Method for removing halides from Welz oxide

Abstract

The present disclosure relates to a method for removing halides from Waelz oxide containing halides. According to this method, halides contained in Waelz oxide, particularly insoluble fluorides such as CaF2 which are difficult to remove under normal pressure conditions and exist in an insoluble state, can be effectively removed, thereby reducing the additional process for adjusting the concentration of fluorine or chlorine present in the electrolyte in the valuable metal recovery process and reducing costs.

Description

[Technical field]

[0001] This disclosure relates to a method for removing halides from halide-containing Waelz Oxides, and to a method for recovering valuable metals from the halide-depleted Waelz Oxide cake. [Background technology]

[0002] The Waelz process is a method for obtaining oxide cakes from steel mill waste such as electric furnace dust or other recycled materials using a rotary kiln called a Waelz kiln. The oxides obtained by this process are called Waelz oxides and are usually highly enriched in zinc or other valuable metals.

[0003] Valuable metal recovery processes (e.g. zinc recovery processes) using raw materials such as weltz oxide undergo a dissolution process in an acid such as sulfuric acid, followed by an electrolysis process using the dissolution as an electrolyte. In order for such raw materials to be directly used for valuable metal recovery in the electrolysis process, the fluorine (F) and chlorine (Cl) contents in the raw materials must not be high. If these components accumulate in the electrolyte, problems such as electrode corrosion and current efficiency reduction can occur. When weltz oxide is used as a raw material for valuable metal recovery processes, such raw materials contain halides, especially fluorides such as PbF2 or ZnF2 that are carried over from steelmaking dust or are present in the raw materials during the production of weltz oxide. These fluorides react with CaO in the weltz oxide production process to produce the insoluble fluoride CaF2, which creates the problem of having to remove the CaF2 in a later process. To solve this problem, various methods are used to remove the halides present in the weltz oxide.

[0004] Methods for this include the atmospheric alkaline washing process, in which soda ash (Na2CO3) is used to remove halides under atmospheric pressure conditions, and the selective precipitation process of fluorine (F) by adding CaCO3, Ca(OH)2, and aluminum sulfate (Al2(SO4)3) to the Welz oxide solution.

[0005] In the case of the normal pressure alkaline cleaning process, the removal rate of water-soluble chlorine (Cl) is over 99%, but in the case of fluorine, it exists as insoluble CaF2, and even if 300 kg of soda ash is added per ton of raw material, the fluorine removal rate remains at around 69%.

[0006] In the selective fluorine precipitation process, the cake obtained by washing the Welz oxide with an alkali under normal pressure is dissolved in zinc electrolysis wastewater (Zn Spent), and then CaCO3, Ca(OH)2, and aluminum sulfate are added to selectively precipitate fluorine, which makes it possible to remove fluorine from the solution up to about 56mg / L. However, there is a problem in that a large amount of gypsum (CaSO4) is generated by adding CaCO3, Ca(OH)2, and aluminum sulfate. Summary of the Invention [Problem to be solved by the invention]

[0007] The present disclosure has been devised to solve the above problems, and an object of the present disclosure is to increase the removal rate of fluorine from Weltz oxide.

[0008] The present disclosure also aims to solve the problem of large amounts of gypsum being generated during the treatment of Weltz oxide.

[0009] It is also an object of the present disclosure to provide a method for removing halides from Weltz's oxide using a pressurized alkaline wash process using an autoclave. [Means for solving the problem]

[0010] One embodiment of the present disclosure relates to a method for removing halides from a Weltz oxide containing a halide, the method including a pressurized alkali washing step in which a Weltz oxide cake containing a Weltz oxide is heated together with an alkali under pressure to remove the halide.

[0011] In a method according to an embodiment of the present disclosure, halides that are difficult to remove from Weltz oxides by normal pressure alkaline washing, particularly insoluble fluorine (F), can be removed under pressurized conditions using an autoclave.

[0012] In one embodiment, the method for removing halides may further include a repulping step in which the cake obtained from the pressurized alkaline washing step is stirred with water to remove halides. Through this step, residual water-soluble halides remaining in the cake obtained from the pressurized alkaline washing step can be removed with water.

[0013] In one embodiment, in the pressurized alkaline wash step, the alkali may be soda ash or caustic soda.

[0014] In one embodiment, the amount of soda ash may be 100 kg to 300 kg per ton of the Weltz oxide cake.

[0015] In one embodiment, the pressurized pressure in the pressurized alkaline washing step may be 2 to 3 atmospheres.

[0016] In one embodiment, the reaction temperature in the pressurized alkaline washing step may be 140°C to 160°C.

[0017] In one embodiment, the pressurized alkaline washing step may be carried out for 1 hour to 3 hours.

[0018] In one embodiment, the repulping step may be carried out by stirring with water at 50°C to 70°C.

[0019] In one embodiment, the repulping step may be carried out for 1 hour to 2 hours.

[0020] In one embodiment, the halide may be at least one of fluorine or chlorine.

[0021] In one embodiment, the pressurized alkaline washing step may be carried out in an autoclave.

[0022] In one embodiment, the halide removal process may further include a repulp cake recovery step of recovering dehalogenated cake from the repulping step.

[0023] One embodiment of the present disclosure relates to a method for recovering valuable metals from Weltz oxides, which may include (1) a pressurized alkaline washing step of heating a Weltz oxide cake containing Weltz oxides together with an alkali under pressurized conditions, (2) a repulping step of stirring the cake obtained from the pressurized alkaline washing step with water, (3) a repulp cake recovery step of recovering the cake obtained from the repulping step, and (4) a step of recovering valuable metals via an acid dissolution step and an electrolysis step.

[0024] In one embodiment, the valuable metal may be zinc, lead, iron, or copper. Effect of the Invention

[0025] The method according to an embodiment of the present disclosure can increase the removal rate of halides contained in the Weltz oxide and can reduce the amount of secondary raw materials used by carrying out the reaction under pressurized conditions. In addition, the method according to the present disclosure does not require a process for further removing fluorine, unlike the atmospheric alkaline washing process, and does not generate by-products such as gypsum, so the cost of treating by-products can be reduced.

[0026] The method according to one embodiment of the present disclosure can effectively remove halides contained in the Weltz oxide, particularly insoluble fluorides such as CaF2, which are difficult to remove under normal pressure conditions and exist insoluble. This can reduce the additional process for adjusting the concentration of fluorine or chlorine present in the electrolyte in the valuable metal recovery process, thereby reducing costs. [Brief description of the drawings]

[0027] [Figure 1] FIG. 1 is a schematic diagram of a halide removal method according to one embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] The various embodiments or examples described in this document are illustrated for the purpose of clearly explaining the technical idea of ​​the present disclosure, and are not intended to limit the same to specific embodiments. The technical idea of ​​the present disclosure includes various modifications, equivalents, and substitutes of each embodiment or example described in this document, and embodiments or examples that are selectively combined from all or a part of each embodiment or example.

[0029] One embodiment of the present disclosure relates to a method for removing halides from a halide-containing Weltz oxide.

[0030] In the present disclosure, "Weltz oxide" generally refers to the main product of the Weltz process or Weltz process. Here, "Weltz process" or "Weltz process" generally refers to a metallurgical process for reprocessing zinc-containing residual materials, such as zinc-containing electric furnace steel dust, in a rotary tube furnace or rotary kiln. In the present disclosure, the Weltz oxide may include zinc oxide (ZnO) as a main component. In the present disclosure, the Weltz oxide may include lead, iron, copper, or oxides thereof. In addition, the Weltz oxide may generally include halides such as fluorine (e.g., fluorine or fluoride) or chlorine, and may also include other harmful contaminants such as lead.

[0031] In one embodiment, the method for removing halides includes a pressurized alkaline washing step (S100) in which a cake containing Weltz oxide is heated under pressure with an alkali to remove halides. In one embodiment, the pressurized alkaline washing step (S100) may be performed by stirring a Weltz oxide cake containing Weltz oxide with an alkali. Such a pressurized alkaline washing step (S100) is a step for previously removing halides that are difficult to remove under normal pressure alkaline washing conditions, and in particular, it is possible to remove or purify about 90% or more of fluorine, such as CaF2, that is insoluble in the Weltz oxide.

[0032] The principle of the pressurized alkaline washing step (S100) is as shown in Reaction Scheme 1 below.

[0033] CaF2+Na2CO3=2NaF+CaCO3…(Reaction 1)

[0034] In one embodiment, the alkali may be soda ash or caustic soda. Soda ash may mean sodium carbonate (Na2CO3), in particular sodium carbonate anhydrous. Caustic soda may mean sodium hydroxide (NaOH). In one embodiment, the alkali may be administered to the process in an amount of 100 kg to 300 kg per tonne of cake containing the Welz oxide. The amount of alkali administered to the process may preferably be 120 kg to 250 kg, more preferably 150 kg to 200 kg per tonne of Welz oxide cake.

[0035] In one embodiment, the pressurized pressure in the pressurized alkaline washing step (S100) may be 2 to 3 atmospheres.

[0036] In one embodiment, the reaction temperature of the pressurized alkaline washing step (S100) may be 140°C to 160°C.

[0037] In one embodiment, the pressurized alkaline washing step (S100) may be carried out for 1 hour to 3 hours, and the execution time may be preferably 1.5 hours to 3 hours, and more preferably 2 hours to 3 hours.

[0038] In one embodiment, the method for removing halides may further include a repulping step (S200) in which the cake obtained from the pressurized alkaline washing step (S100) is stirred with water to remove halides. The repulping step (S200) is a step for removing or purifying water-soluble halides that cannot be removed in the pressurized alkaline washing step (S100) and remain in the cake.

[0039] In one embodiment, the repulping step (S200) may be performed by stirring with water at 50° C. to 70° C. The temperature may be preferably 55° C. to 70° C., and more preferably 60° C. to 70° C.

[0040] In one embodiment, the repulping step (S200) may be carried out for 1 hour to 2 hours, and the time may be preferably 1.5 hours to 2 hours.

[0041] In each embodiment, if the conditions (e.g., alkali dosage, pressure, temperature, or time) under which the pressurized alkaline washing step (S100) or the repulping step (S200) are performed are less than the minimum values ​​for each condition, halides may not be sufficiently removed, and if the maximum values ​​are exceeded, the efficiency or economics of the process may be adversely affected.

[0042] In one embodiment, the halide may be fluorine and / or chlorine. The halide contained in the Weltz oxide may exist in various forms, and may be used without limitation as long as it is in a form in which fluorine and / or chlorine atoms can be contained as a compound.

[0043] In one embodiment, the pressurized alkaline washing step (S100) may be performed in an autoclave. The autoclave may be a vertical autoclave or a horizontal autoclave. The vertical autoclave may include an inlet for injecting a process liquid, an outlet for discharging the process liquid, an oxygen inlet for supplying oxygen to the process liquid, an agitator for mixing the process liquid, an outer shell, an acid-resistant brick layer, an acid-resistant metal layer, and a cap ring.

[0044] In one embodiment, the method for removing halides may further include a repulp cake recovery step (S300) for recovering dehalogenated cake from the repulping step (S200).

[0045] One embodiment of the present disclosure may relate to a method for recovering valuable metals from Weltz oxides, the method including: (1) a pressurized alkaline washing step (S100) of heating a cake containing Weltz oxides together with an alkali under pressurized conditions; (2) a repulping step (S200) of stirring the cake obtained from the pressurized alkaline washing step (S100) with water; (3) a repulp cake recovery step (S300) of recovering the cake obtained from the repulping step (S200); and (4) a step of recovering the valuable metals through an acid dissolution step and an electrolysis step. In one embodiment, the valuable metal may be zinc, lead, iron, or copper.

[0046] The configuration and effects of the present disclosure will be described in more detail below with reference to examples. However, these examples are provided for illustrative purposes only to aid in understanding the present disclosure, and the scope and scope of the present disclosure are not limited to the following examples.

[0047] [Example 1] Waelz oxide containing 0.25% fluorine and 7.55% chlorine was used as the raw material. In the pressurized alkaline washing process, 180g / L of the raw material was mixed with water, and 120kg of soda ash (Na2CO3) was added per ton of Waelz oxide raw material. The mixture thus prepared was heated to 140℃ in an autoclave and reacted with stirring for 2 hours.

[0048] A cake was obtained from the pressurized alkaline washing step (S100). The cake thus obtained was mixed with 150 g / L of water at 60° C. in the repulping step (S200) and stirred for 2 hours to remove halides.

[0049] The fluorine and chlorine contents in the cake obtained after the pressurized alkaline washing process and the cake obtained in the repulping process were measured using a combustion ion chromatography system (Thermo Fisher Scientific; model name: AQF-2100H).

[0050] [Example 2] The experiment was conducted in the same manner as in Example 1, except that the amount of soda ash added in the pressurized alkaline washing process was adjusted to 150 kg per ton of cake added.

[0051] [Example 3] The experiment was conducted in the same manner as in Example 1, except that the amount of soda ash added in the pressurized alkaline washing process was adjusted to 200 kg per ton of cake added.

[0052] [Example 4] The same experiment as in Example 1 was performed, except that the reaction temperature in the pressurized alkaline washing process was adjusted to 150°C.

[0053] [Example 5] The same experiment as in Example 1 was performed, except that the reaction temperature in the pressurized alkaline washing process was adjusted to 150° C. and the amount of soda ash added was adjusted to 150 kg per ton of cake added.

[0054] [Example 6] The same experiment as in Example 1 was performed, except that the reaction temperature in the pressurized alkaline washing process was adjusted to 150° C. and the amount of soda ash added was adjusted to 200 kg per ton of cake added.

[0055] [Example 7] The same experiment as in Example 1 was performed, except that the reaction temperature in the pressurized alkaline washing process was adjusted to 160°C.

[0056] [Example 8] The same experiment as in Example 1 was performed, except that the reaction temperature in the pressurized alkaline washing process was adjusted to 160° C. and the amount of soda ash added was adjusted to 150 kg per ton of cake added.

[0057] [Example 9] The same experiment as in Example 1 was performed, except that the reaction temperature in the pressurized alkaline washing process was adjusted to 160° C. and the amount of soda ash added was adjusted to 200 kg per ton of cake added.

[0058] [Comparative Example 1] The same experiment as in Example 1 was performed, except that in the alkaline washing process, the reaction temperature was adjusted to 80° C. under normal pressure conditions, and the amount of soda ash added was adjusted to 150 kg per ton of cake added.

[0059] [Comparative Example 2] The same experiment as in Example 1 was performed, except that in the alkaline washing process, the reaction temperature was adjusted to 85° C. under normal pressure conditions, and the amount of soda ash added was adjusted to 150 kg per ton of cake added.

[0060] [Comparative Example 3] The same experiment as in Example 1 was performed, except that in the alkaline washing process, the reaction temperature was adjusted to 90° C. under normal pressure conditions, and the amount of soda ash added was adjusted to 150 kg per ton of cake added.

[0061] [Comparative Example 4] The same experiment as in Example 1 was performed, except that in the alkaline washing process, the reaction temperature was adjusted to 95° C. under normal pressure conditions, and the amount of soda ash added was adjusted to 150 kg per ton of cake added.

[0062] The reaction conditions and the fluorine and chlorine contents present in the cake for the above examples and comparative examples are shown in Table 1 below. [Table 1]

[0063] According to Table 1, when the pressurized alkaline washing process was performed according to one embodiment of the present disclosure, the fluorine content in the Weltz oxide was reduced by at least about 80%. On the other hand, when the alkaline washing process was performed under normal pressure conditions, the fluorine content in the Weltz oxide was reduced by about 50%, which indicates that the conventional process cannot effectively remove fluorine present in insoluble CaF2. It can also be confirmed that the fluorine content is further reduced when the repulping process is performed after the pressurized alkaline washing process according to one embodiment of the present disclosure. Furthermore, according to Table 1, when the repulping process is performed after the pressurized alkaline washing process according to one embodiment of the present disclosure, the final chlorine content is reduced by at least 80% compared to the content of the alkaline washed cake. On the other hand, when the repulping process is performed after the alkaline washing process under normal pressure conditions, the final chlorine content is hardly reduced compared to the alkaline washed cake.

[0064] Finally, according to the method of one embodiment of the present disclosure, it was possible to remove about 85% to about 90% of the fluorine content present in the raw material Weltz oxide, and about 99% of the chlorine content. Such results show that the method of one embodiment of the present disclosure can significantly and effectively remove halides contained in the Weltz oxide.

[0065] Although the present invention has been described in connection with certain embodiments herein, it should be understood that various modifications and changes may be made without departing from the spirit and scope of the present invention as would be understood by one of ordinary skill in the art to which the present invention pertains, and such modifications and changes are to be considered as falling within the scope of the claims appended hereto.

Claims

1. A method for removing halides from a halide-containing Weltz oxide, comprising: a pressurized alkali washing step in which the Weltz oxide cake containing the Weltz oxide is heated together with an alkali at a temperature of 140°C to 160°C under a pressure of 2 to 3 atmospheres to remove halides; A repulping step in which the cake obtained from the pressurized alkaline washing step is stirred with water at 50°C to 70°C to remove halides, The amount of said alkali is 100 kg to 300 kg per ton of said Welz oxide cake.

2. 2. The method for removing halides according to claim 1, wherein in the pressurized alkaline washing step, the alkali is soda ash or caustic soda.

3. 2. The method of claim 1 further comprising a repulp cake recovery step of recovering a dehalogenated cake from said repulping step.

4. (1) a pressurized alkali washing step in which a Weltz oxide cake containing Weltz oxides is heated together with an alkali at a temperature of 140°C to 160°C under a pressure of 2 to 3 atmospheres; (2) a repulping step in which the cake obtained from the pressurized alkaline washing step is stirred with water at 50°C to 70°C; (3) a repulp cake recovery step for recovering a cake obtained from the repulping step; (4) A step of recovering valuable metals through an acid dissolution step and an electrolysis step, The amount of said alkali is 100 kg to 300 kg per ton of said Weltz oxide cake.

5. A method for recovering valuable metals from Weltz oxides as described in claim 4, wherein the valuable metal is zinc, lead, iron, or copper.

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