Quantitative determination of rare earth elements

Abstract

To provide a method of accurately quantifying rare earth elements in a rare earth oxalic acid compound by a dry method.SOLUTION: A rare earth element quantification method and related techniques are provided, the method involving supplying 5 mol or more of oxygen to a furnace per 1 mol of a rare earth oxalate when supplying oxygen or a gas containing oxygen into the furnace while furnace temperature is in a range of 300-500°C during a process of heating and oxidatively decomposing the rare earth oxalate in the furnace while increasing the temperature.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for quantitatively determining the amount of rare earth elements in rare earth compounds, and more particularly to a method for quantitatively determining the amount of rare earth elements with high accuracy by converting rare earth oxalate compounds into oxides. [Background technology]

[0002] Generally, rare earth elements refer to scandium, yttrium, and lanthanides (lanthanum, etc.). These elements can be added to alloys with other metal elements to improve durability and magnetic properties, for example. For this reason, rare earth elements are used in a variety of electronic components.

[0003] Rare earth elements exist in rare earth compounds produced from mines, etc. However, because the production of rare earth compounds is limited, their prices are comparable to those of precious metals. As a result, when trading rare earth compounds, it is necessary to calculate the content of rare earth elements in rare earth compounds accurately and with little error.

[0004] Rare earth compounds come in various forms. A wet method is known for determining the content of rare earth elements, in which rare earth compounds such as rare earth hydroxides and rare earth organic acid compounds are dissolved in acid, and the resulting solution is quantified using ICP emission spectrometry, atomic absorption spectrometry, or ICP mass spectrometry. However, these methods have a relative standard deviation of about 1-2%, and this error directly affects the transaction amount, so they cannot be considered optimal.

[0005] On the other hand, a dry method for quantifying rare earth elements in rare earth compounds is also known. Non-Patent Document 1 describes a method in which the magnesium alloy to be quantified is heated and sintered to convert the rare earth elements into oxides, and then the rare earth elements are analyzed by a gravimetric method. In Non-Patent Document 1, the rare earth elements in the magnesium alloy are separated as oxalates, the filter paper is incinerated at around 500°C, and the rare earth elements are converted into oxides at 950°C, and the total content of the rare earth elements is calculated from the weight. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] JIS H1345:1998 "Quantitative method for rare earth elements in magnesium alloys" Summary of the Invention [Problem to be solved by the invention]

[0007] The method described in Non-Patent Document 1 is a method for quantitatively separating rare earth elements as oxalates. Non-Patent Document 1 describes that when the rare earth content is between 5% (m / m) and 10% (m / m), the sample weight is 1 g. Values ​​over 10% (m / m) are not described. In other words, according to the contents of Non-Patent Document 1, the rare earth element content has an upper limit of 100 mg (= 10% (m / m) x 1 g). Considering the accuracy of the balance, the method of Non-Patent Document 1 cannot be said to be suitable for analysis that requires accuracy.

[0008] Non-Patent Document 1 does not specifically describe the firing method other than the temperature. If the method of Non-Patent Document 1 is carried out in a closed furnace, the necessary oxygen will be insufficient when the filter paper is incinerated or when the rare earth oxalate is oxidized and decomposed, resulting in incomplete combustion. In that case, soot (carbon) will remain in the furnace or sample, which may cause a positive error when weighing the remaining rare earth oxide by gravimetry.

[0009] Generally, carbon decomposes in air at about 500°C (i.e., carbon turns into CO2), but in a reducing atmosphere with insufficient oxygen, it is difficult to decompose until it reaches 1000°C or higher. In a reducing atmosphere with insufficient oxygen, it may not be possible to decompose at the 950°C described in Non-Patent Document 1.

[0010] An object of the present invention is to provide a method for accurately quantifying rare earth elements in rare earth oxalate compounds in a dry manner. [Means for solving the problem]

[0011] As a result of extensive research to achieve the above-mentioned object, the inventors have discovered that the generation of carbon due to a lack of oxygen can be prevented by introducing a certain amount of oxygen in a temperature range just before carbon becomes CO2 and at which organic matter is easily oxidized and decomposed (i.e., carbon-containing groups are easily released from rare earth elements).

[0012] The aspects of the present invention made based on the above findings are as follows. The first aspect of the present invention is This is a method for quantifying rare earth elements in the process of heating and oxidatively decomposing rare earth oxalates in a furnace, in which oxygen or a gas containing oxygen is supplied into the furnace when the furnace temperature is between 300°C and 500°C, and at least 5 moles of oxygen are supplied into the furnace for every 1 mole of rare earth oxalate.

[0013] The second aspect of the present invention is the invention according to the first aspect, For every 1 mole of rare earth oxalate, 20 moles or more of oxygen is supplied into the furnace.

[0014] A third aspect of the present invention is the invention according to the first or second aspect, The rare earth element of interest is scandium, When the rare earth element is taken as 100% by weight, the content of metal elements other than the rare earth element is less than 0.1% by weight.

[0015] A fourth aspect of the present invention is the invention according to any one of the first to third aspects, When the temperature inside the furnace is between 300°C and 500°C, oxygen or a gas containing oxygen is supplied into the furnace, and then the inside of the furnace is heated to 800°C or higher.

[0016] A fifth aspect of the present invention is the invention according to any one of the first to fourth aspects, The heating rate during heating is 50°C / min or less from 300°C to 500°C.

[0017] A sixth aspect of the present invention is the invention according to any one of the first to fifth aspects, The furnace is a closed furnace.

[0018] A seventh aspect of the present invention is a method for quantifying a rare earth element, which calculates the content of the rare earth element from the rare earth oxide produced in the invention according to any one of the first to sixth aspects. Effect of the Invention

[0019] According to the present invention, a method for accurately quantifying rare earth elements in rare earth oxalate compounds in a dry manner can be provided. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] The embodiments of the present invention are described below. In this specification, "to" indicates a value greater than or equal to a given value and less than or equal to a given value. Note that the present invention is not limited to the following embodiments, and can be modified as appropriate without departing from the gist of the present invention.

[0021] The present embodiment has the following configuration. "A method for quantifying rare earth elements in the process of heating and oxidizing rare earth oxalates (rare earth compounds) in a furnace, in which oxygen or a gas containing oxygen is supplied into the furnace when the furnace temperature is between 300°C and 500°C, and 5 moles or more of oxygen is supplied into the furnace for each mole of rare earth oxalate."

[0022] Rare earth compounds include oxides, hydroxides, sulfates, oxalates, and their complex salts. These can be converted to stable oxides by oxidation. For example, scandium oxalate, one of the rare earth oxalates, can produce scandium oxide by the reaction shown in the following formula 1. Sc2[(COOH)2]3+3 / 2O2→Sc2O3+6CO2↑ (Formula 1)

[0023] There is no limitation on the content of rare earth elements in the rare earth compound, but as shown in the Examples section below, this embodiment is applicable even when the rare earth compound contains more than 10% by weight of rare earth elements (or 15% by mass or more, or 20% by mass or more).

[0024] In addition, when the rare earth element (e.g., scandium) to be quantified in the rare earth compound to be heated in the furnace is taken as 100% by weight, the content of elements other than the rare earth element is preferably less than 0.1% by weight, more preferably less than 0.01% by weight. In the above example, the metal elements other than the rare earth element to be quantified are elements other than scandium (e.g., yttrium, iron, sodium, etc.), excluding hydrogen, rare gas elements, carbon, nitrogen, and oxygen.

[0025] By converting the rare earth oxalates into their oxides, the weight of the rare earth elements can be calculated from the weight of the oxides, and the content of the rare earth elements in the sample can be calculated by knowing the original sample weight.

[0026] However, the inventors have found a problem with Non-Patent Document 1, namely, in order to obtain an oxide for accurately quantifying oxalate, it is necessary to supply oxygen during the reaction, as shown in formula 1.

[0027] If the oxygen supply is insufficient, it becomes difficult for oxalic acid to completely oxidize and decompose, resulting in a non-oxidizing atmosphere that is more likely to produce carbon. Specifically, in the above formula (1), before scandium oxide, i.e., Sc2O3, is obtained, it becomes easier for carbon monoxide, carbon dioxide, and carbonate ions to be coordinated with scandium to be produced. This is ultimately one of the causes of the carbon mentioned above. Once carbon is produced, it remains as a residue because its decomposition temperature is over 1000°C. When this happens, the amount of carbon is added to the weight of the oxide, making it impossible to accurately calculate the weight of the rare earth element.

[0028] Thermal analysis has revealed that in the oxidative decomposition reaction by heating in an oxygen atmosphere, the oxidative decomposition reaction occurs significantly (i.e., decarbonization from scandium oxalate occurs) in the temperature range of 300°C to 500°C (or 600°C). In this temperature range, it is desirable to introduce oxygen or a gas containing oxygen, such as air, into the reaction site (so-called furnace) to promote the reaction.

[0029] There is no limitation on the furnace, and it may be a closed furnace (e.g., a furnace that can be opened and closed with a lid) or an open-air furnace (e.g., one without a lid). However, the problems of the present invention become more serious in a closed furnace, and it is also a closed furnace that can remarkably enjoy the effects of the present invention. In any case, the vessel for oxidizing the rare earth compound by heating is called the furnace, and the part in which the rare earth compound is placed is called the inside of the furnace.

[0030] Considering the above formula 1, for example, in the case of scandium oxalate, 1.5 moles of oxygen are required per mole. On the other hand, in reality, it is difficult to contribute all of the oxygen in the furnace used during firing to the reaction. In view of this, it is preferable to supply 5 moles or more of oxygen to the furnace per mole of rare earth oxalate, more preferably 7 moles or more, even more preferably 10 moles or more, and particularly preferably 20 moles or more. The "amount of oxygen supplied to the furnace" here refers to the amount of oxygen in the total supply of oxygen or oxygen-containing gas.

[0031] There is no limitation on the method of heating, but combustion heating is preferable to realize heating to several hundred degrees C. There is no limitation on the method of heating, but examples include an electric furnace and a gas furnace.

[0032] The temperature inside the furnace may be measured, for example, by a thermometer attached to the top plate or side wall when a closed furnace is used, or may be measured, for example, by a thermometer attached to the side wall when an open-air furnace is used.

[0033] Oxygen or a gas containing oxygen includes oxygen gas, a mixed gas of oxygen and other substances (nitrogen, rare gases, etc.), and air. Moreover, oxygen as used herein includes heavy oxygen.

[0034] There is no limitation on the method for supplying oxygen or a gas containing oxygen into the furnace. In the case of a closed furnace, the gas may be introduced from outside the furnace toward the inside of the furnace. In this case, even if the gas is introduced, the temperature inside the furnace should not deviate from the range of 300 to 500° C. Also, exhaust is performed to keep the pressure inside the furnace at a moderate level. In the case of an open-type furnace, air may be introduced and exhausted by penetrating the side wall of the furnace into the furnace, and in the case of a closed furnace, air or oxygen may be introduced through an inlet and exhausted through an exhaust port.

[0035] Among rare earth compounds, the following findings have also been made regarding rare earth oxalates. That is, when heating rare earth oxalates, the generation of carbon or the occurrence of dissipation due to ignition or the like that would prevent quantitative measurement can be suppressed by controlling the heating rate. Specifically, the heating rate is preferably 70°C / min or less at 300°C to 500°C, more preferably 50°C / min or less. There is no lower limit to the heating rate, but in consideration of work efficiency, for example, 1°C / min, preferably 10°C / min, can be mentioned.

[0036] When the temperature inside the furnace is between 300°C and 500°C, oxygen or a gas containing oxygen is supplied into the furnace (first heating stage), and then it is preferable to heat the furnace to 800°C or higher (second heating stage). This makes it possible to further suppress the generation of carbon and carbon monoxide, and to convert all of the rare earths in the rare earth compounds into rare earth oxides.

[0037] If there is residual oxygen in the reaction field, the oxidation reaction will proceed even at temperatures above 500°C. In that case, the oxidation reaction will not proceed even if the reaction field is heated to 800°C or higher, and there is no need to heat the reaction to temperatures above 800°C (the second heating step).

[0038] Through the above operations, the content of the rare earth element is calculated from the rare earth oxide. For example, the calculation method may be to calculate the weight of the rare earth element from the weight of the oxide as described above. EXAMPLES

[0039] The present embodiment will be described below, however, the technical scope of the present invention is not limited to the following embodiment.

[0040] <Examples 1 and 2, Comparative Examples 1 and 2> In each of the examples described below, a balance made by Saritorius EXTEND, a closed muffle furnace made by Yamato Scientific FP412, and a magnetic crucible made by Nikkato were used.

[0041] 1 g to 2 g of scandium oxalate was weighed out into a porcelain crucible, which was then placed in a muffle furnace and heated at a heating rate of 10° C. per minute. The weighed amounts in each example are shown in Table 1 below.

[0042] From 300°C to 500°C (heating for 20 minutes at 10°C per minute), in the examples, air was introduced into the furnace at 300 ml per minute. The introduction method was to introduce air into the furnace by a pump through a pipe from a through hole in the muffle furnace. The amount of air introduced and the amount of oxygen in each example are as shown in Table 1 below. The amount of oxygen (M) can be calculated from the heating time, the total amount of air introduced, and the oxygen content in the air.

[0043] Then, from 500°C to 800°C, the introduction of air was stopped and the temperature was increased at a rate of 10°C per minute.

[0044] Heating was stopped at 800°C, and the specimen was allowed to cool to room temperature, after which the remaining amount was weighed on a balance and the scandium content was calculated assuming the remaining amount to be scandium oxide. The results for each example are shown in Table 1.

[0045] On the other hand, in Comparative Example 1, the amount of air introduced was 50 ml / min. In Comparative Example 2, air was initially present in the furnace, but after the start of heating, air was not introduced. The other conditions were the same as in Example 1. [Table 1]

[0046] From Table 1, in Comparative Example 1, where the number of moles of oxygen in the total amount of air introduced per mole of scandium oxalate was just over 3 moles, the scandium content was high and coloring was observed in the residue after heating. This coloring was also observed in Comparative Example 2, where the amount of air introduced (i.e., the amount of oxygen supplied) was zero. In these examples, it is presumed that the amount of oxygen supplied was insufficient for the oxidative decomposition reaction, and as a result, undecomposed materials remained, which resulted in the apparent scandium content being calculated to be high.

[0047] On the other hand, in Examples 1 and 2, no coloring was observed as in Comparative Examples 1 and 2, and the scandium content was almost the same, and the scandium content in Examples 1 and 2 was lower than that in Comparative Examples 1 and 2. As a result, it is presumed that almost no carbon residue was generated in Examples 1 and 2, and the values ​​in Examples 1 and 2 are close to the true value. This test result demonstrated the significance of supplying 5 moles or more of oxygen to 1 mole of rare earth oxalate into the furnace.

[0048] <Examples 3 to 5> Tests were conducted in the same manner as in Example 1, except that, among the conditions in Example 1, the temperature inside the furnace was between 300°C and 500°C, and the heating rate when oxygen or a gas containing oxygen was supplied into the furnace was changed as shown in Table 2 below. The results are shown in Table 2. Table 2 also lists the results of Example 1. [Table 2]

[0049] As can be seen from Table 2, in Examples 3 to 5, the scandium content was approximately the same and was lower than the value in Comparative Example 1. This is because there was almost no positive error as in Comparative Example 1.

[0050] On the other hand, in Examples 4 and 5, the samples were slightly dull. Compared with the results of Example 1, there was a slight positive error in Examples 4 and 5. In Examples 4 and 5, the heating rate during heating exceeded 50°C / min from 300°C to 500°C. This test result demonstrated the significance of setting the heating rate during heating to 50°C / min or less from 300°C to 500°C.

Claims

1. In a process of heating and oxidatively decomposing a rare earth oxalate not containing filter paper in a furnace, when oxygen or a gas containing oxygen is supplied into the furnace at a furnace temperature between 300° C. and 500° C., 10 moles or more of oxygen are supplied into the furnace per mole of the rare earth oxalate to promote the oxidative decomposition reaction; A method for quantifying rare earth elements, wherein the content of metal elements other than the rare earth elements is less than 0.1% by weight when the rare earth elements to be quantified are taken as 100% by weight.

2. 2. The method for quantifying rare earth elements according to claim 1, wherein 20 moles or more of oxygen are supplied to the furnace per mole of rare earth oxalate.

3. 3. The method for quantifying a rare earth element according to claim 1, wherein the rare earth element to be quantified is scandium.

4. 4. The method for quantifying rare earth elements according to claim 1, wherein oxygen or a gas containing oxygen is supplied into the furnace when the temperature inside the furnace is between 300° C. and 500° C., and then the inside of the furnace is heated to 800° C. or higher.

5. The method for quantifying rare earth elements according to any one of claims 1 to 4, wherein the heating rate during heating is 50°C / min or less from 300°C to 500°C.

6. The method for quantifying rare earth elements according to any one of claims 1 to 5, wherein the furnace is a closed furnace.

7. A method for quantifying rare earth elements, comprising calculating the content of rare earth elements from the rare earth oxide produced by the method according to any one of claims 1 to 6.

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