| Summary: | 碩士 === 國立成功大學 === 環境工程學系碩博士班 === 98 === The fine fraction of contaminated soil particles (clay and silt) tends to concentrate with heavy metals, therefore, it is important to find effective ways of separation between coarse and fine particles on pollution control of heavy- metals contaminated soils. In this study, an attrition scrubber was performed to investigate the influence of scrubbing conditions, including slurry concentration, scrubbing time, impeller speed and chemical reagents, on separation or enrichment of heavy metals in heavy metal-contaminated soils. In addition, through sequential extraction experiments and leaching tests, their chemical characteristics including fractionation pattern of heavy metals and leaching behavior of contaminated soil before and after scrubbing were compared.
From chemical characterization, the soil used was contaminated with Cu, Pb, Zn, Ni, Hg and Cr and their concentrations exceeded the regulatory threshold established by the Environmental Protection Agency of Taiwan (EPA, R.O.C.). The appropriate condition for separating Cu, Pb, Zn, Ni, Hg and Cr from the metal-contaminated soil or concentrating them into a particular soil fraction (＜45 μm) was at 70 % of solid slurry, scrubbing time of 20 minutes and impeller speed of 2000 rpm. In this condition, the separation efficiency of heavy metals followed the order : Cu (78%) ＞ Zn(69%) ＞ Hg(68%) ＞ Pb(58%) ＞ Ni(48%) ＞ Cr(30%), and the enrichment efficiency of heavy metals followed the order : Pb(276%) ＞ Zn(257%) ＞ Ni?Cu(218%) ＞ Cr(195%) ＞ Hg(153%).
According to the sequential extractions and leaching tests, the difference in fractionation pattern of heavy metals were not significant but changed of heavy metals contents in coarse and fine particles was observed after scrubbing. Cu, Pb, Zn and Ni existed as the forms of Fe/Mn-oxide but residual bounding for Hg and Cr was shown. The results of leaching tests indicated the leaching concentrations of heavy metals from fine particles were higher over a wide pH range. It was because Pb and Zn were gender metals, their leaching concentrations could be measured at high and low pH. While the leaching of Cu and Ni was obvious under acidic condition, this may cause by the bonding of both Cu and Ni were in the form of Fe/Mn oxide. In addition, the leaching behavior of Hg and Cr at high pH were presumably related to the forms of residual bounding.
From the view of the regulatory threshold of hazardous industrial waste (TCLP), the metal-contaminated soil fulfill the regulatory threshold before and after scrubbing, therefore, they can be regarded as ordinary industrial waste. However scrubbing with appropriate conditions, 40 wt.% of soil may be reuesd in environment and achieved the aim of waste reduction.
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