KR20050047193A - Preparation of iron-coated sand and water treatment using said sand - Google Patents

Abstract

The present invention relates to a method of manufacturing iron-coated sand and a water treatment method using the sand, according to the present invention after adding an iron compound to the sand, such as Jumjin, together with water to make a slurry 90% of moisture under heating or reduced pressure The iron-coated sand, prepared by removing the abnormalities and then drying for 1 to 24 hours at a temperature of 100 to 550 ° C., is filled with a conventional manganese coated sand in a filtration device, and used as trivalent from arsenic-containing raw water of various pH. And both pentavalent arsenic can be removed economically and efficiently.

Description

Manufacturing method of iron coated sand and water treatment method using this sand {PREPARATION OF IRON-COATED SAND AND WATER TREATMENT USING SAID SAND}

The present invention relates to a process for the production of iron coated sand containing a large amount of iron, and to a method of water treatment using this sand as an adsorbent, in particular a method for efficiently removing arsenic from arsenic-containing raw water.

Recently, the problem of contamination of heavy metals including arsenic in the soil and groundwater near the waste and abandoned mines has been seriously raised, but the arsenic immobilization method or removal to prevent the arsenic, especially harmful among these heavy metals, from being moved / diffused from the pollutant source in advance There is insufficient research on the method.

As a method for removing arsenic, coprecipitation / precipitation, ion exchange, adsorption, reverse osmosis, nanofiltration, and electrodialysis reversal are widely studied. Among them, adsorption using activated alumina or iron-coated sand (ICS) is widely used.

Existing iron-coated sand support used in the removal of arsenic is a quartz yarn made of 99.5% or more of the sand composition of quartz is expensive and the content of coated iron is limited, so the adsorption capacity of arsenic is not satisfactory. In addition, the conventional iron-coated sand is prepared by adding a ferric compound aqueous solution to quartz yarn and injecting air at 25 ° C. for a certain time, repeating the coating process several times to remove more than 90% moisture, and then freeze-drying. The manufacturing process has the disadvantage of being very complicated.

In addition, the above methods are known to be effective in the removal of pentavalent arsenic, but inefficient in the treatment of trivalent arsenic. Therefore, in order to remove trivalent arsenic, trivalent arsenic is converted into pentavalent arsenic by oxidation using oxygen, ozone, chlorine, hypochlorite, permanganic acid, hydrogen peroxide, Fenton oxidation, photochemical reaction, pH control, and the like. After the preliminary step, the arsenic is removed by applying the above methods.

However, most of these oxidation methods have a disadvantage in that the oxidation rate is slow, a lot of processing time is required, a large amount of by-products are generated, and the cost is excessive.

Accordingly, it is an object of the present invention to prepare iron coated sand containing a large amount of iron so as to economically and efficiently remove arsenic from trivalent and pentavalent arsenic-containing raw water, and using the iron coated sand as an adsorbent. And it provides a water treatment method using the existing manganese coated sand as a trivalent arsenic oxidant.

In order to achieve the above object, in the present invention, the iron compound is added to the sand together with water to make a slurry, followed by removing at least 90% of moisture under heating or reduced pressure, and then drying at a temperature of 100 to 550 ° C. for 1 to 24 hours. Including, provides a method for producing iron-coated sand.

The present invention also provides a water treatment method comprising passing arsenic-containing raw water through a filtration device sequentially filled with manganese coated sand from the raw water inlet and the iron coated sand produced according to the method of the present invention. do.

Hereinafter, the present invention will be described in detail.

Iron-coated sand according to the present invention, unlike conventional iron-coated sand obtained by coating iron on quartz sand several times and then freeze-dried at a temperature near 25 ℃, the iron compound in the sand, such as Jumjin It is prepared by adding together the slurry and evaporating more than 90% of moisture under heating or reduced pressure and then drying it for 1 to 24 hours at high temperature, that is, high temperature of 100 to 550 ° C. It is very useful as an arsenic adsorbent because it has excellent arsenic adsorption capacity in almost all pH ranges up to strong base.

In the present invention, the removal of more than 90% of the water from the slurry of the sand and iron compounds may be variously performed by conventional heating or vacuum evaporation, the final drying temperature and drying time is iron coated on sand It is impossible to achieve the desired stability and economical efficiency if it is out of the above range as an optimal condition to secure the stability and economical efficiency of manufacturing.

Jumjin yarn of the sand support used in the present invention is a representative standard yarn in Korea, compared to the quartz yarn used in the prior art, has the advantage that it can be easily obtained in the country and economically advantageous. Conventional quartz yarns are used because of the fact that they are 99.5% or more quartz on the sand support, making it easy to characterize the coated iron.

In addition, the iron compound used in the present invention may be an iron salt such as FeCl ₃ , Fe (NO ₃ ) ₃ and Fe ₂ O ₃ , which iron compound may be used in an amount of 4 to 6% of the sand weight.

The filtration system for removing arsenic from raw water by filling the iron coated sand (ICS) of the present invention thus obtained in the filtration apparatus and then passing the arsenic-containing raw water through the packed layer is shown in FIG. 1. In Fig. 1, raw water can be introduced from the bottom as well as from the top, and solids in the raw water are additionally removed by filtration in the process of arsenic in the raw water being adsorbed and removed by the iron-coated sand.

In this case, mainly considering that the valent arsenic is adsorbed and removed, and the trivalent arsenic is difficult to adsorb, according to the method of the present invention, the trivalent arsenic by filling the manganese-coated sand (MCS) to the raw water inflow Can be smoothly removed. That is, trivalent arsenic is first oxidized to pentavalent arsenic by using manganese coated sand (MCS) as an oxidant, and then the pentavalent arsenic may be adsorbed and removed by the iron coated sand (ICS) of the present invention. The MCS / ICS filtration system, further filled with manganese coated sand at the feed inlet, is shown in FIG. 2.

Manganese-coated sand used in the present invention is added to the quartz sand with a manganese compound (for example 0.5% of the weight of quartz sand) with water to make a slurry and dried at 80 to 100 ℃ to evaporate more than 90% moisture The remaining solid can be produced by heating at 150 to 200 ° C. for at least 48 hours, and Mn (NO ₃ ) ₂ is suitable as the manganese compound.

Furthermore, FIG. 3 shows a stereo-type filtration system modified based on the MCS / ICS filtration system of FIG. 2. In the filtration system of FIG. 3, the MCS is located at the top and bottom of the filtration device, the ICS is located in the middle, and the raw water is simultaneously introduced from the upper and lower parts and discharged to the outlet located at the middle. Trivalent arsenic in the raw water is oxidized to pentavalent arsenic in the MCS section and adsorbed and removed in the ICS section. This system requires less site and there is no expansion and flow of media to enable stable operation and high filtration speed.

According to the present invention, by placing the chemical flocculation tank in advance of the MCS / ICS filtration system, it is possible to efficiently remove substances, particularly phosphates, which interfere with arsenic removal from arsenic-containing raw water. That is, after injecting and mixing the chemicals into the raw water in the flocculation tank to form a floc, the formed floc is removed while passing through the filtering device. The raw water treatment process combining the coagulation bath and the MCS / ICS filtration system is shown in FIG. 4, which is a device that can minimize the influence of substances that interfere with arsenic adsorption.

5 shows an MCS / ICS filtration system applied at right angles with the required depth and thickness to the groundwater flow direction in-situ. Through the system configuration of FIG. 5, arsenic may be efficiently removed while maintaining the flow of groundwater.

As such, the iron coated sand prepared according to the method of the present invention contains a greater amount of iron than conventionally used adsorbents and exhibits excellent arsenic adsorption in almost all pH ranges, which together with manganese coated sand Filling the filtration system can economically and efficiently remove both trivalent and pentavalent arsenic from arsenic-containing raw water at various pHs.

Hereinafter, the present invention will be described in more detail based on the following Examples and Comparative Examples. However, the following examples are not intended to limit the invention only.

Manufacture of Iron Coated Sand

Example 1

Jumjin sand was used as a sand support, and 500 mL of 10% FeCl ₃ aqueous solution of pH 10 was added to 1 kg of Jumjin sand, and about 90% of water was removed using a vacuum distillation with uniform stirring. The remaining solids were dried at various temperature and time conditions as shown in Table 1 to produce iron coated ordered yarns. For comparison, based on a known manufacturing method, adding the aqueous FeCl ₃ solution to the existing Aldrich quartz company and injecting air at 25 ° C. for 2 hours and then pouring about 90% of water 4 times Repeated. Finally, the resulting solids were freeze-dried for 24 hours to prepare iron coated quartz yarn.

The iron-coated sand prepared as described above was put in distilled water of pH 2 and left at room temperature for 24 hours, and the dissolution rate of iron over time was measured and shown in Table 1 below.

Sample Name Sand support Dry condition Iron content (mg / kg) Iron dissolution rate (%) Temperature (℃) Hours (hrs) 1 hours 3 hours 6 hours 24 hours existing Quartz yarn 0 ℃ or less 24 4200 0.14 0.23 0.43 0.50 ICS-1 Jumunjin 105 24 8550 0.97 1.99 2.69 4.37 ICS-2 550 One 6610 0.82 1.38 1.95 2.55 ICS-3 2 6220 0.48 0.93 1.16 1.71 ICS-4 3 6430 0.41 0.83 1.25 2.02 ICS-5 4 6990 0 0.50 0.50 2.0

From the above Table 1, the iron coated order produced by the manufacturing method according to the present invention has a large amount of attached iron (up to about 2 times higher than the case of using the existing quartz yarn) and the dissolution rate of iron also increases overall It can be seen.

On the other hand, it can be seen that when the drying time at 550 ℃ at various time conditions, the elution rate of iron at pH 2 decreases as a whole longer drying time, but the difference in significant dissolution rate according to drying time above pH 3 Could not be found. Therefore, the optimum drying time at 550 ° C. in the production of the iron coated sand of the present invention in consideration of acid resistance is preferably not more than 2 hours.

Arsenic adsorption capacity test

Example 2

Arsenic adsorption experiments were carried out using the conventional quartz yarn and ICS-1 prepared in Example 1 under a condition of pH 4.5 and a ratio of adsorbent / adsorbent of 200 mL / g with respect to an aqueous solution of 1.0 ppm of concentration. .

Arsenic concentration of the aqueous solution was measured to calculate the arsenic residual ratio over time and is shown in FIG. 6. As can be seen from the graph of Figure 6, when using the iron coated quartz yarn is removed about 28% of the pentavalent arsenic after 60 minutes, in the case of iron coated order of the present invention all of the pentavalent arsenic after 20 minutes Removed.

Example 3

For the aqueous pentavalent arsenic solution with a concentration of 1.0 ppm, the above example was carried out under conditions of 200 mL / g of adsorbate / adsorbent with NaNO ₃ fixed at ionic strength of 10 ⁻² M and pH change from 2 to 12. Arsenic adsorption experiments were carried out using the conventional quartz yarn and ICS-1 prepared in step 1.

After 24 hours, the arsenic adsorption rate (%) according to each pH was measured and shown in FIG. As can be seen from Figure 7, the conventional iron-coated quartz yarn arsenic adsorption rate gradually dropped at a pH of 7 or more, showing a arsenic adsorption rate of 60% in the strong basic region, while the iron coated order of the present invention pH 12 also showed a high arsenic adsorption rate of more than 90%. As such, it can be seen that the iron-coated ordered yarn of the present invention has excellent arsenic adsorption capacity in almost all pH ranges from strong acidity to strong basicity.

Arsenic Oxidation Performance Test

Example 4

For a trivalent arsenic aqueous solution having a concentration of 1.0 ppm, using a filtration system filled with 2.41 g of ICS-1 prepared in Example 1 and 2.41 g of MCS prepared by coating manganese on quartz yarn at pH 4.5, respectively, Hexavalent arsenic oxidation and pentavalent arsenic adsorption experiments were performed.

A graph showing the fraction of pentavalent arsenic in total arsenic with respect to the oxidation ability of trivalent arsenic to pentavalent arsenic is shown in FIG. 8. From FIG. 8, as a result of analysis of arsenic oxidation state of the arsenic aqueous solution flowing out after 20 hours of arsenic adsorption experiment, it was confirmed that trivalent arsenic was oxidized to pentavalent arsenic as MV was passed through MCS.

As such, the iron coated sand prepared according to the method of the present invention contains a greater amount of iron than conventionally used adsorbents and exhibits excellent arsenic adsorption in almost all pH ranges, which together with manganese coated sand Filling the filtration system can economically and efficiently remove both trivalent and pentavalent arsenic from arsenic-containing raw water at various pHs.

1 is a cross-sectional view showing a filtration system for removing arsenic from an influent (raw water), filled with iron coated sand (ICS) according to the present invention,

FIG. 2 is a cross-sectional view of the MCS / ICS filtration system further filled with manganese coated sand (MCS) at the feed water inlet in the filtration system of FIG. 1, FIG.

3 is a cross-sectional view of a stereo-type filtration system based on the MCS / ICS filtration system of FIG.

4 is a schematic diagram of a treatment process that undergoes a coagulation bath prior to the MCS / ICS filtration system;

5 is a cross-sectional view of the MCS / ICS filtration system applied at right angles to the groundwater flow direction in-situ, FIG.

6 is a graph showing the levels of pentavalent arsenic removal over time of the present invention and conventional iron coated sand,

7 is a graph showing the valent arsenic adsorption rate (%) according to the pH of the present invention and conventional iron-coated sand.

FIG. 8 is a graph showing the oxidation ability (as a result of arsenic oxidation state analysis) of trivalent arsenic to pentavalent arsenic by the MCS / ICS filtration system of the present invention.

Claims (5)

Adding iron compound to the sand together with water to make a slurry and then heating or depressurizing to remove more than 90% of the moisture and then drying for 1 to 24 hours at a temperature of 100 to 550 ℃, manufacturing method of iron coated sand . The method of claim 1, Wherein the iron compound is an iron salt selected from at least one of FeCl ₃ , Fe (NO ₃ ) ₃ and Fe ₂ O ₃ . The method of claim 1, Using an iron compound in an amount of 4 to 6% by weight of the sand. A method of treating water comprising passing arsenic-containing raw water from a raw water inlet to a filtration device sequentially filled with manganese coated sand and the iron coated sand prepared according to claim 1. The method of claim 4, wherein Water treatment method characterized in that the arsenic-containing raw water is subjected to the chemical flocculation tank.