JP3687014B2 - Treatment method of chromium-containing iron ore - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a welding or fusing process of chromium-containing alloy steel such as stainless steel or ferrochrome. As for chromium-containing iron ores such as chromium oxides and chromium salts generated by various heat treatments such as dissolution of metallic chromium, extremely harmful hexavalent chromium contained in the iron ore is temporarily stored in the factory. The present invention relates to a detoxification method for chromium-containing slag that prevents damage to human bodies and wastewater pollution due to dust scattering and elution into rainwater during disposal.
[0002]
[Prior art]
When welding chromium-containing alloy steel, especially welding rods that use a welding flux or flux-cored wire (FCW), the so-called slag generated by melting the flux adheres to the weld line after welding. To do.
Therefore, these slags are generated when the core wire or wire of the welding rod is melted by the welding heat together with the flux, and a part of the core wire and the wire, and further the chromium-containing alloy steel as the welding base material is melted. At the same time, some of it will be scattered as welding fumes, or part of it will be transferred into the slag.
By the way, when welding a chromium-containing alloy steel such as stainless steel, a welding rod or welding wire having a composition almost similar to that of the base material to be welded is used as a conventional means for welding construction. According to the test results conducted by the present inventors, it was confirmed that a part of chromium in these alloy components was contained in a state converted to hexavalent chromium designated as a hazardous substance.
According to the study conducted by the inventor in detail about this phenomenon, a part of chromium contained in the core wire, the wire, and the welding base material is about the lime series that is the main component in the flux by the welding heat. Reacts with calcium carbonate, calcium carbonate and calcium fluoride for lime thread flux, and calcium carbonate and titanium oxide for lime titania-based fluxes, such as chromate or chromate such as calcium chromate All are considered to be oxidized to hexavalent chromium.
In other words, as a proof, some of the components in the welding slag are extremely soluble in water, and the diphenylcarbagit method, which is a colorimetric analysis method for hexavalent chromium in JIS factory effluent, is used for the aqueous solution. When the color was developed according to the above, reddish purple coloration was recognized very clearly, and the presence of hexavalent chromium was confirmed.
In addition, the amount of hexavalent chromium in this case is proved to be proportional to the chromium content contained in the welding rod core wire, welding wire or welding base material used, and also proportional to the amount of slag or flux collected. It was done.
In this way, hexavalent chromium contained in weld slag has the property of being easily dissolved in water, so if an operator touches it with a sweaty hand, it immediately dissolves and adheres to the hand, face and other parts. There is a possibility that hexavalent chromium may enter the mouth of the skin, and after the welding work, these welding slag is removed from the welded base metal by grinding work with a sander, grinder, etc. or hammering work with a hammer. It is usual to peel off.
The weld slag thus peeled off is swept up and temporarily stored in the field outside the factory, and is currently exposed to wind and rain.
On the other hand, during the manufacturing process of chromium-containing alloy steel such as stainless steel, or from the melting process of ferrous chrome, metal chromium, etc. of steelmaking materials, and the continuous casting process and hot rolling process after casting, the same as the above welding slag A large amount of iron slag containing a large amount of hexavalent chromium is discharged, but these slag are also collected and temporarily stored in the field outside the factory, and are currently exposed to wind and rain.
The extremely harmful hexavalent chromium contained in the chromium-containing slag such as chromium oxide and chromium salt in such storage state is scattered during the process from floor soil and temporary storage to disposal in the factory. The present situation is extremely high in the risk of damage to human bodies due to elution into water and rainwater, soil contamination, groundwater contamination, and drainage pollution.
As is obvious, the harmfulness of this hexavalent chromium is harmful because it affects the mucous membranes and skin of the human body, and perforation of the nasal septum and carcinogenic effects on the nose, lungs, throat, etc. have been observed due to prolonged suction This is why it is designated as a substance.
In addition, if this seed slag is left outdoors and easily dissolved in rainwater, hexavalent chromium is very strictly regulated as industrial wastewater according to the Water Pollution Control Law.
These facts also prove extremely harmful.
A method that can be considered as a means for safely and harmlessly treating this seed slag with a conventionally known technique is to first pulverize the slag, soak it in water, extract hexavalent chromium from the slag, filter it, In addition, ferrous sulfate or sodium sulfite is added to the filtrate to reduce hexavalent chromium to trivalent chromium, and further, an alkaline agent such as slaked lime is added to precipitate chromium hydroxide, which is separated. Although only a method of removing can be found, such a treatment method is very complicated and troublesome, and these reducing agents require a long time for the treatment because of a mild chemical reaction. In the case of ferrous sulfate, There is a defect that a large amount of iron ions eventually precipitate as ferric hydroxide, and in the case of sodium sulfite, sulfurous acid gas is generated during its handling, which is harmful to the human body. There is a point.
Because of these disadvantages, the above treatment method is not practically used. However, as an alternative treatment method, hexavalent chromium in such harmful chromium-containing slag (welded slag) is used. There is no effective means for fundamentally avoiding the danger, and the current situation is that it is unavoidably left unattended while knowing the danger.
[0003]
[Problems to be solved by the invention]
In response to this situation, the present inventor reduced harmful hexavalent chromium, which is easily soluble in water, in this kind of chromium-containing iron ore into extremely harmless trivalent chromium that is insoluble in water by an extremely simple treatment. We propose a new treatment method that can be safely and quickly detoxified.
[0004]
[Means for Solving the Problems]
In view of the above-mentioned problems, the following is proposed as means for solving this problem.
Chromium-containing alloy steel such as stainless steel and ferrochrome. Ascorbic acid, a metal salt of ascorbic acid, or a kind of ammonium salt on the surface of the chrome-containing slag generated by heat treatment such as melting, rolling, welding, fusing, etc. of metallic chromium By spraying or immersing a solution containing two or more kinds as the main component, hexavalent chromium contained in the slag is reduced to trivalent chromium and rendered harmless, and the processing of the slag after dredging is made safe. It is in the processing method of the chromium containing iron ore characterized by the above-mentioned.
[0005]
[Action]
Ascorbic acid or ascorbic acid or ascorbic acid metal salt or ammonium salt alone or a solution containing two or more of them is sprayed or immersed in the slag of chromium-containing alloy steel. In addition, the strong and rapid reducing power of the derivatives thereof has an effect of detoxifying hexavalent chromium contained in the slag into harmless trivalent chromium.
In addition, ascorbic acid is acidic with respect to the alkalinity of weld slag by adding and blending a PH indicator that changes color with PH to the above solution. It is extremely convenient to determine the appropriate amount of
The solvent of the solution is preferably water, but is not limited to this, and does not prevent the use of other solvents such as alcohol, and a surfactant is used so that the solution can penetrate well into the mines. Further, it is more effective if glycerin or the like is added in order to impart wettability.
In addition, the shape of the slag is from powder to large nodules, and the state of permeation of the solution acting on this is not uniform, so the nodules are pre-crushed or pulverized, The penetration rate of the solution into the slag increases, and there is an effect of further increasing the reduction efficiency of hexavalent chromium to trivalent chromium.
In addition, it is not always necessary to reduce the total amount of hexavalent chromium contained in the iron slag to trivalent chromium. Practically, the hexavalent chromium present in the surface layer portion of the iron slag where the solution can permeate is trivalent. If it is reduced to chromium and detoxified, there is no particular problem. However, when it is reused as landfill, bulking material, aggregate, etc., it is sufficient to use the solution by crushing or grinding in advance according to the purpose. It is necessary to consider detoxification.
[0006]
【Example】
Example 1
When welding SUS316 material, welding was performed using a D316-15 lime-coated arc welding rod defined in JIS-Z3221 as the welding rod, and the weld slag generated in the welded part was cooled after cooling the weld base metal. The sample was peeled and collected, and a filter paper moistened with pure water was affixed. After 1 minute, the filter paper was peeled off, and the affixed surface was regulated by the spectrophotometric analysis method for chromium in JIS steel. When an acetone solution of 25% diphenylcarbagit was added dropwise, a reddish purple color was clearly observed, and the presence of hexavalent chromium was clearly confirmed.
Therefore, for the same weld slag collected from other welds, a 5% aqueous solution of ascorbic acid was sprayed using a gun spray, allowed to dry, and then pasted with filter paper moistened with pure water again as described above, After 1 minute, the filter paper was peeled off and a 0.25% acetone solution of diphenylcarbagit was dropped on the applied surface, but no reddish purple color was observed and no hexavalent chromium was detected. confirmed.
Example 2
When welding SUS304 material, lime equivalent to D308L-16 of JIS-Z3221. The welded slag was removed from the welded piece after 10 days from the welding using a titania-based coated arc welding rod, and the welded slag was removed and collected. Similarly, when comparing before and after the application of a 5% aqueous solution of ascorbic acid, a large amount of hexavalent chromium was detected before the application of the aqueous solution, whereas no hexavalent chromium was found after the application of the aqueous solution. It was not detected and it was confirmed that it was made safe and harmless.
Example 3
In welding construction of SUS304 material, after welding construction was performed using a flux-cored wire (FCW) equivalent to YF308L-C of JIS-Z3323, the adhered welding slag was peeled off and collected. As compared with before and after the spraying of the aqueous solution of ascorbic acid using the same method, the detection of hexavalent chromium was confirmed although the detection of hexavalent chromium was slightly less than that of the coated arc welding rod. From the part sprayed with 2.5% aqueous solution of ascorbic acid, no hexavalent chromium was detected.
Example 4
At the time of welding of chromium molybdenum steel, after welding using a lime-based covered arc welding rod corresponding to JIS-DT2516 as the welding rod, the adhering slag was peeled off and collected. As a result of comparison between before and after the application of the aqueous solution of ascorbic acid in the same manner as in the example, the detected amount of hexavalent chromium before the application was much smaller than that in the case of welding SUS304 material, but the presence of hexavalent chromium in the direction of the arrow. Was confirmed in the weld slag and weld fumes.
Then, when 3% ascorbic acid aqueous solution was sprayed, no hexavalent chromium was detected.
Example 5
When a comparative test was conducted with respect to the concentration of the ascorbic acid aqueous solution in Example 2, it was not practical at 0.1% or less, although the effect was recognized as it was, but it was not practical, but about 0.5% From the above, a significant reduction effect is recognized at an appropriate amount used, and in the case of a higher concentration than that, a smaller amount may be used, and it may be appropriately selected according to the amount of welding slag, and in particular. It has been confirmed that it may be appropriately determined according to the amount of chromium contained in the welding rod core wire, the welding wire, and the welding base material.
Example 6
After pulverizing the nodular chromium-containing iron ore collected from the production process of stainless steel, 0.25% of diphenylcarbadiite specified in the spectrophotometric analysis method of chromium in JIS steel was obtained in the same manner as in Example 1. When the acetone solution was dropped, a reddish purple color was clearly recognized, and the presence of hexavalent chromium was clearly confirmed.
Therefore, another 5% aqueous solution of ascorbic acid was sprayed on a similar collected chrome-containing slag using a gun spray, left to dry, and then affixed with filter paper moistened with pure water again as described above. After the lapse of time, the filter paper was peeled off and a 0.25% acetone solution of diphenylcarbagit was dropped onto the affixed surface, but no reddish purple color was observed and no hexavalent chromium was detected. It was.
Example 7
As a result of the same test as in Example 6, the presence of hexavalent chromium was confirmed for the chromite slag collected from ingots of ferrochrome and metal chrome as steelmaking materials. A 5% aqueous solution of ascorbic acid was used with a gun spray. After spraying, it was confirmed that no hexavalent chromium was detected.
Example 8
In place of ascorbic acid in the above examples, each metal derivative or ammonium salt of ascorbic acid was used alone or in combination of two or more to test the reduction effect of hexavalent chromium by the same method. Although the effect was slightly inferior to the above, it was confirmed that almost the same effect was obtained by appropriately increasing the concentration.
[0007]
【The invention's effect】
According to the present invention, the welding slag peeled off from the welded portion after the chrome-containing alloy steel is welded, and the extremely harmful hexavalent chrome present in the chrome-containing slag discharged from the chrome-containing alloy steel manufacturing process can be quickly and Since it is possible to make it harmless safely, the weld slag, factory floor soil on which chrome-containing slag dust has accumulated, these welded slag being collected and temporarily stored, chrome-containing slag, or This makes it possible to effectively and safely render the pollutant at the disposal site safe.
In the present invention, in place of conventionally known reducing agents, the present invention is preferably carried out by finding ascorbic acid and its derivatives which are safe and harmless to the human body as well as the reducing agent itself. There is no adverse side effect, and it is extremely beneficial for the health and safety of factory workers who frequently come in contact with these dangerous pollutants and workers involved in the processing of the pollutants. This makes it possible to prevent harmful pollution such as soil pollution, groundwater pollution, marine river pollution, etc. due to hexavalent chromium eluted by the

Claims (1)

Chromium-containing slag generated by heat treatment such as melting, rolling, welding, fusing, etc. of chromium-containing alloy steel such as stainless steel, ferrochrome, and metallic chromium is crushed or crushed, and ascorbic acid or By spraying or immersing a solution containing one or more of ascorbic acid metal salt or ammonium salt as a main component, hexavalent chromium contained in the slag is reduced to trivalent chromium and rendered harmless. A method for treating a chromium-containing iron ore characterized in that the treatment of the iron ore is made safe.