A method for harmless treatment of rare earth smelting waste residue

Abstract

The application discloses a harmless treatment method of rare earth smelting waste residue, and relates to the technical field of hazardous waste treatment and disposal. First, organic barium salt is added to the rare earth smelting waste residue, and after stirring reaction is completed, carbonated mineralization bacteria culture solution is added to induce mineralization reaction. After the reaction is completed, the rare earth smelting waste residue is pressed and compacted, carbonized and cured, and dried after curing, so that the harmless treatment of the rare earth smelting waste residue is realized. The method for the harmless treatment of the rare earth smelting waste residue is green, environment-friendly, can reduce the radioactivity of the rare earth smelting waste residue in situ, has good cementing effect on the rare earth smelting waste residue, and does not affect subsequent secondary utilization.

Description

Technical Field

[0001] This invention relates to the field of hazardous waste treatment and disposal technology, and in particular to a method for the harmless treatment of rare earth smelting waste residue. Background Technology

[0002] Rare earth minerals are polymetallic associated minerals, containing not only iron, niobium, and rare earth elements, but also large amounts of the radioactive elements thorium and uranium. Due to the low industrial value of thorium and the low grade of uranium, the vast majority of thorium and uranium introduced into the ore ends up in the waste residue. This significantly increases the radioactivity of the rare earth smelting waste residue compared to the natural environment. Improper disposal not only threatens the ecological environment and human health but also leads to resource waste. Therefore, developing a harmless treatment technology for rare earth smelting waste residue is of great significance for the long-term effective treatment and disposal of rare earth smelting waste residue and the sustainable development of the rare earth industry.

[0003] Currently, solidification / stabilization technologies are the main technologies for the harmless disposal of hazardous waste, including cement solidification and asphalt solidification technologies. However, cement solidification technology is prone to problems such as uneven mixing, premature or delayed solidification, and high leaching rates of pollutants during operation; asphalt solidification technology is prone to combustion when sealing waste containing oxidants. In addition, these technologies have disadvantages such as high cost, large volume increase, and difficulty in reusing the solidified rare earth tailings.

[0004] In recent years, microbial-induced mineralization and solidification of tailings / slag has attracted considerable attention from researchers. Microbial-induced carbonate precipitation (MICP) technology for solidifying rare earth smelting waste offers advantages such as environmental friendliness, low cost, and small footprint, without affecting subsequent reuse processes and reducing resource waste. The MICP process has several driving mechanisms. One relies on urease produced by microorganisms to decompose urea, forming carbonate ions that combine with exogenous calcium ions to form calcium carbonate precipitate. Another utilizes carbonic anhydrase to catalyze the formation of carbonate ions from carbon dioxide, ultimately resulting in calcium carbonate precipitate. The carbonate ions formed during MICP can also form carbonates with heavy metals and radioactive nuclides, reducing their mobility and bioavailability. However, urease-driven MICP may produce high concentrations of ammonium ions and ammonia as byproducts, potentially harming the environment and human health. High concentrations of ammonia can lead to eutrophication, hypoxia, and harm to aquatic organisms; ammonia can also form heavy metal-ammonia complexes, enhancing the mobility of heavy metal ions. When calcium chloride is used as a calcium source, the chloride ions introduced along with exogenous calcium ions may further pollute groundwater. In contrast, carbonic anhydrase bacteria can avoid producing high concentrations of ammonium ions and ammonia, reducing the possibility of secondary pollution. Furthermore, while the traditional MIP process can bind rare earth smelting waste slag, its effectiveness in reducing the radiation dose from the smelting waste slag is limited. When using MIP technology to treat low-level radioactive rare earth waste slag, if carbonic anhydrase bacteria can be used, utilizing calcium sulfate in the rare earth tailings as a calcium source, and reducing the amount of urea and calcium chloride used, the possibility of secondary pollution will be effectively reduced, achieving harmless treatment. Summary of the Invention

[0005] The purpose of this invention is to provide a method for the harmless treatment of rare earth smelting waste residue, so as to solve the problems existing in the prior art and realize the harmless treatment of rare earth smelting waste residue.

[0006] To achieve the above objectives, the present invention provides the following solution:

[0007] This invention provides a method for harmlessly treating rare earth smelting waste residue, comprising the following steps:

[0008] (1) Add organic barium salt to rare earth smelting waste residue and stir to react;

[0009] (2) Add carbonate mineralizing bacteria culture solution to the rare earth smelting waste residue after step (1) to induce mineralization reaction.

[0010] (3) The rare earth smelting waste residue after step (2) is compacted under pressure, carbonized and cured, and then dried after curing to achieve the harmless treatment of rare earth smelting waste residue.

[0011] Furthermore, the reaction temperature for the induced mineralization reaction is 25–37°C, and the reaction time is 1–14 days;

[0012] Furthermore, the specific activity of the rare earth smelting waste residue is less than 4 × 10⁻⁶. 11 Bq / kg.

[0013] Furthermore, the OD of the carbonate mineralizing bacteria culture medium 600 The value ranges from 0.5 to 2.5.

[0014] Further, the organic barium salt is barium acetate or barium lactate; in step (1), the organic barium salt is added in the form of a solution, and the concentration of the organic barium salt solution is 0.01 to 0.5 mol / L.

[0015] Further, the organic barium salt solution is added to the rare earth smelting waste residue at a solid-liquid ratio of 1g:0.3-0.8mL.

[0016] Furthermore, the stirring reaction temperature in step (1) is 10–35°C, and the reaction time is 0.5–24 h.

[0017] In step (1), taking barium acetate as an example, the reaction equation is as follows: CaSO4+Ba(CH3COO)2→BaSO4+Ca(CH3COO)2. In step (2), after adding carbonate mineralizing bacteria and solidifying culture medium, calcium acetate is converted into calcium carbonate, carbon dioxide and water. The reaction equation is as follows: Ca(CH3COO)2→CaCO3+CO2+H2O.

[0018] Furthermore, the rare earth smelting waste residue is a solid waste generated after rare earth minerals are extracted by hydrometallurgical processes, which contains a large amount of calcium sulfate and calcium sulfate dihydrate.

[0019] Furthermore, the carbonate-mineralizing bacteria culture medium is a culture medium of one or more carbonate-mineralizing strains. The inoculation ratio is 1-3% (bacterial solution / culture medium).

[0020] The culture medium used for the carbonate mineralizing bacteria culture broth consists of molasses 1–3 g / L, soybean peptone 1–5 g / L, potassium dihydrogen phosphate 0.1–0.5 g / L, and zinc sulfate 0.05–0.5 g / L. The initial pH of the culture medium is 6–9; the carbonate mineralizing bacteria culture broth is obtained after culturing for 24–48 hours.

[0021] Furthermore, the carbonate mineralizing strains include Bacillus mucilaginosus (CGMCC1.0910), Bacillus subtilis (ATCC 6633), Oligotrophomonas radiata (ACTT DSM14405T), or Rhodopseudomonas palustris (ATCC 17001).

[0022] Furthermore, the solidified culture medium consists of molasses 1-3 g / L, soybean peptone 1-5 g / L, potassium dihydrogen phosphate 0.1-0.5 g / L and zinc sulfate 0.05-0.5 g / L.

[0023] Furthermore, the carbonization curing temperature is 20–35°C, and the carbonization curing humidity is 70% ± 5%; the gas used for carbonization curing is carbon dioxide or industrial waste gas containing carbon dioxide, with a gas concentration of 20%–100% and a gas pressure of 0–0.20 MPa.

[0024] This invention first reconstructs the phase composition of rare earth smelting waste slag. By adding barium acetate solution to the waste slag and mixing it uniformly, after a certain reaction time, the calcium sulfate in the waste slag is converted into barium sulfate and calcium acetate. Then, a carbonate mineralizing agent and culture medium are added to the waste slag. Through microbial-induced mineralization, the calcium acetate is decomposed and converted into calcium carbonate. The formation of barium sulfate effectively reduces radiation dose, and the formation of calcium carbonate binds the rare earth smelting waste slag together, preventing wind erosion and the migration and diffusion of pollutants, thus achieving the goal of harmless disposal of rare earth smelting waste slag. The treatment method of this invention is simple and environmentally friendly.

[0025] The present invention discloses the following technical effects:

[0026] This invention applies organic barium salts to microbial-induced carbonate precipitation technology, which induces the production of biogenic calcium carbonate by carbonate mineralizing bacteria, while simultaneously binding rare earth smelting waste slag together to form a whole. This effectively reduces the risk of rare earth smelting waste slag migrating and spreading with the wind and the leaching of pollutants. In addition, barium sulfate is also generated in the reaction system and doped into the rare earth smelting waste slag, which can effectively reduce the radiation dose of the rare earth smelting waste slag.

[0027] The method for harmlessly treating rare earth smelting waste slag of the present invention has the advantages of being green, environmentally friendly, reducing the radioactivity of rare earth smelting waste slag in situ, and having a good cementing effect on rare earth smelting waste slag without affecting subsequent secondary utilization.

[0028] The barium salt used in this invention is organic barium acid, which reacts with rare earth smelting waste slag to form barium sulfate and organic calcium acid. Carbonate mineralizing bacteria can further convert the organic calcium acid into biogenic calcium carbonate, achieving the purpose of cementing the rare earth smelting waste slag. This invention does not require the addition of a calcium source; it uses calcium sulfate, calcium sulfate dihydrate, and the converted organic calcium acid from the rare earth smelting waste slag as the calcium source, resulting in low cost, minimal weight gain during the treatment process, and minimal volume increase.

[0029] Traditional urea decomposition-driven microbial mineralization processes produce high concentrations of ammonium ions and ammonia as byproducts, which may harm the environment and human health. High concentrations of ammonia can lead to eutrophication, hypoxia, and harm to aquatic organisms; ammonia can also form heavy metal-ammonia complexes with heavy metals, thereby enhancing the mobility of heavy metal ions. This invention uses carbonate mineralizing bacteria to convert organic acid calcium into biogenic calcium carbonate without adding urea, thus avoiding secondary pollution from ammonium ions and ammonia.

[0030] Traditional microbial-induced calcium carbonate precipitation processes typically use calcium chloride as the calcium source. When microorganisms utilize this calcium source to form biogenic calcium carbonate, chloride ions introduced along with exogenous calcium ions may migrate within the reaction system, potentially further contaminating groundwater. This invention eliminates the need for an additional calcium source and reduces the introduction of chloride ions during the treatment process, mitigating the environmental risks to groundwater caused by chloride ion migration. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0032] Figure 1 This is a process flow diagram of the present invention.

[0033] Figure 2 The images show the XRD patterns of rare earth smelting waste residue after treatment in the control group and examples 1-4 of this invention. Detailed Implementation

[0034] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0035] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0036] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0037] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and its embodiments are merely exemplary.

[0038] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0039] Analysis of the composition of rare earth smelting waste revealed that it contains large amounts of calcium sulfate and calcium sulfate dihydrate, suggesting a potential conversion into calcium carbonate. Comparison of the solubility products of different sparingly soluble substances showed that barium sulfate (1.1 × 10⁻⁶) was the most abundant. -10 )< Calcium carbonate (3.36×10 -9 Barium carbonate (5.1×10) -9 )< Calcium sulfate (9.1×10 -6 Based on the principle of conversion from sparingly soluble substances to even less soluble substances, when a soluble barium salt solution is added to rare earth smelting waste slag, calcium sulfate and calcium sulfate dihydrate react with barium ions to form even less soluble barium sulfate, releasing some calcium ions. These calcium ions can serve as a calcium source in the subsequent MIP process, forming calcium carbonate precipitate. Therefore, by adding barium salt solution to adjust the MIP process, first forming barium sulfate and organic acid calcium, a remediation effect can be achieved while avoiding secondary pollution, truly achieving harmless treatment of rare earth smelting waste slag.

[0040] In the following embodiments and control groups of this invention, the main constituent elements of rare earth smelting waste slag before treatment were: Ca, 12.143%; Fe, 9.994%; S, 8.061%; P, 0.849%; Ce, 0.81%; Ba, 0.644%; Pb, 0.506% and Th, 0.495%. XRF results before treatment of the rare earth smelting waste slag showed that the main components were: CaO, 29.80%; SO3, 24.95%; P2O5, 18.47%; Fe2O3, 17.36%; CeO2, 1.04%; Nd2O3, 1.03%; and others, 7.35%.

[0041] control group

[0042] (1) Add deionized water to 100g of rare earth smelting waste residue at a solid-liquid ratio of 1g:0.3mL, stir evenly for 30min at 25℃, and let stand for 1h.

[0043] (2) Add 20 mL of deionized water to the rare earth smelting waste residue from step (1), stir thoroughly, and incubate at room temperature for 7 days.

[0044] (3) After the cultivation is completed, the rare earth smelting waste residue from step (2) is compacted under pressure, and then dried after pressure carbonization curing to complete the treatment. The carbonization curing temperature is 30℃, the carbonization curing humidity is 70%, carbon dioxide gas is used for carbonization curing, the gas concentration is 20%, and the gas pressure is 0.1MPa.

[0045] The obtained samples underwent α and β activity tests, radon concentration tests, wind tunnel experiments, unconfined compressive strength tests, and leaching experiments for heavy metals and radionuclides. α and β activities were measured using an MR-50 radiation detector according to the operating manual. Radon evolution rate was measured using a RAD7. Wind erosion loss was measured using an AF1300 wind tunnel test instrument, with test wind speeds of 6, 9, and 12 m / s. Unconfined compressive strength was measured using a general-purpose compression tester. Leachate solutions were prepared using the sulfuric acid-nitric acid method. The content of heavy metal elements in the leachate was determined using a flame atomic absorption spectrophotometer, and the content of rare earth element Ce and radionuclides Th and U was determined using inductively coupled plasma atomic emission spectrometry.

[0046] The radiation dose to the control group before treatment was 0.535 μSv / h, which decreased to 0.412 μSv / h after treatment, a reduction of 0.123 μSv / h. The radon excretion rate per surface after treatment was 0.312 Bq·m³. -2 ·s -1 The radon release rate on both sides was 0.162 Bq·m³. -2 ·s -1The leaching concentrations of Cu, Pb, Zn, and Cd were 10.407, 60.613, 6.697, and 2.264 mg / kg, respectively; the leaching concentrations of Th and U were 0.613 and 0.236 mg / kg, respectively. After treatment, the unconfined compressive strength of the cemented body was 0.34 MPa, and the wind erosion losses at 6, 9, and 12 m / s were 0.3378, 0.9970, and 1.2750 g / min, respectively. The Ce content was 0.81% before treatment and 0.81% after treatment.

[0047] Implementation Example 1

[0048] (1) Add 0.1mol / L barium acetate solution to 100g of rare earth smelting waste residue at a solid-liquid ratio of 1g:0.3mL, stir evenly at 30℃ for 60min, and let stand for 24h to convert part of the calcium sulfate in the waste residue into barium sulfate and calcium acetate.

[0049] (2) Add 20 mL of OD to the rare earth smelting waste residue. 600 The 1.0% carbonate mineralizing bacteria culture solution was thoroughly stirred and incubated at room temperature for 7 days. The carbonate mineralizing bacteria culture solution was obtained by inoculating a solidified medium with 1% *Bacillus mucilaginosus* (CGMCC1.0910) and 1% *Bacillus subtilis* (ATCC 6633) and incubating for 24 hours. The solidified medium consisted of 3 g / L molasses, 5 g / L soybean peptone, 0.5 g / L potassium dihydrogen phosphate, and 0.05 g / L zinc sulfate.

[0050] (3) After the cultivation is completed, the rare earth smelting waste residue from step (2) is compacted under pressure, and then dried after pressure carbonization curing to complete the harmless treatment. The carbonization curing temperature is 30℃, the carbonization curing humidity is 70%, carbon dioxide gas is used for carbonization curing, the gas concentration is 30%, and the gas pressure is 0.1MPa.

[0051] The detection method was the same as the control group. After the harmless treatment in Example 1, the radiation dose of rare earth smelting waste slag decreased from 0.535 μSv / h to 0.292 μSv / h, a reduction of 0.243 μSv / h, which is 1.98 times the reduction of the control group. The radon gas evolution rate of the rare earth smelting waste slag decreased by 30.77% compared with the control group. The leaching rates of heavy metals Cu, Pb, Zn, and Cd in the rare earth smelting waste slag decreased by 36.85%, 66.74%, 44.38%, and 62.15% respectively compared with the control group. The leaching rates of radionuclides thorium and uranium in the rare earth smelting waste slag decreased by 32.79% and 21.61% respectively compared with the control group. Therefore, after treatment by this method, the unconfined compressive strength can be significantly improved, and the radiation dose, wind erosion loss, and leaching concentration of heavy metals and radionuclides can be reduced.

[0052] The XRD results of the processed samples are shown in the figure. Figure 2 XRD results showed that the rare earth smelting waste slag contained a large amount of calcium sulfate and calcium sulfate dihydrate before harmless treatment. After harmless treatment, a large number of diffraction peaks of barium sulfate and diffraction peaks of biogenic calcium carbonate (calcite, aragonite and spheroidite) formed under the action of carbonate mineralizing bacteria appeared.

[0053] After treatment, the compressive strength of the cemented body of the rare earth smelting waste slag obtained in Example 1 was 1.47 MPa, which was 4.32 times that of the control group. The wind erosion losses of the cemented body at 6 m / s, 9 m / s, and 12 m / s after treatment were 0.2688 g / min, 0.5988 g / min, and 0.9626 g / min, respectively, which were reduced by 20.43%, 39.93%, and 24.50% compared with the control group. The Ce element content before treatment was 0.81%, and the content after treatment was also 0.81%. The rare earth element content before and after treatment remained basically unchanged, indicating that this method does not affect the secondary utilization of rare earth smelting waste slag.

[0054] Implementation Example 2

[0055] (1) Add 0.2 mol / L barium acetate solution to 100g of rare earth smelting waste residue at a solid-liquid ratio of 1g:0.3mL, stir evenly at 35℃ for 60min, and let stand for 24h to convert part of the calcium sulfate in the waste residue into barium sulfate and calcium acetate.

[0056] (2) Add 20 mL of OD to the rare earth smelting waste residue. 600 The carbonate mineralizing bacteria culture medium was prepared at 2.0 μL and incubated at room temperature for 14 days after thorough stirring. The carbonate mineralizing bacteria culture medium was obtained by inoculating a solidified medium with 3% *Bacillus mucilaginosus* (CGMCC1.0910), 3% *Bacillus subtilis* (ATCC 6633), 1% *Oligotrophomonas rhizophilus* (ACTTDSM14405T), and 1% *Rhodopseudomonas palustris* (ATCC 17001), and incubating for 24 hours. The solidified medium consisted of 2.5 g / L molasses, 4.5 g / L soybean peptone, 0.4 g / L potassium dihydrogen phosphate, and 0.03 g / L zinc sulfate.

[0057] (3) After the cultivation is completed, the rare earth smelting waste residue from step (2) is compacted under pressure, and then dried after pressure carbonization curing to complete the harmless treatment. The carbonization curing temperature is 35℃, the carbonization curing humidity is 75%, carbon dioxide gas is used for carbonization curing, the gas concentration is 50%, and the gas pressure is 0.2MPa.

[0058] The detection method was the same as the control group. After the harmless treatment in Example 2, the radiation dose of rare earth smelting waste slag decreased from 0.535 μSv / h to 0.313 μSv / h, a reduction of 0.222 μSv / h, which is 1.80 times the reduction of the control group. The radon gas evolution rate of the rare earth smelting waste slag decreased by 28.53% compared with the control group. The leaching rates of heavy metals Cu, Pb, Zn, and Cd in the rare earth smelting waste slag decreased by 41.52%, 67.91%, 45.59%, and 61.40% respectively compared with the control group. The leaching rates of radionuclides thorium and uranium in the rare earth smelting waste slag decreased by 54.00% and 30.93% respectively compared with the control group. Therefore, after treatment by this method, the unconfined compressive strength can be significantly improved, and the radiation dose, wind erosion loss, and leaching concentration of heavy metals and radionuclides can be reduced.

[0059] The XRD results of the processed samples are shown in the figure. Figure 2 XRD results showed that the spectrum was similar to that of Example 1, proving the formation of barium sulfate and biogenic calcium carbonate formed under the action of carbonate mineralizing bacteria.

[0060] After treatment, the compressive strength of the solidified rare earth smelting waste slag was 1.49 MPa, which was 4.38 times that of the control group. The wind erosion losses of the solidified body at 6 m / s, 9 m / s, and 12 m / s were 0.2636 g / min, 0.5944 g / min, and 0.9394 g / min, respectively, which were reduced by 21.97%, 40.38%, and 26.32% compared with the control group. The Ce element content before treatment was 0.81%, and the content after treatment was 0.80%. The difference in rare earth element content before and after treatment was not significant, indicating that this method does not affect the secondary utilization of rare earth smelting waste slag.

[0061] Implementation Example 3

[0062] (1) Add 0.2 mol / L barium acetate solution to 100g of rare earth smelting waste residue at a solid-liquid ratio of 1g:0.5mL, stir evenly at 30℃ for 60min, and let stand for 12h to convert part of the calcium sulfate in the waste residue into barium sulfate and calcium acetate.

[0063] (2) Add 30 mL of carbonate mineralizing bacteria and solidification culture medium to the rare earth smelting waste residue, stir thoroughly, and incubate at room temperature for 14 days. The carbonate mineralizing bacteria culture solution was obtained by inoculating 2% Bacillus mucilaginosus (CGMCC1.0910) and 1% Rhodopseudomonas palustris (ATCC 17001) into the solidification culture medium and incubating for 24 h. The solidification culture medium consisted of 3 g / L molasses, 4.5 g / L soybean peptone, 0.4 g / L potassium dihydrogen phosphate, and 0.05 g / L zinc sulfate.

[0064] (3) After the cultivation is completed, the rare earth smelting waste residue from step (2) is compacted under pressure, and then dried after pressure carbonization curing to complete the harmless treatment. The carbonization curing temperature is 30℃, the carbonization curing humidity is 70%, carbon dioxide gas is used for carbonization curing, the gas concentration is 25%, and the gas pressure is 0.15MPa.

[0065] The detection method was the same as the control group. After the harmless treatment in Example 3, the radiation dose of rare earth smelting waste slag decreased from 0.535 μSv / h to 0.279 μSv / h, a reduction of 0.256 μSv / h, which is 2.08 times the reduction of the control group. The radon gas evolution rate of the rare earth smelting waste slag was reduced by 37.82% compared with the control group. The leaching rates of heavy metals Cu, Pb, Zn, and Cd were reduced by 38.34%, 67.85%, 46.81%, and 68.86% respectively compared with the control group; the leaching rates of radionuclides thorium and uranium were reduced by 61.66% and 47.03% respectively compared with the control group. Therefore, after treatment by this method, the unconfined compressive strength can be significantly improved, and the radiation dose, wind erosion loss, and leaching concentration of heavy metals and radionuclides can be reduced.

[0066] The XRD results of the processed samples are shown in the figure. Figure 2 XRD results showed that the spectrum was similar to that of Example 1, proving the formation of barium sulfate and biogenic calcium carbonate formed under the action of carbonate mineralizing bacteria.

[0067] After treatment, the compressive strength of the solidified rare earth smelting waste slag was 1.68 MPa, which was 4.94 times that of the control group. The wind erosion losses of the solidified body at 6 m / s, 9 m / s, and 12 m / s were 0.2162 g / min, 0.5564 g / min, and 0.7832 g / min, respectively, which were reduced by 36.00%, 44.19%, and 38.57% compared with the control group. The Ce element content before treatment was 0.81%, and the content after treatment was 0.79%. The difference in rare earth element content before and after treatment was not significant, indicating that this method does not affect the secondary utilization of rare earth smelting waste slag.

[0068] Implementation Example 4

[0069] (1) Add 0.2 mol / L barium acetate solution to 100g of rare earth smelting waste residue at a solid-liquid ratio of 1g:0.8mL, stir evenly at 35℃ for 60min, and let stand for 24h to convert part of the calcium sulfate in the waste residue into barium sulfate and calcium acetate.

[0070] (2) Add 30 mL of carbonate mineralizing bacteria and solidification culture medium to the rare earth smelting waste residue, stir thoroughly, and incubate at room temperature for 14 days. The carbonate mineralizing bacteria culture solution was obtained by inoculating 3% Bacillus mucilaginosus (CGMCC1.0910) and 3% Bacillus subtilis (ATCC 6633) into the solidification culture medium and culturing for 24 h. The solidification culture medium consisted of 3 g / L molasses, 5 g / L soybean peptone, 0.4 g / L potassium dihydrogen phosphate, and 0.01 g / L zinc sulfate.

[0071] (3) After the cultivation is completed, the rare earth smelting waste residue from step (2) is compacted under pressure, and then dried after pressure carbonization curing to complete the harmless treatment. The carbonization curing temperature is 35℃, the carbonization curing humidity is 75%, carbon dioxide gas is used for carbonization curing, the gas concentration is 20%, and the gas pressure is 0.10MPa.

[0072] The detection method was the same as the control group. After the harmless treatment in Example 4, the radiation dose of rare earth smelting waste slag decreased from 0.535 μSv / h to 0.292 μSv / h, a reduction of 0.243 μSv / h, which is 1.98 times the reduction of the control group. The radon gas evolution rate of the rare earth smelting waste slag was reduced by 19.55% compared with the control group. The leaching rates of heavy metals Cu, Pb, Zn, and Cd were reduced by 41.65%, 68.98%, 44.44%, and 56.76% respectively compared with the control group; the leaching rates of radionuclides thorium and uranium were reduced by 60.85% and 57.20% respectively. Therefore, after treatment by this method, the unconfined compressive strength can be significantly improved, and the radiation dose, wind erosion loss, and leaching concentration of heavy metals and radionuclides can be reduced.

[0073] The XRD results of the processed samples are shown in the figure. Figure 2 XRD results showed that the spectrum was similar to that of Example 1, proving the formation of barium sulfate and biogenic calcium carbonate formed under the action of carbonate mineralizing bacteria.

[0074] After treatment, the compressive strength of the solidified rare earth smelting waste slag was 1.39 MPa, which was 4.09 times that of the control group. The wind erosion losses of the treated cemented body at 6 m / s, 9 m / s, and 12 m / s were 0.1596 g / min, 0.5606 g / min, and 0.6338 g / min, respectively, which were reduced by 52.75%, 43.77%, and 50.29% compared with the control group. The Ce element content before treatment was 0.81%, and the content after treatment was 0.80%. The difference in rare earth element content before and after treatment was not significant, indicating that this method does not affect the secondary utilization of rare earth smelting waste slag.

[0075] The above results show that the original rare earth smelting waste slag samples contained a large amount of calcium sulfate and calcium sulfate dihydrate. After treatment by the harmless treatment method of the present invention, the diffraction peak intensities of calcium sulfate and calcium sulfate dihydrate decreased in Examples 1, 2, 3, and 4, and diffraction of barium sulfate and biogenic calcium carbonate (calcite, aragonite, and aragonite) appeared. This indicates that after treatment by the method of the present invention, barium sulfate and biogenic calcium carbonate are generated in the reaction system, which can bind the rare earth smelting waste slag particles together. While reducing the radiation dose, this can prevent the rare earth smelting waste slag particles from being dispersed by the wind and causing air pollution, and reduce the leaching content of heavy metal elements and radionuclides.

[0076] Table 1. Radiation dose of rare earth smelting waste residue before and after treatment in each group.

[0077]

[0078]

[0079] Table 2 Radon emission rates of rare earth smelting waste slag before and after treatment in each group

[0080]

[0081] Table 3. Content of heavy metals and radionuclides in sulfuric acid-nitric acid leaching solutions of rare earth smelting waste before and after treatment.

[0082]

[0083] Table 4. Unconfined compressive strength and wind erosion loss of cementitious structures before and after treatment for each group.

[0084]

[0085] Table 5 Ce content before and after treatment in each group

[0086]

[0087]

[0088] The method for harmless treatment of rare earth waste provided by this invention alleviates the storage pressure of waste residue storage facilities while reducing its impact on the surrounding environment.

[0089] The above-described embodiments are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Any modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for harmlessly treating rare earth smelting waste residue, characterized in that, Includes the following steps: (1) Add organic barium salt to rare earth smelting waste residue and stir to react; (2) Add carbonate mineralizing bacteria culture solution to the rare earth smelting waste residue after step (1) to induce mineralization reaction; (3) Pressurize and carbonize the rare earth smelting waste residue after step (2), and dry it after curing to achieve the harmless treatment of rare earth smelting waste residue. The organic barium salt is barium acetate or barium lactate; in step (1), the organic barium salt is added in the form of a solution, and the concentration of the organic barium salt solution is 0.01 to 0.5 mol / L.

2. The method according to claim 1, characterized in that, The organic barium salt solution was added to the rare earth smelting waste residue at a solid-liquid ratio of 1 g: 0.3-0.8 mL.

3. The method according to claim 1, characterized in that, The stirring reaction temperature in step (1) is 10-35℃ and the reaction time is 0.5-24 h.

4. The method according to claim 1, characterized in that, The rare earth smelting waste residue is a hazardous solid waste generated after rare earth minerals are extracted through hydrometallurgical processes.

5. The method according to claim 1, characterized in that, The carbonate mineralizing bacteria culture medium is a culture medium for one or more carbonate mineralizing strains.

6. The method according to claim 5, characterized in that, The carbonate mineralization strains include Bacillus mucilaginosus, Bacillus subtilis, Oligotrophic rhizobium, or Rhodopseudomonas palustris.

7. The method according to claim 5, characterized in that, The culture medium used for the carbonate mineralizing bacteria culture solution consists of molasses 1-3 g / L, soybean peptone 1-5 g / L, potassium dihydrogen phosphate 0.1-0.5 g / L, and zinc sulfate 0.05-0.5 g / L.

8. The method according to claim 1, characterized in that, The carbonization curing temperature is 20–35°C, and the carbonization curing humidity is 70% ± 5%; the carbonization curing gas atmosphere is a carbon dioxide atmosphere.

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