JPS6133622B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is an inorganic material that has a layered crystal structure and has the property of selectively capturing Li ⁺ from cations.
It concerns Li ⁺ selective ion exchangers. Alkali titanate having a layered crystal structure represented by A ₂ Ti _o O _2o+1 (A is an alkali metal, n is 3 or 4) (hereinafter abbreviated as "A-type compound")
In , the bond between the alkali metal ion (A ⁺ ) between the layers and the oxygen in the (Ti _o O _2o+1 ) ^2- layer of the host is relatively weak, so A ⁺ has a cation exchange ability. The present inventors particularly treated the A-type compound with an acid to form a compound having the composition of H ₂ Ti ₃ O ₇ (hereinafter abbreviated as "NaH-type compound") and H ₂ Ti ₄ O ₉ .
Compounds with the composition H ₂ O (hereinafter referred to as "KH type compounds")
It has been discovered that various cations (inorganic and organic cations) can be incorporated between the layers formed by (Ti _o O _2o+1 ) ^2- with high efficiency. In other words, it has been found that these compounds can function as ion exchangers. The present invention has further advanced research based on this technical background, and has succeeded in providing an ion exchanger having the property of selectively taking in Li ⁺ from cations in particular. That is, the present invention provides a NaH type compound obtained by acid treatment of Na ₂ Ti ₃ O ₇ having a layered crystal structure as a Li ⁺ selective ion exchanger. A in the type A compound, ie, the compound represented by A ₂ Ti _o O _2o+1 , generally includes various alkali metals such as sodium (Na) and potassium (K). However, sodium trititanate with n=3 and n
It is limited to those using potassium tetratitanate of =4 as a starting material. This is because this type of A-type compound has a stable layered crystal structure. These A
Of course, type compounds can be used as cation exchangers as they are, but compounds that have been treated with an acid, that is, NaH type and KH type compounds, are used as cation exchangers when directly adding cations to the A type compounds. This is based on the experience that it is difficult to properly incorporate the ions between the layers formed by (Ti _o O _2o+1 ) ^2- when reacted with (Ti o O 2o+1 ) 2-. and,
The reason why an alkaline titanate ion exchanger with a high cation exchange capacity is obtained when sodium trititanate or potassium tetratitanate is treated with acid to dealkalize it is due to the basicity between H ⁺ and other cations. This is thought to be due to the fact that a difference occurs, which becomes the driving force for the reaction. In addition, in research by the present inventor, a compound obtained by acid treatment of Na ₂ Ti ₃ O ₇ was found to be
It is clear that it has a composition of H ₂ Ti ₃ O ₇ . In this way, NaH type compounds or KH type compounds obtained by acid-treating an A type compound having a layered crystal structure and dealkalizing the interlayer alkali,
Protons between the layers and various cations can be easily ion-exchanged, and it can be used as a highly efficient ion exchanger. In the case of NaH-type compounds, as shown in the examples below, the reaction rate differs greatly in the ion exchange reaction with alkali metal ions, and the ions with smaller ionic radius are incorporated into the layer faster, resulting in Li ⁺ >Na It becomes slower in the order of ⁺ > K ⁺ . Therefore, Li ⁺ is taken up from the mixed alkaline aqueous solution the fastest, and selectivity for Li ⁺ is expressed. On the other hand, with KH-type compounds, there is no significant difference in reaction rate, and therefore, when the purpose is to selectively adsorb Li ⁺ with the smallest ionic radius from inorganic ions, KH-type compounds are a sufficient selection. Therefore, only NaH type compounds, that is, compounds having a composition of H ₂ Ti ₃ O ₇ effectively exhibit Li ⁺ selectivity. Based on this knowledge, the present invention uses the above-mentioned ion exchanger as an ion exchanger having Li ⁺ selectivity.
This allows us to provide a new H ₂ Ti ₃ O ₇ compound.
According to the present invention, it is possible to selectively recover Li ⁺ mixed in various inorganic ions and organic ions, which contributes to the effective use of valuable Li resources. In other words, the abundance of Li in the earth's crust is small.
Although the amount is only 20ppm, its uses are wide-ranging, such as as materials for nuclear fusion reactors and lithium batteries, and as the demand for it is expected to increase in the future, an effective means of recovering it will be put into practical use. The benefits associated with this are considered to be very large. Examples of the present invention and comparative examples will be described below. Example Titanium dioxide (TiO ₂ ) and sodium carbonate (Na ₂ CO ₃ ), which are special grade reagents, were mixed at a molar ratio of 2.9:1, and the mixture was placed in a porcelain crucible and heated at 800°C in an electric furnace for 20 hours. Fired. After thoroughly pulverizing and mixing this, it was calcined again at a temperature of 800° C. for 20 hours to obtain a white powder of sodium trititanate (one of the A-type compounds mentioned above, referred to as an Na-type compound). Next, 1 g of this Na-type compound was added to 0.1N, 0.5N and 1.0N.
It was immersed in 200 ml of specified hydrochloric acid and allowed to react at a temperature of 60°C for 3 days. At this time, the reaction aqueous solution was stirred with a stirrer for 3
The procedure of stirring for a certain period of time, then allowing it to stand, removing the supernatant liquid, and adding fresh aqueous hydrochloric acid solution was repeated five times to complete the progress of the reaction. As a result, all reaction products were the same compound (NaH type compound). NaH type compounds will be described below. The following experimental results confirmed that the NaH type compound has a composition of H ₂ Ti ₃ O ₇ . It was confirmed by atomic absorption spectrometry of the aqueous solution that NaH-type compounds contain almost no alkali metals. Also,
The Na-type compound is a monoclinic compound, and the inventors also indexed the NaH-type compound based on the monoclinic system. Their lattice constants are: Na type compound a = 8.571 Å, b = 3.804 Å, c = 9.135 Å, β = 101.57° NaH type compound a = 8.080 Å, b = 3.752 Å, c = 9.178 Å, β = 101.27° The value of a, which corresponds to the interlayer distance, decreased due to the acid treatment, but the values of b, c, and β did not change significantly. This indicates that the interlayer Na ⁺ of the NaH type compound was replaced by small H ⁺ by the acid treatment, and that the structure of the host (Ti ₃ O ₇ ) ^2- layer was maintained. Furthermore, when differential thermal analysis was performed on NaH-type compounds in the range from room temperature to 800℃, there was no change up to 250℃, and between 250 and 360℃.
An endothermic peak accompanied by weight loss was observed at °C.
From this weight loss, the amount of H ₂ O in the NaH type compound was determined. Furthermore, when the infrared absorption spectrum of the NaH type compound was measured, stretching vibrations of H-O were observed at 3050 to 3300 cm ^-1 , indicating a H-O bond, but at 1600 cm
Bending vibration of H-O-H near ^-1 was not observed, indicating that NaH-type compounds do not have interlayer water, and the incorporated H ⁺ becomes structural water between the layers. Its composition is H It turned out to be ₂ Ti ₃ O ₇ . We also investigated the cation exchange properties of this NaH type compound. First, add 0.1M ACl to 0.5g of NaH type compound.
and AOH (A is Li, Na or K) aqueous solution 40ml
were added according to the composition shown in Table 1, and an ion exchange reaction was carried out at a temperature of 60° C. for 3 days.

[Table] The reaction products were analyzed using X-ray diffraction, atomic absorption spectrometry, colorimetry, differential thermal analysis, etc.
Table 2 shows the chemical formulas of each reaction product calculated based on these results.

[Table] Thus, it was found that the NaH type compound hardly undergoes an ion exchange reaction while immersed in an aqueous chloride solution. On the other hand, it was found that when immersed in an aqueous hydroxide solution, 15 to 63% of the interlayer H ⁺ of the NaH type compound was ion-exchanged to A ⁺ , although this differed depending on the type of A ⁺ . Since there is a large difference in the ion exchange rate between chloride and hydroxide aqueous solutions, we next investigated the PH dependence of this reaction. 0.1M NaCl
Mix NaOH aqueous solution, pH is 8.0, 9.0, 10.0,
Aqueous solutions of 11.0, 12.0 and 12.5 were prepared, and 0.5 g of the NaH type compound was added to 40 ml of each of these aqueous solutions, and an ion exchange reaction was carried out at a temperature of 60° C. for 3 days. The results are shown in Figure 1. Thus, the ion exchange rate was expressed by a curve with a sharp rise around pH 11 to 12, indicating that the ion exchange rate was high in the high pH range. Next, in a hydroxide aqueous solution showing a high exchange rate,
We investigated the time course of the ion exchange reaction of NaH-type compounds. 0.5g of NaH-type compound and 0.1M AOH (A is Li,
40 ml of an aqueous solution (Na and K) was added and ion exchange reactions were carried out at a temperature of 60° C. for 1 hour, 3 hours, 6 hours, 1 day, 2 days and 3 days, respectively. The results are shown in Figure 2. The ion exchange rate is
In a 0.1M LiOH aqueous solution, it becomes about 45% in 1 hour, increases with time, reaches about 63% in 2 days, and then remains almost constant. In a 0.1M NaOH aqueous solution, it becomes about 18% in 1 hour, then increases with time, reaching about 44% in 3 days. 0.1M
In a KOH aqueous solution of , it is about 5% in 1 hour, and increases to about 11% over the next 3 days. In this way, since the reaction with Li ⁺ is the fastest, Li ⁺ is taken up from the mixed alkaline aqueous solution the fastest, and the following experiment was conducted based on the assumption that the Li ⁺ selectivity caused by this would be expressed. The ion selectivity of ion exchange reactions for Li ⁺ , Na ⁺ and K ⁺ was investigated. 0.1M LiOH,
Add 0.5 g of NaH type compound to a mixed aqueous solution of 40 ml each of NaOH and KOH aqueous solutions,
The ion exchange reaction was carried out for 3 days at a temperature of .degree. As a result, the molar ratio of Li:Na:K in the reaction product was 1.00:0.26:0.01, and it was found that Li ⁺ with the smallest ionic radius was incorporated the most. In other words, the exchange amount of Li ⁺ is the second largest
It shows extremely high Li ⁺ selectivity, four times that of Na ⁺ . Comparative Example Titanium dioxide and potassium carbonate (K ₂ CO ₃ ), which are special grade reagents, were mixed at a molar ratio of 3.5:1 and calcined under the same conditions as in the example. One of them was called a K-type compound). Next, 1 g of this K-type compound was acid-treated under the same conditions as in the example. As a result, all reaction products were the same compound (KH type compound). The KH type compounds will be described below. It was confirmed from the following experimental results that the KH type compound has a composition of H ₂ Ti ₄ O _{9.H 2} O. It was confirmed by atomic absorption spectrometry of the aqueous solution that the KH type compound does not contain alkali metal ions. In addition, K-type compounds are monoclinic compounds, and KH
For type compounds, the inventors also indexed them based on the monoclinic system. Their lattice constants are: K type compound a = 18.25 Å, b = 3.791 Å, c = 12.01 Å, β = 106.4° KH type compound a = 18.77 Å, b = 3.750 Å, c = 11.62 Å, β = 104.6° The acid treatment increased the value of a corresponding to the interlayer distance, but the other values of b, c, and β did not change significantly. This means that the interlayer K ⁺ (radius 1.33 Å) of the K-type compound is slightly larger than the hydronium ion.
This shows that H ₃ O ⁺ (1.40 Å) was substituted, and the structure of the host (Ti ₄ O ₉ ) ^2- layer was maintained. Furthermore, when differential thermal analysis was performed on the KH type compound in the range from room temperature to 800°C, endothermic peaks accompanied by weight loss were observed at 40-90°C and 90-250°C. From this weight loss, the amount of H ₂ O in the KH type compound was determined. Furthermore, when the infrared absorption vector of the KH type compound is measured, the H ^- O stretching vibration and
The bending vibration of H-O-H near 1600 cm ^-1 was observed, indicating the presence of H ₂ O. From the above, it is clear that H ₃ O ⁺ incorporated into the KH type compound becomes free water (interlayer water) between the layers, and its composition is
It was found to be H ₂ Ti ₄ O ₉ ·H ₂ O. We also investigated the cation exchange properties of this KH type compound. First, 0.5g of KH type compound, 0.1M ACL and
Add 40ml of AOH (A is Li, Na or K) aqueous solution to the third
The combinations shown in the table were added and an ion exchange reaction was carried out at a temperature of 60 degrees for 3 days.

【table】

[Table] The reaction products were analyzed in the same manner as in Example 2. Table 4 shows the chemical formulas of each reaction product calculated based on those results.

[Table] Thus, it was found that the KH type compound hardly caused an ion exchange reaction while immersed in an aqueous chloride solution. On the other hand, when immersed in an aqueous hydroxide solution,
Although it depends on the type of A ⁺ , the interlayer of KH type compound
It was found that 75-85% of H ⁺ and H ₃ O ⁺ was ion-exchanged to A ⁺ . Next, the PH dependence of the reaction was investigated in the same manner as in the examples.
Mix 0.1M KCl and KOH aqueous solutions and adjust the pH.
Aqueous solutions of 8.0, 9.0, 10.0, 11.0, 12.0 and 12.5 were prepared, and 0.5 g of the KH type compound was added to each of 40 ml of these aqueous solutions, and an ion exchange reaction was carried out at a temperature of 60° C. for 3 days. The results are shown in Figure 3. In this way, the ion exchange rate was expressed by a curve with a sharp rise around pH 11 to 12, indicating that the ion exchange rate was high in the high pH range. In hydroxide aqueous solution showing the next highest exchange rate
We investigated the time course of the ion exchange reaction of KH type compounds. 0.1M AOH (A is Li,
40 ml of an aqueous solution (Na and K) was added, and the ion exchange reaction was carried out at a temperature of 60° C. for 1 hour, 3 hours, 6 hours, 1 day, 2 days, and 3 days, respectively. The results are shown in Figure 4. The ion exchange rate is
In a 0.1M LiOH aqueous solution, it reaches about 75% in one hour and remains almost constant at this value thereafter. 0.1M
In NaOH aqueous solution, about 60% in 1 hour, about 60% in 2 hours
65%, then reaches about 70% and remains almost constant.
In a 0.1M KOH aqueous solution, it reaches approximately 82% in 1 hour and remains approximately constant at this value thereafter. Thus, in KH type compounds, Li ⁺ , Na ⁺ and K ⁺
All reactions were rapid, and no difference in reaction rate was observed. Finally, the ion selectivity of the ion exchange reaction for Li ⁺ , Na ⁺ and K ⁺ was investigated. 0.1M
40ml each of LiOH, NaOH and KOH aqueous solutions
0.5 g of the KH type compound was added to the mixed aqueous solution, and an ion exchange reaction was carried out at a temperature of 60° C. for 3 days. As a result, Li:Na:K in the reaction product
The molar day of is 1.00:0:0.51, and it was found that, like the NaH type, Li ⁺ with the smallest ionic radius is taken in the most. But in this case Li ⁺
The amount of the following ions almost doubles, and the exchange amount of Li ⁺ is only about twice that of K ⁺ , which is the second largest, so the Li ⁺ selectivity is insufficient.

[Brief explanation of the drawing]

1 and 2 show embodiments of the present invention;
The figure is a graph showing the pH dependence of the ion exchange reaction of the NaH type compound, and Figure 2 is a graph showing the time course of the ion exchange reaction of the NaH type compound in an aqueous alkali hydroxide solution. Figures 3 and 4 show comparative examples;
FIG. 3 is a graph showing the pH dependence of the ion exchange reaction of the KH type compound, and FIG. 4 is a graph showing the time course of the ion exchange reaction of the KH type compound in an aqueous alkali hydroxide solution.

Claims (1)

[Claims] 1. A Li ⁺ selective ion exchanger comprising a compound having a composition of H ₂ Ti ₃ O ₇ obtained by acid treatment of Na ₂ Ti ₃ O ₇ having a layered crystal structure.