Hexavalent Chromium Removal by Zerovalent Iron
Date Issued
2005
Date
2005
Author(s)
Liu, Ching-Wen
DOI
zh-TW
Abstract
Chromium is a common pollutant in groundwater in industrial region because it is a raw material which is often used by many industries. Zero valent iron has been widely used in remediation of groundwater pollution. The potential for using zero valent iron to treat chromium pollution in situ has been concerned in recent years. The surface area and the passivity of the passive film on the iron surface are very important factors for chromium removal by zero valent iron. The surface area for nanolized iron is much larger and the passive film for nanolized iron is much thinner than that for commercial powder iron. Therefore, the chromium removal rate in nanolized iron system should be much higher than that in commercial powder iron system. The efficiencies of chromium removal in nanolized iron and commercial powder iron (J. T. Baker) systems were compared in this work.
Three factors, co-existing anions (Cl-, SO42-, NO3-, ClO4- and PO43-), initial pH and temperature affected on chromium removal were investigated in commercial powder iron system. The same factors except the temperature were investigated in nanolized iron system. The kinetics of the chromium removal reaction was also examined in this study.
The results show that the existence of chloride and sulfate ions can increase the rate of chromium removal by zero valent iron in commercial powder iron system. Otherwise existence of the phosphate, perchloride and nitrate ions can reduce the rate of chromium removal by zero valent iron in commercial powder iron system. However, in nanolized iron system, the influences of chloride, sulfate, nitrate and perchloride ions on chromium removal rate were very relatively insignificant. But the existence of phosphate ion can still decrease the chromium removal rate.
The chromium removal per unit weight of iron in nonalized iron system was much larger than that in commercial powder iron system. This phenomenon indicates the destruction of passive film is the rate-determining step for chromium removal by zero valent iron in commercial powder iron system but is not in nonalized iron system.
Both the removal rate of chromium decreased when the initial pH of chromium is higher. As chromium involves chloride, the kinetic of chromium removal by commercial powder iron follows pseudo-first-order reaction. But in the nanolized iron system, the kinetic follows pseudo-second-order. The chromium removal rate increased with the increase of temperature.
Key words: chromium, commercial powder iron, nanolized iron, pH, kinetic
Subjects
六價鉻
商業鐵粉
奈米鐵
pH
反應動力
chromium
commercial powder iron
nanolized iron
kinetic
Type
thesis
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