鐵-矽或鋁-矽二元氧化物吸附砷酸鹽與鉻酸鹽

Abstract

隨著科技、工業進步，方便人類的同時卻也產生了許多汙染，重金屬汙染即為一例。砷及鉻為人類工業活動所產生之常見重金屬汙染物。當環境中，存在高濃度的砷或鉻，勢必對環境生態造成衝擊，故移除砷和鉻有其必要性。本研究以合成Fe-Si及Al-Si之二元氧化物吸附水溶液中之砷酸鹽及鉻酸鹽，進而討論砷酸鹽或鉻酸鹽和不同二元氧化物之間的吸附差異。實驗方法為以100 mL 10 g SiO2(s) L-1與10 mL 0.5 M Fe(NO3)3或Al(NO3)3混合，將pH值調整至5，定量至1L後進行合成、老化24小時，形成本研究所使用之二元氧化物。由界達電位可知Fe-Si二元氧化物之零電點較Al-Si二元氧化物低，Fe-Si與Al-Si二元氧化物之零電點分冸為6.4和8.5，因此在吸附砷酸鹽或鉻酸鹽時，皆以Al-Si系統之吸附量較高。而隨著pH下降，Fe-Si系統吸附砷酸鹽或鉻酸鹽的量上升々Al-Si系統在pH 5時吸附砷酸鹽與鉻酸鹽皆有最大吸附量。由離子強度效應及FT-IR分析可知在二元氧化物系統吸附砷酸鹽與鉻酸鹽可能為內圈錯合。等溫吸附實驗結果以Langmuir等溫吸附模式擬合後，砷酸鹽最大吸附量於Fe-Si和Al-Si系統分冸為22.27及33.33 (mg g-1)々鉻酸鹽最大吸附量分冸為19.69及20.41 (mg g-1)。動力吸附實驗結果顯示吸附砷酸鹽系統約在3小時平衡々吸附鉻酸鹽系統約6小時達平衡。經由砷酸鹽與鉻酸鹽競爭吸附結果，可知砷酸鹽會抑制鉻酸鹽吸附，因此可知二元氧化物對砷酸鹽的親和力較高。藉由不同濃度之磷酸脫附，於Fe-Si與Al-Si系統中以310 (mg L-1)磷酸最多脫附分冸為49及65 %之砷酸鹽々Fe-Si與Al-Si系統中，62 (mg L-1)磷酸即可脫附95及77%之鉻酸鹽，因此可知本研究合成之二元氧化物對砷酸鹽有較高的移除潛力。

Technological and industrial progress benefit human beings and also generate a lot of pollution. Arsenate (As (V)) and chromate (Cr (VI)) are common heavy metal pollutants produced by human industrial activities. There is high concentrations of As (V) or Cr (VI) in the environments, it will be impacted and produced the environmental and ecosystem problems. Therefore, it is necessary to remove As (V) and Cr (VI). The objectives of this study are to investigate the adsorption of As (V) and Cr (VI) in aqueous solution by synthetic Fe-Si and Al-Si binary oxides, and to compare the differences between As (V) and Cr (VI) on binary oxides. Experimental method was to mix 100 mL 10 g SiO2 L-1 and 10 mL 0.5 M Fe (NO3)3 or Al (NO3)3, then the pH adjusted to about 5, and quantitative to 1L, aging for 24 hours, it is the binary oxides. The zeta potential showed zero-point charge (pH zpc) of Fe-Si binary oxide is lower than Al-Si binary oxide, and the pH zpc of Fe-Si and Al-Si binary oxides is 6.4 and 8.5, respectively. Therefore, the adsorption capacity of Al-Si binary oxide is higher than that of Fe-Si binary oxide . With the decline in pH , the adsorption of As (V) and Cr (VI) increased on Fe-Si system; but the maximum adsorption of As (V) and Cr (VI) is at pH 5 on Al-Si system. The effects of ionic strength and FT-IR analysis showed that the adsorption of As (V) and Cr (VI) on the binary oxide system can be inner-sphere complex. The isotherm experiments fit with the Langmuir equation, the maximum adsorption of As (V) on Fe-Si and Al-Si system were 22.27 and 33.33 (mg /g), respectively; the maximum adsorption of Cr (VI) was 19.69 and 20.41 (mg /g), respectively. Kinetic experiments showed that the adsorption of As (V) reached equilibrium is about 3 hours; the adsorption of Cr (VI) reached equilibrium is about 6 hours. By competitive adsorption of As (V) and Cr (VI), As (V) can inhibit the absorption of Cr (VI). Therefore, binary oxides have higher affinity to As (V) rather than Cr (VI). The desorption of As (V) by 310 (mg L-1) phosphate showed that As(V) desorbed 49% and 65% on Fe-Si and Al-Si system, respectively; and Cr (VI) is desorbed 95% and 77% by 62 (mg L-1) phosphate on Fe-Si and Al-Si system, respectively. Thus, binary oxides possess higher adsorption potential to As(V) than Cr (VI).