Method for producing aqueous sodium manganate solution

Abstract

To provide a method for producing an aqueous solution of sodium manganate having high solubility from a by-product of a smelting process of a metal containing manganese dioxide at a low production cost.SOLUTION: A method for producing an aqueous sodium manganate solution, comprising an oxidation step of heating a slurry obtained by mixing a manganese compound containing manganese dioxide and an aqueous sodium hydroxide solution in an oxidizing atmosphere in a temperature range of 200 °C or more and 700 °C or less to oxidize tetravalent manganese to hexavalent manganese, and a leaching step of immersing a solid containing hexavalent manganese obtained in the oxidation step in an alkaline aqueous solution to leach out hexavalent manganese as manganate ions.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a technique for recovering compounds such as manganese dioxide, which are produced as by-products in zinc smelting processes, as an aqueous solution of sodium manganate. [Background technology]

[0002] In zinc electrolytic smelting, manganese impurities are deposited on the anode surface as manganese dioxide (anode scale), or the deposited manganese dioxide falls off the anode surface and accumulates at the bottom of the electrolytic cell as a precipitate (electrolytic precipitate). Traditionally, by-products containing manganese compounds, primarily manganese dioxide, have been discarded. However, these by-products often contain a high manganese dioxide content (approximately 70% MnO2). From the perspectives of valuable metal recovery and cost reduction, it is desirable to recover and reuse manganese from these by-products. Furthermore, when potassium permanganate oxidation absorption, a type of oxidation absorption method, is used in the denitrification process at flue gas treatment facilities such as smelters, a precipitate (denitrified precipitate) consisting primarily of manganese dioxide is generated as a by-product. This denitrified precipitate also often contains approximately 70% MnO2, making its effective use desirable.

[0003] As a technique for recovering manganese from manganese dioxide, for example, Patent Document 1 discloses a technique for producing potassium manganate from manganese ore or manganese dioxide as an intermediate in the production of potassium permanganate. Furthermore, Example 1 of Patent Document 2 discloses a technique for producing an aqueous sodium permanganate solution from manganese dioxide and sodium hydroxide by electrolytic oxidation. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 62-270421 [Patent Document 2] Japanese Patent Application Publication No. 1-172360 Summary of the Invention [Problem to be solved by the invention]

[0005] The technology disclosed in Patent Document 1 involves spraying a slurry of a mixture of manganese dioxide-containing ore and potassium hydroxide into a high-temperature reaction vessel to obtain powdered potassium manganate. However, when considering the reuse of manganate in a smelting process, for example, in an exhaust gas denitrification process, the manganate is preferably recovered in the form of an aqueous solution, since the manganate is brought into countercurrent contact with exhaust gas containing nitrogen oxides in the form of an aqueous solution. Furthermore, the potassium hydroxide used in the technology disclosed in Patent Document 1 is expensive, and the potassium permanganate produced when the produced potassium manganate is disproportionated has low solubility, which is a problem.

[0006] The technology disclosed in Patent Document 2 involves oxidizing tetravalent manganese contained in manganese dioxide to a valence of heptavalent manganese by electrolytic oxidation and recovering it as an aqueous solution of permanganate ions, but the need for an electrolytic oxidation process results in high production costs. Furthermore, considering reuse in the smelting process, it is not necessary to increase the oxidation number of manganese to a valence of heptavalent manganese.

[0007] In view of the above problems, the technical problem to be solved by the present invention is to provide a method for producing an aqueous solution of sodium manganate from the above-mentioned by-product containing manganese dioxide, which method can be produced at low production cost and in which the solubility of the permanganate produced when the manganese salt is disproportionated is higher than that of the potassium salt. [Means for solving the problem]

[0008] As a result of extensive research conducted by the present inventors to achieve the above-mentioned object, the present invention described below has been completed. That is, in order to achieve the above object, the present invention provides: [1] A method for producing an aqueous sodium manganate solution is provided, which includes an oxidation step of mixing a manganese compound containing manganese dioxide with an aqueous sodium hydroxide solution to obtain a slurry, and heating the slurry in an oxidizing atmosphere at a temperature ranging from 200°C to 700°C to oxidize tetravalent manganese to hexavalent manganese, and a leaching step of immersing the hexavalent manganese-containing solid obtained in the oxidation step in an alkaline aqueous solution to leach manganese as manganate ions. [2] In the method for producing an aqueous sodium manganate solution according to [1] above, in the oxidation step, it is preferable that the concentration of the aqueous sodium hydroxide solution is set to 2 mol / L or more and 17 mol / L or less, and that the aqueous sodium hydroxide solution and the manganese compound containing manganese dioxide are mixed at a molar ratio of sodium hydroxide to manganese dioxide (NaOH / MnO2) of 2.2 or more and 2.8 or less. [3] In the method for producing a sodium manganate aqueous solution according to [1] or [2] above, in the leaching step, a solid permanganate may be added to the alkaline aqueous solution in which a solid material containing hexavalent manganese has been immersed. [Effects of the Invention]

[0009] By using the method for producing a sodium manganate aqueous solution of the present invention, it has become possible to recover manganese from manganese compounds mainly containing manganese dioxide, which have conventionally been discarded, and reuse the manganese in a smelting process without causing the above-mentioned problems. DETAILED DESCRIPTION OF THE INVENTION

[0010] [Sodium manganate aqueous solution] In this specification, the sodium manganate aqueous solution refers to the hydroxide ions (OH - ) except for the manganate ion (MnO4 2- ), and the cationic species of the counter ions contained in the aqueous solution are sodium ions (Na +Here, manganese is recovered in the form of hexavalent manganate ions in order to reuse the aqueous sodium manganate solution obtained by the present invention as an oxidizing agent. The aqueous sodium manganate solution obtained by the production method of the present invention contains impurities that are inevitably contained in the production process, but the impurities are allowed to be present in concentrations and amounts that do not cause problems in the process of using the aqueous sodium manganate solution or in the subsequent wastewater treatment process.

[0011] [Manganese compounds] In the method for producing an aqueous sodium manganate solution of the present invention, the manganese compounds from which manganese can be recovered include by-products produced at the anode during zinc electrolytic refining and manganese compounds containing manganese dioxide (denitrated precipitates) produced in the denitration step, as well as manganese compounds containing manganese dioxide as a main component, such as manganese dioxide reagent. Manganese oxides such as trimanganese tetroxide can also be used as raw materials. In the method for producing an aqueous sodium manganate solution of the present invention, the manganese content in the by-product containing a manganese compound, which is a starting material, is preferably 50% by mass to 100% by mass in terms of manganese dioxide.

[0012] [Sodium hydroxide] Hexavalent manganate can be obtained by oxidizing tetravalent manganese dioxide under basic conditions. In the method for producing a sodium manganate aqueous solution of the present invention, sodium hydroxide (NaOH) is used instead of the commonly used potassium hydroxide (KOH) to achieve basic conditions. Sodium hydroxide is used as the alkali because the price of sodium hydroxide is lower than that of potassium hydroxide and the solubility of the resulting sodium permanganate is higher than that of potassium permanganate. If the solubility is low, the aqueous solution may need to be heated depending on the use conditions, so it is preferable to use a sodium salt as the alkali. In the method for producing a sodium manganate aqueous solution of the present invention, the purity of the sodium hydroxide used may be at the same level as that of an industrial chemical.

[0013] In the method for producing a sodium manganate aqueous solution of the present invention, the mixing ratio of the manganese compound containing manganese dioxide as the main component and sodium hydroxide is preferably such that the molar ratio (NaOH / MnO2) of sodium hydroxide to manganese dioxide contained in the manganese compound is 2.2 or more and 2.8 or less.

[0014] In the method for producing a sodium manganate aqueous solution of the present invention, alkali is used in both the oxidation step and the leaching step. 6+ It is desirable that the cost of the alkali required for the recovery of the manganate salt (hereinafter referred to as the alkali cost) be low. In the method for producing an aqueous sodium manganate solution of the present invention, it is judged to be cost-effective when the sum of the alkali costs in both steps is lower than that in the case where potassium hydroxide is used as the alkali.

[0015] [Oxidation process] In the method for producing a sodium manganate aqueous solution of the present invention, a slurry obtained by mixing the manganese compound and an aqueous solution of sodium hydroxide is heated in an oxidizing atmosphere to oxidize tetravalent manganese to hexavalent manganese. The oxidizing atmosphere can be oxygen, a mixed gas of oxygen and an inert gas, or air. The heating temperature is preferably 200°C or higher and 700°C or lower. A heating temperature lower than 200°C may result in a low yield of sodium manganate when the roasting residue is leached. Furthermore, a heating temperature higher than 700°C tends to increase energy costs. While the heating time is not particularly specified in the present invention, the heating conditions may be adjusted to, for example, about 0.5 to 1.0 hours, taking production costs into consideration.

[0016] The concentration of the aqueous sodium hydroxide solution mixed with the manganese compound is preferably 2 mol / L to 17 mol / L. If the concentration of the aqueous sodium hydroxide solution is less than 2 mol / L, the amount of water relative to the amount of manganese increases, which tends to increase the energy cost in the roasting step. On the other hand, if the concentration exceeds 17 mol / L, the yield of sodium manganate may decrease when the roasting residue is leached. By the above oxidation treatment, the oxidation number of manganese increases from tetravalent to hexavalent according to the reaction of the following formula (1), and solid sodium manganate is produced in the by-product containing manganese compounds. MnO2+2NaOH+1 / 2O2→ Na2MnO4+H2O …(1) Hereinafter, in this specification, the solid by-product that has been subjected to the oxidation treatment is referred to as roasting residue.

[0017] [Leaching process] In the method for producing a sodium manganate aqueous solution of the present invention, the roasting residue containing sodium manganate obtained in the oxidation step is immersed in an alkaline aqueous solution to leach sodium manganate. Hereinafter, the reason for carrying out the leaching treatment in an alkaline aqueous solution is that the eluted manganate ions are likely to undergo the disproportionation reaction of formula (2) below in a neutral or acidic environment. When the disproportionation reaction occurs, permanganate ions and solid manganese dioxide are produced, resulting in a decrease in the recovery rate of water-soluble manganese. 3Na2MnO4+2H2O → 2NaMnO4+MnO2+4NaOH …(2)

[0018] The aqueous solution used in the leaching treatment preferably has a sodium hydroxide concentration of 1 mol / L or more. In the method for producing a sodium manganate aqueous solution of the present invention, there is no particular restriction on the upper limit of the pH of the leaching treatment, but it is preferable to set the sodium hydroxide concentration to 2 mol / L or less to avoid excessive use of alkali. The leaching temperature is preferably 20°C or higher and 80°C or lower. If the leaching temperature is lower than 20°C, the dissolution rate of manganese will decrease. If the leaching temperature is higher than 80°C, water will evaporate rapidly, making the liquid balance more likely to change.

[0019] The alkaline aqueous solution used in the leaching treatment may be an aqueous solution containing a hydroxide of an alkali metal such as sodium or potassium dissolved therein. However, from the viewpoints of availability and the saturated dissolved amount of sodium manganate finally obtained, it is preferable to use an aqueous solution of sodium hydroxide. Although not particularly specified in the production method of the present invention, it is preferable that the concentration of the sample roasted residue be 6 g / L or more and 20 g / L or less when carrying out the leaching treatment. It is also preferable to stir the reaction solution during the leaching treatment. After the leaching treatment, a portion of the roasting residue may remain in a solid state without dissolving in the alkaline aqueous solution used in the leaching treatment. Hereinafter, in this specification, the solid matter remaining in the aqueous solution without dissolving is referred to as the leaching residue.

[0020] In the method for producing an aqueous sodium manganate solution of the present invention, a solid permanganate such as potassium permanganate or sodium permanganate may be present in the alkaline aqueous solution used in the leaching step to promote the leaching reaction. In this case, the permanganate is considered to have the effect of suppressing the disproportionation reaction. Furthermore, the presence of a solid permanganate promotes the dissolution of the leaching residue, thereby increasing the manganese recovery efficiency. In this case, the amount of permanganate added can be such that the mass ratio of permanganate to roasting residue is 0 or more and 1 or less, preferably 0.2 or more and 0.5 or less, and more preferably 0.33.

[0021] [Separation and recovery process] In the method for producing an aqueous sodium manganate solution of the present invention, the leaching residue is separated from the aqueous solution containing the leaching residue obtained by the leaching treatment using a known solid-liquid separation means to obtain an aqueous sodium manganate solution. The solid-liquid separation means can be, for example, pressure filtration using a filter. In the examples of the present invention described below, solid-liquid separation was carried out using a hydrophilic PTFE membrane filter (H010A047A or H010A142C) manufactured by Advantec as the filter and a stainless steel holder with a tank (KST-47 or KST-142) manufactured by Advantec as the filter holder, at a filtration pressure of 0.4 MPa. Hereinafter, the aqueous solution from which the leaching residue has been separated will be referred to as the leaching solution. [Example]

[0022] [Measurement of Mn content in solids] The Mn content in the solid material (test material) containing manganese compounds from which manganese was recovered and the roasting residue used in the examples and comparative examples of the present invention was measured by the following procedure. The main components of the manganese compounds analyzed in this example are manganese dioxide, in which the oxidation state of manganese is tetravalent, and sodium manganate, in which the oxidation state of manganese is hexavalent. Manganese dioxide is insoluble in ordinary acids, and sodium manganate is not a stable substance in acidic solutions. Therefore, Mn, an ion that is stable in acidic solutions, was used. 2+ and the Mn 2+ Specifically, the analysis sample was added to a solution of 30 mass% hydrogen peroxide and nitric acid, and manganese dioxide was converted into Mn 2+ The reaction was as follows: If the solid matter did not dissolve completely when dissolved at room temperature using nitric acid, heating or the addition of hydrochloric acid was carried out as necessary. MnO2+H2O2+2H + → Mn 2+ +O2+2H2O Thereafter, the solution was diluted, and the Mn concentration was measured by ICP-OES (Agilent, 720 ICP-OES), and the Mn content of the solid matter was calculated.

[0023] [Measurement of Mn content in leaching solution] The Mn content of the leaching solution containing sodium manganate, which is a product of manganese recovery, shown in the examples and comparative examples of the present invention was measured by the following procedure. Sodium manganate is unstable and gradually disproportionates, so it is necessary to dissolve the stable ion Mn 2+ and the Mn 2+ Specifically, 30 mass% hydrogen peroxide and nitric acid were added to the leaching solution appropriately to reduce the manganate ions to divalent manganese ions. The reaction formula is as follows: MnO4 2- +2H2O2+4H + → Mn 2+ +2O2+4H2O The reduced solution was then diluted, and the Mn concentration was measured using an ICP-OES (Agilent, 720 ICP-OES) to calculate the amount of Mn in the leaching solution.

[0024] [Oxidation state of Mn] In the oxidation process described above, in addition to hexavalent manganese, pentavalent manganese, i.e., manganite, may be produced. The oxidation number of manganese present in the aqueous solution obtained by the leaching process can be confirmed by the following procedure. When barium nitrate is added to the leaching solution obtained by the above-mentioned leaching treatment, barium manganate (BaMnO4), a hexavalent manganese compound, precipitates. When the precipitate is separated by a known solid-liquid separation method, manganite ions (MnO4), a pentavalent manganese compound, remain in the aqueous solution. 3- When the Mn concentration in the leaching solution from which the barium manganate was separated and removed was measured by ICP-AES, the Mn concentration was at the detection limit, so it is believed that all of the Mn in the leaching solution obtained by the leaching treatment is hexavalent manganate ions. Even if pentavalent manganite is present in the roasting residue, it is believed that the following disproportionation reaction occurs in the aqueous solution during leaching, converting it to hexavalent manganate ions. 2Na3MnO4+2H2O → Na2MnO4+MnO2+4NaOH …(3)

[0025] [Mn recovery yield] The yield of hexavalent manganese recovered from a test raw material containing a manganese compound by the method for producing a sodium manganate aqueous solution of the present invention (hereinafter referred to as Mn leaching rate) is calculated by the following formula (4). Mn leaching rate (%) = (amount of Mn in leaching solution - amount of Mn in added KMnO4) / amount of Mn in roasting residue × 100 ... (4) By using the method for producing an aqueous sodium manganate solution of the present invention, a Mn leaching rate of 20% or more can be obtained.

[0026] [Example 1] A slurry was obtained by mixing 3.00 g of anode scale as the test material with an 8.91 mol / L NaOH aqueous solution. Here, anode scale refers to a solid material composed primarily of manganese dioxide that deposits on an anode during the zinc electrowinning process at a zinc smelter. In this invention, the anode scale was used as a roasting sample after undergoing the pretreatment described below. The anode scale was dried in a dryer, crushed in a vibration mill, and then subjected to a dry vibration sieve to obtain anode scale particles with a particle size of 150 μm or less. The anode scale was then mixed with pure water heated to 60°C in a beaker and stirred for 30 minutes with a stirrer. Subsequently, pressure filtration was performed to separate the solid and liquid, and the resulting solid was dried and used as the test sample. This was because anode scale that had not been pretreated would have coarse particles and would be contaminated with acid from the zinc electrolyte, which could potentially reduce the reactivity of manganese dioxide with sodium manganate during roasting.

[0027] In this example, the Mn content in the anode scale was 44 mass%, the manganese content was 1.31 g, and the molar ratio of sodium to manganese dioxide (Na / MnO2) was 2.5. The slurry was placed in a pure nickel crucible and heated to 500°C in an air atmosphere using a muffle furnace (Yamato Scientific Co., Ltd., FP413) to obtain a roasted residue. The heating conditions were a temperature rise time of 30 minutes and a holding time of 60 minutes, and after heating, the furnace was cooled to room temperature.

[0028] 3.00 g of the roasted residue obtained in the oxidation treatment was taken and placed in a glass conical beaker together with 1.0 g of solid potassium permanganate (KMnO4). A 1 mol / L aqueous solution of NaOH was added, and the mixture was leached while stirring with a magnetic stirrer. The leaching conditions were 60°C for 30 minutes. The Mn content in the leachate obtained in this example was 6+ The amount of manganese extracted was 0.29 g, and the Mn leaching rate was 22%. The manganese contained in the obtained leachate was confirmed to be hexavalent manganese by the method described above in [Oxidation number of Mn].

[0029] In this example, the unit weight of Mn6+ The alkali cost required for the recovery of Mn was 0.5 for the oxidation process and 0.5 for the leaching process, with the alkali cost in Comparative Example 1 described later taken as 1. Table 1 shows the conditions for the oxidation process and the leaching process, and Table 2 shows the Mn 6+ The results of recovery are shown in the table (the same applies to the following examples).

[0030] [Example 2] The oxidation treatment and leaching treatment were carried out under the same conditions as in Example 1, except that the test material was an electrolytic precipitate. 6+ The electrolytic precipitate was collected. Here, the term "electrolytic precipitate" refers to the solid matter that precipitated on the anode during the zinc electrowinning process at a zinc smelter, which fell off the anode and settled at the bottom of the electrolytic cell. In the present invention, the electrolytic precipitate was subjected to the pretreatment described below and then used as a roasting sample. The electrolytic precipitate was dried in a dryer, pulverized in a vibration mill, and then sieved using a dry vibration sieve to obtain an electrolytic precipitate with a particle size of 150 μm or less. The anode scale was then mixed with pure water heated to 60°C in a beaker and stirred for 30 minutes using a stirrer. Pressure filtration was then performed to separate the solid from the liquid, and the resulting solid was dried and used as a test sample. This was because electrolytic precipitate without pretreatment was coarse-grained and had acid from the zinc electrolyte attached to it, which could potentially deteriorate the reactivity of manganese dioxide with sodium manganate during roasting.

[0031] In this example, the Mn content in the test raw material was 46 mass%, the Mn leaching rate was 24%, and the alkali cost was 0.4 in the oxidation step and 0.4 in the leaching step, totaling 0.4, assuming that the alkali cost in Comparative Example 1 described below was 1.

[0032] [Example 3] The oxidation and leaching treatments were carried out under the same conditions as in Example 1, except that the test material was a special grade MnO2 reagent. 6+ was recovered.

[0033] In this example, the Mn content in the test raw material was 63 mass%, the Mn leaching rate was 36%, and the alkali cost was 0.3 in the oxidation step and 0.3 in the leaching step, totaling 0.3, assuming that the alkali cost in Comparative Example 1 described below was 1.

[0034] [Example 4] The oxidation and leaching treatments were carried out under the same conditions as in Example 1, except that the test material was wastewater treatment sediment. 6+ The wastewater treatment precipitate is a solid material primarily composed of manganese dioxide, obtained by reducing industrial wastewater containing permanganate ions with hydrogen peroxide and sulfuric acid in order to meet the wastewater standards stipulated in the Water Pollution Control Act. Specifically, this solid material was obtained by adding 30 mass% hydrogen peroxide to an aqueous potassium permanganate solution with a Mn concentration of 8 g / L, and then adding 95 mass% sulfuric acid during reduction to maintain the pH at around 2. The reaction formula is shown below. The slurry obtained after reduction was subjected to solid-liquid separation by pressure filtration, and the resulting solid was dried and used as the test sample.

[0035] In this example, the Mn content in the test raw material was 47% by mass, the Mn leaching rate was 40%, and the alkali cost was 0.3 in the oxidation step and 0.3 in the leaching step, totaling 0.3, assuming that the alkali cost in Comparative Example 1 described below was 1.

[0036] [Example 5] The oxidation treatment and leaching treatment were carried out under the same conditions as in Example 1, except that the test material was a denitrified precipitate. 6+ Here, the denitrified product is a solid substance mainly composed of manganese dioxide, which is a by-product of the reaction in which NOx is oxidized and absorbed by potassium permanganate solution during the exhaust gas treatment process.

[0037] In this example, the Mn content in the test raw material was 47% by mass, the Mn leaching rate was 42%, and the alkali cost was 0.3 in the oxidation step and 0.2 in the leaching step, totaling 0.2, assuming that the alkali cost in Comparative Example 1 described below was 1.

[0038] [Example 6] In the oxidation treatment, 10 g of special grade MnO2 reagent was used as the test material, and 33 mL of NaOH aqueous solution was mixed. In the leaching treatment, potassium permanganate (KMnO4) was not added. Except for this, oxidation treatment and leaching treatment were carried out under the same conditions as in Example 1. 6+ was recovered.

[0039] In this example, the Mn content in the test raw material was 63 mass%, the Mn leaching rate was 35%, and the alkali cost was 0.3 in the oxidation step and 0.3 in the leaching step, totaling 0.3, assuming that the alkali cost in Comparative Example 1 described below was 1.

[0040] [Comparative Example 1] The oxidation treatment and leaching treatment were carried out under the same conditions as in Example 3, except that the alkali mixed with the test material in the oxidation treatment step was KOH and the heating temperature was 400°C. 6+ In this comparative example, the roasting residue was 3.02 g.

[0041] In this comparative example, the Mn leaching rate was high at 60%, but because the unit price of the KOH used was higher than that of NaOH, the alkali cost exceeded the costs of Examples 1 to 6 when comparing only the oxidation process, only the leaching process, and the total cost.

[0042] [Table 1]

[0043] [Table 2]

[0044] The method for producing a sodium manganate aqueous solution of the present invention is economically advantageous because it is less expensive per unit amount of recovered manganese than the commonly used potassium salt, even though the same manganate is used. Furthermore, when comparing the solubility as permanganate, sodium salts have a higher solubility than conventional potassium salts, so when manganate becomes permanganate through disproportionation or the like, the handling risk of clogging of piping or pumps due to crystallization is relatively lower with sodium salts than with potassium salts.

Claims

1. A method for producing an aqueous sodium manganate solution, comprising: an oxidation step of mixing a manganese compound including manganese dioxide with an aqueous sodium hydroxide solution to obtain a slurry, and heating the slurry in an oxidizing atmosphere at a temperature in the range of 200°C to 700°C to oxidize tetravalent manganese to hexavalent manganese; a leaching step of immersing the hexavalent manganese-containing solid obtained by the oxidation step in an alkaline aqueous solution to leach the hexavalent manganese as manganate ions; A method for producing a sodium manganate aqueous solution, comprising:

2. In the oxidation step, the concentration of the aqueous sodium hydroxide solution is set to 2 mol / L or more and 17 mol / L or less, and the aqueous sodium hydroxide solution and the manganese compound containing manganese dioxide are mixed in a molar ratio of sodium hydroxide to manganese dioxide (NaOH / MnO ２ 2. The method for producing a sodium manganate aqueous solution according to claim 1, wherein the molten manganate is mixed at a concentration of 2.2 to 2.

8.

3. 2. The method for producing a sodium manganate aqueous solution according to claim 1, wherein in the leaching step, a solid permanganate is added to the alkaline aqueous solution in which the solid material containing hexavalent manganese has been immersed.

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