WO2009157620A1

WO2009157620A1 - Method of recovering a compound comprising manganese from dust of electronic furnace

Info

Publication number: WO2009157620A1
Application number: PCT/KR2008/006599
Authority: WO
Inventors: Suk Jo Jung; Jeong Min Kim; Sung Il Jo; Youn Chul Kim
Original assignee: Dongbu Fine Chemicals Co Ltd
Current assignee: Dongbu Fine Chemicals Co Ltd
Priority date: 2008-06-25
Filing date: 2008-11-10
Publication date: 2009-12-30
Anticipated expiration: 2010-12-25

Abstract

Disclosed is a method for recovery of manganese based compounds from dust of an electric furnace, comprising:(i) a first refining process that includes acid cleaning dust containing Mn and filtering the treated dust to recover alkali metals contained in the dust which is dissolved in a filtrate solution, so as to increase content of Mn in the filtered powder mixture (sludge of the dust); (ii) a reduction process that heats the sludge together with a reducing agent to prepare reduced powder; (iii) an impurity removal process that includes dissolving the reduced powder obtained by the reduction process in acid to prepare a solution, adjusting the pH of the solution in a range of 4 to 7 and filtering the solution, so as to remove impurities except Mn in a sludge state and prepare a solution containing dissolved Mn except the impurities; (iv) a process for precipitation of an Mn compound that includes adjusting the pH of the solution without the impurities due to the impurity removal process in a range of 9 to 12 to precipitate the Mn compound; and (v) a process for recovering the Mn compound that includes separating the Mn compound obtained by the precipitation process from the precipitate, and washing and drying the separated product. The present invention is effective for commercial recovery of manganese contained in dust in a state of an Mn compound, and also for additionally recovery of alkali metal compounds as well as byproducts such as ammonium sulfate depending on types or kinds of acid and base used in production of the Mn compound.

Description

METHOD OF RECOVERING A COMPOUND COMPRISING MANGANESE FROM DUST OF ELECTRONIC FURNACE

Technical Field

[1] The present invention relates to a method of recovering a compound comprising manganese from dust of an electric furnace, which is usually generated in a smelting process.

[2] More particularly, the present invention relates to a method of recovering a manganese based compound (often referred to as "Mn compound") from dust of an electric furnace and, at the same time, of recovering other additional materials such as alkali metal compounds or byproducts such as ammonium sulfate according to types of acid and base used in production of Mn compounds. Background Art

[3] It is generally known that metal substances contained in dust of an electric furnace are substantially impossible to be recovered under commercial conditions. Thus, the electric furnace dust (referred to as "dust") has been generally discarded as industrial waste.

[4] When the dust itself is used in construction and/or asphalt materials without any pre- treatment, a plurality of harmful metal substances contained in the dust certainly cause environmental pollution. Accordingly, the dust was substantially unable to be utilized in the related art.

[5] With conventional technologies, Mn compounds and other metal substances contained in dust have not been preferably recovered in view of commercial applications, leading to economic disadvantages. Also, there is a problem of incurring expenses to discard the dust as an industrial waste.

[6] Korean Patent Laid-Open No. 2003-0028006 discloses a process for production of manganese sulfate which includes mixing 43 to 45 wt.% of concentrated sulfuric acid, 60 to 70 wt.% of ferromanganese alloy iron electric furnace dust and 6 to 7 wt.% of ferromanganese, heating the mixture at 95⁰C for 5 hours to proceed a reaction thereof, filtering the reaction product, adding 3 to 4 wt.% of metal zinc powder to the filtrate to remove a heavy metal moiety, and concentrating and drying the purified product. However, such conventional technique has problems of environmentally serious harmfulness and significant energy consumption owing to heating at 95⁰C for a long period of time, thus leading to impossibility in commercial applications. Disclosure of Invention Technical Problem [7] Accordingly, the present invention is directed to solve the problems described above in regard to conventional methods and an object of the present invention is to provide a method of recovering manganese based compounds (often referred to as "Mn compounds") from dust of an electric furnace with improvements in view of commercial applications (often referred to as "commercial recovery").

[8] Another object of the present invention is to provide a method of commercially recovering Mn compounds from dust of an electric furnace and, at the same time, of recovering additional materials including byproducts such as ammonium sulfate according to types of acid and base used in production of Mn compounds as well as alkali metal compounds such as sodium sulfate, potassium sulfate, and so forth. Technical Solution

[9] In order to accomplish the above objects, the present invention provides a method of recovering an Mn compound which comprises acid cleaning dust of an electric furnace containing manganese then filtering the washeddust to remove alkali metals such as potassium (K), sodium (Na), lithium (Li) and the like contained in the dust and dissolving the alkali metals in a filtrate to be removed through a first refining process, so as to increase content of Mn in the filtered powder mixture (sludge of the dust).

[10] The method of recovering an Mn compound according to the present invention also includes heating the filtered powder mixture (that is, the sludge) obtained from the first refining process together with a reducing agent to conduct a reduction thereof, so as to improve acid solubility of manganese.

Advantageous Effects

[11] The present invention is effective for commercial recovery of manganese contained in dust of an electric furnacein a state of an Mn compound, and also may additionally recover alkali metal compounds as well as byproducts such as ammonium sulfate depending on types or kinds of acid and base used in production of the Mn compound. Brief Description of Drawings

[12] The above objects, features and advantages of the present invention will become more apparent to those skilled in the related art in conjunction with the accompanying drawings. In the drawings:

[13] Figs. 1 and 2 are flow charts showing a process for recovering Mn compounds contained in dust of an electric furnace according to the present invention. Best Mode for Carrying out the Invention

[14] Hereinafter, the present invention will be apparent from the following detailed description with reference to the accompanying drawings.

[15] As shown in Figs. 1 and 2, a recovery method of an Mn compound according to the present invention comprises: (i) a first refining process that includes acid cleaning dust containing Mn and filtering the treated dust to recover alkali metals contained in the dust which is dissolved in a filtrate, so as to increase content of Mn in the filtered powder mixture (sludge of the dust); (ii) a reduction process that heats the filtered powder mixture (sludge) together with a reducing agent to prepare reduced powder; (iii) an impurity removal process that includes dissolving the reduced powder obtained by the reduction process in acid to prepare a solution, adjusting the pH of the solution in a range of 4 to 7 and filtering the solution, so as to remove impurities except Mn in a sludge state and prepare a solution containing dissolved Mn except the impurities; (iv) a process for precipitation of an Mn compound that includes adjusting the pH of the solution without the impurities owing to the impurity removal process in a range of 9 to 12 to precipitate the Mn compound; and (v) a process for recovering the Mn compound that includes separating the Mn compound obtained by the precipitation process from the precipitate, and washing and drying the separated product.

[16] Figs. 1 and 2 are flow charts showing procedures of the method for recovering the

Mn compound according to the present invention.

[17] Such Mn compound may include, for example, Mn O , MnSO -H O, KMnO , MnCO

, MnO , MnO, Mn, or MnCl, etc.

[18] The dust containing Mn used as a starting material in the present invention may include at least 10% by weight ("wt.%") of Mn, preferably at least 20 wt.% of Mn and, at the same time, at least 5 wt.% of other alkali metals such as potassium (K), sodium (Na), etc., more preferably at least 10 wt.% of the alkali metals.

[19] Above all, a first refining process is performed by acid cleaning dust containing Mn and filtering the washed dust to prepare a sludge including filtered powder (sludge) as well as a filtrate.

[20] The acid cleaning may use hydrochloric acid, nitric acid and/or sulfuric acid with a concentration of 0.1 N to 5N.

[21] In this case, the alkali metals such as K or Na contained in the dust are dissolved in the filtrate and separated from the filtered powder mixture (sludge) containing Mn, and thus, in turn, recovered.

[22] Accordingly, Mn content in the filtered powder mixture (sludge) obtained by the first refining process increases, thereby allowing commercially available recovery of Mn compounds.

[23] Drying the filtrate obtained from the first refining process allows additional recovery of alkali metal compounds such as potassium sulfate, potassium nitrate, potassium chloride, sodium sulfate, etc.

[24] Representative examples of such alkali metal compounds may include potassium compounds, lithium compounds and/or sodium compounds, and the potassium compounds may be exemplified by potassium sulfate (K 2 SO 4 ), potassium nitrate (KNO ), potassium chloride (KCl), etc.

[25] Next, a reduction processing is carried out by heating the filtered powder mixture

(sludge) obtained from the first refining process together with a reducing agent to form reduced powder.

[26] With regard to manganese ingredients contained in the dust, each Mn containing substance (often referred to as "Mn substance") used as a raw material has a variation in acid solubility depending on conditions thereof and the acid solubility levels of Mn substances are determined by, for example: Mn > MnO > Mn O > Mn O > MnO .

^{J r} 3 4 2 3 2

Maximum leach rate of each Mn substance in acid may be defined by: Mn=100%, MnO= 100%, Mn O =67%, Mn O =50%, and MnO =1%. Under this circumstance, it is

3 4 2 3 2 required to convert an Mn substance into elementary Mn or a state of MnO in order to increase yield of Mn. For the elementary Mn, hydrogen is generated during dissolving Mn in acid and a risk of severe exothermic reaction and/or explosion may result, thus causing a problem in maintenance thereof. Therefore, most preferable is an MnO type raw material if acid is used to leach Mn.

[27] The reduction process is performed to convert an Mn substance contained in the dust into an MnO material.

[28] The reducing agent used in the reduction process may include at least one selected from activated carbon, coal, coke, charcoal and graphite powder having a carbon content of at least 50%.

[29] In order to convert an Mn substance into an MnO material, a reduction roasting process may be applied to heat the reduced powder together with a reducing agent. If the reducing agent is at least one selected from gaseous materials such as hydrogen, methane, carbon monoxide and the like, the reduction roasting process may proceed at a relatively low temperature of 300 to 500⁰C for 30 minutes to 6 hours until the Mn substance is completely reduced into the MnO material. However, the above process has disadvantages that a reductive gas is excessively consumed and a reduction furnace having an explosion proof structure is required. Accordingly, the reducing agent may preferably comprise carbon based materials disclosed above, which are cheap and convenient to handle and have favorable reduction properties. If a lower grade reducing agent with a carbon content of less than 50% is used, there may be problems such as increases in consumption of the reducing agent, amount of a leach liquor required and load of an impurity removal process.

[30] An amount of the reducing agent to be used in the disclosed reduction process may range from 3 to 15 wt.%, more preferably 4 to 7 wt.% relative to the weight of the filtered powder mixture (sludge) requiring reduction. However, the amount of the reducing agent may be varied according to the constitutional composition of the filtered powder mixture (sludge) and is not particularly limited thereto. [31] The reduction process is performed at 500 to 1,000⁰C for 0.5 to 4 hours, and more preferably at 700 to 75O⁰C for 1 to 2 hours.

[32] Subsequently, the powder obtained from the reduction process is subjected to an impurity removal process that comprises dissolving the reduced powder in acid, adjusting pH of the solution to 4 to 7, and filtering the solution to remove impurities except Mn in a sludge state, then, to prepare the solution containing dissolved Mn without the impurities.

[33] The acid used herein may include hydrochloric acid, nitric acid and/or sulfuric acid.

The pH value of the solution (as the leach liquor) may be adjusted using any alkaline solution such as sodium hydroxide, potassium hydroxide, ammonium hydroxide, etc.

[34] MnO included in the reduced powder is dissolved in acid, for example, HCl, by the following reaction:

[35] MnO + 2HCl → MnCl 2 + H2O => Mn²⁺ + 2Cl^" + H 2O

[36] Therefore, 2 moles of HCl is required to completely dissolve 1 mole of MnO.

[37] In practical applications, since the powder includes different impurities consuming

HCl, HCl is preferably added in an amount of 2.2 to 2.4 moles to 1 mole of MnO.

[38] If a concentration of the acid is too low, acid leaching in the impurity removal process described above may cause difficulty in pH adjustment. Whereas, if the acid concentration is excessively high, the leach liquor has an increased viscosity and encounters a problem in a solid- liquid separation process. Thus, a suitable concentration of the acid may range from 0.1 to 5N. Since adding an acid solution to the reduced raw material causes a rapid exothermic reaction, the reduced raw material should be slowly added in a powder form to the acid solution.

[39] For a practical process for impurity removal, the reduced powder is added to the acid solution while stirring the solution at 400 rpm to adjust the pH value of the leach liquor in a range of 1 to 4, such that Fe dissolved in the solution is precipitated in a form of Fe(OH) simultaneously with dissolution of the powder in the acid residue. With about pH 4, a leaching rate of Mn drastically decreases and most of the added powder remains as the leach residue in the solution. That is, if the pH value is above 4, addition of the powder for increasing pH value causes a sharp increase in an amount of the leach residue, leading to the increased load of the solid-liquid separation process while reducing Mn recovery. Accordingly, for the leach liquor with a pH above 4, adding an alkaline solution with a concentration of 0.05 to 0.5N to the leach liquor preferably results in an increase of the pH value to 5 to 6. After stopping addition of the alkaline solution at pH 5 to 6, stirring for about 2 hours terminates precipitation of impurities such as Cu, Al, etc. in the form of hydroxides thereof. Fe, Al, Cu and similar ingredients existing as the impurities in the leach liquor are precipitated in the form of hydroxides during the leaching and pH adjustment processes while Si is adsorbed to the precipitated hydroxides. However, very little Mn is converted into hydroxides thereof and thus remains in a solution state.

[40] The impurities such as Cu, Al, etc. are typically separated and removed in a sludge state by a filtering process.

[41] Following this, the resultant Mn solution without the other impurities, which is obtained from the impurity removal process involving the precipitation of impurities as disclosed above, is adjusted to have a PH of 9 to 12 using the alkaline solution so as to precipitate an Mn compound.

[42] Lastly, the precipitated Mn compound is separated by a filtering process, followed by washing and drying the filtered material to recover only the Mn compound.

[43] The recovered Mn compound is pulverized and packaged depending on uses thereof.

[44] The filtrate formed during the recovery process may be dried and additionally treated for recovering various byproducts.

[45] Such byproducts may include, for example, ammonium chloride (NH Cl), potassium chloride (KCl), calcium chloride (CaCl ), sodium chloride (NaCl), ammonium sulfate [(NH ) SO ], potassium sulfate (K SO ), calcium sulfate (CaSO ), sodium sulfate (Na SO ), ammonium nitrate (NH NO ), potassium nitrate (KNO ), calcium nitrate [Ca(NO ) ], sodium nitrate (NaNO ), and so forth.

[46] According to the present invention, there is provided a process for recovery of a potassium compound which includes acid cleaning electric dust containing Mn and K, filtering the washed dust to remove a K moiety from the dust while dissolving the same in a filtrate, and then, drying the filtrate containing dissolved K, so as to recover the K compound.

[47] Exemplary embodiments of the method for recovering Mn compounds according to the present invention will be described in more detail as follows. However, the scope of the present invention is not limited to the following examples.

[48] EXAMPLE 1

[49] Dust including 20 wt.% of Mn and 21 wt.% of K was introduced to a IN sulfuric acid solution, stirred for 1 hour and acid washed. The washed solution was filtered and treated by a first refining process, so as to separate the solution into a filtrate containing dissolved K as an alkali metal and a filtered powder portion (sludge) containing Mn.

[50] The sludge obtained from the first refining process had improved Mn content of 40 wt.%.

[51] The filtrate obtained from the first refining process was dried to additionally recover potassium sulfate (K SO ).

[52] Next, a reduction process was performed by adding activated carbon, as a reducing agent, to the sludge in an amount of 3 wt.% (relative to weight of the sludge) and heating the mixture at 75O⁰C for 1 hour, resulting in the reduced powder.

[53] Following this, an impurity removal process was performed by dissolving the reduced powder in 3.5N sulfuric acid to prepare a solution, drop-adding ammonium hydroxide to the solution to adjust the pH of the same to 5.5, and filtering the solution to remove impurities except Mn in a sludge state and to produce a solution containing dissolved Mn without the impurities.

[54] Subsequently, a precipitation process was performed by drop-adding ammonium hydroxide to the solution containing dissolved Mn without the impurities obtained from the impurity removal process, so as to precipitate an Mn oxide (Mn O ) present in the solution.

[55] Lastly, the precipitated Mn O formed by the precipitation process, was subjected to

3 4 a series of processes for separation, washing, drying, pulverization and packaging so as to recover only Mn O as a final product.

[56] In addition, the remaining solution after recovery of Mn O was dried to recover ammonium sulfate [(NH ) SO ] as a byproduct.

[57] The recovered Mn O exhibited improved purity of about 60%.

[58] EXAMPLE 2

[59] Dust including 20 wt.% of Mn and 21 wt.% of K was introduced to a IN hydrochloric acid solution, stirred for 1 hour and acid washed. The washed solution was filtered and treated by a first refining process, so as to separate the solution into a filtrate containing dissolved K as an alkali metal and a filtered powder portion (sludge) containing Mn.

[60] The sludge obtained from the first refining process had improved Mn content of 40 wt.%.

[61] The filtrate obtained from the first refining process was dried to additionally recover potassium chloride (KCl)

[62] Next, a reduction process was performed by adding activated carbon, as a reducing agent, to the sludge in an amount of 3 wt.% (relative to weight of the sludge) and heating the mixture at 75O⁰C for 1 hour, resulting in the reduced powder.

[63] Following this, an impurity removal process was performed by dissolving the reduced powder in 3.5N sulfuric acid to prepare a solution, drop-adding sodium hydroxide to the solution to adjust the pH of the same to 5.5, and filtering the solution to remove impurities except Mn in a sludge state and to produce a solution containing dissolved Mn without the impurities.

[64] Subsequently, a precipitation process was performed by drop-adding sodium hydroxide to the solution containing dissolved Mn without the impurities obtained from the impurity removal process, so as to precipitate Mn 3 O 4 present in the solution.

[65] Lastly, the precipitated Mn O formed by the precipitation process, was subjected to a series of processes for separation, washing, drying, pulverization and packaging so as to recover only Mn O as a final product.

[66] In addition, the remaining solution after recovery of Mn O was dried to recover sodium sulfate (Na SO ) as a byproduct.

[67] The recovered Mn O exhibited improved purity of about 60%.

[68] EXAMPLE 3

[69] Dust including 20 wt.% of Mn and 21 wt.% of K was introduced to a IN nitric acid solution, stirred for 1 hour and acid washed. The washed solution was filtered and treated bya first refining process, so as to separate the solution into a filtrate containing dissolved K as an alkali metal and a filtered powder portion (sludge) containing Mn.

[70] The sludge obtained from the first refining process had improved Mn content of 40 wt.%.

[71] The filtrate obtained from the first refining process was dried to additionally recover potassium nitrate (KNO ).

[72] Next, a reduction process was performed by adding activated carbon, as a reducing agent, to the sludge in an amount of 3 wt.% (relative to weight of the sludge) and heating the mixture at 75O⁰C for 1 hour, resulting in the reduced powder.

[73] Following this, an impurity removal process was performed by dissolving the reduced powder in 3.5N sulfuric acid to prepare a solution, drop-adding calcium hydroxide to the solution to adjust the pH of the same to 5.5, and filtering the solution to remove impurities except Mn in a sludge state and to produce a solution containing dissolved Mn without the impurities.

[74] Subsequently, a precipitation process was performed by drop-adding calcium hydroxide to the solution containing dissolved Mn without the impurities obtained from the impurity removal process, so as to precipitate Mn O present in the solution.

[75] Lastly, the precipitated Mn O formed by the precipitation process, was subjected to

3 4 a series of processes for separation, washing, drying, pulverization and packaging so as to recover only Mn O as a final product. [76] In addition, the remaining solution after recovery of Mn O was dried to recover

3 4 calcium sulfate as a byproduct.

[77] The recovered Mn O exhibited improved purity of about 60%.

[78] EXAMPLE 4

[79] Dust including 20 wt.% of Mn and 21 wt.% of K was introduced to a IN sulfuric acid solution, stirred for 1 hour and acid washed. The washed solution was filtered and treated by a first refining process, so as to separate the solution into a filtrate containing dissolved K as an alkali metal and a filtered powder portion (sludge) containing Mn.

[80] The sludge obtained from the first refining process had improved Mn content of 40 Wt. %.

[81] The filtrate obtained from the first refining process was dried to additionally recover

[82] Next, a reduction process was performed by adding activated carbon, as a reducing agent, to the sludge in an amount of 3 wt.% (relative to weight of the sludge) and heating the mixture at 75O⁰C for 1 hour, resulting in the reduced powder.

[83] Following this, an impurity removal process was performed by dissolving the reduced powder in 3.5N hydrochloric acid to prepare a solution, drop-adding ammonium hydroxide to the solution to adjust the pH of the same to 5.5, and filtering the solution to remove impurities except Mn in a sludge state and to produce a solution containing dissolved Mn without the impurities.

[84] Subsequently, a precipitation process was performedby drop-adding ammonium hydroxide to the solution containing dissolved Mn without the impurities obtained from the impurity removal process, so as to precipitate Mn O present in the solution.

[85] Lastly, the precipitated Mn O formed by the precipitation process, was subjected to a series of processes for separation, washing, drying, pulverization and packaging so as to recover only Mn O as a final product.

[86] In addition, the remaining solution after recovery of Mn O was dried to recover ammonium chloride (NH Cl) as a byproduct.

[87] The recovered Mn O exhibited improved purity of about 60%.

[88] EXAMPLE 5

[89] Dust including 20 wt.% of Mn and 21 wt.% of K was introduced to a IN hydrochloric acid solution, stirred for 1 hour and acid washed. The washed solution was filtered and treated by a first refining process, so as to separate the solution into a filtrate containing dissolved K as an alkali metal and a filtered powder portion (sludge) containing Mn.

[90] The sludge obtained from the first refining process had improved Mn content of 40 wt.%.

[91] The filtrate obtained from the first refining process was dried to additionally recover

KCl

[92] Next, a reduction process was performed by adding activated carbon, as a reducing agent, to the sludge in an amount of 3 wt.% (relative to weight of the sludge) and heating the mixture at 75O⁰C for 1 hour, resulting in the reduced powder.

[93] Following this, an impurity removal process was performed by dissolving the reduced powder in 3.5N sulfuric acid to prepare a solution, drop-adding sodium hydroxide to the solution to adjust the pH of the same to 5.5, and filtering the solution to remove impurities except Mn in a sludge state and to produce a solution containing dissolved Mn without the impurities. [94] Subsequently, a precipitation process was performedby drop-adding sodium hydroxide to the solution containing dissolved Mn without the impurities obtained from the impurity removal process, so as to precipitate Mn O present in the solution.

[95] Lastly, the precipitated Mn O formed by the precipitation process, was subjected to a series of processes for separation, washing, drying, pulverization and packaging so as to recover only Mn O as a final product.

[96] In addition, the remaining solution after recovery of Mn O was dried to recover sodium chloride (NaCl) as a byproduct.

[97] The recovered Mn O exhibited improved purity of about 60%.

[98] EXAMPLE 6

[99] Dust including 20 wt.% of Mn and 21 wt.% of K was introduced to a IN nitric acid solution, stirred for 1 hour and acid washed. The washed solution was filtered and treated by a first refining process, so as to separate the solution into a filtrate containing dissolved K as an alkali metal and a filtered powder portion (sludge) containing Mn.

[100] The sludge obtained from the first refining process had improved Mn content of 40 wt.%.

[101] The filtrate obtained from the first refining process was dried to additionally recover KNO 3

[102] Next, a reduction process was performed by adding activated carbon, as a reducing agent, to the sludge in an amount of 7 wt.% (relative to weight of the sludge) and heating the mixture at 75O⁰C for 1 hour, resulting in the reduced powder.

[103] Following this, an impurity removal process was performed by dissolving the reduced powder in 3.5N hydrochloric acid to prepare a solution, drop-adding calcium hydroxide to the solution to adjust the pH of the same to 5.5, and filtering the solution to remove impurities except Mn in a sludge state and to produce a solution containing dissolved Mn without the impurities.

[104] Subsequently, a precipitation process was performed by drop-adding calcium hydroxide to the solution containing dissolved Mn without the impurities obtained from the impurity removal process, so as to precipitate Mn O present in the solution.

[105] Lastly, the precipitated Mn O formed by the precipitation process, was subjected to a series of processes for separation, washing, drying, pulverization and packaging so as to recover only Mn O as a final product.

[106] In addition, the remaining solution after recovery of Mn 3 O 4 was dried to recover calcium chloride as a byproduct.

[107] The recovered Mn O exhibited improved purity of about 60%. [108] EXAMPLE 7 [109] Dust including 20 wt.% of Mn and 21 wt.% of K was introduced to a IN sulfuric acid solution, stirred for 1 hour and acid washed. The washed solution was filtered and treated by a first refining process, so as to separate the solution into a filtrate containing dissolved K as an alkali metal and a filtered powder portion (sludge) containing Mn.

[110] The sludge obtained from the first refining process had improved Mn content of 40 wt. %.

[I l l] The filtrate obtained from the first refining process was dried to additionally recover

[112] Next, a reduction process was performed by adding activated carbon, as a reducing agent, to the sludge in an amount of 7 wt.% (relative to weight of the sludge) and heating the mixture at 75O⁰C for 1 hour, resulting in the reduced powder.

[113] Following this, an impurity removal process was performed by dissolving the reduced powder in 3.5N nitric acid to prepare a solution, drop-adding ammonium hydroxide to the solutionto adjust the pH of the same to 5.5, and filtering the solution to remove impurities except Mn in a sludge state and to produce a solution containing dissolved Mn without the impurities.

[114] Subsequently, a precipitation process was performed by drop-adding ammonium hydroxide to the solution containing dissolved Mn without the impurities obtained from the impurity removal process, so as to precipitate Mn O present in the solution.

[115] Lastly, the precipitated Mn O formed by the precipitation process, was subjected to a series of processes for separation, washing, drying, pulverization and packaging so as to recover only Mn O as a final product.

[116] In addition, the remaining solution after recovery of Mn O was dried to recover [(NH ) SO ] as a byproduct.

4 2

[117] The recovered Mn O exhibited improved purity of about 60%.

[118] EXAMPLE 8

[119] Dust including 20 wt.% of Mn and 21 wt.% of K was introduced to a IN hydrochloric acid solution, stirred for 1 hour and acid washed. The washed solution was filtered and treated by a first refining process, so as to separate the solution into a filtrate containing dissolved K as an alkali metal and a filtered powder portion (sludge) containing Mn.

[120] The sludge obtained from the first refining process had improved Mn content of 40 wt.%.

[121] The filtrate obtained from the first refining process was dried to additionally recover KCl

[122] Next, a reduction process was performed by adding activated carbon, as a reducing agent, to the sludge in an amount of 7 wt.% (relative to weight of the sludge) and heating the mixture at 75O⁰C for 1 hour, resulting in the reduced powder. [123] Following this, an impurity removal process was performed by dissolving the reduced powder in 3.5N nitric acid to prepare a solution, drop-adding sodium hydroxide to the solution to adjust the pH of the same to 5.5, and filtering the solution to remove impurities except Mn in a sludge state and to produce a solution containing dissolved Mn without the impurities.

[124] Subsequently, a precipitation process was performed by drop-adding sodium hydroxide to the solution containing dissolved Mn without the impurities obtained from the impurity removal process, so as to precipitate Mn O present in the solution.

[125] Lastly, the precipitated Mn O formed by the precipitation process, was subjected to

3 4 a series of processes for separation, washing, drying, pulverization and packaging so as to recover only Mn O as a final product. [126] In addition, the remaining solution after recovery of Mn O was dried to recover

3 4 sodium nitrate as a byproduct.

[127] The recovered Mn O exhibited improved purity of about 60%.

[128] EXAMPLE 9

[129] Dust including 20 wt.% of Mn and 21 wt.% of K was introduced to a IN nitric acid solution, stirred for 1 hour and acid washed. The washed solution was filtered and treated by a first refining process, so as to separate the solution into a filtrate containing dissolved K as an alkali metal and a filtered powder portion (sludge) containing Mn.

[130] The sludge obtained from the first refining process had improved Mn content of 40 wt.%.

[131] The filtrate obtained from the first refining process was dried to additionally recover KNO

[132] Next, a reduction process was performed by adding activated carbon, as a reducing agent, to the sludge in an amount of 7 wt.% (relative to weight of the sludge) and heating the mixture at 75O⁰C for 1 hour, resulting in the reduced powder.

[133] Following this, an impurity removal process was performed by dissolving the reduced powder in 3.5N nitric acid to prepare a solution, drop-adding calcium hydroxide to the solution to adjust the pH of the sameto 5.5, and filtering the solution to remove impurities except Mn in a sludge state and to produce a solution containing dissolved Mn without the impurities.

[134] Subsequently, a precipitation process was performed by drop-adding calcium hydroxide to the solution containing dissolved Mn without the impurities obtained from the impurity removal process, so as to precipitate Mn O present in the solution.

[135] Lastly, the precipitated Mn O formed by the precipitation process, was subjected to a series of processes for separation, washing, drying, pulverization and packaging so as to recover only Mn O as a final product. [136] In addition, the remaining solution after recovery of Mn O was dried to recover calcium nitrate as a byproduct.

[137] The recovered Mn O exhibited improved purity of about 60%.

[138] EXAMPLE 10

[139] After the reduced powder prepared according to Example 1 was dissolved in sulfuric acid, the solution was heated to recover MnO as an Mn oxide.

[140] The recovered MnO exhibited improved purity of about 60%.

[141] EXAMPLE 11

[142] After the reduced powder prepared according to Example 2 was dissolved in hydrochloric acid, the solution was dried to recover MnCl as an Mn compound.

[143] The recovered MnCl exhibited improved purity of about 60%.

[144] EXAMPLE 12

[145] After the reduced powder prepared according to Example 3 was dissolved in nitric acid, the solution was in contact with carbon dioxide gas to recover MnCO as an Mn compound.

[146] The recovered MnCO exhibited improved purity of about 60%.

[147] EXAMPLE 13

[148] After the reduced powder prepared according to Example 5 was dissolved in sulfuric acid, the solution was dried to recover MnSO -H O as an Mn compound.

[149] The recovered MnSO -H O exhibited improved purity of about 60%.

[150] EXAMPLE 14

[151] Dust including 20 wt.% of Mn and 21 wt.% of K was introduced to a IN sulfuric acid solution, stirred for 6 hours and acid washed. The washed solution was filtered to prepare a filtrate containing dissolved K as an alkali metal, followed by drying the solution to recover potassium sulfate.

[152] The recovered potassium sulfate exhibited improved purity of about 65%.

[153] EXAMPLE 15

[154] Dust including 20 wt.% of Mn and 21 wt.% of K was introduced to a IN nitric acid solution, stirred for 6 hours and acid washed. The washed solution was filtered to prepare a filtrate containing dissolved K as an alkali metal, followed by drying the solution to recover potassium nitrate.

[155] The recovered potassium nitrate exhibited improved purity of about 65%.

[156] EXAMPLE 16

[157] Dust including 20 wt.% of Mn and 21 wt.% of K was introduced to a IN hydrochloric acid solution, stirredfor 6 hours and acid washed. The washed solution was filtered to prepare a filtrate containing dissolved K as an alkali metal, followed by drying the solution to recover potassium chloride.

[158] The recovered potassium chloride exhibited improved purity of about 65%. Industrial Applicability

[159] As is apparent from the description disclosed above, the present invention is effective to recover Mn compounds from dust of an electric furnace and, at the same time, to additionally recover alkali metal compounds.

[160] Although the present invention has been described in connection with the exemplary embodiments illustrated in the drawings, it is only illustrative. It will be understood by those skilled in the art that various modifications and equivalents can be made to the present invention. Therefore, the true technical scope of the present invention should be defined by the appended claims.

Claims

[1] A method for recovery of a manganese based compound from dust of an electric furnace comprising:

(i) a first refining process that includes acid cleaning dust containing manganese (Mn) and filtering the treated dust to recover alkali metals contained in the dust which is dissolved in a filtrate, so as to increase content of Mn in the filtered powder mixture (sludge of the dust);

(ii) a reduction process that heats the sludge together with a reducing agent to prepare reduced powder;

(iii) an impurity removal process that includes dissolving the reduced powder obtained by the reduction process in acid to prepare a solution, adjusting the pH of the solution in a range of 4 to 7 and filtering the solution, so as to remove impurities except Mn in a sludge state and prepare a solution containing dissolved Mn except the impurities;

(iv) a process for precipitation of an Mn compound that includes adjusting the pH of the solution without the impurities due to the impurity removal process in a range of 9 to 12 to precipitate the Mn compound; and (v) a process of recovering the Mn compound that includes separating the Mn compound obtained by the precipitation process from the precipitate, and washing and drying the separated product.

[2] The method according to claim 1, wherein the Mn compound contained in the dust is at least one compound selected from a group consisting of Mn O , MnSO •H 2 O, KMnO 4 , MnCO 3 , MnO 2 , MnO, Mn and MnCl.

[3] The method according to claim 1, wherein the filtrate containing dissolved alkali metal obtained from the first refining process is dried to recover an alkali metal compound.

[4] The method according to claim 3, wherein the alkali metal compound is at least one compound selected from a group consisting of a potassium compound, a lithium compound and a sodium compound.

[5] The method according to claim 3, wherein the potassium compound is at least one compound selected from potassium sulfate (K SO ), potassium nitrate (KNO ) and potassium chloride (KCl).

[6] The method according to claim 1, wherein the filtrate obtained in the process of recovering the Mn compound is dried to recover a byproduct.

[7] The method according to claim 6, wherein the byproduct is at least one selected from a group consisting of ammonium chloride (NH Cl), potassium chloride

4

(KCl), calcium chloride (CaCl ), sodium chloride (NaCl), ammonium sulfate [(NH ) SO ], potassium sulfate (K SO ), calcium sulfate (CaSO ), sodium sulfate

4 2 4 2 4 4

(Na SO ), ammonium nitrate (NH NO ), potassium nitrate (KNO ), calcium nitrate [Ca(NO ) ] and sodium nitrate (NaNO ).

[8] The method according to claim 1, wherein the dust of an electric furnace includes at least 10 wt.% of Mn and at least 5 wt.% of alkali metal.

[9] The method according to claim 1, wherein the reducing agent used in the reduction process isat least one selected from a group consisting of activated carbon, coal, coke, charcoal and graphite powder having a carbon content of at least 50%.

[10] The method according to claim 1, wherein the reducing agent used in the reduction process is used in an amount of 3 to 15 wt.% relative to weight of the filtered powder mixture (sludge).

[11] The method according to claim 1, wherein the reducing agent used in the reduction process is used in an amount of 4 to 7 wt.% relative to weight of the filtered powder mixture (sludge).

[12] The method according to claim 1, wherein the reduction process is performed at

500 to 1,000⁰C for 0.5 to 4 hours.

[13] The method according to claim 1, wherein the reduction process is performed at

700 to 75O⁰C for 1 to 2 hours.

[14] The method according to claim 1, wherein the pH of leach liquor formed during acid leaching in the impurity removal process is adjusted using an alkaline solution.

[15] The method according to claim 1, wherein the pH of the filtrate in the precipitation process is adjusted using an alkaline solution. [16] A process for recovery of a potassium compound contained in dust of an electric furnace comprising: acid cleaning the dust of an electric furnace containing

Mnand K; filtering the washed dust to remove a K moiety from the dust while dissolving the same in a filtrate; and then, drying the filtrate containing dissolved

K so as to recover the K compound. [17] The process according to claim 16, wherein the K compound is at least one compound selected from a group consisting of potassium sulfate (K SO ), potassium nitrate (KNO ) and potassium chloride (KCl).