Selective extraction and recovery of heavy metals from MSWI reaction ash by xanthate process

• Main Authors: Chien-Chih Lin, 林建志
• Other Authors: Juu-En Chang
• Format: Others
• Language: zh-TW
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/93461106917454969489

碩士 === 國立成功大學 === 環境工程學系碩博士班 === 91 === The reaction ash from municipal solid waste incinerator（MSWI） contains various kinds of heavy metals. Landfill disposal not only disobeys the spirit of resource reuse but also wastes the landfill space. In this research, multiple stage acid extraction processes were utilized to extract metals from reaction ash and the feasibility of heavy metals recovered from the extractants by xanthate (chelating agent) was also investigated. The optimal dosage of acid extraction was examined by semi-dynamic leach tests (SDLT). Afterward, the selective extraction procedure was explored by stepwise acidic liquid addition. At the mean time, the recovery of heavy metals by three kinds of xanthates（KEX, KBX and ISX）and various xanthate/metal molar ratio was also investigated. The UV-vis spectroscopy, elemental analysis and Fourier transform infrared (FTIR) analyses were conducted to explicate a fundamental understanding of the formed metal-xanthate complex's structure and the resudial species in the leachates. These results were addressed to evaluate the optimal procedure for selective extraction and recovery of heavy metals from MSWI reaction ash by xanthate process. The results from the selective extraction of MSWI reaction ash showed that the optimal dosage of acid extraction could be found by the relationship between the pH and heavy metal concentration of the leachate. It was concluded to be a two-stage extraction. In the first stage acid extraction, a great amount of Zn ion (about 1000 mg/l) was leached out from the MSWI reaction ash as the leachate's pH decreased to 5. But the leached Cu and Pb ions were not remarkable at the same time. In the second stage acid extraction, adding more acid dosage to the residual of the first stage extraction, the Zn、Cu and Pb ions leached about 100〜200mg/l while the leachate's pH decrease to 1. And then, three kinds of xanthate were used for heavy metal removal/recovery from the two stage leachates. The performance of xanthate process for Zn removal/recovery from the first stage leachate showed that KEX, KBX were capable of treating Zn-containing wastewate to meet the Taiwan EPA's effluent regulation (Zn: 5 mg/l) when KBX/Metal molar ratio of 2, and KEX/Metal molar ratio of 2.6. The formed Zn-EX complex and Zn-BX complex contained 14~25 % and 15~20 % Zn, indicateing both complexes were worth recovering. In the heavy metal removal/recovery of the second stage extraction leachate, Zn, Cu and Pb ions could be selective removed/recovered by ISX combined with KBX. Firstly, the Cu and Pb ions could be removed by ISX, but the Zn ions were not. The residual Zn ions were then totally removed by adding KBX to the solutions. After the ISX combined with KBX treatment, the residual leachate could pass the Taiwan EPA's effluent regulations. In summary, the heavy metals, such as Zn, Cu and Pb, could be separated from the MSWI reaction ash by two-stage acid extraction and then to be enriched by xanthate recovery. The treated MSWI reaction ash passed the TCLP, and could be reused in the environment or landfilled without further treatment. The two-stage acid extraction combined with xanthate recovery processes colud be used as an environmentally friendly method for treating MSWI reaction ash.