Method for increasing leaching rate of galvanized scrap steel through double-source driving

Abstract

The invention discloses a method for increasing the leaching rate of galvanized scrap steel through double-source driving, relates to the technical field of metallurgy, and aims at solving the problem that an existing method for leaching zinc from the galvanized scrap steel with the high leaching rate is long in time consumption. The method comprises the following steps: pouring a sufficient alkaline leaching solution into a working container in an alternating magnetic field, putting to-be-treated galvanized scrap steel, applying ultrasonic waves to two ends of the container, keeping the temperature of the solution in a temperature range suitable for alkaline leaching, and carrying out alkaline leaching under the common driving of two energy sources of the alternating magnetic field and the ultrasonic waves; the method is simple in steps and equipment, convenient and fast to operate and capable of remarkably improving the extraction rate of surface zinc.

Description

Technical Field

[0001] The invention relates to the technical field of metallurgy, and in particular to a method for increasing the leaching rate of galvanized scrap steel by dual-source driving. Background Art

[0002] Steel has excellent mechanical properties and is the manufacturing material for many equipment, but it is easily corroded and damaged. In order to prevent steel from being corroded, it is often necessary to perform surface treatment on the steel. Among them, galvanizing on the surface of steel is a method with excellent anti-corrosion performance, low cost and wide application, such as in automobile manufacturing, refrigerators, construction industry, ventilation and heating facilities, and home appliance manufacturing.

[0003] Due to the application of galvanized steel, it is inevitable that galvanized steel waste, processing scraps, defective products, recycled materials from waste equipment, etc. will be generated in the production process. A lot of galvanized scrap steel is also generated. These scrap steels can be recycled and smelted for steel manufacturing, which has extremely high economic benefits. However, if the galvanized scrap steel is not treated and directly returned to the furnace for smelting, the zinc on the surface of the scrap steel will form zinc-containing dust during the smelting process. This is a hazardous waste, causing environmental pollution or increasing the cost of dust treatment.

[0004] At present, the prior art also has a scheme for recycling and processing waste galvanized steel materials. For example, in the invention patent application with publication number CN108301021A, entitled "A method for extracting high-purity flaky metallic zinc powder from the surface of waste galvanized steel plates", it is disclosed that the waste scraps of galvanized steel plates are leached with a 1-10M strong alkaline solution. The injection amount of the strong alkaline solution is 3-5 cubic meters of the strong alkaline solution for 1 ton of raw material. After soaking at a constant temperature of 10-100°C for 30-240 minutes, the zinc content in the analyzed solution is 2 0~50g / L is used to determine that the dezincification of the raw material waste galvanized steel plate is completed, and then zinc is extracted from the leachate, wherein the leaching rate of zinc can reach 97%~99.5%. However, if this method wants to achieve this leaching rate, it takes a long time. For example, the extraction rate of surface zinc after soaking for 120 minutes given in the embodiment is 97~98%, the extraction rate of surface zinc after soaking for 180 minutes is 98~99.5%, and the extraction rate of surface zinc after soaking for 240 minutes is 98%-99%. Excessive leaching time is not conducive to production.

[0005] For another example, in the invention patent application with the publication number CN114032402A and the title of "Method for Recycling Zinc from Galvanized Steel Sheets", it is disclosed that the galvanized steel sheets are soaked and stirred in an alkali solution with a concentration of 1 to 10 mol / L at a temperature of 10 to 100 °C. When the zinc concentration in the solution reaches 10 to 20 g / L, 1 to 10 mol / L of the alkali solution is added to continue soaking and stirring to obtain an alkali leaching solution. The total soaking time is 10 to 240 min. This invention can improve the leaching rate of galvanized sheets, but it is also based on a relatively long leaching time. For example, in its examples, the extraction rate of the surface zinc reaches 99.995% after soaking for 50 + 40 minutes, and the extraction rate of the surface zinc reaches 99.996% after soaking for 90 + 60 minutes. Moreover, in order to achieve the effect of high leaching rate, the galvanized steel sheets need to be crushed into small pieces for alkali leaching, the process is relatively complex, and the operation of adding different alkali solutions is more unsuitable for production, requiring more raw material storage space and personnel configuration process. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for enhancing the leaching rate of galvanized scrap steel by dual-source drive, so as to solve the problem that the existing methods for leaching zinc from galvanized scrap steel with a relatively high leaching rate take a long time.

[0007] To achieve the above purpose, the present invention provides the following technical solution: A method for enhancing the leaching rate of galvanized scrap steel by dual-source drive, including the following specific contents: Pour a sufficient amount of alkali leaching solution into a working container under an alternating magnetic field. After putting the galvanized scrap steel to be treated, apply ultrasonic waves at both ends of the container, and keep the solution temperature within the temperature range suitable for alkali leaching, and perform alkali leaching under the joint drive of two energy sources, namely the alternating magnetic field and ultrasonic waves.

[0008] Preferably, during the above alkali leaching process, the magnetic induction intensity of the alternating magnetic field is 10 -5 ~10 -3 T, the frequency is 10 to 280 Hz; the ultrasonic power is 15 to 500 W, the ultrasonic frequency is 30 to 120 kHz; the concentration of the alkali leaching solution is 5 to 15 mol / L, the alkali leaching temperature is 20 to 95 °C, and the alkali leaching time is 1 to 40 min.

[0009] Preferably, before pouring the alkali leaching solution into the working container, the alkali leaching solution is preheated and heated up. The working container uses a device with a heating function, and the solution temperature is monitored during the alkali leaching process.

[0010] Preferably, the above working container is made of insulating material.

[0011] Preferably, the above alkali leaching solution is a NaOH / KOH solution.

[0012] Preferably, the solid-liquid ratio of the above galvanized scrap steel to the alkali leaching solution is 1:5 to 11.

[0013] Preferably, a conveyor belt that is insulating and alkali-resistant is used to transport the galvanized scrap steel material to be processed, and a part of the conveyor belt carrying the galvanized scrap steel passes through the alkali leaching solution in the working container through a turning wheel.

[0014] Preferably, during the above alkali leaching process, the temperature is maintained at 40 °C, the concentration of the alkali leaching solution is 10 mol / L, the magnetic induction intensity of the alternating magnetic field is 10 -4 T, the frequency is 200 Hz, the ultrasonic frequency is 47 kHz, the ultrasonic power is 18 w, and when the alkali leaching time is 20 min, the extraction rate of zinc on the surface layer of the galvanized scrap steel reaches 99%.

[0015] Compared with the prior art, the beneficial effects of the present invention are:

[0016] The method for enhancing the leaching rate of galvanized scrap steel by dual-source drive, by placing the galvanized scrap steel in a working container with an alternating magnetic field, the electromagnetic oscillation generated by the alternating magnetic field in the galvanized scrap steel to be processed will change the electrode potential. At the same time, ultrasonic waves are applied at both ends of the container, and alkali leaching is carried out under the co-driving of the alternating magnetic field and ultrasonic waves. Compared with the prior art, the leaching rate can be significantly increased, and the extraction rate of zinc on the surface layer can reach 99% in only 20 minutes; the steps and equipment of this method are simple, the operation is convenient and fast, and it can be used for production speed-up such as the reuse of galvanized scrap steel and the recovery of coating metals, and is suitable for industrial production applications. Description of the Drawings

[0017] Figure 1 It is a schematic diagram of the leaching process of an embodiment of the present invention. Detailed Embodiments

[0018] The method of the present invention aims to greatly shorten the leaching time of zinc on the surface layer of galvanized scrap steel, thereby reducing the production time cost. For details, refer to Figure 1 A method for enhancing the leaching rate of galvanized scrap steel by dual-source drive of the present invention includes:

[0019] Pour a sufficient amount of alkali leaching solution (it is known that it should at least cover the material and should be in excess relative to the surface zinc coating to be leached) into the working container with an alternating magnetic field. After putting the galvanized scrap steel to be processed, apply ultrasonic waves at both ends of the container, keep the solution temperature within the temperature range suitable for alkali leaching, and carry out alkali leaching with the co-assistance of the alternating magnetic field and ultrasonic waves. The working container is preferably made of insulating material to avoid being affected by the alternating magnetic field..

[0020] For reference during the alkali leaching process, the magnetic induction intensity of the alternating magnetic field is preferably 10 -5 ~10 -3T, with a frequency of 10 - 280 Hz (the frequency of the AC power supply connected to the magnetic induction coil); the ultrasonic power is preferably 15 - 500 W, and the ultrasonic frequency is preferably 30 - 120 kHz; the concentration of the alkali leaching solution is preferably 5 - 15 mol / L, the alkali leaching temperature is preferably 20 - 95 °C, and the alkali leaching time only needs 1 - 40 min. When it is more than 30 min, the zinc leaching rate on the surface of the galvanized scrap steel can reach more than 99.99%. The following is further illustrated by examples;

[0021] In addition, the above alkali leaching solution can adopt NaOH / KOH solution. Further optionally, the solid-liquid ratio of the galvanized scrap steel to the alkali leaching solution is 1:5 - 11. This is only for reference in implementation, and it can be determined according to the specific production process in practice. For example, in order to achieve automated production, an insulating and alkali-resistant conveyor belt can be used to transport the galvanized scrap steel material to be processed, and a part of the conveyor belt carrying the galvanized scrap steel can pass through the alkali leaching solution in the working container through a turning wheel. In this common immersion and transportation mode in various fields, the alkali leaching solution can be used in excess, and even a drainage system and a liquid addition pump can be added to the working container to maintain the concentration of the alkali solution in the working container, etc. Temperature control can also be achieved by heating the alkali leaching solution outside the working container and then recycling it to the working container. However, these are not the key points protected by the present invention and can be improved by referring to the existing technology. Just pay attention to insulation and alkali resistance, so it will not be elaborated here.

[0022] In an optional implementation manner, before the alkali leaching solution is poured into the working container, the alkali leaching solution is preheated and heated up. Further preferably, the working container can adopt a device with a heating function, and the solution temperature is monitored during the alkali leaching process. A digital display thermometer with a sensor can also be used to assist in monitoring the temperature. Of course, a working container with temperature control can also be used.

[0023] Refer to Figure 1 , in the present invention, the alternating magnetic field can be provided by a magnetic induction coil connected to an alternating current. This is the prior art and will not be elaborated here. The specific direction of the magnetic field does not affect the required effect of the present invention. In the present invention, the alternating magnetic field is to generate electromagnetic oscillation in the galvanized scrap steel to be processed, thereby changing the electrode potential, increasing the overpotential, and thus increasing the reaction current density. See the following mechanism analysis for details; the specific method of applying ultrasonic waves at both ends of the container is the prior art, such as fixing the ultrasonic wave generating device on the outer wall of the container, etc. Of course, ultrasonic waves can also be applied at the bottom of the container. However, in order to reduce the influence of the alternating magnetic field on the ultrasonic instrument, it is best as Figure 1 shown, the ultrasonic instrument is set outside the coil. Similarly, a container into which the ultrasonic equipment can be poured or a container with ultrasonic heating and temperature control equipment at the same time can be used. It should be understood that the focus of the present invention does not lie in the form of the container. The key lies in the required unit operations including: ultrasonic waves and alternating magnetic fields. Since it can also be carried out at room temperature, heating and temperature control of the alkali leaching solution are not necessary.

[0024] The raw materials used in the following examples are galvanized scrap steel, which has a stable source and low price, and the zinc content is 0.3 - 4%.

[0025] Example 1

[0026] The galvanized scrap steel used in this example is an electro-galvanized sheet, and the zinc content on its surface layer accounts for about 0.5%. Heat the 5mol / L NaOH solution to 75°C, pour it into a temperature-controlled container with ultrasonic generators at both ends and keep the temperature at 75°C. Immerse the galvanized sheet in the solution, and insert the container with the galvanized sheet into a magnetic induction coil. The magnetic induction intensity of the alternating magnetic field provided is 10 -3 T, the frequency is 50 Hz. Turn on the ultrasonic wave, the ultrasonic frequency is 47kHz, and the ultrasonic power is 36w. Take out the galvanized sheet after soaking for 5 minutes, wash the residual NaOH solution on the surface and air-dry it and weigh it. The mass of the galvanized sheet decreases from 25.660 at the beginning to 25.540g, and the reduction amount accounts for about 0.468% of the total weight. The extraction rate of zinc on the surface layer of the galvanized sheet is about 93%.

[0027] Example 2

[0028] The galvanized scrap steel used in this example is the same as that in Example 1, and the parameter conditions are also the same as those in Example 1. Only the alkali immersion time is increased. Take out the galvanized sheet after soaking for 10 minutes, wash the residual NaOH solution on the surface and air-dry it and weigh it. The mass decreases from 25.660 to 25.535g, and the reduction amount accounts for about 0.487% of the total weight. The extraction rate of zinc on the surface layer of the galvanized sheet is greater than 97%, and the effect of alkali immersion for 120 minutes in the existing technology can be achieved in only 10 minutes.

[0029] Example 3

[0030] The galvanized scrap steel used in this example is a hot-dip galvanized sheet, and the zinc content on its surface layer accounts for about 2%. Pour the 10mol / L NaOH solution into a temperature-controlled container with ultrasonic generators at both ends, heat it and keep the temperature at 40°C. Immerse the galvanized sheet in the solution, and insert the container with the galvanized sheet into a magnetic induction coil. The magnetic induction intensity of the alternating magnetic field provided is 10 -4 T, the frequency is 200 Hz. Turn on the ultrasonic wave, the ultrasonic frequency is 47kHz, and the ultrasonic power is 18w. Take out the galvanized sheet after soaking for 20 minutes, wash the residual NaOH solution on the surface and air-dry it and weigh it. The mass decreases from 28.780 to 28.210g, and the reduction amount accounts for 1.981% of the total weight. The extraction rate of zinc on the surface layer of the galvanized sheet exceeds 99%, and the effect of alkali immersion for 240 minutes in the general existing technology can be achieved in only 20 minutes.

[0031] Example 4

[0032] The galvanized scrap steel used in this embodiment is hot-dip galvanized sheet, and the zinc content on its surface layer accounts for about 4%. Heat the 10 mol / L NaOH solution to 85 °C, pour it into a temperature-controlled container with ultrasonic generators at both ends and keep the temperature at 85 °C. Immerse the galvanized sheet in the solution, and insert the container with the galvanized sheet into the magnetic induction coil. The magnetic induction intensity of the alternating magnetic field provided is 10 -3 T, the frequency is 200 Hz. Turn on the ultrasound, the ultrasonic frequency is 63 kHz, and the ultrasonic power is 80 w. After soaking for 30 minutes, take out the galvanized sheet, wash the residual NaOH solution on the surface and air-dry it and weigh it. The mass decreases from 26.530 to 25.469 g, and the reduction amount exceeds 3.999% of the total weight. The extraction rate of zinc on the surface layer of the galvanized sheet exceeds 99.98%.

[0033] Since the method of the present invention performs alkali leaching under the co-driving of two energy sources, alternating magnetic field and ultrasonic wave, it can be adjusted in terms of various parameters of the two. If a higher extraction rate is to be achieved, there is no need for an ultra-long alkali leaching time. However, since the method of the present invention can reach an extraction rate of 99% in 20 minutes, and even exceed 90% in 5 minutes, specifically, it can be calculated according to production costs and outputs which process parameters are more economical, rather than blindly pursuing the extreme extraction rate.

[0034] To further illustrate the advantages of the solution of the present invention, the following uses two relatively excellent existing technologies introduced in the background technology. By reproducing the solutions recorded in the embodiments of their specifications and performing a total of 20 minutes of alkali leaching in the same way as in Example 3 of the present invention, the experimental situation is as follows:

[0035] Comparative Example 1:

[0036] Adopt the solution in the existing patent CN108301021A, and the zinc content on the surface layer of the used galvanized scrap steel plate is 1.2%;

[0037] Crush the galvanized scrap steel plate to a geometric size of 10 - 50 cm and put it into the leaching container. According to the description in its specification, add 3 cubic meters of strong alkali solution to 1 ton of galvanized scrap steel, and add sodium hydroxide solution with a concentration of 5 M for leaching; control the temperature at 85 °C during leaching. After soaking for 20 minutes, take it out and detect and calculate that the extraction rate of zinc on the surface layer of the galvanized scrap steel is only 21.5%.

[0038] Comparative Example 2:

[0039] Adopt the solution in the existing patent CN114032402A, and the zinc content on the surface layer of the used galvanized scrap steel plate is 2%;

[0040] Wash the uncrushed galvanized scrap steel plate to remove impurities and oil on the surface.

[0041] Mix the cleaned galvanized waste steel plates with 240 g / L NaOH, stir and soak for 10 minutes at 15 revolutions per minute, and the soaking temperature is 85 °C.

[0042] After 10 minutes, add 200 g / L NaOH. The volume ratio of 240 g / L NaOH to 200 g / L NaOH is 1.5:0.8, and the total solid-liquid ratio of the galvanized waste steel plates to the two alkaline solutions is 1:3 - 10.

[0043] After adding, keep the temperature at 85 °C, continue stirring and soaking for another 10 minutes, then take out and detect. The extraction rate of zinc on the surface of the galvanized waste steel is only 8.5%.

[0044] The above two comparative examples prove that the wide range of alkaline soaking time disclosed in the prior art is not the time with excellent effect, but only the time that can be implemented and can leach the surface zinc.

[0045] Before conducting the experiments of the present invention, a large number of assumptions and theoretical analyses were carried out. The analysis process related to the content of the present invention is as follows:

[0046] Dissolution reaction mechanism of the surface zinc of galvanized waste steel in alkaline solution

[0047] Anode (oxidation): Zn(s) + 4OH − → [Zn(OH)4] 2− + 2e −

[0048] Cathode (reduction): 2H2O + 2e − → H2(g) + 2OH −

[0049] The overall reaction equation is: Zn(s) + 2OH − + 2H2O → [Zn(OH)4] 2− + H2(g)

[0050] The Gibbs free energy ΔG of the whole reaction can be calculated by the sum of the ΔG of the two half-reactions. The ΔG of each half-reaction is related to the standard electrode potential. In electrochemistry, the relationship between the electrode potential (E) and the Gibbs free energy change (ΔG) of the related reaction is as follows:

[0051] ΔG° = -nFE°

[0052] Where n is the number of electrons transferred, F is the Faraday constant, and E° is the standard electrode potential. The electromotive force of the overall reaction is the E° of the cathode minus the E° of the anode (as the reduction potential).

[0053] [Zn(OH)4] 2− + 2e− → Zn + 4OH − Its E°(anodic reduction) = -1.199 V. Therefore, the potential for the anodic oxidation reaction is +1.199 V.

[0054] 2H2O + 2e − → H2 + 2OH − Its standard reduction potential E°(cathode) = -0.828 V (relative to the standard hydrogen electrode).

[0055] The total electromotive force E°cell = E°cathode - E°anode (reduction potential), i.e., E°cell = (-0.828 V) - (-1.199 V) = 0.371 V.

[0056] Here n = 2 mol of electrons and F = 96485 C / mol, so ΔG° = -2 * 96485 * 0.371 ≈ 71592 J / mol, i.e., ΔG°≈ -71.6 kJ / mol < 0. This indicates that the dissolution reaction of zinc in an alkaline solution can proceed spontaneously under standard conditions.

[0057] Reinforcement mechanism of electromagnetic oscillation

[0058] From the perspective of electrochemical kinetics, according to the Butler - Volmer equation

[0059]

[0060] where i is the reaction current density, i0 is the exchange current density, α is the transfer coefficient, n is the number of electrons transferred in the reaction (n = 2 for this reaction), F is the Faraday constant (96485 C / mol), η is the overpotential, R is the gas constant, and T is the temperature. Applying an alternating magnetic field to generate electromagnetic oscillation in the metal will change the electrode potential, increase the overpotential η, and thus increase the reaction current density i;

[0061] According to Faraday's law, the reaction rate v is proportional to the current density i:

[0062]

[0063] Reinforcement mechanism of ultrasonic wave

[0064] According to Fick's first law:

[0065]

[0066] In the formula, represents the diffusion rate; is called the diffusion coefficient (m² / s), is the concentration gradient. The symbol " " indicates that the diffusion direction is the opposite of the concentration gradient. The vibration of ultrasonic waves can increase the diffusion coefficient and thus increase the diffusion rate .

[0067] The overall reaction rate is jointly determined by the electrochemical step and the mass transfer step:

[0068]

[0069] The electrochemical rate ∝ , the mass transfer rate ∝ ; The alternating magnetic field increases , the ultrasonic wave increases , and the synergistic effect significantly accelerates the overall reaction.

[0070] From the above analysis, it is not difficult to see that whether ultrasonic assistance is used alone, alternating magnetic field assistance is used alone, or the synergistic effect of alternating magnetic field and ultrasonic wave is used together, it is beneficial to the surface zinc leaching during the alkaline leaching of galvanized scrap steel. However, from the actual experimental results, especially from the results of Example 3 and the comparative example, the acceleration effect achieved by using the two in synergistic assistance is unexpected, and the high rate brought by it far exceeds the expectation in theoretical analysis.

[0071] The above is only a preferred embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope defined by the claims.

[0072] The parts not detailed in the present invention are all well-known technologies to those skilled in the art.

Claims

1. A dual-source driven method for improving the leaching rate of galvanized scrap steel, characterized in that: The method includes the following specific contents: pouring a sufficient amount of alkali leaching solution into a working container in an alternating magnetic field, placing the galvanized scrap steel to be processed, applying ultrasonic waves at both ends of the container, maintaining the solution temperature in a temperature range suitable for alkali leaching, and carrying out alkali leaching under the joint drive of the alternating magnetic field and ultrasonic waves as two energy sources.

2. The method for improving the leaching rate of galvanized scrap steel by dual-source drive according to claim 1, characterized in that: During the alkali leaching process, the magnetic induction intensity of the alternating magnetic field is 10 -5 ~10 -3 T, frequency is 10-280 Hz; ultrasonic power is 15-500 W, ultrasonic frequency is 30-120 kHz; concentration of alkali immersion solution is 5-15 mol / L, alkali immersion temperature is 20-95°C, and alkali immersion time is 1-40 min.

3. The method for improving the leaching rate of galvanized scrap steel by dual-source drive according to claim 1, characterized in that: Before the alkali leaching solution is poured into the working container, the alkali leaching solution is preheated and the working container adopts a device with a heating function, and the solution temperature is monitored during the alkali leaching process.

4. The method for improving the leaching rate of galvanized scrap steel by dual-source drive according to claim 1, characterized in that: The working container is made of insulating material.

5. The method for improving the leaching rate of galvanized scrap steel by dual-source drive according to claim 1, characterized in that: The alkaline leaching solution is a NaOH / KOH solution.

6. The method for improving the leaching rate of galvanized scrap steel by dual-source drive according to claim 1, characterized in that: The solid-to-liquid ratio of the galvanized scrap steel to the alkaline immersion solution is 1:5-11.

7. The method for improving the leaching rate of galvanized scrap steel by dual-source drive according to claim 1, characterized in that: An insulated and alkali corrosion-resistant conveyor belt is used to transport the galvanized scrap steel material to be processed, and a part of the conveyor belt carrying the galvanized scrap steel is passed through the alkali leaching solution in the working container through a steering wheel.

8. A method for improving the leaching rate of galvanized scrap steel by dual-source drive according to any one of claims 1 to 7, characterized in that: During the alkali leaching process, the temperature was maintained at 40°C, the concentration of the alkali leaching solution was 10 mol / L, and the magnetic induction intensity of the alternating magnetic field was 10 -4 When the frequency is 200 Hz, the ultrasonic frequency is 47kHz, the ultrasonic power is 18w, and the alkali immersion time is 20min, the extraction rate of zinc on the surface of galvanized scrap steel reaches 99%.

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