A biological cementation filling method and system for tailings sand based on urease from bacteria sources

Abstract

The present invention discloses a method and system for bio-cementing filling of tailings sand based on bacterial urease. Active, highly fluid, and bio-safety-risk-free bacterial urease is extracted from urease-producing microorganisms, and this urease is used to cement the tailings sand filled in the goaf, which can improve the strength of the goaf filling body. At the same time, to improve the utilization and cementing efficiency of the tailings sand, the tailings sand is screened according to different particle size ranges, and the mixing method and the permeation grouting method are respectively used for filling. The treatment liquid prepared based on bacterial urease has advantages such as good fluidity, high bio-safety level, and environmental friendliness, solving the problem of weak stability that it is difficult or even impossible to repair after the filling body mainly made of cement cracks. At the same time, the solution provided by the present invention can play an excellent role in both anaerobic and aerobic goaf environments, and can also reduce the energy supply and environmental pollution pressure of cement production by reducing the amount of cement used or replacing cement.

Description

Technical Field

[0001] The present invention relates to the technical field of goaf filling, and particularly to a biological cementation filling method and system for tailings sand based on bacterial urease. Background Art

[0002] A large amount of tailings are generated during the mining, beneficiation, and smelting processes of mineral resources. Stacking them in tailings ponds not only occupies a large amount of land, but also may induce disasters such as landslides and debris flows due to the collapse of tailings ponds, posing a serious threat to people's lives and property safety. For tailings containing heavy metals, their random stacking may also pollute the surrounding soil, surface water, and groundwater, affecting the ecological environment. In response to the above problems, various tailings resource utilization schemes have been proposed at home and abroad. For example, tailings sand is used as a filling material for goafs in underground mining of mines. The existing tailings filling technology for goafs is to mix tailings sand with a certain proportion of cement and water evenly to form a filling slurry for filling the goaf. Obviously, cement is the main cementing material in the existing tailings filling technology for goafs. However, this technology mainly has the following defects: (1) Cement production consumes a large amount of energy resources and emits a large amount of air pollutants such as dust, sulfur dioxide, nitrogen oxides, etc. into the atmosphere, as well as carbon dioxide gas that causes the "greenhouse effect"; (2) The filling body mainly composed of cement is prone to cracking under the influence of factors such as temperature and blasting vibration after consolidation, and it is difficult to repair in-situ with cement slurry, resulting in a decrease in the stability of the goaf after filling; (3) The fluidity of the cement-based filling slurry is poor, and it is not easy to enter the small gaps in the goaf or is prone to form cavities in the filling body, thereby affecting the strength of the goaf filling body. Summary of the Invention

[0003] Therefore, it is necessary to provide a biological cementation filling method and system for tailings sand based on bacterial urease to solve the problems of environmental pollution, high energy consumption, low compressive strength of the filling body, and easy cracking caused by the filling method using cement as the main cementing material in the existing technology.

[0004] To achieve the above object, the present invention provides a biological cementation filling method for tailings sand based on bacterial urease, including the following steps:

[0005] Extraction of bacterial urease: First, subject the cultured urease-producing bacteria liquid to low-temperature ultrasonic crushing, and then perform low-temperature high-speed centrifugation extraction to obtain bacterial urease liquid;

[0006] Preparation of cementing liquid: Mix calcium chloride and urea with the same molar mass with a certain volume of water and stir to obtain a cementing liquid;

[0007] Preparation of treatment liquid: First, adjust the pH value of the bacterial urease liquid to weakly acidic, and then mix it with a certain volume of the cementing liquid to obtain a treatment liquid;

[0008] Tailings sand classification, screening the tailings sand into first tailings sand, second tailings sand and third tailings sand. The particle size of the first tailings sand is greater than 1.18 mm, the particle size of the second tailings sand is greater than 0.425 mm and less than or equal to 1.18 mm, and the particle size of the third tailings sand is less than or equal to 0.425 mm;

[0009] Goaf filling, including deep goaf filling and near-surface goaf filling. The deep goaf filling adopts the one-phase permeation grouting method. First, mix the first tailings sand and the second tailings sand to form aggregate and fill it into the deep goaf, and then inject the treatment liquid into the filled deep goaf by the one-phase permeation grouting method at preset time intervals; The near-surface goaf filling adopts a method combining mixing filling and two-phase permeation grouting. First, mix the third tailings sand, the cementing liquid and the bacterial urease to obtain a filling slurry, and fill the filling slurry into the goaf for mixing filling, and then inject the bacterial urease liquid and the cementing liquid into the near-surface goaf filled with the filling slurry respectively and successively by the two-phase permeation grouting method at preset time intervals.

[0010] In the above technical solution, the bacterial liquid urease is extracted from urease-producing bacteria, and the urease is used to induce the deposition of calcium carbonate with cementing and filling effects, and the tailings sand filled in the goaf is in-situ cemented and solidified. This biological cementing filling method is different from some filling materials and methods based on microbial action reported. For example, at present, in order to solve the problem of a large amount of space occupied by CO2 geological sequestration and the environmental negative effects brought by traditional cement-based cementing filling materials, carbonic anhydrase bacteria are used to convert CO2 into CO3 2- Then, it combines with a calcium source to form calcium carbonate gel, and the calcium carbonate gel cements the aggregate to form a cementing filling material to mineralize and sequester CO2. The direct use of carbonic anhydrase bacteria in this technology may pose a biosafety risk to the ecological environment, with low treatment efficiency, and is restricted by factors such as whether the application scenario contains oxygen during the application process of this technology.

[0011] In the present invention, calcium chloride and urea with the same molar mass are mixed and stirred with a certain volume of water to obtain a cementing liquid. Among them, calcium chloride is used to provide a Ca 2+ source, and urea hydrolyzes under the action of bacterial urease to generate ammonium ions and carbonate ions, and combines with Ca 2+ to form calcium carbonate deposition with cementing and filling effects, cementing the tailings sand filled in the goaf into a whole and filling its pores, so as to achieve the purpose of improving the strength of the filling body and reducing its permeability.

[0012] The present invention sorts tailings sand from a concentrator into different size grades. The sorting is carried out using a vibrating screen. Through manual control or a pre - edited control program, the tailings sand is screened into three different particle size ranges: greater than 1.18 mm, greater than 0.425 mm and less than or equal to 1.18 mm, and less than or equal to 0.425 mm. For the first tailings sand (coarse aggregate) with a particle size greater than 1.18 mm and the second tailings sand (fine aggregate) with a particle size between 0.425 mm and 1.18 mm, they are mixed in a certain volume ratio to form an aggregate and sent to a goaf deeper from the ground. Then, a treatment liquid prepared from a bacterial urease solution and a cementing liquid is injected. That is, a method combining mixing filling and two - phase permeation grouting is used for the goaf. For the third tailings sand with a particle size less than 0.425 mm, a method combining mixing filling and two - phase permeation grouting is adopted. That is, the third tailings sand is first mixed with the bacterial urease solution and the cementing liquid to prepare a fluid - like filling slurry, and then the filling slurry is used to fill a goaf closer to the ground surface.

[0013] It should be noted that for the three different size grades of tailings sand with irregular shapes, when referring to their sizes, it means the equivalent particle size of the tailings sand.

[0014] The one - phase permeation grouting method for the deep goaf referred to in the present invention is to first mix the first tailings sand and the second tailings sand to form an aggregate and fill it into the deep goaf, and then inject the treatment liquid prepared from the bacterial urease and the cementing liquid into the filled deep goaf at a preset interval time; for the method combining mixing filling and two - phase permeation grouting for the near - surface goaf, it is to first mix the third tailings sand, the cementing liquid and the bacterial urease to obtain a filling slurry, and carry out mixing filling of the filling slurry into the goaf, and then inject the bacterial urease solution and the cementing liquid into the filled near - surface goaf at a preset interval time respectively for in - situ reinforcement by two - phase permeation grouting.

[0015] The method for biological cementation filling of tailings sand based on bacterial urease provided by at least one embodiment of the present invention uses Sporosarcina pasteurii as the urease - producing bacterium. Sporosarcina pasteurii is a facultative anaerobic spore - forming bacterium, which is an enzyme - producing microorganism, isolated from soil, non - pathogenic and has excellent environmental friendliness and extreme alkali resistance.

[0016] The method for biological cementation filling of tailings sand based on bacterial urease provided by at least one embodiment of the present invention, in the step of extracting the bacterial urease, the temperature during low - temperature ultrasonic crushing is controlled to be less than or equal to 30 °C, and the concentration of the bacterial liquid is monitored in real time. When the low - temperature ultrasonic crushing process is in the OD of the urease - producing bacterial liquid 600Terminate when the value is lower than 0.1. During the low-temperature high-speed centrifugation extraction, the temperature is controlled at 4°C, the rotation speed is 10,000 r / min, and the time is 10 min to 15 min to ensure the activity of bacterial urease, so as to achieve the advantages of no biosafety risk, high treatment efficiency, and applicability in both aerobic and anaerobic environments.

[0017] In the method for bio-cementing and filling tailings sand based on bacterial urease provided by at least one embodiment of the present invention, in the preparation of the treatment liquid, the pH value of the bacterial urease solution is adjusted by hydrochloric acid or acetic acid with a concentration lower than 2.0 M, and its pH value is adjusted to 5.5 - 6.5. Adjusting the pH value of the bacterial urease solution to this range can avoid the immediate occurrence of biochemical reactions in the prepared treatment liquid to induce calcium carbonate deposition, that is, provide a window period for the transmission of the treatment liquid to ensure that the treatment liquid can be more evenly injected into the pores of the tailings sand. At the same time, within this pH value range, the bacterial urease in the treatment liquid can have good activity, which is beneficial to the hydrolysis of urea in the treatment liquid into ammonium ions and carbonate ions, and promotes the combination of CO3 2- with Ca 2+ to form calcium carbonate deposition with excellent cementing and filling effects.

[0018] During the filling of the deep mined-out area, the second tailings sand and the first tailings sand form aggregates with a mass ratio of 2:1 to 4:3, and the molar concentrations of calcium chloride and urea in the treatment liquid are 0.75 M to 1.25 M, and the urease activity is greater than or equal to 3 mM / min. In this way, an excellent cementing body can be formed between the calcium carbonate induced by the treatment liquid and the aggregates.

[0019] In the method for bio-cementing and filling tailings sand based on bacterial urease provided by at least one embodiment of the present invention, during the filling of the near-surface mined-out area, the third tailings sand is mixed with the cementing liquid and the bacterial urease at a solid-liquid ratio of 2:1 to 2.5:1 to obtain a filling slurry. The molar concentrations of calcium chloride and urea after mixing the cementing liquid and the bacterial urease solution are 0.75 M to 1.25 M, and the urease activity is greater than or equal to 3 mM / min. During mixing and filling, the bacterial urease solution and the cementing liquid are mixed with the third tailings sand and then injected into the mined-out area together. During this process, the amount of urease will not be lost. However, when using two-phase permeation grouting, the bacterial urease solution first enters the gaps of the filling body formed by the filling slurry, and when the subsequently injected cementing liquid reaches the corresponding gap position, part of the urease will be discharged. Therefore, the urease activity of the bacterial urease solution used in the two-phase grouting method needs to be higher than the urease activity after mixing the urease solution and the cementing liquid during mixing and filling to ensure the in-situ reinforcement effect after mixing and filling. Therefore, in a preferred solution, the urease activity of the bacterial urease solution is greater than or equal to 10 mM / min, and the molar concentrations of calcium chloride and urea in the cementing liquid are 0.75 M to 1.25 M.

[0020] The tailings sand biocement filling method based on bacterial urease provided by at least one embodiment of the present invention. After the first deep goaf filling, when injecting the treatment liquid into the filled deep goaf by the one-phase permeation grouting method at a preset time interval, the volume of the treatment liquid injected each time is 1.2 to 1.3 times the total pore volume of the tailings sand; after the first near-surface goaf filling, when injecting the sum of the bacterial urease liquid and the cementing liquid into the filled near-surface goaf by the two-phase permeation grouting combination method at a preset time interval, the volume is 1.2 to 1.3 times the total pore volume of the tailings sand. Among them, the preset time intervals involved in both the deep goaf filling and the near-surface goaf filling are 20h to 28h.

[0021] It should be noted that the total pore volume of the tailings sand here refers to the total pore volume measured or calculated before injecting the treatment liquid for in-situ reinforcement for the next time. Therefore, it is easy to understand that as the number of in-situ reinforcement treatment times increases, the value of the "total pore volume of the tailings sand" will continuously decrease to nearly 0, and then the injection of the treatment liquid or the injection of the bacterial urease liquid and the cementing liquid for in-situ reinforcement treatment can be stopped.

[0022] In the second aspect, the present invention also provides a tailings sand biocement filling system based on bacterial urease to implement the tailings sand biocement filling method based on bacterial urease in the first aspect. The system includes:

[0023] Central integrated control system;

[0024] Bacterial urease extraction subsystem, including urease-producing bacteria expansion culture equipment, ultrasonic crushing equipment, cooling equipment, bacterial liquid concentration real-time monitoring equipment, temperature monitoring equipment, low-temperature high-speed centrifugation equipment, low-temperature storage equipment, and pH value adjustment equipment;

[0025] Cementing liquid preparation and feeding subsystem, including calcium chloride and urea raw material storage equipment, feeding and stirring equipment, and cementing liquid storage equipment;

[0026] Tailings sand grading subsystem, including a layered oscillating screening device and the first tailings, second tailings, and third tailings bins connected thereto;

[0027] Filling slurry mixing subsystem, including a bacterial urease conveying device, a cementing liquid conveying device, a third tailings conveying device, and a filling slurry mixing bin; and

[0028] Goaf filling subsystem, including a first tailings and second tailings mixing and feeding device, and a bacterial urease liquid and cementing liquid preparation of the treatment liquid mixing and feeding device.

[0029] Different from the prior art, the above technical scheme provides a goaf biocementing material based on bacterial urease liquid extracted from urease-producing bacteria to replace the traditional goaf filling slurry with cement as the main raw material, which can avoid the use of cement to generate a large amount of dust during the production process, and there are problems of high energy consumption and environmental pollution. It is an environmentally friendly cementing material, and also reduces the filling cost to a certain extent. Specifically, the present invention screens the tailings sand according to different particle size ranges, and respectively adopts a one-phase infiltration grouting method and a mixing filling method combined with a two-phase infiltration grouting method for in-situ cementation and solidification, which greatly improves the utilization rate of the tailings sand. Due to the reduction or replacement of cement, the reduction in cement consumption will inevitably reduce the energy supply and pollution pressure of cement production. When factors such as blasting vibration cause the filling body to have cracks and reduce strength, the in-situ reinforcement treatment can continue to be carried out to repair the damaged parts, thereby improving the weak stability problem of the filling body mainly using cement that cannot be repaired after cracking. At the same time, the use of bacterial urease liquid improves the fluidity and biological safety of the filling slurry, so that every tiny gap in the filling body can be filled, significantly improving the compressive strength of the filling body in the goaf. Furthermore, the solution provided by the present invention can play an excellent role in both anaerobic and aerobic goaf environments, providing a new idea of ​​biocementation filling that is more green, environmentally friendly, efficient and safe for goaf filling. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a flow chart of a tailings sand biocementation filling method based on bacterial urease according to a specific embodiment of the present invention;

[0031] Figure 2 This is a schematic diagram of a tailings sand biocementation filling system based on bacterial urease according to a specific embodiment of the present invention;

[0032] Figure 3 This is a schematic diagram of a goaf applicable to a biocementation filling of tailings sand based on bacterial urease according to a specific embodiment of the present invention;

[0033] Figure 4 This is a real shot of a sample of the third tailings sand and treatment fluid cementation in a specific embodiment of the present invention;

[0034] Figure 5 This is a real shot of a sample of cementation in which the first tailings and the second tailings are formed into aggregates with a mass ratio of 4:3 and the treatment liquid in a specific embodiment of the present invention. DETAILED DESCRIPTION

[0035] In order to explain the technical content, structural features, achieved objectives and effects of the technical solution in detail, the following is a detailed description in conjunction with specific embodiments and accompanying drawings.

[0036] As used herein, the term "embodiment" means that the specific features, structures, or characteristics described in connection with the embodiments can be included in at least one embodiment of the present application. The term "embodiment" that appears in various positions in the specification does not necessarily refer to the same embodiment, nor does it particularly limit its independence or relevance to other embodiments. In principle, in the present application, as long as there is no technical contradiction or conflict, the technical features mentioned in each embodiment can be combined in any way to form corresponding implementable technical solutions.

[0037] Unless otherwise defined, the meanings of the technical terms used herein are the same as those commonly understood by those skilled in the technical field to which the present application belongs; the use of the relevant terms herein is only for describing specific embodiments and is not intended to limit the present application.

[0038] In the description of the present application, the term "and / or" is an expression used to describe the logical relationship between objects, indicating that there can be three relationships. For example, A and / or B means: the existence of A, the existence of B, and the simultaneous existence of A and B. In addition, the character " / " herein generally represents an "or" logical relationship between the associated objects before and after.

[0039] In the present application, terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual quantitative, primary-secondary, or sequential relationship between these entities or operations.

[0040] Without further limitation, in the present application, the use of the terms "comprising", "including", "having", or other similar expressions in a statement is intended to cover non-exclusive inclusion. These expressions do not exclude the possibility that there may be additional elements in the process, method, or product that includes the said elements, such that a process, method, or product that includes a series of elements may include not only those defined elements, but also other elements not explicitly listed, or elements inherent to such process, method, or product.

[0041] The same as the understanding in the "Examination Guidelines", in the present application, expressions such as "greater than", "less than", "exceeding", etc. are understood not to include the recited number; expressions such as "above", "below", "within", etc. are understood to include the recited number. In addition, in the description of the embodiments of the present application, the meaning of "a plurality of" is two or more (including two), and similar expressions related to "many" are understood in the same way, such as "multiple groups", "multiple times", etc., unless otherwise specifically defined.

[0042] In the description of the embodiments of the present application, the spatially related expressions used, such as "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "perpendicular", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., the indicated orientation or positional relationship is based on the orientation or positional relationship shown in the specific embodiment or the drawings. It is only for the convenience of describing the specific embodiments of the present application or for the reader's understanding, rather than indicating or implying that the device or component referred to must have a specific position, a specific orientation, or be constructed or operated in a specific orientation. Therefore, it should not be construed as a limitation on the embodiments of the present application.

[0043] Unless otherwise clearly specified or limited, in the description of the embodiments of the present application, the terms "installed", "connected", "joined", "fixed", "set", etc. should be understood in a broad sense. For example, the "connection" can be a fixed connection, a detachable connection, or an integral setting; it can be a mechanical connection, an electrical connection, or a communication connection; it can be directly connected, or indirectly connected through an intermediate medium; it can be the communication inside two components or the interaction relationship between two components. For those skilled in the art to which the present application pertains, the specific meanings of the above terms in the embodiments of the present application can be understood according to specific circumstances.

[0044] During the mining, beneficiation, and smelting processes of actual mineral resources, a large amount of tailings generated are left unused or piled up in tailing ponds for a long time, which not only causes waste of tailings and land resources, but also has many adverse effects on the environment due to factors such as rainfall, for example, resulting in surface runoff containing heavy metal waste liquid, and landslides and debris flows induced by the collapse of tailing ponds. If the resource recovery and utilization of tailings can be realized locally, multiple benefits in terms of economy, society, and ecological environment will be achieved, effectively solving the long-standing problem of tailings.

[0045] In addition, the mined - out areas generated during the exploitation of mineral resources need to be filled in time to effectively prevent surface subsidence and ecological damage in the mining area. Currently, the commonly used mined - out area filling materials are mainly gangue, cement, paste, etc. When using the slurry or high - water materials of the above - mentioned materials to fill the mined - out area, especially when there is an inclination in the mined - out area, an unconnected space will appear above the filling body, seriously affecting the filling effect of the mined - out area, causing an increase in the roof subsidence amount, and being unfavorable for the protection of surface buildings. When using a filling body with cement as the main material, there will also be problems such as dust pollution, cracks that cannot be repaired in time, poor strength and stability of the filling body, and too high filling cost.

[0046] The inventors of the present invention actively explored a comprehensive solution for the low-cost treatment and disposal of tailings to "turn waste into treasure" and the high-strength and high-stability filling of goafs. They introduced bacterial urease extracted from urease-producing bacteria to in-situ cement and solidify the tailings filled in the goaf to meet the strength requirements of the filling body in the goaf. At the same time, this technology can achieve the goal of economically, efficiently, stably, and environmentally filling the goafs generated in the mining, beneficiation, and smelting of various types of mineral resources in China, and can well restore the ecological environment of the mining area.

[0047] In this embodiment, Sporosarcina pasteurii is purchased as the urease-producing bacterium. Please refer to Figure 1 and Figure 2 , in a specific implementation scheme, the present invention provides a biological cementation filling method for tailings sand based on bacterial urease, including the following steps:

[0048] Prepare a culture medium by mixing yeast extract with a mass concentration of 20 g / L, 15 g / L NH4Cl, and 12 g / L Ni(Cl)2, and adjust the pH value to 9.2 to 9.3 with a 5 mol / L NaOH solution.

[0049] Place the prepared culture medium in an autoclave and sterilize it at a temperature of 121 °C for 30 min. After sterilization, cool the culture medium to below 30 °C.

[0050] Inoculate the mother bacteria of Sporosarcina pasteurii onto the sterilized culture medium and place the culture medium on a constant-temperature shaking incubator for scale-up culture under the condition of a constant temperature of 30 °C.

[0051] After culturing the mother bacteria of Sporosarcina pasteurii for 10 h to 12 h, obvious turbidity appears in the culture medium. Take a small amount of bacterial sample and add it to urea with a concentration of 1.1 mol / L. The volume ratio of urea to bacteria is 9:1. Measure the activity of the mother bacteria of Sporosarcina pasteurii with the conductivity value. When the change value of the conductivity is between 0.1 mS / cm / min and 0.2 mS / cm / min, the scale-up culture can be ended, and the cultured bacteria are stored at 4 °C.

[0052] Extract bacterial urease from the cultured Sporosarcina pasteurii liquid. Adopt the method of low-temperature ultrasonic disruption, and control the temperature of the bacterial liquid during the urease extraction process below 30 °C through a cooling device to ensure that the extracted bacterial urease has good urease activity; at the same time, monitor the concentration of the bacterial liquid, i.e., the OD 600 value, in real time during the low-temperature ultrasonic disruption process. When the OD 600 value of the bacterial liquid is lower than 0.1, terminate the ultrasonic disruption; after the ultrasonic disruption is completed, put the bacterial liquid into a high-speed refrigerated centrifuge device and centrifuge it at 4 °C and 10,000 r / min for 10 min to 15 min. After centrifugation, take the supernatant to obtain the bacterial urease liquid.

[0053] Cementing fluid preparation: Calcium chloride and urea with the same molar mass are stirred and mixed evenly with a certain volume of water to obtain a cementing fluid, which is then transported to a cementing fluid storage bin for storage.

[0054] Treatment fluid preparation: The pH value of the bacterial urease solution is adjusted to 5.5 - 6.5 using hydrochloric acid or acetic acid with a concentration lower than 2M, and then mixed with a certain volume of the cementing fluid to obtain a treatment fluid with a molar concentration of calcium chloride and urea of 0.75M - 1.25M and a urease activity greater than or equal to 3 mM / min.

[0055] The present invention uses the classified tailings of a concentrator as the aggregate for subsequent backfilling of the mined - out area. First, the tailings slurry from the concentrator is thickened and settled by a high - efficiency thickener, and then the tailings sand is washed with water to remove the chemical substances remaining on the surface of the tailings sand after beneficiation. The washed tailings sand is screened and classified into first - class tailings sand, second - class tailings sand, and third - class tailings sand. The particle size of the first - class tailings sand is greater than 1.18 mm, the particle size of the second - class tailings sand is greater than 0.425 mm and less than or equal to 1.18 mm, and the particle size of the third - class tailings sand is less than or equal to 0.425 mm. The three types of classified tailings sands are stored in different vertical sand bins respectively. Since the shape of the tailings sand is mostly irregular, the particle size described in the present invention is the equivalent particle size of the tailings sand screened by vibrating screens with different aperture specifications.

[0056] Please refer to Figure 3 , the tailings sand with a particle size greater than 0.425 mm is treated by the method of first backfilling and then in - situ grouting reinforcement. That is, the second - class tailings sand with a particle size greater than 0.425 mm and less than or equal to 1.18 mm and the first - class tailings sand with a particle size greater than 1.18 mm are mixed into an aggregate in a ratio of 3:2 and then backfilled into the deep mined - out area. Then, the bacterial urease solution and the cementing fluid are mixed in a certain volume ratio to prepare a treatment fluid with a molar concentration of calcium chloride and urea of 0.75M and a urease activity greater than or equal to 3 mM / min, and it is injected into the mined - out area filled with the aggregate formed by the second - class tailings sand and the first - class tailings sand. It should be noted that before mixing the bacterial urease solution with the cementing fluid, the pH value of the bacterial urease solution needs to be adjusted to the range of 5.5 - 6.5. Thereafter, every 20 h - 28 h, the prepared treatment fluid can be used to carry out in - situ reinforcement treatment on the tailings sand filled in the mined - out area until the strength of the filling body in the mined - out area reaches the expected compressive strength of 1.5 MPa - 2.5 MPa required by the "Mine Safety Regulations".

[0057] The tailings sand with a particle size less than 0.425 mm (the third tailings sand) is used to prepare the filling slurry by the mixing method. The tailings sand with a particle size less than 0.425 mm (the third tailings sand) is fed into a mixer and mixed with the bacterial urease solution and the cementing solution. The treatment solution formed by the third tailings sand, the bacterial urease solution and the cementing solution is prepared with a solid-liquid ratio (mass: volume) of 2:1 to prepare the filling slurry required for filling, and is fed into the goaf through the filling pipeline. This is the mixing filling. Thereafter, the in-situ reinforcement treatment can be carried out on the goaf near the surface that has been filled by the mixing filling and the two-phase infiltration grouting method of the bacterial urease solution and the cementing solution every 20 h to 28 h until the strength of the goaf filling body reaches 1 MPa to 1.5 MPa required by the "Mine Safety Regulations". Note that for the above two in-situ reinforcement treatment methods, the total volume of the treatment solution injected each time or the total volume of the bacterial urease solution and the cementing solution injected is 1.2 to 1.3 times the total pore volume of the tailings sand (i.e., over-injection). The liquid after the reaction of the previous treatment injection (hereinafter referred to as the waste liquid) and the over-injected treatment solution of this treatment will be discharged through the drain valve on the filling retaining wall at the bottom of the goaf. After a certain number of treatments, a sample block is made by sampling in the hopper (please refer to Figure 4 ) and its compressive strength is tested, and the quality of the filling body is monitored in combination with the strength monitoring system.

[0058] In this embodiment, the urease solution extracted from urease-producing bacteria is used, the tailings sand of the concentrator is used as the aggregate, and according to the characteristics of the urease-cemented tailings sand, after the tailings sand is automatically screened, different cementing filling methods are adopted according to the particle size, and multiple cementing treatments are carried out for goaf filling, effectively turning the tailings sand into "treasures from waste", with high environmental compatibility, having the advantages of no biosafety risk, high treatment efficiency, no need for aerobic environment, strong compressive strength of the filling body, and long-term stability without cracking.

[0059] To implement the above filling method, the present invention also provides a tailings sand biocement filling system based on bacterial urease, which is mainly composed of several subsystems such as a central integrated control system, a bacterial urease extraction subsystem, a cementing solution preparation and feeding subsystem, a tailings sand grading subsystem, a filling slurry mixing subsystem, and a goaf filling subsystem.

[0060] Among them, the bacterial urease extraction subsystem includes a urease-producing bacteria expansion and cultivation device, an ultrasonic crushing device, a cooling device, a bacterial liquid concentration monitoring device, a low-temperature high-speed centrifugal extraction device, and a pH value adjustment device.

[0061] The cementing solution preparation and feeding subsystem includes a calcium chloride solution and urea raw material storage device, a stirring and feeding device, and a cementing solution storage device.

[0062] The tailings sand grading subsystem includes a layered oscillating screening device and the first tailings sand, the second tailings sand, and the third tailings sand storage bins connected thereto.

[0063] The filling slurry mixing subsystem includes a bacterial urease delivery device, a cementing liquid delivery device, a third tailings delivery device, a filling slurry mixing bin, and a filling slurry storage bin.

[0064] The goaf filling subsystem includes a mixing and feeding device for the first and second tailings, and a mixing and feeding device for preparing the treatment liquid from the bacterial urease solution and the cementing liquid.

[0065] The central integrated control system includes a cementing liquid concentration monitoring device, a filling slurry flow control device, a filling body strength detection system, a bacterial solution temperature control system, a bacterial concentration monitoring system, and an emergency protection system.

[0066] (1) Cementing liquid concentration monitoring device

[0067] This device is mainly used to control the cementing liquid concentration within a reasonable range (2 mol / L - 4 mol / L).

[0068] (2) Filling slurry flow control device

[0069] This device is mainly used to control the flow rate of the filling slurry to prevent the flow rate from being too slow or too fast, which may affect the filling quality.

[0070] (3) Filling body strength detection system

[0071] The function of this system is to detect whether the strength of the filling body meets the standard, so as to determine the number of in-situ reinforcement treatments and whether in-situ repair is required.

[0072] (4) Bacterial solution temperature control system

[0073] This system ensures that the culture temperature and storage temperature of bacteria are within a certain reasonable range, so as to control the temperature during the ultrasonic extraction of bacterial urease not to exceed 30 °C, thereby ensuring that the bacteria and the extracted bacterial urease have good activity.

[0074] (5) Bacterial concentration monitoring system

[0075] The function of this system is to monitor the OD 600 value (i.e., the optical density value of the bacterial solution under the condition of 600 nm, which is used to characterize the concentration of bacteria in the bacterial solution) of the bacterial solution in real time, so as to control whether to stop ultrasonic fragmentation; when the OD 600 value of the bacterial solution is less than 0.1, ultrasonic fragmentation can be stopped.

[0076] (6) Emergency protection system

[0077] This system is mainly used to deal with the sudden situation of slurry leakage in the filling pipeline. It can pause the grouting in time for repair.

[0078] The biocement filling system provided in this embodiment is scheduled by a central controller, with a high degree of automation and does not require a large amount of manpower input. It can intelligently separate the tailings sand from the concentrator.

[0079] Different from the above embodiment, in another tailings sand biocement filling method based on bacterial urease provided by the present invention, calcium chloride solution and urea are stirred and mixed at the same molar mass to obtain a treatment solution with a molar concentration of 1M and a urease activity greater than or equal to 3 mM / min. When the third tailings sand is mixed and stirred with the mixed solution of the cementing liquid and bacterial urease, the solid-liquid ratio is 2.5:1 for mixing to obtain the filling slurry. After filling the near-surface goaf with the filling slurry, then every 26 h, the bacterial urease solution with a urease activity greater than or equal to 10 mM / min and the cementing liquid with a molar concentration of calcium chloride and urea of 1.25M are successively injected into the near-surface goaf filled with the filling slurry by the two-phase permeation grouting method.

[0080] The second tailings sand with a particle size greater than 0.425 mm and less than or equal to 1.18 mm and the first tailings sand with a particle size greater than 1.18 mm are mixed in a ratio of 2:1 to form aggregate, and then filled into the deep goaf. Then, the treatment solution formed by bacterial urease and the cementing liquid with a molar concentration of 1M and a urease activity greater than or equal to 3 mM / min is injected. The drain valve on the filling retaining wall at the bottom of the goaf is opened to drain the waste liquid, and then every 20 h, the treatment solution formed by bacterial urease and the cementing liquid with a molar concentration of 1M and a urease activity greater than or equal to 3 mM / min is injected again. And the treatment solution injected each time needs to be freshly prepared to ensure that the urease has sufficient activity. The volume of the treatment solution injected in the latter injection is 1.2 - 1.3 times the total pore volume of the tailings sand. The strength of the goaf filling body is tested to be about 2.0 MPa, meeting the expected compressive strength of 1.5 MPa - 2.5 MPa required by the "Mine Safety Regulations".

[0081] In some other specific embodiments, when implementing deep goaf filling, the second tailings sand and the first tailings sand are formed into aggregates with a mass ratio of 4:3, and the bacterial urease and the cementing liquid are mixed with the same molar mass to form a treatment liquid with a molar concentration of 1.25 M and a urease activity of greater than or equal to 3 mM / min. During in-situ reinforcement, the time interval can also be slightly extended according to the actual situation. For example, the treatment liquid of the re-prepared bacterial urease and the cementing liquid is injected into the deep goaf every 28 h, and the volume of the treatment liquid injected in the subsequent injection is about 1.2 times the total pore volume of the tailings sand. Relevant records such as time and injection volume should be made for each injection. When the third tailings sand is mixed and stirred with the mixed liquid of the cementing liquid and the bacterial urease, the solid-liquid ratio is 2.3:1 to obtain the filling slurry. After filling the near-surface goaf with the filling slurry, then every 28 h, the bacterial urease solution with a urease activity of greater than or equal to 10 mM / min and the cementing liquid with a molar concentration of 0.75 M containing calcium chloride and urea are successively injected into the near-surface goaf filled with the filling slurry by the two-phase permeation grouting method.

[0082] Please refer to Figure 4 The actual picture of the cemented specimen of the third tailings sand, the bacterial urease solution and the cementing liquid shown, and Figure 5 The actual picture of the cemented specimen of the aggregate formed by the first tailings sand and the second tailings sand with a mass ratio of 4:3 and the treatment liquid shown.

[0083] Figure 4 and Figure 5 The unconfined compressive strength of the cemented specimens of the two tailings sands shown is about 2.0 MPa, meeting the expected compressive strength of 1.5 MPa - 2.5 MPa required by the "Mine Safety Regulations", indicating that by using the technical solution of the present invention, the tailings sand filled in the goaf can be reinforced by the bacterial urease solution in combination with the cementing liquid to obtain good compressive strength of the filling body.

[0084] It should be noted that although the above embodiments have been described in this article, the patent protection scope of the present invention is not limited thereby. Therefore, based on the innovative concept of the present invention, the changes and modifications made to the embodiments described in this article, or the equivalent structural or equivalent process transformations made by using the content of the specification and drawings of the present invention, and directly or indirectly applying the above technical solutions to other related technical fields, are all included in the patent protection scope of the present invention.

Claims

1. A biological cementation filling method for tailings sand based on urease from bacteria sources, characterized in that, It includes the following steps: Extraction of bacterial urease: The urease-producing bacteria liquid obtained by amplification culture is first subjected to low-temperature ultrasonic disruption, and then low-temperature high-speed centrifugation is carried out for extraction to obtain bacterial urease liquid. Preparation of cementing liquid: Calcium chloride and urea with the same molar mass are mixed and stirred with water to obtain the cementing liquid. Preparation of treatment liquid: First, the pH value of the bacterial urease liquid is adjusted to weakly acidic, and then it is mixed with the cementing liquid to obtain the treatment liquid. Classification of tailings sand: The tailings sand is screened into first tailings sand, second tailings sand, and third tailings sand. The particle size of the first tailings sand is greater than 1.18 mm, the particle size of the second tailings sand is greater than 0.425 mm and less than or equal to 1.18 mm, and the particle size of the third tailings sand is less than or equal to 0.425 mm. Goaf filling: It includes deep goaf filling and near-surface goaf filling. The deep goaf filling adopts the one-phase permeation grouting method. The second tailings sand and the first tailings sand form aggregate in a mass ratio of 2:1 to 4:3 and are filled into the deep goaf. Then, the treatment liquid is injected into the filled deep goaf by the one-phase permeation grouting method at preset time intervals. The molar concentration of calcium chloride and urea in the treatment liquid is 0.75 M to 1.25 M, and the urease activity is greater than or equal to 3 mM / min. The near-surface goaf filling adopts a method combining mixing filling and two-phase permeation grouting. The third tailings sand and the treatment liquid are mixed at a solid-liquid ratio of 2:1 to 2.5:1 to obtain a filling slurry. The molar concentration of calcium chloride and urea in the treatment liquid is 0.75 M to 1.25 M, and the urease activity is greater than or equal to 3 mM / min. And the filling slurry is used for mixing filling into the goaf, and then the bacterial urease liquid and the cementing liquid are respectively and successively injected into the near-surface goaf filled with the filling slurry by the two-phase permeation grouting method at preset time intervals.

2. The biological cementation filling method for tailings sand based on bacterial urease according to claim 1, wherein The urease-producing bacteria is Sporosarcina pasteurii.

3. The biological cementation filling method for tailings sand based on bacterial urease according to claim 1, wherein, In the step of extracting the bacterial urease, the temperature during the low-temperature ultrasonic disruption is controlled to be less than or equal to 30 °C. The low-temperature ultrasonic disruption process is terminated when the OD 600 value of the urease-producing bacteria solution is lower than 0.

1. The temperature during the low-temperature high-speed centrifugation extraction is controlled to be 4 °C, the rotation speed is 10,000 r / min, and the time is 10 min to 15 min.

4. The biological cementation filling method for tailings sand based on urease from bacterial sources according to claim 1, characterized in that, In the preparation of the treatment liquid, the pH value of the bacterial urease liquid is adjusted by hydrochloric acid or acetic acid with a concentration lower than 2.0 M, and its pH value is adjusted to 5.5 to 6.

5.

5. The bio-cementation filling method for tailings sand based on urease from microbial sources according to claim 1, characterized in that, In the two-phase permeation grouting method, the urease activity of the bacterial urease liquid is greater than or equal to 10 mM / min, and the molar concentration of calcium chloride and urea in the cementing liquid is 0.75 M to 1.25 M.

6. The method for bio-cementation filling of tailings sand based on urease from microbial sources according to claim 1, wherein After the first deep goaf filling, when the treatment liquid is injected into the filled deep goaf by the one-phase permeation grouting method at preset time intervals, the volume of the treatment liquid injected each time is 1.2 to 1.3 times the total pore volume of the tailings sand. After the first near-surface goaf mixing filling, the sum of the volumes of the bacterial urease liquid and the cementing liquid injected into the filled near-surface goaf by the two-phase permeation grouting method at preset time intervals is 1.2 to 1.3 times the total pore volume of the tailings sand.

7. The method for bio-cementation filling of tailings sand based on microbial urease according to claim 1, characterized in that, The preset time interval is 20 h to 28 h.

8. A tailings sand bio-cementation filling system for implementing the tailings sand bio-cementation filling method based on bacterial urease as described in any one of claims 1-7, characterized in that, It includes: Central integrated control system; Bacterial urease extraction subsystem, including urease-producing bacteria amplification culture equipment, ultrasonic disruption equipment, cooling equipment, real-time monitoring equipment for bacterial liquid concentration, temperature monitoring equipment, low-temperature high-speed centrifugation equipment, low-temperature storage equipment, and pH value adjustment equipment; The cementing liquid preparation and feeding subsystem includes calcium chloride and urea raw material storage equipment, feeding and stirring equipment, and cementing liquid storage equipment; The tailings sand classification subsystem includes a layered oscillating screening device and the first tailings, second tailings, and third tailings bins connected thereto; The filling slurry mixing subsystem includes a bacterial urease conveying device, a cementing liquid conveying device, a third tailings conveying device, and a filling slurry mixing bin; and The goaf filling subsystem includes a mixing and feeding device for the first tailings and the second tailings, and a mixing and feeding device for the bacterial urease solution and the cementing liquid preparation treatment liquid.

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