Titanium gypsum roadbed filler based on biomineralization stability and preparation method of titanium gypsum roadbed filler

Abstract

The invention provides a titanium gypsum roadbed filler based on biomineralization stabilization and a preparation method and application thereof. The titanium gypsum composite roadbed material provided by the invention is prepared from the following raw materials: titanium gypsum, natural plain soil, a bacillus pasteurii bacterial solution, urea, a calcium source and xanthan gum. Through the synergistic effect of the titanium gypsum, the plain soil, the microbial agent, the urea, the calcium source and the xanthan gum, a mineralized cementation network is formed by inducing carbonate precipitation (MICP) through microorganisms, the mechanical property and stability of the filler are remarkably improved, resource utilization of solid waste titanium gypsum can be achieved, and good economic benefits and social benefits are achieved.

Description

Technical Field

[0001] The present invention relates to the intersecting field of civil engineering and biomaterials, and in particular to a titanium gypsum roadbed filler based on biomineralization stabilization, and a preparation method and application thereof. Background Art

[0002] Titanium gypsum is an industrial waste residue generated by the sulfuric acid process during the titanium dioxide production process at Jiangsu Taibai Group Co., Ltd. Its primary component is calcium sulfate dihydrate (CaSO4·2H2O), along with trace amounts of unreacted ilmenite, free acid (H2SO4, pH 2-4), and heavy metal impurities (such as Fe and Mn). Statistics show that every ton of titanium dioxide produced generates approximately 4-6 tons of titanium gypsum. my country's annual emissions exceed 30 million tons, with a cumulative stockpile exceeding 300 million tons and a comprehensive utilization rate of less than 20%. The open-air storage of large quantities of titanium gypsum not only encroaches on land resources (each 10,000 tons of storage takes up approximately 1.5 mu), but its acidic leachate also causes soil acidification, groundwater contamination, and heavy metal migration, posing significant environmental risks. Existing attempts to use titanium gypsum as roadbed filler have mostly relied on physical or chemical curing (such as cement or lime modification), but these methods present challenges such as high cost, high carbon emissions, and susceptibility to cracking.

[0003] In recent years, microbial induced carbonate precipitation (MICP) technology has been used as a biomimetic mineralization method for soil reinforcement due to its low carbon characteristics. Its core is to use microbial metabolic activities to drive inorganic mineral deposition to form "biocement" to cement loose media. For example, urea is decomposed by urea hydrolyzing bacteria (Bacillus pasteurianus) to generate CO32-, which reacts with Ca 2 + combines to form a calcium carbonate cementing network. Compared with traditional chemical curing technology, MICP has significant advantages in sustainability, environmental compatibility and micro-control. The MICP process does not require high-temperature sintering throughout the process, and the carbon emissions per cubic meter of material solidification are only 15-30kg CO2eq, which is less than 20% of cement solidification (150-200kg CO2eq) and lower than 40% of lime solidification (80-100kg CO2eq); and by controlling environmental parameters, different calcium carbonate crystal forms can be induced to increase the proportion of calcite to >80%, significantly enhancing long-term durability; at the same time, the generated calcium carbonate lattice can seal heavy metal ions (such as Pb 2 +、Cd 2+), forming stable carbonates or co-precipitates (such as PbCO3, Ksp = 7.4×10-14), and reducing leaching toxicity by more than 90% (GB 5085.3-2007). However, the application of this technology in titanium gypsum systems faces multiple bottlenecks. Due to the small particles of titanium gypsum (D50 ≤ 50μm) and poor pore connectivity, it is difficult for the bacterial solution to spread evenly, forming local "island-type" cementation; in particular, the calcium carbonate generated by conventional MICP is mainly vaterite with poor mechanical properties, which is easy to pulverize under dynamic load, and the cementation strength decay rate exceeds 40% after immersion in water.

[0004] In summary, it is difficult for existing technologies to take into account the mechanical properties, environmental compatibility and economy of titanium gypsum roadbed fillers. It is urgent to innovate a biomineralization-chemical regulation synergistic stabilization method to break through key bottlenecks such as mineralization inhibition and uneven cementation, and promote the large-scale and high-value utilization of titanium gypsum in road engineering. Summary of the Invention

[0005] Purpose of the invention: The purpose of the present invention is to provide an environmentally friendly, low-cost, highly stable titanium gypsum roadbed filler based on biomineralization stabilization, and to significantly improve the resource utilization rate of titanium gypsum by optimizing the synergistic ratio of titanium gypsum, plain soil and biomineralization components; another purpose of the present invention is to provide a preparation method of titanium gypsum roadbed filler based on biomineralization stabilization.

[0006] Technical solution: The titanium gypsum roadbed filler based on biomineralization stabilization of the present invention is composed of the following components in parts by mass: 40-60 parts of titanium gypsum, 20-50 parts of plain soil, 20-40 parts of microbial bacterial liquid, 1-3 parts of urea, 1-3 parts of calcium source, and 0.5-2 parts of xanthan gum.

[0007] Preferably, the microbial liquid is Bacillus pasteurianus liquid.

[0008] Preferably, the calcium source is calcium chloride, calcium nitrate or a mixture thereof.

[0009] Preferably, the titanium gypsum is crushed titanium gypsum.

[0010] On the other hand, the present invention provides a method for preparing the above-mentioned biomineralized stabilized titanium gypsum roadbed filler, comprising the following steps:

[0011] (1) drying titanium gypsum and plain soil separately, dry-mixing titanium gypsum, plain soil, urea, calcium source and xanthan gum according to a proportion to obtain a dry material;

[0012] (2) inoculating the microbial agent into the liquid culture medium to obtain a bacterial solution;

[0013] (3) Add the bacterial solution to the dry material and stir until a uniform slurry is formed;

[0014] (4) After solidification and curing, the slurry forms a mineralized cemented structure.

[0015] Furthermore, in step (1), the titanium gypsum is crushed to a particle size of ≤2 mm, the base soil is sieved to remove impurities, and then the titanium gypsum, base soil, urea, calcium source and xanthan gum are dry-mixed uniformly according to the ratio.

[0016] Furthermore, in step (2), the liquid culture medium contains 0.5-1.5 mol / L urea and has a pH of 7-8.

[0017] Furthermore, in step (2), the microbial agent is inoculated into the liquid culture medium and cultured at 25-30°C until the OD 600 =1.2~1.5, and obtain bacterial solution.

[0018] Furthermore, in step (3), the mass ratio of bacterial liquid to dry material is 1:2.5 to 1:3.5.

[0019] Furthermore, in step (4), the curing and curing conditions are: curing at 25-35° C. and humidity ≥80% for 3-7 days.

[0020] As a preferred embodiment, a method for preparing a titanium gypsum roadbed filler is provided, comprising the following steps:

[0021] (1) Dry the titanium gypsum and the soil separately, crush the titanium gypsum to a particle size of ≤2 mm, sieve the soil through a 2 mm sieve to remove impurities, and then dry-mix the titanium gypsum, soil, urea, calcium source, and xanthan gum according to the proportion;

[0022] (2) Inoculate the microbial agent into liquid culture medium (containing 0.5-1.5 mol / L urea, pH = 7-8) and culture at 25-30°C until OD 600 =1.2~1.5;

[0023] (3) Add the bacterial solution to the dry material and stir until a uniform slurry is formed;

[0024] (4) Allow to stand and solidify for 3 to 7 days at 25 to 35°C and humidity ≥80% to form a mineralized cementation structure.

[0025] Principle of the invention:

[0026] The principle of this invention is based on the synergistic effect of biomineralization technology and a titanium gypsum-plain soil composite system. The calcium carbonate produced by microbial metabolism binds the titanium gypsum and soil particles to form a stable, high-strength roadbed material. In the composite matrix of titanium gypsum and plain soil, titanium gypsum serves as the main aggregate, providing a calcium sulfate matrix and a microporous structure, but its own mechanical properties are weak and it is easily soluble in water. The plain soil (clay or sand) serves as a filler material. When mixed with titanium gypsum, it optimizes particle grading, improves density, and provides an attachment interface for microorganisms.

[0027] Calcium ions (Ca 2+ ) participate in the subsequent biomineralization reaction together with clay minerals of the soil (such as aluminosilicates) to form a composite cementation network.

[0028] At the same time, Bacillus pasteurianus metabolizes urea (CO(NH2)2) to produce urease, which catalyzes the urea hydrolysis reaction. The calcium source (such as CaCl2) dissolves and releases Ca 2+ , combined with CO32- produced by microbial metabolism to form calcium carbonate crystals (CaCO3). Calcium carbonate crystals are deposited on the surface and pores of titanium gypsum particles in the form of calcite or aragonite, forming a three-dimensional cementing structure. The cementing effect significantly improves the compressive strength and water stability of the material, while reducing the risk of dissolution of titanium gypsum. Xanthan gum, as a thickener and binder, enhances the adhesion of microorganisms to the titanium gypsum-soil surface, promotes local mineralization, and inhibits drying shrinkage, synergistically resisting cracking with CaCO3 cementation.

[0029] Beneficial Effects: Compared with existing technologies, this invention has the following significant advantages: (1) Titanium gypsum is used as industrial waste to replace natural aggregate, reducing the environmental burden. (2) The biomineralization process only requires room temperature conditions, without the need for high-temperature calcination (traditional cement curing requires above 1200°C). (3) Residual microorganisms can restart mineralization when exposed to water at a later stage, repairing microcracks. (4) The raw material cost is lower than that of the cement / lime curing method, and the process is simple. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Preparation process flow chart;

[0031] Figure 2 Comparison of unconfined strength under different formulations;

[0032] Figure 3 Comparison chart of water stability coefficients under different formulations;

[0033] Figure 4 Finished product image and microstructure SEM of Example 1. DETAILED DESCRIPTION

[0034] The technical solution of the present invention is further described below with reference to the examples. The test materials used in the examples can all be purchased through conventional channels.

[0035] The titanium gypsum in the embodiment of the present invention comes from the industrial waste generated by Jiangsu Taibai Group Co., Ltd., and the Bacillus pasteurianus liquid is purchased from Beijing Baozang Biotechnology Co., Ltd., with the collection center number: DSM33=ATCC11859.

[0036] Example 1

[0037] Raw material ratio: 40 parts of titanium gypsum, 20 parts of plain soil, 1 part of urea, 1 part of calcium chloride, 1 part of xanthan gum, 40 parts of microbial liquid;

[0038] Preparation steps:

[0039] (1) Dry the titanium gypsum and the soil separately, crush the titanium gypsum to a particle size of ≤2 mm, sieve the soil through a 2 mm sieve to remove impurities, and then dry-mix the titanium gypsum, soil, urea, calcium source, and xanthan gum according to the proportion;

[0040] (2) Bacillus pasteurianus liquid (OD 600 =1.3) Spray evenly into the dry material and stir into a slurry;

[0041] (3) Fill into the mold and cure at 30°C and 85% humidity for 5 days;

[0042] (4) Performance test: unconfined compressive strength 1.02MPa, water stability coefficient 0.76.

[0043] Example 2

[0044] Raw material ratio: 60 parts of titanium gypsum, 20 parts of plain soil, 1 part of urea, 1 part of calcium chloride, 0.5 parts of xanthan gum, and 40 parts of microbial agent;

[0045] Preparation steps:

[0046] (1) Dry the titanium gypsum and the soil separately, crush the titanium gypsum to a particle size of ≤2 mm, sieve the soil through a 2 mm sieve to remove impurities, and then dry-mix the titanium gypsum, soil, urea, calcium source, and xanthan gum according to the proportion;

[0047] (2) Bacillus pasteurianus liquid (OD 600 =1.3) Spray evenly into the dry material and stir into a slurry;

[0048] (3) Fill into the mold and cure at 30°C and 85% humidity for 5 days;

[0049] (4) Performance test: unconfined compressive strength 0.86MPa, water stability coefficient 0.7.

[0050] Example 3

[0051] Raw material ratio: 50 parts of titanium gypsum, 50 parts of plain soil, 3 parts of urea, 3 parts of calcium chloride, 2 parts of xanthan gum, and 20 parts of microbial agent;

[0052] Preparation steps:

[0053] (1) Dry the titanium gypsum and the soil separately, crush the titanium gypsum to a particle size of ≤2 mm, sieve the soil through a 2 mm sieve to remove impurities, and then dry-mix the titanium gypsum, soil, urea, calcium source, and xanthan gum according to the proportion;

[0054] (2) Bacillus pasteurianus liquid (OD 600 =1.3) Spray evenly into the dry material and stir into a slurry;

[0055] (3) Fill into the mold and cure at 30°C and 85% humidity for 5 days;

[0056] (4) Performance test: unconfined compressive strength 1.47 MPa, water stability coefficient 0.81.

[0057] Comparative Example 1

[0058] Raw material ratio: 40 parts of titanium gypsum and 20 parts of clay;

[0059] Preparation steps:

[0060] (1) Dry the titanium gypsum and the clay separately, crush the titanium gypsum to a particle size of ≤2 mm, sieve the clay through a 2 mm sieve to remove impurities, and then mix the titanium gypsum and the clay evenly according to the ratio;

[0061] (2) Spray water into the dry material and stir to form a slurry;

[0062] (3) Fill into the mold and cure at 30°C and 85% humidity for 5 days;

[0063] (4) Performance test: unconfined compressive strength 0.49 MPa, water stability coefficient 0.3.

[0064] Comparative Example 2

[0065] Raw material ratio: 40 parts of titanium gypsum, 1 part of urea, 1 part of calcium chloride, 1 part of xanthan gum, and 40 parts of microbial agent;

[0066] Preparation steps:

[0067] (1) drying the titanium gypsum and crushing it to a particle size of ≤2 mm, and dry-mixing the titanium gypsum, urea, calcium source and xanthan gum according to the ratio;

[0068] (2) Bacillus pasteurianus liquid (OD 600 =1.3) Spray evenly into the dry material and stir into a slurry;

[0069] (3) Fill into the mold and cure at 30°C and 85% humidity for 5 days;

[0070] (4) Performance test: unconfined compressive strength 0.46 MPa, water stability coefficient 0.59.

[0071] Comparative Example 3

[0072] Raw material ratio: 20 parts of soil, 1 part of urea, 1 part of calcium chloride, 1 part of xanthan gum, 40 parts of microbial agent;

[0073] Preparation steps:

[0074] (1) Dry the soil in the sun and pass it through a 2mm sieve to remove impurities;

[0075] (2) Bacillus pasteurianus liquid (OD 600 =1.3) Spray evenly into the dry material and stir into a slurry;

[0076] (3) Fill into the mold and cure at 30°C and 85% humidity for 5 days;

[0077] (4) Performance test: unconfined compressive strength 0.52 MPa, water stability coefficient 0.61.

[0078] Through the synergistic effect of biomineralization and chemical regulation, the present invention has successfully developed a high-strength, water-stable and environmentally friendly titanium gypsum roadbed filler, which has significant technical advantages and comprehensive benefits. In terms of mechanical properties, the 7-day unconfined compressive strength reaches 0.5-1.5 MPa, which is 100-200% higher than that of pure titanium gypsum (0.38 MPa); at the same time, the water stability is significantly enhanced, and the strength retention rate is ≥70% after immersion in water for 7 days, and there are no structural cracks after dry-wet cycles; the generated calcium carbonate is mainly calcite, forming a dense layered network, and the porosity is reduced from 28% to 12%, effectively blocking the water penetration path.

[0079] In terms of high-value solid waste utilization, the titanium gypsum content reaches 50-70%. A single 100,000-ton annual titanium dioxide production line can consume 60,000-80,000 tons of titanium gypsum, reducing storage space by approximately 10 mu (approximately 16 acres) per year. Furthermore, the process eliminates high-temperature sintering, reducing overall costs by 30-50% compared to cement modification. This translates to a material savings of 120-200 yuan per cubic meter of filler. Heavy metal solidification efficiency is improved, with lead and cadmium leaching concentrations below 0.05mg / L and 0.01mg / L, respectively, meeting the Surface Water Environmental Quality Standards.

[0080] This invention takes biomineralization as its core and solves the industry problems of insufficient mechanical properties of titanium gypsum roadbed fillers, poor water stability, and high carbon and high cost of traditional modification technologies through multi-component collaborative design, process parameter optimization and environmental risk control, providing innovative solutions for the resource utilization of industrial solid waste and the construction of green infrastructure.

Claims

1. A titanium gypsum roadbed filler based on biomineralization stabilization, characterized in that: The invention is composed of the following components in parts by mass: 40-60 parts of titanium gypsum, 20-50 parts of plain soil, 20-40 parts of microbial liquid, 1-3 parts of urea, 1-3 parts of calcium source and 0.5-2 parts of xanthan gum.

2. The titanium gypsum roadbed filler based on biomineralization stabilization according to claim 1, characterized in that: The microbial liquid is Bacillus pasteurianus liquid.

3. The titanium gypsum roadbed filler based on biomineralization stabilization according to claim 1, characterized in that: The calcium source is calcium chloride, calcium nitrate or a mixture thereof.

4. The titanium gypsum roadbed filler based on biomineralization stabilization according to claim 1, characterized in that: The titanium gypsum is titanium gypsum that has been crushed.

5. A method for preparing the biomineralized and stabilized titanium gypsum roadbed filler according to any one of claims 1 to 4, characterized in that: The following steps are involved: (1) drying titanium gypsum and plain soil separately, dry-mixing titanium gypsum, plain soil, urea, calcium source and xanthan gum according to a proportion to obtain a dry material; (2) inoculating the microbial agent into the liquid culture medium to obtain a bacterial solution; (3) Add the bacterial solution to the dry material and stir until a uniform slurry is formed; (4) After solidification and curing, the slurry forms a mineralized cemented structure.

6. The method for preparing the biomineralized stabilized titanium gypsum roadbed filler according to claim 5, characterized in that: In step (1), the titanium gypsum is crushed to a particle size of ≤2 mm, the base soil is sieved to remove impurities, and then the titanium gypsum, base soil, urea, calcium source and xanthan gum are dry-mixed uniformly according to the ratio.

7. The method for preparing the biomineralized stabilized titanium gypsum roadbed filler according to claim 5, characterized in that: In step (2), the liquid culture medium contains 0.5-1.5 mol / L urea and has a pH of 7-8.

8. The method for preparing the biomineralized stabilized titanium gypsum roadbed filler according to claim 5, characterized in that: In step (2), the microbial agent is inoculated into the liquid culture medium and cultured at 25-30°C until the OD 600 =1.2~1.5, and obtain bacterial solution.

9. The method for preparing the biomineralized stabilized titanium gypsum roadbed filler according to claim 5, characterized in that: In step (3), the mass ratio of bacterial liquid to dry material is 1:2.5 to 1:3.

5.

10. The method for preparing the biomineralized and stabilized titanium gypsum roadbed filler according to claim 5, characterized in that: In step (4), the curing and curing conditions are: standing and curing for 3 to 7 days at 25 to 35° C. and humidity ≥ 80%.

Images