Methods for oxidizing hypophosphite ions and phosphite ions, purification of electroless nickel plating wastewater, and recycling of phosphorus

Abstract

This invention eliminates the problems of conventional oxidation methods for purifying electroless nickel plating wastewater and provides a method for purifying electroless nickel plating wastewater and recovering phosphates for recycling using a simple apparatus, quickly, at low cost, and effectively. [Solution] This method for purifying electroless nickel plating wastewater is characterized by comprising: a first step of adding an iron salt to hypophosphate ions and phosphite ions to purify the treated water to a total phosphorus concentration of 16 mg / L or less; a second step of oxidizing the hypophosphate ions and phosphite ions to orthophosphate ions using an air oxidation catalyst consisting of an iron salt and an iodide salt to recover iron(III) phosphate; a third step of eluting orthophosphate ions from iron(III) phosphate; and a fourth step of converting orthophosphate ions into phosphate salts.

Description

[Technical Field]

[0001] The present invention relates to a method for purifying wastewater consisting of an aqueous solution containing hypophosphate ions and / or phosphite ions, such as electroless nickel plating wastewater. [Background technology]

[0002] Electroless nickel plating, which uses hypophosphate ions as a reducing agent, is used in a wide range of fields, including surface treatment of electronics-related equipment, automobile parts (disc brakes, etc.), aircraft parts, electromagnetic shielding materials, and metallization of plastics. However, wastewater from such electroless nickel plating contains large amounts of phosphorous acid and hypophosphate. Since phosphorus compounds contribute to the eutrophication of the environment, such as lakes and closed bodies of water, the discharge of phosphorus is strictly regulated. When disposing of the wastewater, it is necessary to reduce the phosphorus concentration to below the regulated value (a phosphorus concentration of 16 mg / L is stipulated in the Ministerial Ordinance for Establishing Wastewater Standards (Prime Minister's Office Ordinance No. 35 of June 21, 1971)), and the development of high-performance purification methods is eagerly awaited.

[0003] On the other hand, since phosphorus is a valuable resource, there is a need for effective ways to utilize phosphorus-containing wastewater, and methods of resource recovery by oxidizing hypophosphate and phosphite ions to orthophosphate ions have also been considered.

[0004] For example, Patent Document 1 presents a method for oxidizing hypophosphite ions to phosphite ions by adding a copper salt to plating wastewater containing hypophosphite ions and heating it. (Japanese Patent Publication No. 58-119389) Furthermore, Patent Document 2 presents a method for oxidizing a solution containing hypophosphite ions to phosphite ions by contacting it with a boron-nickel compound. (Japanese Patent Publication No. 6-263414) Furthermore, Patent Document 3 presents a method for oxidizing a solution containing hypophosphite ions to phosphite ions by contacting it with metallic palladium. (Japanese Patent Publication No. 6-279009) Patent Document 4 presents a method in which an electroless plating reaction is carried out by contacting an electroless nickel plating aging solution with nickel powder, nickel ions in the aging solution are separated and recovered as nickel metal, and the separated mother liquor is reacted with gypsum or mineral acid and calcium hydroxide to separate and recover calcium phosphite. (Japanese Patent Publication No. 9-176861) Furthermore, Patent Document 5 presents a method for oxidizing plating wastewater containing hypophosphite ions by contacting it with fine wires or cotton-like iron or nickel. (Japanese Patent Publication No. 2019-118908) Patent Document 6 presents a method for oxidizing plating wastewater containing hypophosphite ions and / or phosphite ions to phosphoric acid by reacting it with hydrogen peroxide in the presence of tungstic acid and / or molybdic acid. (Japanese Patent Publication No. 1-310793) Patent Document 7 presents a method for decomposing metal salts and sodium hypophosphite in high-concentration plating wastewater using a catalyst selected from the group consisting of metals and compounds of Group 8 of the periodic table, and then oxidatively decomposing organic acids and sodium phosphite in the high-concentration wastewater using a sodium hypochlorite-based oxidizing agent. (Japanese Patent Publication No. 61-120688) Patent Document 8 presents a method for oxidizing phosphite ions and / or hypophosphite ions to orthophosphate ions by adding hydrogen peroxide to plating wastewater containing hypophosphite ions and / or phosphite ions and irradiating it with ultraviolet light. (Japanese Patent Publication No. 4-338284) Patent Document 9 presents a method for oxidizing hypophosphite ions to orthophosphate ions by contacting an aqueous solution containing hypophosphite ions with colloidal particles of an amorphous compound composed of boron and nickel under conditions where the pH of the aqueous solution is 7.0 to 11.0, and a method for oxidizing orthophosphate ions to orthophosphate ions by contacting an aqueous solution containing phosphite ions with colloidal particles of an amorphous compound composed of boron and nickel under conditions where the pH of the aqueous solution is 2.0 to 5.0. (Japanese Patent Publication No. 2010-100875) Patent Document 10 presents a method for oxidizing hypophosphate and phosphite ions to orthophosphate ions by hydrothermal reaction treatment in a pressure-resistant sealed container in the presence of at least one metal ion selected from nickel ions, cobalt ions, and copper ions. (Japanese Patent Publication No. 10-85769) Patent Document 11 describes a method in which electroless nickel plating waste liquid is brought into contact with a chelating resin to adsorb and separate nickel from the nickel complex, the adsorbed nickel is eluted and recovered with acid, and the waste liquid after nickel separation is decomposed into water and carbon dioxide by ozone under ultraviolet irradiation with a high-pressure mercury lamp, the hypophosphite ions and / or phosphite ions are oxidized, and then a precipitating agent is added to recover it as phosphate. (Japanese Patent Publication No. 11-226596) Patent Document 12 presents a method for stabilizing a plating bath by suppressing its decomposition without using harmful metals, by using an electroless nickel plating bath containing at least an iron ion source and an iodine ion source. (Japanese Patent Publication No. 2010-132949) [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] (Unexamined Japanese Patent Publication No. 58-119389) [Patent Document 2] (Unexamined Japanese Patent Publication No. 6-263414) [Patent Document 3] (Unexamined Japanese Patent Publication No. 6-279009) [Patent Document 4] (Unexamined Japanese Patent Publication No. 9-176861) [Patent Document 5] (Japanese Patent Publication No. 2019-118908) [Patent Document 6] (Unexamined Japanese Patent Publication No. 1-310793) [Patent Document 7] (Unexamined Japanese Patent Publication No. 61-120688) [Patent Document 8] (Unexamined Japanese Patent Publication No. 4-338284) [Patent Document 9] (Japanese Patent Application Laid-Open No. 2010-100875)

Patent Document 10

Patent Document 11

Patent Document 12

Non-Patent Document

[0006]

Non-Patent Document 1

Disclosure of the Invention

Problems to be Solved by the Invention

[0007] However, in the conventional method of oxidizing waste liquid containing high-concentration hypophosphite ions and / or phosphite ions to produce orthophosphate ions, the oxidation is difficult and insufficient, the chemical cost is high, and furthermore, a long treatment time, a special reactor or equipment is required, and there are problems such as complicated operation and difficult handling of chemicals, so it has not been fully satisfactory.

[0008] That is, in Patent Document 1 (Japanese Patent Application Laid-Open No. 58-119389) using a copper salt as an oxidizing agent, Patent Document 2 (Japanese Patent Application Laid-Open No. 6-263414) using a boron-nickel compound catalyst, Patent Document 3 (Japanese Patent Application Laid-Open No. 6-279009) using a metal palladium catalyst, Patent Document 4 (Japanese Patent Application Laid-Open No. 9-176,861) using nickel powder, and Patent Document 5 (Japanese Patent Application Laid-Open No. 2019-118908) using fine wire or cotton-like iron or nickel, oxidation from hypophosphite ions to phosphite ions is possible, but oxidation to orthophosphate ions is difficult.

[0009] In addition, in Patent Document 6 (Japanese Patent Application Laid-Open No. 1-310793), which uses a large amount of tungstic acid and / or molybdic acid catalyst and hydrogen peroxide as an oxidizing agent, and in Patent Document 7 (Japanese Patent Application Laid-Open No. 61-120688), which uses a catalyst selected from the group consisting of metals of Group 8 of the periodic table of elements and their compounds and sodium hypophosphite as an oxidizing agent, not only is the chemical cost high, but the oxidation to phosphite ions and orthophosphate ions is insufficient.

[0010] In Patent Document 8 (Japanese Patent Application Laid-Open No. 4-338284), not only are the chemicals of hydrogen peroxide as an oxidizing agent and the equipment cost for ultraviolet irradiation high, but the oxidation to orthophosphate ions is insufficient.

[0011] In Patent Document 9 (Japanese Patent Application Laid-Open No. 2010-100875), although hypophosphite ions and / or phosphite ions can be oxidized to orthophosphate ions, the reaction time is long, and the oxidation conditions from hypophosphite ions to phosphite ions and from phosphite ions to orthophosphate ions are very different, so the operation is complicated. In addition, the chemical cost in the production of the amorphous compound catalyst composed of boron and nickel used is high, new waste liquid is generated, and the produced catalyst is deactivated by drying, so it is not easy to store.

[0012] In Patent Document 10 (Japanese Patent Application Laid-Open No. 10-85769), although hypophosphite ions and / or phosphite ions can be oxidized to orthophosphate ions, because it is a hydrothermal reaction in a pressure-resistant sealed container in the presence of metal ions such as nickel ions, the equipment cost is high, and the reaction time is also long, so it is not economical.

[0013] In Patent Document 11 (Japanese Patent Application Laid-Open No. 11-226596), since the waste liquid after nickel separation is treated with ozone under ultraviolet irradiation by a high-pressure mercury lamp, the equipment and running costs are high and it is not economical.

[0014] In the aforementioned Patent Document 12 (Japanese Patent Publication No. 2010-132949), it is known that the decomposition of the plating bath can be suppressed by using an electroless nickel plating bath containing an iron ion source and an iodide ion source. However, it has been confirmed that even when using the dilute iron ion and iodide ion sources described, the effect of oxidizing hypophosphate and phosphite ions to orthophosphate ions cannot be obtained.

[0015] As a result of diligent research to solve the above problems, the present invention aims to provide a method for purifying and recycling electroless nickel plating wastewater by safely, quickly, and effectively treating problems such as oxidation of hypophosphate ions and / or phosphite ions using a simple device, and recovering orthophosphate ions. [Means for solving the problem]

[0016] The aforementioned technical problems can be solved by the present invention as follows. In other words, the present invention is a method for oxidizing hypophosphate ions and / or phosphite ions to orthophosphate ions at room temperature and atmospheric pressure by adding an iron salt and an iodide salt to an aqueous solution containing hypophosphate ions and / or phosphite ions and bringing it into contact with air by aeration (Invention 1).

[0017] According to the present invention, by adding an iron salt and an iodide salt, iodine and iron(II) ions are generated. This iodine oxidizes hypophosphite ions and phosphite ions to orthophosphate ions and simultaneously regenerates them as iodide ions. Furthermore, the iron(II) ions are oxidized by contact with air through aeration and regenerated as iron(III) ions. Thus, the regenerated iodide ions and regenerated iron(III) ions generate iodine and iron(II) ions, and function as an air oxidation catalyst in a continuous and repetitive manner, providing a method for oxidizing hypophosphite ions and phosphite ions.

[0018] According to the present invention, by adding iron salts and iodide salts, the oxidation reaction of hypophosphite ions and / or phosphite ions proceeds rapidly with spontaneous and high reactivity from both a thermodynamic and kinetic standpoint. Because it functions as an air oxidation catalyst, atmospheric oxygen can be used as the oxidizing agent. Furthermore, because it is a substance with abundant domestic resources and a stable supply in large quantities, it reduces chemical costs, maintains low toxicity and low environmental impact, and provides a method for the complete oxidation of hypophosphite ions and phosphite ions.

[0019] Furthermore, the present invention comprises a first step of purification by adding an iron salt to an aqueous solution containing hypophosphate ions and / or phosphite ions, and separating and recovering a precipitate containing iron(III) hypophosphate and / or iron(III) phosphite and treated water with a total phosphorus concentration of 16 mg / L or less; a second step of adding the precipitate containing iron(III) hypophosphate and / or iron(III) phosphite produced in the first step, or hypophosphate ions and / or phosphite ions and an iron salt, to an aqueous solution containing an iodide salt, contacting it with air by aeration to oxidize it to orthophosphate ions, and after neutralization separating and recovering a precipitate containing iron(III) phosphate and an aqueous solution containing an iodide salt; and an alkali metal such as sodium hydroxide. This method for purifying electroless nickel plating wastewater is characterized by comprising: a third step of adding a precipitate containing iron(III) phosphate produced in the second step or iron(III) phosphate to an aqueous solution containing an alkali metal carbonate such as sodium carbonate and calcium hydroxide, thereby eluting orthophosphate ions, and separating and recovering the aqueous solution containing orthophosphate ions and the precipitate containing iron(III) hydroxide; and a fourth step of purifying the electroless nickel plating wastewater by adding an alkaline earth metal salt to the aqueous solution containing orthophosphate ions produced in the third step or the aqueous solution containing orthophosphate ions, thereby separating and recovering the precipitate containing phosphate and treated water with a total phosphorus concentration of 16 mg / L or less (Invention 2).

[0020] According to the present invention, in the first step, phosphorus components are separated and recovered from an aqueous solution containing hypophosphate and / or phosphite ions; in the second step, the recovered phosphorus components are oxidized to iron(III) phosphate; in the third step, orthophosphate ions are eluted from iron(III) phosphate; and in the fourth step, orthophosphate ions are converted to phosphate salts. By carrying out all four steps in a series, a method is provided that can recycle phosphorus and purify electroless nickel plating wastewater.

[0021] Furthermore, the present invention relates to the method for purifying an aqueous solution containing hypophosphate ions and / or phosphite ions in the first step, which involves adding an iron salt or a precipitate containing iron(III) hydroxide produced in the third step to the aqueous solution containing hypophosphate ions and / or phosphite ions, and then separating and recovering the precipitate containing iron(III) hypophosphate and / or iron(III) phosphite produced in the first step into treated water with a total phosphorus concentration of 16 mg / L or less for purification, as described in Invention 2. (Invention 3)

[0022] According to the present invention, by adding a sufficient amount of iron salt at pH 3 to 11, iron(III) phosphite, which has very low solubility, is precipitated, and iron(III) hypophosphate, which does not have low solubility, is precipitated in proportion to the amount of iron(III) ions added, thereby providing a method for purifying electroless nickel plating in treated water with a total phosphorus concentration of 16 mg or less.

[0023] According to the present invention, a method for purifying electroless nickel plating is provided that produces iron(III) hypophosphate and / or iron(III) phosphate at low cost using iron salts or recycled iron(III) hydroxide from hypophosphate ions and / or phosphate ions.

[0024] Furthermore, the present invention relates to a method for purifying electroless nickel plating as described in Invention 3, wherein the oxidation method for the precipitate containing iron(III) hypophosphate and / or iron(III) phosphate or hypophosphate ions and / or phosphite ions in the second step is to add the precipitate containing iron(III) hypophosphate and / or iron(III) phosphate or hypophosphate ions and / or phosphite ions produced in the first step to an aqueous solution containing an iron salt and an iodide salt or an iodide salt produced in the second step, bring it into contact with air by aeration to oxidize it to orthophosphate ions, and after neutralization separate and recover the precipitate containing iron(III) phosphate produced in the second step and the aqueous solution containing the iodide salt produced in the second step. (Invention 4)

[0025] According to the present invention, a low-cost method for purifying electroless nickel plating can be provided by rapidly and completely oxidizing iron(III) phosphate and regenerated iodide salts by contacting them with air using iron salts and iodide salts, from hypophosphite ions and / or phosphite ions.

[0026] Furthermore, the present invention relates to a method for purifying electroless nickel plating wastewater as described in Invention 3 or 4, wherein the method for eluting orthophosphate ions from the precipitate containing iron(III) phosphate or iron(III) phosphate in the third step is to add the precipitate containing iron(III) phosphate or iron(III) phosphate produced in the second step to an aqueous solution containing an alkali metal hydroxide such as sodium hydroxide or an alkali metal carbonate such as sodium carbonate and calcium hydroxide, to elute orthophosphate ions, and then separate and recover the aqueous solution containing orthophosphate ions and the precipitate containing iron(III) hydroxide produced in the third step. (Invention 5).

[0027] According to the present invention, a method for purifying electroless nickel plating is provided that produces orthophosphate ions and regenerated iron(III) hydroxide from iron(III) phosphate using alkali metal hydroxide or alkali metal carbonate and calcium hydroxide at low cost.

[0028] Furthermore, the present invention relates to a method for purifying electroless nickel plating wastewater as described in Invention 3 to 5, wherein the method for converting an aqueous solution containing orthophosphate ions in the fourth step to phosphate is to add an alkaline earth metal compound to the aqueous solution containing orthophosphate ions in the fourth step, and separate and recover the precipitate containing phosphate produced in the fourth step and treated water with a total phosphorus concentration of 16 mg / L or less, thereby purifying and recycling the phosphate (Invention 6).

[0029] According to the present invention, a method for purifying electroless nickel plating can be provided using alkaline earth metal compounds instead of orthophosphate ions as phosphates.

[0030] According to the present invention, by adding a sufficient amount of alkaline earth metal compounds at a pH of 4.0 to 5.5, dihydrogen phosphate, which has extremely low solubility, is precipitated, and a method for purifying electroless nickel plating with treated water containing a total phosphorus concentration of 16 mg / L or less can be provided. [Effects of the Invention]

[0031] According to the method of the present invention, it is possible to easily completely oxidize hypophosphate and phosphite ions to orthophosphate ions in electroless nickel plating wastewater, which was previously difficult to do, thus enabling a high degree of purification of phosphorus-containing wastewater from the electroless nickel plating process. Furthermore, the method of the present invention contributes to the recovery and recycling of phosphorus from plating wastewater, which was a source of environmental pollution.

[0032] According to the present invention, the oxidation reaction of hypophosphite ions and / or phosphite ions in electroless nickel plating wastewater, which was previously difficult to remove, proceeds rapidly and spontaneously from a thermodynamic and kinetic standpoint by adding iron salts and iodide salts. Since it functions as an air oxidation catalyst, atmospheric oxygen can be used as an oxidizing agent. Furthermore, because it is a substance that is abundant in domestic resources and has a stable supply in large quantities, the cost of the chemicals is reduced, and phosphorus can be recycled by rapidly and completely oxidizing hypophosphite ions and phosphite ions while maintaining low toxicity and low environmental impact.

[0033] According to the present invention, the phosphorus component in electroless nickel plating wastewater can be purified to 16 mg / L or less.

[0034] According to the present invention, the air oxidation catalyst, which consists of an iron salt and an iodine salt, can be easily recycled.

[0035] According to the present invention, the process can be carried out with equipment of a simple structure, the scale can be easily increased or decreased, and on-site production of orthophosphates and advanced purification of electroless nickel plating wastewater can be performed adjacent to the place of use. [Brief explanation of the drawing]

[0036] [Figure 1] Figure 1 illustrates the air oxidation catalysts for hypophosphite ions and phosphite ions according to the present invention. [Figure 2] Figure 2 illustrates the separation, recovery, purification, oxidation, and separation and recovery method of hypophosphate ions and / or phosphite ions, and orthophosphate ions according to the present invention. [Figure 3] Figure 3 illustrates the apparatus for the separation, recovery, purification, oxidation, and separation and recovery of hypophosphate and / or phosphite ions, and orthophosphate ions according to the present invention. [Best Mode for Carrying Out the Invention]

[0037] The configuration of the present invention can be described in more detail as follows.

[0038] First, the air oxidation catalysts for hypophosphate and phosphite ions according to the present invention will be described using drawings and formulas.

[0039] The catalyst used in this invention is a mixture of an iron salt and an iodine salt. Figure 1 illustrates the continuous reaction of air oxidation of hypophosphite ions and phosphite ions that occurs using this catalyst. Under conditions where iron salts and iodine salts are added to hypophosphate and phosphite ions, and air is aerated, the following half-reaction equations (Equation 1), (Equation 2), (Equation 3), (Equation 4), and (Equation 5) hold true, and the reactions shown in (Equation 6), (Equation 7), (Equation 8), and (Equation 9) occur repeatedly and continuously. First, the iodide ions produced from the iodide salt are oxidized by iron(III) ions, resulting in the reaction (Equation 6) which produces iodine and iron(II) ions. The hypophosphite ion is oxidized by iodine, and the reaction (Equation 7) occurs, producing phosphite ions and iodide ions. The phosphite ion is oxidized by iodine, and the reaction (Equation 8) occurs, producing orthophosphate ions and iodide ions. Iron(II) ions are oxidized by oxygen, and the reaction (Equation 9) occurs, producing iron(III) ions and water. According to equations (3) and (4), the potential of the hypophosphate ion is 0.500 V, and the potential of the phosphite ion is 0.276 V. Therefore, from a thermodynamic standpoint, substances with a redox potential of 0.500V or higher spontaneously undergo oxidation reactions with both hypophosphite and phosphite ions. However, simply having a redox potential exceeding 0.500V does not guarantee that a reaction sufficient for practical use will proceed. In fact, simply aerating with atmospheric oxygen, which has a redox potential of 1.23V, does not cause air oxidation reactions of hypophosphite and phosphite ions (Reference Example 1). In addition, from a reaction kinetics perspective, the reaction will not proceed rapidly unless the activation energy is sufficiently low. Furthermore, in order to maintain economic efficiency in the oxidation reactions of hypophosphite and phosphite ions, it is essential to utilize the inexhaustible oxygen available in the atmosphere by using a catalyst. Therefore, substances that can function as catalysts for the air oxidation of hypophosphite ions and phosphite ions are required to have an oxidation-reduction potential in the range of 0.500V to 1.23V and to react rapidly with hypophosphite ions, phosphite ions, and oxygen. More preferably, the substance can be separated from orthophosphate ions, has a low environmental impact, is abundant as a domestic resource, has low drug costs, and is supplied stably. A catalyst that satisfies these conditions is a mixture of iron salts and iodine salts. As shown below, from a thermodynamic standpoint, the Gibbs free energy values ​​for the reactions shown in (Equation 6), (Equation 7), (Equation 8), and (Equation 9) are negative, so all reactions occur spontaneously. Since ΔG = -nFE = -2 × 96500 × (0.770V - 0.535V) = -45.355 kJ / mol < 0, (Equation 6) reacts spontaneously. Since ΔG = -nFE = -2 × 96500 × (0.535V - 0.276V) = -49.987 kJ / mol < 0, (Equation 7) reacts spontaneously. Since ΔG = -nFE = -2 × 96500 × (0.535V - 0.50V) = -6.755 kJ / mol < 0, (Equation 8) reacts spontaneously. Since ΔG = -nFE = -4 × 96500 × (1.23V - 0.77V) = -177.56 kJ / mol < 0, (Equation 9) reacts spontaneously. In addition, equations (6), (7), (8), and (9) are practical reactions because, from a reaction kinetics perspective, their respective activation energies are small and they proceed rapidly in a chain reaction. From the perspectives of economics, thermodynamics, reaction kinetics, resources, and environmental protection, iron salts and iodine salts are selected as air oxidation catalysts for hypophosphite ions and phosphite ions.

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[0040] The iron salt used as a catalyst may be one or more feedstocks selected from the following: iron(III) hypophosphate, iron(III) phosphate, iron(III) nitrate, iron(III) sulfate, iron(III) citrate, iron(III) ammonium citrate, iron(III) EDTA, iron(III) chloride, iron(III) hydroxide, iron(III) oxyhydroxide, or iron(II) nitrate, iron(II) chloride, iron(II) sulfate, iron(II) acetate, iron(II) lactate, or iron(II) lactate.

[0041] The iodide salt used as a catalyst may be one or more raw materials selected from the following raw materials: iodine, potassium iodide, sodium iodide, iron(II) iodide, iron(III) iodide, calcium iodide, hypoiodite, iodite, iodate, periodic acid, potassium hypoiodite, potassium iodate, potassium iodate, potassium periodate, sodium hypoiodite, sodium iodate, sodium iodate, sodium periodate, and ammonium iodate.

[0042] The concentration of hypophosphate and / or phosphate ions is preferably 0.10 mol / L to 1.0 mol / L. The composition of the catalyst is such that the molar ratio of iron(III) ions to phosphorus contained in the wastewater (iron(III) ions / phosphorus) is The pH is preferably between 0.5 and 6, and the molar ratio of iodide salt to phosphorus contained in the wastewater (iodide salt / phosphorus) is preferably between 1 and 3. Furthermore, the temperature is preferably 70°C or higher, and the pH is preferably 2 or lower.

[0043] Next, the separation, recovery, purification, oxidation, and recovery methods and apparatus for hypophosphate and / or phosphate ions, as well as for orthophosphate ions, will be described using diagrams and equations.

[0044] In the electroless nickel plating wastewater purification method according to Invention 2 to 6, the target electroless nickel plating wastewater is the wastewater from an electroless nickel plating solution using a hypophosphate such as sodium hypophosphite as a reducing agent, from which nickel ions have been removed by an adsorbent, an alkaline agent, etc., and is a nickel ion-removed wastewater containing hypophosphite ions and / or phosphite ions.

[0045] Figure 2 illustrates the separation, recovery, purification, oxidation, and recovery method of hypophosphate ions and / or phosphite ions and orthophosphate ions used in the present invention, where 21 is a reactor for separation, recovery, and purification of hypophosphate ions and / or phosphite ions, 22 is a valve for supplying nickel ion removal wastewater containing hypophosphate ions and / or phosphite ions, 23 is a valve for supplying iron salts, 24 is a precipitate containing iron(III) hypophosphate and / or iron(III) phosphite produced in the first step, 25 is a valve for draining treated water from which hypophosphate ions and / or phosphite ions have been removed, 26 is a valve for discharging precipitate 24, 27 is an air oxidation aeration tank for hypophosphate ions and / or phosphite ions, and 28 is an iodide salt supply tank. The valves shown are: supply valve, 29 is an air pump for supplying air, 210 is a precipitate containing iron(III) phosphate produced in the second step, 211 is a valve for discharging precipitate 210, 212 is a reactor for eluting orthophosphate ions, 213 is a valve for supplying sodium hydroxide, 214 is a precipitate containing iron(III) hydroxide produced in the third step, 215 is an orthophosphate ion produced in the third step, 216 is a valve for discharging precipitate 214, 217 is a valve for discharging orthophosphate ions, 218 is a reactor for recovering phosphate ions, 219 is a valve for supplying calcium salt, 220 is a precipitate containing phosphate produced in the fourth step, 221 is a valve for draining treated water from which the orthophosphate component has been removed, and 222 is a valve for recovering precipitate 220.

[0046] In the first step according to inventions 2-6, in the reaction tank 21, the reactions of (formula 10) and (formula 11) occur between hypophosphate ions and / or phosphite ions supplied from valve 22 and iron salt supplied from valve 23, generating a precipitate 24 containing iron(III) hypophosphate and / or iron(III) phosphite to be produced in the first step. By separating the precipitate 24 from the treated water, the hypophosphate ions and / or phosphite ions are separated and recovered, and the purified treated water is discharged from valve 25.

[0047] The pK1 of hypophosphite ions is 1.23, and the pK1 of phosphite ions is 1.5, with a pK2 of 6.7. Therefore, below pH 3, the hydrogen ion concentration is high, and most of it exists as hypophosphite and phosphite, making it difficult to form precipitates with iron(III) ions. On the other hand, above pH 11, the hydroxide ion concentration is high, and iron(III) ions exist as iron(III) hydroxide, making it difficult to form precipitates with hypophosphite and phosphite ions. In other words, between pH 3 and 11, when sufficient iron(III) ions are present, the solubility of iron(III) hypophosphite is not small, but precipitation occurs due to the reaction in (Equation 10). Also, because the solubility of iron(III) phosphite is extremely small, precipitation occurs due to the reaction in (Equation 11). Therefore, the total phosphorus concentration decreases depending on the amount or number of times iron(III) ions are added.

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[0048] To separate and purify hypophosphate ions and / or phosphite ions in the first step of the present invention 2 to 6, an iron(III) ion supply material selected from iron(III) nitrate, iron(III) sulfate, iron(III) chloride, iron(III) hydroxide, iron(III) oxyhydroxide, iron, or a precipitate 214 containing iron(III) hydroxide produced in the third step is used as the iron(III) ion supply material, preferably with a molar ratio of iron(III) ions to phosphorus contained in the wastewater (iron(III) ions / phosphorus) of 1 or more, and a pH value of 3 to 11, and the water temperature may be room temperature. More preferably, the molar ratio (iron(III) ions / phosphorus) is 6 or more, and the addition of iron salt and separation of phosphorus components are repeated 5 or more times.

[0049] In the second step according to inventions 2-6, the precipitate 24 is injected into the aeration tank 27 from the valve 26. In the aeration tank 27, the air oxidation of the precipitate 24 is promoted by supplying iodide salt from the valve 28 and air from the air pump 29, thereby generating a precipitate 210 containing iron(III) phosphate, which is produced in the second step.

[0050] In the third step according to inventions 2-6, precipitate 210 is injected into the reaction vessel 212 from valve 211. In the reaction vessel 212, the reaction (formula 12) occurs between sodium hydroxide supplied from valve 213 and precipitate 210, producing precipitate 214 containing iron(III) hydroxide to be produced in the third step and orthophosphate ions 215 to be produced in the third step. By separating precipitate 214 and orthophosphate ions 215, precipitate 214 is discharged from valve 216 and sent to valve 23.

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[0051] In the third step of the present invention (2-6), to elute orthophosphate ions, the precipitate containing iron(III) phosphate produced in the third step is added to an aqueous solution containing an alkali metal hydroxide such as sodium hydroxide or an alkali metal carbonate such as sodium carbonate and calcium hydroxide, the pH is adjusted to 12 or higher, and the mixture is stirred at room temperature. A preferred pH value is 13 or higher.

[0052] In the fourth step according to steps 2-6 of the present invention, orthophosphate ions 215 are injected into the reaction vessel 218 from valve 217. In the reaction vessel 218, the calcium salt supplied from valve 219 and the orthophosphate ions 215 react according to formula 13, producing a precipitate 220 containing the phosphate to be manufactured in the fourth step. By separating the precipitate 220 from the treated water, the treated water from which the phosphate component has been removed is discharged from valve 221. The precipitate 220 is recovered from valve 222.

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[0053] Since the pK1 of the orthophosphate ion is 2.12, the pK2 is 7.21, and the pK3 is 12.67, when sufficient calcium ions are present at a pH of 2.12 or higher, the solubility of phosphate is extremely low and it precipitates, so the total phosphorus concentration of the treated water can be reduced to 16 mg / L or less. Furthermore, when using phosphates as fertilizer, dihydrogen phosphate ions are often used as the orthophosphate ion form from the viewpoint of solubility after application. Therefore, considering the form of the orthophosphate ion and the treatment efficiency, a more preferable pH is 4.0 to 5.5.

[0054] To recover orthophosphate ions in the fourth step of the present invention 2-6, the pH of the aqueous solution containing orthophosphate ions should be adjusted to 3-12 using a calcium ion supply material selected from calcium chloride, calcium hydroxide, calcium carbonate, calcium sulfate, calcium oxalate, and calcium acetate, and the water temperature should be kept at room temperature while stirring. Preferably, the pH value is 4-6 and the temperature is 50 degrees Celsius or higher.

[0055] Next, using Figure 3, the detailed structure of the method and apparatus for the separation, recovery, purification, oxidation, and recovery of hypophosphite ions and / or phosphite ions, and phosphoric acid will be explained. In the figure, 31 is a stirring motor, 32 is a stirring blade, 33 is a solid-liquid separation filter, 34 is a heater, 35 is a diffuser, 36 is a cooling water supply port, 37 is a cooling water drain port, 38 is a cooling pipe for separating air and iodine, 39 is a magnet for removing iodine adhering to the cooling pipe, 310 is a filter for reducing vaporized iodine, 311 is a transport pump for precipitate 210, 312 is a stirring motor, 313 is a stirring blade, 314 is a transport pump for precipitate 214, 315 is a solid-liquid separation filter, 316 is a stirring motor, 317 is a stirring blade, and 318 is a solid-liquid separation filter.

[0056] In the aeration tank 27, the aqueous solution containing the precipitate 24 and iodide salt is heated to over 70°C by the heater 34. The iodine vaporized by aeration using the air supply air pump 29 and diffuser pipe 35 is cooled by the cooling pipe 38 and separated from the air by adhering to the inner wall surface of the cooling pipe as solid iodine. The recovered iodine can be supplied back to the aeration tank 27 from the cooling pipe 38 by moving the iodine removal magnet 39 up and down. Vaporized iodine remaining in the exhaust is removed by passing through a filter 310 containing a reducing agent such as ascorbic acid and then exhausted. [Examples]

[0057] The present invention will be described in more detail below with reference to examples, but it goes without saying that the scope of the present invention is not limited to these examples.

[0058] The concentrations of hypophosphate, phosphite, and orthophosphate ions in the solution were analyzed using a portable total nitrogen / total phosphorus meter, model number TNP-10 (Toa DKK Co., Ltd.). The orthophosphate ion concentration in the sample was measured as phosphate phosphorus concentration by molybdenum blue spectrophotometric analysis (Non-Patent Literature 1). Furthermore, the hypophosphate and phosphite ion concentrations in the sample were measured as total phosphorus concentration by molybdenum blue spectrophotometric analysis after adding potassium peroxodisulfate and sulfuric acid to the sample, heating it, and oxidizing all of it to phosphate phosphorus.

[0059] This section describes the first step, in which an iron salt is added to an aqueous solution containing hypophosphate ions and / or phosphate ions, and the precipitate containing iron(III) hypophosphate and / or iron(III) phosphate produced in the first step is separated and recovered to purify the treated water with a total phosphorus concentration of 16 mg / L or less.

[0060] <Preparation of an aqueous solution containing hypophosphate ions> Dissolve 0.050 mol of reagent-grade sodium hypophosphite monohydrate in 500 mL of deionized water to obtain a solution of 0.10 mol / LPO2 3- An aqueous solution was prepared.

[0061] <Example 1> 0.10 mol / LPO2 3- 500 mL of the aqueous solution was placed in a beaker, iron(III) nitrate was added to the solution to make it 0.20 mol / L, and the pH was adjusted to 5.0 using sodium hydroxide. The mixture was then stirred at room temperature using a magnetic stirrer at 300 rpm for 10 minutes, and the aqueous solution was filtered. The filtrate was sampled. Iron(III) nitrate was added again to the filtrate to make it 0.20 mol / L, and the same procedure was repeated six times. The samples were centrifuged, and the total phosphorus concentration of the supernatant was measured, and the results are shown in Table 1. The "phosphorus removal rate," which indicates the proportion of phosphorus components removed, was defined by Equation 14. [Table 1]

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[0062] <Preparation of aqueous solution containing phosphite ions> Dissolve 0.10 mol of reagent-grade disodium phosphite pentahydrate in 1.0 L of deionized water to make 0.10 mol / LPO3 3- An aqueous solution was prepared.

[0063] <Example 2> 0.10 mol / LPO3 3- 1.0 L of aqueous solution was placed in a beaker, and iron(III) nitrate was added to the solution to adjust the concentrations to 0, 0.010, 0.050, 0.10, 0.30, and 0.60 mol / L. The pH was adjusted to 5.0 using sodium hydroxide, and the solution was stirred at room temperature using a magnetic stirrer at 300 rpm for 30 minutes. The aqueous solution was then sampled. The samples were centrifuged, and the total phosphorus concentration of the supernatant was measured. The results are shown in Table 2. [Table 2]

[0064] The second step involves adding a precipitate containing iron(III) hypophosphate and / or iron(III) phosphate produced in the first step, or a hypophosphate ion and / or phosphate ion and iron salt, to an aqueous solution containing an iodide salt or an iodide salt produced in the second step, bringing it into contact with air by aeration to oxidize it to orthophosphate ions, and after neutralization, separating and recovering the precipitate containing iron(III) phosphate produced in the second step and the aqueous solution containing the iodide salt produced in the second step.

[0065] For the practical test, a 100 mL flask was used, equipped with a reflux condenser to condense the evaporated water vapor, the aqueous solution was stirred with a magnetic stirrer, and heating was performed using a water bath equipped with a temperature control device. The air pump used for supplying air was the "Air Pump Ei (Kotobuki Kogyo Co., Ltd.)" with a discharge rate of 1 L / min.

[0066] <Preparation of an aqueous solution containing hypophosphate ions> Dissolve reagent-grade sodium hypophosphate monohydrate in deionized water to make a solution of 1.0 mol / LPO2. 3- An aqueous solution was prepared.

[0067] <Example 3> 1.0 mol / LPO2 3- 100 mL of aqueous solution was placed in a flask. 0.30 mol of iron(III) chloride, 0.10 mol of potassium iodide, and hydrochloric acid were added to this solution to adjust the pH to 1.0. A Liebig condenser was then connected to the flask. A tube was passed through the Liebig condenser, and the solution was stirred with a magnetic stirrer while aerating at 1.0 L / min. The solution was heated in a water bath while maintaining a temperature of 90°C. A sample of the aqueous solution was taken every 30 minutes. The sample was eluted for phosphate ions using sodium hydroxide, separated for iron components by centrifugation, the pH was adjusted, and the orthophosphate ion concentration was measured. The results are shown in Table 3. The "oxidation rate of phosphorus," which indicates the proportion of phosphorus components oxidized, was defined by Equation 15. [Table 3]

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[0068] <Adjustment of Aqueous Solution Containing Phosphite Ions> Dissolve 0.10 mol of reagent-grade disodium phosphite pentahydrate in 100 mL of ion-exchanged water to prepare a 1.0 mol / L PO3 3- aqueous solution.

[0069] <Comparative Example 1> Put 100 mL of 1.0 mol / L PO2 3- [[ID=!17]]aqueous solution into a flask, add 0.000179 mol of iron(III) nitrate nonahydrate, 0.00314 mol of potassium iodide, and hydrochloric acid to this solution to adjust the pH to 5, and then connect a Liebig condenser to the flask. Pass a tube through the Liebig condenser, stir with a magnetic stirrer while aerating at 1.0 L / min, and heat while maintaining the liquid temperature at 90 °C with a water bath. After 90 minutes, sample the aqueous solution. The sample was eluted with sodium hydroxide to elute phosphate ions, the iron component was separated by centrifugation, the pH was adjusted, and the orthophosphate ion concentration was measured. Incidentally, the orthophosphate ion concentration was not detected. This result supports that the oxidation of phosphite does not proceed sufficiently with the use of extremely small amounts of iron and iodine, as described in the background art.

[0070] <Example 4> [[ID=2!5]]Put 100 mL of 1.0 mol / L PO3 3- [[ID=2!7]]aqueous solution into a flask, add 0.30 mol of iron(III) chloride, 0.10 mol of potassium iodide, and hydrochloric acid to this solution to adjust the pH to 1.0, and then connect a Liebig condenser to the flask. Pass a tube through the Liebig condenser, stir with a magnetic stirrer while aerating at 1 L / min, and heat while maintaining the liquid temperature at 90 °C with a water bath. Sample the aqueous solution every 30 minutes. The sample was eluted with sodium hydroxide to elute orthophosphate ions, the iron component was separated by centrifugation, the pH was adjusted, and the orthophosphate ion concentration was measured. The results are shown in Table 4.

Table 4

[0071] Examples 5 and 6 were conducted to optimize the conditions for the second step, in which an iron salt and an iodide salt are added to an aqueous solution of hypophosphate and / or phosphite ions to oxidize the hypophosphate and / or phosphite ions to orthophosphate ions.

[0072] <Preparation of aqueous solution containing phosphite ions> Dissolve reagent-grade disodium phosphite pentahydrate in deionized water to make 0.10 mol / LPO3 3- An aqueous solution was prepared.

[0073] <Example 5> 0.10 mol / LPO3 3- 100 mL of aqueous solution was placed in a flask, and iron(III) nitrate was added to the solution to adjust the concentrations to 0.025, 0.15, 0.30, and 0.60 mol / L. 0.030 mol of potassium iodide and hydrochloric acid were added to adjust the pH to 1.0, and a Liebig condenser was connected to the flask. A tube was passed through the Liebig condenser, and the solution was stirred with a magnetic stirrer while aerating at 1.0 L / min. The solution was heated in a water bath for 30 minutes while maintaining a temperature of 90°C, and the aqueous solution was sampled. The sample was eluted for phosphate ions using sodium hydroxide, separated for iron component by centrifugation, adjusted for pH, and measured for orthophosphate ion concentration. The results are shown in Table 5. It was shown that adding 0.30 mol / L of iron(III) ions was sufficient. [Table 5]

[0074] <Example 6> 0.10 mol / LPO3 3-100 mL of aqueous solution was placed in a flask. 0.060 mol of iron(III) nitrate, 0.030 mol of potassium iodide, and hydrochloric acid were added to this solution to adjust the pH to 1.0. A Liebig condenser was then connected to the flask. A tube was passed through the Liebig condenser, and the solution was stirred with a magnetic stirrer while aerating at 1.0 L / min. The solution was then heated in a water bath for 30 minutes, changing the temperature, and the aqueous solution was sampled. The sample was eluted for orthophosphate ions using sodium hydroxide, separated from the iron component by centrifugation, adjusted to pH, and the orthophosphate ion concentration was measured. The results are shown in Table 6. A temperature of 70°C or higher was found to be preferable. [Table 6]

[0075] The third step involves adding a precipitate containing iron(III) phosphate produced in the second step, or iron(III) phosphate itself, to an aqueous solution containing an alkali metal hydroxide such as sodium hydroxide or an alkali metal carbonate such as sodium carbonate and calcium hydroxide, to elute orthophosphate ions, and then separating and recovering the aqueous solution containing orthophosphate ions from the precipitate containing iron(III) hydroxide produced in the third step.

[0076] <Example 7> 500 mL of 0.10, 0.50, 1.0, 1.5, and 2.0 mol / L sodium hydroxide aqueous solutions were mixed with 0.066 mol of iron(III) phosphate. The mixtures were stirred at room temperature using a magnetic stirrer at 300 rpm for 5 minutes, and the aqueous solutions were sampled. The samples were centrifuged, and the orthophosphate ion concentration of the supernatant was measured. The results are shown in Table 7. As shown in Table 7, it was demonstrated that adding 1.5 mol / L was sufficient. The "orthophosphate ion elution rate," which indicates the proportion of orthophosphate ions eluted, was defined by Equation 16. [Table 7]

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[0077] The fourth step involves adding an alkaline earth metal salt to an aqueous solution containing orthophosphate ions produced in the third step, and then separating and recovering the precipitate containing phosphate produced in the fourth step.

[0078] <Preparation of aqueous solution containing orthophosphate ions> Dissolve 0.050 mol of reagent-grade disodium hydrogen phosphate dodecahydrate in 500 mL of deionized water to make 0.10 mol / LPO4 3- An aqueous solution was prepared.

[0079] <Example 8> 0.10 mol / LPO4 3- 500 mL of aqueous solution was placed in a beaker, calcium chloride was added to the solution to adjust the concentrations to 0.020, 0.050, and 0.10 mol / L, and the pH was adjusted to 5.0 using sodium hydroxide. The solution was then stirred at room temperature using a magnetic stirrer at 300 rpm for 30 minutes, and the aqueous solution was sampled. The sample was centrifuged, and the orthophosphate ion concentration of the supernatant was measured. The results are shown in Table 8. The "orthophosphate ion recovery rate," which indicates the proportion of orthophosphate ions recovered, was defined by Equation 17. [Table 8]

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[0080] In the first step, an iron salt is added to an aqueous solution containing hypophosphate and / or phosphite ions, and the precipitate containing iron(III) hypophosphate and / or iron(III) phosphate produced in the first step is purified by separation and recovery into treated water with a total phosphorus concentration of 16 mg / L or less. This paper describes whether the precipitate containing iron(III) hydroxide produced in the third step is suitable for use as an iron salt in the first step.

[0081] The aqueous solution obtained after the reaction in Example 7 was filtered, and the precipitate containing iron(III) hydroxide produced in the third step was dried. 4.1 g of the precipitate containing iron(III) hydroxide produced in the third step was obtained.

[0082] <Example 9> 0.10 mol / LPO3 3- 500 mL of the aqueous solution was placed in a beaker, and 3.0 g of the precipitate containing iron(III) hydroxide produced in the third step was added to this solution. The pH was adjusted to 5.0 using hydrochloric acid, and the mixture was stirred at room temperature at 300 rpm for 30 minutes using a magnetic stirrer. The aqueous solution was then sampled. The sample was centrifuged, and the total phosphorus concentration of the supernatant was measured. The result was below the detection limit, indicating that the phosphorus component was completely removed from the aqueous solution, demonstrating that the precipitate containing iron(III) hydroxide produced in the third step is suitable for use as an iron salt in the first step.

[0083] In the second step, an iodine salt or an aqueous solution containing an iodine salt produced in the second step is combined with a precipitate containing iron(III) hypophosphate and / or iron(III) phosphate produced in the first step, or with hypophosphate ions and / or phosphate ions and iron salts. This mixture is then brought into contact with air by aeration to oxidize to orthophosphate ions, and after neutralization, the precipitate containing iron(III) phosphate produced in the second step and the aqueous solution containing the iodine salt produced in the second step are separated and recovered. This section describes whether the aqueous solution containing the iodine salt produced in the second step is reusable.

[0084] The aqueous solution used in Example 3 was collected, sodium hydroxide was added to adjust the pH to 5, and the phosphorus component was completely precipitated as iron(III) phosphate. The solution was then filtered to remove the phosphorus component, and 98 mL of the aqueous solution containing the iodide salt produced in the second step was collected.

[0085] The aqueous solution used in Example 2 was collected, filtered, and the precipitate containing iron(III) phosphate produced in the first step was dried. 31.8 g of the precipitate containing iron(III) phosphate produced in the first step was obtained.

[0086] 1.0 g of the precipitate containing iron(III) phosphite produced in the first step was added to 100 mL of a 1.5 mol / L sodium hydroxide aqueous solution. The mixture was stirred at 300 rpm for 10 minutes using a magnetic stirrer to elute the phosphite ions, and the aqueous solution was sampled. The sample was centrifuged, and the total phosphorus concentration of the supernatant was measured. The result was 0.314 mol / L, indicating that 1.0 g of the precipitate containing iron(III) phosphite produced in the first step contained 0.00314 mol of phosphite ions as the phosphorus component.

[0087] <Example 10> 98 mL of an aqueous solution containing the iodite salt produced in the second step was placed in a flask. 10 g of the precipitate containing iron(III) phosphite produced in the first step and hydrochloric acid were added to adjust the pH to 1.0. A Liebig condenser was then connected to the flask. A tube was passed through the Liebig condenser, and the solution was stirred with a magnetic stirrer while aerating at 1.0 L / min. The solution was heated in a water bath for 90 minutes while maintaining a liquid temperature of 90°C, and the aqueous solution was sampled. The sample was eluted of phosphate ions using sodium hydroxide, the iron components were separated by centrifugation, the pH was adjusted, and the orthophosphate ion concentration was measured. A orthophosphate ion concentration of 0.32 mol / L was detected, indicating that the contained phosphate ions were completely oxidized. The aqueous solution containing the iodite salt produced in the second step was shown to be reusable.

[0088] This section describes the continuity across all four stages of the process: the first, second, third, and fourth stages.

[0089] Based on the 0.0314 mol of phosphate ions contained in 10 g of the iron(III) phosphate precipitate produced in the first step, the "orthophosphate ion content," which indicates the proportion of orthophosphate ions contained in the precipitate or aqueous solution produced, was defined by Equation 18. According to Equation 18, the precipitate containing iron(III) phosphate produced in the first step has a orthophosphate ion content of 0%.

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[0090] 10 g of the precipitate containing iron(III) phosphite produced in the first step and 100 mL of deionized water were placed in a flask. To this solution, 0.30 mol of iron(III) chloride, 0.10 mol of potassium iodide, and hydrochloric acid were added to adjust the pH to 1.0, and then a Liebig condenser was connected to the flask. A tube was passed through the Liebig condenser, and the mixture was stirred with a magnetic stirrer while aerating at 1 L / min. The solution was heated in a water bath for 90 minutes while maintaining a liquid temperature of 90°C, and the aqueous solution was sampled. The sample was eluted of phosphate ions using sodium hydroxide, the iron component was separated by centrifugation, the pH was adjusted, and the orthophosphate ion concentration was measured. The result was 0.307 mol / L, and according to Equation 18, the orthophosphate ion content of the aqueous solution containing the iodide salt produced in the second step was 97.8%.

[0091] Sodium hydroxide was added to the aqueous solution containing the iodide salt produced in the second step to neutralize it to pH 5.0, and the orthophosphate ions were precipitated as iron(III) phosphate. The precipitate was separated and recovered by filtration and dried. 17.2 g of precipitate containing iron(III) phosphate produced in the second step was obtained.

[0092] 500 mL of a 1.5 mol / L sodium hydroxide aqueous solution was mixed with 17.2 g of a precipitate containing iron(III) phosphate produced in the second step. The mixture was stirred at room temperature using a magnetic stirrer at 300 rpm for 5 minutes, and the aqueous solution was sampled. The sample was centrifuged, and the concentration of orthophosphate ions in the supernatant was measured. The result was 0.0542 mol / L, indicating that 0.0271 mol of orthophosphate ions were eluted. According to Equation 18, the orthophosphate ion content of the aqueous solution containing orthophosphate ions produced in the third step was 86.3%.

[0093] The aqueous solution containing orthophosphate ions produced in the third step was filtered, and 0.050 mol of calcium chloride was added to 496 mL of the resulting aqueous solution containing 0.0542 mol / L orthophosphate ions. The pH was adjusted to 5.0 using sodium hydroxide, and the mixture was stirred at room temperature at 300 rpm for 30 minutes using a magnetic stirrer. The aqueous solution was then sampled. The sample was centrifuged, and the orthophosphate ion concentration of the supernatant was measured. The result was 0.00477 mol / L, indicating that 0.0257 mol of phosphate was produced. According to Equation 18, the orthophosphate ion content of the precipitate containing phosphate produced in the fourth step was 81.9%. This demonstrated continuity throughout all four steps: the first, second, third, and fourth steps.

[0094] <Reference Example 1> 1.0 mol / LPO2 3- 100 mL of the aqueous solution was placed in a flask and stirred with a magnetic stirrer while aerating at 1.0 L / min through a tube. After 30 minutes, the aqueous solution was sampled and the orthophosphate ion concentration was measured. No orthophosphate ions were detected. [Explanation of Symbols]

[0095] 21 Separation, recovery, and purification reactor for phosphite ions and / or phosphite ions 22. Valve for supplying nickel ion removal waste liquid containing hypophosphate ions and / or phosphate ions. 23. Valve for supplying iron salts 24. Precipitate containing iron(III) hypophosphate and / or iron(III) phosphate produced in the first step. 25. Valves for treated water wastewater from which phosphite ions and / or phosphite ions have been removed. 26 Sediment 24 Discharge Valve 27. Air oxidation aeration tank for hypophosphate ions and / or phosphate ions 28 Valve for supplying iodide salt 29. Air pump for supplying air 210 Precipitate containing iron(III) phosphate produced in the second step 211 Sediment 210 Discharge Valve 212 Elution reactor for orthophosphate ions 213 Valve for supplying sodium hydroxide 214 Precipitate containing iron(III) hydroxide produced in the third step 215 Orthophosphate ions produced in the third step 216 Sediment 214 Discharge valve 217 Valve for discharging orthophosphate ions 218 Reactor for phosphate ion recovery 219 Calcium salt supply valve 220 Precipitate containing phosphate produced in the fourth step 221 Valve for treated water wastewater from which orthophosphate components have been removed 222 represents the sediment recovery valve, and 220 represents the sediment recovery valve. 31. Stirring motor 32 stirring blades 33. Filters for solid-liquid separation 34 Heater 35 Air diffuser 36 Cooling water supply port 37 Cooling water drain 38 Cooling tube for separating air and iodine 39 Magnet for removing iodine deposits from cooling tubes 310 Filter for reducing vaporized iodine 311 Transport pump for precipitate 210 312 Agitation motor 313 Agitator blade 314 Transport pump for precipitate 214 315 Solid-liquid separation filter 316 Agitation motor 317 Agitator blade 318 Solid-liquid separation filter

Claims

1. A method for oxidizing hypophosphate ions and / or phosphite ions to orthophosphate ions at normal pressure by adding an iron salt and an iodide salt to an aqueous solution containing hypophosphate ions and / or phosphite ions and bringing it into contact with air by aeration.

2. The first step involves adding an iron salt to an aqueous solution containing hypophosphate ions and / or phosphate ions, and separating and recovering the precipitate containing iron(III) hypophosphate and / or iron(III) phosphate from the treated water with a total phosphorus concentration of 16 mg / L or less to purify the water. The second step involves adding the precipitate containing iron(III) hypophosphate and / or iron(III) phosphate produced in the first step, or hypophosphate ions and / or phosphate ions and an iron salt, to an aqueous solution containing an iodide salt, contacting it with air by aeration to oxidize it to orthophosphate ions, and after neutralization, separating and recovering the precipitate containing iron(III) phosphate and the aqueous solution containing an iodide salt. A method for purifying electroless nickel plating wastewater, characterized by comprising: a third step of adding a precipitate containing iron(III) phosphate produced in the second step or iron(III) phosphate to an aqueous solution containing an alkali metal carbonate such as sodium carbonate and calcium hydroxide, thereby eluting orthophosphate ions, and separating and recovering the aqueous solution containing orthophosphate ions and the precipitate containing iron(III) hydroxide; and a fourth step of purifying the electroless nickel plating wastewater by adding an alkaline earth metal salt to the aqueous solution containing orthophosphate ions produced in the third step or an aqueous solution containing orthophosphate ions, thereby separating and recovering the precipitate containing phosphate and treated water with a total phosphorus concentration of 16 mg / L or less.

3. The method for purifying an aqueous solution containing hypophosphate ions and / or phosphite ions in the first step is to add an iron salt or a precipitate containing iron(III) hydroxide produced in the third step to the aqueous solution containing hypophosphate ions and / or phosphite ions, and purify the solution by separating and recovering the precipitate containing iron(III) hypophosphate and / or iron(III) phosphite produced in the first step into treated water with a total phosphorus concentration of 16 mg / L or less, as described in claim 2.

4. A method for purifying electroless nickel plating according to claim 3, wherein the method for oxidizing the precipitate containing iron(III) hypophosphate and / or iron(III) phosphate or hypophosphate ions and / or phosphate ions in the second step is to add the precipitate containing iron(III) hypophosphate and / or iron(III) phosphate or hypophosphate ions and / or phosphate ions produced in the first step to an aqueous solution containing an iron salt and an iodide salt or an iodide salt produced in the second step, bring it into contact with air by aeration to oxidize it to orthophosphate ions, and after neutralization separate and recover the precipitate containing iron(III) phosphate produced in the second step and the aqueous solution containing the iodide salt produced in the second step.

5. A method for purifying electroless nickel plating wastewater according to claim 3 or 4, wherein the method for eluting orthophosphate ions from the precipitate containing iron(III) phosphate or iron(III) phosphate in the third step is to add the precipitate containing iron(III) phosphate or iron(III) phosphate produced in the second step to an aqueous solution containing an alkali metal hydroxide such as sodium hydroxide or an alkali metal carbonate such as sodium carbonate and calcium hydroxide, to elute orthophosphate ions, and then separate and recover the aqueous solution containing orthophosphate ions and the precipitate containing iron(III) hydroxide produced in the third step.

6. A method for purifying electroless nickel plating wastewater according to claims 3 to 5, wherein the method for converting an aqueous solution containing orthophosphate ions in the fourth step to phosphate is to add an alkaline earth metal compound to the aqueous solution containing orthophosphate ions in the fourth step, and separate and recover the precipitate containing phosphate produced in the fourth step and treated water with a total phosphorus concentration of 16 mg / L or less, thereby purifying and recycling the phosphate.

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