A method for the chemical and biological synergistic treatment of acid leach uranium groundwater

Abstract

The application discloses a method for treating acid in-situ leaching uranium groundwater by chemical and biological synergy, and belongs to the technical field of groundwater treatment. The method is characterized by adding an iron chelating agent to acid in-situ leaching uranium groundwater, chelating high-concentration ferrous ions to form stable iron chelates; then based on the dual effects of hydroxyl radical chemical oxidation of the continuous single-electron transfer pathway of the ferrous chelates and biological oxidation of acidophilic iron-oxidizing bacteria in the groundwater, chelates of ferric ions are rapidly formed and hydrolyzed to form ferric hydroxyl sulfate precipitates, thereby removing more than 90% of the dissolved iron and a small part of the sulfate in the acid in-situ leaching uranium groundwater; subsequently, a small amount of lime is used for neutralization, so that the discharge of pollutants such as uranium, manganese and nickel in the groundwater can meet the standards. The method can reduce the consumption of the lime used for neutralization and the generation of metal waste by more than 50% in the treatment of acid in-situ leaching groundwater, and is efficient, stable, economical and practical.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of groundwater treatment, and particularly relates to a method for treating acid in-situ leaching uranium groundwater by means of chemical and biological cooperation. BACKGROUND

[0002] Uranium (U) is an important nuclear fuel, and there are mainly three mining methods for uranium ore resources: underground mining, open-pit mining and in-situ leaching mining. In-situ leaching mining of uranium is a method of directly leaching uranium metal in-situ in the ore deposit, that is, the leaching agent is injected into the ore-bearing layer from the injection hole to interact with the ore, and the uranium-containing solution is lifted to the ground surface through the pumping hole, and then the uranium metal is recovered by ion exchange method. According to the different leaching agents, in-situ leaching of uranium is mainly divided into acid method, alkali method and neutral method. The acid in-situ leaching of uranium technology using sulfuric acid as the main leaching agent has been widely used in the mining of loose sandstone type uranium deposits since the 1980s, and is the key development direction of natural uranium production in China. However, due to the injection of a large amount of sulfuric acid into the ore-bearing aquifer during the in-situ leaching production process, the target element uranium in the ore layer is leached out, and at the same time, a large number of coexisting elements are also dissolved and released. Therefore, in the underground ore-bearing aquifer, high-acidity wastewater containing radionuclides (uranium, radium-226), sulfate (8000-15000 mg / L), soluble ferrous iron (1000-1500 mg / L), and various heavy metal pollutants such as Cu / Mn / Ni will be formed.

[0003] In the prior art, the treatment methods for acid in-situ leaching uranium groundwater mainly include chemical precipitation (lime neutralization, etc.), chemical reduction (zero-valent iron reduction, etc.), physical and chemical separation (coagulation-ultrafiltration, electrodialysis, ion exchange, membrane capacitive deionization, etc.), and biological remediation (biological denitrification, sulfate reduction, etc.). Due to the very complex composition of acid in-situ leaching uranium groundwater, especially the typical characteristics of extremely acidic (pH<2.5) and high concentration of soluble ferrous iron and sulfate, the chemical and physical methods often have the bottleneck problems of high reagent consumption, large amount of waste residue, complex process management, and high cost in practical application. In addition, the existing biological methods also have unsatisfactory treatment effect or the effect is acceptable but it is difficult to be applied on a large scale. This is mainly because: ① the functional bacteria (denitrifying bacteria and sulfate-reducing bacteria) used in the past are neutrophilic bacteria, which grow very slowly under the condition of pH<5.0, resulting in a long biological treatment cycle; ② the sulfate content in the acid in-situ leaching uranium groundwater is high, and the dissolved organic carbon is scarce (<50 mg / L), so a large amount of organic carbon (acetic acid, sodium lactate, glycerol, etc.) needs to be added for biological sulfate reduction, which leads to the COD and sulfide content of the effluent exceeding the standard; ③ biological denitrification can remove nitrate but cannot remove high-concentration soluble iron in the groundwater, resulting in the secondary treatment of coupling chemical or physical method still facing the above-mentioned bottleneck problems.

[0004] Therefore, it is urgent to explore a new method of treating acid in-situ leaching of uranium groundwater with economic and efficient characteristics. SUMMARY

[0005] 1. Problem to be solved

[0006] The present application is directed to one of the problems existing in the prior art of treating acid in-situ leaching of uranium groundwater, such as high consumption of chemicals, large amount of waste residue, high cost, difficulty in removing soluble ferrous iron, and unstable effect, etc. A new method of chemical and biological synergistic treatment of acid in-situ leaching of uranium groundwater is provided, which can economically and efficiently treat such groundwater according to the typical characteristics of high acidity, high ferrous iron, and high sulfate of acid in-situ leaching of uranium groundwater.

[0007] 2. Technical solution

[0008] In order to solve the above problems, the technical solution adopted by the present application is as follows:

[0009] The present application provides a method of chemical and biological synergistic treatment of acid in-situ leaching of uranium groundwater, which comprises the following steps:

[0010] S1, adding an iron chelator to the acid in-situ leaching of uranium groundwater, which can chelate Fe 3 + , Fe 2+ in the groundwater into Fe 3+ chelate, Fe 2+ chelate;

[0011] S2, aeration and stirring to rapidly oxidize Fe 2+ chelate in the groundwater into Fe 3+ chelate by chemical and microbial oxidation, and the formed Fe 3+ chelate is hydrolyzed to generate yellow-brown ferric hydroxyl sulfate solid.

[0012] Further, the above-mentioned method of chemical and biological synergistic treatment of acid in-situ leaching of uranium groundwater further comprises the following steps:

[0013] S3, the effluent is neutralized with lime.

[0014] Further, the above-mentioned S2 further comprises adding any one or more of rope-shaped, spherical, and ring-shaped fillers before aeration, and the addition of fillers can make the ferric hydroxyl sulfate solid accumulate on the fillers, thereby facilitating collection.

[0015] Further, the filling volume ratio of the above-mentioned fillers is 30% to 80%.

[0016] Further, the above-mentioned iron chelator includes any one or more of tea polyphenols, propionic acid, protocatechuic acid, hydroxylamine hydrochloride, and ferric ammonium citrate.

[0017] Further, the chelating agent is added in an amount of 5-50 mg / L.

[0018] Further, the aeration includes bringing the dissolved oxygen content in the water to 2-4 mg / L.

[0019] Further, the stirring speed is 100-200 rpm, and the stirring time is 8-15 h.

[0020] Further, the temperature of the chemical and microbial oxidation reaction is 20-35 °C.

[0021] Further, the lime neutralization includes adding lime in an amount of 1-2 g / L.

[0022] 3. Beneficial effects

[0023] Compared with the prior art, the present application has the beneficial effects that:

[0024] (1) The present application provides a method for treating acid in-situ leaching of uranium groundwater by chemical and biological synergy, which chelates high-concentration ferrous ions (Fe 2+ ) in acid in-situ leaching of uranium groundwater by chelating agents, and converts them into ferrous chelates (Fe 2+ chelates) in whole or in part: on the one hand, due to the significant reduction of the redox potential of ferrous chelates, it is beneficial to the chemical oxidation of hydroxyl radicals by continuous single-electron transfer pathway; on the other hand, compared with ferrous ions, ferrous chelates have better bioavailability and are more easily biologically oxidized by endogenous abundant acidophilic iron-oxidizing bacteria in acid in-situ leaching of uranium groundwater. Under the synergistic effect of chemical oxidation and biological oxidation, high-concentration ferrous ions in acid in-situ leaching of uranium groundwater can be rapidly oxidized into ferric chelates, and hydrolyzed to form hydroxyl ferric sulfate minerals, thereby efficiently removing high-concentration dissolved iron in groundwater.

[0025] (2) The present application provides a method for treating acid in-situ leaching of uranium groundwater by chemical and biological synergy, which first rapidly removes more than 90% of iron (including Fe 3+ and Fe 2+ ) and a small amount of sulfate in acid in-situ leaching of uranium groundwater by the synergistic effect of chemical oxidation and biological oxidation, and then combines with the secondary treatment of lime neutralization to further achieve the discharge standard of uranium, manganese and other heavy metal pollutants. Compared with the existing direct lime neutralization method, the present method can reduce the lime consumption and the generation amount of metal waste by more than 50% in the treatment.

[0026] (3) The application provides a method for treating acid in-situ leaching of uranium underground water by using chemical and biological synergy, wherein the iron chelating agent is a widely-sourced, cheap and easily-obtained chemical; meanwhile, the method uses indigenous bacteria (acidophilic iron-oxidizing bacteria) rich in the acid in-situ leaching of uranium underground water as functional bacteria, and does not need to inoculate other functional bacteria, thereby avoiding the difficulty of adapting to the extremely acidic environment of the acid in-situ leaching of uranium underground water by the exogenous functional bacteria; in addition, the whole treatment process is carried out at room temperature and normal pressure, and the reaction is mild, the operation is simple, and the method is good in economic practicability. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a photograph of the hydroxyl ferric sulfate mineral gathered on the filler in Example 1.

[0028] Figure 2 is a SEM graph of the hydroxyl ferric sulfate mineral gathered on the filler in Example 1.

[0029] Figure 3 is an XRD graph of the hydroxyl ferric sulfate mineral gathered on the filler in Example 1.

[0030] Figure 4 is a comparison of the solid phase sediment condition generated in Example 1 and the solid phase sediment condition generated by direct lime neutralization treatment.

[0031] Figure 5 is the original water sample, the water sample in the treatment process, and the final effluent water sample in Example 1. DETAILED DESCRIPTION

[0032] The application will be further described below in combination with specific examples.

[0033] It should be noted that the terms such as "upper", "lower", "left", "right", "middle" and the like cited in the present specification are only for the convenience of clear description, and are not intended to limit the scope of implementation, and the change or adjustment of the relative relationship is also regarded as the scope of implementation of the application without substantial change of the technical content.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the application belongs; the term "and / or" used herein includes any and all combinations of one or more related listed items.

[0035] Unless otherwise specified, the specific conditions in the examples are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used are not specified by the manufacturer, and are all conventional products that can be purchased on the market.

[0036] As used herein, the term“about” is used to provide flexibility to a given term, measurement, or value. The degree of flexibility of a particular variable will be readily determined by one of skill in the art.

[0037] As used herein, the term“at least one of’ is intended to mean one or more of the listed items. For example,“at least one of A, B, and C” explicitly includes just A, just B, just C, and combinations thereof.

[0038] Concentrations, amounts, and other numerical data can be presented herein in a range format. It is to be understood that such range format is used merely for convenience and brevity and should be construed as having been followed to following the principle of including and disclosing all the individual values reasonably encompassed within that range. For example, a numerical range of about 1 to about 4.5 should be interpreted to include not only the explicitly recited values of 1 to about 4.5, but also include individual values and sub-ranges within the indicated range, for example, 1, 2, 3, and 4 and sub-ranges like 1 to 3, 2 to 4, etc. The same principle applies to ranges reciting only one numerical value, such as“less than about 4.5,” which should be interpreted to include all the values and ranges above the upper limit of the ranges. Such interpretations are used only when in context appropriate understanding of one or both of the number range terms will facilitate appreciation of specific application circumstances. Furthermore, such interpretation should apply regardless of the breadth of the range or the characteristics being described.

[0039] Example 1

[0040] The present example provides a method for chemically and biologically synergistically treating acid in-situ leaching uranium groundwater.

[0041] Water sample: groundwater extracted from an acid in-situ leaching uranium area in Yili region of Xinjiang, the pH of the water sample is 2.2, the total dissolved iron content is 1316 mg / L, among which Fe 2+ content is 1216 mg / L, SO4 2- content is 8087 mg / L, total organic carbon TOC content is 1.3 mg / L, conductivity is 8.0 mS / cm, U content is 15.1 mg / L, heavy metal ion Cu, Mn, Ni content is 1.0 mg / L, 75 mg / L, 5.6 mg / L, respectively.

[0042] The present example is directed to the treatment of the above water sample, including the following steps:

[0043] S1, 30 mg / L of tea polyphenol (as iron chelate) is added to the above acid in-situ leaching uranium groundwater sample, mixed at 25°C for 5 min, and the ferrous tea polyphenol chelate is obtained, and the Fe 2+ is completely chelated into Fe 2+ chelate;

[0044] S2, to the acid leaching uranium groundwater sample, add BZ-C type rope filler (Jiangsu Aiwu Environmental Protection) with a filling volume ratio of 30%, under the conditions of air aeration (water dissolved oxygen content reaches 2.0 mg / L), 150 rpm stirring and 25℃, react for 12h, and use dimethyl sulfoxide capture method to detect, the concentration of hydroxyl radical (·OH) in the reaction system is 28μM, through the synergistic effect of ·OH chemical oxidation and endogenous acidophilic iron-oxidizing bacteria biological oxidation, a large amount of yellow-brown precipitate is generated on the rope filler Figure 1 , the SEM and XRD detection of the precipitate is shown in Figure 2 and Figure 3 , which shows that the precipitate generated on the filler is hydroxyl ferric sulfate mineral. Detect the treated groundwater, the pH value is 2.8, the oxidation rate of ferrous iron in the groundwater is 99% (o-phenanthroline colorimetry), and the total iron precipitation rate is 99%.

[0045] S3, collect the solid precipitate on the filler, add 1.55g / L of lime to the above treated groundwater, adjust the pH to 8.5, 25℃ and 120 rpm stirring for 2h, and then separate the solid and liquid to obtain the solid waste residue and the final effluent.

[0046] As can be seen from Figure 4 , the solid residue generated after lime neutralization in the present application has a compact structure and a small volume. Figure 5 As can be seen from , the final effluent after treatment in the present application has a clear and transparent appearance, and the pollutant concentration can meet the discharge standard.

[0047] Example 2

[0048] The water sample of the present example is the same as that of Example 1, and the specific steps are as follows:

[0049] S1, add 10mg / L of propionic acid and 5mg / L of ferric ammonium citrate to the acid leaching uranium groundwater sample, shake and mix at 30℃ for 1h to obtain Fe 2+ chelate;

[0050] S2, add ZZ type ring filler (Jiangsu Aiwu Environmental Protection) with a filling volume ratio of 60% to the above acid leaching uranium groundwater sample, under the conditions of air aeration (water dissolved oxygen content reaches 3.0 mg / L), 100 rpm stirring and 30℃, react for 9h, and use dimethyl sulfoxide capture method to detect, the concentration of ·OH in the reaction system is 22μM, through the double effect of ·OH chemical oxidation and acidophilic iron-oxidizing bacteria biological oxidation, a large amount of yellow-brown precipitate appears on the ring filler, the precipitate is detected by SEM and XRD, and the precipitate generated on the ring filler is hydroxyl ferric sulfate mineral. Detect the treated groundwater, the pH value is 2.9, the oxidation rate of ferrous iron in the groundwater is 99% (o-phenanthroline colorimetry), and the total iron precipitation rate is 93%.

[0051] S3, collecting the solid precipitate on the annular packing, adding 1.22 g / L of lime to the above treated groundwater, adjusting the pH to 8.5, stirring at 25 °C and 120 rpm for 2 h, and then performing solid-liquid separation to obtain a solid-phase waste residue and final effluent.

[0052] Comparative Example 1

[0053] This comparative example uses a biological iron oxidation method inoculated with Thiobacillus ferrooxidans to treat acid leaching uranium groundwater (i.e., without adding chelating agents, only biological oxidation). The test water sample is the same as in Example 1, and the specific steps are as follows:

[0054] (1) Culturing of Thiobacillus ferrooxidans;

[0055] (2) Inoculating Thiobacillus ferrooxidans (Thiobacillus ferrooxidans LX5) into the water sample to achieve a number of ~ 10 8 individuals / mL.

[0056] (3) Placing the above culture in a shaking bed, oscillating at 25 °C and 150 rpm for 96 h, and no ·OH production is detected throughout the reaction process by the dimethyl sulfoxide capture method, and a yellow-brown precipitate is generated; detection shows that the oxidation rate of ferrous iron is 95%, and the total iron precipitation rate is 45%.

[0057] (4) Lime neutralization: adding 2.29 g / L of lime to the above treated groundwater, adjusting the pH to 8.5, stirring at 25 °C and 120 rpm for 2 h, and then performing solid-liquid separation to obtain a solid-phase waste residue and final effluent.

[0058] Comparative Example 2

[0059] This comparative example uses a sulfate biological reduction method to treat acid leaching uranium groundwater, and the water sample is the same as in Example 1, and the specific steps are as follows:

[0060] (1) Adding 2.86 g / L of lime to the groundwater to adjust the pH to 5.0 or above;

[0061] (2) Enrichment culture of sulfate-reducing bacteria: using a culture medium (g / L): K2HPO40.5, NH4Cl 1.0, Na2SO41.0, CaCl2·2H2O 0.1, MgSO4·7H2O 2.0, DL-sodium lactate 2.0, yeast paste 1.0, FeSO4·7H2O 0.5, resazurin 1.0, distilled water 1 L, and enriching sulfate-reducing bacteria from the sludge in the secondary sedimentation tank of a sewage treatment plant. Before enrichment culture, adjust the pH of the sludge to 5.0 with H2SO4, and place it in a shaking bed at 150 r / min anaerobic culture at 30 °C for 96 h.

[0062] (3) To the above water sample after lime neutralization, 6.5 g / L of sodium lactate is added, and sulfate-reducing bacteria is inoculated at a volume ratio of 10%, and is treated under anaerobic sealing at 30°C and 150 rpm oscillation for 96 h, and black precipitate is generated. After detection, the pH value is 7.2, the contents of uranium U, Cu and Ni are not detected, and the content of Mn is 22 mg / L.

[0063] (4) The above treated water sample is subjected to solid-liquid separation to obtain metal waste residue and final effluent.

[0064] Comparative Example 3

[0065] The direct lime neutralization (chemical precipitation) method is used to treat acid leaching uranium underground water, and the water sample is the same as that in Example 1, and the specific steps are as follows:

[0066] (1) 3.52 g / L of lime is added to the water sample to adjust the pH to 8.5;

[0067] (2) It is placed in a shaking bed and oscillated at 25°C and 150 rpm for 5 h, and a large amount of gray-black flocculent precipitate is generated;

[0068] (3) The above generated precipitate is placed in a measuring cylinder and allowed to stand and settle to separate, and the water quality indexes of the effluent and the volume and dry weight of the solid phase sediment are detected.

[0069] Table 1 Comparison of treatment effects of acid leaching uranium underground water in Example 1 and Comparative Examples 1-3

[0070]

[0071] From the removal indexes of pollutants in acid leaching uranium underground water, the method can achieve the same treatment effect as the existing lime neutralization method, and can reduce the lime consumption and metal waste residue generation by 50% in lime neutralization disposal, and at the same time, the treatment time is obviously better than the existing biological iron oxidation method and biological sulfate reduction method without adding chelating agent.

Claims

1. A method for the synergistic chemical and biological treatment of groundwater extracted using acid leaching, characterized in that, The method includes the following steps: S1, adding an iron chelating agent to the groundwater from acid leaching of uranium; S2 is used for aeration and stirring to remove Fe from the groundwater. 2+ Chelate chemistry and microbial oxidation to Fe 3+ Chelates, forming Fe 3+ The chelate undergoes simultaneous hydrolysis; the aeration is carried out when the dissolved oxygen content in the water reaches 2~4 mg / L.

2. The method for synergistic chemical and biological treatment of groundwater extracted by acid leaching according to claim 1, characterized in that, The method further includes the following steps: S3, the effluent is neutralized with lime.

3. The method for synergistic chemical and biological treatment of groundwater extracted by acid leaching according to claim 2, characterized in that, The amount of lime added for lime neutralization is 1~2 g / L.

4. A method for the synergistic chemical and biological treatment of groundwater extracted using acid leaching, according to any one of claims 1-3, characterized in that, The iron chelating agent includes any one or more of tea polyphenols, propionic acid, protocatechuic acid, and ferric ammonium citrate.

5. The method for synergistic chemical and biological treatment of groundwater extracted by acid leaching according to claim 4, characterized in that, The amount of the iron chelating agent added is 5~50 mg / L.

6. The method for synergistic chemical and biological treatment of groundwater extracted by acid leaching according to claim 5, characterized in that, Before aeration, S2 also includes the addition of any one or more of rope-shaped, spherical, and annular packing materials.

7. A method for the synergistic chemical and biological treatment of groundwater extracted using acid leaching, as described in claim 6, characterized in that, The filling volume ratio of the filler is 30% to 80%.

8. The method for synergistic chemical and biological treatment of groundwater extracted by acid leaching according to claim 7, characterized in that, The stirring speed is 100~200 rpm, and the stirring time is 8~15 h.

9. A method for the synergistic chemical and biological treatment of groundwater extracted by acid leaching according to claim 8, characterized in that, The chemical and microbial oxidation is carried out at temperatures ranging from 20 to 35°C.

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