JPS62121690A - Method for removing arsenic in geothermal water - Google Patents

Abstract

PURPOSE:To efficiently contact arsenic in a liquid with an iron precipitate, by enlarging the specific surface area of the iron precipitate by coating a fine particulate filler with the iron precipitate and passing arsenic-containing geothermal water through the bed of the iron precipitate. CONSTITUTION:The geothermal water of a geothermal water storage tank 3 is introduced into a packed tower 2 under pressure by a quantitative pump 4 through a heating apparatus 5. On the way of the introduction of said geothermal water, a small amount air is introduced into geothermal water by an air pump to supply oxygen therein, and excessive air is exhausted to the outside of the tower 2 through the air valve 6 provided to the upper part of the packed bed 2. The packed bed 2 is packed with fine anthracite particles coated with an iron precipitate. The fine particulate filler coated with the iron precipitate of which the arsenic removing capacity has decreased is backwashed and further coated with the iron precipitate. By this method, an iron/arsenic ratio can lowered to reduce the concn. of arsenic in geothermal water down to extremely minute quantity.

Description

Detailed Description of the Invention (a) Technical Field The present invention provides a method for removing arsenic from geothermal water, in particular, by using fine particles whose surface is coated with iron precipitates such as basic iron sulfate and iron hydroxide. By passing the water to be treated through the packed layer, the arsenic and iron precipitates in the water to be treated are brought into sufficient contact reaction,
The present invention relates to a method for removing arsenic from geothermal water that can remove arsenic from water to be treated with an extremely small iron/arsenic ratio.

(b) Background Art Aqueous solutions, particularly geothermal water, often contain 1 to 10 ppm of arsenic. Therefore, in order to release or use this, 0. It is necessary to remove O to an environmental standard value of 5 ppm or less.

Generally, to remove arsenic, iron groups are added to the water to be treated.
e (OH)a and combine it with As to form As5+
is FeAs04*nH2O, and As3 is FeAs
A method of co-precipitation with Fe (OH)z as O2*n)+20 has been carried out.

In this case, since As3+ has a lower reactivity than As5+, an oxidizing agent such as NaC40 is usually added to oxidize As3+ to As5+, which is co-precipitated with TeFe(OH)z.

However, this method requires a large amount of iron salt and oxidizing agent to remove As from the water to be treated to an environmental standard value.

This is because the iron salts added to the treated water coagulate as Fe (OH)3 precipitates, reducing the surface area that comes into contact with arsenic, and the floating precipitates still remain in the treated water containing arsenic even after stirring. A flows at the same speed as A in the water to be treated.
There are few opportunities for contact with s, and a large amount of iron salt is required,
Furthermore, the residual arsenic concentration is also high.

(C) Disclosure of the Invention The method of the present invention involves the use of arsenic gas containing a certain amount of air in a column filled with fine particles coated with iron precipitates such as basic iron sulfate or iron hydroxide. The arsenic contained in the geothermal water is removed by pressurizing the geothermal water with a pump and passing it through at a constant flow rate.

As a result, arsenic in the geothermal water not only comes into contact with iron precipitates due to the movement of ions, but also efficiently reacts with the iron precipitates that coat the surface of the fine-grained filling area, not only through collisions due to flow or contact due to turbulence. The residual arsenic concentration is removed until it becomes a trace amount.

Also, the iron precipitate covering the fine-grained filler can be a thin layer, so that the iron/arsenic ratio can be extremely small.

If geothermal water continues to be removed for a long period of time by passing through the fine-grained packed bed coated with iron precipitates as described above, the arsenic concentration in the treated water will gradually rise, so the arsenic concentration in the treated water will gradually rise. Arsenic-free water is rapidly pumped in for backwashing to remove iron precipitates that have reacted with arsenic, and then a new coat of iron precipitates is applied to continue removing arsenic.

Furthermore, if ferrous ions are added to the geothermal water before it is injected into the fine-grained packed tower and the water is forced to pass through the fine-grained packed tower together with air, the ferrous ions are gradually oxidized by the oxygen in the air, and the ferrous ions are gradually oxidized by the oxygen in the air. By coating the surface of the grain filler, it is possible to efficiently remove arsenic.

In this case, the iron precipitate that coats the surface of the fine-grained packing gradually grows and causes clogging, so it is regenerated by backwashing.

The material for the fine filler is preferably an insoluble material that does not disintegrate in water, such as anthracite, coke, sand, pumice 2 synthetic resin, etc.

Hereinafter, the method of the present invention and its effects will be specifically explained with reference to Examples.

(d) Examples Example 1 FIG. 1 shows a de-arsenization test apparatus using a fine-grained packed layer coated with iron precipitate in advance.

1 has a height of 100011111 in a sealed and heat-insulated packed tower 2 equipped with an air valve 6 made of a hard glass tube with a diameter of 271.
Particle size filled up to 1.5 mm, 0.8 m below the sieve
The anthracite fine grains are sieved with an M sieve and are coated with iron precipitates.

Reference numeral 3 denotes a geothermal water storage tank that has cooled down during transportation, and this geothermal water is forced into the packed tower 2 through a heating device 5 by a metering pump 4.

The geothermal water heated as described above is pressurized into the packed tower 2 by the flow vibrator, but in the middle of the process, a small amount of air is pressurized by the air pump 7 to supply oxygen to the geothermal water. Air is discharged to the outside of the column 2 by an air valve 6 at the top of the packed column 2.

The temperature of the geothermal water that has passed through the fine-grained anthracite layer l covered with iron precipitates drops to 60°C, but the arsenic in the geothermal water is removed to an extremely small amount as shown in Table 1.

Note that if arsenic removal treatment is performed by passing geothermal water through the packed tower 2 for a long period of time, the arsenic removal ability will gradually decrease.

Therefore, the fine grain packing 1 coated with iron precipitates whose arsenic removal ability has decreased is backwashed, and the treatment is continued with the iron precipitates coated anew.

As shown in Table 1, the analytical value of the iron precipitate recovered by backwashing shows that the iron/arsenic ratio is extremely low.

(The following is a blank space) Fig. 2 shows a test device for efficiently coating fine-grained fillers with iron precipitates.

The packed column 2 was filled with anthracite fine particles 1 as in Example 1.

8 is a ferrous sulfate solution storage tank containing nutrients;
Iron-oxidizing bacteria are added inside to promote the oxidation of ferrous ions. This ferrous sulfate solution has a pH of 4 to 5, preferably 4 to 4.5,
An air pump 10 is interposed in the middle of the flow pipe that supplies the anthracite fine particles to the packed column 2 by the pump 9, and a small amount of air is forced in, supplying oxygen to the ferrous sulfate solution, and removing excess air. The air is discharged from the air valve 6 of the packed tower 2.

The results of processing with this device are shown in Table 2.

In addition, in this test, in order to determine the arsenic removal ability, sulfuric acid
As''+ ions are added to the iron solution.
(Margins below) Example 2 Figure 3 shows that ferrous ions were added to geothermal water and allowed to pass through the fine-grained packing, thereby reducing the iron precipitate. This figure shows a test device that performs arsenization while coating the surface of a fine-grained filler.

The packed tower 2 is filled with anthracite fine particles 1 as in Example 1, and the geothermal water heated by the heating device 5 is compressed into the packed tower 2, but a small amount is pumped by the air pump 6 on the way. The air is injected under pressure to supply oxygen to the geothermal water.

Further, the ferrous sulfate solution in the storage tank 8 is added little by little to the packed tower 2 using a metering pump 9.

However, as shown in Table 3, although the arsenic removal results were not satisfactory for the first few days until the anthracite fine grains were coated with iron precipitates, good results were obtained after that. I understand.

(Left below) (E) Effects of the invention As described above, the present invention increases the specific surface area of the iron precipitate by coating the iron precipitate with a fine-grained filler, and in this fixed iron precipitate layer, Since arsenic-containing geothermal water is passed through, arsenic in the liquid and iron precipitates can be brought into contact efficiently.

Therefore, the iron/arsenic ratio required for arsenic removal can be made extremely small, and the arsenic concentration in geothermal water can be removed to an extremely low level.

Furthermore, although ion exchange resins require chemicals for regeneration, the method of the present invention has various advantages such as being able to regenerate the fine particle packed bed by backwashing with arsenic-free water. .

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing an example of the apparatus used to carry out the method of the present invention, Fig. 2 is an explanatory diagram of an apparatus for pre-coating the fine grain packing with iron precipitates, and Fig. 3 is an explanatory diagram showing an example of the apparatus used to carry out the method of the present invention. FIG. 2 is an explanatory diagram showing an example of another apparatus for carrying out the present invention, which performs arsenization while coating the surface of a fine-grained filler. Symbol explanation 1 - Anthracite fine-grain packed bed 2 - Packed tower 3 - Geothermal water storage tank 4 Constant volume pump 5 - Kerr heating device 6 - Air valve 7
- Air pump 8 - Ferrous sulfate storage tank 9 Constant volume pump A - Liquid supply B - Discharge liquid Patent applicant Dowa Koei Co., Ltd. Agent Patent attorney Asaga - Fuo Hot; -, 1 +1

Claims (3)

[Claims] (1) Removal of arsenic in geothermal water characterized by removing arsenic by passing the geothermal water through a layer of fine-grained packed material coated with iron precipitates such as basic iron sulfate and iron hydroxide. Method. (2) The fine particles are coated with the iron precipitate by aerating the iron sulfate solution to supply oxygen, and then circulating the iron sulfate solution through the fine particle packing layer. How to remove arsenic from geothermal water. (3) The method for removing arsenic from geothermal water according to claim 1, wherein ferrous ions are contained or added to the geothermal water.