JPS62158111A - Recoverying method for silica from geothermal water - Google Patents

Abstract

PURPOSE:To produce SiO2 having high purity stably by depositing dissolved SiO2 in geothermal water by adding polyethyleneimine to the water, then removing polyethyleneimine by thermal decomposition. CONSTITUTION:Since a large amt. of SiO2 is dissolved in the geothermal water generated in a geothermal power plant, etc., polyethyleneimine having 500-1,000,000mol.wt. is added to the geothermal water in the form of aq. soln. of 10-1,000ppm concn. to cause deposition of dissolved SiO2 in the form of fine particles having 0.02mum particle size. Deposited fine SiO2 particles coagulate and precipitate in the form of coarse massive gel having ca. 0.5-1.0cm particle size. The precipitated SiO2 particles are washed with water and separated by filtration repeatedly, then heated for about 2hr at >=600 deg.C to remove remaining polyethyleneimine by thermal decomposition. Thus, SiO2 having 97-98% purity expressed in terms of pure SiO2 content is stably produced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for recovering silica (5t02) from geothermal hot water containing a large amount of dissolved silicic acid.

(Prior Art) Silica (5in2) is a substance that exists abundantly in nature, and is used in a wide range of industries depending on its purity.

High-purity silica is used, for example, as a raw material for metal silicon, which is in increasing demand for semiconductor applications.

As the raw material mentioned above, SiO□ purity is about 9
Crystals of 9 or more, silica sand, silica stone, etc. are used.
Almost all of these are imported from overseas such as Brazil and India. Since silica is a very stable oxide, it is common to reduce it at high temperatures using carbon as a ring agent to produce crude silicon, which is then further refined to produce metallic silicon.

High-purity silica will continue to be in high demand, but it is only produced in a limited number of countries around the world, and it is highly dependent on political and transportation conditions, making it an unstable resource and not available in all quantities. .

On the other hand, silica of ordinary purity is widely used in large quantities for ceramics and as a raw material for ferrosilicon.

Silica of general purity is widely distributed both domestically and internationally, so its raw material supply and price are relatively stable compared to the high-purity products mentioned above.

However, depending on the application, there are many cases where the permissible amounts of specific components are strict.

For example, iron powder is specified in the glass manufacturing industry. Most industrially produced glasses are 5 ilicate glasses and usually contain 65 to 75 5i02'i. 5102
As a source, silica sand is used, and the silica sand is SiO□
The purity is about 92 to 98%, and it contains various impurities depending on its origin. A2203 as an impurity
+Fe2O31C, LO, MfO+TiO2, etc., and since Fe2O3 colors glass, the allowable amount in the glass is strictly controlled.

In the glass manufacturing process, iron is introduced from sources other than raw materials. For example, contamination comes from mixers, transport equipment, and refractories on the walls of melting furnaces. Therefore, it is desirable to set even stricter regulations on the iron content in glass raw materials than the above conditions.

As mentioned above, high-purity silica raw materials are supplied from a limited number of countries, and there are many unstable factors such as political situations and changes in the supply-demand balance. Although silica raw materials of general purity are not high-purity varieties, there are many that have strict regulations depending on their use and impurity components, but it is not always easy to obtain raw materials with little variation in purity.

Therefore, securing a stable source of high-purity, low-cost silica is
This has become an important issue.

On the other hand, since the energy crisis caused by the oil crisis, diversification of energy supplies has been promoted through the development of alternative energy sources to oil. Among these new energies, geothermal energy is expected to be used not only for power generation but also for greenhouse horticulture, crop cultivation, district heating, livestock breeding, etc. by supplying hot water.

The fluids used in geothermal power generation and the like are high-temperature fluids such as steam and hot water that have accumulated in high-temperature reservoirs underground and are drawn above ground. In general, geothermal fluids.

It consists of two phases: steam and hot water, and various substances are dissolved in it while natural water from meteoric water or magma is stored in a high-temperature reservoir. That is, in hot water, Hack + KCJ-+ C, C4+ S10 + Cc
Contains CO3, H2s, etc.

In particular, silica exists as silicic acid in geothermal water, and
Generally, the content is about 500 to 1200 ppm as 102.

During the process of extracting hot geothermal water to the surface for use, there is a flash of steam and a drop in temperature, which causes the silicic acid content in the geothermal water to become supersaturated. As a result, a problem has arisen in which silica scale precipitates in above-ground facilities that utilize geothermal energy and in underground reinjection wells for hot water after steam separation, and the use of silica scale precipitation inhibitors and desiliconization are being carried out in some areas. There is.

As a desiliconization method, for example, an electrode made of iron or the like is inserted into a hot water retention tank and electrolysis is performed using this as an anode, and silica is coagulated and precipitated in the form of iron hydroxide using the cation basin of the eluted iron. As shown in Japanese Patent Publication No. 59-9820, a method has been proposed in which a c,2+ type substance is added to geothermal water and the silica content in the geothermal water is separated and removed as calcium salt. However, in either method, the separated silica has not been effectively utilized because it contains large amounts of iron, C, etc., and is economical.

(Problems to be Solved by the Invention) The present invention attempts to recover silica (S10□) from geothermal water containing a large amount of silicic acid and to utilize it effectively.

Additionally, by removing the silicic acid content dissolved in the geothermal water, we can obtain geothermal water with almost no scale adhesion, contributing to the effective use of geothermal energy. It was aimed at

(Another means to solve the problem) That is, the present invention adds polyethyleneimine to geothermal water to precipitate silicic acid, and then separates the precipitated silicic acid.
This method recovers silica by thermally decomposing polyethyleneimine after drying.

By adding polyethyleneimine to hot geothermal water containing a large amount of silicic acid, the dissolved silicic acid can easily form a gel, precipitate, and separate. The separated silicic acid is washed with water, dried, and then calcined at several hundred degrees Celsius to thermally decompose the polyethyleneimine and leave silica (5in2), which can be recovered. The silica recovered in this manner has a fairly high purity as SiO□ of 97 to 98, and is stable with little compositional fluctuation.

Washing silicic acid separated from geothermal water and silica after firing with high-purity water or a dilute acidic aqueous solution is effective in increasing the purity.

The polyethyleneimine (Polyet, hyleneimine) used in the present invention is
A chain polymer compound as shown in the following formula,
Generally, ethyleneimine is produced by three methods: carbon dioxide, hydrochloric acid, hydrobromic acid, p-toluenesulfonic acid, and aluminum chloride.

Polyethyleneimine is a colorless to pale yellow viscous liquid represented by the following formula, which is soluble in water and is used as an agent for increasing the wet strength of dust, anion exchange resin, and paper.

-[-CH2CH2NH-). The polyethyleneimine used in the present invention preferably has a molecular weight of about 500 to 1 million, and more preferably about 10,000 to 100,000.

If the molecular weight is too low, the aggregation effect will be weak and it will not be effective. Further, those having a high molecular weight of 1 million or more are not water-soluble and are not suitable for the purpose of the present invention.

To add polyethyleneimine to geothermal water, it is possible to directly add polyethyleneimine, but if you want the reaction to proceed uniformly in a short time, use an aqueous solution and add 10 ppp of polyethyleneimine.
It is preferable to use it at a concentration of about m to 100 ppm.

In this case, the effects of the present invention will be recognized even if the geothermal water is high temperature immediately after it has been ejected from a production well, or if the temperature has been lowered by temporarily placing it in a storage tank or the like. It will be done.

By adding polyethyleneimine, silicic acid in the geothermal water precipitates as fine particles of about 0.02 μm, and these particles further aggregate to form coarse lumps of about 0.5 to 1 m and settle. Sedimentation is complete within 1 minute after addition, so the silica gel can be washed with water by discarding the supernatant, adding clean water, stirring, and repeating the procedure to allow sedimentation to occur again. . Furthermore, it can be easily separated from water using P paper, f cloth, or the like. The silica separated in this way becomes a cream and is rubbed into metal steel (with an opening of about 0.1 to 1 μm) to separate contaminants such as sand and mud. In this way, - can be passed. Since the silica obtained at this stage also contains a large amount of polyethyleneimine, it is heated to the decomposition temperature of polyethyleneimine to thermally decompose it and remove the polyethyleneimine. When heating is carried out in the atmosphere in an ordinary electric furnace, it is desirable that the temperature be 600° C. or higher for about 2 hours. Silica gelled from geothermal water is washed with polyethyleneimine and f
A certain amount of the separately dried material was changed in increments of 100°C from 100°C to 1000°C as the furnace temperature, and 2 times at each temperature.
After heating for a period of time, the amount of carbon in each calcined silica was measured using a carbon analyzer, and an example of the results, which were further converted to the amount of polyethyleneimine, is shown in FIG. From this figure, it can be seen that by setting the heating temperature to 600° C. or higher, polyethyleneimine in the silica can be almost completely removed.

Preferably, heating is performed at a higher temperature, about SOO°C.・(Example) Example 1 Geothermal water spouted from a geothermal production well (total phosphorus concentration 680
ppm) was collected and once stored at around room temperature, a polyethyleneimine aqueous solution (a degree 1100pp) was added to the polyethyleneimine aqueous solution (a degree 1100pp) so that the weight of polyethyleneimine relative to the weight of geothermal water was 0.00.
When added and stirred at a ratio of 4, coarse silica gel was produced in about 10 seconds.

This liquid was centrifuged, the total amount of silica in the supernatant was measured,
The amount of gelled silica was determined relative to the amount of supersaturated silica, and the recovery rate of silica was calculated using the following formula.

Here, the saturated solubility was determined by actual measurement from the geothermal water emitted from the well. Table 1 shows the measurement results of the recovery rate.

Table 1: Recovery rate of silica in geothermal water Furthermore, the separated silica gel is washed several times with water to remove fine contaminants such as sand.
μm). Further, the silica gel containing polyethyleneimine in the f solution was dried at 100°C for 2 hours, and then fired at 800°C for 2 hours in an electric furnace to thermally decompose and remove the polyethyleneimine. Table 2 shows the analysis results of the composition of the silica thus obtained.

Table 2 Composition analysis results of silica wt% Example 2 Silicic acid in geothermal water was removed using the apparatus shown in FIG. Geothermal water spouted from a production well (not shown) is guided through a pipe 6 and stored in a storage tank S with a molecular weight of 1.
oooo polyethyleneimine aqueous solution (l OOmas
s ppm) is mixed by weight with the geothermal water weight by weight of polyethyleneimine electrolytic corrosion (00004 weight) and introduced into the silica sedimentation separation tank 4. The inside of the silica sedimentation separation tank has a multi-stage structure, and overflow is repeated in sequence, so that only the upper permeate is supplied to the reinjection well through the pipe 7. On the other hand, since the generated coarse silica gel settles to the bottom of the sedimentation separation in a few minutes, the coarse gel is discharged and collected from the discharge port installed at the bottom. sio□ in geothermal water before adding polyethyleneimine is 68
The S concentration in the geothermal water before entering the reinjection well was 0 ppm.
iO□ was 273 ppm, and a remarkable reduction effect was observed. The silica gel taken out from the outlet is
After washing with water, filtration, drying, and calcination, the obtained silica 5i
As a result of quantifying 02, the purity was 979%.

Water washing is carried out by adding clean water to the slurry mixture taken out from the outlet, stirring it, allowing it to stand, allowing the silica to settle, and then discarding the supernatant liquid, repeating the process several times. , I did it. For filtration, cotton P cloth was used. After drying at 105°C for 2 hours in an electric furnace in an atmospheric atmosphere, it was fired at 800°C for 2 hours in an electric furnace.

Furthermore, the particle size after pulverizing the obtained silica is on average 2
Since the flux was less than 00 to 300 mesh, it was used as a welding flux for steel materials and its weldability was examined.

Conventionally, silica sand is used to mix TiO2 and CeLCO3 with water glass and coat the surface of an iron core (called a core wire), and this is used as a welding rod. When the silica obtained by this method was used as a substitute, there was almost no difference in weldability such as arc condition, occurrence of nupata, slag condition, and pead appearance compared to conventional products.

(Effects of the invention) The present invention is a method for recovering silica from geothermal water using polyethyleneimine, and compared to conventional methods of mining underground resources, relatively high-purity silica can be stably extracted. It is a simple substance, and the purification method is simple. Additionally, the effect of suppressing scale formation in geothermal recovery equipment can also be obtained as a secondary effect.

The characteristic of the obtained silica is that it can be easily pulverized to obtain fine particles. In addition, this method has excellent features such as gel formation, water washing, filtration, and other operations that can be performed while in a liquid state, so that they can be carried out effectively in compact equipment adjacent to a geothermal well.

[Brief explanation of drawings]

Figure 1 shows the results of silica separated from polyethyleneimine being passed through, washed with water, dried, heated in an electric furnace, measured with a carbon analyzer, and the obtained carbon content was converted to the amount of polyethyleneimine. , Figure 1 plotted against heating temperature
, FIG. 2 is a diagram showing an example of an apparatus for recovering silica in geothermal water for carrying out the present invention. 1... Chemical injection pump 2... Polyethyleneimine 3... Polyethylene imine dissolution tank/storage tank 4... Silica sedimentation separation tank 5... Sedimentation gel
6... Piping 7... Piping Fig. 1 Heating temperature (°C) 1: Chemical injection pump 2: Polyethyleneimine dissolving tank 3: Polyethyleneimine storage tank 6: Piping 7: Piping

Claims (2)

[Claims] (1) Geothermal water characterized by adding polyethyleneimine to geothermal water to precipitate silicic acid, separating and drying the precipitated silicic acid, and then thermally decomposing the polyethyleneimine to recover silica. How to recover silica from. (2) The molecular weight of polyethyleneimine is 500 to 1000
000. A method for recovering silica from geothermal water according to claim 1.