KR20060107658A - Novel purifying method of calcinate - Google Patents

Abstract

The present invention relates to a novel method for refining limestone, and more particularly, the method for refining limestone of the present invention is to treat calcium lime powder with an acid solution to extract calcium ions to obtain a calcium ion solution, and to calculate calcium from the calcium ion solution. Precipitating ions to obtain a calcium precipitate, and washing the calcium precipitate to purify the anion impurities to obtain calcined lime.

By purifying limestone by the refining method according to the present invention, it is possible to obtain high-quality raw and hydrated lime with high purity and high purity of 99% or more that can be used for food and pharmaceutical calcium compounds in a simpler step.

Limestone, quicklime, hydrated lime, refining method, high yield, high quality, high activity

Description

Novel Purification Method of Limestone {NOVEL PURIFYING METHOD OF CALCINATE}

1 is a process chart briefly showing a purification process of limestone of the present invention,

Figure 2 is a photograph showing the result of precipitation of cationic impurities at pH 11,

Figure 3 is a photograph showing the result of the calcium ion precipitation reaction at pH 12.6 in the calcium ion recovery step,

Figure 4 is an XRD graph of the crystal phase of the calcium precipitate obtained as a result of calcium ion precipitation reaction in the recovery of calcium ions, Figure 4a is a XRD measuring the crystal phase of the calcium precipitate according to the implementation of step No. 4-3 of Example 4 It is a graph and FIG. 4B is process No. of Example 4. FIG. XRD graph of the crystal phase of the calcium precipitate according to Examples 4-4,

5 is a photograph showing the color change before and after purification,

Figure 6 is a photograph comparing the calcium precipitate recovered after the implementation of the process Nos. 4-10 and 4-11 of Example 4,

Figure 7 is a photograph showing the precipitation state according to the change of precipitation conditions in the calcium ion precipitation reaction (a: aging, b: cooling, c: heat treatment),

8 is a photograph showing the change in the microstructure of CaO according to the calcination temperature (a: 900 ℃, b: 1000 ℃, c: 1100 ℃ d: 1200 ℃) (temperature rising rate: 10 ℃ / min, holding time: 1 hr) ,

9 is a photograph showing the change in the microstructure of CaO according to the calcination time (a: 0 hours, b: 1 hour, c: 2 hours, d: 3 hours) (calcination temperature: 1000 ℃, heating rate: 10 ℃ / min).

 [Industrial use]

The present invention relates to a method for purifying limestone, and more particularly, to a method for purifying limestone which can obtain high purity and high activity raw and hydrated lime in high yield by a simple process.

[Prior art]

Limestone is a kind of trade name in the form of mining limestone commercially used, but recently limestone is also commonly referred to as limestone. Limestone is calcite in mineralogical terms and the theoretical chemical composition is composed of 56.0 wt% CaO and 44.0 wt% CO ₂ , but limestones produced in Korea are generally MgO, Al ₂ O ₃ , Fe ₂ O ₃ Or it contains a large amount of various impurities such as SiO ₂ , which is not only low purity, but also the basic characteristics of raw materials such as low activity and non-uniform particle size are not good, so it can be applied as a raw material or subsidiary material to high value-added industries such as high quality steel and environment and fine chemical process. This is impossible.

Limestone has been reported to have about 300 uses, including not only as limestone ore itself, but also as lime and calcium compounds. Among the various uses of limestone, cement and steel industry can be used as a mass use of limestone in modern industrial society. In Korea, there is no significant change in the structure in which the steel and cement industry accounts for most of the limestone demand, but recently, the trend of Korean limestone demand is rapidly increasing every year due to the high value-added chemical and food and pharmaceutical additives. Korea Institute of Geoscience and Mineral Resources, Analysis of development trends of major mineral raw materials (2001).

Since the amount of high purity and high white ore is limited among the limestones existing in Korea, the import volume of high-grade raw materials and high-grade powder products for high value-added uses is increasing, and the domestic competitiveness of domestic limestone-related manufacturing industry is weakening. According to the results of the survey and analysis on the domestic production status, consumption performance by each use, and market structure, some ore is imported and used due to the decrease in average grade of domestic limestone and the lack of high whiteness ore. High quality research on ore is considered to be necessary (Korea Mining Promotion Agency, manufacturing technology of high-functional complex calcium carbonate).

In addition, as the demand for high-grade lime products is increasing greatly, it is required to secure advanced technology and process development for industrial lime.In the food and pharmaceutical calcium field, high purity, high activity, particle size control, There is an urgent need to develop linking technologies for fine powder hydrophobic control technology and various advanced technologies.

In order to solve the above problems, an object of the present invention is to provide a method for purifying limestone which can obtain high purity and high activity raw and calcined lime in a high yield in a simple process.

In order to achieve the above object, the method for purifying limestone according to the present invention is to treat calcium lime (CaCO ₃ ) powder with an acid solution to extract calcium ions to obtain a calcium ion solution, and to precipitate calcium ions from the calcium ion solution. After obtaining the calcium precipitates, washing the calcium precipitates to purify the anion impurities to obtain calcined lime (Ca (OH) ₂ ).

The method for purifying limestone of the present invention may further include calcining the limestone powder before the calcium ion extraction, or calcining it after preparing Ca (OH) ₂ to obtain quicklime (CaO).

Hereinafter, the present invention will be described in more detail.

 In the present invention, by using various acids in limestone purification, by adjusting the solubility of limestone according to the change of the initial concentration and the input amount of the acid solution, and by optimizing the heating temperature, the type of basic solution, the dosing method and the input amount to recover the dissolved calcium ion High purity and high activity of raw and hydrated lime were obtained in high yield.

1 is a process chart briefly showing a purification process of limestone of the present invention. Referring to Figure 1, the method for purifying limestone of the present invention comprises the steps of: treating calcium lime powder obtained from limestone ore with an acid solution to extract calcium ions to obtain a calcium ion solution (S1); Precipitating calcium ions from the calcium ion solution to obtain a calcium precipitate (S2); And washing the calcium precipitate to purify the anion impurities to obtain calcined lime (S3).

The limestone is preferably used in the form of a powder by grinding the limestone ore during purification, more preferably, limestone powder having a particle size of 100 to 200 mesh (mesh). In the case of limestone powder having the particle size range, the extraction of calcium ions is easier and preferable.

First, the limestone powder was dissolved in an acid solution to extract calcium ions in the limestone, and the residues (Fe, Al, Si, etc.) remaining without dissolution were filtered out. The calcium ion extraction time is preferably 10 to 60 minutes, more preferably 20 to 30 minutes, including the subsequent filtration time. If the extraction time is less than 10 minutes, the amount of calcium ions to be extracted is not enough, and even if more than 60 minutes, the amount of calcium ions to be extracted does not change significantly.

Acids usable during the extraction of calcium ions include hydrochloric acid (HCl), sulfuric acid (H ₂ SO ₄ ), nitric acid (HNO ₃ ), and the like; And it is preferable to use 1 type selected from the group which consists of weak acid containing citric acid, acetic acid, etc., More preferably, it is citric acid. Strong acids, including hydrochloric acid or nitric acid, have the advantage that the amount of base added in the subsequent calcium ion recovery process is small and the pH can be easily adjusted, and weak acids such as citric acid selectively dissolve only calcium (Ca) and dissolution characteristics. This similar magnesium (Mg) does not dissolve well, so it is possible to remove most of the impurities to be removed in the extraction process has the advantage that there is no need to go through a separate cationic impurity purification process. In the case of using hydrochloric acid, it is preferable to use it as an aqueous solution of 30 to 40% concentration, and it is preferable to use it as an aqueous solution of 65 to 75% of nitric acid and 90 to 100% of sulfuric acid.

When the acid used in the extraction of calcium ions is a strong acid, the acid solution is preferably used in an amount of 500 to 2000 parts by weight, more preferably in an amount of 1000 to 1500 parts by weight, based on 100 parts by weight of limestone. If the amount of the strong acid is less than 500 parts by weight, the amount of calcium to be extracted is not preferable, and if it is more than 2000 parts by weight, the amount of the basic solution used for the extraction of calcium ions increases, which is not preferable.

When the acid used in the extraction of calcium ions is a weak acid, the acid solution is preferably used in an amount of 1500 to 3000 parts by weight, more preferably in an amount of 2000 to 2500 parts by weight, based on 100 parts by weight of limestone. If the amount of weak acid is less than 1500 parts by weight, the amount of calcium to be extracted is not preferable. If the amount of the weak acid exceeds 3000 parts by weight, the amount of the basic solution used for the extraction of calcium ions increases, which is not preferable.

It is preferable that pH of the calcium ion solution obtained after the said calcium ion extraction is 3.0-3.5, More preferably, it is 3.0-3.4. If the pH is less than 3.0, Ca precipitation is difficult, and if the pH exceeds 3.5, Ca recrystallization occurs is not preferable.

 In the case of extracting calcium ions using acid during the limestone refining process, Fe, Al, Si, etc. are not extracted much, but magnesium can be extracted with calcium. This is because magnesium belongs to alkaline earth metals such as calcium and has similar characteristics. Therefore, the method may further include a process for removing cationic impurities extracted together with calcium ions after the extraction of calcium ions. In particular, when using a strong acid, the extraction amount of magnesium may be increased than when using a weak acid, it is preferable to go through the cationic impurity purification process when calcium is extracted using a strong acid.

More specifically, after the calcium extraction step, it is preferable to remove the cationic impurities such as magnesium, iron, and the like extracted during the calcium ion extraction using a basic solution, react with OH ⁻ ions, precipitate in the form of a hydroxide, and filter and remove them. At this time, since precipitates such as magnesium hydroxide (Mg (OH) ₂ ) or iron hydroxide (Fe (OH) ₃ ) precipitated are colloidal and amorphous, Al and Si extracted together when extracting calcium ions by their strong surface adsorption amount Will be copulated.

The basic solution usable in the cationic impurity purification may be one selected from the group consisting of a strong base solution containing sodium hydroxide (NaOH) aqueous solution and a weak base solution containing ammonia (NH ₄ OH) water. The NH ₄ OH water is preferably used at a concentration of 25 to 35%.

The addition amount of the basic solution used in the cationic impurity purification is preferably added until the final pH of the calcium ion solution becomes 10.5 to 12.5, more preferably 11 to 11.5. If the final pH range of the solution is less than 10.5, precipitation of Mg ions hardly occurs, and if it exceeds 12.5, Ca may precipitate together with the temperature, which is not preferable.

 In addition, during the cationic impurity purification, when the impurity precipitation pH is reached, it is preferable to heat to a temperature range of 70 to 100 ℃, more preferably 80 to 100 ℃. When heated within the above temperature range, the precipitation of Mg is activated to increase the purification efficiency of impurities. However, if the temperature is less than 70 DEG C, precipitation formation is insignificant, and if it exceeds 100 DEG C, evaporation of the extract is undesirable.

Thereafter, calcium ions are precipitated from the calcium ion solution obtained after the extraction of the calcium ions or after purification of the cationic impurities, and the precipitates are filtered to recover the calcium precipitates. The calcium ions may be precipitated by heat treatment or basic solution treatment.

When the calcium ion is precipitated by heat treatment, the heating temperature is preferably 70 to 100 ° C, more preferably 80 to 100 ° C. If the temperature is less than 70 ℃ precipitation is insignificant, if it exceeds 100 ℃ calcium ion extract is evaporated is not preferred. In particular, when extracting calcium ions using weak acid such as citric acid, after adjusting the pH of initial calcium ion extract to 3.2 to 3.4, stirring and raising the temperature to 80-100 ℃, high purity and high recovery can be obtained have.

In addition, when calcium ions are precipitated by adding a basic solution, when the basic solution is added to the calcium ion solution, the extracted calcium ions are precipitated in the form of hydroxide. The basic solution that can be used may be selected from the group consisting of a strong base solution containing sodium hydroxide (NaOH) aqueous solution and a weak base solution containing ammonia (NH ₄ OH) water. The NH ₄ OH is preferably used at a concentration of 25 to 35%.

 It is preferred to add until the final pH of the calcium ions is 12 to 14, more preferably 12.5 to 13.5. If the final pH is less than 12, the precipitation of calcium ions is insignificant and undesirable. If the pH is above 14, the precipitation is activated, but the amount of basic solution added to raise the pH is not preferable.

As a result of the experiment on the actual limestone refining process, the calcium precipitate recovered using NaOH as the cationic impurity purification solvent and calcium ion recovery solvent was used as NH ₄ OH as the cationic impurity purification solvent and NaOH was used in the calcium ion recovery step. The concentration of cationic impurities was lower than that of the precipitated calcium precipitate. In addition, when NaOH was used for both cationic impurity purification and calcium ion recovery, the concentration of Na in the calcium precipitate was measured to be higher than that of NH ₄ OH for cationic impurity purification. In other words, although the use of NaOH is effective in lowering the concentration of other impurities, Na itself may act as an impurity in the final product when used excessively.

In addition, when NH ₄ OH was used to recover calcium ions, precipitation did not occur, which made it difficult to recover calcium ions. Calcium ion precipitation occurs from about pH 12.5, whereas the addition of weak base NH ₄ OH does not increase the pH of the solution to pH 12.5 where calcium ions will precipitate. That is, it is more preferable to add NaOH when recovering calcium ions.

In addition, when the weak acid citric acid was used as the calcium ion extraction solvent, the overall impurity content was higher than that of the strong acid HCl. It is thought that the content of impurities extracted during the extraction of calcium ions is smaller than that of other acids, whereas the precipitation does not occur well when the impurities are purified, so that cationic impurities cannot be removed by precipitation. Precipitation is less likely when citric acid is used because citric acid itself is an organic acid having a chain structure, and the chain structure of the acid interferes with the precipitation of the precipitate. In addition, when citric acid is used, an excess of a base solvent is required for impurity purification or calcium ion recovery than when HCl or HNO ₃ is used. This is due to the fact that citric acid is a weak acid, which is added in excess of strong acid when the pH is lowered for extraction of calcium ions. HCl or HNO ₃ reacts 1: 1 with NaOH, but citric acid reacts with three carboxyl groups (-COOH). Because it requires more base for neutralization. For this reason, the concentration of Na was also higher because the amount of NaOH added was higher than that of calcium recovery in the solution from which calcium was extracted using HCl.

Calcium recovery was highest when HCl was used as a calcium extraction solvent and NaOH was used continuously. When citric acid is used, the recovery rate is lower than that of using HCl, which is believed to be the result of less precipitation than using HCl. In addition, when NH ₄ OH and NaOH were used as the cationic impurity purification solvents, the recovery rate was not significantly different with the extraction using HCl. However, when citric acid was used, the calcium ion recovery rate when NaOH was used as the cationic impurity purification solvent was It was somewhat higher than when NH ₄ OH was used.

In order to increase the precipitation effect during the precipitation reaction, there are aging method and heat treatment method. If the precipitate formed in the solution is left together with the mother liquor, small and unstable crystals disappear and large and stable crystals grow gradually. This phenomenon is called aging. In addition, since the precipitation occurs more easily and safely as the temperature is higher, a method of making a precipitate in a solution by using the same principle, and then heating to increase the particles of the precipitation is also called heat treatment. Aging and heat treatment of precipitates remove small and unstable precipitates, grow larger precipitates with less impurities that adsorb to the precipitate, and make crystals perfect.

Therefore, the method may further include the step of selectively increasing the temperature to a temperature range of 70 to 100 ℃ upon recovery of calcium ions by the addition of the basic solution. More preferably, it is 80-100 degreeC. If the temperature is less than 70 ℃ precipitation is insignificant, if it exceeds 100 ℃ calcium ion extract is evaporated is not preferred. In particular, when the calcium ion in limestone is extracted using citric acid and recovered with ammonia water, when the precipitation generation pH is reached, heating can further increase the Ca precipitation effect.

Thereafter, to remove chlorine ions (Cl ⁻ ) and residual base solvents, which are anion impurities remaining in lime, the mixture is washed 2 to 3 times with distilled water and dried to obtain calcareous lime (Ca (OH) ₂ ).

In addition, the purification method of the present invention may optionally be purified after calcining the limestone powder before calcium ion extraction in the step S1. In addition, after obtaining the hydrated lime in step S3 it may further comprise the step of obtaining calcined lime (CaO).

Scheme 1 below shows the calcining reaction of limestone.

In the case of calcination of limestone as in Scheme 1, the endothermic reaction occurs only at the atmospheric decomposition temperature of 898 ° C. under 100% CO ₂ atmosphere, and the heat of reaction required for this reaction must be supplied from outside. The calcination of limestone is usually carried out through three important speed processes: first, heat transfer by radiation and convection between the surrounding gas and the limestone particles, and second, in the chemical reaction and limestone layer at the interface between the limestone and quicklime. Heat transfer, third, is the diffusion of CO ₂ gas out through the resulting quicklime layer.

Scheme 1

CaCO ₃ → CaO + CO ₂

The calcining degree of general lime is classified into combustion, light and small, and small lime is called burnt lime in the state of large specific surface area, large porosity, and high reactivity. do. If calcined burnt lime is heated at a high temperature for a long time, fine crystals gradually fuse and the entire volume shrinks. This type of quicklime is generally referred to as minor quicklime, and it is called minor quicklime to further increase the calcination to extremely low hydration reactivity.

The present invention is characterized by obtaining burnt quicklime. However, since burned quicklime has a large specific surface area and a reaction is easy to occur, the process proceeds quickly. Therefore, an optimum calcining temperature and time must be determined in order to obtain burnt quicklime.

The thermal characteristics of limestone were measured using TG-DTA (Thermo gravimetric Analyzer / Differential Thermal Analyzer), which showed that the mass was gradually decreased above 700 ℃ and the reaction was completed at 850 ℃, which is somewhat lower than the theoretical value. . Therefore, the calcining temperature for the limestone is preferably carried out in the range of 850 ° C to 1200 ° C, more preferably 1000 to 1100 ° C. If it is less than 850 ° C, quicklime (CaO) and calcined lime (Ca (OH) ₂ ) coexist and are not preferable. If it exceeds 1200 ° C, aggregation due to intergranular particle growth occurs, which is not preferable. In addition, the calcination time is preferably performed for 30 minutes to 3 hours, more preferably 30 minutes to 1 hour. If the calcination time is less than 30 minutes, limestone is unbaked, which is not preferable, and if it exceeds 3 hours, intergranular phenomena appear, which is disadvantageous for producing high quality quicklime.

The color of quicklime (CaO) is also related to the iron content in the gemstones. Iron in the oxidizing atmosphere reacts with CaO to become pale yellow by the production of calcium ferrite, etc. In the reducing atmosphere, iron is reduced to become metallic iron or lower oxide, so that the surface is white. In addition, impurities in limestone react little with lime at low temperatures of 900 to 930 ° C, but when the temperature is high, they are strongly bound to lime, resulting in various problems such as silicate, aluminate, and ferrite. It can also produce complex compounds.

Therefore, when calcining purified calcined lime (Ca (OH) ₂ ) to prepare quicklime (CaO), even when the calcined lime is calcined at a long time or at a high temperature, the reactivity (activity) decreases due to grain growth. Therefore, in order to obtain a high quality lime product, it is preferable to calcinate at a low temperature as short as possible. Therefore, calcination at the temperature range of 850 to 1200 ℃, more preferably 1000 to 1100 ℃ is preferable. If it is less than 850 ° C., quicklime (CaO) and calcined lime (Ca (OH) ₂ ) coexist and are not preferable. If it exceeds 1200 ° C., there is a fear that particle aggregation occurs.

In addition, the holding time during calcination is preferably carried out for 30 minutes to 2 hours, more preferably 30 minutes to 1 hour. If the calcination time is less than 30 minutes, limestone is unbaked, which is not preferable. If it exceeds 2 hours, intergranular phenomena appear, which is disadvantageous for producing high quality quicklime.

That is, since the increase in particle size is not suitable for the production of quicklime of fine powder, calcining for 1 hour at 1000 ° C to 1100 ° C in order to prepare finer lime from calcined lime is advantageous for inhibiting quicklime crystal growth and producing high quality quicklime. Do.

Limestone purification method of the present invention is to adjust the solubility of limestone according to the change of the initial concentration of the acid and the input amount using a variety of acid, and to optimize the type, dosing method, dosage of the basic solution for the recovery of dissolved calcium ion.

Therefore, by purifying limestone according to the present invention, it is possible to provide high-quality raw and hydrated lime of high purity and high activity of 99% or more that can be used as food and pharmaceutical calcium compounds in a simple process in high yield.

Hereinafter, preferred examples are provided to aid in understanding the present invention. However, the following examples are provided only to more easily understand the present invention, and the present invention is not limited to the following examples.

EXAMPLE

Example  1. Basic Characterization of Limestone Ore

1) limestone composition analysis

Before the calcium ion was extracted from limestone to prepare high-purity raw lime, various kinds of limestones (A to D, manufactured by Taeyoung Stone Co., Ltd.) were purchased and analyzed.

The components of limestone were measured by XRF (X-Ray Fluorescence Analysis), quantitative analysis of impurities other than Ca was quantitatively analyzed using Inductively Coupled Plasma (ICP) according to KS E-3071 standard, and Si was analyzed by ICP. And quantitative analysis of the results of the weight analysis method. The measurement results are shown in Table 1 below (unit: wt%).

Limestone A Limestone B Limestone C Limestone D Ca 98.76 93.73 89.02 52.56 Mg 0.23 4.21 1.78 0.97 Fe 0.31 0.65 2.18 3.86 Al 0.16 0.39 1.94 7.55 Si 0.28 0.71 3.56 31.69 K 0.07 0.11 1.11 2.24 Mn 0.07 0.08 0.04 0.21 S 0.01 0.06 0.03 0.05 Sr 0.11 0.05 0.09 0.16 P - 0.02 0.02 0.08 Ti - - 0.23 0.45 Ni - 0.01 - - Total 100.00 100.00 100.00 100.00

As shown in Table 1, as a result of XRF analysis, limestone contains the most Ca, and Mg, Si, Al, Fe, and other materials (other components: K, Mn, S, Sr, P, Ti, and Ni) It could be confirmed that it contains a large amount compared to.

As a result, the extraction of calcium ion at pH 3.0 showed the lowest impurity content in the calcium ion solution.

Example  2. Calcium ion extraction

To determine the impurity content according to the acid type, the impurity content was analyzed after varying the acid type. Strong acids of HCl and HNO ₃ and slightly acidic citric acid were used.

First, a powder of limestone B having a particle size of 100 mesh was dissolved in an acid solution for 20 minutes to extract calcium ions (final pH 3.2), and the remaining residues which were not dissolved were filtered out. Thereafter, the amount of impurities in the calcium ion extract was measured using ICP. The results are shown in Table 2 below (unit: wt%).

Process No. Calcium ion extraction solvent Mg Fe Al Si 2-1 HCl 3.20 0.04 0.19 0.25 2-2 HNO ₃ 3.21 0.07 0.19 0.26 2-3 Citric acid 0.98 0.07 0.14 0.20

As can be seen from Table 2, when extracting calcium ions by treating the acid, the amount of Fe, Al and Si was not extracted much, but Mg was extracted with a considerable amount. In the case of using HCl and HNO ₃ as strong acids, the amount of Mg extracted was about 80% of the raw material, and most of them were extracted with Ca. However, when using citric acid as the weak acid, about 25% was used. Less magnesium was extracted.

In addition, the impurities were analyzed after varying the pH in order to determine the calcium ion extraction amount and the impurities purification effect according to the pH change.

The limestone B powder having a particle size of 100 mesh was used for 20 minutes using various citric acid solutions to vary the pH of the calcium ion solution to extract calcium ions. Each was measured using ICP. The results are shown in Table 3 below (unit: wt%).

Process No. PH of calcium ion solution Impurity Content in Calcium Ion Solution Content of insoluble substances Mg Fe Al Si Ca Mg Fe Al Si Etc. 2-4 2.5 2.50 0.33 0.12 0.17 15.99 6.80 4.03 18.32 37.29 17.57 2-5 3.0 1.98 0.37 0.14 0.22 16.32 7.39 4.07 18.33 36.30 17.59 2-6 3.5 2.26 0.40 0.15 0.18 40.70 6.26 3.00 14.37 25.07 10.60

As a result, the extraction of calcium ion at pH 3.0 showed the lowest impurity content in the calcium ion solution.

Example  3. Cationic Impurity Purification

Fe and Mg, which were extracted together during the extraction of calcium ions, were purified with OH ^- ions to form hydroxides.

In order to precipitate and purify impurities such as Fe and Mg by hydroxides, various kinds of basic solvents were added to the calcium extract solution containing impurities, respectively, and the precipitation reaction was performed. As the basic solvent, a strong base NaOH and a weak base NH ₄ OH were used.

First, the powder of limestone B having a particle size of 100 mesh was treated with nitric acid solution for 20 minutes to extract calcium ions (final pH 3.0), and the remaining undissolved residue was filtered off to obtain a calcium ion solution. The basic solution was then added until the pH of the calcium ion solution reached 11 to precipitate impurities. Thereafter, the precipitate was filtered to remove impurities. Figure 2 is a photograph of the result of precipitation of cationic impurities at pH 11.

The concentration of cationic impurities in the supernatant obtained after removing the precipitate was measured. The results are shown in Table 4 below (unit: wt%).

Process No. Calcium ion extraction solvent Cationic Impurities Purification Solvent Mg Fe Al Si 3-1 HCl NH ₄ OH 0.46 4.3 × 10 ^-4 0.001 0.024 3-2 HCl NaOH 0.43 3.5 × 10 ^-4 0.006 0.061 3-3 HNO ₃ NaOH 0.45 1.6 × 10 ^-4 0.005 0.045

As shown in Table 4, the amount of Mg in the calcium extract from which the cationic impurities were removed with the basic solvent was significantly reduced compared with the results of Table 3 above. This is the result of Mg dissolved in solution reacted with OH ^- and precipitated as Mg (OH) ₂ . In addition, other impurities, Fe, were removed with Fe (OH) ₃ , and Al and Si were also removed by the precipitation reaction due to the coprecipitation caused by the formation of Fe (OH) ₃ and Mg (OH) ₂ .

Process No. of Example 3 Comparing the results using NH ₄ OH and NaOH in 3-1 and 3-2, respectively, there was no significant difference, but the removal efficiency was slightly higher when NaOH was used. In addition, the results by HNO ₃ and HCl were found to be similar.

In general, Ca is precipitated as Ca (OH) ₂ at pH 13 or higher, but there is a high possibility of precipitation as CaOH ⁺ ions even at lower pH. As a result, the process No. The precipitates precipitated in 3-1 and 3-2 were analyzed by ICP to determine whether Ca was precipitated. Table 5 shows the analysis results for Ca in the precipitate at pH 11 (unit: wt%).

Process No. Calcium ion extraction solvent Cationic Impurity Purification Solvent Calcium content in the precipitate 3-1 HCl NH ₄ OH 11.01 3-2 HCl NaOH 16.61

The results in Table 5 show that the co-precipitated Ca content during Mg precipitation is about 14% on average. It was also shown that the content of co-precipitated Ca was somewhat higher than that of NH ₄ OH when NaOH was used.

Example  4. Recovery of Calcium Ions

(1) Calcium ion recovery by basic solution treatment after cationic impurity removal process

Calcium ion was recovered from the calcium ion solution by the basic solution treatment after the cation impurity removal process.

NaOH aqueous solution and NH ₄ OH aqueous solution were used as base solutions to recover calcium ions in the form of a hydroxide, respectively. The steps before the recovery of calcium ions used a solvent described in Table 6 below. The precipitation of calcium ions is known to occur when the pH is 13 or more, but in actual experiments it occurred at 12.5 or more. Above pH 12.3, a large amount of basic solution should be added to raise the pH to 0.1. In this experiment, calcium precipitation was performed at pH 12.6. Figure 3 is a photograph showing the results of calcium precipitation reaction at pH 12.6 in the calcium ion recovery process.

Afterwards, the impurity content in the calcium precipitate generated as a result of calcium precipitation reaction at pH 12.6 was analyzed by ICP. The results are shown in Table 6 below (unit: wt%).

Process No. Calcium ion extraction solvent Cationic Impurity Purification Solvent Calcium ion extraction solvent Mg Fe Al Si Na 4-1 Citric acid NH ₄ OH NaOH 0.303 0.073 0.076 0.086 0.675 4-2 Citric acid NaOH NaOH 0.235 0.056 0.072 0.049 1.466 4-3 HCl NH ₄ OH NaOH 0.078 0.003 0.016 0.077 0.360 4-4 HCl NaOH NaOH 0.060 0.002 0.005 0.105 0.685 4-5 HCl NH ₄ OH NH ₄ OH - - - - -

As can be seen from Table 6, the calcium precipitates extracted using NaOH as the cationic impurity purification solvent and the calcium ion recovery solvent as in the steps No. 4-2 and 4-4 are the steps No. 4-1 and 4-3. As described above, the concentration of cationic impurities was lower than that of calcium precipitates extracted using NH ₄ OH as the cationic impurity purification solvent and NaOH as the calcium ion recovery solvent. However, Process No. 2 using NaOH for both cationic impurity purification and calcium ion recovery. In the case of 4-2 and 4-4, the concentration of Na in the calcium precipitate was determined using step ₄ using NH ₄ OH for the purification of cationic impurities. It was measured higher than in 4-1 and 4-3. In addition, the process No. using NH ₄ OH in the recovery of calcium ions. In case of 4-5, precipitation did not occur and calcium ions could not be recovered.

In addition, when the weak acid citric acid is used as the calcium ion extraction solvent (steps No. 4-1 and 4-2), the overall impurity content is higher than that when the strong acid HCl is used (steps No. 4-3 and 4-4). appear. In addition, when citric acid was used, the concentration of Na in the calcium precipitate was also higher because an excess base solvent (NaOH) was used for cationic impurity purification and calcium ion recovery than when HCl was used.

In addition, XRF analysis was performed to determine the calcium purity of the calcium precipitates recovered in the processes Nos. 4-1 to 4-4. The results are shown in Table 7 below (unit: wt%).

element Process No. 4-1 4-2 4-3 4-4 Ca 98.51 98.70 99.85 99.88 Mg 0.63 0.45 0.099 0.077 Al ND ND ND ND Si 0.13 0.15 0.014 0.010 Cl 0.013 0.016 0.025 0.026 S ND ND 0.012 0.077 Na 0.49 0.55 ND ND

(In Table 7, ND means not detected.)

As a result, Ca purity reached 98% or higher under all reaction conditions.

In addition, the recovery of calcium ions when the recovery of calcium ions by the method of the above steps No. 4-1 to 4-4 was examined.

The recovery rate of calcium ions was calculated using Equation 1 below, and the results are shown in Table 8 below.

Process No. Calcium ion recovery rate (%) 4-1 88-90 4-2 88-90 4-3 90-92 4-4 90-92

As a result, the calcium recovery was the highest in the case of the process No. 4-4 using HCl and NaOH continuously as the calcium extraction solvent. In the case of step No. 4-2 using citric acid, the recovery was lower than that using HCl. In addition, when NH ₄ OH and NaOH were used as the cationic impurity purification solvents, the recovery rate was not significantly different when HCl was extracted. However, when citric acid was used, the calcium ion recovery rate when NaOH was used as the cationic impurity purification solvent was It was somewhat higher than when NH ₄ OH was used.

In addition, XRD analysis was performed on the dried calcium precipitates to find out which crystal phase the calcium ions recovered in this experiment were recovered. The results are shown in FIGS. 4A and 4B.

4A is the process No. XRD graph of the crystal phase of the calcium precipitate according to the practice of 4-3, Figure 4b is the process No. It is an XRD graph which measured the crystal phase of the calcium precipitate according to the implementation of 4-4.

XRD analysis showed that the calcium ions were recovered in the form of Ca (OH) ₂ .

In addition, the whiteness of limestone B before purification and limestone B after step No. 4-1 was measured using a white meter to determine the color change of limestone before and after purification. The measurement results are shown in Table 9 below.

Whiteness Before refining 75-78 After purification 92-95

As shown in Table 9, the whiteness of the limestone after purification increased to 15 or more than 90 before purification.

5 is a photograph of the color change of limestone B before and after purification. The left side of FIG. 5 is a photograph of limestone powder before purification, and the right side of FIG. 5 is a powder photograph obtained after purification. As shown in FIG. 5, it is easy to visually distinguish that the color of the powder after purification is much whiter than before purification.

The results of the experiment were limestone B having a purity of about 94% of calcium, and the application of the experimental method was examined using limestone D having a very low purity of calcium.

By applying the above-described experimental method was analyzed calcium precipitate which purified impurities from limestone D. Impurities in calcium precipitates, Mg, Fe, Al, Si and Na, were analyzed using ICP, and Ca purity and other impurities were analyzed using XRF. The results are shown in Table 10 below (unit: wt%).

Process No. Calcium ion extraction solvent Cationic Impurity Purification Solvent Calcium Ion Recovery Solvent Ca Cl S Mg Fe Al Si Na 4-6 Citric acid NH ₄ OH NaOH 98.02 0.061 ND 0.838 0.05 0.087 0.307 0.605 4-7 Citric acid NaOH NaOH 98.12 0.062 ND 0.580 0.03 0.065 0.204 0.880 4-8 HCl NH ₄ OH NaOH 98.32 0.047 ND 0.303 0.01 0.058 0.234 0.460 4-9 HCl NaOH NaOH 98.83 0.059 0.027 0.250 0.01 0.056 0.205 0.560

(In Table 10, ND means not detected.)

Impurity purification using limestone D showed that the purity of Ca reached 98%.

2) Recovery of calcium ions by basic solution treatment after skipping cation impurities removal process

In order to simplify the process, calcium ions were extracted with citric acid, and then a calcium recovery process was immediately attempted without removing cationic impurities.

Using limestone B and D, respectively, NaOH was used as a calcium ion recovery solvent.

Limestone B powder having a particle size of 100 mesh was treated with citric acid to extract calcium ions (final pH 3.2), and the remaining undissolved residue was filtered off to obtain a calcium ion solution. NaOH aqueous solution was added to the obtained calcium ion solution until the pH of the solution became pH 12.6, and calcium ion was precipitated and recovered (preparation No. 4-10).

Limestone D was purified in the same manner as described above (step No. 4-11).

The composition of recovered calcium precipitate was analyzed by ICP and XRF. The results are shown in Table 11 below (unit: wt%).

element Process No. Limestone B purified by the practice of 4-10 Process No. Limestone D purified by the practice of 4-11 Ca 98.22 97.56 Cl 0.0077 0.0068 S ND ND Mg 0.53 0.63 Fe 0.14 0.18 Al 0.061 0.082 Si 0.095 0.52 Na 0.47 0.87

(In Table 11, ND means not detected.)

As a result, in the case of limestone B which is somewhat higher in calcium purity, the purity of calcium was about 98.2%, and the purity of limestone D was about 97.6%. Limestone D is thought to be due to the high content of Si, which precipitates Si as Ca precipitates during Ca recovery.

Figure 6 is the process No. Photographs comparing the calcium precipitates recovered after 4-10 and 4-11. As shown in FIG. 6, the resultant using limestone B was white (left), but in the case of using limestone D, light yellow (right) was affected by impurities.

3) Recovery of calcium ions by heat treatment after basic solution treatment

Hereinafter, the effects of precipitation conditions on precipitation state during calcium ion precipitation were examined.

Figure 7 is a photograph showing the precipitation state according to the change of precipitation conditions during the calcium ion precipitation reaction (a: aging, b: cooling, c: heat treatment).

Figure 7a shows the change in the calcium ion-extracted solution after leaving the calcium ion-extracted solution for 120 minutes before filtering after precipitation of the calcium precipitate in step No. 4-10, Figure 7b is calcium precipitation After the pH reached, the calcium ions after cooling to 0 ℃ is shown in the extracted solution, Figure 7c is a photograph showing the change in the calcium ions extracted solution after heating to 80 ℃ after reaching the calcium precipitation pH.

As shown in FIG. 7, precipitation was not performed under aging and cooling conditions, and Ca precipitation was actively performed only under heat treatment conditions.

In addition, the basic solution was used to extract calcium ions during the extraction of calcium ions, and then heated to a temperature range of 90 to 100 ° C. to determine the purity and recovery of Ca. The results are shown in Table 12 below.

Tablet No. Calcium ion extraction solvent Cationic Impurity Removal Solvent Calcium Ion Recovery Solvent Ca (% by weight) % Recovery 4-12 Citric acid - NaOH 99.12 90-92 4-13 HCl NH ₄ OH NaOH 99.85 90-95 4-14 HCl NaOH NaOH 99.88 90-95

When compared with the results in Table 8, it can be seen that the recovery is more improved.

In addition, the impurity content in the calcium precipitate by heat treatment (Heating) was measured.

In order to compare the heat treatment effect, the calcium precipitate obtained in step No. 4-9 and the calcium extract obtained in step No. 4-14 were used. The results are shown in Table 13 below (unit: wt%).

Process No. Whether heat treatment Mg Fe Al Si 4-9 No heat treatment 0.235 0.062 0.072 0.049 4-14 Heat treatment 0.132 0.056 0.075 0.038

As a result, the other cationic impurities did not change significantly in the concentration of the impurities, but the concentration of Mg decreased slightly.

4) Calcium ion recovery by heat treatment

After obtaining a calcium ion solution using citric acid, calcium ion was precipitated while heating to 70-100 degreeC, stirring a calcium extract, without using a basic solution.

Experimental results showed that the Ca purity of the final product was more than 99%, the recovery was also excellent from 90 to 92%.

Example  5. Purification with quicklime

Since the limestone physical properties vary with the calcining temperature and time of the limestone, the effect of this change on the calcium purity after the purification reaction was tested.

Limestone B powder having a particle size of 100 mesh was calcined by heat treatment at 1100 ° C. for 1 hour to obtain quicklime B. The obtained quicklime B was treated with citric acid solution for 20 minutes to extract calcium ions (final pH 3.0), and undissolved residues were filtered off to obtain a calcium ion solution. 5 M aqueous NaOH solution was added until the pH of the calcium ion solution reached 11 to precipitate cationic impurities in the calcium ion solution. Thereafter, the precipitate was filtered to remove impurities. A 5 M aqueous NaOH solution was added to the cationic impurity removal solution until the pH of the solution reached pH 12.6 to recover calcium ions as a precipitate (step No. 5-1).

Limestone D was also calcined and purified in the same manner as described above (step No. 5-2).

When purified from quicklime obtained by calcining limestone, quicklime B showed a calcium purity of 99.75% and quicklime D showed a calcium purity of 98.4%. Compared with Process No. 4-4 of Table 8 and Process No. 4-9 of Table 8, which are purified from limestone (CaCO ₃ ), a large difference in calcium purity is obtained when purified from calcined CaO. There was no. In the case of using CaO, calcium ions were recovered in the form of Ca (OH) ₂ after purification.

Example  6. Anion Impurity Purification

The anion Cl ⁻ present as an impurity in the XRF analysis result was removed by washing with distilled water sufficiently when recovering calcium ions. By dissolving sufficiently washed with distilled water a Ca (OH) Ca are not washed with ₂ (OH) ₂ in nitric acid using IC (Ion Chromatography) Cl ^- analyze the content of the ion and investigated the effects of the washing process. The results are shown in Table 14 below (unit: wt%).

Process No. Ca extraction solvent Cationic Impurity Purification Solvent Calcium Ion Recovery Solvent Cl ^- content before washing Cl ^- content after washing 6-1 Citric acid NaOH NaOH 0.13 0.082 6-2 HCl NaOH NaOH 0.10 0.065

From Table 14, it was confirmed that the content of Cl ⁻ was reduced by about 36% only by washing with distilled water.

Example  7. Crystal Growth Control

The Ca (OH) ₂ from the calcination temperature to precipitate calcium recovered in Ca (OH) ₂ to produce a calcium oxide (CaO) were selected from 900 ℃ as CaCO ₃ calcination temperature.

High-quality slaked lime purified from impurities by temperature (900, 1000, 1100, 1200 ° C), hourly (1000 ° C-1, 2, 3hr), and by temperature increase rate (900, 1000, 1100, 1200 ° C-5 ° C / min , 10 ℃ / min) calcined lime was prepared according to the calcination conditions.

Calcined lime was calcined under various calcining conditions by temperature and time, and the effects of calcining conditions on calcined lime were investigated.

 Figure 8 is a photograph showing the change in the microstructure of CaO according to the calcination temperature (a: 900 ℃, b: 1000 ℃, c: 1100 ℃ d: 1200 ℃) (heating rate: 10 ℃ / min, calcination time: 1 hour ).

As shown in FIG. 8, when calcined at 900 ° C. (a), the limestone particle size was 0.5 to 1.0 μm, and the particle size increased as the temperature was increased.

9 is a photograph showing the microstructure change of CaO according to the calcination time (a: 0 hours, b: 1 hour, c: 2 hours, d: 3 hours) (calcination temperature: 1000 ℃, temperature rising rate: 10 ℃ / min).

As shown in FIG. 9, the microstructure of the quicklime according to the calcination time at the calcination temperature of 1000 ° C. showed no change in the average particle diameter until one hour of calcination, and only a decrease in the derivative was confirmed. However, when the calcination time was more than 2 hours, the particles started to grow and the particles began to aggregate with each other.

As a result, it can be seen that the effect of the calcining temperature and the calcining time is large as the calcining conditions for producing the quick-acting fine lime. In addition, as a result of measuring the activity of the prepared quicklime and slaked lime (CAA), the slaked lime was 60 seconds, quicklime was measured as 1 minute 20 seconds.

By refining limestone by the refining method according to the present invention, high-quality raw and hydrated lime with high purity and high activity, which can be used for food and pharmaceutical calcium compounds, can be obtained in high yield, especially when purified using citric acid. The cationic impurity purification step can be omitted, making the limestone purification step simpler.

Claims (18)

a) treating the limestone powder with an acid solution to extract calcium ions to obtain a calcium ion solution; b) precipitating calcium ions from the calcium ion solution to obtain calcium precipitates; And c) washing the calcium precipitate to purify the anion impurities to obtain calcined lime (Ca (OH) ₂ ). Purification method of limestone comprising a. The method according to claim 1, wherein the limestone powder in step a) has a particle size of 100 to 200 mesh. The method of claim 1, wherein the acid in step a) is a strong acid including hydrochloric acid, sulfuric acid and nitric acid; And a weak acid including citric acid and acetic acid. The method of claim 1, wherein when the acid used in step a) is a strong acid, the acid solution is used in an amount of 500 to 2000 parts by weight based on 100 parts by weight of limestone. The method of claim 1, wherein when the acid used in step a) is a weak acid, the acid solution is used in an amount of 1500 to 3000 parts by weight based on 100 parts by weight of limestone. The method of claim 1, wherein the calcium ion solution obtained in step a) has a pH of 3.0 to 3.5. The method of claim 1, further comprising, after the extraction of calcium ion in step a), adding a basic solution to the obtained calcium ion solution to precipitate and purify cationic impurities in the calcium ion solution. 8. The method of claim 7, wherein the basic solution used for the purification of the cationic impurities is a strong basic solution containing an aqueous sodium hydroxide solution; And a weakly basic solution containing aqueous ammonia. The method of claim 7, wherein the basic solution used for the purification of the cationic impurities is added until the final pH of the calcium ion solution is 10.5 to 12.5. The method of claim 7, wherein the cationic impurities are heated to 70 to 100 ° C. after the cationic impurity precipitation pH is reached. The method of claim 1, wherein in step b), calcium ion precipitation is performed by a method selected from the group consisting of heat treatment, basic solution treatment, and basic solution addition and heat treatment. 12. The method of claim 11, wherein the heat treatment is performed in a temperature range of 70 to 100 ° C. 12. The method of claim 11, wherein the basic solution is a strong basic solution containing an aqueous sodium hydroxide solution; And a weakly basic solution containing aqueous ammonia. 12. The method of claim 11, wherein the basic solution is added until the final pH of the calcium ion solution is 12 to 14. The method of claim 1, further comprising calcining the limestone powder before the calcium ion extraction of step a) to obtain quicklime (CaO). The method according to any one of claims 1 to 15, further comprising the step of obtaining calcined lime after obtaining the calcined lime of step c). The method of claim 1, wherein the calcining step is limestone purification method characterized in that carried out at a temperature range of 850 to 1200 ℃. The method of claim 1, wherein the calcining step is performed for 30 minutes to 2 hours.

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