Method for producing lead iodide

Abstract

To provide a method for industrially advantageously producing lead iodide of high purity and low water content in good yield.SOLUTION: The method for producing lead iodide includes a step of bringing lead oxide into contact with hydroiodic acid.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing lead iodide, and more particularly to an industrially advantageous method for producing lead iodide with high purity and low water content. [Background technology]

[0002] Lead iodide is useful in a variety of applications, including as an anode active material in solid electrolyte batteries, paints, pigments, and materials for detectors of X-rays and gamma rays, and more recently as a raw material for perovskite solar cells. Patent Document 1 discloses a method for producing lead iodide for solid electrolyte batteries, in which the reaction molar ratio of a water-soluble lead salt such as lead nitrate to hydroiodic acid or an alkali metal salt thereof is increased to be greater than the theoretical reaction molar ratio, and hydroiodic acid or an alkali metal salt thereof is reacted with lead nitrate. Non-Patent Document 1 investigates the effects of pH and lead nitrate concentration during the reaction when lead iodide is produced by reacting lead nitrate with potassium iodide using a double jet precipitation method. Patent Document 2 discloses a method for producing hydroiodic acid, which includes a step of heat-treating an aqueous solution containing formic acid and iodine, the aqueous solution having a total concentration of iodine and iodide ions within a predetermined range, and a method for obtaining an aqueous metal iodide solution by mixing the hydroiodic acid with a metal compound. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 59-009858 [Patent Document 2] Japanese Patent Application Publication No. 2018-111618 [Non-patent literature]

[0004] [Non-Patent Document 1] Open Chemistry Journal,2019,6,pp.52-65 Summary of the Invention [Problem to be solved by the invention]

[0005] The method for producing lead iodide disclosed in Patent Document 1 has problems such as the production of nitric acid or nitric acid compounds such as alkali metal nitrates as by-products, which require a large amount of water to remove. In addition, if nitric acid compounds remain in lead iodide, moisture absorption occurs easily, which causes a decrease in the water content and purity of lead iodide. Non-Patent Document 1 describes that when lead nitrate and hydroiodic acid are reacted under neutral or alkaline conditions, a compound with the chemical formula Pb(OH)I is produced as a by-product. It has also been reported that Pb(OH)I decomposes into water, lead iodide, and lead oxide when left unattended (see ACS Materials Lett., 2021, 3, pp. 351-355), and the presence of Pb(OH)I affects the purity and water content of lead iodide. Patent Document 2 only comprehensively lists lead compounds as examples of metal compounds that can be mixed with hydroiodic acid, and does not mention any specific examples of obtaining an aqueous metal iodide solution, much less the possibility of obtaining lead iodide as a solid with high purity. Therefore, there is a need for a method that can produce high-purity lead iodide industrially and advantageously.

[0006] An object of the present invention is to provide a method for producing highly pure lead iodide having a low water content in a high yield and in an industrially advantageous manner. As a result of extensive research, the present inventors have found that the above-mentioned problems can be solved by applying a reaction using lead oxide as a raw material, and have thus completed the present invention. [Means for solving the problem]

[0007] The present invention has the following aspects. [1] A method for producing lead iodide, comprising the step of contacting lead oxide with hydroiodic acid. [2] The method for producing lead iodide according to [1], wherein the concentration of hydrogen iodide in the hydroiodic acid is 5% by mass or more and 57% by mass or less, and the lead oxide is reacted in the presence of 2.2 moles or more and 100 moles or less of hydrogen iodide per mole of lead atoms contained in the lead oxide. [3] The method for producing lead iodide according to [1] or [2], wherein the lead oxide contains a compound represented by PbO. [4] The method for producing lead iodide according to any one of [1] to [3], wherein the content of Pb(OH)I in the reaction mixture is 1 mass % or less based on the total mass of the solid content contained in the reaction mixture. [5] Lead iodide obtained by any of the manufacturing methods [1] to [4], with a water content of 20 ppm or less and a purity of 99.9% or more. [Effects of the Invention]

[0008] According to the present invention, lead iodide having high purity and low water content can be produced industrially advantageously with good yield. DETAILED DESCRIPTION OF THE INVENTION

[0009] The present invention is a method for producing lead iodide, which comprises contacting lead oxide with hydroiodic acid. The lead oxide used in the production method of the present invention may be a compound represented by the chemical formula PbO, or a compound represented by the chemical formula PbO2 or Pb3O4, and these compounds may be used alone or in combination of two or more. Among these, in the production method of the present invention, it is preferable that the lead oxide contains a compound represented by PbO, and it is more preferable to use a compound represented by PbO alone as the lead oxide. Furthermore, from the viewpoint of increasing the purity of lead iodide obtained by the production method of the present invention, it is preferable to use lead oxide having a small content of metal impurities other than lead. In other words, it is preferable to use lead oxide with a purity of 98% or more, more preferably lead oxide with a purity of 99% or more, and even more preferably lead oxide with a purity of 99.9% or more.

[0010] The concentration of hydrogen iodide in the hydroiodic acid used in the production method of the present invention is not particularly limited, but from the viewpoint of smoothly proceeding the reaction, suppressing undesired side reactions, and easily obtaining high-purity lead iodide with good productivity, it is usually preferably 1% by mass or more, more preferably 5% by mass or more, even more preferably 8% by mass or more, and even more preferably 10% by mass or more. Furthermore, from the viewpoint of ease of reaction operation and economic efficiency, the concentration of hydrogen iodide in hydroiodic acid is preferably 57% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less, and even more preferably 20% by mass or less. Note that 57% by mass is the upper limit of the hydrogen iodide content in hydroiodic acid.

[0011] In the production method of the present invention, the amount of hydrogen iodide used relative to lead oxide is usually preferably 2.2 mol or more, more preferably 3 mol or more, and even more preferably 5 mol or more, per mol of lead atom contained in lead oxide, from the viewpoints of smoothly proceeding the reaction and easily obtaining high-purity lead iodide with good productivity. Furthermore, from the viewpoints of ease of reaction operation and economy, the amount of hydrogen iodide used relative to lead oxide is preferably 100 mol or less, more preferably 50 mol or less, and even more preferably 25 mol or less, per mol of lead atom contained in lead oxide. In the production method of the present invention, it is preferable that the concentration of hydrogen iodide in hydroiodic acid is 5% by mass or more and 57% by mass or less, and that lead oxide is reacted in the presence of 2.2 moles to 100 moles of hydrogen iodide per mole of lead atoms contained in the lead oxide.

[0012] The production method of the present invention is characterized by including a step of contacting lead oxide with hydroiodic acid. The contact between lead oxide and hydroiodic acid may be carried out either by adding hydroiodic acid to lead oxide and mixing them, or by adding lead oxide to hydroiodic acid and mixing them. There is no particular restriction on the order of addition, but while lead oxide is poorly soluble in water, for example, contacting powdered lead oxide with hydroiodic acid will cause a reaction to form lead iodide, which also generates reaction heat. Therefore, from the viewpoint of facilitating the reaction operation and reaction control and easily obtaining lead iodide with high purity and high yield, it is preferable to prepare in advance 2.2 to 100 moles of hydrogen iodide per mole of lead atom contained in lead oxide as hydroiodic acid having a hydrogen iodide concentration of 5 to 57 mass%, and then add powdered lead oxide to the prepared solution for reaction. The powdered lead oxide may be added all at once or gradually, but gradually adding the powdered lead oxide is preferable from the viewpoint of facilitating the reaction operation and reaction control.

[0013] Furthermore, the content of Pb(OH)I in the reaction mixture is preferably 1% by mass or less, based on the total mass of the solids contained in the reaction mixture. In other words, the content of Pb(OH)I in the product isolated from the reaction mixture after the reaction is preferably 1% by mass or less, based on the total mass of the product. The content of Pb(OH)I may be below the detection limit. In the production method of the present invention, the pH of the reaction mixture when contacting lead oxide with hydroiodic acid is 1 or less, and it is presumed that the by-production of Pb(OH)I hardly occurs. Therefore, it is believed that high-purity lead iodide can be easily obtained.

[0014] The production method of the present invention may be carried out either in an air atmosphere or in an inert gas atmosphere such as nitrogen, helium, or argon. The production method of the present invention can be carried out under atmospheric pressure, elevated pressure, or reduced pressure, but is preferably carried out under atmospheric pressure from the viewpoint of ease of operation. The reaction temperature varies depending on the concentration of hydroiodic acid, the type of lead oxide used, and the amount of hydrogen iodide relative to the lead atoms contained in the lead oxide, but from the viewpoint of industrially advantageously proceeding with the reaction, it is preferably 0° C. or higher, more preferably 20° C. or higher, and even more preferably 30° C. or higher. The reaction temperature is preferably 100° C. or lower, more preferably 90° C. or lower, and even more preferably 80° C. or lower. The reaction time varies depending on the concentration of hydroiodic acid, the type of lead oxide used, the amount of hydrogen iodide relative to the lead atoms contained in the lead oxide, and the reaction temperature, but is usually in the range of 30 minutes to 48 hours.

[0015] The lead iodide thus obtained can be isolated and purified by methods commonly used for isolating and purifying compounds. For example, the reaction mixture can be filtered to recover the solid, which can then be washed with water and dried to obtain lead iodide. In the production method of the present invention, lead iodide having a water content of 20 ppm or less can be obtained by filtering the reaction mixture and drying the recovered solid. The drying temperature is not particularly limited, but is usually in the range of 10°C to 180°C, and preferably in the range of 25°C to 150°C. The drying time is also not particularly limited, but is usually in the range of 1 minute to 24 hours, and preferably in the range of 10 minutes to 12 hours. The manufacturing method of the present invention uses lead oxide as a raw material, and the product, lead iodide, does not contain impurities derived from nitrate compounds, so the water content can be reduced to 20 ppm or less. The water content of lead iodide after such drying is more preferably 10 ppm or less, and even more preferably 8 ppm or less. The water content after drying at 120°C for 3 hours may be 0 ppm. Furthermore, the production method of the present invention makes it easy to obtain lead iodide with a purity of 99.9% or higher. This purity is preferably 99.95% or higher, and may be 99.98% or higher. As described above, the production method of the present invention does not contain a nitrate compound, so moisture absorption is easily suppressed, and an increase in water content can be suppressed. Furthermore, the production of by-products such as Pb(OH)I, which cause impurities, is extremely low, making it easy to obtain high-purity lead iodide. That is, the present invention also relates to lead iodide having a water content of 20 ppm or less and a purity of 99.9% or more, which is obtained by the production method of the present invention.

[0016] The resulting lead iodide can be effectively used in a variety of applications, including as a material for X-ray and gamma-ray detectors, a raw material for perovskite solar cells, photography, gold plating, bronze luster finishes, paints, pigments, printing, and imitation gold.

[0017] Although the method for producing lead iodide of the present invention has been described above, the present invention is not limited to the configurations of the above-described embodiments. For example, the method for producing lead iodide of the present invention may have any other additional configuration in addition to the configurations of the above-described embodiments, or may be replaced with any other configuration that produces a similar effect. [Example]

[0018] The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following examples. Example 1 A separable flask was charged with 900 g of a 19% by mass aqueous solution of hydroiodic acid [a mixture of 300 g of 57% hydroiodic acid and 600 g of ion-exchanged water; equivalent to 1.337 mol of hydrogen iodide], and while stirring at room temperature (25°C), powdered lead oxide (PbO; purity of 99.0% or higher) was added little by little until a total of 15.0 g of lead oxide (PbO; 0.0672 mol) was added, followed by further stirring for 24 hours. The slurry reaction mixture was filtered, and the recovered solid was further washed with ion-exchanged water until the filtrate became transparent (a total of 500 g of ion-exchanged water was used), and then dried in a dryer at 120°C for 3 hours, yielding 29.5 g of lead iodide (isolation yield 95.2%). 1.0 g of the obtained lead iodide was weighed out and heated at 250°C to evaporate the water. The water content was analyzed using a Karl Fischer moisture meter (Hiranuma Sangyo Co., Ltd.'s "AQV-2200AS," which was equipped with the same company's "EV-2000" moisture evaporator), and was found to be less than 5 ppm. In addition, 1.0 g of the obtained lead iodide was weighed out and dissolved in a mixture of 10 mL of concentrated nitric acid and 10 mL of ion-exchanged water, and the solution was heated above 100 °C to remove the iodine as vapor. The resulting colorless, transparent liquid was diluted to a volumetric flask of 50 mL to prepare Reference Solution A. 1 mL of this Reference Solution A was then diluted to a volumetric flask of 100 mL to prepare the sample. Analysis of this sample using ICP-MS (Agilent Technologies 7900 ICP-MS) revealed that the total content of trace metal impurities other than lead, including Na, Fe, Cu, Zn, Rh, Sn, Cs, Ba, Ce, Au, and Tl, was 364 ppm. Furthermore, the content of Pb(OH)I in the obtained lead iodide was analyzed using an X-ray diffractometer (Rigaku Corporation's "SmartLab") and found to be below the detection limit. From the above analysis results, it was determined that the water content of the obtained lead iodide was 20 ppm or less and the purity was 99.9% or more.

[0019] Example 2 The same procedure as in Example 1 was carried out except that the total amount of powdered lead oxide (PbO) added was changed from 15.0 g to 30.0 g (0.1344 mol), thereby obtaining 59.28 g of lead iodide (isolation yield 95.7%). The water content of the obtained lead iodide was analyzed in the same manner as in Example 1 and was found to be 5 ppm or less. Furthermore, 1.0 g of the obtained lead iodide was weighed out, and a sample was prepared in the same manner as in Example 1 and analyzed by ICP-MS. The total content of Na, Fe, Cu, Zn, Rh, Sn, Cs, Ba, Ce, Au, and Tl detected as trace metal impurities other than lead was 604 ppm. Furthermore, the content of Pb(OH)I in the obtained lead iodide was analyzed in the same manner as in Example 1 and was found to be below the detection limit. From the above analysis results, it was determined that the water content of the obtained lead iodide was 20 ppm or less and the purity was 99.9% or more.

[0020] Example 3 The same procedure as in Example 1 was carried out, except that 900 g of a 9.5 mass % hydroiodic acid aqueous solution [a mixture of 150 g of 57% hydroiodic acid and 750 g of ion-exchanged water; equivalent to 0.668 mol of hydrogen iodide] was used instead of 900 g of a 19 mass % hydroiodic acid aqueous solution, and the total amount of powdered lead oxide (PbO) added was changed from 15.0 g to 30.0 g (0.1344 mol), to obtain 58.8 g of lead iodide (isolation yield 94.9%). The water content of the obtained lead iodide was analyzed in the same manner as in Example 1 and was found to be 10 ppm. Furthermore, 1.0 g of the obtained lead iodide was weighed out, and a sample was prepared in the same manner as in Example 1 and analyzed by ICP-MS. The total content of Na, Fe, Cu, Zn, Rh, Sn, Cs, Ba, Ce, Au, and Tl detected as trace metal impurities other than lead was 394 ppm. Furthermore, the content of Pb(OH)I in the obtained lead iodide was analyzed in the same manner as in Example 1 and was found to be below the detection limit. From the above analysis results, it was determined that the water content of the obtained lead iodide was 10 ppm or less and the purity was 99.9% or more.

[0021] Example 4 The same operation as in Example 1 was carried out, except that 900 g of a 5.7 mass % hydroiodic acid aqueous solution [a mixture of 90 g of 57% hydroiodic acid and 810 g of ion-exchanged water; equivalent to 0.401 mol of hydrogen iodide] was used instead of 900 g of a 19 mass % hydroiodic acid aqueous solution, and the total amount of powdered lead oxide (PbO) added was changed from 15.0 g to 30.0 g (0.1344 mol), to obtain 58.5 g of lead iodide (isolation yield 94.4%). The water content of the obtained lead iodide was analyzed in the same manner as in Example 1 and was found to be 8 ppm. Furthermore, 1.0 g of the obtained lead iodide was weighed out, and a sample was prepared in the same manner as in Example 1 and analyzed by ICP-MS. The total content of Na, Fe, Cu, Zn, Rh, Sn, Cs, Ba, Ce, Au, and Tl detected as trace metal impurities other than lead was found to be 520 ppm. Furthermore, the content of Pb(OH)I in the obtained lead iodide was analyzed in the same manner as in Example 1 and was found to be below the detection limit. From the above analysis results, it was determined that the water content of the obtained lead iodide was 10 ppm or less and the purity was 99.9% or more.

[0022] Reference example 1 The same procedure as in Example 1 was carried out, except that 700 g of a 5.13 mass % hydroiodic acid aqueous solution [a mixture of 63 g of 57% hydroiodic acid and 637 g of ion-exchanged water; equivalent to 0.281 moles of hydrogen iodide] was used instead of 900 g of a 19 mass % hydroiodic acid aqueous solution, and the total amount of powdered lead oxide (PbO) added was changed from 15.0 g to 30.0 g (0.1344 moles), to obtain 57.1 g of lead iodide (isolation yield 92.2%). The pH of the reaction mixture at the end of the reaction was greater than 1 and equal to or less than 2. The content of Pb(OH)I in the obtained lead iodide was analyzed in the same manner as in Example 1 and was found to be 1.5 mass%. Therefore, taking into consideration the water content and the content of trace metal impurities other than lead, the purity of the obtained lead iodide was determined to be less than 98.5%.

[0023] Comparative Example 1 A separable flask was charged with 300 g of a 9.5 mass % aqueous solution of hydroiodic acid [a mixture of 50 g of 57% hydroiodic acid and 250 g of ion-exchanged water; equivalent to 0.223 mol of hydrogen iodide], and while stirring at room temperature (25°C), a solution prepared by dissolving 21.5 g of lead nitrate (PbNO; 0.065 mol) in 78.5 g of ion-exchanged water was added little by little. After the addition was completed, the mixture was further stirred for 24 hours. The slurry reaction mixture was filtered, and the recovered solid was further washed with ion-exchanged water until the filtrate became transparent (a total of 2000 g of ion-exchanged water was used), and then dried in a dryer at 120°C for 3 hours, yielding 25.59 g of lead iodide (yield 85.6%). The water content of the obtained lead iodide was analyzed in the same manner as in Example 1 and was found to be 1.1%. Furthermore, 1.0 g of the obtained lead iodide was weighed out, and a sample was prepared and analyzed by ICP-MS in the same manner as in Example 1. The total content of Na, Fe, Cu, Zn, Rh, Sn, Cs, Ba, Ce, Au, and Tl detected as trace metal impurities other than lead was 450 ppm. Furthermore, the content of Pb(OH)I in the obtained lead iodide was analyzed in the same manner as in Example 1 and was found to be below the lower limit of detection. From the above analysis results, it was determined that the water content of the obtained lead iodide was 1.1% and the purity was 98% or more but less than 99%. [Industrial Applicability]

[0024] The lead iodide obtained by the production method of the present invention is useful for a variety of applications, taking advantage of its properties of high purity and low water content.

Claims

1. A method for producing lead iodide, comprising the step of contacting lead oxide with hydroiodic acid.

2. 2. The method for producing lead iodide according to claim 1, wherein the concentration of hydrogen iodide in the hydroiodic acid is 5% by mass or more and 57% by mass or less, and the lead oxide is reacted in the presence of 2.2 moles or more and 100 moles or less of hydrogen iodide per mole of lead atoms contained in the lead oxide.

3. 2. The method for producing lead iodide according to claim 1, wherein the lead oxide contains a compound represented by PbO.

4. The method for producing lead iodide according to any one of claims 1 to 3, wherein the content of Pb(OH)I in the reaction mixture is 1 mass% or less based on the total mass of the solid content contained in the reaction mixture.

5. Lead iodide having a water content of 20 ppm or less and a purity of 99.9% or more, obtained by the manufacturing method of any one of claims 1 to 4.