Preparation method of granular oxide adsorbent, and water treatment method using same

Abstract

The present invention relates to a preparation method of a granular oxide adsorbent for water treatment in which a metal oxide is bound to the surface of polymer particles, and more specially, to a preparation method of a granular oxide adsorbent, comprising the following steps: putting polymer particles in an acidic solution; adding polymer particles to a metal oxide aqueous solution and adjusting a pH; and washing and drying the obtained product. Accordingly, a granular oxide adsorbent prepared by the preparation method is provided and is utilized in water treatment and the like.

Claims

1. A method for preparing a granular oxide adsorbent, having metal oxide on an acid-treated surface of a polymer particle, comprising the steps of: placing polymer particles in an acidic solution, thereby treating a surface of the polymer particle so that a metal oxide can be bound to the surface of the polymer particle; washing the surface-treated polymer particles; adding the surface-treated polymer particles to an aqueous metal oxide solution, adjusting the pH of the aqueous metal oxide solution to a range of from pH 5 to pH 10 while agitating the solution, thereby forming the metal oxide on the acid-treated surface of the polymer particle; and washing and drying the polymer particles, having metal oxide on the acid-treated surface thereof; wherein the metal oxide is one or more types selected from the group consisting of iron oxide, aluminum oxide, and titanium oxide.

2. The method for preparing a granular oxide adsorbent of claim 1, wherein a polymer of the polymer particles to be treated with an acid in the acidic solution has a sulfonate group.

3. The method for preparing a granular oxide adsorbent of claim 2, wherein the polymer of the polymer particles is sulfonated polystyrene.

4. The method for preparing a granular oxide adsorbent of claim 1, wherein the acidic solution is one or more types selected from the group consisting of hydrochloric acid, nitric acid and sulfuric acid.

5. The method for preparing a granular oxide adsorbent of claim 4, wherein a pH of the acidic solution ranges from pH 1 to pH 3.

6. The method for preparing a granular oxide adsorbent of claim 1, wherein the metal oxide is one or more types selected from the group consisting of ferrihydrite, magnetite, hematite and goethite.

Description

DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a block diagram of a hybrid system of granular iron oxide particles and an ultrafiltration membrane.

(2) FIG. 2 shows the appearances of a ferrihydrite granular adsorbent and a magnetite granular adsorbent, which are iron oxide-coated granular adsorbents, according to one example of the present invention.

(3) FIG. 3 shows a graph evaluating an organic matter removal rate by a granular ferrihydrite adsorbent according to one example of the present invention.

(4) FIG. 4 shows an isothermal adsorption graph of powdery and granular ferrihydrite adsorbents according to one example of the present invention.

(5) FIG. 5 shows graphs of transmembrane pressure changes for flow rates in various operating conditions through a PVDF membrane (a) and a PES membrane (b) according to one example of the present invention.

(6) FIG. 6 shows a graph showing adsorption capability changes according to the regeneration of a granular oxide adsorbent according to one example of the present invention.

MODE FOR DISCLOSURE

(7) Hereinafter, the present invention will be described in more detail with reference to examples. However, the following examples are for illustrative purposes only, and the scope of the present invention is not limited to these examples.

Example 1: Preparation of Polymer Particles

(8) Polymer particles were prepared by placing polystyrene particles having a sulfonate group with an average diameter ranging from 0.6 mm to 0.7 mm in ultrapure water, placing them for 24 hours at room temperature after adjusting the pH to pH 2 with hydrochloric acid, washing several times with ultrapure water, and then completely drying in an oven.

Example 2: Preparation of Ferrihydrite Granular Oxide Adsorbent

(9) An aqueous ferrihydrite solution was prepared by introducing FeCl.sub.3 to distilled water and adjusting the final concentration to 10 g Fe/L, the polymer particles of Example 1 were immersed therein, and were agitated for approximately 12 hours. The pH was adjusted to pH 7 by adding an aqueous sodium hydroxide solution to the mixture. The mixture was agitated for approximately 48 hours so that the oxide was favorably formed in the polymer particles. The mixture was dried by being placed for 48 hours at room temperature. A ferrihydrite granular adsorbent was prepared by washing the dried mixture with ultrapure water several times for additional purification, and drying in a vacuum oven for approximately 48 hours at room temperature.

Example 3: Preparation of Magnetite Granular Oxide Adsorbent

(10) An aqueous magnetite solution was prepared by introducing FeSO.sub.4 to distilled water and adjusting the final concentration to 10 g Fe/L, the polymer particles of Example 1 were immersed therein, and were agitated for approximately 12 hours. The pH was adjusted to pH 11 by adding an aqueous sodium hydroxide solution to the mixture. The mixture was agitated for approximately 48 hours so that the oxide was favorably formed in the polymer particles. The mixture was dried by being placed for 48 hours at room temperature. A magnetite granular adsorbent was prepared by washing the dried mixture with ultrapure water several times for additional purification, and drying in a vacuum oven for approximately 48 hours at room temperature.

Experimental Example

(11) 1) Properties of Raw Water

(12) For performance tests of the granular oxide adsorbents prepared in Example 2 and Example 3, influent raw water of Duryu Water Treatment Plant in Daegu, Korea, was used as feed water. The raw water was stored at 4 C. before use. The raw water was equilibrated for 2 hours at room temperature before the tests began. Then the raw water was treated with a 200 m filter (Melt-Blown Bonded Cartridge Filter Pore-Cell Micro filter EP8P-LTC, Clean & Science, Korea) in order to remove turbidity and large particles, and used as the feed water. Specific qualities of the raw water are shown in Table 1.

(13) TABLE-US-00001 TABLE 1 Item Value pH 7.23 Turbidity, NTU 0.297 Total Organic Carbon, mg/L 2.05 UV.sub.254, cm.sup.1 0.036 SUVA, L/mg-m 1.76 Electrical Conductivity, s/cm 278 Aluminum, mg/L 0.056 Calcium, mg/L 27.06

(14) 2) Operating Condition of Membrane and Membrane Filtration System

(15) An ultrafiltration membrane made of polyvinylidene fluoride (PVDF) having a pore size of approximately 40 nm was used after being made as a module having an effective membrane length of 25 cm and an effective membrane area of 13.35 cm.sup.2. The ultrafiltration membrane was immersed in ultrapure water for 24 hours before the tests. In order to remove preservatives from the membrane surface in advance, all the membranes were washed by flowing an alkaline solution near pH 10 added with NaOH through the system.

(16) A hybrid ultrafiltration membrane process was operated at a constant flow rate having a constant flux of 50 l/m.sup.2-hr (corresponding to 1.11 ml/min as a flow rate). Specific pretreatment column and operating conditions are shown in Table 2.

(17) TABLE-US-00002 TABLE 2 Operating Condition Value Column Diameter, cm 1.5 Hydraulic Loading Rate, m/h 0.556~0.600 Flow Rate, mL/min 1.112 Bead Volume, mL 16.68 Empty Bed Contact Time, min 15

(18) All batch adsorption tests were carried out by placing a proper amount of each of iron oxide slurry and iron oxide coating beads (the granular adsorbent of the present invention) in a glass beaker at a constant temperature (232 C.), and under a constant concentration condition in 150 rpm and 100 ml raw water using a stirring rod. For the adsorption, isothermal adsorption tests and kinetic tests were carried out using time intervals of a constant cycle. In the iron oxide slurry adsorption tests, the concentration of organic matters dissolved in water after removing the adsorbent using a 0.45 m filter (Milipore, USA) immediately after the adsorption. The empty bed contact time (EBCT) in the fixed adsorption column was set to 2 to 15 minutes, and the contact time was optimized by removing natural organic matter. Operating conditions of various iron oxide coating beads loaded in the column are shown in Table 3.

(19) TABLE-US-00003 TABLE 3 Operating Condition Value Effective Membrane Length, cm 25 Effective Membrane Area, cm.sup.2 13.35 Flux, L/m.sup.2hr 50 Supply Water Flow Rate, mL/min 1.11 Backwashing Flow Rate, mL/min 84.8 Backwashing Pressure, kPa 100 Temperature, C. 23 2 Adsorption Bed Reactor Type Up-flow Column Size: diameter (cm) length (cm) 1.5 5.2

(20) 3) Analysis Method

(21) An FE-SEM (Hitachi S-4300, Japan) was used to observe the changes in the bead surface and the membrane surface, and an EDS (EDX-350, Hitachi, Japan) was used to check the iron content in the elements that may be discovered in the bead surface. Total organic carbon was analyzed using a total organic carbon analyzer (Sievers 820, GE, USA) after removing particulates using a 0.45 m, microfilter membrane (Millipore, USA). UV254 was measured at a wavelength of 254 nm in a quartz cell using a spectrophotometer (DR-4000, Hach, USA), and turbidity Was measured using a turbidimeter (2100P, Hach, Germany).

(22) In addition, inorganic matters were analyzed through an inductively coupled plasma emission spectrometer (DV2100, Perkinelmer, USA) equipped with a MiraMist nebulizer (Perkinelmer, USA) after preparing a sample in accordance with an ICP pretreatment procedure of a standard method. For the molecular weight distribution analysis of dissolved materials in water was performed using a. GPC (CTS30, YOUNGLIN, KOREA), and other qualities of raw water were analyzed using a pH meter (pH 330i, wtw, Germany) and an electrical conductivity meter (cond 340i, wtw, Germany).

(23) 4) Evaluation on Iron Oxide Coated Granular Adsorbent Surface Properties

(24) The surfaces of the granular oxide adsorbents obtained in Examples 2 and 3 were observed using a video microscope, and the results are shown in FIG. 2.

(25) As shown in FIG. 2, the color was brown after being coated with ferrihydrite (FIG. 2(a)) and the color was black after being coated with magnetite (FIG. 2(b)), and it was identified that the bead surface was evenly well-coated.

(26) 5) Estimation of Proper Adsorbent Dose

(27) The kinetic test described above was carried out for natural organic matter in order to estimate proper adsorbent doses in a continuous membrane process (FIG. 3).

(28) When examining the organic matter removal rate according to the ferrihydrite granular adsorbent dose as shown in FIG. 3, the removal rate reached approximately 22% when the dose became approximately 10 g/l, and even when the dose was further increased, the organic matter removal rate maintained 23%.

(29) Based on the kinetic test result, the adsorption rate coefficient (k) value and the adsorption capacity (q.sub.e) value of dissolved organic carbon by powdery and granular ferrihydrite adsorbents were measured applying a pseudo-second order model for each operating condition, and the result showed that the adsorption capacity was similar, however, the adsorption rate was 3 times higher for the granular type. The specific results of pseudo-second order dynamic model application for natural organic matter adsorption by powdery and granular ferrihydrite adsorbents are as shown in Table 4, and the measurements were carried out under the conditions of powdery ferrihydrite of 400 mg/l as Fe, granular ferrihydrite of 8 g beads/l (416 mg/l as Fe), and natural organic matter initial, concentration of 2.05 mg/l.

(30) TABLE-US-00004 TABLE 4 Adsorbent K (g/mg-min) q.sub.e (mg/g) R.sup.2 Powdery Iron Oxide 0.144 1.423 0.955 Granular Iron Oxide 0.407 1.130 0.988

(31) In addition, the isothermal adsorption test result demonstrated that the granular iron oxide adsorption mechanism included monolayer adsorption (FIG. 4).

(32) 6) Organic Matter Removal Evaluation and Membrane Permeability Changes in Adsorption and Membrane Filtration Processes

(33) Based on the test results described above, organic matter removal and membrane permeability changes were observed using a hybrid process of an adsorbent (e.g., powdery ferrihydrite, granular ferrihydrite, granular magnetite) and a membrane, in addition to a single membrane process. When the organic matter removal efficiency by a single adsorption process was compared, all adsorbent types showed similar removal rates of 20 to 24%.

(34) In addition, FIG. 5 shows transmembrane pressure changes for cumulative water volume treated under each operating condition. In FIG. 5, is a case in which a PVDF membrane is used, and (b) is a case in which a PES membrane is used. As shown in FIG. 5, it was demonstrated that the transmembrane pressure reached up to 100 kPa when the water volume per membrane surface area reaches approximately 1,000 l in a single ultrafiltration process. Meanwhile, when the magnetite granular adsorbent was used, the transmembrane pressure reached approximately 60 kPa from initial 50 kPa when treating with 1,000 l/m.sup.2, and when the granular ferrihydrite adsorbent was used, the transmembrane pressure reached 45 kPa when treating with the same volume (1,000 l/m.sup.2), and it was seen that the membrane fouling was markedly improved.

(35) 7) Analysis of Organic Matter Molecular Weight Distribution Changes Before and After Adsorption

(36) Organic matter molecular weight distribution changes were measured for the samples before and after adsorption in order no understand the cause of marked reduction in membrane fouling when pretreatment removing 20% of dissolved organic carbon by adsorption is carried out.

(37) As a result, 3 main peaks were identified, and the first among them appeared at a molecular weight of 1000 kDa, the second peak at 220 kDa, and the third peak at 26 to 64 kDa. The first peak had a UV.sub.260 value of approximately 0.43 cm.sup.1 as a macro organic molecule included in raw water, however, the UV.sub.260 value greatly decreased to 0.1 cm.sup.1 or less after the adsorption treatment. In addition, the initial UV.sub.260 value of the second peak was approximately 0.45 cm.sup.1, and the initial UV.sub.260 value of the third peak was 0.4 cm.sup.1.

(38) 8) Evaluation on Regeneration Efficiency of Adsorbent

(39) FIG. 6 compares the regeneration efficiency of granular ferrihydrite and magnetite adsorbents. Through FIG. 6, it was demonstrated that the removal rate is similar to the initial dissolved organic carbon removal rate after regeneration regardless of the granular oxide types, and it was seen that the dissolved organic carbon removal rate generally appeared somewhat high when the granular ferrihydrite adsorbent was introduced.