Method of rapid treatment of heavy metal sludge and preparation of ferrite magnets

Abstract

A method of rapid treatment of heavy metal sludge and preparation of ferrite magnets comprises the following steps of: providing a sludge with at least zinc and ferrous metals; adding an iron-containing substance to the sludge; acid washing the sludge by sulfuric acid and adding the iron-containing substance to obtain an acid wash solution with zinc and iron ions; neutralizing the acid wash solution with sodium hydroxide to form a hydroxide precipitate; and passing into the air and heating the acid wash solution with a microwave ultrasonic method to make the hydroxide precipitate undergo a ferrite reaction to obtain a ferrite magnet with amorphous structure.

Description

[Technical Field]

[0001] This invention relates to a sludge treatment method, and more particularly to a method for rapidly treating heavy metal sludge and preparing it into ferrite magnets. [Previous Technology]

[0002] Wire rod sludge is a depleted and finite metal resource of man-made minerals and cannot be regenerated. Currently, the main method used is to treat wire rod sludge containing heavy metals by smelting in order to improve the recovery of valuable metals. Although the method of treating heavy metal sludge with ferrite magnets can achieve the purpose of waste resource reuse, the traditional ferrite magnet reaction time requires more than 90 minutes and consumes a lot of energy. [Summary of the Invention]

[0003] In view of the above, one object of the present invention is to provide a method for rapidly treating heavy metal sludge and preparing it into ferrite magnets, so as to solve the problems of the above-mentioned prior art.

[0004] To achieve the aforementioned objective, the present invention provides a method for rapidly treating heavy metal sludge and preparing it into a ferrite magnet, comprising the following steps: providing sludge, the sludge containing at least zinc and iron metals; adding iron-containing substances to the sludge; performing an acid washing step on the sludge and iron-containing substances using sulfuric acid to obtain an acid washing solution containing zinc and iron ions; neutralizing the acid washing solution with sodium hydroxide to form a hydroxide precipitate; and introducing air and heating the neutralized acid washing solution by microwave ultrasonic method for 20 minutes to allow the hydroxide precipitate to undergo a ferrite magnet reaction to obtain a ferrite magnet with a crystalline structure, wherein the microwave power of the microwave ultrasonic method is 300 watts and the ultrasonic power is 300 watts.

[0005] The molar ratio of zinc ions to iron ions in the pickling solution is between 1:2 and 1:10.

[0006] The molar ratio of zinc ions to iron ions in the pickling solution is 1:4.

[0007] The temperature of the ferrite magnet reaction is controlled between 50 degrees Celsius and 90 degrees Celsius.

[0008] The temperature of the ferrite magnet reaction is controlled at 70 degrees Celsius.

[0009] The air flow rate is between 0.1 and 4 liters per minute (LPM).

[0010] The air flow rate is 2 liters / minute.

[0011] The pH value of sodium hydroxide is between 9 and 13.

[0012] Among them, the iron-containing substance is iron filings.

[0013] The microwave ultrasonic method further includes stirring the hydroxide precipitate in the pickling solution at a stirring speed between 150 rpm and 200 rpm.

[0014] As described above, the method for rapid treatment of heavy metal sludge and preparation of ferrite magnets according to the present invention may have one or more of the following advantages:

[0015] (1) The present invention uses microwave ultrasound as a heating method to carry out ferrite magnet reaction, which can greatly reduce the time of traditional water bath heating.

[0016] (2) The present invention can complete the ferrite magnet reaction in only 22% of the time of conventional technology by means of microwave ultrasonic heating.

[0017] (3) The filtrate treated by the ferrite magnetization technology of the present invention meets the discharge standards for effluent and meets the leaching standards of the Toxicity Characteristic Leaching Procedure (TCLP), thus achieving the purpose of harmless treatment.

[0018] In order to enable you to have a better understanding of the technical features and technical effects of the present invention, the following are preferred embodiments and detailed descriptions.

Implementation Method

[0019] To facilitate understanding of the technical features, content, advantages, and effects of this invention, the invention is described in detail below with reference to accompanying drawings and embodiments. The drawings used are for illustrative and supplementary purposes only and may not represent the actual scale and precise configuration of the invention after implementation. Therefore, the scale and configuration of the accompanying drawings should not be used to interpret or limit the scope of the invention in actual implementation. Furthermore, for ease of understanding, the same elements in the following embodiments are indicated by the same symbols.

[0020] Wire rod sludge is a depleted and finite metal resource of man-made minerals and cannot be regenerated. Currently, the main method used is to treat wire rod sludge containing heavy metals by smelting in order to improve the recovery of valuable metals. Although the method of treating heavy metal sludge with ferrite magnets can achieve the purpose of waste resource reuse, the reaction time of ferrite magnets in traditional technology requires more than 90 minutes and consumes a lot of energy.

[0021] This invention utilizes microwave ultrasound as the heating method for the ferrite magnet reaction, significantly reducing the time required for traditional water bath heating. Furthermore, Oxidation-Reduction Potential (ORP) monitoring results show that this invention can complete the ferrite magnet reaction within 20 minutes using microwave ultrasound heating, meaning it requires only 22% of the time of traditional techniques. In addition, water quality analysis results indicate that the filtrate treated with this ferrite magnetization technology meets effluent discharge standards. XRD identification confirms it as a ferrite magnet crystal product, and the treated solid product meets the Toxicity Characteristic Leaching Procedure (TCLP) leaching standard, achieving the goal of harmless treatment.

[0022] This invention involves using a microwave ultrasonic method combined with sulfuric acid to extract zinc sulfate from zinc (Zn) and iron (Fe) wire sludge and ferrous sulfate produced by the reaction, and adding sodium hydroxide (NaOH) as a reactant to form a ferrite magnet. The system then utilizes microwaves for rapid synthesis. Please refer to Figure 1, which is a flowchart illustrating the method for rapidly treating heavy metal sludge and preparing ferrite magnets according to this invention. The method for rapidly treating heavy metal sludge and preparing ferrite magnets according to this invention includes the following steps: Step 1 (S1), providing a sludge containing at least zinc and iron metals; Step 2 (S2), adding an iron-containing substance to the sludge; Step 3 (S3), acid washing the sludge and the iron-containing substance with sulfuric acid to obtain an acid washing solution containing zinc and iron ions, wherein the molar ratio of zinc ions to iron ions in the acid washing solution is 1:2 to 1:10; Step 4 (S4), performing a neutralization reaction by neutralizing the acid washing solution with sodium hydroxide to form a hydroxide precipitate; Step 5 (S5), introducing air and heating the neutralized acid washing solution for 20 minutes using a microwave ultrasonic method to carry out a ferrite magnet reaction to obtain a ferrite magnet with a crystalline structure.

[0023] Specifically, in step 1, this invention provides, for example, sludge, such as wire sludge, wherein the wire sludge contains at least zinc and iron metals. This invention uses zinc-containing wire sludge as a reactant. The total concentration and TCLP of the wire sludge are detected using standard detection methods (microwave digestion atomic spectroscopy and toxicity leaching test). The properties of the wire sludge are shown in Table 1. The wire sludge contains high amounts of zinc (Zn) ions and iron (Fe) ions, with initial concentrations of 4,793.8 and 15,862 mg / kg, respectively, and TCLP concentrations of 10.43 and 60.85, respectively.

[0024] Table 1: Properties of wire rod sludge metal ions iron ions Zinc ions Original concentration (mg / kg) 15,862 4,793.8 TCLP concentration (mg / kg) 60.85 10.43

[0025] In step 2, this invention adds an appropriate amount of iron-containing substances such as iron filings to the sludge. In step 3, this invention uses sulfuric acid to perform an acid washing step on the sludge and iron-containing substances to obtain an acid washing solution containing zinc ions and iron ions, wherein the molar ratio of zinc ions to iron ions (Fe2+) in the acid washing solution is controlled between 1:2 and 1:10. The concentration of sulfuric acid is 2N H2SO4, and the amount used is a solid-liquid ratio of 1:6. This invention can determine the amount of iron-containing substances such as iron filings to be added by calculating the amount of divalent iron ions required for the ferrite magnet ([M] / [Fe2+] = 1:2~1:10, where M represents the total concentration of zinc ions) in a zinc sulfate solution. In this invention, the preferred molar ratio of zinc ions to iron ions is 1:4.

[0026] In step 4, this invention uses sodium hydroxide as a base to neutralize the pickling solution, thereby forming a hydroxide precipitate. The pH value of the sodium hydroxide is between 9 and 13, and preferably 13.

[0027] In step 5, air with a flow rate between 0.1 and 4 LPM is introduced to carry out the oxidation reaction, and the neutralized pickling solution is heated using microwave ultrasound for 20 to 25 minutes to carry out the ferrite magnet reaction, thereby transforming the sodium hydroxide precipitate from an amorphous type into a mesocrystalline ferrite magnet, and embedding the heavy metal ions (zinc ions) contained in the sludge into the crystalline structure of the ferrite magnet to become a stabilizing substance. Preferably, the air flow rate is 2 L / min, and the microwave and ultrasound power are both 300 watts. The temperature of the ferrite magnet reaction is controlled between 50°C and 90°C, preferably between 70°C. The microwave ultrasound method further includes stirring the hydroxide precipitate in the pickling solution at a stirring speed between 150 rpm and 200 rpm. The microwave ultrasound machine used in this work is the XO-SM50 microwave ultrasound machine manufactured by Nanjing Xianou Instrument Manufacturing Co., Ltd., for performing microwave ultrasound.

[0028] Table 2: Effect of microwave ultrasonic reaction time on ferrite magnetization reaction (Time dependence for TCLP of ZnFe2O4), wherein the microwave power of the microwave ultrasonic method is 300 watts, the ultrasonic power is 300 watts, the air flow rate is 2 liters / minute, the temperature is 70 degrees Celsius, and the reaction time is 20 minutes. Time (minutes) 5 10 15 20 25 Fe (ppm) 2.2 1.8 0.4 0.3 0.2 Zn (ppm) 2.3 1.1 1.0 0.2 0.1

[0029] Table 2 shows the effect of microwave ultrasonic reaction time on the ferrite magnetization reaction. During the reaction, a Zn / Fe molar ratio of 1:4, pH 13, aeration rate of 2 LPM (Liter Per Minute), and a reaction time of 20 minutes were used when the temperature reached above 70°C. As shown in Table 2, after 20 minutes of reaction, TCLP analysis revealed that the zinc concentration decreased to 0.2 ppm. The microwave ultrasonic reaction time affects the formation of the ferrite magnet; TCLP analysis showed that the longer the reaction time, the lower the leaching of both iron and zinc.

[0030] Table 3 shows the ORP results of zinc ferrite magnets prepared from actual zinc sludge under different microwave time conditions. In this study, zinc sulfate and ferrous sulfate obtained by microwave extraction with sulfuric acid were extracted from wire sludge and iron filings and reacted in a ferrite magnet solution. The experiment was conducted under the aforementioned experimental conditions. The ORP reaction changes in the aqueous solution were monitored and observed. When the reaction proceeded for 5 minutes, the ORP increased significantly. This may be due to the release of H+ from the decomposition of Fe(OH)2+ to neutralize the OH- in the aqueous solution. The ORP curve tended to stabilize after about 20 to 25 minutes. Regarding the change in redox potential, due to the change in reaction rate, when Fe(III) undergoes hydrolysis, the [OH-] generated by the pH adjustment is consumed by the H+ generated by the hydrolysis reaction, thus reaching a stable state. This result also means that the ferrite magnet reaction has been completed. In addition, according to the ORP observation results, when the reaction temperature is reached and aeration begins, the ORP curve will rise sharply after 5 minutes of microwave treatment. Subsequently, the ORP changes will maintain a small increase until it reaches its maximum value at about 20 minutes, and then maintain a small decrease in the reaction time thereafter.

[0031] Table 3: ORP results analysis of zinc ferrite magnets prepared from sludge under different microwave time conditions. Among them, the microwave power of the microwave-ultrasonic method was 300 watts, and the ultrasonic power was 300 watts (air flow rate was 2 liters / minute, temperature was 70 degrees Celsius, and reaction time was 20 minutes). Time (minutes) 0 5 10 15 20 25 ORP -158 -102 -63 -25 3 4

[0032] The Zn / Fe molar ratio plays a crucial role in the formation of ferrite magnets. According to the reaction equation, Fe²⁺ is essential for ferrite magnet production; therefore, converting 1 molar of zinc ions requires 2 molars of iron ions to generate 1 molar of ZnFe₂O₄. The ferrite magnet reaction formula indicates that increasing the molar amount of iron ions is beneficial for ferrite magnet formation and increases its yield. Furthermore, while excess iron ions can coat the zinc ions in the ferrite magnet reaction, the high temperature may cause the continuous generation of ferrous ions during oxidation, leading to the formation of γ-Fe₂O₃ or α-FeOH.

[0033] Table 4 shows the effect of the Zn / Fe molar ratio on the ferrite magnet. In this invention, the Zn / Fe molar ratio was set between 1:2 and 1:10, the temperature was controlled above 70℃, and the reaction time was 20 minutes. As shown in Table 4, the ferrite magnet formed when the Zn / Fe molar ratio increased exhibited better properties. TCLP analysis showed that at a molar ratio of 1:4, the zinc leaching decreased from 0.64 ppm to 0.18 ppm. At molar ratios of 1:8 and 1:10, the TCLP analysis showed even lower reductions. Therefore, a higher molar ratio relatively improves the stability of heavy metal leaching after zinc ion treatment with the ferrite magnet. Although the concentration at a 1:10 molar ratio is far below the effluent standard, it requires the addition of more iron. Therefore, a Zn / Fe molar ratio of 1:4 was chosen as the most suitable ratio.

[0034] Table 4: Effect of Zn / Fe molar ratio on ferrite magnets. Among them, the microwave power of the microwave-ultrasonic method is 300 watts, the ultrasonic power is 300 watts, the air flow rate is 2 liters / minute, the temperature is 70 degrees Celsius, and the reaction time is 20 minutes. Mörby 1:2 1:4 1:6 1:8 1:10 Fe (ppm) 0.62 0.31 0.27 0.21 0.11 Zn (ppm) 0.64 0.18 0.18 0.17 0.06

[0035] To understand the XRD results of zinc ferrite magnets prepared from actual zinc sludge under microwave power conditions, the XRD crystal phase analysis of the ferrite magnet reaction precipitation product is shown in Figure 2. Figure 2 shows the XRD pattern of zinc ferrite magnets. Figure 2 shows the changes in the peak values ​​of the ferrite magnet reaction precipitation product. After comparison with standard spectra, it was found that the strongest peaks of zinc ferrite magnets appeared at 2θ = 35.78 and 63.14. The experimental conditions in Figure 2 were: microwave power of 300 watts, ultrasonic power of 300 watts, air flow rate of 2 liters / minute, temperature of 70 degrees Celsius, and reaction time of 20 minutes. The spectrum shows that because the proportion of other elements in the zinc sludge is relatively low, the peak intensity of zinc ferrite magnets is relatively strong, with the main peak intensity between 60 and 120. Furthermore, the rapid reaction method using microwave and ultrasound can help the growth of the zinc ferrite magnet crystal image.

[0036] In summary, the above experimental results show that the Zn / Fe molar ratio is 1:4, the reaction temperature is 70℃, and the ORP monitoring results indicate that the microwave ultrasonic system can complete the reaction within 20 minutes, requiring only 22% of the traditional time. Water quality analysis results show that the filtrate treated with ferrite magnetization technology meets the discharge standards. XRD identification results confirm that it is a ferrite magnet crystal product, and the treated solid product meets the TCLP (Toxicity characteristic leaching procedure) leaching standard, achieving the purpose of harmless treatment and allowing for further reuse.

[0037] The above description is merely illustrative and not restrictive. Any equivalent modifications or alterations made without departing from the spirit and scope of this invention should be included in the appended claims. [Simplified Explanation of the Diagram]

[0039] Figure 1 is a schematic flowchart of the method for rapid treatment of heavy metal sludge and preparation of ferrite magnets according to this invention.

[0040] Figure 2 is the XRD pattern of zinc ferrite magnet.

Claims

1. A method for rapidly treating heavy metal sludge and preparing ferrite magnets, comprising the following steps: providing a sludge containing at least zinc and iron metals; adding an iron-containing substance to the sludge; performing an acid washing step on the sludge and the iron-containing substance using sulfuric acid to obtain an acid washing solution containing zinc and iron ions; neutralizing the acid washing solution with sodium hydroxide to form a hydroxide precipitate; and introducing air and heating the neutralized acid washing solution using a microwave ultrasonic method to cause the hydroxide precipitate to undergo a ferrite magnet reaction to obtain a ferrite magnet with a crystalline structure, wherein the microwave power of the microwave ultrasonic method is 300 watts, the ultrasonic power is 300 watts, and the ferrite magnet reaction time is between 20 and 25 minutes.

2. The method for rapidly treating heavy metal sludge and preparing it into ferrite magnets as described in claim 1, wherein the molar ratio of zinc ions to iron ions in the pickling solution is between 1:2 and 1:

10.

3. The method for rapidly treating heavy metal sludge and preparing it into ferrite magnets as described in claim 1, wherein the molar ratio of zinc ions to iron ions in the pickling solution is 1:

4.

4. The method for rapidly treating heavy metal sludge and preparing it into ferrite magnets as described in claim 1, wherein the temperature of the ferrite magnet reaction is controlled between 50 degrees Celsius and 90 degrees Celsius.

5. The method for rapidly treating heavy metal sludge and preparing it into ferrite magnets as described in claim 1, wherein the temperature of the ferrite magnet reaction is controlled at 70 degrees Celsius.

6. The method for rapidly treating heavy metal sludge and preparing it into ferrite magnets as described in claim 1, wherein the air flow rate is between 0.1 and 4 liters per minute (LPM).

7. The method for rapidly treating heavy metal sludge and preparing it into ferrite magnets as described in claim 1, wherein the air flow rate is 2 liters / minute.

8. The method for rapidly treating heavy metal sludge and preparing it into ferrite magnets as described in claim 1, wherein the pH value of sodium hydroxide is between 9 and 13.

9. The method for rapidly treating heavy metal sludge and preparing it into a ferrite magnet as described in claim 1, wherein the iron-containing substance is iron filings.

10. The method for rapidly treating heavy metal sludge and preparing it into a ferrite magnet as described in claim 1, wherein the microwave ultrasonic method further comprises stirring the hydroxide precipitate in the pickling solution at a stirring speed between 150 rpm and 200 rpm.

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