KR100388035B1 - Method for preparing magnesium sulfate aqueous solution from magnesia chromium waste refractory - Google Patents

Abstract

The present invention relates to a method for producing an aqueous solution of MgSO ₄ from magnesia chromium waste refractories,

In preparing an aqueous solution of MgSO ₄ using magnesia-chromium waste refractory, the waste refractory is pulverized to a 100% mesh content and reacted with sulfuric acid diluted to a concentration of 10-30% to free MgO in waste refractory. Elution was carried out to dissolve the metal iron component with divalent iron ions, hexavalent chromium, and then filtered to separate the residue. Hydrogen peroxide solution was added to the remaining reaction solution to convert the divalent iron ion into Fe (OH) _3. The reaction solution was neutralized to pH 7-8 by adding Mg (OH) ₂ , and then treated in the form of Cr (OH) ₃ , and the produced sludge was filtered to prepare an aqueous solution of MgSO ₄ .

According to the above, by using the magnesia-chromium waste refractory, which is mostly disposed of, MgSO ₄ aqueous solution can be used to effectively utilize free MgO powder, and the residue separated during the reaction can increase the hot load strength during regeneration refractory preparation. Since it does not lower, it can be recycled as a refractory raw material.

Description

Method for producing magnesium sulfate aqueous solution from magnesia chromium waste refractory

The present invention relates to a method for producing an aqueous magnesium sulfate solution from magnesia chromium waste refractory, and more particularly, to remove the metal iron, free CaO and hexavalent chromium components contained in the magnesia-chromium waste refractory, and extract only magnesium to extract MgSO. ₄ relates to a method for producing an aqueous solution.

The magnesia-chromium refractory has excellent corrosion resistance against slag, molten metal, molten cement clinker, etc., and Cr ₂ O ₃ is a high temperature oxide with melting point of 2265 ° C. A considerable amount is used in the process, nonferrous metallurgy and cement manufacturing process.

However, Cr ₂ O ₃ reacts with CaO, which is a main component of slag or cement clinker, to form hexavalent chromium. The hexavalent chromium thus formed is a major problem in recycling waste refractories as a refractory material.

Therefore, it is currently required to recycle magnesia-chromium waste refractory materials through stabilization treatment.

As one of the recycling methods, John Noga et al. Dissipated the hexavalent chromium component in the waste refractory through charity separation and water washing to separate and collect the magnesia-chromium waste refractories, and to remove Fe using a magnet after grinding. Water treatment is carried out, and the remaining residues are dried to make the water less than 0.1%, and then recycled as a raw material for regeneration refractory materials (Ceram, Eng. Sci. Proc 15 [2], p73-77 ( 1994).

However, there is a problem in using the waste refractories treated in this way as a raw material of the regenerated refractory.

That is, the metal iron is not removed by the method as described above, the iron infiltrated in the refractories made of recycled refractory is melted together as the temperature rises, the hot load strength is reduced, the steelmaking process of steel mill In the degassing process (RH-OB), the slag component is infiltrated on the moving surface of the magnesia-chromium waste refractory, and there is a problem in that the variation of the component occurs, and during disposal, the elevation of the landfill due to the expansion of free MgO There is a problem that causes the phenomenon.

In addition, even after washing the residue obtained during the reaction, Petty, AV et al., As mentioned in "Bureau of Mines RI 8685, 1982," hydrated free MgO and free CaO in the magnesia-chromium refractory matrix, thereby producing regenerated refractory materials. If there is a problem of generating calcium hydroxide and magnesium hydroxide.

That is, as Ca (OH) ₂ and Mg (OH) ₂ are generated as in Schemes 1 and 2 below, the volume is expanded to cause cracking in the dry molding.

CaO + H ₂ O → Ca (OH) ₂

MgO + H ₂ O → Mg (OH) ₂

Accordingly, an object of the present invention is to provide a method for preparing an aqueous solution of MgSO ₄ by releasing only MgO components from magnesia-chromium waste refractory.

1 is a process schematic diagram of preparing an aqueous solution of MgSO ₄ using the magnesia-chromium waste refractory material of the present invention.

According to the invention,

In preparing an aqueous solution of MgSO ₄ using magnesia-chromium waste refractory,

(a) The waste refractory is pulverized so that the waste refractory becomes 100% through 140 mesh and reacted with sulfuric acid diluted to a concentration of 10-30% to elute free MgO in the waste refractory and divalent iron ion of the metal iron component. Dissolving with water and dissolving hexavalent chromium;

(b) filtering the sulfuric acid reaction solution to separate the residues;

(c) separating the residue and adding hydrogen peroxide solution to the remaining reaction solution to oxidize the divalent iron ions dissolved in step (a) with Fe (OH) ₃ ;

(d) treating the trivalent chromium dissolved in step (a) in the form of Cr (OH) ₃ by removing Mg (OH) ₂ and neutralizing the reaction solution to pH 7-8, and removing residual sulfuric acid; And

(e) filtering the neutralized reaction solution to remove the sludge produced in the steps (c) and (d); provides a method for producing an aqueous solution of MgSO ₄ from magnesia chromium-based waste refractory.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

In the present invention, not only can an aqueous solution of MgSO ₄ be prepared from the magnesia-chromium waste refractory that has been disposed of, but it does not contain impurities present in the waste refractory, thereby obtaining a recyclable residue as a refractory material.

1 is a process schematic diagram of preparing an aqueous solution of MgSO ₄ using the magnesia-chromium waste refractory material of the present invention.

Referring to FIG. 1, in step (a) of the present invention, the waste refractory is pulverized such that the amount passed through 140mesh is 100%. In this case, when the waste refractory is pulverized so that the passage amount of 140 mesh is not 100%, free MgO cannot be completely eluted.

The pulverized waste refractories are reacted with 10-30% sulfuric acid. The sulfuric acid used at this time is diluted to 10-30% concentrated sulfuric acid. When the concentration of sulfuric acid used is less than 10%, the concentration of sulfuric acid is low and the free MgO remains unreacted. When the concentration of sulfuric acid exceeds 30%, the hydrate of MgSO ₄ ㆍ 7H ₂ O is formed, resulting in loss of MgSO ₄ produced. This is undesirable because it occurs.

Since the sulfuric acid reaction itself is a rapid exothermic reaction, there is no need to heat treatment separately.

Through the sulfuric acid reaction, the metal iron infiltrated into the moving surface of the waste refractory is dissolved with divalent iron ion in the form of FeSO ₄ , the hexavalent chromium component is dissolved in the form of CrO ₃ , and the free MgO component reacts with SO ₄ ions. Is dissolved in MgSO ₄ form.

Here, the hexavalent chromium component is present in the waste refractory by forming a small amount of hexavalent chromium CrO ₃ as shown in Equation 3 below when Cr ₂ O ₃ present in the magnesia-chromium refractory reacts with slag or CaO, the main component of the cement clinker. Done.

Cr ₂ O ₃ + 2CaO + O ₂ → 2CaOCrO ₃

The hexavalent chromium present in this way may be reduced in the presence of divalent iron ions when the pH of the solution is acidic in the filtrate solution after the reaction between the magnesia-chromium waste refractory and sulfuric acid, as shown in Equation 4 below. Metal iron, which is present as a contaminant on the infiltrating surface of the refractory, is already dissolved in the form of divalent iron ions in the solution due to sulfuric acid, so it is reduced to trivalent chromium without a separate divalent iron ion.

2CrO ₃ + 6FeSO ₄ + 6H ₂ SO ₄ → Cr ₂ (SO ₄ ) ₃ + 3Fe ₂ (SO ₄ ) ₃ + 6H ₂ O

That is, when trace amounts of hexavalent chromium (generally 2-3 ppm) are detected in waste refractories, or when treating waste iron refractories with metal iron, FeSO ₄ produced by such sulfuric acid reaction is sufficient to form hexavalent chromium. It can be reduced to trivalent chromium, thus eliminating the need for a separate water treatment plant for reprocessing hexavalent chromium.

In case of using magnesia-chrome waste refractories for cement clinker that contain only a large amount of hexavalent chromium in the amount of about 1000 ppm, a small amount of Fe powder may be added to the sulfuric acid reaction to make FeSO ₄ to promote the reaction of Equation 4. . In this case, the amount of iron powder to be administered is preferably used as the equivalent ratio of hexavalent chromium present.

As described above, hexavalent chromium can be easily treated by reacting magnesia-chromium waste refractories with sulfuric acid. Also, by preparing an aqueous solution of MgSO ₄ using a free MgO component, conventionally, during production of regenerated refractories when free MgO remains It can completely prevent cracking phenomenon that can occur.

In step (b), the residue is separated from the sulfuric acid reaction solution. Solid-liquid separation is sufficient to separate the residue.

By the sulfuric acid reaction as described above, the metal iron component and the hexavalent chromium component are removed and the free MgO component is extracted, and then the obtained residue is a spinel having ((Mg, Fe) (Al, Cr) ₂ O ₄ ) as the main crystal phase. It is constructed and can be washed and then recycled as refractory raw materials or chrome ore.

Conventionally, since metal iron remained in the residue, when the refractory was manufactured, the metal iron was infiltrated in the refractory, and melted when the temperature was raised during manufacture, thereby lowering the hot load strength of the regenerated refractory. However, in the residue obtained according to the present invention, the metal iron was completely This eliminates the benefit of solving this problem perfectly.

In step (c), hydrogen peroxide solution is added to the separated reaction solution to oxidize the divalent iron ions dissolved in step (a) to Fe (OH) ₃ .

This is to be taking into account that it should be clear, colorless to commercialize a MgSO ₄ solution to the later ABS resin coagulant or the like, Therefore, strictly limit the iron content of which is incorporated into the aqueous solution of MgSO ₄ can prevent the yellowing of the ABS resin.

That is, by adding hydrogen peroxide, FeSO ₄ , which is mostly in a divalent state, or reacted with hexavalent chromium in step (b), oxidizes iron ions present in the form of Fe ₂ (SO ₄ ) ₃ to form Fe (OH) _3. It will precipitate in form.

It is preferable to add the amount of hydrogen peroxide administered here more than equivalent ratio of the divalent iron ion to oxidize. When hydrogen peroxide is added in an amount less than the equivalent of iron ions, divalent iron ions cannot be completely oxidized to trivalent iron ions, and thus, divalent iron ions remain in the aqueous solution of MgSO ₄ , which is not preferable.

In step (d), Mg (OH) ₂ is added as a pH regulator to neutralize the reaction solution to pH 7-8. As for the same processes, and thereby precipitating the chromium present in the above step (a) to Cr ₂ (SO _{4) 3} forms a Cr (OH) ₃ form, and at the same time used for the reaction in the step (a) all of the remaining sulfuric acid Remove neutralization.

If the pH is less than 7, the trivalent chromium is not completely removed, so the solution becomes pale green, and if it is 8 or more, more than necessary Mg (OH) ₂ is used.

In step (e), the produced sludge is filtered to obtain an aqueous solution of MgSO ₄ . That is, by removing the sludge Fe (OH) ₃ generated in the step (c) and the sludge produced in the step (d), Cr (OH) ₃ by filtration to completely remove the Fe and Cr components in the aqueous solution of MgSO ₄ can do.

Hereinafter, the present invention will be described through examples.

<Example>

In the present embodiment, magnesia-chromium refractory materials produced during degassing refining (RH-OB) during steelmaking were used in steel mills, and chemical compositions thereof are shown in Table 1 below.

MgO (% by weight) Cr ₂ O ₃ (% by weight) Al ₂ O ₃ (wt%) Fe ₂ O ₃ (% by weight) SiO ₂ (% by weight) CaO (% by weight) 57.9 20.2 10.6 8.8 1.6 0.9

<Example 1>

Optimum Grinding Particle Size of Magnesia-Chromium Waste Refractories

In this example, the waste refractory was pulverized such that 30 mesh, 100 mesh, and 140 mesh passages were 100%, respectively, as described in Table 2, and sulfuric acid reaction was performed using 20% sulfuric acid. The residue was separated and neutralized by administering Mg (OH) ₂ to the separated MgSO ₄ solution so that the pH of the solution was 7, and then the produced sludge was removed.

The free MgO content of the starting waste refractories was 40% by weight based on the relative strength analysis through XRD analysis or thermogravimetric analysis after forced hydration of the waste refractories.

The free MgO removal rate was investigated by thermogravimetric analysis from the obtained MgSO ₄ aqueous solution and the residue component.

division Particle diameter Free MgO Removal Rate Sulfuric acid concentration Comparative Example 1 100% pass through 30mesh 85% 20% Comparative Example 2 100% pass through 140mesh 95% 20% Inventive Example 100% pass through 140mesh 100% 20%

As shown in the above table, as in Comparative Example 1, the removal rate of free MgO was 85% when the particle size of the waste refractory pulverized powder was 100%.

On the other hand, as in Comparative Example 2, the removal rate of free MgO was 100% when the 100mesh passage was 100%. Therefore, in order to completely remove the free MgO in the waste refractories, it is preferable to grind finely so that the amount of passage of 140 mesh becomes 100% as in the invention example.

<Example 2>

Optimal sulfuric acid concentration

In this example, the optimal sulfuric acid concentration during the sulfuric acid reaction from waste refractory was investigated.

The waste refractory was pulverized so that the passage amount of 140mesh was 100%, and sulfuric acid was reacted while changing sulfuric acid concentration to 5,10,30,35% as shown in Table 3 below.

The residue was removed and neutralized by administering Mg (OH) ₂ to pH 7 of the separated MgSO ₄ solution, and then the resulting slurry was removed to prepare an aqueous solution of MgSO ₄ .

Free MgO content was measured by thermogravimetric analysis in the same manner as in Example 1 to determine the removal rate of free MgO.

division Sulfuric Acid Concentration Used Remarks Comparative Example 1 5% Unreacted free MgO remaining Inventive Example 1 10% Good removal rate of free MgO Inventive Example 2 30% Good removal rate of free MgO Comparative Example 2 35% MgSO ₄ MgSO ₄ losses due to hydrate crystallizing

As shown in the above table, in Comparative Example 1, when the concentration of sulfuric acid is added at 5%, there is a problem in that unreacted free MgO remains because the concentration of sulfuric acid is low.

Meanwhile, Comparative Example 2, as in the concentration of sulfuric acid as high as 35% is not preferable because the solution MgSO ₄ MgSO ₄ and is in the form of MgSO ₄ 7H this hydrate is a loss generated in the form of O _2.

Therefore, as for sulfuric acid, it is preferable to use the density | concentration about 10 to 30% like invention examples 1-2.

<Example 3>

MgSO ₄ Effect of Hydrogen Peroxide and pH on Removal of Iron Ions from Solution

In this example, the effects of hydrogen peroxide and pH on the removal of iron ions in MgSO ₄ solution were investigated. The iron (II) to be removed contained 2 mg / ml in MgSO ₄ solution.

The waste refractory was pulverized so that the passage amount of 140mesh was 100% and sulfuric acid reaction was performed using 20% sulfuric acid. The residue was separated and the hydrogen peroxide solution was added to the separated MgSO ₄ solution at a ratio of 0, 0.5, and 1 equivalents to the Fe ⁺² molar ratio, as described in Table 4, and then described in Table 4 using Mg (OH) ₂ . PH was adjusted to 4,7,4.5, 7, 9 and neutralized.

The produced sludge was removed to prepare an aqueous solution of MgSO ₄ . The presence of Fe ⁺² and Cr components from the aqueous solution of MgSO ₄ was investigated using ICP (Inductively Coupled Plasma), and the color of the solution was visually observed.

division Equivalent Ratio of Divalent Iron Ion and H ₂ O ₂ and pH of Solution Remarks Comparative Example 1 Molar ratio of H ₂ O ₂ / Fe ⁺² = 0pH = 4 Fe ⁺² and Cr component present (solution color = green) Comparative Example 2 Molar ratio of H ₂ O ₂ / Fe ⁺² = 0.5pH = 7 In that the Fe ⁺² MgSO ₄ the solution remaining in the incomplete oxidation of Fe ⁺² (solution color = green) Comparative Example 3 Molar ratio of H ₂ O ₂ / Fe ⁺² = 1pH = 4.5 Cr is not completely removed and Cr remains in MgSO ₄ solution (solution color = light green) Inventive Example H ₂ O ₂ / Fe ⁺² Molar ratio = 1 pH = 7 Colorless MgSO due to removal of Fe and Cr ₄ Comparative Example 4 Molar ratio of H ₂ O ₂ / Fe ⁺² = 1pH = 9 Excessive Mg (OH) ₂ for pH adjuster

As shown in the above table, when the pH of the solution was adjusted to about 4 using Mg (OH) ₂ without adding hydrogen peroxide solution as in Comparative Example 1, the MgSO ₄ solution contained a divalent iron ion and a trivalent chromium component. It is not preferable because the color is green.

Meanwhile, as in Comparative Examples 2 to 3, the molar ratio of hydrogen peroxide to the molar ratio of divalent iron ions contained in MgSO ₄ was added at 0.5 and 1.0, respectively, and the pH of the solution was maintained at 7 and 4.5 using Mg (OH) ₂ , respectively. In the case of filtration, Comparative Example 2 has a problem in that divalent iron ions remain in MgSO ₄ due to incomplete oxidation of divalent iron ions. In Comparative Example 3, trivalent chromium is not completely removed. It is not preferable because it is light green.

Therefore, as in the invention example, the hydrogen peroxide solution was preferably added to the equivalent ratio of divalent iron ions and the pH of the solution was adjusted to 7 ~ 8 using Mg (OH) ₂ , the solution as in the case of Comparative Example 4 The pH of 8 is not preferable because excess Mg (OH) ₂ is used more than necessary.

According to the above, by using the magnesia-chromium waste refractory, which is mostly disposed of, MgSO ₄ aqueous solution can be used to effectively utilize free MgO powder, and the residue separated during the reaction can increase the hot load strength during regeneration refractory preparation. Since it does not lower, it can be recycled as a refractory raw material.

Claims (2)

In preparing an aqueous solution of MgSO ₄ using magnesia-chromium waste refractory, (a) The waste refractory is pulverized so that the waste refractory becomes 100% through 140 mesh and reacted with sulfuric acid diluted to a concentration of 10-30% to elute free MgO in the waste refractory and divalent iron ion of the metal iron component. Dissolving with water and dissolving hexavalent chromium; (b) filtering the sulfuric acid reaction solution to separate the residues; (c) separating the residue and adding hydrogen peroxide solution to the remaining reaction solution to oxidize the divalent iron ions dissolved in step (a) with Fe (OH) ₃ ; (d) treating the trivalent chromium dissolved in step (a) in the form of Cr (OH) ₃ by removing Mg (OH) ₂ and neutralizing the reaction solution to pH 7-8, and removing residual sulfuric acid; And (e) filtering the neutralized reaction solution to remove the sludge produced in the steps (c) and (d); MgSO ₄ aqueous solution preparation method from magnesia chromium waste The method of claim 1, wherein the amount of hydrogen peroxide added in step (c) is greater than or equal to the equivalent ratio of divalent iron ions.