JP2007283168A - Adsorbent and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology for adsorbing arsenic and a component harmful for other environments at a high efficiency. <P>SOLUTION: The adsorbent can be manufactured by a step for reacting a material containing an oxide of a rare earth metal with an acidic chemical, forming this to a hydroxide by an alkaline chemical, and further oxidizing the hydroxide by an oxidizing agent. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an adsorbent with good immobilization performance and a method for producing the same.

  As a method for removing arsenic, fluorine, and boron using rare earth metals, a method is known in which a water-soluble rare earth metal compound is added to the water to be treated to generate a substance to be removed and an insoluble salt to remove ( For example, Patent Document 1 and Patent Document 2).

  However, according to the method described in Patent Document 1 and the like described above, an agglomeration treatment is necessary for the solid-liquid separation of the insoluble salt, and for the recovery and reuse of the added rare earth metal compound, This insoluble salt needs to be redissolved and solid-liquid separated again, so that the operation is complicated and it is difficult to reuse the rare earth metal compound. Moreover, since there is a problem that unreacted rare earth metal is eluted depending on the concentration of the water to be treated, there is also a problem that it is necessary to strictly control the concentration of the rare earth metal compound to be added.

  On the other hand, there has been reported a technique for obtaining an arsenic insolubilizing treatment agent mainly composed of a hydrated oxide of a rare earth metal by hydrating a cerium oxide waste used for polishing glass as a raw material (Patent Document 3). ). According to this technique, a rare earth compound and arsenic produce a compound by an irreversible reaction between a rare earth metal hydrated oxide and arsenic, and as a result, arsenic is immobilized (insolubilized).

JP 11-235594 A Japanese Patent Laid-Open No. 11-47765 JP 2001-200366 A

  However, the technique described in Patent Document 3 has a problem that the component other than arsenic that is harmful to the environment has low immobilization performance.

In a glass abrasive waste used as a raw material for a fixing agent, trivalent cerium oxide and tetravalent cerium oxide are usually mixed. And when these abrasive waste and hydration treatment, the greater the better the amount of trivalent cerium hydroxide as compared to tetravalent cerium hydroxide _{(Ce (OH) 4) (} Ce (OH) 3). However, for example, hexavalent chromium, selenium (tetravalent), selenium (hexavalent), boron, mercury, antimony, and other components other than arsenic, tetravalent cerium hydroxide (Ce (OH) ₄ ) is more highly fixed. Shows ability. However, the technique described in Patent Document 3 does not include a step of oxidizing the rare earth compound to adjust the valence.

  In Patent Document 3, attention is not paid to the quality of abrasive waste. In obtaining waste abrasives, they are usually flocked using a PAC agent (polyaluminum chloride) and a sulfuric acid band (aluminum sulfate) to form a dehydrated cake, and the waste abrasives are collected. Therefore, even after hydrating the waste abrasive, the above component is contained in an amount of 20 to 40% by weight when the solid content is 100%. That is, since the waste abrasive contains a component having no immobilization performance such as an aluminum-based component, the immobilization efficiency of the arsenic insolubilizing agent obtained by hydrating the waste abrasive is lowered.

  Therefore, not only arsenic but also technology that can fix highly harmful components such as hexavalent chromium, selenium (tetravalent), selenium (hexavalent), boron, mercury, antimony, etc. It is an object of the present invention to provide.

  In order to solve the above problems, the present invention reacts a material containing an oxide of a rare earth metal with an acidic agent, forms it into a hydroxide with an alkaline agent, and further converts the hydroxide with an oxidizing agent. Provided is a method for producing an adsorbent characterized by oxidation. Furthermore, the present invention also provides an adsorbent characterized in that a main component is a rare earth metal compound obtained by oxidizing a rare earth metal hydroxide. The present invention is characterized in that an oxide of a trivalent rare earth metal such as cerium is oxidized to a tetravalent state by including a step of adjusting the valence.

  According to the present invention, it is possible to fix not only arsenic but also harmful components such as hexavalent chromium, selenium (tetravalent), selenium (hexavalent), boron, mercury, and antimony with high efficiency. Has an effect.

  Below, the manufacturing method of the adsorption agent of this invention is demonstrated in detail. The adsorbent of the present invention reacts mineral raw materials containing rare earth metal oxides, abrasives and waste abrasives with acidic chemicals to form hydroxides with alkaline chemicals, and further includes hydrogen peroxide and the like. It can be obtained by oxidizing a trivalent rare earth metal and adjusting its valence by oxidizing with an oxidizing agent.

  In a preferred embodiment of the present invention, the rare earth metal is a group consisting of cerium (Ce), samarium (Sm), neodymium (Nd), gadolinium (Gd), lanthanum (La), yttrium (Y) and praseodymium (Pr). However, it is not limited to them.

  By steps 1 to 3 shown below, the ratio of trivalent cerium hydroxide can be reduced and the ratio of tetravalent cerium hydroxide can be increased. The process is shown below. In addition, the case where cerium is used as the rare earth metal in the following Step 1 to Step 3 will be described as an example. Can do.

  The adsorbed material adsorbed by the adsorbent of the present invention is selected from the group consisting of arsenic, fluorine, boron, lead, cadmium, mercury, antimony, chromium, molybdenum, selenium, phosphorus, thallium, indium and bismuth. However, it is not limited to them.

(Process 1)
An acidic chemical such as hydrochloric acid (HCl) is added to the waste abrasive and reacted at 50 to 100 ° C. for 1 hour to several days to dissolve the components. In this step 1, a rare earth metal oxide such as cerium oxide is used as its salt. By this reaction, trivalent cerium becomes a trivalent salt, and tetravalent cerium becomes a tetravalent salt.
2Ce ₂ 0 ₃ + 6HCl → CeC1 ₃ + H ₂ 0
CeO ₂ + 4HCl → CeC1 ₄ + H ₂ 0

  The reaction temperature in step 1 is 50 to 100 ° C., preferably 65 to 90 ° C., but is not limited to this range. The reaction time is also 1 hour to several days, preferably 12 to 48 hours, but is not limited thereto. The acid used is preferably hydrochloric acid, but is not limited thereto, and various inorganic acids or organic acids can be used as long as cerium oxide can be converted into a salt thereof.

(Process 2)
Neutralize by adding an alkaline agent such as NH ₄ OH to about pH 8. As a result, cerium, which is a salt such as chlorine, precipitates as trivalent or tetravalent cerium hydroxide hydrate (Ce (OH) ₄ .nH ₂ 0). This precipitate can be recovered by a filter press method or the like.
CeC1 ₃ + 3NH ₄ 0H → Ce (OH) ₃ (sedimentation) + 3NH ₄ Cl
CeC1 ₄ + 4NH ₄ 0H → Ce (OH) ₄ (precipitation) + 4NH ₄ Cl

In Step 2, the alkaline chemical is added until the acidic chemical is neutralized and the cerium hydroxide hydrate is sufficiently precipitated. The alkaline agent used here is preferably NH ₄ OH, but various alkaline agents generally used for acid neutralization can be used.

(Process 3)
An oxidant such as hydrogen peroxide (H ₂ 0 ₂ ) is added to the cerium hydroxide recovered in step 2 and reacted at pH 4 to 5 to oxidize the hydroxide. By performing the oxidation treatment in this step 3, trivalent cerium hydroxide becomes tetravalent cerium hydroxide hydrate (Ce (OH) ₄ · nH ₂ 0), thus hexavalent chromium and selenium (tetravalent). Adsorption efficiency for selenium (hexavalent), boron, mercury, antimony, etc. can be increased.
Ce (OH) ₃ + H ₂ 0 ₂ → Ce (0H) ₄ + H ₂ 0

  The oxidizing agent used here is hydrogen peroxide, potassium permanganate, potassium dichromate, sulfur dioxide, chlorine, sodium bismuthate, persulfate, bromate, hypochlorite, hypobromine. Although it is at least 1 sort (s) selected from the group which consists of an acid salt, it is not limited to them.

  Here, the steps 2 and 3 have been described as separate steps. However, after the step 1, an alkaline chemical and an oxidizing agent may be added at the same time and processed in one step. Since the number of steps can be reduced, it is industrially advantageous. However, since the reaction efficiency tends to decrease when the treatment is performed in one step, it is better to use a separate step when it is desired to increase the yield.

  The reaction time in step 3 is 6 to 24 hours, preferably 12 to 24 hours, but is not limited to this range. The pH during the reaction is preferably 4 to 5, but is not limited thereto, and the most appropriate pH can be appropriately selected for oxidizing cerium hydroxide from trivalent to tetravalent.

  In the present invention, a filter press method can be employed in the step of dewatering the waste abrasive or the like. As a result, the amount of water in the dehydrated cake can be reduced, and the treatment concentration in steps 1 and 2 can be increased. Furthermore, since the treatment tank can be further reduced in size and the amount of drug added can be reduced, the pH required for the reaction can be adjusted with the addition of a small amount of drug. Other methods for preparing dehydrated cakes that have been used conventionally have the disadvantage that the moisture content varies.

Further, in the step of recovering the waste abrasive, the abrasive dispersed in water can be aggregated, flocked and recovered using an iron-based aggregating agent. Ferric chloride is most suitable as the iron-based flocculant used. As shown by the following formula, when ferric chloride (FeCl ₃ ) is used as the inorganic flocculant, in step 2, iron hydroxide (Fe (OH) ₃ ) having adsorption performance is obtained. Thereby, the content rate of the component without adsorption performance can be lowered, and the efficiency of adsorption can be improved.
FeCl ₃ + 3NH ₄ 0H → Fe (OH) ₃ (precipitation) + 3NH ₄ Cl

  Examples of the present invention will be described below, but the following examples do not limit the scope of the present invention. In addition, the following composition display is a mass% display.

Example 1
In order to produce the adsorbent of the present invention, a waste abrasive having the following composition (1) was used.
<Waste abrasive composition (1)>
CeO ₂ : 8% Ce ₂ 0 ₃ : 7% La ₂ 0 ₃ : 5% A1 ₂ 0 ₃ : 20% Moisture content: 60%

  This waste abrasive uses polyaluminum chloride as an inorganic flocculant. The dehydration method is a filter press method. An appropriate amount of water was added to the waste abrasive having the above composition (1), concentrated hydrochloric acid (35% -HCl) was added, and the mixture was reacted at 75 ° C. for 12 hours to dissolve the components.

Thereafter, aqueous ammonia (25% -NH ₄ 0H) was added while confirming the pH to adjust to pH 8. Suspend the precipitated components, add hydrogen peroxide (70% concentration -H ₂ 0 ₂ ) to adjust the pH to 4.5-5, and react until hydrogen peroxide is decomposed to produce tetravalent cerium hydroxide. Allowed to settle. Excess water was removed by a filter press method. As a result, the following adsorbent was obtained and named “Composition A”.
Composition A Ce (OH) ₄ : 19% La (OH) ₃ : 6% Al (OH) ₃ : 25% Moisture content: 50%

(Example 2)
In order to produce the adsorbent of the present invention, a waste abrasive having the following composition (2) was used.
<Waste abrasive composition (2)>
CeO ₂ : 5% Ce ₂ 0 ₃ : 15% La ₂ 0 ₃ : 5% A1 ₂ 0 ₃ : 15% Other 5% Moisture content: 55%

  This waste abrasive uses polyaluminum chloride as an inorganic flocculant. The dehydration method is a filter press method. An appropriate amount of water was added to the waste abrasive having the above composition (2), concentrated hydrochloric acid (35% -HCl) was added, and the mixture was reacted at 75 ° C. for 12 hours to dissolve the components.

Thereafter, aqueous ammonia (25% -NH ₄ 0H) was added while confirming the pH to adjust to pH 8. Suspend the precipitated components, add hydrogen peroxide (70% concentration -H ₂ 0 ₂ ) to adjust the pH to 4.5-5, react until hydrogen peroxide decomposes, and add tetravalent cerium hydroxide. Allowed to settle. Excess water was removed by a filter press method. As a result, the following adsorbent was obtained and named “Composition B”.
Composition B Ce (OH) ₄ : 25% La (OH) ₃ : 6% A1 (0H) ₃ : 18% Others 6% Moisture content: 45%

(Example 3)
In order to produce the adsorbent of the present invention, a waste abrasive having the following composition (3) was used.
<Waste abrasive composition (3)>
CeO ₂ : 8% Ce ₂ 0 ₃ : 20% La ₂ 0 ₃ : 5% FeCl ₃ : 5% A1 ₂ 0 ₃ : 3% Other 4% Moisture content: 55%

  This waste abrasive uses ferric chloride as the main inorganic flocculant and additionally uses polyaluminum chloride. The dehydration method is a filter press method. An appropriate amount of water was added to the waste abrasive having the above composition (3), concentrated hydrochloric acid (35% -HCl) was added, and the mixture was reacted at 75 ° C. for 12 hours to dissolve the components.

Thereafter, aqueous ammonia (25% -NH ₄ 0H) was added while confirming the pH to adjust to pH 8. Suspend the precipitated components, add hydrogen peroxide (70% concentration -H ₂ 0 ₂ ) to adjust the pH to 4.5-5, react until hydrogen peroxide decomposes, and add tetravalent cerium hydroxide. Allowed to settle. Excess water was removed by a filter press method. As a result, the following adsorbent was obtained and named “Composition C”.
Composition C Ce (OH) ₄ : 30% La (OH) ₃ 6% Fe (OH) ₃ 6% Al (OH) ₃ 3% Other 5% Moisture content 50%

Example 4
Furthermore, the adsorbent of the present invention was produced using a material having the following composition (4).
<Unused abrasive composition (4)>
CeO ₂ : 15% Ce ₂ 0 ₃ : 45% La ₂ 0 ₃ : 20% Pr ₆ O ₁₁ : 5% Nd ₂ 0 ₃ : 5.5% Others 10%

  This material uses an unused abrasive, contains little moisture, has a high content of cerium oxide, and a low content of chemical components other than rare earth compounds. The following treatment was performed using this material. An appropriate amount of water was added to the composition (4), concentrated hydrochloric acid (35% -HCl) was added, and the mixture was reacted at 75 ° C. for 12 hours to dissolve the components.

Thereafter, aqueous ammonia (25% -NH ₄ 0H) was added while confirming the pH to adjust to pH 8. Suspend the precipitated components, add hydrogen peroxide (70% concentration -H ₂ 0 ₂ ) to adjust the pH to 4.5-5, react until hydrogen peroxide decomposes, and add tetravalent cerium hydroxide. Allowed to settle. Excess water was removed by a filter press method. As a result, the following adsorbent was obtained and named “Composition D”.
Composition D Ce (OH) ₄ : 33% La (OH) ₃ : 11% Nd (OH) ₃ : 3% Pr (OH) ₃ : 3% Other 5% Moisture content: 45%

(Comparative Example 1)
In order to produce the adsorbent of the comparative example, a waste abrasive having the following composition (2) was used.
<Waste abrasive composition (2)>
CeO ₂ : 5% Ce ₂ 0 ₃ : 15% La ₂ 0 ₃ : 5% A1 ₂ 0 ₃ : 15% Other 5% Moisture content: 55%

  This waste abrasive uses polyaluminum chloride as an inorganic aggregate. The dehydration method is a filter press method. The waste abrasive composition was processed according to the method of Patent Document 3 (Japanese Patent Laid-Open No. 2001-200266) using the composition (2).

Add 5 L of hydrochloric acid (5M-HCl) and 25 L of pure water to 100 g of waste abrasive, stir, heat-treat at 130 ° C for 1 hour and 30 minutes, cool, and then check the pH with NaOH. The solid was obtained by adjusting to 6-7 and centrifuging. As a result, the following adsorbent was obtained and named “Composition E”.
Composition E Ce (OH) ₃ : 16% Ce (OH) ₄ : 6% La (OH) ₃ : 6% Al (OH) ₃ : 16% Other 6% Moisture content: 50%

Table 1 summarizes the adsorbents obtained in Examples 1 to 4 and Comparative Example, that is, compositions A to E. In Table 1, the unit is mass%, and the parentheses indicate the proportion of each component in the solid component. In all Examples, a tetravalent cerium compound (Ce (OH) ₄ ) was contained in an amount of 10% by mass or more, and the ratio in the solid component was also contained in an amount of 20% by mass or more. It can be seen that an adsorbent containing a large amount of tetravalent rare earth metal compound can be obtained by the present invention.

(Confirmation of effect)
<Adsorption capacity evaluation method>
0.25 g of the adsorbents of composition A to E was weighed, put into 25 ml of various component solutions having a concentration of 100 mg / L, shaken for 24 hours, filtered, and the filtrate was used as a measurement solution. Table 1 shows the adsorption capacities (mg) of various components per gram of the press cake product of the adsorbents having the compositions A to E. Arsenic (As), chromium (Cr: hexavalent), selenium (Se: tetravalent), selenium (Se: hexavalent), boron (pH 6.5), mercury (mercury nitrate) are quantified by ICP analysis. It was.

In addition, the reagent used as said various components is as follows.
Arsenic: Na ₂ HAsO ₄
Boron: Fluorine metaborate: NaF
Hexavalent chromium: Potassium dichromate, nitric acid (0.01 mol / 1) mercury <mercury nitrate>: Mercuric nitrate, nitric acid (0.5 mol / l) solution Selenium (tetravalent): Selenium oxide (IV), nitric acid ( 0.1 mol / l) Solution selenium (hexavalent): Sodium selenium (VI) acid (Na ₂ SeO ₄ ) dissolved in acid and used.

  As shown in Table 2, the adsorption capacity of the obtained adsorbent was increased by about 1.5 times by incorporating a rare earth compound oxidation process when treating used abrasives (Examples 1 and 2). . Further, by using a combination of an iron-based inorganic agglomerated material in the used abrasive recovery process as a starting material, the adsorption performance was more than doubled (Example 3). Furthermore, when an unused abrasive is used as a starting material, the unused abrasive contains a high concentration of rare earth metal oxides such as cerium and lanthanum. An agent could be obtained (Example 4).

  The present invention makes it possible to produce an adsorbent that efficiently fixes harmful substances such as arsenic, hexavalent chromium, selenium (tetravalent), selenium (hexavalent), boron, mercury, and antimony. The adsorbent of the present invention can be used as an adsorbent of a contaminating component with respect to contaminated soil and contaminated water, an insolubilizing agent, a fixing agent, a flocculant and the like. Therefore, the adsorbent provided by the present invention can be introduced into a detoxification treatment facility for an object to be adsorbed, which contributes to improvement of the environment.

Claims (11)

  A method for producing an adsorbent, comprising reacting a material containing a rare earth metal oxide with an acidic agent, forming the hydroxide with an alkaline agent, and further oxidizing the hydroxide with an oxidizing agent. .   The method for producing an adsorbent according to claim 1, wherein the rare earth metal oxide and the hydroxide are recovered by a filter press method.   The method for producing an adsorbent according to claim 1 or 2, wherein a material containing an iron-based flocculant in addition to the rare earth metal oxide is used.   The rare earth metal is at least one selected from the group consisting of cerium (Ce), samarium (Sm), neodymium (Nd), gadolinium (Gd), lanthanum (La), yttrium (Y), and praseodymium (Pr). It exists, The manufacturing method of the adsorption agent as described in any one of Claims 1-3 characterized by the above-mentioned.   The oxidizing agent comprises hydrogen peroxide, potassium permanganate, potassium dichromate, sulfur dioxide, chlorine, sodium bismuth, persulfate, bromate, hypochlorite and hypobromite. The method for producing an adsorbent according to any one of claims 1 to 4, wherein the adsorbent is at least one selected from the group.   The adsorbed material adsorbed by the adsorbent is at least one selected from the group consisting of arsenic, fluorine, boron, lead, cadmium, mercury, antimony, chromium, molybdenum, selenium, phosphorus, thallium, indium and bismuth. The method for producing an adsorbent according to any one of claims 1 to 5, wherein the adsorbent is provided.   An adsorbent comprising, as a main component, a rare earth metal compound obtained by oxidizing a rare earth metal hydroxide.   The rare earth metal is at least one selected from the group consisting of cerium (Ce), samarium (Sm), neodymium (Nd), gadolinium (Gd), lanthanum (La), yttrium (Y), and praseodymium (Pr). The adsorbent according to claim 7, wherein the adsorbent is present.   The adsorbent to be adsorbed by the adsorbent is at least one selected from the group consisting of arsenic, fluorine, boron, lead, cadmium, mercury, antimony, chromium, molybdenum, selenium, phosphorus, thallium, indium and bismuth. The adsorbent according to claim 7 or 8, wherein the adsorbent is present.   The adsorbent according to any one of claims 7 to 9, wherein the content of the tetravalent cerium compound is 10% by mass or more.   11. The adsorbent according to claim 7, wherein a content of the tetravalent cerium compound is 20% by mass or more among solid components contained in the adsorbent. .