Method for solidifying heavy metal ions in nickel slag filling material

Abstract

The invention discloses a method for solidifying heavy metal ions in a nickel slag filling material, and belongs to the technical field of mine filling materials. The method comprises the following steps: sequentially carrying out anoxic pyrolysis (200-250 DEG C, O2 < = 3%), CO2 mineralization (300-350 DEG C, CO2 > = 90%) and liquid nitrogen shock cooling (the cooling rate is > = 50 DEG C / min) on the nickel slag to form an amorphous silicate glass body; and then mixing the thermally activated nickel slag with amino-functionalized activated carbon and MOFs loaded nano silicon dioxide, adding calcium-based montmorillonite, adding water, stirring, and hardening at normal temperature, so that heavy metal ions in the nickel slag filling material can be cured. The leaching rate of solidified and hardened heavy metal ions is lower than the national standard limit value of 1 mg / L, the compressive strength reaches 28.1 MPa, 15 tons of CO2 can be sealed for storage when every ten thousand tons of nickel slag are treated, and the method has high stability, low carbon property and industrial application potential.

Description

Technical Field

[0001] The present invention belongs to the technical field of mine filling materials, and specifically relates to a method for solidifying heavy metal ions in a nickel slag filling material. Background Art

[0002] Nickel slag generated during the mining process contains high concentrations of heavy metal ions such as chromium and cadmium. If directly used as a filling material, the leaching of heavy metals will cause serious pollution to soil and groundwater. Traditional nickel slag treatment methods mainly include physical sequestration, chemical stabilization, and bioremediation, etc., but they all have limitations such as high costs, increased carbon emissions, insufficient long-term stability, cumbersome operations, and difficulty in large-scale application.

[0003] CN 118702459 B discloses a nano-modified all-solid waste mine filling material, which enhances the material properties through nano-silica / titanium dioxide, but the nano-materials are costly and the process is complex; CN 104492372 A proposes a fly ash-nickel slag composite adsorbent material, but it focuses on wastewater treatment and does not solve the problem of heavy metal solidification in nickel slag itself in the filling material. Summary of the Invention

[0004] One technical problem solved by the present invention is to provide a method for solidifying heavy metal ions in a nickel slag filling material, with the heavy metal leaching rate being lower than the national standard limit of 1 mg / L, the compressive strength reaching 28.1 MPa, and 15 tons of CO2 being sequestered for every ten thousand tons of nickel slag treated, having both high stability, low carbon characteristics, and potential for industrial application.

[0005] To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0006] A method for solidifying heavy metal ions in a nickel slag filling material, after crushing the nickel slag to a particle size of <2 mm, performing multi-stage thermal activation to obtain thermally activated nickel slag: then mixing it with thermally activated nickel slag, amino-functionalized activated carbon, and metal-organic framework (MOFs)-supported nano-silica, adding calcium-based montmorillonite (Ca-MMT), and stirring with water until the slurry fluidity is 30 - 40 s, and hardening at room temperature for 72 hours, then the heavy metal ions (Cr, Cd) in the nickel slag filling material can be solidified; preferably, stirring with water until the slurry fluidity is 35 s.

[0007] In the above method, the multi-stage thermal activation of nickel slag is specifically as follows:

[0008] a) Anaerobic pyrolysis: Conduct anaerobic pyrolysis for 1 - 2 hours in an environment with an oxygen content of less than 3% and a temperature of 200 - 250 °C to remove volatile organic compounds in the nickel slag and promote the conversion of free Cd to CdS; preferably, the O2 content is 1.5% - 2.5%;

[0009] b) CO2 mineralization: Transfer the product of step a to a condition where the CO2 content is greater than 90%, the temperature is 300 - 350 °C, and the pressure is 0.5 - 1 MPa for 1 - 2 hours of CO2 mineralization to convert the heavy metal oxides in the nickel slag into carbonates; preferably, 300 - 340 °C, CO2 concentration 92% - 98%;

[0010] c) Quenching and amorphization: Adopt the method of liquid nitrogen jet cooling with a cooling rate ≥ 50 °C / min to rapidly cool the nickel slag to below 50 °C, forming an amorphous silicate glass body to lock heavy metal ions; preferably, the cooling rate is 50 - 70 °C / min to 30 - 45 °C.

[0011] In the said method, the CO2 is sourced from a power plant flue gas capture system with a purity ≥ 90%.

[0012] In the said method, the mass ratio of thermally activated nickel slag, amino-functionalized activated carbon, and MOFs-supported nano-silica is 6:2:2, 7:2:1, or 5:3:2; the addition amount of calcium-based montmorillonite is 5% of the mass of the nickel slag; the amino-functionalized activated carbon, MOFs-supported nano-silica, and calcium-based montmorillonite form a functionalized nano-composite material.

[0013] In the said method, the amino-functionalized activated carbon is prepared by immersing activated carbon in an ethanol solution containing 3-aminopropyltriethoxysilane and reacting at 80 °C for 6 hours, followed by washing and drying.

[0014] In the said method, the specific surface area of the activated carbon ≥ 800 m 2 / g, pore size 2 - 5 nm; preferably, the specific surface area of the activated carbon is 800 - 900 m 2 / g, pore size 3 nm; the mass fraction of 3-aminopropyltriethoxysilane is 10%.

[0015] In the said method, the MOFs-supported nano-silica is prepared by dispersing nano-SiO2 in a Zn(NO3)2 solution, adding 2-methylimidazole, and hydrothermal reacting at 60 °C for 12 hours.

[0016] In the said method, the particle size of nano-SiO2 is 50 - 100 nm, specific surface area 300 - 400 m 2 / g; the concentration of the Zn(NO3)2 solution is 0.1 mol / L; the molar ratio of Zn 2+ to 2-methylimidazole is 1:4; preferably, the particle size of nano-SiO2 is 60 - 100 nm, specific surface area 350 m 2 / g.

[0017] The method involves ion-exchanging calcium-based montmorillonite with 1 mol / L CaCl2 solution for 24 hours, centrifuging and drying it. The interlayer spacing is 1.2 - 1.5 nm, and the cation exchange capacity (CEC) ≥ 100 meq / 100 g. Preferably, the interlayer spacing is 1.2 - 1.4 nm, and the cation exchange capacity (CEC) is 100 - 110 meq / 100 g.

[0018] Amino-functionalized activated carbon targets and adsorbs Cr(VI) through mercapto (-SH) and amino (-NH2); MOFs loaded with nano-silica release chelating sites at pH > 7 to specifically capture Cd 2+ ; Calcium-based montmorillonite induces heavy metals to form layered double hydroxides through ion exchange, and the three work together to improve the heavy metal solidification efficiency and long-term stability.

[0019] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0020] (1) Through multi-stage thermal activation, free heavy metals are converted into stable chemical forms (sulfides, carbonates, and amorphous phases). Combining the targeted adsorption and mineral-induced effects of functionalized nanocomposites, the leaching rates of Cr and Cd are reduced to 0.02 mg / L and 0.04 mg / L respectively, far lower than the national standard limit of 1 mg / L.

[0021] (2) Using CO2 captured from power plant flue gas as a mineralizer to achieve carbon resource utilization and form a net negative carbon process.

[0022] (3) The liquid nitrogen quenching technology combined with the normal temperature hardening process greatly reduces the comprehensive energy consumption compared with the traditional high-temperature sintering method, and no complex equipment is required.

[0023] (4) The compressive strength of the solidified body reaches 28.1 MPa, which is suitable for the fields of mine filling and building materials, expanding the resource utilization scenarios of nickel slag. Specific embodiments

[0024] The following combines specific embodiments to further clarify the present invention. The embodiments are implemented on the premise of the technical solution of the present invention. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention.

[0025] Example 1

[0026] 1. Preparation of functionalized nanocomposites

[0027] Amino-functionalized activated carbon:

[0028] Activated carbon (specific surface area 850 m 2Immerse the activated carbon (specific surface area 900 m² / g, pore diameter 3 nm) in a 10% (mass fraction) ethanol solution of 3-aminopropyltriethoxysilane (APTES), react at 80 °C for 6 hours, wash and dry to obtain amino-functionalized activated carbon with a thiol density of 5.2 mmol / g.

[0029] ZIF-8@SiO2:

[0030] Disperse nano-SiO2 with a particle size of 60 nm and a specific surface area of 350 m² / g in a 0.1 mol / L Zn(NO3)2 solution, add 2-methylimidazole (molar ratio of Zn:2-methylimidazole = 1:4), and carry out a hydrothermal reaction at 60 °C for 12 hours with a loading rate of 87%. 2 / g of nano-SiO2 was dispersed in 0.1 mol / L Zn(NO3)2 solution, 2-methylimidazole was added (molar ratio of Zn 2+ :2-methylimidazole = 1:4), and hydrothermal reaction was carried out at 60 °C for 12 hours with a loading rate of 87%.

[0031] Calcium-based montmorillonite (Ca-MMT):

[0032] Carry out ion exchange of calcium-based montmorillonite (CEC = 110 meq / 100 g) with 1 mol / L CaCl2 solution for 24 hours, centrifuge and dry to obtain a layer spacing of 1.3 nm.

[0033] 2. Thermal activation and composite solidification of nickel slag

[0034] (1) Crush the nickel slag to a particle size <2 mm and carry out the following steps in sequence:

[0035] Anoxic pyrolysis: 200 °C, O2 content 2%, time 1.5 hours;

[0036] CO2 mineralization: 320 °C, CO2 concentration 95%, pressure 0.8 MPa, time 1.5 hours;

[0037] Quenching and amorphization: Spray cooling with liquid nitrogen, cooling rate 60 °C / min to 40 °C.

[0038] (2) Mix the thermally activated nickel slag, amino-functionalized activated carbon and ZIF-8@SiO2 in a mass ratio of 6:2:2, and add 5% Ca-MMT;

[0039] (3) Add water and stir until the slurry fluidity is 35 s, pour it into a mold and cure at room temperature for 72 hours to solidify the heavy metal ions in the nickel slag filling material.

[0040] Example 2

[0041] 1. Preparation of functionalized nanocomposites

[0042] Amino-functionalized activated carbon:

[0043] The activated carbon (specific surface area 900 m 2The activated carbon (specific surface area 800 m² / g, pore diameter 3 nm) was immersed in a 10% ethanol solution of 3-aminopropyltriethoxysilane (APTES) and reacted at 80 °C for 6 hours. After washing and drying, amino-functionalized activated carbon with a thiol density of 5.5 mmol / g was obtained.

[0044] ZIF-8@SiO2:

[0045] The nano-SiO2 with a particle size of 80 nm and a specific surface area of 350 m² / g was dispersed in a 0.1 mol / L Zn(NO3)2 solution, and 2-methylimidazole was added (molar ratio of Zn:2-methylimidazole = 1:4). Hydrothermal reaction was carried out at 60 °C for 12 hours with a loading rate of 90%. 2 / g was dispersed in 0.1 mol / L Zn(NO3)2 solution, and 2-methylimidazole was added (molar ratio of Zn 2+ :2-methylimidazole = 1:4), and hydrothermal reaction was carried out at 60 °C for 12 hours with a loading rate of 90%.

[0046] Calcium-based montmorillonite (Ca-MMT):

[0047] The calcium-based montmorillonite (CEC = 105 meq / 100 g) was ion-exchanged with 1 mol / L CaCl2 solution for 24 hours, centrifuged and dried, and the interlayer spacing was 1.4 nm.

[0048] 2. Thermal activation and composite curing of nickel slag

[0049] (1) The nickel slag was crushed to a particle size <2 mm and the following steps were carried out in sequence:

[0050] Anoxic pyrolysis: 230 °C, O2 content 1.5%, time 2 hours;

[0051] CO2 mineralization: 340 °C, CO2 concentration 92%, pressure 1 MPa, time 1 hour;

[0052] Quenching and amorphization: Liquid nitrogen injection cooling, cooling rate 70 °C / min to 30 °C.

[0053] (2) The thermally activated nickel slag, amino-functionalized activated carbon and ZIF-8@SiO2 were mixed at a mass ratio of 7:2:1, and 5% Ca-MMT was added;

[0054] (3) Water was added and stirred until the fluidity of the slurry was 35 s, and then it was poured into a mold and cured at room temperature for 72 hours.

[0055] Example 3

[0056] 1. Preparation of functionalized nanocomposites

[0057] Amino-functionalized activated carbon:

[0058] The activated carbon (specific surface area 800 m² 2(The activated carbon with a pore size of 3 nm and a specific surface area of 1000 m² / g was immersed in a 10% ethanol solution of 3-aminopropyltriethoxysilane (APTES) and reacted at 80 °C for 6 hours. After washing and drying, amino-functionalized activated carbon with a thiol density of 4.8 mmol / g was obtained.)

[0059] ZIF-8@SiO2:

[0060] Mesoporous SiO2 with a particle size of 100 nm and a specific surface area of 350 m² 2 / g was dispersed in a 0.1 mol / L Zn(NO3)2 solution, and 2-methylimidazole (molar ratio of Zn 2+ :2-methylimidazole = 1:4) was added. The hydrothermal reaction was carried out at 60 °C for 12 hours with a loading rate of 83%.

[0061] Calcium-based montmorillonite (Ca-MMT):

[0062] Sodium-based montmorillonite (CEC = 100 meq / 100 g) was ion-exchanged with a 1 mol / L CaCl2 solution for 24 hours, centrifuged and dried, with an interlayer spacing of 1.2 nm.

[0063] 2. Thermal activation and composite curing of nickel slag

[0064] (1) The nickel slag was crushed to a particle size of <2 mm and subjected to the following steps in sequence:

[0065] Anoxic pyrolysis: 250 °C, O2 content of 2.5%, time of 1 hour;

[0066] CO2 mineralization: 300 °C, CO2 concentration of 98%, pressure of 0.5 MPa, time of 2 hours;

[0067] Rapid quenching and amorphization: Liquid nitrogen jet cooling, cooling rate of 50 °C / min to 45 °C.

[0068] (2) The thermally activated nickel slag, amino-functionalized activated carbon and ZIF-8@SiO2 were mixed in a mass ratio of 5:3:2, and 5% Ca-MMT was added;

[0069] (3) Water was added and stirred until the fluidity of the slurry was 35 s, and then it was poured into a mold and cured at room temperature for 72 hours.

[0070] The solidified and hardened bodies of the above examples were tested for the Cd leaching rate according to GB / T 14848-2017 "Groundwater Quality Standard", and the Cr(VI) leaching rate was tested according to HJ 557-2009 "Solid Waste Leaching Toxicity Leaching Method - Horizontal Oscillation Method". The compressive strength of the hardened bodies was tested according to GB / T 17671-2021 "Test Method for the Strength of Cement Mortar (ISO Method)". The data are shown in Table 1.

[0071] Table 1 Performance test results of the solidified and hardened bodies prepared in Examples 1-3

[0072] Index Example 1 Example 2 Example 3 Cd leaching rate (mg / L) 0.03 0.04 0.03 Cr(VI) leaching rate (mg / L) 0.02 0.03 0.02 Compressive strength (MPa) 28.1 26.3 23.8 <![CDATA[Carbon footprint (kg CO2 / ton)]]> -100 -120 -90

[0073] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for solidifying heavy metal ions in nickel slag filling material, characterized in that: The following steps are involved: (1) Crushing the nickel slag to a particle size of <2 mm and performing multi-stage thermal activation to obtain thermally activated nickel slag: (2) mixing thermally activated nickel slag, amino-functionalized activated carbon, and MOFs-loaded nano-silica, and adding calcium-based montmorillonite; (3) Add water and stir until the slurry fluidity is 30-40 seconds, and harden at room temperature to solidify the heavy metal ions in the nickel slag filling material.

2. The method according to claim 1, characterized in that: The multi-stage thermal activation is specifically: a) Anoxic pyrolysis: 1-2 hours at an oxygen content of ≤3% and a temperature of 200-250°C; b) CO2 mineralization: react for 1-2 hours at a CO2 concentration ≥ 90%, a temperature of 300-350°C, and a pressure of 0.5-1MPa; c) Rapid cooling and amorphization: Use liquid nitrogen spray to cool to below 50°C, with a cooling rate of ≥50°C / min, so that the nickel slag is quickly cooled to below 50°C to form an amorphous silicate glass body.

3. The method according to claim 2, characterized in that: In step b), CO2 comes from the flue gas capture system of the power plant, with a purity of ≥90%.

4. The method according to claim 1, characterized in that: The mass ratio of thermally activated nickel slag, amino-functionalized activated carbon, and MOFs-loaded nano-silica is 6:2:2, 7:2:1, or 5:3:2; and the added amount of calcium-based montmorillonite is 5% of the mass of the nickel slag.

5. The method according to claim 1, characterized in that: The amino-functionalized activated carbon is prepared by immersing the activated carbon in an ethanol solution containing 3-aminopropyltriethoxysilane and reacting the solution at 80° C. for 6 hours.

6. The method according to claim 5, characterized in that: The specific surface area of ​​the activated carbon is ≥800m 2 / g, pore size 2-5nm.

7. The method according to claim 1, characterized in that: The MOFs loaded nano silicon dioxide is prepared by dispersing nano SiO2 in a Zn(NO3)2 solution, adding 2-methylimidazole, and hydrothermal treatment at 60°C for 12 hours, and the ZIF-8 loading rate is ≥85%.

8. The method according to claim 7, characterized in that: The particle size of SiO2 is 50-100nm and the specific surface area is 300-400m 2 / g; the concentration of Zn(NO3)2 solution is 0.1mol / L; Zn 2+ The molar ratio of 2-methylimidazole is 1:

4.

9. The method according to claim 1, characterized in that: The calcium-based montmorillonite is treated by ion exchange with a 1 mol / L CaCl2 solution for 24 hours, and has an interlayer spacing of 1.2-1.5 nm and a cation exchange capacity of ≥100 meq / 100 g.