Reduction of Nitrate by Zero-valent Zinc and Pd/Zn Bimetallic Particles
Date Issued
2006
Date
2006
Author(s)
Hung, I-Chun
DOI
zh-TW
Abstract
硝酸鹽與亞硝酸鹽為地下水中常見污染物，以含氮肥料為主要滲入來源，若累積將危害環境生態與人體健康。現行處理技術包括薄膜逆滲透、離子交換、生物脫硝、化學還原法等。本研究主要探討成本低、時間短之化學還原技術。研究指出零價金屬擁有強大還原能力可用以去除水中硝酸鹽 (NO3-)及含鹵有機物（HOCs），其中以零價鐵與零價鋅為代表。然而，在降解硝酸鹽反應中發現零價鐵系統之產物幾乎皆為氨；零價鋅系統之產物為氮氣與氨。因此，本研究主要探討零價鋅系統降解硝酸鹽之氮氣產生比例。
雙金屬技術藉由金屬表面的直接接觸產生電子轉移的反應，可改善單一零價金屬之低反應活性與改變反應途徑而提升產氮氣比例。本研究以批次實驗分別選取銅、鈀、鎳、鉑等第二金屬作為與零價鋅合成雙金屬觸媒。實驗證明雙金屬可產生兩階段反應途徑：一、硝酸鹽被零價鋅降解為大量亞硝酸鹽與少量氨；二、雙金屬機制將亞硝酸鹽還原為氮氣及氨，產氮氣比例優於單一零價鋅系統。本研究結果顯示Pd/Zn0的雙金屬脫硝系統在最適操作條件下有最佳氮氣生成效果：(1)曝氮氣系統之產氮氣比例優於曝氬氣系統；(2)最適Pd/Zn0雙金屬加藥量為2.85 g/L；(3)氮氣產量隨第二金屬鈀之負載量增加而上升，並在10%時有最佳效果。
Nitrate derived mainly from nitrogenous fertilizer is one of common pollutants in groundwater, and it would endanger ecological environment and human health. Existing technologies embrace reverse osmosis, ion exchange, biological denitrification, chemical reduction and so forth. This study centered on low costs and short time chemical reduction technique in which zero-valent metal was taken as reaction material to degrade nitrate in water. In this study, the product of nitrate reduction by zero-valent iron is almost ammonium, and that by zero-valent zinc both nitrogen and ammonium dominated. Moreover, copper, palladium, nickel, and platinum were chosen as catalysts to promote the reaction of nitrate and zero-valent zinc, and Pd/Zn exhibited optimum results. Evidences show zero-valent zinc reduced nitrate to a great of nitrite and less ammonium, and then bimetallic Pd/Zn degrade nitrite to nitrogen and ammonium. Finally, experimental factors including Pd loadings, initial concentration of nitrate, amount of Pd/Zn usage, and kinds of exposing gas were taken into consideration in term of reaction rate and nitrogen selectivity.
With the abundance of data from experimental factors that reveal (1) Pd loadings increase, N2 yield increase; (2) initial concentration of nitrate is between 40 mg-N L-1 and 50 mg-N L-1, N2 yield raises to 36.5%; (3) amount of Pd/Zn usage reaches 0.5g and then N2 yield promotes to 64.4%; (4) 40% N2 yield can be obtained by exposing nitrogen and 5% Pd/Zn.
Subjects
雙金屬
硝酸鹽
鈀
鋅
零價金屬
Bimetallic
Nitrate
Palladium
Zero-valent
Zinc
Type
thesis
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