Method for purifying aqueous solution containing compound capable of forming nickel complexes

Abstract

To provide a method for treating nickel-containing wastewater containing nickel-complexing compounds.SOLUTION: The wastewater is treated by combining the following two steps: (step 1) A decomposition step where an oxidizing agent and an oxidation decomposition catalyst are applied to the wastewater to decompose compounds capable of forming complexes with nickel in the wastewater; (step 2) An insolubilization step where a heavy metal insolubilization agent and a flocculant are applied to the wastewater after undergoing the (step 1).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a purification method for removing nickel from an aqueous solution containing a compound capable of forming a complex with nickel. [Background technology]

[0002] Zinc alloy plating offers superior corrosion resistance compared to zinc plating and is therefore widely used in electronic and automotive components. Alkaline zinc-nickel alloy plating baths are particularly used for fuel components, which require high corrosion resistance, and engine components, which are exposed to high temperatures. To solubilize zinc and nickel in the plating solution, the bath contains compounds capable of forming complexes with nickel, such as organic acids like citric acid and gluconic acid, ethylenediaminetetraacetic acid (EDTA), cyanide, amines, ammonia, polyphosphates, and polyethyleneimine (PEI). Therefore, wastewater from these factories contains heavy metals like zinc and nickel, as well as compounds capable of forming complexes with nickel, such as EDTA and PEI.

[0003] Nickel is a harmful heavy metal designated as a Class 1 designated chemical substance under the Act on Reporting, etc. of Releases to the Environment of Chemical Substances and Promotion of Improvements to Their Management, and is set as a monitoring item in the environmental standards for water pollution, making wastewater treatment increasingly important.In addition, China has set an emission standard value of 0.1 mg / L in Table 3 of the Plating Pollutant Discharge Standards (GB-21900-2008, hereinafter abbreviated as Table 3 Standard), and effective treatment technology is required.

[0004] Aqueous solutions containing nickel and zinc have been treated in wastewater treatment facilities using methods such as the hydroxide method, in which iron ions and an alkali metal hydroxide are added to make the solution alkaline, and nickel, zinc ions, etc. are precipitated as hydroxides together with the iron ions and other contained ions, and the nickel and zinc are separated from the aqueous solution before being discharged. Techniques other than the hydroxide method for removing various heavy metal elements contained in wastewater have also been proposed, such as a coagulation / separation removal method using the addition of an inorganic or organic coagulant, and an adsorption / removal method using activated carbon, an inorganic adsorbent, or an organic polymer material.

[0005] However, in many cases, wastewater from plating factories, electronic and mechanical parts manufacturing factories, automobile factories, etc. contains compounds that have the ability to form complexes with nickel, and nickel cannot be treated using the hydroxide method, coagulation separation removal method, or adsorption removal method mentioned above.

[0006] In addition to the above methods, there is a separation and removal method that utilizes the fact that dithiocarbamic acid salts form insoluble chelate complexes with nickel ions. However, when compounds with strong complex-forming properties with nickel, such as EDTA and PEI, are included, dithiocarbamic acid reacts preferentially with zinc over nickel, and the effectiveness of nickel purification treatment in nickel- and zinc-containing wastewater is insufficient.

[0007] In response to this problem, a method is known in which a compound capable of forming a complex with a heavy metal is first chemically oxidized, followed by an insolubilization treatment of the heavy metal. For example, chemical treatments such as the electrolytic oxidation method (see, for example, Patent Document 1) and the hydrogen peroxide-ferrous salt method (see, for example, Patent Document 2) have been proposed.

[0008] However, for example, the electrolytic oxidation method consumes a large amount of electrical energy, and the nickel concentration after treatment does not meet the standards in Table 3. As for the hydrogen peroxide-ferrous salt method, although it meets the standards in Table 3, the added ferrous salt becomes insoluble iron salt, which significantly increases the amount of excess sludge, resulting in higher excess sludge treatment costs.

[0009] Meanwhile, methods have been proposed for chemically oxidizing compounds capable of forming complexes with heavy metals in wastewater using chlorine-based chemicals (see, for example, Patent Document 3). However, the methods described in these patent documents require the use of expensive separation membranes to separate heavy metals from the wastewater after oxidation treatment, and furthermore, the separation membranes are not effective in removing nickel from the wastewater after oxidation treatment. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Patent Publication No. 2022-186460 [Patent Document 2] Patent Publication No. 2023-167782 [Patent Document 3] Patent application 2015-511828 Summary of the Invention [Problem to be solved by the invention]

[0011] The present invention has been made in view of the above-mentioned background art, and an object of the present invention is to provide a purification method capable of efficiently and significantly reducing the nickel concentration in an aqueous solution containing a compound capable of forming a complex with nickel, nickel, and zinc. [Means for solving the problem]

[0012] As a result of extensive research aimed at solving the above-mentioned problems, the present inventors have found that a simple method can be used to significantly reduce the nickel content in an aqueous solution containing a compound capable of forming a complex with nickel, and nickel and zinc, and have thus completed the present invention.

[0013] That is, the present invention has the following gist. [1] A method for treating wastewater containing nickel, comprising the following two steps: (Step 1) a decomposition step in which an oxidizing agent and an oxidative decomposition catalyst are allowed to act on the wastewater to decompose compounds capable of forming complexes with nickel in the wastewater; and (Step 2) An insolubilization step in which a heavy metal insolubilizer and a flocculant are allowed to act on the wastewater after the (step 1) step. [2] The method for treating wastewater according to [1], wherein the wastewater further contains zinc. [3] The method for treating wastewater according to [1] or [2], wherein the oxidizing agent is at least one selected from the group consisting of chlorine oxides, chloric acids and their salts, and hydrogen peroxide. [4] The method for treating wastewater according to any one of [1] to [3], wherein the oxidative decomposition catalyst is an oxidative decomposition catalyst comprising Ni oxide and a carrier that serves as an ion exchanger. [5] The method for treating wastewater according to any one of [1] to [4], further comprising, after step 1, a step of separating the wastewater from the oxidative decomposition catalyst. [6] The method for treating wastewater according to any one of [1] to [5], wherein the heavy metal insolubilizer is a salt of dithiocarbamic acid. [7] The method for treating wastewater according to any one of [1] to [6], wherein the flocculant is at least one selected from the group consisting of inorganic flocculants and polymer flocculants. [8] The method for treating wastewater according to any one of [1] to [7], wherein the amount of nickel contained in the treated wastewater is 0.1 mg / L or less. [Effects of the Invention]

[0014] The wastewater treatment method of the present invention is extremely useful industrially because it can reduce the nickel concentration to 0.1 mg / L or less even in a nickel-containing aqueous solution that is difficult to purify (for example, a nickel-containing aqueous solution that contains a compound capable of forming a complex with nickel or that also contains zinc). DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention will be described in detail below.

[0016] The wastewater treatment method of the present invention is a method for removing heavy metals, particularly nickel, from wastewater, particularly heavy metal-containing wastewater, especially wastewater containing nickel and zinc, and includes the following steps 1 and 2. (Step 1) a decomposition step in which an oxidizing agent and an oxidative decomposition catalyst are allowed to act on the wastewater to decompose compounds capable of forming complexes with nickel in the wastewater; (Step 2) An insolubilization step in which a heavy metal insolubilizer and a flocculant are allowed to act on the wastewater subjected to (Step 1). The wastewater treatment method of the present invention may also include a pre-treatment COD concentration measurement step and a heavy metal concentration measurement step for determining the amounts of oxidizing agent and oxidative decomposition catalyst to be applied to the wastewater to be treated in the decomposition step, and the effects of heavy metal insolubilizer and coagulant to be applied in the insolubilization step.

[0017] In the wastewater treatment method of the present invention, the wastewater to be treated is not particularly limited, but examples thereof include industrial wastewater and domestic wastewater, and more specifically, examples thereof include wastewater from plating factories, metal processing factories, and automobile factories.

[0018] In the present invention, the heavy metals contained in the wastewater are not particularly limited, and may include, in addition to nickel, one or more heavy metals selected from the group consisting of cadmium, chromium, copper, iron, mercury, lead, zinc, palladium, gold, silver, platinum, cobalt, indium, molybdenum, antimony, tin, titanium, zirconium, manganese, and tungsten. Specifically, for example, wastewater from a metal processing factory contains both nickel and zinc, and it is possible to simultaneously reduce the concentrations of both heavy metals to low levels.

[0019] The wastewater to which the treatment method of the present invention is applied contains compounds capable of forming complexes with heavy metals, such as citric acid, gluconic acid, oxalic acid, tartaric acid, succinic acid, EDTA, ethylenediamine, triethanolamine, diethylenetriamine, and PEI.

[0020] <Disassembly process> Step 1 in the wastewater treatment method of the present invention is a decomposition step in which an oxidizing agent and an oxidative decomposition catalyst are allowed to act on wastewater, particularly wastewater containing heavy metals, especially wastewater containing nickel, to decompose compounds capable of forming complexes with heavy metals, particularly compounds capable of forming complexes with nickel, in the wastewater. There is no particular restriction on the order of adding the oxidizing agent and the oxidative decomposition catalyst in step 1 of the wastewater treatment method of the present invention, but from the viewpoint of ease of adjustment, it is preferable to add the oxidizing agent followed by the oxidative decomposition catalyst.

[0021] (oxidizing agent) The oxidizing agent of the present invention is a compound that transfers oxygen atoms to a target substrate compound or a substance that deprives electrons from a target substrate in an oxidation-reduction reaction, and is selected from the group consisting of chlorine, hypochlorous acid, sodium hypochlorite, calcium hypochlorite, sodium chlorite, chlorine dioxide, sodium chlorate, chloroisocyanuric acid, dichloroisocyanuric acid, trichloroisocyanuric acid, bromochloromethylhydantoin, hydrogen peroxide, etc. Furthermore, these oxidizing agents may be used alone or in combination. From the viewpoints of ease of handling and availability, chlorine, sodium hypochlorite, calcium hypochlorite, and hydrogen peroxide are particularly preferred. The amount of oxidizing agent added in the present invention is not particularly limited and can be adjusted appropriately depending on the COD concentration in the wastewater. For example, the oxidizing agent is added in an amount, in terms of weight concentration ratio, of 0.1 to 300 times, more preferably 1 to 150 times, and particularly preferably 1 to 50 times, the COD concentration in the wastewater.

[0022] (oxidative decomposition catalyst) The oxidative decomposition catalyst of the present invention is composed of Ni oxide and a carrier for supporting the Ni oxide. In the oxidative decomposition catalyst of the present invention, examples of Ni oxides include NiO, Ni2O3, Ni3O4, NiO2, and NiOOH. The Ni oxide used in the present invention may be a single particle of a metal oxide or a metal oxide supported on an ion exchanger. However, it is preferable to support Ni oxide because increasing the surface area can improve the decomposition efficiency. The carrier in the present invention is an ion exchanger, and either an inorganic ion exchanger or an organic polymer ion exchanger can be suitably used. Specific examples of inorganic ion exchangers include zeolite, metal powder, and zirconia, but zeolite is preferred because it is stable over a wide pH range, does not decompose in the presence of an oxidizing agent, and is readily available. The zeolite compound used as the carrier in the present invention is not particularly limited, but a large-pore zeolite having a 12-membered ring structure is particularly preferred, and the SiO2 / Al2O3 molar ratio is preferably 5-80, and more preferably 5-50. Examples of organic polymer ion exchangers include hydrocarbon-based ion exchangers having exchange groups such as sulfonic acid groups, carboxylic acid groups, phosphonic acid groups, and phenolic hydroxyl groups, and fluorine-based ion exchangers. However, fluorine-based cation exchangers are preferred in terms of heat resistance, chemical resistance, and flexibility in shape selection. The fluorine-based cation exchanger used as the support in the present invention is not particularly limited, but those having sulfonic acid groups or carboxylic acid groups are preferred in terms of their bonding strength with Ni oxide. The fluorine-based cation exchanger may be in the form of a membrane, sphere, or fiber. In the present invention, the method for supporting Ni oxide on the support is not particularly limited, and examples thereof include a method in which the support is impregnated with a suspension or solution of Ni oxide and then dried to allow the Ni oxide to be attached to the support surface, and a method in which the support is modified with Ni salt by ion exchange or the like and then the nickel atoms are oxidized. Methods for impregnating or attaching Ni oxide include physical mixing and mechanical alloying. Methods for oxidizing after ion exchange include contacting the support with an aqueous Ni salt solution and then connecting it with an oxidizing agent. The amount of Ni supported on the oxidative decomposition catalyst of the present invention is not particularly limited, but if it is too small, the catalyst will have few active sites, resulting in a slow decomposition rate or insufficient decomposition of coordination compounds. On the other hand, if the amount of oxidative decomposition catalyst supported on the support is too large, Ni aggregation or other factors may reduce the catalyst surface area and activity. Therefore, the amount of Ni supported on the support is preferably 1 to 10 wt % of the weight of the support, and more preferably 1 to 5 wt %. The concentration of the oxidative decomposition catalyst added in the present invention is not particularly limited and is determined by the amount of compounds capable of forming complexes with nickel contained in the wastewater to be treated. The higher the concentration of the oxidative decomposition catalyst added, the faster the decomposition rate of compounds capable of forming complexes with nickel, but if the concentration is too high, the equipment will become larger and the capital investment will increase. If the amount of oxidative decomposition catalyst is too small, the decomposition rate will decrease, and there is a possibility that the amount of wastewater to be treated will not be able to be treated. The amount of oxidative decomposition catalyst added per liter of wastewater is preferably 100 mg / L to 500 g / L, more preferably 1 g / L to 300 g / L, and particularly preferably 5 g / L to 50 g / L. In step 1 of the wastewater treatment method of the present invention, the pH when the oxidizing agent and the oxidative decomposition catalyst are allowed to act is not particularly limited. However, if the pH is too low, Ni oxides may be ionized and eluted, resulting in a decrease in catalytic activity. Therefore, a pH of 5 to 13 is preferred, more preferably 6 to 10, and particularly preferably 7 to 9. In step 1 of the wastewater treatment method of the present invention, if the pH fluctuates during the treatment, it may be adjusted by adding an acid or alkali as appropriate so that the pH falls within the above range. The treatment format for step 1 in the wastewater treatment method of the present invention is not particularly limited, and any commonly used format such as a fixed bed, fluidized bed, moving bed, or suspended bed can be used, or a combination of these can be used. In addition, any of a continuous system, a batch system, or a semi-batch system can be used.

[0023] <Insolubilization process> The wastewater treated in step 1 of the present invention is subjected to a treatment operation to separate the wastewater from the oxidative decomposition catalyst. There are no particular limitations on the separation method, and examples include sand filtration, belt press, sedimentation in a settling tank, and filter paper filtration. Although there is no particular restriction on the order of addition of the heavy metal insolubilizer and the flocculant in step 2 of the wastewater treatment method of the present invention, it is preferable to add the flocculant after the addition of the heavy metal insolubilizer from the viewpoint of treatment efficiency. Regarding the timing for applying the flocculant, the heavy metal insolubilizer is added to the wastewater, and the mixture is mixed by stirring for 1 to 60 minutes, preferably 2 to 30 minutes, more preferably 5 to 10 minutes, before the flocculant is applied.

[0024] (Heavy metal insolubilizer) The heavy metal insolubilizer of the present invention is a salt of dithiocarbamic acid. It is not particularly limited as long as it is a compound having a dithiocarbamyl group in the molecule. For example, it may be a compound obtained by reacting an amine compound having at least one amino group selected from the group consisting of primary amino groups and secondary amino groups with carbon disulfide and an alkali metal hydroxide. A compound obtained by reacting an amine compound having two or more amino groups selected from the group consisting of primary amino groups and secondary amino groups with carbon disulfide and an alkali metal hydroxide is more preferred.

[0025] Specific examples of the amine compound having at least one amino group selected from the group consisting of a primary amino group and a secondary amino group include dimethylamine, diethylamine, piperazine, pyrrolidine, piperidine, diethylenetriamine, N-(2-aminoethyl)piperazine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, heptaethyleneoctamine, polyethyleneimine, and a condensate of polyethyleneimine and benzyl chloride.

[0026] The amine compound that forms the dithiocarbamic acid salt is not particularly limited as long as it has at least one amino group selected from the group consisting of a primary amino group and a secondary amino group. However, from the viewpoints of nickel treatment performance and compound stability, reaction products of pyrrolidine, piperazine, tetraethylenepentamine, diethylamine, or dimethylamine with carbon disulfide and an alkali metal hydroxide are preferred. Among these, the dithiocarbamic acid salt of tetraethylenepentamine is a composition in which the raw material, tetraethylenepentamine, contains analogs [see formulas (2) to (4)] in addition to the linear form [see formula (1) below], which is the main component. To further enhance nickel treatment performance and compound stability, reaction products of piperazine or dimethylamine with carbon disulfide and an alkali metal hydroxide are more preferred because they do not have these drawbacks.

[0027] [ka]

[0028] As the alkali metal hydroxide used to prepare the salt of dithiocarbamic acid, sodium hydroxide and potassium hydroxide are particularly preferred because of their easy availability.

[0029] As the ammonium used for preparing the salt of dithiocarbamic acid, an aqueous ammonium solution is particularly preferred in terms of availability and ease of handling.

[0030] (flocculant) The flocculant of the present invention is an inorganic flocculant or a polymer flocculant.

[0031] The inorganic flocculant is not particularly limited, but examples thereof include iron compounds such as ferric chloride or ferrous sulfate, and aluminum compounds such as aluminum sulfate or polyaluminum chloride. It is preferable to use commercially available products of these inorganic flocculants as they are.

[0032] The polymer flocculant is not particularly limited, but examples thereof include acrylic acid polymers, acrylamide polymers, and dimethylaminoethyl methacrylate polymers. Among these, acrylic acid polymers are preferred because of their excellent nickel removal. It is preferable to use commercially available products of these polymer flocculants as they are.

[0033] There is no particular restriction on the order of addition of the inorganic flocculant and polymer flocculant, but from the viewpoint of treatment efficiency, it is preferable to add the polymer flocculant after the inorganic flocculant. The timing for acting the polymer flocculant may be such that the inorganic flocculant is added to the wastewater, and the wastewater is mixed by stirring for 1 to 60 minutes, preferably 2 to 30 minutes, more preferably 5 to 10 minutes, and then the polymer flocculant is acted on.

[0034] The wastewater to which the polymer flocculant has been added is preferably stirred, and the stirring time is usually selected from the range of several minutes to 2 hours.

[0035] After the series of steps are completed, the water to be treated is subjected to solid-liquid separation, which can be carried out by a conventional method such as filtration, centrifugation, or sedimentation. [Example]

[0036] The present invention will be specifically described below, but it should not be construed that the present invention is limited to these examples.

[0037] (Nickel concentration analysis method) The nickel concentration in the aqueous solution was measured using an ICP emission spectrometer (ICPE-9800, manufactured by Shimadzu Corporation).

[0038] (Zinc concentration analysis method) The zinc concentration in the aqueous solution was measured using an ICP emission spectrometer (ICPE-9800, manufactured by Shimadzu Corporation).

[0039] (COD concentration analysis method) The COD concentration in the aqueous solution was measured in accordance with JIS K 0102-17.

[0040] Preparation example (oxidizing agent) The following compounds manufactured by Tosoh Corporation were used as oxidizing agents: 12% sodium hypochlorite.

[0041] (Oxidative decomposition catalyst A) The oxidative decomposition catalyst A used was prepared according to the following method. 119 parts by weight of nickel chloride hexahydrate (Kishida Chemical Co., Ltd.) was placed in a beaker and dissolved in 446 parts by weight of pure water to obtain a 1 mol / L aqueous nickel chloride solution. 250 mL of 1 mol / L nickel chloride aqueous solution was placed in a 500 mL beaker, and 30 g of Y-type zeolite (manufactured by Tosoh Corporation) with a SiO2 / Al2O3 molar ratio of 5.5 was added as a carrier. The mixture was stirred at 70 °C for 2 hours and then filtered through 5C filter paper. The resulting filter residue and 250 mL of a newly prepared 1 mol / L nickel chloride aqueous solution were added to a 500 mL beaker, stirred at 70 °C for 2 hours, then filtered through 5C filter paper. The filter residue was washed with water. 20 parts by weight of the resulting dried residue and 1230 parts by weight of 0.2 mol / L sodium hydroxide aqueous solution (manufactured by Kishida Chemical Co., Ltd.) were added and stirred for 10 minutes. After stirring, 180 parts by weight of 12% sodium hypochlorite (manufactured by Tosoh Corporation) was added, the temperature was raised to 75 °C, and the mixture was stirred for 2 hours. The reaction solution was filtered through 5C filter paper, and the filter residue was washed with water. The resulting filtration residue was dried at 75°C for 12 hours to obtain an oxidative decomposition catalyst with a Ni content of 3.5 wt%.

[0042] (Oxidative decomposition catalyst B) The oxidative decomposition catalyst B used was prepared according to the following method. 119 parts by weight of nickel chloride hexahydrate (Kishida Chemical Co., Ltd.) was placed in a beaker and dissolved in 446 parts by weight of pure water to obtain a 1 mol / L aqueous nickel chloride solution. 250 mL of 1 mol / L nickel chloride aqueous solution was placed in a 500 mL beaker, and 30 g of beta-type zeolite (manufactured by Tosoh Corporation) with a SiO2 / Al2O3 molar ratio of 40 was added as a carrier. The mixture was stirred at 70 °C for 2 hours and then filtered through Advantec 5C filter paper. The resulting filter residue and 250 mL of a newly prepared 1 mol / L nickel chloride aqueous solution were added to a 500 mL beaker and stirred at 70 °C for 2 hours. The mixture was then filtered through Advantec 5C filter paper, and the filter residue was washed with water. 20 parts by weight of the resulting dried residue and 245 parts by weight of 0.2 mol / L sodium hydroxide aqueous solution (manufactured by Kishida Chemical Co., Ltd.) were added and stirred for 10 minutes. After stirring, 35 parts by weight of 12% sodium hypochlorite (manufactured by Tosoh Corporation) were added, and the mixture was heated to 75 °C and stirred for 2 hours. The reaction solution was filtered through Advantec 5C filter paper, and the filter residue was washed with water. The resulting filtration residue was dried at 75°C for 12 hours to obtain an oxidative decomposition catalyst with a Ni content of 1.8 wt%.

[0043] (Preparation of salts of dithiocarbamic acid) The heavy metal insolubilizer used was prepared according to the following method. After mixing 112 g of piperazine (manufactured by Tosoh Corporation) and 386 g of pure water, 306 g of 48 wt % potassium hydroxide (manufactured by Kishida Chemical Co., Ltd.) and 196 g of carbon disulfide (manufactured by Kishida Chemical Co., Ltd.) were added dropwise alternately in four portions at 25°C while stirring in a nitrogen stream. After stirring for one hour, an aqueous solution containing 40 wt % of the compound represented by the following formula (5) (dipotassium piperazine-1,4-bis(carbodithioate)) was obtained.

[0044] [ka]

[0045] (inorganic flocculant) The following aqueous solution was used as the inorganic flocculant: An aqueous solution (30 wt % polyaluminum chloride aqueous solution) prepared by adding 30 g of polyaluminum chloride (Kishida Chemical Co., Ltd.) to water to make a total of 100 g.

[0046] (polymer flocculant) OA-23 (weak anionic polymer) manufactured by Organo Corporation was used as the polymer flocculant.

[0047] [Example 1] The nickel, zinc, and PEI concentrations in the wastewater were adjusted to 1 mg / L, 1 mg / L, and 500 mg / L, respectively, and the COD concentration in the aqueous solution was measured according to JIS K 0102-17. The COD concentration was 800 mg / L. 300 mL of the wastewater was placed in a 500 mL beaker placed in a jar tester. Then, while stirring at 150 rpm, 12 g of 12% sodium hypochlorite (concentration: 40 g / L) and 6 g of the oxidative decomposition catalyst A (concentration: 20 g / L) were added, the pH of the reaction solution was adjusted to 8.5, and the mixture was stirred at room temperature for 1 hour. The wastewater was then filtered using Advantec 5C filter paper, and the filtrate was poured into a 500 mL beaker newly installed in the jar tester. Next, while stirring at 150 rpm, 15 mg of an aqueous solution containing 40 wt% of the dithiocarbamic acid salt (50 mg / L dithiocarbamic acid concentration) was added and stirred for 10 minutes. Next, 300 mg of a 30 wt% aqueous solution of polyaluminum chloride (hereinafter abbreviated as PAC) (90 mg PAC, 300 mg / L concentration) was added, and hydrochloric acid was added to adjust the pH to 7. The solution was stirred at 150 rpm for 5 minutes. Next, 300 mg of OA-23 (1000 mg / L concentration) was added as a polymer flocculant and stirred at 50 rpm for 5 minutes. After stirring, the solution was left to stand for 5 minutes, and then filtered using Advantec 5A filter paper. The nickel and zinc concentrations of the treated aqueous solution were measured. The results are shown in Table 1.

[0048] [Example 2] The nickel and zinc concentrations in the aqueous solution after treatment were measured in the same manner as in Example 1, except that the chemicals added were changed to those shown in Table 1. The results are shown in Table 1.

[0049] [Comparative Example 1] The nickel, zinc, and PEI concentrations in the wastewater were adjusted to 1 mg / L, 1 mg / L, and 500 mg / L, respectively, and the COD concentration in the aqueous solution was measured according to JIS K 0102-17. The COD concentration was 800 mg / L. 300 mL of the wastewater was placed in a 500 mL beaker placed in a Jar Tester, and then 12 g of 12% sodium hypochlorite (concentration: 40 g / L) was added while stirring at 150 rpm to adjust the pH of the reaction solution to 8.5, followed by stirring at room temperature for 1 hour. The wastewater was then filtered using Advantec 5C filter paper, and the filtrate was poured into a 500 mL beaker newly installed in the jar tester. Next, while stirring at 150 rpm, 15 mg of an aqueous solution containing 40 wt% of the dithiocarbamic acid salt (50 mg / L dithiocarbamic acid concentration) was added and stirred for 10 minutes. Next, 300 mg of a 30 wt% aqueous solution of polyaluminum chloride (hereinafter abbreviated as PAC) (90 mg PAC, 300 mg / L concentration) was added, and hydrochloric acid was added to adjust the pH to 7. The solution was stirred at 150 rpm for 5 minutes. Next, 300 mg of OA-23 (1000 mg / L concentration) was added as a polymer flocculant and stirred at 50 rpm for 5 minutes. After stirring, the solution was left to stand for 5 minutes, and then filtered using Advantec 5A filter paper. The nickel and zinc concentrations of the treated aqueous solution were measured. The results are shown in Table 1.

[0050] Comparative Example 2 The nickel, zinc, and PEI concentrations in the wastewater were adjusted to 1 mg / L, 1 mg / L, and 500 mg / L, respectively, and the COD concentration in the aqueous solution was measured according to JIS K 0102-17. The COD concentration was 800 mg / L. 300 mL of the wastewater was placed in a 500 mL beaker placed in a jar tester, and then 6 g of the oxidative decomposition catalyst A (concentration: 20 g / L) was added while stirring at 150 rpm. The pH of the reaction solution was adjusted to 8.5, and the mixture was stirred at room temperature for 1 hour. The wastewater was then filtered using Advantec 5C filter paper, and the filtrate was poured into a 500 mL beaker newly installed in the jar tester. Next, while stirring at 150 rpm, 15 mg of an aqueous solution containing 40 wt% of the dithiocarbamic acid salt (50 mg / L dithiocarbamic acid concentration) was added and stirred for 10 minutes. Next, 300 mg of a 30 wt% aqueous solution of polyaluminum chloride (hereinafter abbreviated as PAC) (90 mg PAC, 300 mg / L concentration) was added, and hydrochloric acid was added to adjust the pH to 7. The solution was stirred at 150 rpm for 5 minutes. Next, 300 mg of OA-23 (1000 mg / L concentration) was added as a polymer flocculant and stirred at 50 rpm for 5 minutes. After stirring, the solution was left to stand for 5 minutes, and then filtered using Advantec 5A filter paper. The nickel and zinc concentrations of the treated aqueous solution were measured. The results are shown in Table 1.

[0051] Comparative Example 3 The nickel, zinc, and PEI concentrations in the wastewater were adjusted to 1 mg / L, 1 mg / L, and 500 mg / L, respectively, and the COD concentration in the aqueous solution was measured according to JIS K 0102-17. The COD concentration was 800 mg / L. 300 mL of the wastewater was placed in a 500 mL beaker placed in a jar tester. Next, while stirring at 150 rpm, 15 mg of an aqueous solution containing 40 wt% of the dithiocarbamic acid salt (50 mg / L dithiocarbamic acid concentration) was added and stirred for 10 minutes. Next, 300 mg of a 30 wt% aqueous solution of polyaluminum chloride (hereinafter abbreviated as PAC) (90 mg PAC, 300 mg / L concentration) was added, and hydrochloric acid was added to adjust the pH to 7. The solution was stirred at 150 rpm for 5 minutes. Next, 300 mg of OA-23 (1000 mg / L concentration) was added as a polymer flocculant and stirred at 50 rpm for 5 minutes. After stirring, the solution was left to stand for 5 minutes, filtered using Advantec 5A filter paper, and the nickel and zinc concentrations of the treated solution were measured. The results are shown in Table 1.

[0052] The nickel and zinc concentrations in the aqueous solution after treatment were measured in the same manner as in Example 1, except that the chemicals added were changed to those shown in Table 1. The results are shown in Table 1.

[0053] Comparative Example 4 The nickel, zinc, and PEI concentrations in the wastewater were adjusted to 1 mg / L, 1 mg / L, and 500 mg / L, respectively, and the COD concentration in the aqueous solution was measured according to JIS K 0102-17. The COD concentration was 800 mg / L. 300 mL of the wastewater was placed in a 500 mL beaker placed in a jar tester. Then, while stirring at 150 rpm, 12 g of 12% sodium hypochlorite (concentration: 40 g / L) and 6 g of the oxidative decomposition catalyst A (concentration: 20 g / L) were added, the pH of the reaction solution was adjusted to 8.5, and the mixture was stirred at room temperature for 1 hour. The wastewater was then filtered using 5C filter paper manufactured by Advantec Co., Ltd., and the nickel and zinc concentrations in the treated aqueous solution were measured. The results are shown in Table 1.

[0054] [Table 1]

[0055] The nickel concentration in the treated water in Table 1 was determined to be OK if it met the standard value in Table 3, and NG if it did not.

[0056] In Examples 1 and 2, in which an oxidizing agent and an oxidative decomposition catalyst were applied in step 1 and a heavy metal insolubilizing agent and a flocculant were applied in step 2, the nickel concentration in the treated water satisfied the nickel Table 3 standard.

[0057] In contrast, Comparative Example 1, in which no oxidizing agent was used in Step 1, and Comparative Example 2, in which no oxidative decomposition catalyst was used in Step 1, failed to satisfy the nickel Table 3 standard. In Comparative Example 3 in which step 1 was not performed and Comparative Example 4 in which step 2 was not performed, the nickel concentration in the treated water was 0.47 to 0.51 mg / L, and the standards in Table 3 were not met.

Claims

1. A method for treating wastewater containing nickel, comprising the following two steps: (Step 1) a decomposition step in which an oxidizing agent and an oxidative decomposition catalyst are allowed to act on the wastewater to decompose compounds capable of forming a complex with nickel in the wastewater; (Step 2) An insolubilization step in which a heavy metal insolubilizer and a flocculant are allowed to act on the wastewater after (Step 1).

2. 2. The method for treating wastewater according to claim 1, wherein the wastewater further contains zinc.

3. 2. The method for treating wastewater according to claim 1, wherein the oxidizing agent is at least one selected from the group consisting of chlorine oxides, chloric acids and their salts, and hydrogen peroxide.

4. 2. The method for treating wastewater according to claim 1, wherein the oxidative decomposition catalyst comprises an Ni oxide and a carrier that serves as an ion exchanger.

5. 2. The method for treating wastewater according to claim 1, further comprising a step of separating the wastewater from the oxidative decomposition catalyst after step 1.

6. 2. The method for treating wastewater according to claim 1, wherein the heavy metal insolubilizing agent is a salt of dithiocarbamic acid.

7. 2. The method for treating wastewater according to claim 1, wherein the flocculant is at least one selected from the group consisting of inorganic flocculants and polymer flocculants.

8. 2. The method for treating wastewater according to claim 1, wherein the amount of nickel contained in the treated wastewater is 0.1 mg / L or less.

Images