Fly ash modification method and application in heavy metal adsorption of neodymium iron boron extraction wastewater

Abstract

The invention belongs to the technical field of neodymium-iron-boron waste modification application, and relates to a neodymium-iron-boron waste modification method and application of the neodymium-iron-boron waste modification method in wastewater heavy metal adsorption. And adding the fly ash crude product into water, fully stirring and uniformly mixing, removing upper turbid liquid, and heating and drying the solid to obtain the fly ash FA. The method comprises the following steps: adding Na2FeO4 into fly ash FA, and uniformly mixing to obtain FA / Na2FeO4; the preparation method comprises the following steps: adding FA / Na2FeO4 into a lanthanum chloride solution in a stirring state, carrying out shaking reaction for at least 3 hours, centrifuging after the reaction is finished, and drying and grinding a solid obtained by centrifuging to obtain La / FA / Na2FeO4 powder; compared with a traditional treatment method, the treatment effect is better, the sludge generation amount is small, and the follow-up treatment cost is reduced. According to the technical scheme, various heavy metal ions in wastewater can be effectively removed, the turbidity and chromaticity of a water body are reduced, it is ensured that the water body is free of peculiar smell, and the residual quantity of the heavy metal ions is remarkably reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of fly ash modification and application, and relates to a fly ash modification method and application in heavy metal adsorption of NdFeB extraction wastewater. Background Art

[0002] NdFeB permanent magnet materials are widely used in modern industry. With the continuous increase of their production, the amount of NdFeB waste is also increasing. In the process of waste recycling, the extraction process will produce a large amount of wastewater containing heavy metals. If these heavy metals are directly discharged without proper treatment, they will cause serious harm to the ecological environment such as soil and water bodies, and also waste precious metal resources. Therefore, it is of great significance to carry out research on the removal of heavy metals in the wastewater of NdFeB waste recycling extraction.

[0003] There is a certain research foundation in the recycling of NdFeB waste and wastewater treatment at home and abroad. Some traditional wastewater treatment methods such as chemical precipitation are used in the removal of certain heavy metals, but there are problems such as limited removal efficiency and easy secondary pollution; and sulfur-containing compounds such as sodium sulfide are used to remove heavy metals in water bodies, which can easily cause the water to become smelly; ion exchange and adsorption methods have also been explored for such wastewater treatment, but there is still a need for in-depth research on the specific process optimization and practical application of NdFeB extraction wastewater. Summary of the invention

[0004] Aiming at the problems existing in the treatment of traditional NdFeB permanent magnet material extraction wastewater, the present invention proposes a novel fly ash modification method and its application in heavy metal adsorption of NdFeB extraction wastewater.

[0005] In order to achieve the above object, the present invention is implemented by adopting the following technical solutions: A fly ash modification method, the steps are as follows: (1) The crude fly ash is added into water and stirred thoroughly to mix evenly. After removing the upper turbid liquid, the solid is heated and dried to obtain fly ash FA.

[0006] (2) Add Na2FeO4 to fly ash FA and mix them evenly to obtain FA / Na2FeO4.

[0007] (3) Add FA / Na2FeO4 to the lanthanum chloride solution under stirring, shake the solution for at least 3 hours, centrifuge after the reaction is completed, dry and grind the solid obtained by centrifugation to obtain La / FA / Na2FeO4 powder.

[0008] Preferably, the heating and drying temperature in step (1) is 100-110°C, and the heating and drying time is 20-24h; and the mass ratio of fly ash FA to Na2FeO4 in step (2) is (9-12):1.

[0009] Preferably, the concentration of the lanthanum chloride solution in step (3) is 80-150 mmol / L; the shaking reaction temperature is 25°C, the solid drying temperature is 70-75°C, and the drying time is 20-24h.

[0010] The La / FA / Na2FeO4 NdFeB prepared by the above method is used for heavy metal adsorption in wastewater extraction. The application method is: add sodium hydroxide solution to the wastewater to adjust the pH to 8-9, add La / FA / Na2FeO4 powder, stir and precipitate, add SS reagent, then add polyaluminum ferrosilicate solution, continue stirring and reacting, and then filter.

[0011] Preferably, the SS reagent is prepared by the following method: 4 g of copper reagent and 25 g of sodium sulfide are weighed, respectively added with water and stirred to dissolve, then mixed and transferred to a 500 mL volumetric flask and fixed to volume.

[0012] Mechanism analysis: Fly ash, as a common industrial solid waste, has a certain potential for heavy metal ion adsorption, but its original adsorption performance is limited. Selecting a suitable method to modify fly ash can effectively improve its ability to adsorb heavy metals. After the scheme proposed in the present invention is modified by sodium ferrate and lanthanum chloride, the surface of the final material has abundant hydroxyl groups, siloxane groups and newly introduced active sites such as iron oxides and lanthanide compounds, which can react with heavy metal ions on the surface. Heavy metal ions such as Ni²⁺ and Co²⁺ have empty orbitals and can form coordination bonds with lone pairs of electrons provided by atoms such as oxygen and nitrogen in these active groups, so that heavy metal ions are adsorbed on the surface of fly ash. And this surface complexation has strong selectivity and stability. In addition, under alkaline conditions, the surface of fly ash is negatively charged, and heavy metal cations are easily adsorbed.

[0013] When sulfide ions meet heavy metal ions, since most heavy metal sulfides have extremely low solubility product constants (Ksp), they will quickly combine to form corresponding heavy metal sulfide precipitates. The sulfur atom in the copper reagent molecule has a strong coordination ability. When the copper reagent is added to a solution containing heavy metal ions (such as Cu²⁺, Ni²⁺, Cd²⁺, Zn²⁺, etc.), the lone pair of electrons on its sulfur atom will form a coordination bond with the empty orbital of the heavy metal ion, and a complex reaction will occur. Taking copper ions as an example, the copper reagent reacts with Cu²⁺ to form a stable copper diethyldithiocarbamate (Cu(DDTC)2) complex. This complex has a relatively low solubility and precipitates from the solution. The thiocarbamate group is tightly bound to the heavy metal ion, reducing the activity of the heavy metal ion, and this binding mode is conducive to multiple complex molecules approaching and aggregating each other, eventually forming a larger particle precipitate, which is easy to separate from the solution.

[0014] Polysilicate aluminum iron (PSAF) is an inorganic polymer polymerized by aluminum, iron, silicon and other elements through hydroxyl groups. It has abundant active groups, such as hydroxyl (-OH), aluminum oxygen bond (-Al-O-), iron oxygen bond (-Fe-O-) and silicon oxygen bond (-Si-O-), which form a relatively complex network or chain structure, making PSAF present a complex hydrolysis and polymerization form in aqueous solution. It is more effective than the commonly used coagulants such as polyaluminum chloride (PAC) and polyferric chloride (PFC), and cheaper than organic polymer flocculants (OPF). In addition to having good electrical neutralization, adsorption, bridging and net capture and sweeping effects, it forms large and dense floccules, has good decolorization and odor removal effects, and has the advantage of fast sedimentation rate. Thereby accelerating the removal rate of heavy metal ions.

[0015] Compared with the prior art, the advantages and positive effects of the present invention are: 1. The application of this heavy metal removal process effectively reduces the discharge of heavy metals in wastewater into the environment, reduces the risk of pollution to surrounding soil and water bodies, helps protect the ecological environment, improves regional ecological quality, and also has positive significance for biodiversity protection.

[0016] 2. From the perspective of cost, although the preparation of adsorbents and precipitants and the operation of equipment require a certain amount of investment, compared with traditional treatment methods, its treatment effect is better and the amount of sludge produced is less, which reduces the subsequent treatment cost. At the same time, from the perspective of resource recovery, the recovery of heavy metals accumulated in sludge also has certain economic value, which improves the economic benefits of the entire NdFeB waste recovery process. The technical solution of the present invention can effectively remove a variety of heavy metal ions in wastewater, reduce water turbidity and chromaticity, ensure that the water is odorless, and significantly reduce the residual amount of heavy metal ions. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 These are SEM characterization images of different samples in the preparation process of Example 1, where A1-A3 are SEM images of FA powder obtained after coarse fly ash pretreatment at different magnifications; B1-B3 are SEM images of FA / Na2FeO4 powder at different magnifications; C1-C3 are SEM images of La / FA / Na2FeO4 powder at different magnifications.

[0018] Figure 2 A is the EDS analysis result of FA powder, Figure 2 B is the EDS analysis result of FA / Na2FeO4 powder. Figure 2 C is the EDS analysis result of La / FA / Na2FeO4 powder.

[0019] Figure 3This is the EDS mapping of La / FA / Na2FeO4 powder.

[0020] Figure 4 These are the X-ray diffraction spectra of three different samples: FA, FA / Na2FeO4 and La / FA / Na2FeO4. DETAILED DESCRIPTION

[0021] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described below in conjunction with specific embodiments. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[0022] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways than those described herein. Therefore, the present invention is not limited to the specific embodiments of the following disclosure.

[0023] Example 1 Fly ash pretreatment: 100 g of coarse fly ash was added to 1 L of deionized water and washed for 0.5 h at 25 °C with a stirring rate of 200 rpm to remove soluble compounds. After washing, it was allowed to stand naturally for 2 min, and then the upper turbid liquid was removed, and the remaining solid was placed in an oven at 105 °C and dried for 24 h to obtain FA.

[0024] Na2FeO4 modified fly ash (FA / Na2FeO4): weigh 5 g of pretreated fly ash and mix evenly with 0.5 g of Na2FeO4 to obtain FA / Na2FeO4.

[0025] Preparation of La / FA / Na2FeO4 solid: 4 g FA / Na2FeO4 was added to 200 mL of 100 mmol / L lanthanum chloride solution under stirring at 100 rpm to form a mixture of lanthanum and FA / Na2FeO4. The mixture was stirred for 3 hours at 25°C to complete the reaction. The solid was then recovered by centrifugation, washed twice with deionized water, and dried at 70°C for 24 hours to obtain La / FA / Na2FeO4. The dried La / FA / Na2FeO4 solid was ground into a fine powder with uniform particle size.

[0026] Preparation of SS reagent: Weigh 4g of copper reagent (sodium diethyldithiocarbamate) and 25g of sodium sulfide, place them in beakers respectively, add water and stir manually with a glass rod to dissolve, then mix and transfer to a 500mL volumetric flask and make up to volume, referred to as SS reagent.

[0027] Preparation of polyaluminium silicate ferric (PSAF) dilution solution: Add 2.5 g of polyaluminium silicate ferric to 1000 mL of water and stir with a glass rod to achieve full hydrolysis.

[0028] Determination of heavy metal content: Collect wastewater samples from the extraction workshop and use the ICP method to detect the initial content of heavy metal ions in the water samples. Then take 1000mL of wastewater, adjust the pH to 8-9 with 5mol / L sodium hydroxide solution while stirring (300 rpm), add 1.5g of the prepared La / FA / Na2FeO4 powder, stir and precipitate at 200rpm for 0.5h, then add 1mL of the above SS reagent, and then add 1mL of polyaluminum ferrosilicate (2.5g / L) solution diluted with water, continue stirring for 0.5h, filter at normal pressure, take the filtrate for heavy metal ion content determination, and detect the heavy metal residue in the solution.

[0029] SEM, EDS and XRD were used to characterize the different powder samples in this example. Figure 1 A- Figure 1 C are the electron microscope images of FA, FA / Na2FeO4 and La / FA / Na2FeO4, Figure 2 are the EDS scanning results of different samples. Figure 3 This is the surface scan mapping of La / FA / Na2FeO4. Figure 4 These are the X-ray diffraction spectra of three different samples: FA, FA / Na2FeO4 and La / FA / Na2FeO4. Figure 1 It can be seen from A that the coarse ash after pretreatment is mainly spherical particles with a smooth surface. Figure 1 B shows that the surface of the particles becomes uneven and wrinkled after Na2FeO4 pre-oxidation, thus providing more binding sites for subsequent modification. Figure 1 From the C, after pre-oxidation and modification with lanthanum chloride, the irregularity of the spherical particles increases, the surface is obviously coated, and it is fragmented. The increase of rough structure and specific surface area is more conducive to the adsorption process. From the EDS results, Na2FeO4 is pre-oxidized on the surface of fly ash, and lanthanum oxide is generated after reacting with lanthanum chloride, and the loading is relatively uniform. Figure 4 The results show that the main components of fly ash are SiO2, Al2O3 and silicon-aluminum compounds. After mixing with Na2FeO4, the main components did not change significantly, only part of the reducing substances were oxidized, and then continued to react with lanthanum chloride. The diffraction peaks of Al2O3 and silicon-aluminum compounds in the prepared powder samples became weaker, and the diffraction peak of La2O3 was obvious, which proved the formation of lanthanum oxide, and the characteristic diffraction peaks of Fe2O3 and FeCl2 appeared.

[0030] Example 2 Fly ash pretreatment: 100 g of coarse fly ash was added to 1 L of deionized water and washed for 0.5 h at 25 °C with a stirring rate of 200 rpm to remove soluble compounds. After washing, it was allowed to stand naturally for 2 min, and then the upper turbid liquid was removed, and the remaining solid was placed in an oven at 110 °C and dried for 20 h.

[0031] Na2FeO4 modified fly ash (FA / Na2FeO4): weigh 5 g of pretreated fly ash and mix evenly with 0.45 g of Na2FeO4 to obtain FA / Na2FeO4.

[0032] Preparation of La / FA / Na2FeO4 solid: 4 g FA / Na2FeO4 was added to 180 mL of 150 mmol / L lanthanum chloride solution under stirring at 100 rpm to form a mixture of lanthanum and FA / Na2FeO4. The mixture was stirred for 3 hours at 25°C to complete the reaction. The solid was then recovered by centrifugation, washed twice with deionized water, and dried at 75°C for 22 hours to obtain La / FA / Na2FeO4. The dried La / FA / Na2FeO4 solid was ground into a fine powder with uniform particle size.

[0033] The application process of the La / FA / Na2FeO4 powder prepared by the present invention is consistent with that of Example 1.

[0034] The heavy metal treatment effects of the La / FA / Na2FeO4 powders prepared in Example 1 and Example 2 are shown in Table 1 below.

[0035] Table 1 Comparison of heavy metal content in wastewater samples before and after treatment From the test results in Table 1 above, it can be seen that the La / FA / Na2FeO4 powder prepared in Examples 1 and 2 of the present invention has a significant removal effect on common heavy metals in wastewater such as Co, Ni, Cu, Cr, and Zn, and the removal rate of Co by the La / FA / Na2FeO4 powder in Example 1 and the removal rate of Cr by the La / FA / Na2FeO4 powder in Example 2 can both reach 100%.

[0036] The above description is only a preferred embodiment of the present invention and does not limit the present invention in other forms. Any technician familiar with the profession may use the technical content disclosed above to change or modify it into an equivalent embodiment with equivalent changes and apply it to other fields. However, any simple modification, equivalent change and modification made to the above embodiment based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A fly ash modification method, characterized in that: Here are the steps: (1) The crude fly ash is added to water and stirred thoroughly to mix evenly. After removing the upper turbid liquid, the solid is heated and dried to obtain fly ash FA; (2) Na2FeO4 is added to fly ash FA and mixed evenly to obtain FA / Na2FeO4; (3) Add FA / Na2FeO4 to the lanthanum chloride solution under stirring, shake the solution for at least 3 hours, centrifuge after the reaction is completed, dry and grind the solid obtained by centrifugation to obtain La / FA / Na2FeO4 powder.

2. The fly ash modification method according to claim 1, characterized in that: In step (1), the heating and drying temperature is 100-110° C., and the heating and drying time is 20-24 h. In step (2), the mass ratio of fly ash FA to Na2FeO4 is (9-12):

1.

3. The fly ash modification method according to claim 1, characterized in that: In step (3), the concentration of the lanthanum chloride solution is 80-150 mmol / L; the shaking reaction temperature is 25° C., the solid drying temperature is 70-75° C., and the drying time is 20-24 h.

4. Application of La / FA / Na2FeO4 prepared by any one of the methods of claims 1-3 in heavy metal adsorption treatment of NdFeB extraction wastewater, characterized in that: The application method is: add sodium hydroxide solution to the wastewater to adjust the pH to 8-9, add La / FA / Na2FeO4 powder, add SS reagent after stirring precipitation reaction, and then add polyaluminum ferrosilicate solution, continue stirring reaction and filter.

5. The use of La / FA / Na2FeO4 in heavy metal adsorption treatment of NdFeB extraction wastewater according to claim 4, characterized in that: The SS reagent was prepared by the following method: 4 g of copper reagent and 25 g of sodium sulfide were weighed, and water was added to each of them to stir and dissolve them, and then the mixture was mixed and transferred to a 500 mL volumetric flask to make up the volume.

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