Comparison of Zero-Valent Iron and Bimetallic Iron-Aluminum on the Reduction of Aqueous Hexavalent Chromium

• Main Authors: Tai-Yu Chen, 陳泰宇
• Other Authors: Yi-Chu Huang
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/32429452237965149507

碩士 === 國立屏東科技大學 === 環境工程與科學系 === 94 === Due to the rapid industrial development, many pollutants were produced in recent years. Chromium is a raw materials and often used in the industrial manufacturing process such as pigment, paint, fireproofing materials, electroplating, metal processing, and tanning, etc. Chromic compounds, which are toxic to human health, are considered to be the teratogenic and carcinogenic substances. Electroplating wastewater accounts for about 5 to 10 percent volumes of all industrial wastewater. If the wastewater is not properly handled and processed, it may bring about enormous impairments to the environment. In this study, zero-valent iron (Fe0) including micro-scale and nano-scale iron, and bimetallic iron-aluminum (Fe-Al) were utilized to reduce the hexavalent chromium (Cr6+) to the trivalent chromium (Cr3+) which is a less toxic from of chromic compound. The parameters concerned in this study included initial pH value, particle size of Fe0 and Fe-Al, pretreatment of acid-washing process, dosage ratio between Fe0 and Cr6+ (Fe/Cr6+), dosage ratio between Fe-Al and Cr6+ (Fe-Al/Cr6+), and iron contents of Fe-Al. The result shows that acid-washing pretreatment could remove the impurities which were adsorbed by iron particle, and then enhanced the reaction rate. From the characteristic analysis, the surface area of Fe0 was reciprocally proportional to particle size but was directly proportional to the adsorption efficiency, while the surface area of the Fe-Al was directly proportional to particle size and adsorption efficiency. As for the particle sizes, micro-scale Fe was the biggest while the nano-scale Fe was the smallest. The dosage of nano-scale Fe and Fe-Al applied to reduce the same concentration of Cr6+ was only one half of that of micro-scale Fe. As for the final reduction efficiency, Fe0 and Fe-Al could reach to more than 95% with less reactive time as compared with the micro-scale iron. The variation ranges of pH, oxidation-reduction potential (ORP), and dissolved oxygen (DO) were the lowest for Fe-Al and the highest for nano-scale Fe. The reasons for Cr6+ reduction efficiency of Fe-Al better than that of nano-scale Fe were summarized as follows: (1) the variation range of pH of Fe-Al was minimal so as to avoid Cr3+ transforming to Cr6+ during the reduction process, (2) the variation ranges of ORP and DO of Fe-Al were small that favored the follow-up treatment process, (3) the particle size of nano-scale Fe was too small to be recycled. This study shoes micro-scale Fe0 with acid-washing pretreatment, nano-scale Fe0, and Fe-Al can effectively reduce the aqueous Cr6+ and this techinique can be referred as an alternative for treatment of wastewater and remediation of aquifer as well as soil contaminated with chromium.