KR102632611B1 - Method of preparing gypsum and gypsum prepared thereby - Google Patents

Abstract

A method for producing gypsum and gypsum produced by the method are disclosed. The disclosed gypsum manufacturing method is a recycling method for inorganic sludge, which is discharged in large quantities from semiconductor factories and is expected to increase in the future. The amount of water required is compared to the case where inorganic sludge is treated with acid and water is used alone. By drastically reducing the sludge to fluidize for easier handling, the fluidized inorganic sludge is mixed with waste sulfuric acid and calcium compounds to produce a gypsum precursor that can be used as a setting retardant, and a hexavalent chromium reducing agent is added to it to provide an appropriate setting delay effect and hexavalent sludge. This is a method of recycling into plaster that has a chrome removal function.

Description

Gypsum manufacturing method and gypsum manufactured by the method {Method of preparing gypsum and gypsum prepared thereby}

A method for producing gypsum and gypsum produced by the method are disclosed. More specifically, a method for producing gypsum capable of providing gypsum with both a setting delay function and a hexavalent chromium removal function and a gypsum manufactured by the method are disclosed.

There are numerous etching and cleaning processes in the semiconductor production process. Chemicals used in these processes include HF, BOE (a mixed solution of HF and NH ₄ F), H ₂ SO ₄ , H ₂ O ₂ , H ₃ PO ₄ , There are HNO ₃ and HCl, and a large amount of inorganic sludge is generated when these chemicals are used and mixed together to treat the discharged wastewater.

Currently, approximately 500,000 to 600,000 tons of inorganic sludge is discharged every year, and significant growth is expected in the future in industries that require large quantities of semiconductor devices such as electric vehicles, autonomous driving, artificial intelligence, and big data. It is expected that the discharge of solid sludge will also increase significantly.

However, although most of the inorganic sludge is recycled as a cement raw material, there are factors that hinder the cement manufacturing process, such as the highly volatile fluorine content sticking to preheaters, etc., making it difficult to create further demand for cement use. am. Therefore, it is believed that the time has come when another recycling method for inorganic sludge, which is increasing day by day, is needed.

Meanwhile, recently, as ESG management has been strengthened and social interest in carbon neutrality has grown, thermal power generation using coal or high-sulfur bunker oil as fuel has decreased, and the amount of desulfurized gypsum discharged has decreased accordingly, which is used as a setting retardant. The supply of gypsum is becoming scarce.

Meanwhile, chromium contained in cement mainly exists as trivalent chromium, and some of this trivalent chromium is oxidized to hexavalent chromium during the firing process or grinding process. The typical amount of trivalent chromium present in clinker is 100 to 200 ppm, and the amount of chromium that is oxidized to hexavalent chromium during the firing or grinding process is 8 to 20%. In particular, in order to reduce costs and increase the efficiency of kilns, there is a tendency to input various wastes such as coal ash, sewage sludge, waste molding sand, waste tires, and waste synthetic resin, so the amount of total chromium and the amount of hexavalent chromium produced by oxidation is likely to increase further. There is also.

In Europe, the content of hexavalent chromium in all cement products manufactured or imported into Europe has been strictly regulated since January 2005 to not exceed 2 ppm in accordance with the provisions of EU Directive 2005/53/EC. In Korea, it was managed below 30 ppm until 2008, and since 2009, it has been managed below 20 ppm, which is the standard of the autonomous agreement. It is expected that there will soon be a movement in Korea to regulate it below 2 ppm, following the level of regulation in Europe.

In order to meet the regulatory or standard level of hexavalent chromium, various hexavalent chromium reducing agents have been reported. These hexavalent chromium reducing agents are solid or liquid products in the form of metal salts or oxides of iron, manganese, zinc, tin, etc., and solid powder forms have generally been shown to be more effective than liquid products.

However, solid powder is inconvenient to handle because separate equipment is required to add it to cement or dust is generated.

On the other hand, in liquid formulations, the hexavalent chromium reducing agent (for example, metal salt) added to the cement is oxidized due to acceleration of oxidation by moisture and quickly loses its reducing ability. In order to overcome these disadvantages of liquid formulations, solid particles are coated with a material (e.g., polymer) that prevents contact with oxygen and dispersed in an aqueous solution. A triple method is made by surrounding a water-soluble metal salt with an organic solvent and emulsifying it in an aqueous solution. An emulsion method, a method of manufacturing by dissolving, dispersing or suspending tin chloride in water, glycol, glycerol or a mixture thereof, and adding antioxidants, oxygen destroyers, cement grinding aids, cement quality improvers, etc. as additives has been reported. .

Even though liquid formulations have advantages in handling, there is a significant increase in the cost of additional raw materials or manufacturing processes to preserve the reducing ability of hexavalent chromium reducing agents (e.g., metal salts) that play a role in reducing hexavalent chromium, so cement It is a huge economic burden on the industry.

One embodiment of the present invention provides a method for producing gypsum that can provide gypsum with both a setting delay function and a hexavalent chromium removal function.

Another embodiment of the present invention provides gypsum manufactured by the above gypsum manufacturing method.

One aspect of the present invention is,

A step of preparing an inorganic sludge slurry by adding acid to the inorganic sludge discharged from a semiconductor factory to slurry the inorganic sludge (S10);

Mixing and reacting the inorganic sludge slurry, waste sulfuric acid, and calcium compound prepared in step (S10) to produce neutralized gypsum (S20); and

It provides a method for producing gypsum including the step (S30) of producing gypsum by mixing a hexavalent chromium reducing agent with the neutralized gypsum prepared in step (S20).

The inorganic sludge introduced in the step (S10) has a moisture content of 50 to 60% by weight and a dry weight of SiO ₂ 1 to 15% by weight, Al ₂ O ₃ 5 to 20% by weight, and Fe ₂ O ₃ 0.1 to 10%. Weight%, CaO 40-70% by weight, MgO 0.1-2% by weight, SO ₃ 0.1-10% by weight, LOI 10-20% by weight, TiO ₂ 0.01-0.2% by weight, P ₂ O ₅ 1-20% by weight, and It may contain 10 to 20% by weight of F (components other than LOI and F are converted to oxides and expressed).

The acid added in step (S10) may include hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, or a combination thereof.

The inorganic sludge slurry prepared in step (S10) may have a pH of 2.5 to 4.5.

The waste sulfuric acid added to the step (S20) may have a sulfuric acid concentration of 50 to 80% by weight.

The calcium compound added in step (S20) may include slaked lime, calcium carbonate, quicklime, or a combination thereof.

The content of the calcium compound added to the step (S20) may be 1.10 to 1.25 equivalents based on 1 equivalent of the total content of sulfuric acid added to at least one of the steps (S10) and the step (S20).

The hexavalent chromium reducing agent added in the step (S30) is ferrous sulfate (FeSO ₄ ·nH ₂ O, n = 0 to 7), tin sulfate (SnSO ₄ ), tin chloride (SnCl ₂ ), and sodium metabisulfite (Na). ₂ S ₂ O ₅ ), sodium bisulfite (NaHSO ₃ ), sodium sulfite (Na ₂ SO ₃ ), sodium bisulfite (NaHSO ₃ ), sodium hyposulfite (Na ₂ S ₂ O ₄ ), thiourea (NH ₂ CSNH ₂ ) , sodium thiosulfate (Na ₂ S ₂ O ₃ ), sulfur (S), soda sulfide (Na ₂ S), calcium sulfide (CaS), hydrazine dihydro chloride (NH ₂ NH ₂ ·2HCl), hydroxylammonium chloride ([ NH ₃ OH]Cl) or a combination thereof.

The content of the hexavalent chromium reducing agent added in step (S30) may be 10 parts by weight or less based on 100 parts by weight of the neutralized gypsum produced in step (S20).

Another aspect of the present invention is,

A gypsum manufactured by the above gypsum manufacturing method and containing a hexavalent chromium reducing agent is provided.

The gypsum may have an SO ₃ content of 38% by weight or more, a CaO content of 40% by weight or less, and a free moisture content of 18% by weight or less.

The method for producing gypsum according to an embodiment of the present invention can provide gypsum that has both a setting delay function and a hexavalent chromium removal function.

In addition, the gypsum according to one embodiment of the present invention does not require separate addition of a hexavalent chromium reducing agent when pulverizing clinker, and can overcome the disadvantages of solid or liquid hexavalent chromium removers. In other words, when pulverizing clinker, it is possible to simultaneously provide a setting delay effect and a hexavalent chromium removal effect simply by putting gypsum together with the clinker into the crushing equipment and pulverizing it.

Hereinafter, a method for producing gypsum according to an embodiment of the present invention and gypsum produced by the method will be described in detail.

In this specification, “inorganic sludge” refers to filtered solids that remain on the filter cloth of a filter press when sludge formed through a process of coagulating and settling wastewater discharged from a semiconductor factory is filtered through a filter press.

Also, in this specification, “neutralized gypsum” means gypsum whose pH is substantially neutral.

Also, in this specification, “hexavalent chromium reducing agent” refers to a substance that reduces hexavalent chromium to trivalent chromium.

Also, in this specification, “LOI (loss on ignition)” refers to the decrease in mass when the analysis sample is ignited. Specifically, “LOI” occurs as a result of scattering of volatile components derived from water, carbon, sulfur, etc. contained in the sample.

Also, in this specification, “equivalent” refers to the number of grams (i.e., acid-base equivalent) obtained by dividing 1 gram molecular weight of an acid or base by the number of hydrogen atoms or hydroxyl groups that can react as an acid or base. it means.

Additionally, in this specification, “free water” refers to the remaining moisture that is not bound water among the moisture present in gypsum.

The method for producing gypsum according to an embodiment of the present invention includes the steps of adding acid to the inorganic sludge discharged from a semiconductor factory to slurry the inorganic sludge to produce an inorganic sludge slurry (S10), the step (S10) ), mixing and reacting the inorganic sludge slurry, waste sulfuric acid, and calcium compounds to produce neutralized gypsum (S20), and mixing a hexavalent chromium reducing agent with the neutralized gypsum prepared in step (S20). It includes a step of manufacturing gypsum (S30).

The step (S10) is a process of slurrying (fluidizing) the inorganic sludge generated in the process of treating wastewater discharged from a semiconductor factory to make it easier to handle in subsequent processes. The inorganic sludge has a high moisture content of 50 to 60% by weight, and appears to be a hard filter cake, but when it is placed in a grinder or crushed with a hammer, clumps occur and it is not pulverized well. In addition, when a heat treatment process such as drying is performed to pulverize the inorganic sludge, the associated cost is large, and problems such as dust generation arise after drying. Slurrying is necessary to transport the inorganic sludge to a pump and ensure good contact between reactants within the reactor. Usually, slurrying this type of sludge requires adding a lot of water and stirring for a long time. However, in order to use it as a setting retardant plaster, it must meet the free moisture standard (18% by weight or less), so it is not possible to add enough water. Therefore, the present inventor used acid to dissolve the acid-soluble solids to form a solid substance. The idea was that the amount of fluid injected could be significantly reduced and the stirring time could be reduced as the solid structure was broken down, and quite good results were obtained.

Specifically, in the step (S10), the sludge discharged from the semiconductor factory is usually passed through a filter press and then shake off the plate-shaped filtration solids with a thickness of 2 to 3 cm formed between the filter cloths of the filter press. As it falls into the arm roll box, it breaks and becomes inorganic sludge with a random shape of approximately 5 to 20 cm in size. The inorganic sludge has a moisture content of approximately 50 to 60% by weight, but as described above, when pulverized by hitting it with a hammer, etc., it clumps up and becomes difficult to mix and pulverize. In this case, when acid is added, among the solids, substances that dissolve in the acid (inorganic sludge discharged from semiconductors contain Al components in the form of Al(OH) ₃ , Al _n F _m (OH) _{3 n-m} , etc.; various Calcium phosphate in the form of calcium phosphate (there are substances soluble in acids such as Ca ₃ (PO ₄ ) ₂ , CaHPO ₄ , Ca(H ₂ PO ₄ ) ₂ ) dissolves, and at the same time, solid lumps are dismantled and slurrying is promoted. In addition, the amount of fluid required for slurry can be significantly reduced compared to when only water is used. Once the inorganic sludge is slurried (fluidized), it can be transported by a pump, etc., making it easy to handle, and it is advantageous because the reaction occurs quickly and evenly as contact between the contents of the reactor becomes smooth.

The inorganic sludge introduced in the step (S10) has a moisture content of 50 to 60% by weight and a dry weight of SiO ₂ 1 to 15% by weight, Al ₂ O ₃ 5 to 20% by weight, and Fe ₂ O ₃ 0.1 to 10%. Weight%, CaO 40-70% by weight, MgO 0.1-2% by weight, SO ₃ 0.1-10% by weight, LOI 10-20% by weight, TiO ₂ 0.01-0.2% by weight, P ₂ O ₅ 1-20% by weight, and It may contain 10 to 20% by weight of F (components other than LOI and F are converted to oxides and expressed).

The acid added in step (S10) may include hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, or a combination thereof.

The inorganic sludge slurry prepared in step (S10) may have a pH of 2.5 to 4.5 (for example, 3 to 4). If the pH of the inorganic sludge slurry prepared in step (S10) is less than 2.5, it is difficult to handle, such as corrosion of equipment, and if it exceeds 4.5, the solubility of solids decreases, so slurryization may be delayed. For reference, the solid structure of the inorganic sludge may be so hard that it is not possible to slurry it purely with water.

In order for the gypsum to be used as a setting retardant for cement, the present inventor aimed to meet the specifications in Table 1 below, which summarizes the items that must be met as a set retardant through communication with cement manufacturers.

item standard SO ₃ 38% by weight or more CaO 40% by weight or less free pollination 18% by weight or less

The step (S20) is a step of obtaining neutralized gypsum by mixing and reacting the inorganic sludge slurry prepared in step (S10) with waste sulfuric acid and calcium compounds.

The waste sulfuric acid added to the step (S20) may have a sulfuric acid concentration of 50 to 80% by weight. Specifically, in the step (S10), an acid (solution) containing a certain amount of water was added to the inorganic sludge with a high moisture content to make a slurry, so that the moisture content of neutralized gypsum was 18% by weight or less (see Table 1 above). In addition, it is necessary to use high concentration waste sulfuric acid of about 50 to 80% by weight to meet SO ₃ of 38% by weight or more. That is, since the inorganic sludge slurry prepared in step (S10) has a high moisture content and a low SO ₃ content, in order to meet the specifications of gypsum for setting retardation, the sludge slurry has a high concentration as waste sulfuric acid, about 50 to 80 weight. It is desirable to use waste sulfuric acid at % level. In addition, in order to meet the specifications of gypsum for setting retardation in Table 1 above, the input ratio of inorganic sludge slurry, waste sulfuric acid, and calcium compound must be adjusted and mixed. Here, technology based on Korean Patent No. 10-1865882 (“Method for producing gypsum from waste sulfuric acid by dry neutralization method”) was applied.

The calcium compound added in step (S20) may include slaked lime, calcium carbonate, quicklime, or a combination thereof.

The content of the calcium compound added to the step (S20) may be 1.10 to 1.25 equivalents based on 1 equivalent of the total content of sulfuric acid added to at least one of the steps (S10) and the step (S20).

The step (S30) is a step of completing the production of gypsum with a setting delay function and a hexavalent chromium reducing function by mixing the neutralized gypsum prepared in step (S20) with a hexavalent chromium reducing agent.

The hexavalent chromium reducing agent added in the step (S30) is ferrous sulfate (FeSO ₄ ·nH ₂ O, n = 0 to 7), tin sulfate (SnSO ₄ ), tin chloride (SnCl ₂ ), and sodium metabisulfite (Na). ₂ S ₂ O ₅ ), sodium bisulfite (NaHSO ₃ ), sodium sulfite (Na ₂ SO ₃ ), sodium bisulfite (NaHSO ₃ ), sodium hyposulfite (Na ₂ S ₂ O ₄ ), thiourea (NH ₂ CSNH ₂ ) , sodium thiosulfate (Na ₂ S ₂ O ₃ ), sulfur (S), soda sulfide (Na ₂ S), calcium sulfide (CaS), hydrazine dihydro chloride (NH ₂ NH ₂ ·2HCl), hydroxylammonium chloride ([ NH ₃ OH]Cl) or a combination thereof.

The content of the hexavalent chromium reducing agent added in step (S30) may be 10 parts by weight or less based on 100 parts by weight of the neutralized gypsum produced in step (S20).

When all of the above steps (S10) to (S30) are passed, gypsum having both a setting delay function for cement and a hexavalent chromium removal function is manufactured by recycling the inorganic sludge. In particular, the hexavalent chromium reducing agent that has been used so far is effective in solid form, but it often causes agglomeration due to moisture in the powder during the input path and blocks the inlet. On the other hand, if there is no moisture in the powder, dust is formed. This occurred and was inconvenient to handle. In addition, the liquid form of the hexavalent chromium reducing agent has the disadvantage of requiring separate input equipment and rapidly deteriorating the hexavalent chromium removal function over time. Therefore, if the hexavalent chromium removal function is added to gypsum, there is no need to have separate equipment for the injection of the hexavalent chromium reducing agent, and the setting delay function and hexavalent chromium removal function can be achieved by using the existing well-equipped gypsum injection equipment. Since gypsum having , can be input at the same time, separate chemicals for reducing hexavalent chromium and their input equipment can be omitted.

The method for producing gypsum according to an embodiment of the present invention having the above-mentioned structure is a situation in which the present inventor combines inorganic sludge with gypsum to delay setting in a situation where there is an urgent need for development of uses for inorganic sludge and increased production of gypsum for setting delay. The idea was to achieve zero recycling, and in order to increase the commercial value of gypsum, it was designed to further increase the recycling value by adding the additional function of removing hexavalent chromium.

Through the above gypsum manufacturing method, it has become possible to recycle inorganic sludge discharged from semiconductor factories, which are called industrial rice and are expected to continue to grow in the future, into gypsum with a setting delay function and a hexavalent chromium removal function.

Hereinafter, gypsum according to one embodiment of the present invention will be described in detail.

Gypsum according to one embodiment of the present invention is manufactured by a gypsum manufacturing method, and may include a hexavalent chromium reducing agent.

The gypsum may have an SO ₃ content of 38% by weight or more, a CaO content of 40% by weight or less, and a free moisture content of 18% by weight or less.

Hereinafter, the present invention will be described with reference to the following examples, but the present invention is not limited to the following examples.

sample collection

The inorganic sludge sample needed for the experiment was collected from inorganic sludge discharged from S Company, a domestic semiconductor company. The composition of the collected inorganic sludge sample was as shown in Table 2 below.

item SiO ₂ Al ₂ O _{3 Fe2O3 _} CaO MgO Unit (weight%) 5.85 8.20 4.89 51.75 0.56 item SO ₃ TiO ₂ P ₂ O ₅ F LOI Unit (weight%) 1.71 0.08 10.39 15.79 15.92

In Table 2 above, the content of each component is expressed based on the dry weight with moisture (moisture content 58.3% by weight) removed, and the content of each element present in the sample other than F and LOI is expressed by converting it to the content of oxide. will be.

Examples 1-2 and Comparative Examples 1-2: Preparation of gypsum precursor

Put the inorganic sludge sample in a mortar, crush it finely, add 100g of inorganic sludge to each of four 1-liter polypropylene beakers, and then add waste sulfuric acid with a concentration of 54% by weight to each beaker. The contents were added until the pH reached 5, 4, 3, and 2, and the amount of spent sulfuric acid with a concentration of 54% by weight required to prepare the inorganic sludge slurry at each pH was recorded. Also, for comparison, 100 g of water was added to 100 g of inorganic sludge and stirred under the same conditions. The impeller used for stirring was a 77 mm paddle-type impeller made of Teflon. pH was measured using SUNTEX's Model TS-100 pH meter, and the measuring device was directly immersed in inorganic sludge slurry.

pH input cost Slurrying pattern Reference example - 100g inorganic sludge + 100g water Even though the total amount of fluid is relatively large, even finely crushed inorganic sludge retains its shape for a long time and does not turn into slurry. Comparative Example 1 5 100g of inorganic sludge + 18.8g of 54% by weight sulfuric acid It slurries, but takes about 5 minutes. Example 1 4 100g of inorganic sludge + 27.8g of 54% by weight sulfuric acid Immediately turns into slurry after adding sulfuric acid Example 2 3 100g of inorganic sludge + 35.6g of 54% by weight sulfuric acid Immediately turns into slurry after adding sulfuric acid Comparative Example 2 2 100g of inorganic sludge + 42g of 54% by weight sulfuric acid Immediately turns into slurry after adding sulfuric acid

Next, waste sulfuric acid and calcium carbonate with a concentration of 73% by weight were mixed as shown in Table 4 to prepare neutralized gypsum, and the inorganic sludge slurry shown in Table 3 was added to complete the production of gypsum precursor. Specifically, a polypropylene bowl (top diameter 26 cm Sprinkle evenly and mix with a wooden spoon for reaction. Afterwards, when the reaction of neutralized gypsum was almost complete, the inorganic sludge slurry shown in Table 3 was added and mixed well to complete the neutralization reaction to prepare a gypsum precursor. The amount of calcium carbonate added was 1.1 times the equivalent weight of the sulfuric acid added in the previous slurry process and the sulfuric acid added here.

Types of inorganic sludge slurry 73% by weight spent sulfuric acid input amount (g) Calcium carbonate input amount (g) gypsum precursor SO ₃ (% by weight) Free moisture (% by weight) Comparative Example 1 100 200 39.6 16.6 Example 1 100 205 39.9 16.9 Example 2 100 210 40.0 17.2 Comparative Example 2 100 215 40.3 17.4

Evaluation Example 1: Evaluation of initial contact time and daily intensity

When the gypsum precursors prepared in Examples 1 to 2 and Comparative Examples 1 to 2 were added to clinker, the first setting time and one-day strength were measured. The clinker used was obtained in crushed form from a cement company located in Yeongwol, Gangwon-do. First setting time was measured according to KS L ISO 9597 (Cement setting and safety test method). The daily strength was measured by mixing cement:water at a weight ratio of 100:25, kneading the mixture, manufacturing a test specimen in a 2cm The measurement results are shown in Table 5 below.

division First meeting time (minutes) Daily strength (MPa) Neutralized plaster (Reference) 185 34.6 Comparative Example 1 190 34.3 Example 1 185 34.1 Example 2 190 36.4 Comparative Example 2 245 32.1

Referring to Table 5, the gypsum precursor prepared in Example 1 using an inorganic sludge slurry with a pH of 4 was added to clinker and the case of adding the gypsum precursor prepared in Example 2 using an inorganic sludge slurry with a pH of 3. When gypsum precursor was added to clinker, it was found that the setting delay function was adequate and had little effect on strength compared to when neutralized gypsum was added to clinker.

However, when the gypsum precursor prepared in Comparative Example 2 was added to clinker using an inorganic sludge slurry with a pH of 2, the initial setting time increased significantly, the strength slightly decreased, and the side effect of corroding equipment due to the low pH was observed. This is highly likely to occur. For reference, the appropriate initial viewing time is 160 to 210 minutes.

In addition, in the case of Comparative Example 1 (pH 5), where the amount of sulfuric acid added in the slurry step was insufficient, it took about 5 minutes to slurry, which resulted in a decrease in workability.

Evaluation Example 2: Evaluation of hexavalent chromium reduction performance

Gypsum was prepared by adding various hexavalent chromium reducing agents to the gypsum precursor prepared in Example 1 at varying amounts, and mixing the gypsum with crushed clinker in a small ball mill for about 1 hour and then eluting the hexavalent chromium reducing agent. The remaining amount of chromium was analyzed. The types and amounts of each hexavalent chromium reducing agent, and the remaining amount of hexavalent chromium are summarized in Table 6 below. Hexavalent chromium was analyzed according to KS L 5221 on ‘Method for quantitative analysis of hexavalent chromium in cement’. Gypsum was added at a rate of 4.5 parts by weight based on 100 parts by weight of clinker, and the amount of hexavalent chromium reducing agent shown in Table 6 below is converted to the weight ratio of the amount of hexavalent chromium reducing agent contained in 4.5 parts by weight of gypsum to 100 parts by weight of clinker. It was done.

division Input amount (part by weight) Hexavalent chromium residual amount (wtppm) clinker No hexavalent chromium reducing agent added 12.2 Sodium metabisulfite
(Na ₂ S ₂ O ₅ ) 0.025 11.2 0.05 9.6 0.3 7.8 0.6 3.4 sodium sulfite
(Na ₂ SO ₃ ) 0.025 5.1 0.05 1.4 0.3 0.1 0.6 0.0 Sodium hyposulfite (Na ₂ S ₂ O ₄ ) 0.025 0.3 0.05 0.0 Ferrous sulfate
(FeSO ₄ 7H ₂ O) 0.05 5.3 0.3 0.1 thiourea
(CS(NH ₂ ) ₂ 0.3 4.1 0.6 0.3 Sodium bisulfite (NaHSO ₃ ) 0.025 3.4 0.05 0.8 0.3 0.0

The appropriate reducing agent and its input amount can be determined by considering the government's regulatory status, market price, ease of purchase, and the level of hexavalent chromium content in the produced clinker.

Evaluation Example 3: Evaluation of initial contact time and daily intensity

Some gypsum to which the hexavalent chromium reducing agent of Table 6 was applied was added to clinker, and the first setting time and daily strength were measured in the same manner as Evaluation Example 1, and the results are shown in Table 7 below.

division Input amount (part by weight) First meeting time (minutes) Daily strength (MPa) Neutralized Gypsum (Reference):
No inorganic sludge input
No hexavalent chromium reducing agent added 195 33.7 sodium sulfite
(Na ₂ SO ₃ ) 0.05 200 33.9 0.3 200 34.1 Sodium hyposulfite (Na ₂ S ₂ O ₄ ) 0.025 195 33.5 0.05 200 34.0 Ferrous sulfate
(FeSO ₄ 7H ₂ O) 0.05 200 33.8 0.3 210 34.5 thiourea
(CS(NH ₂ ) ₂ 0.3 205 34.3 0.6 210 34.6 Sodium bisulfite (NaHSO ₃ ) 0.025 195 33.8 0.05 200 34.2 0.3 200 34.2

Referring to Table 7 above, it was found that even if a hexavalent chromium reducing agent was added, there was no significant effect on the initial setting time and daily strength.

In the above, preferred embodiments according to the present invention have been described with reference to the examples, but these are merely illustrative, and those skilled in the art will understand that various modifications and other equivalent embodiments are possible therefrom. You will be able to. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims (11)

A step of preparing an inorganic sludge slurry by adding acid to the inorganic sludge discharged from a semiconductor factory to slurry the inorganic sludge (S10);
Mixing and reacting the inorganic sludge slurry, waste sulfuric acid, and calcium compound prepared in step (S10) to produce neutralized gypsum (S20); and
A method of producing gypsum comprising the step (S30) of producing gypsum by mixing a hexavalent chromium reducing agent with the neutralized gypsum prepared in step (S20). According to paragraph 1,
The inorganic sludge introduced in the step (S10) has a moisture content of 50 to 60% by weight and a dry weight of SiO ₂ 1 to 15% by weight, Al ₂ O ₃ 5 to 20% by weight, and Fe ₂ O ₃ 0.1 to 10%. Weight%, CaO 40-70% by weight, MgO 0.1-2% by weight, SO ₃ 0.1-10% by weight, LOI 10-20% by weight, TiO ₂ 0.01-0.2% by weight, P ₂ O ₅ 1-20% by weight, and Method for producing gypsum containing 10 to 20% by weight of F. According to paragraph 1,
The acid introduced in the step (S10) is a method of producing gypsum including hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, or a combination thereof. According to paragraph 1,
The inorganic sludge slurry prepared in step (S10) is a method of producing gypsum having a pH of 2.5 to 4.5. According to paragraph 1,
A method of producing gypsum in which the waste sulfuric acid added in the step (S20) has a sulfuric acid concentration of 50 to 80% by weight. According to paragraph 1,
The calcium compound added in the step (S20) is a method of producing gypsum including slaked lime, calcium carbonate, quicklime, or a combination thereof. According to paragraph 1,
The amount of the calcium compound added to the step (S20) is 1.10 to 1.25 equivalents based on 1 equivalent of the total sulfuric acid added to at least one of the steps (S10) and the step (S20). According to paragraph 1,
The hexavalent chromium reducing agent added in the step (S30) is ferrous sulfate (FeSO ₄ ·nH ₂ O, n = 0 to 7), tin sulfate (SnSO ₄ ), tin chloride (SnCl ₂ ), and sodium metabisulfite (Na). ₂ S ₂ O ₅ ), sodium bisulfite (NaHSO ₃ ), sodium sulfite (Na ₂ SO ₃ ), sodium bisulfite (NaHSO ₃ ), sodium hyposulfite (Na ₂ S ₂ O ₄ ), thiourea (NH ₂ CSNH ₂ ) , sodium thiosulfate (Na ₂ S ₂ O ₃ ), sulfur (S), soda sulfide (Na ₂ S), calcium sulfide (CaS), hydrazine dihydro chloride (NH ₂ NH ₂ ·2HCl), hydroxylammonium chloride ([ NH ₃ OH] Cl) or a combination thereof. According to paragraph 1,
The method of producing gypsum wherein the content of the hexavalent chromium reducing agent added in the step (S30) is 10 parts by weight or less based on 100 parts by weight of the neutralized gypsum produced in the step (S20). Gypsum manufactured by the method for producing gypsum according to any one of claims 1 to 9, and containing a hexavalent chromium reducing agent. According to clause 10,
Gypsum with an SO ₃ content of 38% by weight or more, a CaO content of 40% by weight or less, and a free water content of 18% by weight or less.