WO2008075879A1

WO2008075879A1 - Method of manufacturing raw material for stainless melting using feni containing sludge

Info

Publication number: WO2008075879A1
Application number: PCT/KR2007/006635
Authority: WO
Inventors: Jae-Young Lee; Dae-Young Kim
Original assignee: Research Institute Of Industrial Science & Technology
Priority date: 2006-12-20
Filing date: 2007-12-18
Publication date: 2008-06-26
Also published as: KR100811872B1; JP2010513715A; CN101600809B; JP5343006B2; CN101600809A

Abstract

There is provided a method for manufacturing a raw material for stainless steel using a sludge containing Fe, Ni and Cl. The method comprises: neutralizing a sludge containing Fe, Ni and Cl by adding calcium hydroxide to the sludge at a molar ratio (moles of added calcium hydroxide/ moles of existing Cl) of 0.5-1.5; filtering, drying and pulverizing the sludge prepared in the neutralization operation; mixing 5-15 parts by weight of a reducing agent with pulverized sludge, based on 100 parts by weight of the dried powder; adding 5-15 parts by weight of a cement binder to 100 parts by weight of the mixture powder and forming the mixture powder into mass; and curing the formed mass. The raw material for stainless steel may be used since raw material may be prepared without completely removing Cl from the sludge, and therefore there is no problem about environmental pollutions caused by the Cl evaporation.

Description

METHOD OF MANUFACTURING RAW MATERIAL FOR STAINLESS MELTING USING FENI CONTAINING SLUDGE

Technical Field

[I] The present invention relates to a method for recycling a sludge containing Fe, Ni and Cl, and more particularly, to a method capable of effectively recycling FeNi in sludge by preparing Cl into a stable non- volatile compound. According to the present invention, the sludge containing Fe, Ni and Cl may be used as a raw material for stainless steel.

[2]

Background Art [3] FeNi-containing sludge is formed in an etching process and the like in a method for manufacturing a shadow mask. [4] Shadow masks are continuously etched through an etching operation of locally etching a Ni-containing Fe alloy, e.g., Invar alloy, with an FeCl etching solution. For the etching operation, the Invar alloy is reacted by the following equations, and therefore FeCl and NiCl are formed in a reaction solution.

2 2

[5] Equation 1

[6] 2FeCl 3 + Ni = 2FeCl 2 + NiCl 2

[7] Equation 2

[8] 2FeCl 3 + Fe = 3FeCl 2

[9] When the etching operation progresses to a certain extent, the increased content of

FeCl and NiCl results in the deterioration of the etching performances of the FeCl etching solution, indicating the increase in a fatigue index of the solution. Therefore, when concentration of the FeCl and NiCl is increased to greater than a certain level, the solution should be discarded, and a new FeCl solution should be used to control the fatigue index.

[10] A method for recycling the etching waste solution into a FeCl etching solution has been widely used, including: treating the etching waste solution with Fe powder to substitute Ni with Fe powder and oxidizing the solution with chlorine (Japanese Published Patent No. 1995-87474).

[I I] The FeCl recycling method is related to a method of depositing Ni ions formed in the Equation 1 by electrochemically substituting the Ni ions with Fe powder and depositing the substitute, and this scheme is represented by the following Equation 3.

[12] Equation 3

[13] NiCl + 2Fe = FeNi + FeCl [14] As the method for recycling a FeNi sludge formed in the Equation 3, a method of separately recovering FeOOH and NiO from the FeNi sludge was proposed (Korean Patent Application No. 1998-56697, and its Registered Patent No. 10-0406367). The above-mentioned FeNi sludge recycling method is described in detail, as follows.

[15] That is to say, an FeNi-containing sludge is dissolved in hydrochloric acid to prepare an iron chloride and nickel chloride-containing aqueous solution (pH 3 to 4), and the chloride-containing aqueous solution is exposed to air to oxidize FeCl into FeCl 3.

[16] Next, The FeCl generated thus was reacted to water at pH 3 to 5 to form an orange iron hydroxide (FeOOH) core, and an iron hydroxide sludge was formed at a temperature of 40 to 7O⁰C while adding an alkalline under an oxidation condition so that mole of the alkalline can be maintained to at most twice the mole of Fe in a solution and pH of the solution can be maintained to pH 3 to 5. Subsequently, the iron hydroxide sludge formed thus is filtered to separate the iron hydroxide sludge from a nickel chloride-containing filtrate, and the iron hydroxide sludge is washed with water to obtain iron hydroxide. And, an alkalline is added to the filtrate separated in the fitering process, until pH of the filtrate is pH 10, to precipitate nickel hydroxide. Then, the resulting nickel hydroxide precipitate is filtered and washed with water to obtain the nickel hydroxide. However, the above-mentioned FeNi sludge recycling method has problems that its process is complicated and there is a limit in the use of recovered FeOOH.

[17] Therefore, the present inventors have developed and filed a patent application disclosing a technology of recovering the FeNi sludge as an Fe and Ni-containing metal powder (Korean Patent Application No. 2004-0107059).

[18] When the Fe and Ni-containing metal powder recovered according to the above- mentioned technology was used as a raw material for manufacturing a stainless steel, the metal powder is powdered in the form of dust when the metal powder is added to a converter, which leads to the low recovery rate. Therefore, the technology requires a process of manufacturing an alloy ingot by converting the metal powder into mass.

[19] Furthermore, the present inventors have developed and filed a patent application disclosing a technology of manufacturing a FeNi alloy ingot as a method comprising: reducing a FeNi-containing metal powder with reducing gases such as hydogen and sintering the reduced metal powder (2005-69124).

[20] However, the known methods have problems that the manufacturing cost is high since the methods require a washing process or a heat-treatment process to remove Cl, followed by an additional reduction process.

[21] Disclosure of Invention

Technical Problem

[22] An aspect of the present invention provides a method for manufacturing a raw material for stainless steel capable of being used as a raw material in a melting furnace of an iron mill without completely removing Cl from an FeNi-containing sludge by preparing Cl in the sludge into a stable non- volatile compound.

[23]

Technical Solution

[24] According to an aspect of the present invention, there is provided a method for manufacturing a sludge as a formed FeNi mass, the method including: neutralizing a sludge containing Fe, Ni and Cl by adding calcium hydroxide to the sludge at a molar ratio (moles of added calcium hydroxide/moles of existing Cl) of 0.5-1.5; filtering, drying and pulverizing the sludge prepared in the neutralization operation; mixing 5-15 parts by weight of a reducing agent with pulverized sludge, based on 100 parts by weight of the dried powder; adding 5-15 parts by weight of a cement binder to 100 parts by weight of the mixture powder and forming the mixture powder into mass; and curing the formed mass.

[25] According to one exemplary embodiment of the present invention, the sludge containing Fe, Ni and Cl may be an FeNi-containing sludge that is a secondary waste formed in a process for recycling an etching waste solution that is formed in a method for manufacturing a shadow mask. The reducing agent may be at least one selected from the group consisting of carbon, ferrosilicon and aluminum. The curing of the formed mass may be carried out until a moisture content is less than 10%. And, the forming of the mixture powder may be carried out by palletizing the mixture powder.

[26]

Advantageous Effects

[27] According to the present invention, the FeNi-containing sludge may be used as a raw material for stainless steel since the sludge may be manufactured in a more economical manner and is not harmful to human beings. In addition, the FeNi- containing sludge may be useful to minimize the loss of the raw material, which was caused by the powdering and non-reduction of the FeNi-containing sludge, by directly introducing the resulting raw material into a melting furnace.

[28]

Best Mode for Carrying Out the Invention

[29] Hereinafter, exemplary embodiments of the present invention will be described in more detail.

[30] The present invention is characterized in that FeNi may be used as a valuable resource without any of the environmental problems by completely converting Cl into a non- volatile material instead of removing Cl from a sludge containing Fe, Ni and Cl. The formed mass prepared according to the present invention may apply to the field using FeNi as a valuable resource, and one representative example of the application is a raw material for stainless steel. A separate reduction operation may be omitted since pelletized sludge may be directly introduced into a melting furnace.

[31] The present invention applies to methods capable of manufacturing a formed FeNi mass that is used as raw materials for manufacturing a stainless steel using an Fe/Ni sludge.

[32] There is no particular limitation on the FeNi-containing sludge that may be used in the present invention, but sludges containing Fe and Ni may be used in the present invention. Representative examples of the FeNi-containing sludge that may be used in the present invention include an Fe/Ni-containing sludge that is a secondary waste formed in a process for recycling an etching waste solution that is formed in a method for manufacturing a shadow mask from electronics companies.

[33] According to the present invention, a technology of preparing Cl in the FeNi- containing sludge into a stable non- volatile compound should be first carried out to manufacture a formed FeNi mass through the recycling of the sludge.

[34] A variety of methods was used in the art to completely remove Cl from a Cl- containing sludge, and the known methods include a method for removing Cl including: neutralizing the Cl-containing sludge with a neutralizing agent and washing the neutralized sludge with water to remove Cl, and a method for removing Cl including: heat-treating an FeNi-containing sludge at a temperature range of 600 to 900⁰C. In this case, FeCl is present in the sludge since the formation reaction, e.g., the Equation 3, of the FeNi sludge is carried out in an aqueous solution. Also, a siginif icant amount of Fe and Ni are present in the form of hydroxides since they are passivated during the reaction of the Equation 3, and therefore it is possible to obtain Fe and Ni hydroxides.

[35] When FeCl and Cl are present repectively in the FeNi sludge and the passivated sludge during the reaction of the Equation 3, the facilities may be corroded in the above-mentioned reduction/heat-treatment processes, and the toxic gases and dusts may be discharged in great quantities. Therefore, it is necessary to perform a dechlorination process prior to the reduction/heat-treatment processes.

[36] That is to say, when pH of a Cl-containing sludge is increased to a pH level of 9 to

12 until the sludge reaches an equivalence point (moles of added calcium hydroxide / moles of existing Cl = 0.5) by adding a neutralizing agent usch as Ca(OH) to the Cl- containing sludge, metal components such as FeNi does not react but the Cl-containing components reacts in a manner as described in the following Equations 4 and 5. [37] Equation 4

[38] FeCl₂ + Ca(OH)₂ = Fe(OH)₂ + CaCl₂

[39] Equation 5

[40] 2(Fe₅Ni)(OH)Cl + Ca(OH)₂ = 2(Fe₅Ni)(OH)₂ + CaCl₂

[41]

[42] That is to say, when the neutralizing agent is added to the sludge, Cl in the passivated sludge, as well as FeCl , is neutralized to form CaCl . In this case, since CaCl is a soluble salt, CaCl may be removed through the filtering and subsequent washing of solid materials such as 2(Fe,Ni)(0H) . Therefore, it is possible to use a method for removing Cl without any loss of Fe and Ni.

[43] However, the above-mentioned method has problems regarding the use of much water and the repeated washing process. In particular, since the reaction of Equation 5 proceeds very slowly, 2(Fe₅Ni)(OH)Cl is present in the sludge when the sludge is simply neutralized and filtered. Therefore, the above-mentioned method requires the repeated neutralization and washing processes, which leads to the use of much water and the increase in the manufacturing cost.

[44] However, the present inventors have found in the course of experiments that the following reaction proceeds when excessive Ca(OH) was added until a theoretical equivalence ratio (=moles of added calcium hydroxid/moles of existing Cl) is 0.5 or more, for example, when the excessive Ca(OH) was added at a theoretical equivalence ratio of 1.5/2 = 0.75, and it is thus possible to solve the above-mentioned problems. In this case, pH of the solution is adjusted to a pH level of 12 or more, but not increased to pH 12.6 or more due to the solubility of calcium hydroxide, and therefore the calcium hydroxide remains in the solid form.

[45] Equation 6

[46] FeCl + 1.5Ca(OH) = Fe(OH) + CaCl +0.5 Ca(OH)

[47] Equation 7

[48] 2(Fe₅Ni)(OH)Cl + 1.5 Ca(OH) = 2(Fe₅Ni)(OH) + CaCl +0.5 Ca(OH)

[49]

[50] That is to say, CaCl and the remaining calcium hydroxide remain in the reaction product when the calcium hydroxide is added in an excessive amount over the theoretical equivalence ratio.

[51] When the reaction product is filtered using a filtering machine such as a filter press, three kinds of products are obtained, as follows.

[52] First, reaction products such as Fe(OH) and (Fe₅Ni)(OH) , and (Fe₅Ni)(OH)Cl, which is incorporated into the sludge due to the slow reaction, are present as the FeNi hydroxides in the reaction filtrate.

[53] Second, a significant amount of Cl dissolved in water is removed during a filtering operation since CaCl is soluble in water, but a trace of Cl, which is dissolved in water included in the sludge, is present in the reaction filtrate. [54] Third, some of Ca(OH) is dissolved in water since Ca(OH) has rather low solubility in water. However, the Ca(OH) is recovered at a yield of 80% or more through the filtering of the reaction products.

[55] The first products cause problems such as the loss of raw materials and the environmental pollutions since Cl-containing FeNi hydroxides, for example

(Fe₅Ni)(OH)Cl, is converted into NiCl , and then evaporated in the subsequent addition of a raw material for stainless steel. [56] However, the third product, excessive Ca(OH) , is converted into CaO in a melting furnace, and the resulting CaO preferentially reacts to the first product, (Fe₅Ni)(OH)Cl.

Accordingly, the reaction proceeds as follows. [57] Equation 8

[58] 2(Fe,Ni)(0H)Cl+Ca0=CaCl +2(Fe₅Ni)O +H O

[59] Therefore, the addition of excessive calcium hydroxide results in the formation of

CaCl 2. CaCl 2 does not cause the environmental problems at all since the CaCl 2 is a stable compound that is not discomposed at a high temperature of 1400-1500⁰C in a melting furnace, and particularly formed and stably discharged in the form of slag in the melting furnace.

[60] A molar ratio (=moles of added calcium hydroxide/moles of existing Cl) in which calcium hydroxide is added to the sludge is preferably in a range of 0.5 to 1.5. The lower limit of 0.5 in the molar ratio of the added components is the minimum amount for maintaining a remaining calcium hydroxide, whereas the addition effects of the calcium hydroxide are not improved and the cost of raw material is increased and Ni concentration is low when the molar ratio of the added components exceeds 1.5.

[61] Since a general Cl concentration in the sludge is 10.5% (10.5g Cl=0.295 molCl per

100 g of sludge) in average, it is evident that an amount of added calcium hydroxide is calculated in part(s) by weight and added in a manner in which at least 10.9 g (0.295 x 0.5mol x 74g/mol) up to 32.745 g (0.295 x 1.5 mol x 74g/mol) of the calcium hydroxide is added per 100 g of the sludge.

[62] Meanwhile, the filtered sludge is dried, and then pulverized into powder, and 5-15 parts by weight of a reducing agent is mixed with the sludge powder, based on 100 parts by weight of the dried sludge.

[63] When the content of the reducing agent is less than 5 parts by weight, the reduction reaction is not sufficiently achieved. On the contrary, when the content of the reducing agent exceeds 15 parts by weight, it is difficult to further increase a reduction rate, and the cost for the reducing agent is also high.

[64] The reducing agent is used to reduce the FeNi oxides formed in Equation 8 into metallic FeNi in a melting furnace. This reaction may be referred to as melt reduction reaction since it is carried out in the melting furnace. Such a reducing agent includes, for example, carbon, metal aluminum, ferrosilicon, etc.

[65] The reduction reaction is as follows.

[66] (FeNi)O + C = FeNi +CO

[67] (FeNi)O + Al = FeNi +Al O

[68] (FeNi)O + FeSi = 2FeNi +SiO

[69]

[70] The reducing agent-containing powder may be discharged in the form of dust when the powder is added to a furnace, and therefore the reducing agent-containing powder should be formed into mass.

[71] The formed mass may be manufactured through a process of manufacturing spherical pellet (a pelletizing process) while adding a small amount of water and 5-15% by weight of a cement binder. When the content of the added cement binder is less than 5% by weight, it is difficult to give a desired compressive strength [100 kilograms(kg)/square centimeter(cm2)]of the formed mass, whereas the slag is increasingly formed without hardly increasing the compressive strength of the formed mass when the content of the added cement binder exceeds 15% by weight. As the cement binder, only conventional cement such as Portland cement, blast furnace slag cement and the like may be used herein. These cements contain CaO, SiO 2 , Al 2 O 3 , etc.

[72] As the binder, there is no particular limitation on the kind of cements. However, a cement-based binder may contribute to the induction of non- volatile reaction products of Cl according to the Equation 8 since the binder contains a large amount of a CaO component. There is no limitation on the agglomeration process (forming process), but various methods such as briquetting may be used herein.

[73] In the use of the cement binder, a high strength pellet may be obtained by air-drying a pellet for 5 to 15 days. Thtere is no particular limitation on the drying period, but the final product is preferably dried until their moisture content is less than 10%. When the moisture content of the final product exceeds 10%, a stainless furnace is of poor condition, which leads to the difficult operations in an electric furnace.

[74] The pellet prepared according to the method of the present invention is recovered in the form of ferro-nickel when the pellet is added to a melting furnace, and Cl is discharged in the form of stable slag, for example CaCl . Therefore, it is possible to recover FeNi effectively without any of the environmental problems. The pellet is not limitedly used for the simple addtion to the melting furnace, and the pellet may be also used as a raw material for manufacturing ferro-nickel in a refinery.

[75] Mode for the Invention

[76] Hereinafter, exemplary embodiments of the present invention will be described in more detail.

[77] Examples 1

[78] An FeNi-containing pellet used as a raw material for stainless steel was prepared from an FeNi-containing sludge formed in an FeCl etching solution recycling process, by varying various parameters.

[79] First, it was confirmed that an average Cl content in the FeNi sludge was 10.5%

(10.5 g of Cl=0.295 molCl per 100 g of the sludge), which was determined through the content analysis of the FeNi sludge.

[80] 100 g of the FeNiCl-containing sludge prepared thus was added to \l of water, and the resulting sludge-containing aqueous solution was neutralized by adding a varying amount of different kinds of the neutralizing agents to the aqueous solution (molar ratio to Cl in the sludge). The sludge formed in the aqueous solution during this neutralization operation was filtered in a solid-liquid separator to separate a sludge from a filtering solution. The filtered sludge prepared in the filtering operation was dried, and Cokes, aluminum and ferrosilicon were added respectively to the dried sludges by varying the kind and content of the added reducing agents on the basis of 100 g of the dried sludge.

[81] A varying amount of the cement binder was added on the basis of 100 g of the dried sludge, and pelletized in a pelletizer to prepare spherical pellets having a diameter of 40 mm. The prepared pellets were cured for 7 days until a moisture content is 10% or less, and their compressive strengths were measrued.

[82] Meanwhile, the prepared pellets were heated at 145O⁰C in a stainless electric furnace simulator, and it was then observed whether the reduced products and gases were formed.

[83] The melt-reduced FeNi sludge was divided into a metal phase and a non-metal phase (slag), and ferro-nickel was then separated from the slag phase. The slag components include SiO , CaO, and Al O derived from the cement binder, and the slag components are mixed with non-reduced Fe O and NiO in the case of some samples. It was confirmed that, since Cl in the sludge was present mainly in the forme of CaCl , the Cl was not volatilized but discharged in the form of slag. Then, ratios of the recovered FeNi metal to the total amount of the added FeNi (metallization rate) were calculated, and listed in the following Table 1.

[84] Meanwhile, in order to quantify an amount of formed chlorine gas in an electric furnace simulator, a chlorine-absorbing water trap was installed in the rear end of a heat-treating furnace to collect Cl from the formed gases during the heat treatment, an amount of formed Cl in the solution was measured by quantifying the formed Cl during the heat treatment. Amonuts of the formed Cl during the heat treatment according to the experimental conditions as listed in the following Table 1 were represented in milligram per liter (mg/1), and the results were listed in the following Table 1.

[85] Table 1

[86] It was revealed that Cl was not detected in the Cl analysis trap since the Cl was not formed during the heat treatment when calcium hydroxide was used as the neutralizing agent, but the Cl was detected in the Cl analysis trap when NaOH and NH OH were used as the neutralizing agent. Also, it was seen that the loss of Ni was caused by the volatilization of Cl, and therefore its metallization rate was also low (Comparative examples 1 and 2).

[87] In the case of the amount of the added neutralizing agent, it was revealed that the Cl was volatilized when a molar ratio of the added neutralizing agent to the Cl in the 100 g of the sludge was less than 0.5 (Comparative example 3). It was also revealed that the Cl was not volatilized but discharged in the form of slag when the molar ratio of the added components was in a range of 0.5 to 1.5. However, it was seen that the reduction reaction did not appear, and thus the slag was increasingly formed when the molar ratio of the added components was too high (Comparative example 4).

[88] At least one selected from the group consisting of Cokes (C), metal Al and fer- rosilicon metal may be added as the reducing agent. In this case, it was revealed that the reduction reaction was not sufficiently achieved when the content of the added reducing agent was less than 5% by weight (Comparative example 6), whereas its reduction rate was not further increased when the content of the added reducing agent exceeds 20 parts by weight (Comparative example 5). However, it was revealed that the compressive strength of the pellet was low when the cement binder was added in a very low content (Comparative example 7), and therefore the pellet was inadequately powdered when the pellet was charged in working areas in a falling manner. Also, it was seen that the slag was increasingly formed and the metal reduction rate was rather poor when the cement binder was added in an excessive content (Comparative example 8).

Claims

[1] A method for manufacturing a raw material for stainless steel using an FeNi- containing sludge, the method comprising: neutralizing a sludge containing Fe, Ni and Cl by adding calcium hydroxide to the sludge at a molar ratio (moles of added calcium hydroxide/moles of existing

Cl) of 0.5-1.5; filtering, drying and pulverizing the sludge prepared in the neutralization operation; mixing 5-15 parts by weight of a reducing agent with pulverized sludge, based on 100 parts by weight of the dried powder; adding 5-15 parts by weight of a cement binder to 100 parts by weight of the mixture powder and forming the mixture powder into mass; and curing the formed mass. [2] The method of claim 1, wherein the sludge containing Fe, Ni and Cl is an FeNi- containing sludge that is a secondary waste formed in a process for recycling an etching waste solution that is formed in a method for manufacturing a shadow mask. [3] The method of claim 1, wherein the reducing agent is at least one selected from the group consisting of carbon, ferrosilicon and aluminum. [4] The method of claim 1, wherein the curing of the formed mass is carried out until a moisture content is less than 10%. [5] The method of claim 1, wherein the forming of the mixture powder is carried out by palletizing the mixture powder.