JP3840656B2 - Purification method of aqueous solution and purified aqueous solution - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
This invention exists as an impurity in hydrochloric acid aqueous solution of metal hydrochloride in which metal such as sodium, calcium, potassium, chromium, aluminum, manganese, iron, copper, nickel, cadmium is dissolved in hydrochloric acid, and further hydrochloric acid, for example The present invention relates to a method for removing arsenic compounds and purifying an aqueous solution thereof, and a purified aqueous solution obtained by this purification method.
[0002]
[Prior art]
Hydrochloric acid and aqueous hydrochloric acid solutions of metal hydrochlorides such as sodium, calcium, potassium, chromium, aluminum, manganese, iron, copper, nickel, cadmium, pickling, water treatment chemicals, plating chemicals, dyeing aids, photographic It is widely used for chemicals, preservatives, disinfectants, desiccants, reaction catalysts, and the like, and the presence of impurities, especially the presence of arsenic, is often a major problem when used or recovered and reused.
[0003]
That is, arsenic compounds, particularly arsenic compounds such as hydrogen arsenide and arsenous acid, are highly toxic as is well known, and even if these arsenic compounds are present in trace amounts in metals, they have the property of extremely degrading the properties of the metals. Therefore, arsenic and arsenic compounds as impurities (hereinafter collectively referred to simply as arsenic) are components that are very disliked, and removal of arsenic as impurities is often strongly required. Therefore, there is always a need for an excellent arsenic removal method.
[0004]
Therefore, various methods for removing arsenic in the liquid have been proposed and have been known for a long time. As a general method for removing arsenic, a strong basic ion exchange method, an adsorbent method for adsorption on activated carbon, or Known is the sulfide method for precipitation as arsenic sulfide, and further, the method using coprecipitation or adsorption with metal hydroxides, especially adsorption to iron hydroxides, ion exchange resin method or adsorbent method or sulfide Since physical methods are used in special cases due to high costs, the most commonly used methods are coprecipitation with metal hydroxides or adsorption, and among them, adsorption to iron hydroxides. As a more specific arsenic removal method, the following examples can be given.
[0005]
For example, arsenic and sulfuric acid solution containing heavy metals is adjusted to PH2.0～3.2, warmed while stirring at an oxygen pressure, mainly _{Fe 3 (SO 4) 2 (} OH) 5 · 2H _{A method in which 2} O form of basic iron sulfate is produced and arsenic is coprecipitated and / or adsorbed on the basic iron sulfate to remove it. (For example, see Patent Document 1)
[0006]
An oxidizing agent is added to an acidic solution containing heavy metal and arsenic to oxidize trivalent arsenic in the solution to pentavalent arsenic, and then ferrous salt is added. While maintaining 3.0, ferrous oxide is oxidized by air, oxygen, an oxidizer, or a combination of two or more of the above, so that arsenic is converted to iron arsenate with high arsenic quality from the solution containing the heavy metal. A method of separating and removing the precipitate. (For example, see Patent Document 2)
[0007]
An acidic solution containing arsenic and iron is oxidized to oxidize arsenic and iron in the solution, and further neutralized at the same time as or after the oxidation to obtain a pH of 1.5 to 4.0. A method of removing arsenic by forming a solid content containing arsenic and iron and separating it into solid and liquid. (For example, see Patent Document 3)
[0008]
A method of reducing and removing arsenate ions / or arsenite ions to simple arsenic by reacting arsenate ions / or arsenite ions contained in water with a hydrogen donor in the presence of a catalyst. (For example, see Patent Document 4)
[0009]
[Patent Document 1]
Japanese Patent Publication No. 56-6356 (Claims)
[Patent Document 2]
Japanese Examined Patent Publication No. 62-21728 (Claims)
[Patent Document 3]
JP-A-6-206080 (Claim 1)
[Patent Document 4]
JP-A-9-327694 (Claim 1)
[0010]
[Problems to be solved by the invention]
However, these methods have high running costs, require exhaust gas treatment equipment and high-pressure vessels, are complicated in multiple steps, have poor filterability of precipitates, and improve reactivity by reacting hydrogen (gas) with liquid. There is a problem that a device is necessary.
[0011]
In view of the present situation, the inventor conducted research to find a simpler, safer and more economical method than these arsenic removal methods. As a result, an aqueous solution containing arsenic was added to hydrochloric acid. The present invention has been completed by finding that an acidic aqueous solution can be easily reduced to a simple arsenic (metal) by a reducing agent to form a simple arsenic (metal).
[0012]
[Means for Solving the Problems]
That is, the present invention according to claim 1
A method for purifying an aqueous solution, wherein arsenic contained in an acidic aqueous solution of hydrochloric acid is precipitated and separated using metallic iron or metallic nickel in the absence of Fe ⁺² and ionic or metallic copper .
[0013]
Moreover, this invention is the invention according to claim 2,
In the purification method of the aqueous solution of Claim 1,
The aqueous hydrochloric acid solution is
The metal is dissolved.
[0014]
Moreover, this invention is the invention according to claim 3,
In the purification method of the aqueous solution of Claim 1 or 2,
The aqueous hydrochloric acid solution is
Its pH is 4 or less.
[0015]
Moreover, this invention is the invention according to claim 4,
In the purification method of the aqueous solution in any one of Claims 1-3,
The reduction precipitation is
It is characterized by being carried out at a temperature in the range of 40 ° C to 90 ° C.
[0016]
Furthermore, this invention is the invention according to claim 5,
A purified aqueous solution purified by the method for purifying an aqueous solution according to any one of claims 1 to 4 .
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the aqueous solution purification method of the present invention and the aqueous solution obtained by this purification method will be described more specifically.
[0018]
<Aqueous solution>
In the present invention, the aqueous solution to be purified contains arsenic, and the present invention purifies the aqueous solution by removing arsenic present as an impurity in the aqueous solution. Is required to be acidic with hydrochloric acid, and when purifying a neutral or alkaline aqueous solution, it is necessary to make it acidic with hydrochloric acid, and the pH of the aqueous hydrochloric acid solution is preferably 4 or less, In an aqueous solution having a pH exceeding 4, the efficiency of arsenic precipitation separation may be reduced.
[0019]
In this invention, various hydrochloric acid acidic aqueous solutions can be used, and the most basic one is hydrochloric acid. According to this invention, when arsenic is present as an impurity in hydrochloric acid, Arsenic can be easily removed.
[0020]
Other hydrochloric acid aqueous solutions include sodium, calcium, potassium, chromium, aluminum, manganese, iron, copper, nickel, cadmium, and other metals dissolved in hydrochloric acid. Examples include hydrochloric acid aqueous solution of metal chloride such as sodium, calcium chloride, potassium chloride, chromium chloride, aluminum chloride, manganese chloride, iron chloride, copper chloride, nickel chloride, cadmium chloride.
[0021]
The hydrochloric acid and hydrochloric acid aqueous solution as described above may be prepared for industrial use, reused with recovered products once used for various purposes, or discarded. The present invention can be applied to those in which arsenic is present as an impurity in those aqueous solutions and needs to be removed, and solid metals or metal salts are also soluble in hydrochloric acid aqueous solutions, particularly those dissolved in hydrochloric acid. If so, it can be dissolved to remove arsenic from them as an aqueous solution.
[0022]
<Metal iron, nickel metal>
Metallic iron and nickel metal function as a reducing agent, and when treating hydrochloric acid or metal chloride as described above, it is particularly preferable to use them as powder from the viewpoint of reaction rate.
[0023]
When metallic iron or nickel metal is used, arsenic alone (metal arsenic) is deposited as shown in the following formula 1, but when zinc is used, as shown in the following formula 2, There is a problem in using zinc as a reducing agent because highly toxic hydrogen arsenide is generated.
[0024]
[Formula 1]
H ₃ AsO ₄ + 5Fe + 10HCl → 5FeCl ₂ + 8H ₂ O + 2As ↓
[0025]
[Formula 2]
H ₃ AsO ₄ + 4Zn + 8HCl → 4ZnCl ₂ + 4H ₂ O + AsH ₃ ↑
[0026]
<Precipitation conditions>
For arsenic precipitation, it is only necessary to contact an acidic aqueous hydrochloric acid solution with metallic iron or nickel metal as a reducing agent. Usually, in order to accelerate the reaction, metallic iron or nickel metal is added to the aqueous solution as a powder. In order to accelerate the reaction after the addition, it is desirable to stir the aqueous solution. However, depending on the reaction, hydrogen is generated, and when the generated hydrogen has a stirring effect and the reaction proceeds sequentially, There is no need to stir.
[0027]
The deposition temperature may be room temperature, but it is preferably performed at a temperature of 40 ° C. or higher in order to increase the reaction rate. It should be noted that if the temperature is 90 ° C. or higher, it is necessary to avoid using a special reaction vessel.
[0028]
Since the reaction is an exothermic reaction, the temperature of the aqueous solution rises at the initial stage of the reaction without heating, so the reaction temperature is allowed to rise at the initial stage to prevent overheating from the middle of the reaction. In order to warm up when the heat of reaction decreases, it is preferable to keep the temperature constant using a temperature controller.
[0029]
The deposition time is preferably 1 hour or longer, usually 5 to 8 hours, when the deposition temperature is 80 ° C.
[0030]
Arsenic is reduced and deposited in a metallic state. If the additive is metallic iron powder or the like, it is deposited on the surface of the arsenic, so that it is separated from the aqueous solution by filtering them.
[0031]
[Action]
According to the method for purifying an aqueous solution of the present invention, arsenic ions present in an aqueous hydrochloric acid solution as an impurity are reduced by adding a reducing agent such as metallic iron powder to the aqueous solution and precipitated as simple arsenic (metal arsenic). In this case, the deposited arsenic is deposited on the surface of metal iron powder or the like in an attached state, so that the separation can be easily performed.
[0032]
【Example】
Hereinafter, based on an Example, the purification method of the aqueous solution of this invention and the purified aqueous solution obtained by this purification method are demonstrated in detail.
[0033]
Example 1
32.4 g of nickel metal powder (arsenic concentration 1.24 ppm) was added to 100 ml of 18% hydrochloric acid to which 10 ml of 1000 ppm arsenic standard solution for atomic absorption was added, and reacted at a temperature of 50 ° C. for 2 hours. There has occurred. After completion of the reaction, solid-liquid separation was performed, the solid was washed with ion-exchanged water, and the arsenic concentrations of the liquid, solid and washing liquid were measured.
The arsenic concentration in the liquid was 0.39 ppm, the arsenic concentration in the solid and the cleaning liquid was 1688.6 ppm, 4.06 ppm, and the recovered arsenic was 97.5%.
[0034]
Example 2
An aqueous solution of copper chloride and hydrochloric acid having an arsenic concentration of 0.1% was prepared by adding 3.95 g of disodium hydrogen arsenate heptahydrate to 848 g of an aqueous solution of copper chloride having a copper concentration of 10% and a hydrochloric acid concentration of 8%. .
To this aqueous solution, 81.04 g of iron powder (arsenic concentration: 15 ppm) was added. The temperature was increased by adding iron powder, but the temperature was adjusted to 70 ° C. with a temperature controller and reacted for 3 hours.
After completion of the reaction, solid-liquid separation was performed, and the arsenic concentration in the liquid and the solid was measured. As a result, the arsenic concentration in the aqueous solution was 3.02 ppm, and the arsenic recovery rate was almost 100%.
[0035]
Example 3
After adding 4.16 g of disodium hydrogen arsenate heptahydrate to 1000 g of nickel chloride aqueous solution with a nickel concentration of 1%, 5 ml of 18% hydrochloric acid was added to completely dissolve the arsenate to obtain a chloride with an arsenic concentration of 0.1%. A nickel aqueous solution was prepared. 2.18 g of nickel metal powder (arsenic concentration 30 ppm) was added to this aqueous solution. The temperature was increased by adding nickel metal powder, but the temperature was adjusted to 70 ° C. with a temperature controller and reacted for 4 hours.
After completion of the reaction, solid-liquid separation was performed, and the arsenic concentration in the liquid and the solid was measured. As a result, the arsenic concentration in the aqueous solution was 326 ppm, and the arsenic recovery rate was 97.7%.
The reason why the concentration of arsenic in the aqueous solution is as high as 326 ppm is considered to be that the deposited arsenic adhered to the surface of the nickel metal powder and hindered the progress of the reaction that lost the nickel activity.
[0036]
Reference Example To 1 kg of aqueous iron chloride solution with a hydrochloric acid concentration of about 8% (composition: ferrous chloride 10.5%, chloride chloride, copper ion 3.72%), 4.18 g of disodium hydrogen arsenate heptahydrate was added. It melt | dissolved and it was set as the aqueous solution whose arsenic density | concentration is 1000 ppm. To this aqueous solution, 84.8 g of iron powder was added and reacted. The reaction temperature increased with the heat of reaction, but no heat was added at the beginning of the reaction, and then the temperature was adjusted to 70 ° C. with a temperature controller to continue the reaction.
After completion of the reaction, solid-liquid separation was performed, and the arsenic concentration in the liquid and the solid was measured. As a result, the arsenic concentration in the aqueous solution was 0.1 ppm or less, and the arsenic recovery rate was almost 100%.
The liquid after the reaction was an aqueous ferrous chloride solution containing almost no copper chloride, the precipitated solid was black, and it was judged that arsenic was attached to the surface of the metallic copper. Further, the concentration of hydrogen arsenide was measured with a gas detector tube during the reaction, but it was 0.2 ppm or less of the lower limit of detection.
[0037]
Example 4
When iron powder was added to an acidic aqueous solution of ferric chloride containing ferric chloride and ferric chloride with an arsenic concentration of 1.64 ppm, almost all of the ferric chloride was converted to ferrous chloride. Arsenic was also precipitated, and an aqueous ferrous chloride solution with an arsenic concentration at a detection limit was obtained. In addition, generation of hydrogen arsenide was not observed during the reaction.
[0038]
Example 5
Disodium hydrogen arsenate heptahydrate was added to 1 kg of 35% ferrous chloride aqueous solution so that the arsenic concentration was 1%, and hydrochloric acid was added to completely dissolve the disodium hydrogen arsenate heptahydrate. The temperature of the aqueous solution was adjusted to 70 ° C., and 50 g of electrolytic iron was added and reacted for 12 hours.
The electrolytic iron was covered with a black film. Solid-liquid separation was performed, and the electrolytic iron covered with the black film was washed. The black film was not peeled off by washing, and was dried and immersed in 36% hydrochloric acid, but did not react with hydrochloric acid.
From this, it was found that the black coating was neither iron arsenate nor iron arsenite dissolved in hydrochloric acid, but metal arsenic not dissolved in hydrochloric acid.
[0039]
【The invention's effect】
Method of purifying an aqueous solution of the invention, the arsenic contained as impurities in an aqueous solution of hydrochloric acid, only the addition of metallic iron and metallic nickel as a reducing agent, as a metal arsenic without generating strong arsenide hydrogen gas toxic It can be separated and removed, does not require any special reagent or operation, and does not require expensive equipment such as a gas processing apparatus, and is a highly safe and economical method. Further, since a non-filterable product such as hydroxide does not occur, the separation efficiency is very good.

Claims (5)

A method for purifying an aqueous solution, wherein arsenic contained in an aqueous hydrochloric acid solution is precipitated and separated using metallic iron or metallic nickel in the absence of Fe ⁺² and ionic or metallic copper . The aqueous hydrochloric acid solution is
The method for purifying an aqueous solution according to claim 1, wherein the metal is dissolved. The aqueous hydrochloric acid solution is
The method for purifying an aqueous solution according to claim 1 or 2, wherein the pH is 4 or less. The precipitation separation is
The method for purifying an aqueous solution according to any one of claims 1 to 3, wherein the method is performed at a temperature in the range of 40C to 90C. A purified aqueous solution purified by the method for purifying an aqueous solution according to claim 1.