptions caused by bubbles when the electric field is applied. The mold used in this embodiment is rectangular, and the electric field is applied continuously. The mold is sealed with a film and the mold cover is closed to ensure full contact between the anode and the phosphogypsum mineralization slurry. Vibration can be used to remove bubbles during this process. Connect the power supply and apply a constant current of 450mA for 12 hours. Record the voltage and current values ​​every 6 hours, maintaining an average current density within the range of 0.05±0.01mA / cm². During the continuous application of the electric field, maintain the ambient temperature at 29±1℃.

[0045] After turning off the electric field, open the mold cover and add 410g of 1.5M urea solution and 520g of 10mM NaHCO3 solution to the mold in three portions. Due to the electric field, the water in the slurry undergoes partial electrolysis, releasing H2O. + and OH — This leads to a pH difference within the slurry. After the applied electric field is removed, this pH difference is detrimental to subsequent phosphogypsum mineralization. Therefore, NaHCO3 solution is added to balance the slurry pH. Simultaneously, NH3 produced by urease from the earlier microbial hydrolysis... + A large amount of it is consumed in the mineralization reaction, therefore urea is added to provide NH4+. + This provides conditions for subsequent mineralization. Maintaining an ambient temperature of 29±1℃, mineralization was continued for 6 hours before demolding to obtain precast gypsum board. The mineralization reaction products and processes are as follows:

[0046] Urease hydrolysis: CO(NH2) 2+ + 2H2O Enzymatic hydrolysis → 2NH3 + H2CO3

[0047] Hydroxyapatite precipitate: 10Ca²⁺ + 6PO₄ 3- + 2OH⁻ → Ca 10 (PO4)6(OH)2↓

[0048] Struvite precipitate: Mg²⁺ + NH₄⁻ + + PO4 3- → MgNH4PO4↓

[0049] Calcium carbonate precipitation: Ca 2+ + CO3 2- → CaCO3↓

[0050] Example 2

[0051] The preparation methods and concentrations of the bacterial solution, curing agent, and mineralized dry materials are the same as in Example 1. Specifically, the amounts of phosphogypsum are 10.19 kg, ordinary silicate cement 0.6 kg, calcium chloride 66.7 g, magnesium chloride 45 g, urea 2.7 kg, and water 4.48 kg. Polytetrafluoroethylene (PTFE) is used as the mineralization reaction vessel to prepare standard gypsum blocks of 600 mm × 500 mm × 100 mm. The mold is rectangular, with a fixed lower mold and an openable upper mold. Graphite electrodes, 600 mm × 500 mm × 5 mm in size, are used. The anode is fixed to the upper surface of the mold cavity using an insulating limiting block, and the cathode is fixed to the lower surface. Six extension segments extend vertically from the long edge of the cathode in the lower mold, forming six extension sections. These extensions are only applied to the long sides, omitting the short sides to avoid interference with the electric field. Each extension segment is 90 mm long, 50 mm wide, and 5 mm thick. The spacing between each extension segment is 50 mm. The extension segment electrodes are attached to the inner surface of the mold cavity and extend towards the anode. In this embodiment, the electrodes employ a flexible, integral, segmented, asymmetric design. Due to the significant thickness of the precast gypsum blocks involved, using only the top and bottom electrodes might result in a significantly weaker electric field in the middle of the gypsum slurry compared to the edges, thus affecting the induction of ion movement by the electric field in the central region. Therefore, the top and bottom electrodes are combined with additional side extension electrodes to expand the electric field coverage area. The electric field diffuses from the extension electrodes towards the center along the thickness direction, compensating for attenuation. Wires are connected to the anode and cathode electrodes, with the extension electrodes and main electrodes conducting electricity as a single unit, connected in parallel to a DC regulated power supply. Due to the increased electrode spacing, to maintain the electric field strength within the range of 80–200 V / m and the average current density within the range of 0.04–0.06 mA / cm², while also considering the resistance of *Pasteurella multocida* to the electric field, a power supply of 0–30 V / 0–500 mA is selected. The voltage control mode is constant voltage pulse, with a pulse period of 60 min, a frequency of 40 min on and 20 min off, and a preset voltage of 8–12 V. Intermittent electric fields are beneficial for the recovery of Bacillus pasteurellii activity, especially in the mineralization process of large-volume phosphogypsum. Intermittent power supply can also control the H2 and O2 generated by water electrolysis, reducing the impact of bubbles on the uniformity of mineralization. Since the volume of the phosphogypsum preform in this embodiment is large, the electric field is applied for 20 hours to extend the electric field induction time. Other electric field application operations are the same as in Example 1.

[0052] After turning off the electric field, open the mold cover and add 1100g of 1.5M urea solution and 1500g of 10mM NaHCO3 solution to the mold in three portions. Maintain the ambient temperature at 29±1℃ and continue mineralization for 10 hours before demolding to obtain precast gypsum blocks.

[0053] Example 3

[0054] The preparation methods and concentrations of the bacterial solution, curing agent, and mineralized dry materials were the same as in Example 1. The amounts of phosphogypsum were 270g, ordinary silicate cement 15.4g, calcium chloride 1.7g, magnesium chloride 1.2g, urea 69g, and water 115g. Polytetrafluoroethylene (PTFE) was used as the mineralization reaction vessel to prepare phosphogypsum triple-mold (40mm×40mm×160mm) specimens. The mold was a rectangular semi-enclosed triple mold with a fixed lower mold and no upper mold. Graphite electrodes, 50mm×40mm×3mm in size, were used. The electrodes were arranged with two sections on each side of a single mold cavity, fixed to the sides of the cavity with insulating adhesive. The two sections were located in the 0-50mm range (front electrode) and the 110-160mm range (rear electrode), respectively. All mold cavities had two sections on the left side serving as cathodes and two sections on the right side serving as anodes; corresponding sections on both sides were aligned, with the front cathode opposite the front anode and the rear cathode opposite the rear anode. Because the triple-mold plaster mold is a single mold with multiple cavities and a small volume, it is inconvenient to arrange the electrodes on the upper and lower molds in actual operation. Therefore, this embodiment adopts a side electrode arrangement. Since the triple-mold cavities are isolated and insulated, a segmented side electrode arrangement is used. Miniature terminals are installed at the top of the two cathode sections on the left side of the mold cavity, with wires connected in parallel to the cathode terminal; similarly, the two anode sections on the right side are connected in parallel to a single anode terminal; there are a total of three anode terminals and three cathode terminals. The cathode terminals are connected to the negative busbar of the power supply, and the anode terminals are connected to the positive busbar of the power supply. The power supply is a DC regulated power supply of 0~10V / 0~20mA, with a preset voltage of 4~6V. The electric field is applied continuously for 12 hours; other electric field application operations are the same as in Embodiment 1.

[0055] After turning off the electric field, add 50g of 1.5M urea solution and 100g of 10mM NaHCO3 solution to the mold. Maintain the ambient temperature at 29±1℃ and continue mineralization for 6 hours before demolding to obtain precast gypsum blocks.

[0056] Example 4

[0057] The preparation methods and concentrations of the bacterial solution, curing agent, and mineralized dry materials were the same as in Example 1. Specifically, the amounts of phosphogypsum were 2.33 kg, ordinary silicate cement 134 g, calcium chloride 14.8 g, magnesium chloride 10 g, urea 600 g, and water 1 kg. Polytetrafluoroethylene (PTFE) was used as the mineralization reaction vessel to prepare 390 mm × 190 mm × 190 mm hollow blocks with hole dimensions of 150 mm × 130 mm × 190 mm. The mold was a semi-enclosed hollow block mold with a fixed lower mold and no upper mold. Graphite electrodes were used. The cathode dimensions were 390 mm × 190 mm × 8 mm, insulated and fixed to the lower mold; the anode dimensions were 190 mm × 20 mm × 5 mm, insulated and fixed to the inner wall of the core mold. One cathode was arranged on each of the three faces of each core mold closest to the outer mold edge, for a total of six cathodes. Segmented rigid electrodes were used. Terminals were arranged at both ends of the short side of each cathode and connected in parallel to the negative terminal of the power supply. The terminals of the six anodes were connected in parallel to the positive terminal of the power supply. The power supply is a DC regulated power supply of 0~30V / 0~100mA, with a preset voltage of 10~12V. The electric field is applied continuously for 16 hours, and other operations for applying the electric field are the same as in Example 1.

[0058] After turning off the electric field, add 810g of 1.5M urea solution and 1000g of 10mM NaHCO3 solution to the mold. Maintain the ambient temperature at 29±1℃ and continue mineralization for 8 hours before demolding to obtain precast gypsum hollow blocks.

[0059] Example 5

[0060] The preparation methods and concentrations of the bacterial solution, curing agent, and mineralized dry materials were the same as in Example 1. The amounts of phosphogypsum (1.4 kg), ordinary silicate cement (80 g), calcium chloride (8.9 g), magnesium chloride (6 g), urea (360 g), and water (600 g) were used. Polytetrafluoroethylene (PTFE) was selected as the mineralization reaction vessel to prepare L-shaped gypsum products. The long wing measures 300 mm × 100 mm × 80 mm, and the short wing measures 200 mm × 100 mm × 80 mm. The mold was a semi-enclosed hollow block mold with a fixed lower mold and no upper mold. Graphite electrodes were used. The cathodes were insulated and fixed on the inner side of the long wing (280 mm × 70 mm × 5 mm), the short wing (180 mm × 70 mm × 5 mm), and the corner (80 mm × 80 mm × 5 mm). The anode insulation is fixed on the outer side of the L-shaped structure. The anode with an insulation layer on the outer side of the long wing is 300mm × 80mm × 8mm; the anode with an insulation layer on the outer side of the short wing is 280mm × 70mm × 5mm; and the anode with an insulation layer on the outer corner is 100mm × 80mm × 8mm. Segmented flexible electrodes are used to better fit the corners and edges of the irregularly shaped mold. Each of the long wing, short wing, and corner sections of the L-shaped integral anode has a copper terminal, all connected in parallel to the positive terminal of the power supply. Similarly, each of the long wing, short wing, and corner sections of the cathode has a copper terminal, all connected in parallel to the negative terminal of the power supply. The power supply is a DC regulated power supply (0~30V / 0~50mA), with a preset voltage of 8~10V. The electric field is applied continuously for 14 hours; other operations for applying the electric field are the same as in Example 1.

[0061] After turning off the electric field, add 370g of 1.5M urea solution and 500g of 10mM NaHCO3 solution to the mold. Maintain the ambient temperature at 29±1℃ and continue mineralization for 7 hours before demolding to obtain the precast L-shaped gypsum product.

[0062] Comparative Example 1

[0063] The preparation process and materials for the bacterial solution were the same as in Example 1. The phosphogypsum mineralization slurry was poured into the same mold, and the mold was placed on a vibrating table at a frequency of 50 Hz and an amplitude of 2 mm for 3 minutes to expel air. Excess slurry on the mold surface was scraped off with a scraper to keep the slurry surface smooth. The mold was cured at the same ambient temperature for 12 hours, with the slurry stirred every 4 hours to prevent solid sedimentation from affecting the contact between microorganisms and the slurry, thus reducing mineralization efficiency. The mold surface was covered with sterile plastic wrap, and the mold was allowed to cure under the same conditions for 6 hours before demolding to form a gypsum precast slab.

[0064] Comparative Example 2

[0065] The preparation process and materials for the bacterial solution were the same as in Example 2. The phosphogypsum mineralization slurry was poured into the same mold, and the mold was placed on a vibrating table at a frequency of 50 Hz and an amplitude of 2 mm for 3 minutes to expel air. Excess slurry on the mold surface was scraped off with a scraper to keep the slurry surface smooth. The mold was cured at the same ambient temperature for 20 hours, during which the slurry was stirred with a scraper every 4 hours to prevent solid sedimentation from affecting the contact between microorganisms and the slurry, thus reducing mineralization efficiency. The mold surface was covered with sterile plastic wrap, and the mold was allowed to cure under the same conditions for 10 hours before demolding to form gypsum precast blocks.

[0066] Comparative Example 3

[0067] The comparative example uses the same bacterial solution preparation process as Example 3, the same phosphogypsum mineralization slurry material as Example 3, the same molds, and the same curing conditions. The only difference is whether an electric field is applied and the related operations for the electric field arrangement.

[0068] Comparative Example 4

[0069] The comparative example uses the same bacterial solution preparation process as Example 4, the same phosphogypsum mineralization slurry material as Example 4, the same molds, and the same curing conditions. The only difference is whether an electric field is applied and the related operations for the electric field arrangement.

[0070] Comparative Example 5

[0071] The comparative example uses the same bacterial solution preparation process as Example 5, the same phosphogypsum mineralization slurry material as Example 5, the same molds, and the same curing conditions. The only difference is whether an electric field is applied and the related operations for electric field arrangement.

[0072] Mechanical strength tests were conducted on Examples 1-2 and Comparative Examples 1-2, and the experimental data are shown in Tables 1 and 2:

[0073]

[0074]

[0075] The content of heavy metal ions and toxic and harmful substances in the slurry effluent of Examples 1-5 was tested. The test results were compared with Class III of "DZ / T 0290-2015 Groundwater Quality Standard" and "HJ / T 207-2005 Technical Requirements for Environmental Labeling Products for Building Blocks". The results are shown in Tables 3 and 4.

[0076]

[0077]

[0078] Example 1 and Comparative Example 1 were manufactured according to the standard dimensions specified in GB / T 9775-2025 Paper-faced Gypsum Board. As shown in Table 1, the performance parameters of Example 1 meet the specified limits and can be used as paper-faced gypsum board. Example 2 and Comparative Example 2 were manufactured according to the standard dimensions specified in JCT 698-2010 Gypsum Blocks. As shown in Table 2, the performance parameters of Example 2 meet the specified limits and can be used as gypsum blocks. The heavy metal leachate concentration tests of Examples 1-5 and Comparative Examples 1-5 are shown in Table 3. The heavy metal concentrations all meet the Class III wastewater discharge standard of DZ / T 0290-2015 Groundwater Quality Standard. In the examples, the concentrations of zinc, lead, chromium, nickel, and cobalt were significantly reduced compared to the comparative examples, indicating that the examples effectively solidified some heavy metal ions through electric field induction, achieving good results. The concentration tests of hazardous substance leachate from Examples 1-5 and Comparative Examples 1-5 are shown in Table 4. The contents of the main hazardous substances P, F, and As in phosphogypsum are all lower than the relevant standard limits. The fluoride content meets the requirements of the "HJ / T 207-2005 Environmental Labeling Product Technical Requirements for Building Blocks" standard; the arsenic content meets the Class III standard requirements of the "DZ / T 0290-2015 Groundwater Quality Standard"; and according to the "GB 18599-2020 Standard for Pollution Control of General Industrial Solid Waste Storage and Landfill", the phosphorus content in Examples 1-5 meets the requirements of Class II general industrial solid waste. As shown in Table 4, compared with the comparative examples, the contents of the three hazardous substances in Examples 1-5 are all reduced, with fluoride and phosphorus contents showing a more significant decrease. This indicates that the electric field-induced mineralization of phosphogypsum in the examples has a good effect on the solidification of hazardous substances.

[0079] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for microbial phosphogypsum mineralization based on electric field induction, characterized in that: Includes the following steps: S1, prepare phosphogypsum mineralization slurry by mixing and dispersing mineralized dry materials with microbial inoculum and a solidifying agent containing calcium and magnesium ions; S2 involves applying an electric field during the mineralization process of phosphogypsum slurry. This electric field induces directional migration of ions, promoting the solidification of harmful substances in the precipitate.

2. The method for microbial phosphogypsum mineralization based on electric field induction according to claim 1, characterized in that: In step S2, the applied electric field strength is 80–200 V / m, and the average current density is 0.04–0.06 mA / cm².

3. The method for microbial phosphogypsum mineralization based on electric field induction according to claim 1, characterized in that: In step S2, the electric field is applied and maintained for more than 12 hours by means of continuous or intermittent energization. When the electric field is applied intermittently, at least one of the following methods is used: energizing for 15-25 minutes and then cutting off for 8-10 minutes, energizing for 25-35 minutes and then cutting off for 12-15 minutes, or energizing for 35-45 minutes and then cutting off for 15-20 minutes.

4. The method for microbial phosphogypsum mineralization based on electric field induction according to claim 1, characterized in that: In step S2, after applying an electric field, pH buffer solution is added and the mixture is allowed to stand to obtain mineralized phosphogypsum.

5. The method for microbial phosphogypsum mineralization based on electric field induction according to claim 4, characterized in that: In step S2, the pH buffer solution is a mixture of urea solution and NaHCO3 solution with a concentration of 20% to 30%. After adding the pH buffer solution, it is left to stand for more than 6 hours in an environment with a temperature of 28 to 30°C.

6. The method for microbial phosphogypsum mineralization based on electric field induction according to claim 1, characterized in that: In step S1, the curing agent comprises the following components: a 20-30 mM calcium salt solution, a 6-8 mM magnesium salt solution, and a 1-2 M urea solution.

7. The method for microbial phosphogypsum mineralization based on electric field induction according to claim 6, characterized in that: In step S1, the calcium salt solution is at least one of calcium chloride, calcium oxide, calcium acetate, and calcium lactate; the magnesium salt solution is at least one of magnesium chloride, magnesium acetate, and magnesium sulfate.

8. The method for microbial phosphogypsum mineralization based on electric field induction according to claim 1, characterized in that: In step S1, the preparation of the microbial culture includes the following steps: inoculating Bacillus pasteurellii onto a culture medium for activation, and culturing it in a constant temperature shaker at 28℃~30℃ until the OD600 of the Bacillus pasteurellii culture is 1.8~1.9 and the urease activity is 7.6~7.7mmol / (L∙min), thus obtaining the microbial culture.

9. The method for microbial phosphogypsum mineralization based on electric field induction according to claim 1, characterized in that: The dispersion treatment steps include: adjusting the pH of the mixture to alkaline, and then performing mechanical stirring dispersion and high-frequency vibration dispersion treatment.

10. The method for microbial phosphogypsum mineralization based on electric field induction according to claim 1, characterized in that: The mineralized dry material comprises 35-45 parts by weight of phosphogypsum and 2-5 parts by weight of ordinary silicate cement, and the mass ratio of the curing agent, mineralized dry material and bacterial solution is 1:1.5-2:1-1.5.

Images