Removal of Heavy Metal from Contaminated Harbor Sediments by Acid Washing

• Main Authors: SYU, SYUAN-YAO, 許炫堯
• Other Authors: DONG, CHENG-DI
• Format: Others
• Language: zh-TW
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/76302091652940310204

碩士 === 國立高雄海洋科技大學 === 海洋環境工程研究所 === 105 === This study used the acid washing to remove the heavy metal in the contaminated sediments at three estuaries of Kaohsiung Harbor (Jen-Gen River, Canon River, and Salt River). Effects of reaction time (0−300 min), liquid/solid (5−25), types and concentrations of acids on the removal efficiency of heavy metals (copper (Cu), zinc (Zn), nickel (Ni), cadmium (Cd), chromium (Cr), and lead (Pb)) were investigated. In order the sequence extraction analysis of sediments was carried out to understand the change of the binding form of heavy metals before and after acid washing. The Five binding forms were divided into exchangeable, carbonate, Fe-Mn oxide, organic, and residual fractions. The extraction amounts of metals approached equilibrium values in 15 min. The removal rate of heavy metals increased with an increase in insignificantly liquid/solid ratio and acid concentration. Yet, the removal rate increased for the liquid/solid ratio higher than 10 and the acid concentration more than 0.5 M. The removal rates of Zn (80.1−83.7%), Ni (27.6−30.9%), Cr (20.7−23.9%), and Cd (97.2−98.8%) were similar for using three types of acid (HCl, HNO3, CA) washig, whereas the removal rates of Cu and Pb by HCl (65.3% and 79.4%) and HNO3 washing (65.8% and 76.4%) were more effective than those by CA washing (46.0% and 51.4%). Results showed that the optimal removal efficiencies of Cu, Zn, Ni, Cd, Cr, and Pb in the sediment from Jen-Gen River were 78, 75, 33, 100, 21, and 85%, from Canon River were 57, 92, 22, 100, 26, and 72%, and from Salt River were 61, 81, 37, 96, 25, and 81%, respectively, using 0.5 M HCl, liquid/solid ratio of 10, and washing time of 15 min. The removal efficiency of heavy metals in the carbonate bond form after acid washing was obrionly high (90.1−100%). However, most metals were found to slightly increase in the highly- mobile exchangeable fraction after washing, such as Cu, Zn, Ni, and Cr. The finding may be attributable to the release of heavy metal from the re-adsorption of strong binding fraction to the exchangeable fraction on the surface of particles. Moreover, the removal rates of metals megatively correlate with the guantities of metals in residual fraction. The metals concentration in the treated sediment can be below the soil pollution monitoring standards using the optimal parameters of acid washing except Cr. The treated sediment can be used to reclamation land and other purposes. The results of this study can provide a reference for sediment remediation using acid washing in the future.