KR101078000B1 - Manufacturing of MgSO4 and SiO2 by mechanochemical reaction from Fe-Ni slag - Google Patents

Abstract

The present invention is magnesium sulfate from magnesium oxide and silicon oxide which are useful components in slag by mechanochemical grinding and activation from ferronickel slag, which is generated during the production of ferronickel, which is a raw material for steel and steel, and which is mostly discarded or used as aggregate. It relates to a ferronickel slag treatment method to extract (MgSO ₄ ) and silicon oxide (SiO ₂ ). In particular, the purpose of the present invention is to obtain a high value-added chemical raw material from slag, which is simply waste, and to provide a manufacturing method that can achieve energy saving by minimizing processing energy and simplifying the process by a mechanical chemical method.

Ferronickel slag, mechanochemistry, magnesium sulfate, silicon dioxide

Description

 Manufacturing method of magnesium sulfate and silicon dioxide from ferronickel slag by mechanochemical reaction {Manufacturing of MgSO4 and SiO2 by mechanochemical reaction from Fe-Ni slag}

The present invention is magnesium sulfate from magnesium oxide and silicon oxide which are useful components in slag by mechanochemical grinding and activation from ferronickel slag, which is generated during the production of ferronickel, which is a raw material for steel and steel, and which is mostly discarded or used as aggregate. It relates to a ferronickel slag treatment method to extract (MgSO ₄ ) and silicon oxide (SiO ₂ ). In particular, the present invention relates to a method for obtaining energy-added chemical raw materials from slag, which is a simple waste, and minimizing processing energy by a mechanical chemical method to simplify the process and achieve energy savings.

Recently, 30,000 tonnes of nickel will be produced annually by completing the ferronickel smelting plant to secure economical and stable nickel due to the sudden change in nickel prices. When smelting nickel, ferronickel slag, which is about 30 times the amount of production, is generated as a by-product due to the low raw material quality through complicated connecting production lines such as raw materials, steelmaking, and steelmaking. This ferronickel slag is silicon dioxide (SiO ₂ ) About 55 to 60%, magnesium oxide (MgO) is about 32 to 37% of the main components, and a small amount of calcium oxide (CaO), iron oxide (Fe ₂ O ₃ ), aluminum oxide (Al ₂ O ₃ ). .

Generally, by-product ferronickel slag is recycled in advanced countries such as Japan and Canada as raw materials for cement production, civil engineering materials, concrete aggregates, runway aggregates, and ferronickel slag substitutes. Due to lack of technology and lack of invention due to aggregate or to be buried as is.

Magnesium oxide (MgO) and magnesium oxide are used for domestic use of ferronickel slag.

Since it is a magnesium silicate composed of silicon dioxide (SiO _{2 )} , it is expected to be partially supplied as a magnesium oxide (MgO) source, which is a slag forming agent for steelworks.

For high value of by-products, in Japan, it was used to replace aggregates and sands or to adjust the particle size, and after improving the relevant standard JIS to use ferronickel slag as fine aggregate for concrete, development of land improver on warm stone, zeolite, In recent years, the use of synthetic materials such as silicon carbide, manufacturing magnesium compounds, and the development of functional materials have been made, and effective low-value resources such as concrete aggregates, cement materials, runway aggregates, civil aggregates, ferronickel slag substitutes, etc. It is being used as a situation.

 Magnesium sulfate is also used primarily as a fertilizer and as a supplement to animal feed. It is also used as a building material in the form of sulfated cement, as a conditioner for wool and cotton in the textile industry, and as an emollient in the dyeing industry. Used in the rubber and plastics industry as a coagulant.

 On the other hand, the mechanochemical method (mechanochemistry method) is one of the materials processing methods for the purpose of efficiency, energy saving, and activation in the existing grinding process is currently applied in various fields such as pharmaceutical, agriculture, materials, food, Many inventors and patents are also filed by the present inventors due to the strength increase, dissolution increase, and activation of materials.

  These pulverization and activation processes are applied to the development of nanomaterials, biotechnology, and new materials, and the mechanochemical method of inducing reactivity and activation by injecting energy to the particles during ultrafine pulverization in the submicron region or nanosphere is applied. Many inventions have been made in the field of synthesis and dissolution of materials using technology.

  In particular, planetary mills, vibration centrifuges, vortex mills, etc., which can impart mechanochemical functions, have recently been used. In addition, the conventional pulverization method cannot expect a lot of elution from slag, etc., and it is not possible to induce various reactions due to the inertness of the easy material of the valuable metal component Mg. A continuous method for simultaneously classifying and drying can also be developed and used.

  In the present invention, the present invention intends to continuously use vortex mills, vibration centrifugal mills, etc. as a method of grinding activation for the dissolution of ferronickel slag.

In order to solve the above problems of the raw material supply and by-product utilization, the present invention is excellent in leaching efficiency using mechanical and chemical methods, and energy saving due to the shortening of the treatment process, and the ferronickel slag as a high value-added material It recovers expensive magnesium sulfate (MgSO ₄ ) and silicon oxide (SiO ₂ ) from ferronickel slag for conversion, and can be used as an additive in food and beverage process, water treatment, paint, tire and construction aggregate. The purpose is to use as a public material and a functional material.

When ferronickel slag is removed by MgO, Fe ₂ O ₃ , Al ₂ O ₃ , CaO, etc. by appropriate sulfuric acid treatment, high purity amorphous silica with 20-40 pores and tens to hundreds of m 2 / g specific surface area can be prepared. The porous silica material having excellent reactivity and adsorption can be used as an additive in food and beverage process, water treatment, paint, tire, and the like, and it is also easy to manufacture various silicon base materials, and can be used for water glass and zeolite synthesis.

As can be seen from the above description, the use of the conventional ferronickel slag is only a building material such as sand, it was possible to separate the useful components of magnesium sulfate and silicon dioxide with high purity by the mechanical chemical treatment.

  Existing magnesium oxide is used dolomite or serpentine, while according to the present invention, if purified by using high purity magnesium oxide and silicon dioxide in ferronickel will play a role in resource recycling and environmental protection.

Hereinafter, the present invention will be described.

In the present invention, the ferronickel slag was pulverized to -200mesh and then removed by Fe ₂ O ₃ by the magnetic screening method, was used in the leaching experiment. The sample used for the SiO ₂ preparation experiment was obtained by leaching Mg from ferronickel under optimum leaching conditions with H ₂ SO ₄ , and then washed well with water several times to completely remove residual H ₂ SO ₄ , followed by drying at 110 ° C. . The residue discharged after leaching was used for preparing SiO ₂ without considering the particle size of the residue. The present invention consists of four parts, such as leaching of ferronickel, purification of the leaching solution, production of magnesium sulfate from the leaching solution, production of SiO ₂ , and a flow chart thereof as shown in FIG. 1.

1 is a manufacturing process of magnesium sulfate and silicon dioxide by mechanochemistry from ferronickel slag

Ferronickel → Crushing Magnetic screening → iron H ₂ SO ₄ → Leaching Solid-liquid separation Residue Leachate NaOH
Dissolution ← NaOH Solution Fe ₊₂ -Fe ₊₃
Oxidation ← H ₂ O ₂ ↓ ↓ Solid-liquid separation NaOH solution → Hydrolysis ↓ → residue ↓ Concentration control Solid-liquid separation → Fe (OH) ₃ ↓ ↓ SiO ₂ Purified Leachate ↓ crystallization ↓ MgSO ₄

Table 1. Ferronickel slag chemical composition

(weight %)

Magnesium Oxide (MgO) Silicon oxide
(SiO ₂ ) Iron oxide
(Fe ₂ O ₃ ) Aluminum oxide
(Al ₂ O ₃ ) Calcium oxide
(CaO) Ferronickel slag 35.84 56.37 2 to 5 (T.Fe) 1.55 1.19

Table 2. Chemical Composition of Ferronickel Slag Leachate Used in Purification Experiments

Elements Mg Fe Ca Al Na Cr Ni K Composition (%) 6.58 1.7 0.14 0.63 0.18 170
ppm 142
ppm 77
ppm

 Table 3. Solubility of each hydroxide at 25 ° C

Hydroxides Solubility product Mg (OH) ₂ 1.1 × 10 ^-9 Fe (OH) ₂ 8.0 × 10 ^-16 Fe (OH) ₃ 6.0 × 10 ^-38 Al (OH) ₃ 4.0 × 10 ^-13 Ca (OH) ₂ 5.5 × 10 ^-6 Cr (OH) ₃ 7.0 × 10 ^-31 Ni (OH) ₂ 2.0 × 10 ^-15

Table 4. Chemical Composition of Purified Ferronickel Slag Leachate

Elements Mg Fe Ca Al Na Cr Ni K Composition (%) 6.51 - 0.10 0.53 0.11 120
ppm 112
ppm 55
ppm

≪ Example 1 >

A 1000 ml four-necked flask reactor equipped with a stirrer was installed and used in a heating mantle for leaching H ₂ SO ₄ of ferronickel slag. Leaching was carried out by injecting a H ₂ SO ₄ solution having a controlled concentration into the reactor, adjusting the temperature and charging a ferronickel sample. A solution sample was taken at each time and the leaching rate was calculated by analyzing Mg.

Purification of ferronickel slag leachate was carried out using a hydrolysis method and a solvent extraction method. A 250 ml reactor was used for the purification experiment. For the Fe removal experiment, first, 50 ml of leachate was charged to the reactor, and a predetermined amount of H ₂ O ₂ was added thereto to adjust the pH. As the pH of the solution was adjusted, the iron hydroxide precipitate produced was filtered off and then analyzed for Fe in the solution to calculate the removal rate. NaOH, MgO and CaO were used to adjust the pH of the solution and the efficiency was compared.

The leaching solution was purified and then experiments were conducted to prepare MgSO ₄ and Mg (OH) ₂ . In the production experiment of MgSO ₄ 250ml crystallization tank was used. 200 ml of purified leachate was charged to a crystallization tank, heated to a solution temperature of 90 ° C., and cooled to precipitate MgSO ₄ . At this time, the production rate and purity according to time and cooling rate were investigated. In addition, the crystallization experiment for producing MgSO ₄ directly from the crude leachate was also performed in parallel with the results obtained using the purified leachate.

In the preparation of Mg (OH) ₂ , a 100 ml beaker was used. 50 ml of purified leachate was charged to a beaker, and then the pH was adjusted by adding an appropriately adjusted concentration of NaOH solution to form Mg (OH) ₂ precipitate. The precipitate was washed three times with water, filtered and dried to investigate the physical properties.

The crystal phases of the products obtained through X-ray diffraction experiments were investigated, and pyrolytic behavior was investigated by thermogravimetric analysis.

As a result, H ₂ SO ₄ and HCl can be used as a leaching agent for extracting Mg from ferronickel. In the present invention, H ₂ SO ₄ was selected because of its low cost and high economical efficiency. In addition, the leaching experiment with HCl was also performed to compare the results.

Figure 2 shows the solubility of MgSO ₄ and MgCl ₂ in water produced by leaching ferronickel slag by H ₂ SO ₄ and HCl. As shown in FIG. 2, the solubility of MgCl ₂ is greater than that of MgSO ₄ . In the case of MgSO ₄ , the solubility decreases with increasing temperature at 80 ° C. On the other hand, the solubility of MgCl ₂ is shown to increase continuously with increasing temperature.

The leaching scheme of ferronickel slag by H ₂ SO ₄ can be expressed as follows.

Figure 3 shows the effect of the stirring rate of the solution on the extraction reaction rate of Mg when ferronickel slag leached with 1.0NH ₂ SO ₄ solution at 50 ℃ for 120 minutes. As shown in FIG. 3, there was almost no change in Mg extraction rate according to the stirring speed. Therefore, in all leaching experiments of the present invention, the stirring speed was constant at 500 rpm.

Next, the leaching temperature of 50 ℃ and H ₂ SO ₄ concentration is changed to 0.1 ~ 6.0 N when ferronickel slag leaching is shown the effect on the extraction rate of Mg in FIG.

As shown in FIG. 4, as the H ₂ SO ₄ concentration was increased, the extraction rate of Mg increased significantly. When ferronickel slag was leached with 1.0NH ₂ SO ₄ solution for 120 minutes, the extraction rate of Mg was about 60%, but when the concentration was 6.0N, the extraction rate was about 85%.

H ₂ SO ₄ Since the extraction of Mg was not completed even though the concentration was increased, the effect on leaching temperature was examined. Leaching ferronickel slag with 1.0NH ₂ SO ₄ solution while changing the leaching temperature to 25 ~ 90 ℃ is shown in Figure 5 the results. As the leaching temperature increased, Mg extraction rate increased rapidly. When leaching at 70 ° C, leaching was completed after 120 minutes, but leaching was completed within 30 minutes when leaching at 90 ° C. When leaching for 30 minutes, the extraction rate of Mg was about 100%. Therefore, in the actual operation, the leaching temperature was 90 ° C and the leaching time was 30 minutes.

Next, the leaching experiments of ferronickel slag were carried out while varying the concentration of the mineral liquid to 20-300 g / L to derive the optimum leaching conditions, and the results are shown in FIG. 5. H ₂ SO ₄ The concentration was 10N and the leaching temperature was 100 ° C. As shown in FIG. 5, the extraction rate of Mg was almost constant as much as 97% up to 150 g / L of the mineral liquid concentration, but decreased slightly as the mineral liquid concentration increased to 93.28 and 91.74% at 200 g / L and 300 g / L, respectively. Extraction rate of Mg was 89% at 400g / L mineral solution, but there was a significant problem in solid-liquid separation. Therefore, in order to increase the concentration of mineral liquid, a large particle size sample should be used, and the effect on the extraction rate should be considered.

6 is H ₂ SO ₄ It shows the extraction rate of Mg according to the mineral liquid concentration when leaching at 100 ℃ for 60 minutes at 4N, 10N concentration. When the concentration of mineral liquid was less than 150g / L, the extraction rate of Mg was almost the same at each concentration, but above 4N H ₂ SO ₄ The extraction rate decreased when the solution was used.

The optimum conditions for extracting Mg from ferronickel slag from the leaching test results above are leaching temperature; 100 ℃, leaching time; 60 minutes and H ₂ SO ₄ The concentration was 4N at 150 g / L mineral solution concentration and 10N at 300 g / L mineral solution concentration.

<Example 2>

As can be seen from the results of the leaching test described above, in the case of silica minerals such as ferronickel slag, the temperature should be 90 ° C. or higher for effective leaching. Recently, in order to improve such a problem, the improvement of leaching efficiency using the mechanochemical effect generated during the grinding of ores has attracted much attention. In the present invention, the leaching characteristics of the ferronickel slag pulverized using planetary mills were investigated. As described above, the crystal structure of ferronickel slag by planetary mill turns to amorphous form, which has the same effect as calcining ferronickel slag.

FIG. 7 shows that ferronickel slag was polished for 0 to 120 minutes in planetary wheat, and then leached for 1.0 minute at 50 ° C. with 1.0NH ₂ SO ₄ solution. As shown in FIG. 7, the extraction rate of Mg increased considerably with the increase of the grinding time. In the case of the sample which was not polished, about 63% of Mg was extracted at 120 minutes of leaching, but 100% of Mg was extracted by leaching for 90 minutes. This causes the particle size of the ferronickel slag sample to decrease as it is polished, but it is thought that the change and activation of the crystal structure have a greater influence.

Next, 1.0NH ₂ SO ₄ solution was leached while changing the leaching temperature of the sample which was polished for 30 minutes, and the result is shown in FIG. 8. The effect of mechanochemical effects was great at low leaching temperature or short leaching time, but the reaction time required to extract 100% Mg was almost similar to that of polished.

<Example 3>

As shown in Table 1, ferronickel slag contains Fe, Al, Cr, Ca, and Ni as impurities in addition to the target component Mg. Therefore, when leaching ferronickel slag by H ₂ SO ₄ , these elements It is present as an impurity. Therefore, these impurities must be removed first to prepare a high purity compound from the leaching solution. Fe can be precipitated and removed with Fe (OH) ₃ by adjusting the final acidity of the leachate to pH 4∼4.5 while injecting air in the leaching process. However, in this case, it was concluded that it is suitable to remove from the leaching liquid after the leaching process is completed because it acts as an impurity again in the preparation of the porous silica.

Table 2 shows the chemical composition of the leaching solution obtained by leaching ferronickel slag at 100 ° C. with 10N H ₂ SO ₄ solution. The mineral solution concentration was 300 g / L. As shown in the table, the Fe concentration is the highest among the impurities. Therefore, the present invention focused on the removal of Fe. There are various methods of removing impurities shown in Table 3, but Fe has been widely used to remove by precipitation of hydroxide by hydrolysis. The pH control of the solution is very important for the precipitation of the hydroxide by hydrolysis. The pH should be adjusted in consideration of the concentration of elements present in the solution to remove impurities without loss of Mg.

Table 3 shows the solubility of the hydroxide formed when each element in the leachate was hydrolyzed. As shown in the table, since the solubility of each elemental hydroxide produced by hydrolysis is very low, a sufficient purification effect can be obtained.

First, in order to remove Fe, the pH of the leachate was adjusted to 4.5 to form Fe (OH) ₃ precipitate, which was removed, but the removal rate was only about 18%. The reason is ferronickel slag H ₂ SO ₄ It is considered that Fe is present as Fe ^{+ 2} in the leaching solution. Therefore, Fe ^{+ 2} was first oxidized to Fe ^{+ 3} and then the pH was adjusted to 4.5 to remove Fe. Oxygen, KMnO ₄ , and H ₂ O ₂ may be used as the oxidizing agent, but in the present invention, H ₂ O ₂ was used and pH was adjusted with NaOH.

8 is a diagram showing the results of Fe removal according to the amount of H ₂ O ₂ added. As the amount of H ₂ O ₂ was increased, the Fe removal rate increased, and almost all Fe was removed when the equivalent ratio was added at 1.0.

Since NaOH used as a neutralizing agent is expensive, MgO was used to control the pH of the leachate. As shown in FIG. 9, as the amount of MgO added increases, the leaching solution is neutralized, and the pH is gradually increased. In particular, when 24 g / L MgO was added, the color of the leachate began to appear light brown due to the formation of Fe (OH) ₃ precipitate. When 24 g / L of MgO was added, the pH of the leachate was as low as 1.4, but Fe (OH) ₃ began to be produced due to the high Fe concentration. As the amount of MgO added increased, the amount of Fe (OH) ₃ precipitate increased, so the color of the leaching solution turned dark brown. However, when 30g / L of MgO was added, the precipitate precipitated out of the leaching solution and the viscosity of the solution became very high. Could not be added. Therefore, it was not possible to use MgO as a neutralizer for sulfate solution with high concentration of Mg.

In addition, Fe was removed using CaO as a neutralizing agent, but the reactivity of CaO in H ₂ SO ₄ leachate was not effective.

H ₂ O ₂ was added as an oxidizing agent of Fe ⁺² and the pH of the leachate was adjusted to 4.5 using NaOH as a neutralizing agent to remove Fe, and the chemical composition of the obtained purified leachate is shown in Table 4.

<Example 4>

As shown in Figure 2, the solubility of MgSO _{4 in} the aqueous solution has a large difference depending on the temperature. Therefore, MgSO ₄ may be prepared by crystallization of cooling a saturated solution.

In the present invention, first, the crystallization of MgSO ₄ from the unleached leachate was attempted, and its chemical analysis was performed to examine the behavior of impurities.

4 shows the behavior of impurities when MgSO ₄ is crystallized without purification of the leaching liquid having the composition shown in Table 2. Crystallization was carried out by heating the leachate to 80 ° C. and then cooling by air cooling to stand in air and water cooling with 20 ° C. water.

As shown in the table, the amount of impurities present in the leachate is MgSO ₄ It can be seen that the decision was incorporated. MgSO ₄ prepared by cooling in air MgSO ₄ prepared more water-cooled than crystals In the case of crystals, the incorporation of impurities was small. Therefore, the faster the cooling rate of the leachate, the addition of seed crystals, and washing the resulting crystals is believed to be higher purity.

MgSO ₄ obtained by heating the purified leachate to 80 ° C. and then performing air and water cooling in the same manner as in the previous crystallization experiment. The X-ray diffraction test result of the crystal is shown in FIG. As shown in the figure, it was confirmed that the (A) MgSO ₄ crystal prepared by air cooling was composed of MgSO ₄ 1.25H ₂ O and MgSO ₄ 4H ₂ O phases. On the other hand, the (B) MgSO ₄ crystal prepared by water cooling shows the peak of synthetic Kieserite, which is MgSO ₄ H ₂ O phase.

11 and 12 show MgSO ₄ of (A) and (B), respectively. The figure shows the result of pyrolysis of crystals. Each thermogravimetric curve is very similar and has a high number of (A) MgSO ₄ crystals. There was a slight decrease in the weight of the crystal. In particular, about (A) MgSO ₄ crystal weight loss of about 9% occurred below 100 ℃. Total weight loss is (A) MgSO ₄ Crystals 34.33%, (B) MgSO ₄ The decision was 19.82%.

MgSO ₄ from Serpentine Leachate by Crystallization Method Using Solubility Difference with Temperature Crystals could be prepared. In the case of crystallization of the crude leachate, impurities were severely mixed. Fe was first removed from the leachate and then MgSO ₄ When the crystals were prepared, relatively high purity MgSO ₄ could be obtained.

In the present invention, the optimum conditions for leaching Mg from ferronickel slag using H ₂ SO ₄ for the preparation of Mg compound was established. Optimum leaching condition is temperature; 100 ° C., time; 60 minutes, H ₂ SO ₄ concentration was 4N when the mineral liquid concentration is 150g / L, 10N when the mineral liquid concentration is 300g / L. In addition, the mechanochemical effect of leaching of ferronickel slag with oily wheat was increased by about 50%.

MgSO ₄ was prepared through crystallization after leaching. In addition, as a result of leaching with acid to prepare porous silica powder from ferronickel slag, the average particle diameter of the residue was larger than that of ferronickel slag since the fine impurity particles were dissolved first at the beginning of the leaching reaction. Since most of the leach residues were silica, there was no change in particle size. When ferronickel slag raw material with specific surface area of 21.0㎡ / g and starting size of 62.3Å is leached with 80 ℃, 1.0 ～ 6.0M sulfuric acid for 60 minutes, the specific surface area increases by more than 20 times, resulting in 393 ～ 411㎡ / g and pore size. Was reduced to obtain a porous amorphous silica powder exhibiting about 25 to 26 kPa.

Figure 2 is the solubility curve of MgSO ₄ and MgCl ₂ in water with temperature

Figure 3 is the effect of the stirring speed of the solution on the extraction reaction rate of Mg when leaching with 1.0NH ₂ SO ₄ solution at 50 ℃ for 120 minutes

4 is an effect on the extraction rate of Mg when leaching ferronickel slag while changing the H ₂ SO ₄ concentration to 0.1 ~ 6.0 N

5 is the effect of mineral solution concentration on the extraction of Mg when leaching ferronickel slag with 10N H ₂ SO ₄ solution

Figure 6 shows the extraction rate of Mg according to the concentration of mineral liquid when leaching at 100 ℃ for 60 minutes at 4N, 10N

Figure 7 is the effect of the grinding time on the extraction rate of Mg when leaching with 1.0NH ₂ SO ₄ solution at 50 ℃ for 120 minutes

8 is the effect of the removal of Fe according to the addition amount of H ₂ O _{2 in} the leachate

9 is the amount of change in the pH of the leaching solution is neutralized as the amount of MgO is increased

10 is MgSO ₄ obtained by performing air and water cooling in the same manner as in the crystallization experiment. X-ray diffraction test results

Figure 11 (A) MgSO ₄ prepared by air cooling from the leaching solution Thermogravimetric Analysis Curves of Crystals

12 is (B) MgSO ₄ prepared by water cooling from a leachate Thermogravimetric Analysis Curves of Crystals

Table 1 Ferronickel Slag Chemical Composition

Table 2 Chemical Composition of Ferronickel Slag Leachate Used in Purification Experiments

Table 3 Solubility of each hydroxide at 25 ° C

Table 4 Chemical Composition of Purified Ferronickel Slag Leachate

Claims (3)

Chemical composition is 55% to 60% of silicon dioxide (SiO ₂ ), 32 to 37% of magnesium oxide (MgO), 1 to 2% of calcium oxide (CaO), 2 to 5% of iron oxide (Fe ₂ O ₃ ), oxidation Ferronickel slag of 1 to 2% of aluminum (Al ₂ O ₃ ) is dried and pulverized in a vortex mill, and then activated in a centrifugal vibratory mill or planetary mill, dissolved in sulfuric acid, and then ferro-ferrous. Method for producing magnesium sulfate and silicon dioxide from nickel slag.  The method for producing magnesium sulfate and silicon dioxide from ferronickel slag according to claim 1, wherein a vortex centrifugal vibration mill or a planetary mill capable of mechanochemical reaction is used as the grinding activation method. The method for producing magnesium sulfate and silicon dioxide from ferronickel slag according to claim 1, wherein H ₂ O ₂ is used as an oxidizing agent in the impurity removing method.

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