AU2021105354A4 - A cemented filling method by mineral carbonation of tailings - Google Patents

Abstract

The invention provides a cemented filling method by mineral carbonation of tailings, which belongs to the technical field of industrial wastes utilization. Solid wastes with high calcium and/or magnesium content and low hydration activity were selected as cementitious materials. Firstly, the cementitious materials are crushed, ground, and fully mixed with tailings, water and addictive to prepare the filling slurry. Secondly, the filling slurry is transported to the mine out area by a pipeline. After the goaf is filled, the filling area is sealed and blocked. Thirdly, CO2 is injected into the closed filling area to curing the filling body. Finally, real time monitoring on the status of solid, liquid, and gas at the surrounding rocks and filling body is carried out during the process of carbonation curing, to make sure the stability of surrounding rocks and the meeting the requirements of back and fill mining method. The cementing materials used in this invention were solid wastes that has high calcium and magnesium content, low hydration activity and little utilization rate. It greatly reduces the cost of raw materials used in cemented filling mining method. The invention is a cemented filling method by mineral carbonation of tailings, which has the advantages in simple process, low cost and environmentally clean. 1/2 %AF Figure 1 5 17 Hl rr _cr r r EEL L L LLL LLLLL _ILLLLLL .......... _LLIL -LLLLLL -LLLLLL -LLLLLL -L-L" LLLLLL [ , _LL- LLLLLL _LIILLL _LLLILL _LLLLLL ___LLLLLL LILLLL _LLLLLL LLLLLL -LLLLLL,,., LLLLLL LLLLLL -LLLLLLL -LLLLLLL ,LL -L-L _LLLLLL- _LLLLLL _LIILLL _LLLILL _LLLLLL LLLLLL LLLLL ..-LLLLLL -LLLLLL,,.,-ILLLLLL _LLLLLL LLLLLL _L_ -ILL ',':LILLLL LLLLLL ±LLLL.LL L"LLL LLLLL -LLLLLL LLLLLL 'LLLLLLL _LLLLLL LLLLLL LLLLLJ. LLLLLL -LLLLLLLL _LLLLLL _ LLLLLL _LIILLL _ LLL__L ..,_L-LLL _LLLLLL ILLLILL LLLLLL LLLLLL _LLLLLL -L-L _LLLLLL -LLLLLL ILLLLLL _LLLLLL LLLLLL _LLLLLL ''-LLLLLL ILLLILL LILLLL _-LLLLLL ILLLLLL ___ LLLLLL LLLLLL _L_ ±LL-L L-LLL _LLLLLL ILLLLLL LLLLL LLLLLL LLLLLL LLLLLL -LL-L,,_LLLLLL _LLLLLL _LLILLLLLLLLL -LLLLLL LLLL L -IL LLLLLL LLLLLL LIILLL LLLIlL LLLL -.-LLLLLL ILLLILL LLLLLL LLLLLL __LL LLLLLL _LLLLLL -L-L L LLLL LLLLLL ,-ILLLLLL LL,,LLLL, ILLLILL L 'LL 'LLLLLLLLLLLLLLi, LLLLLLILLLLLl L LL L -ii:_J L LL 'Lli 9 Figure 2

Description

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Figure 2

A cemented filling method by mineral carbonation of tailings

Technical field The invention relates to the technical field of back and fill mining method by tailings cementation, in particular to a cemented filling method by mineral carbonation of tailings

Background technique Cemented filling mining method is one of the green mining measures. The cement used in the cement filling mining method is still mainly Portland cement, which cost accounts for 70 -80% of the entire filling cost. In recent years, solid waste materials (i.e. blast furnace slag and fly ash) have been used to replace Portland cement in large quantities. With the increase in the cost of these solid waste materials, the high cost problem of cemented filling mining method has not solved yet. The application rate of cemented filling mining method stay only 30% in underground mine for a long time. In recent years, researchers have achieved good results in utilizing various solid wastes to replace Portland cement. However, solid wastes with high calcium and magnesium content (i.e. steel slag, construction waste, wollastonite, etc.), has extremely low hydration rate, which is not suitable for cement replacement. The utilization rate of these solid wastes is very low. Take steel slag as an example, the comprehensive utilization rate is about 30% in developing countries (i.e. China).The disposal of a large amount of steel slag takes up lands, wastes resources and pollutes the environment. Enterprises have to pay high environmental taxes. The utilization rate of steel slag in developed countries (i.e. US and Japan) is nearly 100%. However, steel slag is mostly used as aggregate in road construction, which is a low value utilization of the steel slag. Therefore, it is an important task to high value application of the solid waste with high calcium and magnesium content and low hydration activities. The solid waste with high calcium and magnesium content and low hydration activity could consolidation after carbonation curing. Taking steel slag as an example. The main components of steel slag are dicalcium silicate, tricalcium silicate, RO phase (a solid solution composed of MgO, MnO and FeO), calcium aluminate ferrite, free calcium oxide, free magnesium oxide and elemental iron, etc.. The RO phase make the hydration rate of steel slag very low. The free oxides make steel slag products has a poor volume stability. However, the calcium and magnesium containing minerals in the steel slag can quickly react withCO 2 at room temperature, which lead to the carbonated steel slag products have a high early strength. Therefore, the use of the solid wastes with high calcium and magnesium contents (i.e. steel slag, construction wastes) as carbonation cementitious materials infillingbody, can effectively solve the problem of low value utilization of these materials, reduce the cost of cemented filling mining method and enhance the application rate of cemented filling mining method. The invention patent CN109485357A "A GRC Plate Based on Steel Slag Carbonation" discloses a GRC plate prepared by carbonation of steel slag. The characterization is that: the steel slag, quartz sand and glass fiber are uniformly mixed in a certain proportion. Then, the dry mixture is stirred with with water and prepared as a plate using in a stainless steel carbonized mold. The prepared plate is immediately placed into a carbonation box for curing. GRC plates are produced based on carbonation curing of steel slag. The patent uses pureCO 2 for curing, and the CO2 pressure in carbonation curing is 1 to 3MPa. The production conditions are demanding, and the infrastructure and maintenance costs are too high. The invention patent CN10957461OB "A method for efficiently preparing of a low-cost carbonated brick using steel slag" discloses a efficiently preparing method for a low-cost carbonated steel slag brick. The characteristic of the patent is: steel slag, desulfurized gypsum and fine aggregate are mixed to form a solid mixture; then water is added and stirred uniformly; after the moistened powder is pressing and molding, the brick is cured in a carbonation chamber to obtain the carbonated steel slag brick. The cost of the curing process in this patent is low. However, the density of the carbonated steel slag bricks is relatively high, which is not meet the requirements of lightweight in construction bricks. The invention patent CN109608151B "A method for preparing a high-strength carbonated building materials using steel slag powder" discloses a preparing method for a high-strength building materials by carbonation curing of the steel slag powder. The characteristic of the patent is: the steel slag is ground into power; 70%-100% steel slag, %-30% desulfurized gypsum are mixed to form a solid mixture; then water with a mass of 5%-25% of the dry mass is added and stirred evenly; after pressing and molding, the compact is cured in a carbonation chamber to form the high-strength carbonated steel slag building materials. The prepared high-strength carbonated building material consumes a large amount of steel slag. However, if the free calcium and/or magnesium oxides in the steel slag are 100% neutralized has not been reported. The carbonated steel slag building material may have the hidden dangers of volume instability in a long term. This invention patent a cemented filling method by mineral carbonation of tailings, which uses solid waste with high calcium and magnesium content as cementing materials, and tailings as aggregates. The patent not only maximizes the use of industrial solid waste, but also greatly reduces the cost cemented filling mining method. Flue gas after desulfurization and denitrification in iron and steel plants is directly used for carbonation curing, which made the maintenance cost very low. The density of the filling materials has no requirement. Moreover, the long-term volume expansion of the filling materials could effectively support the mine-out area, which enhance the stability of the surrounding rocks. The early strength and long-term strength of the carbonated filling material prepared by the patent could meet the requirements of the filling body. Especially, it has the advantage of high early strength. In addition, the filling body fixes a large amountof C0 2,which could help to mitigate the problem of global warming. The carbonation curing area (filling area) adopts closed and block treatment, and real-time monitoring system, which could ensure the safety and stability of the filling body and surrounding rocks during the carbonation curing processes. The method has the obvious advantages of simple, clean and low costs.

Summary of the invention This intention provides a cemented filling method by mineral carbonation of tailings, which solve the technical problem of low utilization rate of solid waste with high calcium and magnesium contents (i.e. steel slag, construction waste), high cost of cementing materials used in cemented filling mining method, and high cost of CO 2 storage by mineral carbonation. The method includes the following steps: S: Crushed and ground cementitious material into powder. Use the whole tailings as the aggregate; S2: Prepare the filling slurry by fully stirring of the mixture containing cementitious materials, whole tailings in S, water and additives ; S3: Pipelines for injecting CO2 gas was installed in the mine out area before the filling slurry was transported to the goaf.

S4: Transport the filling slurry prepared in S2 to the filling station, and pump to the undergroud goaf. S5: Seal and block the filling area after the goaf is fully filled, to make sure the gas impermeability of the filling area; S6: After sealing the filling area for 24 hours, inject CO 2 gas by pipeline installed in S3 to curing the filling body, to make sure the compressive strength meets the requirements; S7: Real-time monitoring during S4-S6 for early warning, to make sure the safety of the enclosed filling area, Amongst, the cementing materials in S Iis solid wastes with low or no hydration activities, which include steel slag, construction wastes, and solid wastes containing calcium oxide, magnesium oxide, calcium hydroxide, magnesium hydroxide, calcium silicates or magnesium silicates. The cementing materials can react quickly with CO 2 and generate carbonates. The Blaine's number of the cementing materials is ground to 300~700 m 2 /kg. The whole tailings in S Iis made from any type of rocks, include ultramafic , mafic, neutral, acidic, and super-acid tailings. the mass ratio of cement to tailings in S2 is 3:7-1:1; the mass of the additive take up 0~10% of the mass of the cementing materials; and the liquid-solid ratio of the filler slurry is 0.20~0.40. The additive in S2 is catalysts that could promote the carbonation of the filling materials, including sodium carbonate, sodium bicarbonate, acetic acid, citric acid, and desulfurization gypsum, metallurgical slags, fly ashes, carbonic anhydrase, cyanobacteria. The CO2 pipeline is arranged as a plum blossom shape in the mined-out area in S3. The CO 2 pipeline is a perforatedCO 2 diffusion pipeline. The pipe spacing (DI) of theCO 2 gas pipeline is the same as the hole spacing (D2) on the perforatedCO 2 diffusion pipeline, specifically:

DI =D2 = 2R =2 x

where, R is the influence radius of a singleCO 2 release hole; "t"is the carbonation curing time of the cementing materials; s is the cross-sectional area of a single C02 release hole; X is the carbon sequestration potential of the cementing materials per unit mass after t hours of carbonation; n is the number of release holes in theCO 2 pipeline

, v is the flow rateof CO 2 in the main pipeline. The injected CO2 in S6 directly came from flue gas, which CO 2

concentration is 20%-80%. The monitoring and early warning in S7 could real-time and remotely monitoring the stress stateC02 leakage state of the filling body and the surrounding rock in the closed filling areas. The benefits of the above technical solutions in this invention are as follows: (1) The main raw materials of the filling body are solid wastes (slags and tailings), which could disposal a large amount of industrial solid waste at underground mine out areas. The technology turns wastes into treasures, meanwhile solve the environmental problems, such as land occupation and pollution caused by solid wastes stockpile; (2) The main cementing materials of the filling body are low-cost solid wastes with high calcium and magnesium contents (such as steel slag and construction waste). The replacement of Portland cement in cemented filling mining method could lower the cost of the whole process; (3) The carbonation curing of the filling body would fix a large amountof C02,which could assist with mitigation the global warming; (4) This invention patent presents an environment friendly, economical and safe technology.

Attached figures description Figure 1 is the process of the cemented filling system by mineral carbonation of tailings in this invention patent; Fig. 2 is the plan view of the process in closed filling area in the cemented filling method by mineral carbonation of tailings in this invention patent; Fig. 3 is the schematic diagram of the crosse section I-I in Fig. 2. Where, A-cementing material stock bin; B-water stock bin; C tailings stock bin; D-mixing station; E-filling pump; F-CO 2 source; G-valve switch on CO 2 pipeline; H-mine-out Area; I-carbonation influencing scope of a hole on CO 2 pipeline; J-exhaust fan; K-gas detection device; a-CO2 inlet; b-gas outlet; 1-ore body; 2-upper stage transportation roadway; 3- next stage transportation roadway; 4-CO 2 transportation pipeline; 5-filling slurry transportation pipeline; 6-perforated CO2 diffusion pipeline; 7-filling body; 8-gas discharge pipeline in sealed filling body ; 9- closed barrier of the filling area. Specific implementation methods In order to make clearer of the technical problems to be solved, technical solutions and advantages in this invention patent, a detailed description is given below in conjunction with the attached figures and specific implementation samples. The invention provides a cemented filling method by mineral carbonation of tailings. The method includes the following steps: S1: Crushed and ground cementitious material into powder. Use the whole tailings as the aggregate; S2: Prepare the filling slurry by fully stirring of the mixture containing cementitious materials, whole tailings in S1, water and additives ; S3: Pipelines for injecting CO2 gas was installed in the mine out area before the filling slurry was transported to the goaf. S4: Transport the filling slurry prepared in S2 to the filling station, and pump to the undergroud goaf. S5: Seal and block the filling area after the goaf is fully filled, to make sure the gas impermeability of the filling area; S6: After sealing the filling area for 24 hours, inject CO 2 gas by pipeline installed in S3 to curing the filling body, to make sure the compressive strength meets the requirements; S7: Real-time monitoring during S4-S6 for early warning, to make sure the safety of the enclosed filling area, Amongst, the cementing materials in S Iis solid wastes with low or no hydration activities, which include steel slag, construction wastes, and solid wastes containing calcium oxide, magnesium oxide, calcium hydroxide, magnesium hydroxide, calcium silicates or magnesium silicates. The cementing materials can react quickly with CO 2 and generate carbonates. The Blaine's number of the cementing materials is ground to 300~700 m 2 /kg. The whole tailings in S Iis made from any type of rocks, include ultramafic , mafic, neutral, acidic, and super-acid tailings. the mass ratio of cement to tailings in S2 is 3:7-1:1; the mass of the additive take up 0~10% of the mass of the cementing materials; and the liquid-solid ratio of the filler slurry is 0.20~0.40. The additive in S2 is catalysts that could promote the carbonation of the filling materials, including sodium carbonate, sodium bicarbonate, acetic acid, citric acid, and desulfurization gypsum, metallurgical slags, fly ashes, carbonic anhydrase, cyanobacteria.

The CO2 pipeline is arranged as a plum blossom shape in the mined-out area in S3. The CO 2 pipeline is a perforated CO 2 diffusion pipeline. The pipe spacing (D) of the CO 2 gas pipeline is the same as the hole spacing (D2) on the perforated CO 2 diffusion pipeline, specifically:

Di =D2 = 2R=2x

where, R is the influence radius of a single CO 2 release hole; "t"is the carbonation curing time of the cementing materials; s is the cross-sectional area of a single CO2 release hole; X is the carbon sequestration potential of the cementing materials per unit mass after t hours of carbonation; n is the number of release holes in the CO 2 pipeline

, v is the flow rate of CO 2 in the main pipeline. The injected CO2 in S6 directly came from flue gas, which CO 2

concentration is 20%-80%. The monitoring and early warning in S7 could real-time and remotely monitoring the stress state, CO2 leakage state of the filling body and the surrounding rock in the closed filling areas. The specific implementation process is described as follows: Step 1: Steel slag is selected as the carbonation cementing material. Steel slag as received is crushed, ground, and magnetic separated. The blaine's number of ground steel slag is 500 m 2/kg. Whole tailings is used as the aggregate of the filling body. Step 2: As shown in Figure 1, the steel slag treated in step 1 is stored in the cementing material stock bin (A), the whole tailings stored in tailings stock bin (C), and the water stored in the water stock bin (B) are fully mixed in the mixing station (D). The cement to taillings ratio is 3:7. No additives are added. The water to solid ratios in the filling slurry are

0.30, 0.35, and 0.40. Step 3: The abandoned wells, faults or cracks connected with the mined-out area (H) , and the "weak zone" of the caprock is filled and blocked with sealant. CO2 pipelines is set up in a plum blossom pattern (as shown in Figure 1). TheCO 2 pipeline in the mine-out area (H) has holes forCO 2 releasing. The carbonation influencing scope of a hole on CO2 pipeline (I) is a circle with a radius of R. Set up a valve switch on CO2 pipeline (G) at the sideof CO 2 inlet (a), which links theCO 2 source (F). Set exhaust fan (J) and gas detection devices (K) on the pipeline at the side of gas outlet (b). Step 4: The filling slurry prepared in step 2 is pumped to the mine-out area which is blocked in step 3 through the filling pump (E). The filled area is sealed with sealant after the filling is completed. Step 5: After the filling in step 4 is completed and the filling body is sealed and blocked for 24 hours, the flue gas with 20%of CO 2 is

injected for carbonation curing of the filling body. The CO2 gas is continuously supplied for 28 days to complete the curing. Step 6: After the carbonation curing in step 5 is completed, sampling and testing the strength and carbon content of the filling body. Adopt monitoring and early warning measures to make sure the stability and safety of filling bodies and surrounding rocks. The block and seal of the filled area is shown in Figures 2 and 3. Figure 3 shows the layout of theCO 2 pipeline in the sealed filling body. The upper part of the ore body (1) is the upper stage transportation roadway (2). The lower part the ore body (1) is the next stage transportation roadway (3). The upper part of the mine-out area is equipped with the filling slurry transportation pipeline (5). The filling body (7) is equipped with a perforatedCO 2 diffusion pipeline (6), which is connected to the externalCO 2 transportation pipe (4). At the bottom of the filling body (7) set up a gas discharge pipeline (8) and the closed barrier of the filling area (9). Table 1 lists the carbon content and compressive strength of the carbonated filling body in the implementation process.

Table 1 The carbon sequestration and compressive strength value of the prepared filling body

Strength (MPa) Carbon content (00) Number Water-solid ratio 3d 7d 28d 3d 7d 28d 1 0.30 4.67 5.42 6.24 0.72 1.10 1.19 2 0.35 5.45 6.70 6.86 1.07 1.15 1.23 3 0.40 3.26 4.86 5.01 1.09 1.16 1.23

The specific implementation samples mentioned above are the preferred ones in this invention patent. For the ordinary skilled workers in this area, there are several improvements and modifications can be made without departing from the principle of this invention patent. These improvements and modifications should also be regarded as the protection scope of this invention patent.

Claims (1)

1. CLAIMS 1.A cemented filling method by mineral carbonation of tailings is characterized in that it comprises the following steps: Sl: Crushed and ground cementitious material into powder. Use the whole tailings as the aggregate; S2: Prepare the filling slurry by fully stirring of the mixture containing cementitious materials, whole tailings in S1, water and additives ; S3: Pipelines for injecting CO2 gas was installed in the mine out area before the filling slurry was transported to the goaf. S4: Transport the filling slurry prepared in S2 to the filling station, and pump to the undergroud goaf. S5: Seal and block the filling area after the goaf is fully filled, to make sure the gas impermeability of the filling area; S6: After sealing the filling area for 24 hours, inject CO 2 gas by pipeline installed in S3 to curing the filling body, to make sure the compressive strength meets the requirements; S7: Real-time monitoring during S4-S6 for early warning, to make sure the safety of the enclosed filling area, 2. As claim 1 described, the attribute of the cemented filling method by mineral carbonation of tailings is: the cementing materials in S is solid wastes with low or no hydration activities, which include steel slag, construction wastes, and solid wastes containing calcium oxide, magnesium oxide, calcium hydroxide, magnesium hydroxide, calcium silicates or magnesium silicates. The cementing materials can react quickly withCO 2 and generate carbonates. The Blaine's number of the cementing materials is ground to 300~700 m 2 /kg. 3. As claim 1 described, the attribute of the cemented filling method by mineral carbonation of tailings is: the whole tailings in S is made from any type of rocks, include ultramafic , mafic, neutral, acidic, and super-acid tailings. 4.As claim 1 described, the attribute of the cemented filling method by mineral carbonation of tailings is: the mass ratio of cement to tailings in S2 is 3:7~1:1; the mass of the additive take up 0~10% of the mass of the cementing materials; and the liquid-solid ratio of the filler slurry is 0.20~0.40. 5. As claim 1 described, the attribute of the cemented filling method by mineral carbonation of tailings is: the additive in S2 is catalysts that could promote the carbonation of the filling materials, including sodium carbonate, sodium bicarbonate, acetic acid, citric acid, and desulfurization gypsum, metallurgical slags, fly ashes, carbonic anhydrase, cyanobacteria. 6. As claim 1 described, the attribute of the cemented filling method by mineral carbonation of tailings is: the CO 2 pipeline is arranged as a plum blossom shape in the mined-out area in S3. The CO 2 pipeline is a perforated CO2 diffusion pipeline. The pipe spacing (D1) of the CO 2 gas pipeline is the same as the hole spacing (D2) on the perforated CO 2 diffusion pipeline, specifically:

   D1= D2= 2R = 2x

   where, R is the influence radius of a single CO 2 release hole; "t"is the carbonation curing time of the cementing materials; s is the cross-sectional area of a single CO2 release hole; X is the carbon sequestration potential of the cementing materials per unit mass after t hours of carbonation; n is the number of release holes in the CO 2 pipeline ,

   v is the flow rate of CO2 in the main pipeline.

   7. As claim 1 described, the attribute of the cemented filling method by mineral carbonation of tailings is: the the injectedCO 2 in S6 directly came from flue gas, which CO 2 concentration is 20%-80%. As claim 1 described, the attribute of the cemented filling method by

   mineral carbonation of tailings is: the monitoring and early warning in S7

   could real-time and remotely monitoring the stress state, CO 2 leakage

   state of the filling body and the surrounding rock in the closed filling

   areas.