JP3475534B2 - As-containing water treatment equipment - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for treating As-containing water and, more particularly, to co-precipitation treatment by adding Fe ³⁺ and Cl ₂ to As-containing wastewater. Device for [0002] Conventionally, as a method for treating As-containing wastewater, a method of coprecipitating by adding an iron salt is generally used. In this coprecipitation method, As (V) and As (I)
II) and in, it easily co-precipitation than As (III) towards the As (V), also, Fe ³⁺ and Fe ²⁺ and towards the Fe ³⁺ in the Fe ²⁺
It is confirmed that the coprecipitation effect is higher than that of the Japanese Society of Mining Industry (192 1066 ('76 -12) 809). Therefore, in the actual treatment of wastewater containing As, Fe ³⁺ is added to the wastewater containing As and an oxidizing agent is added to oxidize As (III) to As (V).
Generally, coprecipitation is performed at 5 to 8. [0005] In the above-mentioned conventional method, as a facility for injecting Fe ³⁺ and an oxidizing agent, for example, sodium hypochlorite, a storage tank and an injecting pump for these agents are required. However, there are problems in terms of equipment cost, installation area, maintenance management, and the like of the injection equipment. There is also a problem that it is not easy to adjust the addition amounts of Fe ³⁺ and the oxidizing agent. The present invention solves the above-mentioned conventional problems, reduces the cost of the apparatus, reduces the installation area of the apparatus, and reduces the maintenance management, and furthermore, the apparatus for treating As-containing water that can easily control the amount of chemical injection. The purpose is to provide. [0007] The apparatus for treating As-containing water according to the present invention comprises a first circuit in which a NaCl solution is used as an electrolyte and at least the anode is an iron electrode, and at least the anode is an insoluble electrode. A electrolytic cell provided with a second circuit, a reaction tank into which As-containing water is introduced and Cl ₂ and Fe ³⁺ generated in the electrode tank are added, and an outflow from the reaction tank. The liquid is introduced and the Na generated in the electrolytic cell is
It is characterized by comprising a neutralization tank to which OH is added, and a precipitation tank for solid-liquid separation of the effluent of the neutralization tank. In the apparatus for treating As-containing water of the present invention, the following reaction occurs on the anode side of the electrolytic cell. That is, Fe ²⁺ is eluted at the iron anode by the following reaction. In the insoluble anode, Cl ₂ is generated from Cl ⁻ in the electrolytic solution by the following reaction, and Fe ²⁺ is oxidized to Fe ³⁺ by the following reaction by a part of the generated Cl ₂ . Fe → Fe ²⁺ + 2e ⁻ 2Cl ⁻ → Cl ₂ + 2e ⁻ 2Fe ²⁺ + Cl ₂ → 2Fe ³⁺ + 2Cl ⁻ On the other hand, on the cathode side of the electrolytic cell, Na ⁺ in the electrolytic solution is The reaction produces Na and NaOH. Na ⁺ + e ⁻ → Na... Na ⁺ + H ₂ O → 1/2 H ₂ + NaOH Since the electrolytic cell according to the present invention is a diaphragm type having a sealed plug structure, the anode side becomes acidic, and the Cl formed above is formed. ₂ is Cl ₂ gas, and this Cl ₂ gas is blown into the reaction tank, and the Fe ³⁺ generated above is added to the reaction tank. In the reaction tank, As (III) is oxidized to As (V) by the following reaction. This As (V),
The effluent of the reaction tank containing Fe ³⁺ is subjected to pH adjustment in a neutralization tank so that As (V) and Fe
³⁺ co-precipitates. AsO ₃ ^3- + Cl ₂ + H ₂ O → AsO ₄ ^3- + 2HCl ... Fe ³⁺ + AsO ₄ ^3- → FeAsO ₄ (precipitation) ... In the pH adjustment in the neutralization tank, the cathode of the electrolytic cell is used. The NaOH generated by the above reaction is effectively used. The effluent of the neutralization tank is subjected to solid-liquid separation in a precipitation tank, whereby treated water from which As has been removed by coprecipitation with Fe can be obtained as supernatant water. In such a treatment, in the apparatus for treating As-containing water of the present invention, Cl ₂ gas and Fe ³⁺
, Ie, Cl ₂ concentration, Fe ³⁺ concentration and Cl ₂ /
The Fe ³⁺ concentration ratio can be easily adjusted by adjusting the NaCl concentration of the electrolytic solution in the electrolytic cell, the electrolytic voltage, the current density, the electrode area, and the like. Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. FIG. 1 is a system diagram showing one embodiment of the apparatus for treating As-containing water of the present invention. In the figure, 1 is an electrolytic tank, 2 is a reaction tank, 3 is a neutralization tank, and 4 is a sedimentation tank. The electrolytic cell 1 is made up of an anode chamber 1a by diaphragms 1A and 1B.
The cathode chamber 1b is a diaphragm type electrolytic cell in which a NaCl aqueous solution is stored as an electrolytic solution. The electrolytic cell 1 is provided with two circuits, a first circuit 5 and a second circuit 6, and the first circuit includes an iron anode 5A and an iron cathode 5B.
Are provided. Further, the second circuit 6 is provided with a platinum anode 6A and a platinum cathode 6B as insoluble electrodes. 5C and 6C are power supplies. In the first circuit of the electrolytic cell 1, the anode 5A only needs to be made of iron, and the cathode 5B is not limited to iron, but it is generally preferable to use an iron cathode. . Further, the second circuit 6 only needs to have an insoluble electrode for the anode 6A. In addition to the platinum-platinum electrode, a lead oxide-lead oxide electrode, a titanium-titanium electrode or the like can be used. In the anode chamber 1a of the electrolytic cell 1, Fe ³⁺ and Cl ₂ gas are generated by the above-mentioned reactions.
The generated Cl ₂ gas and Fe ³⁺ are added to the reaction tank 2 from the pipes 13 and 14. Raw water (As-containing water) is introduced into the reaction tank 2 from a pipe 11, and the pH is adjusted to 2 to 3 by a pH adjuster added as needed from a pipe 12.
Cl ₂ gas, Fe ³⁺ from the electrolytic cell 1 via pipes 13 and 14
Is added. In this reaction tank 2, As (I
II) is oxidized to As (V) by the above reaction. The effluent from the reaction tank 2 is then introduced into the neutralization tank 3 through a pipe 15. NaOH generated by the above-described reaction in the cathode chamber 1b of the electrolytic cell 1 is added to the neutralization tank 3 through a pipe 16, and a coagulant such as an alkali and a polyacrylamide polymer is added through a pipe 17 to the neutralization tank 3. By adjusting to ８8, As (V) and Fe ³⁺ are coprecipitated and coagulated according to the above reaction. The effluent from the neutralization tank 3 is then introduced into the sedimentation tank 4 through a pipe 18 to be separated into solid and liquid, and the supernatant water is discharged out of the system from a pipe 19 as treated water. The pipe 20 is a supply pipe for an aqueous solution of NaCl, and when the electrolytic solution level of the electrolytic tank 1 is lowered by electrolysis, the aqueous solution of NaCl is stored in the storage tank by operating a replenishing pump in conjunction with a liquid level gauge (not shown). (Not shown). According to the apparatus for treating As-containing water of the present embodiment, the amount of Fe ³⁺ and Cl ₂ generated in the electrolytic cell 1 can be arbitrarily adjusted by adjusting the NaCl concentration of the electrolytic solution, the electrolytic voltage, the current density, the electrode area, and the like. Can be easily adjusted to the concentration, and the need for conventional chemical injection equipment such as a chemical injection pump is eliminated. Further, as an alkali for neutralization, NaOH generated in the electrolytic cell 1 can be effectively used to reduce the cost of chemicals. In such an apparatus for treating As-containing water, the life of the electrodes in the electrolytic cell and the contamination of the diaphragm can be solved by reversing the polarity of the electrodes and performing electrolysis using the anode as a cathode and the cathode as an anode. It can be supplemented to some extent and the practicality is enhanced. Hereinafter, the present invention will be described in more detail with reference to specific examples. Example 1 The treatment apparatus for treating As-containing water shown in FIG.
The hot spring source of As1.5 mg / l was treated. The flow rate of the raw water was 100 liters / minute, and the specifications and conditions of each tank were as follows. Electrolyte Electrolyte: 3.0 wt% NaCl aqueous solution First circuit: iron-iron electrode voltage 5.0 V Second circuit: platinum-platinum electrode voltage 3.5 V Reaction tank pH: 2.5 reaction time : 10 minutes Neutralization tank pH: 6.0 Reaction time: 15 minutes (addition of 1 mg / l of a partial hydrolyzate of polyacrylamide as a polymer) As a result, Cl ₂ was supplied from the electrolytic tank at a rate of 1.0 g / min.
A gas can be obtained, and at the same time, Fe ³⁺ can be obtained at a rate of 0.4 g / min.
Was efficiently coprecipitated. In addition, NaOH was obtained at a rate of 1.2 g / min from the electrolytic cell, and by adding this to the neutralization tank, the amount of alkali required for neutralization could be reduced. At this time, the added amount of Fe ³⁺ was 2.5 times by weight of As in the raw water, and the injected amount of Cl ₂ was 10 ppm.
Met. The As concentration of the obtained treated water is shown in Table 1 As shown in FIG. In the above method, the first circuit voltage and the second circuit voltage are set to the values shown in Table 1, and the amount of Fe ³⁺ added is shown in Table 1 while the Cl ₂ injection amount is kept at 10 ppm.
^{The same operation} was carried out except that the ^{3 +} / As ratio was obtained. As a result, treated water having the As concentration shown in Table 1 could be obtained. According to Table 1, according to the present invention, As ³ can be efficiently used by using Fe ³⁺ , Cl ₂ , and NaOH generated in the electrolytic cell.
Coprecipitation treatment, and in that case, Fe ³⁺ , Cl
₂ It is clear that the amount of addition can be easily adjusted by voltage control or the like. [Table 1] As described in detail above, according to the apparatus for treating As-containing water of the present invention, the As-containing water that is relatively inexpensive, requires a small installation area, and is easy to maintain and manage. An apparatus for coprecipitation of water is provided.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a system diagram showing one embodiment of an apparatus for treating As-containing water of the present invention. [Description of Signs] 1 Electrolyzer 1A, 1B Diaphragm 2 Reaction tank 3 Neutralization tank 4 Precipitation tank 5 First circuit 5A Iron anode 5B Cathode 6 Second circuit 6A Insoluble anode 6B Cathode 7 Electrolyte

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C02F 1/00-1/78

Claims (1)

(57) [Claim 1] A first circuit in which a NaCl solution is used as an electrolyte and at least the anode is an iron electrode, and a second circuit in which at least the anode is an insoluble electrode is provided. A diaphragm type electrolytic cell, As-containing water is introduced, and C generated in the electrode cell
a reaction tank to which l ₂ and Fe ³⁺ are added; a neutralization tank to which an effluent of the reaction tank is introduced and to which NaOH generated in the electrolytic cell is added; an effluent of the neutralization tank A precipitation tank for solid-liquid separation of As.