Effectiveness of Oxide-Amendments in the Stabilization Process of Cu, Pb and Zn in Artificially Contaminated Soil

摘要

Three oxide-bearing amendments - steel shots, spodic horizon and Portland cement were evaluated by sequential extraction procedure and leaching test to determine their ability to reduce heavy metal mobility in metal-spiked soil. The incubation experiment was conducted on surface soil horizon that was contaminated with Cu, Pb and Zn as Cu(NO_3)_2·6H_2O, Pb(NO_3)_2, and Zn(NO_3)_2·6 H_2O. Each metal was introduced at the rate of 5,000 mg·kg~(-1). As soil pH strongly influences heavy metal mobility, especially Zn, in this experiment two levels of soil reaction were tested - pH 4 and pH 6 The rise of pH up to pH 6 was undertaken by the addition of calcium carbonate to contaminated soil after 4 weeks of pre-incubation. Next, oxide-bearing amendments were added at the rate: 0, 1 and 3% (on dry weight basis) and the incubation proceeded further for 12 weeks. When the incubation process was finished leaching test was started. During leaching test, additional pH of leachate was analyzed. Result from leaching test showed that metal mobility changed with soil reaction. When reaction of soil solution was below pH 4.6, metal leaching decreased for Zn < Cu < Pb, but between pH 4.6 and the 8.2 the sequence was Zn < Pb < Cu. Above pH 8.2 of soil solution metals showed completely different mobility pattern, the quantity of metals washed out in the order Cu < Pb < Zn. Among tested amendments, the highest efficiency of stabilization process was obtained with cement, independently of soil pH and the dose of the stabilizer. In the case of steel shot, immobilization of trace elements depended on pH and the dose of amendment, higher reduction of metal mobility was obtained in the soil with 3% of stabilizer dose in CaCO_3-treated soils.