| Summary: | 碩士 === 國立宜蘭大學 === 環境工程學系碩士班 === 101 === Soil washing is one of the extensively used methods to effective removed heavy metals from contaminated soil. The reagents used for extraction the heavy metals are EDTA (ethylenediaminetetraacetic acid), citric acid and HCl.
This study investigates recovery of chelant extraction from soil washing process. The wastewater came from unmixed chelant extraction reagent (0.5 M EDTA) and mixed chelant extraction reagent (0.5 M EDTA: citric acid = 3:7) after washing soil of Cu contaminated farmland. The reuse of waste water containing Cu-EDTA complex based on replace-sedimentation procedures.
Comparing the recovery efficiency differences of iron powder [Fe(0)] and FeCl3 as the substitute agents, we focused on the program's different pH, Fe/Cu molar ratio and reaction time on the procedures. In addition, it explores the efficiency of reuse on unmixed and mixed agents after washing Cu contaminated soil. Results indicated that using FeCl3 as a substitute agent replaced the Cu in mixed reagent and unmixed reagent, doesn't differ much at different condition and the rate of replacement of Cu was lower than 3%. Therefore, we suggested that FeCl3 can’t as the substitute agent for treating the waste water that contained Cu. At the process of the Fe(0) replacement, the best reaction condition was achieved at pH=5-6, Fe/Cu molar ratios of 100/1 and reaction time 7 hours for two kinds of wastewater. The good recovery and purity for EDTA wastewater by acidification precipitation process was carried out. Apply Fe(0) replace-sedimentation procedures, the experimental results show that Cu contents are 22.92% and 11.76% for mixed wastewater and EDTA wastewater, respectively. However, the EDTA recovery for two two kinds of wastewater are 75.3% and 98.5%.
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