JP6820790B2 - Hazardous element removal method and its uses - Google Patents

Description

The present invention relates to a method for removing harmful elements to the human body, and more particularly to a harmful element removing method capable of removing harmful elements easily and at low cost and its use.

Currently, as edible safety and health standards, strict standard values have been set for elements that are harmful to the human body, and techniques for removing such harmful elements are being actively researched.

For example, even in edible salts, strict standard values are set for such harmful elements such as arsenic and mercury. According to the Safety and Health Guidelines for Edible Salt (established on September 10, 2000, revised on October 1, 2013, Japan Salt Industry Association), the standard value of arsenic is 0.2 mg / kg or less. The standard value of mercury is 0.05 mg / kg or less.

In addition, regarding the technology for removing harmful elements, it is essential to remove harmful elements such as arsenic when recovering valuable resources from the geothermal water of the spring source, which is rich in resources. Has been done.

The quality of geothermal water varies depending on the source. In particular, many spring sources in Japan are chloride springs, and NaCl and KCl that can be recovered from those spring sources are valuable resources with high utility value. In addition, lithium, which is a material for secondary batteries and pharmaceuticals, has a high dissolved concentration of about 10 ppm regardless of the source of the spring. If the recovery efficiency of these valuable resources is improved, it is expected that the recovery cost of the valuable resources will be reduced and the business development of the recovery of the valuable resources using geothermal water will be realized.

At present, low-cost and high-efficiency removal technology is difficult at present. If it becomes possible to remove harmful substances such as arsenic efficiently and at low cost, it is expected that various valuable resources can be utilized.

As a conventional method for removing harmful elements, for example, harmful substances containing 70% by mass or more of steelmaking slag having a content of 30% by mass or more, a calcium content of 10% by mass or more, and a silicon content of 10% by mass or less. It is known to include a treatment step of reducing the arsenic content of the treatment target or reducing the arsenic elution amount from the treatment target by bringing the element reducing material into contact with the treatment target (Patent). Reference 1).

Further, for example, as a conventional method for removing harmful elements, ferrous salt is added to selenium (Se) and arsenic (As) -containing wastewater, and then Ca (OH) ₂ and / or CaO is added and reacted to obtain the product. A method for treating selenium (Se) and arsenic (As) -containing wastewater, which is characterized by solid-liquid separation of the treated liquid, is known (see Patent Document 2).

Japanese Unexamined Patent Publication No. 2013-116465 JP-A-2002-192167

However, in the conventional conventional method for removing harmful elements, for example, in the method of bringing the harmful element reducing material into contact with the object to be treated as in Patent Document 1, not only the cost of manufacturing the harmful element reducing material is high but also the treatment is performed. Post-treatment of the harmful element reducing material after contact with the object (for example, disposal or depreciation) also requires a separate cost, which causes a problem that the work is complicated and the cost is high.

Further, in the conventional conventional method for removing harmful elements, for example, in the method of solid-liquid separation of the treatment liquid obtained by reaction as in Patent Document 2, the solid-liquid separation operation itself is not only complicated. There is a problem that the work is not easy because the conditions for solid-liquid separation (pH adjustment, etc.) are severe.

Therefore, it is expected to realize a method for removing harmful elements from raw water containing harmful elements by a simple method, but such a method has not been found at present.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a harmful element removing method for reliably removing harmful elements from raw material water containing harmful elements by a simple method, and to provide an application thereof. ..

As a result of diligent research, the present inventor has carried out two types of co-precipitation treatments continuously from raw material water containing at least harmful elements including mercury and arsenic, so that mercury and arsenic are precipitated from the raw material water. It was found that it was efficiently removed and harmful elements could be easily removed from the raw water.

That is, as the method for removing harmful elements disclosed in the present application, in the method for removing harmful elements from raw material water containing at least harmful elements including mercury and arsenic, oxidation by adding an oxidizing agent to the raw material water is performed. An iron compound and a hydrogen peroxide solution are added to the treatment solution obtained by the step and the oxidation step, and the first precipitate containing at least arsenic produced by the addition is filtered to obtain a first filtrate. Magnesium chloride hydrate and a sodium hydroxide solution are added to the first removal step and the first filtrate obtained by the first removal step, and the addition contains at least arsenic and mercury produced by the addition. Provided are those comprising a second removal step of filtering the precipitate of 2 to obtain a second filtrate.

The flowchart of the harmful element removal method which concerns on 1st Embodiment of this application is shown. The flowchart of the harmful element removal method which concerns on 2nd Embodiment of this application is shown. The flowchart of the harmful element removal method which concerns on 3rd Embodiment of this application is shown. The results of the addition amount of iron and the precipitation component in the first removal step (one-step coprecipitation) of the harmful element removal method according to Example 1 of the present application are shown. The results of the addition amount of hydrogen peroxide solution and the removal rate of arsenic in the first removal step (one-step coprecipitation) of the harmful element removal method according to Example 1 of the present application, and the EDX pattern result are shown. The photograph in the second removal step (two-step co-precipitation) of the harmful element removal method which concerns on Example 1 of this application, the EDX pattern result of a precipitate, and the EDX pattern result of a solution (bittern) are shown. The XRD pattern result which is the separation recovery result of sodium chloride and potassium chloride from the solution (irrigation) obtained in the 2nd removal step (two-step coprecipitation) of the harmful element removal method which concerns on Example 1 of this application is shown. The EDX pattern result of the precipitate obtained in the second removal step (two-step co-precipitation) of the harmful element removal method according to Example 2 of the present application, the EDX pattern result of the solution (irrigation), and the EDX of the solution (bittern). The pattern result is shown. As a result of the amount of iron added in the first removal step (one-step coprecipitation) and the precipitation component of the harmful element removing method according to Example 2 of the present application, the addition of iron in the second removal step (two-step coprecipitation). The results of the amount and the precipitation component, and the EDX pattern result for each addition amount of magnesium chloride hexahydrate for the precipitate obtained in the second removal step (two-step coprecipitation) are shown. The results of the amount of magnesium chloride hexahydrate added to the precipitate obtained in the second removal step (two-step coprecipitation) of the harmful element removal method according to Example 2 of the present application and the component peak intensity, and one The content of each element for each addition amount of hydrogen peroxide for each precipitate obtained by the step coprecipitation and the two step coprecipitation is shown. The results of separation and recovery of sodium chloride and potassium chloride from the solution (irrigation) obtained in the second removal step (two-step coprecipitation) of the harmful element removal method according to Example 2 of the present application are shown.

(First Embodiment)
As shown in FIG. 1, the harmful element removing method according to the first embodiment of the present application is a harmful element removing method for removing the harmful element from the raw material water containing the harmful element containing at least mercury and arsenic. An oxidation step (S1) in which an oxidizing agent is added to the raw material water, and a first method containing at least arsenic produced by adding an iron compound and a hydrogen peroxide solution to the treatment solution obtained by this oxidation step. In the first removal step (S2) of filtering the precipitate of the above to obtain a first filtrate and the first filtrate obtained by this first removal step, magnesium chloride hydrate and a sodium hydroxide solution were added to the first filtrate. It comprises a second removal step (S3) of adding and filtering a second precipitate containing at least arsenic and mercury produced by the addition to obtain a second filtrate.

Hereinafter, the method for removing harmful elements according to the first embodiment of the present application will be described in detail with reference to the flowchart shown in FIG.

(Oxidation process)
First, an oxidizing agent is added to the raw water containing harmful elements including at least mercury (Hg) and arsenic (As) (S1). The raw material water can be either an aqueous solution existing in nature or an artificially produced aqueous solution such as factory effluent, as long as it contains at least harmful elements including mercury and arsenic. As the raw material water existing in the natural world, for example, seawater or geothermal water can be targeted.

Further, the seawater or geothermal water (also referred to as seawater hydrothermal water) as the raw material water is not particularly limited as long as it is general seawater or geothermal water, and for example, the specific gravity d is 1.03. Can be used. The definition of the specific gravity d is a dimensionless number that can be measured using a commercially available hydrometer (for example, standard hydrometer No. 4, manufactured by AS ONE Corporation).

When seawater or geothermal water is used as the raw material water, a solution in which harmful elements are removed from seawater or geothermal water rich in nutrients can be obtained, so that it can be used for various purposes including foods. It can be applied.

In particular, since mercury (Hg) and arsenic (As) among the harmful elements can be efficiently removed by using the harmful element removing method according to the present embodiment (see Examples described later), mercury (Hg) and It can also be applied to the food sector, where arsenic (As) regulations are strict. Such a suitable application example includes the production of salt and bittern from nutrient-rich seawater or geothermal water as a raw material.

The oxidizing agent is not particularly limited, but hydrogen peroxide solution, potassium nitrate, hypochlorous acid, chloric acid, chloric acid, perchloric acid, halogen compounds, permanganate, cerium ammonium nitrate, chromic acid and the like are used. It is preferable to use a hydrogen peroxide solution because it can be handled easily. By adding this oxidizing agent, arsenic (As) is oxidized from As (III) to As (V), and arsenic can be easily precipitated in each of the subsequent removal steps.

(First removal step)
Next, an iron compound and a hydrogen peroxide solution are added to the treatment solution obtained by the above oxidation step, and the first precipitate containing at least arsenic produced by the addition is filtered to obtain a first filtrate. Get (S2).

The iron compound is not particularly limited as long as it is a compound containing iron, but it is preferable to use metallic iron from the viewpoint of ease of handling, and further, it is preferable to use iron nails from the viewpoint of easy availability. .. In addition to this, iron halide can be used, and for example, iron chloride can also be used. By using iron chloride, high reactivity derived from chlorine, which is a halogen element, can be obtained, and the reaction can be further promoted.

The amount of iron used is not particularly limited, but is preferably 25 g to 100 g regardless of the amount of hydrogen peroxide solution, and is, for example, 25 g to 100 g with respect to 5 ml to 10 ml of hydrogen peroxide solution. be able to.

The hydrogen peroxide solution is not particularly limited as long as it is an aqueous solution containing hydrogen peroxide (H ₂ O ₂ ), and for example, a hydrogen peroxide solution having a concentration of 3% can be used.

It is preferable to heat and concentrate such a solution to which iron and hydrogen peroxide solution are added from the viewpoint of further promoting the reaction. This heating / concentration is performed, for example, at 100 ° C., and the specific gravity (d) of the solution is concentrated to 1.21 to 1.22. A reverse osmosis membrane (RO membrane) can also be used for concentration.

The first precipitate is a precipitate containing at least arsenic, and in particular, when seawater or geothermal water is used as the raw material water, not only arsenic but also manganese (Mn) is contained as the precipitate. (See Examples below). It is considered that the addition of H ₂ O ₂ promotes the oxidation of manganese (Mn) and promotes the production (precipitation) of manganese oxide.

The first filtrate refers to a solution obtained by filtering the first precipitate. For this filtration, for example, a 100 μme mesh filter paper (for example, manufactured by Toyo Filter Paper, 131-100) can be used.

(Second removal step)
Next, a magnesium chloride hydrate and a sodium hydroxide solution are added to the first filtrate obtained by the above first removal step, and a second precipitate containing at least arsenic and mercury produced by the addition is added. The material is filtered to obtain a second filtrate (S2).

The magnesium chloride hydrate is not particularly limited, but magnesium chloride hexahydrate (MgCl · 6H ₂ O) can be used. The concentration of the sodium hydroxide solution is not particularly limited.

The second precipitate is a precipitate containing at least arsenic and mercury, and in particular, when seawater or geothermal water is used as the raw material water, not only arsenic and mercury but also manganese (Mn) It will be contained as a precipitate (see Examples below).

As described above, according to the harmful element removing method according to the first embodiment of the present application, arsenic is mainly removed as the first precipitate by the first removing step, and the second removing step is used. As the precipitate of 2, mainly arsenic and mercury are removed, and as a result, a solution in which extremely harmful elements are removed is obtained.

In particular, when seawater or geothermal water is used as the raw material water, most of arsenic and manganese are mainly removed as the first precipitate by the first removal step, and the second removal step removes the majority. As the second precipitate, mainly mercury is removed and the balance of arsenic and manganese is removed, resulting in a solution from which harmful elements have been removed by a very simple method and reliably. It becomes.

As described above, the mechanism by which the method for producing salt according to the present application exerts an excellent effect has not been elucidated in detail, but iron and hydrogen peroxide are added by the first removal step, and mainly arsenic and manganese are added. Magnesium chloride hydrate and sodium hydroxide solution are added (second removal step) to remove most of the arsenic and manganese residue as well as new mercury removal. At the same time, it is presumed that an ionic state is formed that facilitates precipitation.

(Second Embodiment)
In the method for removing harmful elements according to the first embodiment, the raw material water is not particularly limited as long as it is a raw material water containing harmful elements including at least mercury and arsenic, but seawater or geothermal water is particularly used. If so, especially in the case of obtaining a solution from which harmful elements have been removed for food use, it is preferable to neutralize the second filtrate.

From this point of view, the method for removing harmful elements according to the second embodiment of the present application will be described with reference to the flowchart of FIG.

As shown in the flowchart of FIG. 2, the harmful element removing method according to the second embodiment includes the oxidation step (S1) and the first removing step (S2), as in the first embodiment described above. , The second removal step (S3) is included, and an acidic solution is added to the second filtrate obtained by the second removal step to neutralize the second filtrate and neutralize the second filtrate. It includes a neutralization step (S4) for obtaining a solution.

(Neutralization process)
That is, as a subsequent step of the above-mentioned second removal step (S3), an acidic solution is added to the second filtrate obtained by the second removal step (S3) to neutralize the second filtrate. , Obtain a neutral solution (S4). The acidic solution is not particularly limited, but for example, hydrochloric acid can be used.

As described above, by adding the acidic solution to the second filtrate obtained in the second removal step (S3), the alkaline-biased second filtrate is neutralized, and the second filtrate is particularly used in the food field. Will be more suitable.

(Third Embodiment)
In the method for removing harmful elements according to the third embodiment of the present application, sodium chloride is used as the raw material water in the method for removing harmful elements according to the second embodiment, and particularly for food use. You get bittern with it. Furthermore, along with the series of processing, various valuable resources can be recovered at the same time.

That is, in the method for removing harmful elements according to the third embodiment of the present application, as shown in FIG. 3, geothermal water (specific gravity d = 1.03, 100 ° C.) is used as the raw material water, and the second method is described. The oxidation step (S1), the first removal step (S2), and the second removal step (S3) are carried out in the same manner as in the embodiment. Before carrying out the oxidation step (S1), silica (metasilicic acid) can be recovered by cooling the geothermal water by natural cooling. Silica (meta-silicic acid) can be used as a raw material for cosmetics and the like. Further, the oxidation step (S1) can be carried out on the de-silica hot water produced by recovering the silica (meta-silicic acid).

After performing the first removal step (S2) and the second removal step (S3), the process is neutralized with an acidic solution (for example, hydrochloric acid) (S4) to obtain irrigation. Sodium chloride is obtained by heat-crystallizing the obtained irrigation water at 100 ° C.

The obtained sodium chloride (salt) is rich in minerals derived from seawater, and mercury and arsenic are removed (see Examples described later). Depending on the water sampling area of the raw material water, the content of mercury and arsenic may be high, and even if the raw material water is in a region that could not be produced as salt in the past, the harmful element removal method according to the present embodiment is used. As a result, it has an excellent effect that salt rich in minerals derived from seawater can be produced.

Also in the subsequent steps, by using bittern from which the harmful elements have been removed, various resources can be recovered using this bittern as a raw material. For example, the obtained bittern is oxidized by an electrolytic method (using a diamond electrode) or a chlorine method to obtain bromine, frozen crystallization is performed to obtain potassium chloride, and further, the production of this potassium chloride is performed. Boron and lithium (which become Li ₂ CO ₃ by carbonation) can be obtained by performing a carbonation treatment using adsorption / desorption on the bittern (potassium dechloride bittern) obtained at the same time. Lithium can be used as a raw material for batteries and pharmaceuticals.

As described above, in the method for removing harmful elements according to the third embodiment of the present application, various valuable resources using the bittern as a raw material can be recovered by using bittern produced by removing the harmful elements. It has an excellent effect of becoming. It is also possible to obtain sodium chloride (salt) produced by removing the harmful elements.

In particular, in the past, although geothermal water contains abundant minerals, there are many cases where the content of harmful elements such as mercury and arsenic is high, and in normal heating and crystallization, food safety standards are met. It has been considered difficult to produce (salt) sodium chloride (salt) or bittern that meets the requirements, but according to this embodiment, it is possible to produce (salt) sodium chloride (salt) or bittern that meets food safety standards. It has an excellent effect of being possible.

In order to further clarify the features of the present invention, examples are shown below, but the present invention is not limited to these examples.

(Example 1)
As the raw material water, 2000 ml of geothermal water (specific gravity d = 1.03, 100 ° C., pH 7, arsenic content 2.4 ppm) collected from Ibusuki City, Kagoshima Prefecture (spring amount of about 2 m ³ / h) was prepared.

(1-1) First removal step (one-step coprecipitation)
The first removal step (both in one step) was applied to a plurality of samples in which the amount of commercially available iron nails added was changed to 50 to 600 g with 5 ml of hydrogen peroxide solution (3%) with respect to this geothermal water. As a sink), add hydrogen peroxide solution and iron nails, heat to 100 ° C. to concentrate (d = 1.21-1.22), filter with filter paper (Toyo filter paper, 131-100), and then 1 Staged coprecipitation irrigation was obtained. The component content of the obtained precipitate is shown in FIG. From the obtained results, the amount of iron added is preferably 50 to 300 g in which the content of arsenic (As) is in the range of 1.5 to 2.5, and more preferably 50 to 300 g of arsenic (As). It was confirmed that the content was 50 to 100 g contained in the range of 1.5 to 2.0.

Next, the results of the amount of hydrogen peroxide solution (3%) added and the arsenic removal rate in the first removal step (one-step coprecipitation) are shown in FIG. 5 (a) and the table below. The amount of iron nails added was 100 g, and the concentration time after the addition of hydrogen peroxide solution and iron nails was 40 minutes.

From the obtained results, it was confirmed that the addition amount of the hydrogen peroxide solution (3%) was the best when it was 5 ml, and almost 100% was removed. Regarding the precipitate obtained in the case of 5 ml, the EDX pattern result obtained by analyzing the elemental components contained in the precipitate with an energy dispersive fluorescent X-ray analyzer (Rayny EDX-800HS, manufactured by Shimadzu Corporation) is shown in FIG. Shown in b). From the obtained results, it was confirmed that arsenic was removed to less than 0.1 ppm and mercury was also below the detection limit.

(1-2) Second removal step (two-step coprecipitation)
As shown in FIG. 6A, 14 g of magnesium chloride hexahydrate was added to the solution (one-step coprecipitation irrigation) obtained in the first removal step (one-step coprecipitation), and 1M-hydroxide was added. 14 ml of sodium was added to cause coprecipitation, and the mixture was filtered through a filter paper (Toyo filter paper, 131-100) to obtain two-step coprecipitation irrigation.

FIG. 6 (b) shows the results of an EDX pattern in which the elemental components contained in the obtained precipitate were analyzed by an energy dispersive fluorescent X-ray analyzer (Rayny EDX-800HS, manufactured by Shimadzu Corporation). From the obtained results, it was confirmed that mercury was removed by the second removal step (two-step coprecipitation), and that arsenic and manganese were further removed.

For the obtained solution (two-step co-precipitation irrigation, d = 1.27, 60 ml), the elemental components contained in the precipitate were analyzed by an energy dispersive fluorescent X-ray analyzer (Rayny EDX-800HS, manufactured by Shimadzu Corporation). The result of the EDX pattern is shown in FIG. 6 (c). From the obtained results, it was confirmed that mercury was removed by the second removal step (two-step coprecipitation), and arsenic and manganese were further removed, both of which were below the detection limit. ..

(1-3) Recovery of sodium chloride The obtained solution (two-step coprecipitation irrigation, d = 1.27, 360 ml) was heat-crystallized. The XRD pattern results analyzed by a horizontal X-ray structure analyzer (XRD7000, manufactured by Shimadzu Corporation) for the precipitated crystals are shown in FIG. 7 (a). From the obtained results, it was confirmed that sodium chloride (salt) containing 2.8% of potassium and from which harmful elements were removed was obtained.

(1-4) Recovery of Potassium Chloride Further, the obtained solution (two-step coprecipitation irrigation, d = 1.27, 360 ml) was crystallized from potassium chloride according to a freezing crystallization method. The XRD pattern results analyzed by a horizontal X-ray structure analyzer (XRD7000, manufactured by Shimadzu Corporation) for the precipitated crystals are shown in FIG. 7 (b). As is clear from the obtained results, it was confirmed that potassium chloride could be recovered with extremely high separation accuracy.

(Example 2)
Confirmation was performed in the same procedure as above to confirm the reproducibility. In the same manner as above, 4000 ml of geothermal water (specific gravity d = 1.03, 20 ° C., pH 7, arsenic content 2.4 ppm) collected from Ibusuki City, Kagoshima Prefecture (with a discharge amount of about 2 m ³ / h) was prepared as the raw material water. ..

(2-1) One-step co-precipitation and two-step co-precipitation Hydrogen peroxide solution (3%) was 7.5 ml, and iron was added to a plurality of samples in which the addition amount of commercially available iron nails was changed to 5 to 100 g. A nail and 15 ml of hydrogen peroxide solution were added to perform a first removal step (one-step coprecipitation) to obtain one-step coprecipitation water (360 ml, pH 5). _{Furthermore, MgCl 2 6H 2 O: 14g} , 1M-NaOH: with 14 ml, a second removal step (two-step co-precipitation) is performed at 20 ° C., to obtain a pH9 two-stage co-precipitation brine. The pH was adjusted to pH 7 using 1M-HCl.

For the obtained solution (two-step co-precipitation irrigation), the EDX pattern results obtained by analyzing the elemental components contained in the precipitate with an energy dispersive X-ray fluorescence analyzer (Rayny EDX-800HS, manufactured by Shimadzu Corporation) were obtained with iron nails. 8 (a) shows the case where the weight is 12.5 g and the case where the iron nail is 5 g. From the obtained results, it was confirmed that mercury was removed by the second removal step (two-step coprecipitation), and that arsenic and manganese were further removed.

In addition, regarding the obtained solution (two-step co-precipitation irrigation), the elemental components contained in the solution when the iron nail is 12.5 g are energy-dispersive fluorescent X-ray analyzer (Rayny EDX-800HS, manufactured by Shimadzu Corporation). The EDX pattern result analyzed by) is shown in FIG. 8 (b). From the obtained results, it was confirmed that mercury was removed by the second removal step (two-step coprecipitation), and that arsenic and manganese were further removed.

Furthermore, with respect to bittern (d = 1.27) obtained by heating the obtained solution (two-step co-precipitation irrigation), the elemental components contained in the solution were subjected to energy dispersive fluorescent X-ray analyzer (Rayny EDX-). The EDX pattern results analyzed by 800HS (manufactured by Shimadzu Corporation) are shown in FIG. 8 (c). From the obtained results, it was confirmed that mercury was removed by the second removal step (two-step coprecipitation), and that arsenic and manganese were further removed.

Next, the component content of the precipitate in each coprecipitation was confirmed. The results of the amount of iron nails added and the precipitation component in the first removal step (one-step coprecipitation) are shown in FIG. 9A. The second removal step (two-step co-precipitation) second removal step (two-step co-precipitation) results between the mixing amount of the precipitate component iron nail in the (one-step co-precipitation brine (360 ml) / MgCl ₂ 6H ₂ O: 14 g, 1M-NaOH: 14 ml) is shown in FIG. 9 (b). From the obtained results, it was confirmed that arsenic was removed to the detection limit or less, especially when the amount of iron nail added was 25 to 100 g.

Further, the EDX pattern results for each addition amount of magnesium chloride hexahydrate for the precipitate obtained in the second removal step (two-step coprecipitation) are shown in FIG. 9 (c). From the obtained results, it was confirmed that mercury and arsenic were removed below the detection limit.

Next, the results of the addition amount of magnesium chloride hexahydrate and the component peak intensity for the precipitate obtained in the second removal step (two-step coprecipitation) of the harmful element removal method are shown in FIG. 10 (a). Shown. In addition, the dependence on the amount of oxidizing agent (3% -H ₂ O ₂ ) added was confirmed. As a result, for each of the precipitates obtained by the one-step coprecipitation and the two-step coprecipitation, the content of each element for each addition amount of hydrogen peroxide is shown in FIGS. 10 (b) and 10 (c), respectively. Shown in. The horizontal axis of FIG. 10B shows 3% -H ₂ O ₂ addition amount (ml) / geothermal water (4000 ml), and the optimum addition amount condition for As removal is the H ₂ O ₂ addition amount. However, it was confirmed that the amount was 5 to 30 ml. The horizontal axis of FIG. 10B shows 3% -H ₂ O ₂ addition amount (ml) / Fe irrigation (one-step coprecipitation irrigation: 360 ml), and the optimum addition amount condition for As removal is , H ₂ O ₂ addition amount was confirmed to be 5 to 30 ml.

(2-2) Recovery of Sodium Chloride The obtained solution (two-step coprecipitation irrigation, d = 1.27, 360 ml) was heat-crystallized. The XRD pattern results analyzed by a horizontal X-ray structure analyzer (XRD7000, manufactured by Shimadzu Corporation) for the precipitated crystals are shown in FIG. 7 (a). From the obtained results, it was confirmed that sodium chloride (salt) from which harmful elements were removed was obtained with a yield of 80 to 95 g / 4000 ml of geothermal water.

(2-3) Recovery of Potassium Chloride Further, the obtained solution (two-step coprecipitation irrigation, d = 1.27, 360 ml) was crystallized from potassium chloride according to a freezing crystallization method. The XRD pattern results analyzed by a horizontal X-ray structure analyzer (XRD7000, manufactured by Shimadzu Corporation) for the precipitated crystals are shown in FIG. 7 (b). As is clear from the obtained results, it was confirmed that potassium chloride could be recovered with extremely high separation accuracy, and the yield was 1.6 to 2.2 g / 4000 ml of geothermal water.

Claims (5)

In the method for removing harmful elements from raw water containing harmful elements including at least mercury and arsenic, the harmful elements are removed.
An oxidation step of adding an oxidizing agent to the raw water and
An iron compound and a hydrogen peroxide solution are added to the treatment solution obtained by the oxidation step, and the first precipitate containing at least arsenic produced by the addition is filtered to obtain a first filtrate. Removal process and
Magnesium chloride hydrate and sodium hydroxide solution are added to the first filtrate obtained by the first removal step, and the second precipitate containing at least arsenic and mercury produced by the addition is filtered. , A second removal step to obtain a second filtrate,
A method for removing harmful elements, which comprises. In the method for removing harmful elements according to claim 1,
A method for removing harmful elements, wherein the raw material water is seawater or geothermal water. In the method for removing harmful elements according to claim 2,
Harmful element removal, which comprises a neutralization step of adding an acidic solution to the second filtrate obtained by the second removal step to neutralize the second filtrate to obtain a neutral solution. Method. Using the method for removing harmful elements according to claim 3, the neutral solution obtained from seawater or geothermal water as the raw material water is heat-crystallized, and sodium chloride in the neutral solution is filtered. A method for producing sodium chloride, which comprises obtaining. Using the method for removing harmful elements according to claim 3, the neutral solution obtained from seawater or geothermal water as the raw material water is heat-crystallized, and sodium chloride in the neutral solution is filtered. A method for producing bittern, which comprises producing bittern as a filtrate after the filtration.