LIX 84가 고정된 실리카의 제조 및 중금속 이온의 제거 성능 조사

김 종 성, 이 종 협

서울대학교 화학공학과

Preparation of Silica Immobilized with LIX 84 and Performance Evaluation of the Heavy Metal Ion Removal

Jong Sung Kim, Jongheop Yi

School of Chemical Engineering, Seoul National University

Introduction

Inorganic supports immobilized with ion-chelating agents have been received substantial attention for the separation processes of heavy metals from aqueous solutions[1-4].

In the study, the silane coupling method was applied to attach 2-hydroxy-5-nonylacetophenoneoxime (LIX 84) on the surface of the silica for the metal ion removal from aqueous solutions.

Experimental

Preparation of silica immobilized with LIX 84

Three different types of silica beads (Fuji Silysia Chemical Co.) and a silica powder (Aldrich Co.) were used as supports. 3.2 mol/L 2-hydroxy-5-nonylacetophenoneoxime diluted in kerosene (LIX 84, Henkel Co.) was used as a chelating agent without further purification. For chemical treatment of the silica support, 10% (w/w) □-aminopropyltriethoxysilane in toluene (Aldrich Chemical Co.) was used.

Buffer solutions were used to maintain a constant solution pH.

The metal ion concentrations were measured using an Atomic Absorption Spectrometer (Perkin-Elmer, Model 3110).

Silica beads immobilized with LIX 84. l0 g of silica beads were dried at 100℃ in an oven for 3 h. The dried beads were refluxed for 16 h with 100 mL of 10% (w/w) □-aminopropyltriethoxysilane mixture solution with toluene. After washing three times with 100 mL of toluene, followed by two washings with 100 mL of acetone, the treated silica beads were dried in an oven at 100℃ for 13 h. For impregnation with LIX 84, vacuum was applied using a vacuum evaporator for 10 min before introducing the extractant. After the silica beads were fully immersed into the LIX 84, vacuum was applied for 1 h. The impregnated beads were removed, quickly washed with acetone to remove unreacted hydroxyoxime, and then dried under high vacuum at 130℃ for 16 h to evaporate the kerosene. The dried beads were treated with 0.1 M HNO3 on a rotating shaker for 2 h and washed with deionized water. The beads were then air dried at room temperature for 24 h, and then further dried at 110℃ for 5 h in an oven to remove residual water from the interior of the pores. The silica beads thus prepared were kept in an oven at 100℃ until needed. In the study, SBi-L represents adsorbents immobilized with LIX 84 using SBi (i=1, 2, 3). Silica powder immobilized with LIX 84 (SP-L) was prepared using the same procedure as described above, but without the acetone washing after impregnation with LIX 84.

Adsorption and elution of copper ions

The copper adsorption capacities of the adsorbents prepared were investigated by batch operations. 0.2 g of the adsorbent was placed in a flask containing 25 mL of 5 mmol/L copper solutions (pH = 4) and the flask was then placed on a shaker and rotated gently for 48 h.

Transient adsorption experiments were carried out using a packed-column reactor. A pyrex tube (□ 11 mm) was packed with 2.5 g of the adsorbent. The apparatus is composed of a circulation pump and flow meter. 125 mL of feed solution containing of 2 mmol/L copper ion was fed to the reactor and recycled to the solution bath at a rate of 20 ml/min. The solution in the bath was constantly mixed by a magnetic stirrer and 0.5 mL aliquots were removed for analysis.

The break-through experiment was performed for the SP-L using a packed-column reactor. A copper solution (1 mmol/L) was passed through a packed-column (□ 16 mm) loaded with 20 g of the adsorbents at a flow-rate of 5 mL/min. In this case, the copper solution was prepared from deionized water without a buffer solution. The pH of the copper solution was 3.7. The elution experiment was conducted after the SP-L was saturated with the copper ions. A 0.1 M HNO3 solution was fed to the reactor at a rate of 5 ml/min in order to elute the copper ions from the SP-L.

The effect of pH on the adsorption of heavy metals (Cu2+, Ni2+, Co2+, Zn2+, Cd2+) were also studied. 1 g of beads were added to the aqueous solution with each metal concentration of 5 mmol/L and equilibrated for 48 h. Competitive adsorption experiments were carried out using metal aqueous solution containing Cu2+ and one of the following metal ions: Ni2+, Co2+, Zn2+, Cd2+, Ca2+ and Mg2+. In the experiment, 1g of beads was added to the binary aqueous solution, which concentration is 5 mmol/L, and equilibrated for 48 h.

Results and Discussion

The reaction scheme of LIX 84 with divalent metal ions, M2+ may given as

[eqn: rm M^2+~ +~ 2 {HR}~~ □ ~~{MR_2} ~+~ 2H^+]

The effect of solution pH on the adsorption rate of the SB2-L is shown in Fig. 1. Experiments were carried out using a packed-column reactor. The results show the transient relative copper concentration (c/c0) change of the solution with the operation time for a solution pH of 2, 2.5, and 4, respectively. The rate of relative concentration decreased as the solution pH increased.

The break-through experiment was carried out for the SP-L using a packed-column reactor (□ 16 mm). Fig. 2 illustrates the break-through curve for copper ions using the SP-L. As shown in the figure, about 150 bed volumes of feed solution can be passed through at a rate of 5 ml/min without leakage of copper ions into the effluent. When the copper concentration in the effluent was increased up to the saturation point (after about 340 bed volumes), a capacity of 0.401 mmol/g was achieved. This value is 85% of the theoretical capacity based on the amount of LIX 84 impregnated in the SP-L adsorbent.

References

1.	D. Leyden and G. Luttrell, Anal. Chem., 47, 1612 (1975).

2.	C. Fulcher, M. Crowell, R. Bayliss, K. Holland and J. Jezorek, Anal. Chim. Acta, 129, 179 (1980).

3.	M. Marshall and H. Mottola, Anal. Chem., 55, 2089 (1983).

4.	N. Deorkar and L. Tavlarides, Hydrometallurgy, 46, 121 (1997).

Fig. 1 Transient copper concentration change using the

SB2-L with various solution pH.

Copper solution: 2 mmol/L, 125 ml.

Fig. 2 Break-through curve for copper ions using the SP-L.

Copper solution: 1 mmol/L, pH = 3.7. Flow rate: 5 ml/min.

SP-L: 20 g.