JPH04210434A - Dezincification method for galvanized steel plate scrap - Google Patents

Abstract

PURPOSE:To recover steel scrap free from zinc by crushing scraped galvanized steel plate into splinters having curved surface and after dissolving zinc with sulfuric acid, washing and cleaning them successively. CONSTITUTION:The scrap of galvanized steel plate is cut into small pieces having curved surface by the shredder 1. A part of zinc peeled off are separated from zinc adhered splinters by magnetic separator. The splinters adhered with zinc are charged into extraction tank 4, where add sulfuric acid to dissolve adhered zinc. The splinters are contacted with sulfuric acid as full as possible without overlaying by the presence of their curved surfaces and zinc is dissolved completely and sent to stopping tank 5 and after retained in a short time, charged into washing tank 6 and added with hot water to clean the outer surface of splinters completely and then separated from the hot water and dried naturally by the sensible heat, and recycled as high purity steel splinters free from zinc. Sulfuric acid solution incorporating extracted zinc is sent to the adding tank 8 where zinc dust is added and its pH is adjusted, then transferred into oxidation and neutralization tank 9 where hydrogen peroxide is added to oxidize ferrous ion into ferric ion then CaCO3 is added to precipitate Fe ion as ferric hydroxide. Finally, the surfuric acid containing zink is executes electrolyzed in the ZnSO4 electrolysis bath 11 and recovered on the cathod as electrolytic zinc.

Description

[Detailed description of the invention]

[00011

[Industrial Application Field] The present invention removes zinc from galvanized steel sheet scrap to produce high-grade steel scrap as an iron source for cast iron and the like.
This relates to a method for recovering iron sources. [0002] In recent years, the rust prevention of automobile exterior panels has been strengthened, and galvanized steel plates have come to be used for most of the steel plates constituting the vehicle body. Concomitantly, a large amount of zinc-plated steel sheet scrap is generated, and zinc-plating has become a major problem in recycling. That is, galvanized steel sheet scrap is often used as steel scrap for cast iron because the original steel sheet has a very high purity. [0003] During the melting of L oak, a large amount of zinc white is generated in a low frequency melting furnace, which poses a major problem in terms of occupational health. Furthermore, there is the problem that zinc penetrates into the wall of the low-frequency furnace, deposits on the coil, causes a short circuit, causes damage to the coil, and significantly shortens the life of the furnace wall. [0004] Also, in cupola melting, it adheres to the heat exchanger, significantly reducing its performance and, in extreme cases, causing it to lose its function altogether. In addition, a large amount of dust containing zinc is generated, which causes clogging of the filter cloth of the dust collector, and the disposal of the collected dust has become a major problem. [00051L Karuni zinc-plated copper plate has a high purity and high purity close to pure iron to improve deep drawability as described in [1n]
It is a 4 degree steel and is the highest grade steel scrap for cast iron. However, since the problem of zinc during melting as mentioned above has not been resolved, it has been evaluated as low-grade steel scrap and is increasingly used as steel scrap for electric furnace steelmaking, which has become a major problem in terms of iron resources. It has become. For these reasons, a technology for removing zinc from galvanized steel sheet waste prior to melting has been desired not only from the iron casting industry but also from the perspective of recovering the useful metal called zinc. [00061 As a method for removing zinc from galvanized steel sheet scraps, for example, as described in JP-A-6:3-96224, zinc-coated steel sheet scraps are heated at 700 to 900°C.
A method has been proposed in which the plated zinc is heated to an intermetallic compound with iron and then shot blasted to take advantage of the difference in physical properties from the original plate to peel it off. It has the disadvantage that it remains alloyed and cannot be completely removed. Furthermore, iron alloyed with zinc and partially oxidized iron are separated, resulting in a lower iron yield. Furthermore, there still remains the problem of processing dust mainly composed of zinc and iron, which has been peeled off and recovered by blasting. At present, processing of dust containing metal oxides requires a large amount of cost. [0007] Furthermore, as described in Japanese Patent Application No. 55-160754, galvanized steel sheet scraps are held above the melting furnace, and the exhaust heat of the furnace is used to evaporate and recover the zinc, as well as to remove the steel scraps. A method of using it for preheating has been proposed. However, in this method as well as the above-mentioned method, it is necessary to maintain the temperature at around 1100°C in order to distill the plated zinc.
Iron yield decreases due to oxidation of the base metal, and there may be problems in processing the recovered zinc dust. [0008] Furthermore, a method has been proposed in which zinc-plated steel sheet scrap is electrolyzed in an alkaline solution to recover zinc. This method has the advantage that useful zinc can be recovered directly, but has the major disadvantage that the processing time is extremely long and a large amount of steel scrap cannot be processed in a short period of time. [0009]

[Problems to be Solved by the Invention] The present invention comprises (1) a first step of dividing galvanized steel sheet scrap into pieces with predetermined curved surfaces; The second step is extraction, the third step is to stop the reaction of sulfuric acid on the surface of the dezincified steel sheet scraps from which zinc has been removed in the second step, and the dezincified steel sheet scraps that have stopped the reaction in the third step are washed with water. A fourth step is to dry the dezincified steel sheet scraps washed in the fourth step, and a sixth step is to neutralize excess free acid by adding zinc powder to the sulfuric acid solution from which zinc was extracted in the second step. An oxidizing agent is added to the zinc extraction solution obtained in the sixth step to change the dissolved iron ions from divalent to trivalent, and then lime water is added to precipitate and filter the dissolved trivalent iron ions. A method for dezincing galvanized steel sheet scrap, characterized in that it consists of a seventh step and an eighth step of electrolytically recovering zinc from the extract from which iron has been removed in the seventh step, and (2) the method described above. In the -th step, the steel plate layer is 5cm x 5cm or less and has a bulk density of 1. 5t
The above-mentioned (1
) The method for dezincing galvanized steel sheet scrap as described in item 3), characterized in that in the second step, shredder dust collected zinc powder is added to the sulfuric acid solution at the end of zinc extraction to neutralize excess free acid. (4) In the fourth step, the temperature of the washing water is set to 60°C.
The method for dezincing galvanized steel sheet scrap according to the above item (1), (2) or (3), characterized in that hot water is used at ~100°C. It is. [00103 Hereinafter, the present invention will be specifically explained. [00111 FIG. 1 shows a schematic diagram of the dezincing process steps of the present invention. [0012] Each step of the present invention will be explained below. [)013] The -th step is a step of cutting galvanized zinc from galvanized steel sheet scrap into a size that can be easily extracted. The size and shape of galvanized steel sheet waste vary, ranging from extremely large to small, curved and flat plates, and if left as is, it will impede extraction work and efficiency. [00141] Therefore, it has been found that in order to increase and stabilize the extraction efficiency of plated zinc, which will be described later, it is preferable to have a predetermined size, shape, and bulk density. The means to accomplish this is to shred it, preferably with a shredder. That is, when cut with a shredder, the galvanized steel layer is subdivided with an appropriate curvature. In general cutting, galvanized steel sheet scraps are flat plates that tend to stick together, and extraction of overlapping surfaces requires a long time even if the extraction solution is stirred or the steel sheet layers are shaken. By shredding, the steel sheet layer is subdivided and at the same time has an appropriate curvature, which makes it difficult for them to stick together, making the extraction in the next process much more efficient. [0015] However, if the shredder is used to roll it too much, it will be difficult for the extract liquid to penetrate, making it difficult to extract zinc, and there is a risk that moisture will remain during drying in the fifth stage, causing problems such as explosion during dissolution. Therefore, as shown in Figure 2, its dimensions are 5 cm x 5 cm or less, and the bulk density is 1.5 tons.
It was confirmed that zinc can be completely extracted with sulfuric acid when shredded to a value of /m3 or less. That is, when this range is exceeded, for example when the subdivision size is large, the proportion of the overlapping parts of the surfaces increases and extraction of that part is hindered. Furthermore, if the bulk density is increased too much by rounding the material too much, it becomes difficult to extract zinc from the bag-shaped portion. [00161 The second step is a step of extracting zinc from the curved finely divided galvanized steel sheet scrap using sulfuric acid. [001,7] When recovering extracted zinc by electrolysis, it is preferable that the zinc concentration of the extract is higher. Therefore, it is preferable to perform the extraction treatment with an extract having a higher sulfuric acid concentration. Naturally, the higher the sulfuric acid concentration, the higher the extraction rate, but if the sulfuric acid concentration and equivalent Zn cannot be balanced, a problem arises in that the amount of dissolved iron base increases accordingly. [00181 Since the curved and finely divided galvanized steel stratification treated in the first step of the present invention has a property that allows its quantity to be controlled, the sulfuric acid concentration can be controlled by dividing and feeding a predetermined amount of galvanized steel sheet scrap. It is possible to balance the amount of steel plate scrap containing the equivalent amount of Zn, and the melting of the base metal can be minimized. [00191 Figure 3 shows dimensions of 5 x 5 cm, bulk density of 1.0
Amount of steel scraps for extraction: 2 m3 of galvanized steel sheet scraps with a curved surface of t/m3, solvent volume: 2 m3, liquid temperature: room temperature, stirring: none.
This is the relationship between the free sulfuric acid concentration under the extraction conditions of t and the extraction completion time. From this, the preferable concentration of sulfuric acid is such that the concentration of free sulfuric acid is 5 to 1.25 times the amount of free sulfuric acid equivalent to the amount of extracted zinc in the immersed steel sheet layer. If the sulfuric acid concentration is higher than this, no improvement in the extraction rate can be expected, and the risk of dissolution of the base iron in the steel sheet layer increases. Furthermore, as zinc and sulfuric acid approach an equivalence relationship, the extraction rate decreases. Therefore, in order to maintain a practical extraction rate, it is preferred that the amount of sulfuric acid be 1.25 times or more the amount of sulfuric acid equivalent to the amount of Zn to be extracted. [0020] Therefore, the maximum amount of galvanized steel sheet scrap that can be immersed in the solvent amount is divided into a sulfuric acid solution with a concentration in this range,
If only the final input amount is adjusted so that the amount of free sulfuric acid is 1.25 times or more the zinc equivalent, the erosion loss of the steel base is small and the extraction rate can be maintained at a high level. In other words, replacing the extract with a fresh one while the free acid concentration is high increases the extraction rate, but increases the amount of zinc powder added to neutralize the free acid in the sixth step described below. However, continuing extraction in a state where the free acid content is low increases the extraction time, and in order to maintain production capacity, many extraction tanks are required, which increases equipment costs. Therefore, during the final extraction, in order to completely remove Zn from the steel sheet layer, the amount of steel sheet scraps input should be controlled so that the amount of sulfuric acid slightly exceeds the amount of sulfuric acid equivalent to the amount of extracted zinc, preferably 1.25 times the amount shown above. It is preferable. [00211L However, even if such an extraction method is used, a large amount of lime for neutralization is required in the sixth step. In order to solve this problem, metal zinc powder is added to the sulfuric acid solution at the end of the extraction to neutralize the free acid. In one embodiment of the present invention, zinc dust exfoliated during the fragmentation treatment in the first step is used as the zinc dust. This made it possible to dispose of the waste collected dust and save on lime for neutralization. Extraction with relatively high concentrations of sulfuric acid and neutralization of the free acid with zinc dust dramatically increased the processing speed of this method. Furthermore, the extraction rate of zinc is 99.0% or more, the elution rate of iron is very small at 0.4% or less, and the iron yield is high. [00221 In this process, even if the curved surfaced finely divided galvanized steel sheet scraps are in contact with each other, extraction of zinc with sulfuric acid hardly progresses. Therefore, it is necessary to stir the above-mentioned zinc-plated steel sheet scraps, but this stirring can be carried out to the extent that, for example, compressed air is blown into the scraps to completely extract the scraps. This is made possible by shredding the steel plate layer to a predetermined size and appropriate curvature in the first step. Further, by using air in this step, an incidental effect is observed in which some 2#J iron ions are oxidized to become trivalent iron ions. [0023N The third step is a step to stop the reaction of sulfuric acid adhering to the shoulder of the dezincified steel sheet after zinc extraction. By including this stopping step, it is possible to prevent excessive melting of the base metal and to significantly save clean water for washing in the next step. That is, a small amount of sulfuric acid is washed away in this step, and the amount of sulfuric acid carried into the next step is significantly reduced. In this step as well, the effect of stopping is promoted by blowing in compressed air. [0024] The fourth step is a step of washing the dezincified steel sheet layer with water. Another aspect of the invention provides a layer of dezincified steel of about 6
It has been found that by washing with hot water at 0 to 100°C, zinc sulfate, etc. can be washed more completely, and it works effectively in the next drying process. That is, the surface of the dezinced steel sheet layer is very active and easily rusts, but in the fifth drying step, it is dried using equipment that only drains water, and the surface does not rust. This makes it possible to significantly suppress the increase in slag as an iron source for cast iron, as well as the occurrence of rust, which causes depletion of useful components such as St and Mn due to oxidation. In this step, steam is preferably used to raise the temperature of the water. This is because by blowing in steam, heating and stirring can be performed simultaneously. [0025] The fifth step is a drying step. This step is closely related to the fourth step, and when moving from the fourth step to the fifth step, if the water is drained sufficiently, the attached moisture will immediately evaporate due to its own heat and the heat held by the steel plate layer. Auxiliary drying using a small amount of cold air is sufficient. In this process, if the storage area is completely drained, it can also be used as a product storage area for the dezincified steel sheet layer. [0026] The sixth to eighth steps recover the extracted zinc as metallic zinc, and regenerate the sulfuric acid that is the extract liquid.
This is a process for reuse. [0027] The sixth step is a step of neutralizing excess free acid, as mentioned in the second step. In extracts with low free acid content, the dissolution rate of zinc is significantly reduced. Therefore, immersing a galvanized steel sheet layer in such an extraction solution will result in insufficient removal of zinc, reducing its value as an iron source for cast iron, and requiring time for extraction, impairing the economic efficiency of the present invention. To solve this problem, the extraction method described in the second step is used, but this requires an increase in the amount of lime for neutralization. [0028] In order to solve this problem, as described above, the metal zinc powder exfoliated and collected during shredding is added to neutralize it. Since the lead powder is a fine powder, its dissolution rate is high even in a state where there is little free acid, and by providing a reaction tank, excessive addition of -C does not cause problems in subsequent steps. As a result, it is possible to save the amount of lime for neutralization and shorten the processing time of the extraction process, as well as to make effective use of collected dust, which is otherwise difficult to dispose of.7 [0029] The seventh step is This is a step to remove iron that has entered the melt during extraction or Cr, Ni, etc. that have entered the composite plated steel sheet layer, etc., as these are harmful to zinc electrolysis. At this time, divalent iron ions are difficult to completely precipitate and separate by adjusting the pH, so it is necessary to oxidize them with an oxidizing agent. As the oxidizing agent, H202, KMnOn, etc. may be used as appropriate. [00301 Add lime powder etc. to the solution after oxidation p
Adjust to about H5, F' e (OH) 3 and C
r (○■1) 3 is precipitated and separated. [00311 The eighth step is a step of recovering metallic zinc from the saturated zinc sulfate solution obtained in the seventh step by electrolysis. p
After H adjustment, it is electrolyzed and metal zinc is recovered at the cathode.
After melting, it is used as zinc ingot. In addition, the electrolytic solution with a reduced zinc concentration is reused as a zinc extraction solvent. [0032] Through the above eight steps, the zinc on the shoulder of the galvanized steel sheet is recovered and effectively used, and the dezincified steel sheet layer can also be used as an iron source without any problem regardless of the type of melting furnace. Of course, in the present invention, as for the treatment of the extraction solution after the extraction step, depending on the conditions, a method of treating the waste liquid of existing electrolytic galvanizing, that is, a method of adjusting the pH, precipitating and separating Fe and Zn, and disposing it as waste may be used. It is possible to implement. [0033] Next, the present invention will be explained based on examples. [0034]

EXAMPLES Example 1 FIG. 4 is a process outline diagram showing one embodiment of the present invention. [0035] 1 is a shredder, 2 is a shredded galvanized steel plate layer storage area, 3 is a zinc dust storage area, 4 is an extraction tank, 5
is a stop tank, 6 is a cleaning tank, 7 is a drying field, 8 is a zinc dust addition tank, 9 is an oxidation and neutralization tank, ] 0 is a precipitation tank, ] 1 is an electrolytic tank. [0036] A case will be described in which 100 tons of galvanized steel sheet scraps are processed according to the present invention. Galvanized steel sheet scrap is 0.9m
It is plated with zinc with a thickness of m and an average basis weight of 45 g/rn2 (one side). First, press waste from galvanized steel sheets is shredded. As a result, the steel plate layer has a bulk specific gravity of 0. 8t
/rn3], , is cut into steel scraps with a preferred curvature of Ot 7m3. At this point, some of the plated zinc flakes off, but this is separated by a magnetic separator or air separator and is turned into zinc dust, which is then added to the extract in a metal zinc dust addition tank and used for neutralization. The steel scraps are then loaded into the extraction tank using a magnetic crane. 2t/packet. In the extraction tank, zinc is extracted with 2 m' of a solution containing 200 g/l sulfuric acid and 35 g/I zinc at a liquid temperature of 36°C to 39°C. The extraction is completed in about 5 to 10 minutes, during which time air is blown through a nozzle provided at the bottom of the extraction tank to stir the extract. The extracted steel scraps are thrown into a stop tank by reversing the packet. After staying in the stop tank for a very short time, it is immediately put into the cleaning tank. This lasts for several minutes. In the cleaning tank, wash with boiling water at 00°C for about 1.0 minutes. In the second case, steam is blown into the cleaning tank to raise the temperature. After that, it is moved to the drying area by reversing to Heke So 1. The floor of the drying area is a drainer, allowing excess water to fall. In addition, the adhering water evaporates and dries due to its own heat and the heat held by the steel scraps, and the steel scraps do not rust. Dezinced steel scrap is used as a source of high-grade iron for cast iron. [0037] - On the other hand, since the extraction rate of zinc in the extract gradually decreases, when the processing time is about 20 minutes, it is led to the Zn addition tank and added to the zinc dust 1 to adjust the pH to about 4. , cannot be sent to the neutralization tank. In this step, it is preferable to measure the free amount of the extract and manage it accordingly. Thereafter, a new sulfuric acid solution, which is the electrolytic tailing liquid, is injected into the extraction tank. First, 35% H202 is added to the zinc extract in the neutralization tank to oxidize iron ions from 21'ifI'i to trivalent iron. G-202 was used because it is completely harmless and highly effective. Next, Ca and CO3 powders are added to adjust the pH to 5, and iron ions are separated as Fe(OH)3 in the precipitation layer. After drying, the iron sludge is used as raw material for iron manufacturing. [0038] The saturated ZnSO4 solution obtained through this treatment is temporarily stored in a storage tank. This tank is used to adjust the extraction capacity and electrolysis capacity of the equipment. In the electrolytic cell, the bath voltage was 3.5 to 3°6V, the cathode plate AI and the anode plate Pb were used, and the distance between the two poles was 50 m.
The electrolyte is electrolyzed at a current density of 1000 A/m". The electrolytic solution whose zinc content is less than 35 g/l is removed from the electrolytic cell, stored in a storage tank, and used again as an extraction solution. [ [0039] As described above, the results of treating 100 tons of galvanized steel sheet are shown in Table 1.The treatment time, iron yield, dezincing rate, and zinc recovery rate were all very superior compared to the conventional method. I can see that there is. [00401

[Table 1] 00□4]-]

[Effect of the invention] The present invention has made it possible for the first time to completely and massively dezincinate galvanized steel sheet waste before melting it, and by melting the galvanized steel sheet material, In cupolas, there are problems such as heat exchanger clogging, dust collector clogging, and zinc white deposits on the cupola furnace walls, resulting in poor working conditions, shortened furnace wall life, and zinc vapor leakage in low-frequency furnaces. Problems such as short circuits and deterioration of cast iron material due to penetration and precipitation are eliminated. As a result, galvanized steel sheets can be used as high-purity steel scraps as raw materials for cast iron castings. Furthermore, it becomes possible to recover zinc, which is a useful metal, contributing to resource conservation.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the dezincing process of the present invention.

FIG. 2 is a graph showing the relationship between completely extractable steel plate layer size and bulk density.

FIG. 3 is a graph showing the relationship between the sulfuric acid concentration of the extract and the extraction rate.

FIG. 4 is a process outline diagram of one embodiment of the present invention.

[Explanation of symbols]

1... Shredder 2... Galvanized steel plate layer storage area 3... Zinc dust storage area 4... Extraction tank 5... Stop tank 6...
・Cleaning tank 7...Drying place
8... Zinc dust addition tank 9... Oxidation and neutralization tank 10... Sedimentation tank 11... Electrolytic tank

[Figure 1]

[Figure 4]

Claims (4)

[Claims] Claim 1: A first step of dividing galvanized steel sheet scrap into pieces with a predetermined curved surface, a second step of extracting zinc from the finely divided galvanized steel sheet scrap with the curved surface using sulfuric acid; The third step is to stop the reaction of sulfuric acid on the surface of the dezincified steel sheet scrap, which has removed zinc, with fresh water, and the fourth step is to wash the dezincified steel sheet scrap that has stopped the reaction in the third step with water. A fifth step of drying the dezincified steel sheet scrap, a sixth step of neutralizing excess free acid by adding zinc powder to the sulfuric acid solution from which zinc was extracted in the second step, and extraction of the zinc obtained in the sixth step. The seventh step involves adding an oxidizing agent to the solution to change the dissolved iron ions from divalent to trivalent, and then adding lime water to precipitate and filter the dissolved trivalent iron ions. A method for dezincing galvanized steel sheet scrap, comprising an eighth step of electrolytically recovering zinc from the removed extract. Claim 2: In the first step, steel plate scraps are
2. The method for dezincing galvanized steel sheet scrap according to claim 1, wherein the galvanized steel sheet scrap is shredded to a bulk density of 1.5 t/m^3 or less. 3. The galvanized steel sheet scrap according to claim 1 or 2, wherein in the second step, the zinc powder collected by the shredder is added to the sulfuric acid solution at the end of the zinc extraction to neutralize excess free acid. dezincing method. Claim 4: In the fourth step, the temperature of the washing water is set at 60°C.
Claim 1, characterized in that the hot water is from 100°C to 100°C.
2 or 3. Method for dezincing galvanized steel sheet scrap.