Summary: | 碩士 === 中興大學 === 土壤環境科學系所 === 94 === There are some agricultural lands polluted by heavy metals in Taiwan .The over use of phosphate fertilizer may affect the fate of the heavy metals in soil, such as the precipitation of heavy metals as phosphates. The purposes of this study were to develop a sequential chemical extractions (SCE) scheme suitable to fractionate the forms of heavy metals associated with phosphate in neutral and alkali soils contaminated with heavy metals. In order to investigate the forms and fractions of heavy metals and nutrients removed as heavy metals polluted soil washed with HCl solution in remediation process.
In this study, Ching-Tung neutral soil (Soil A) in Changhua city and two Hai-pu alkali soils in Kaohsiung county, (Soil B1, high polluted; Soil B2, media polluted) were collected, air dried, and passed through a 2 mm sieve. This was conducted in three parts: First, contaminated soils were extracted by the common available phosphate analysis methods to analyse both of phosphorus and heavy metals to know how much fraction of heavy metals combined. Second, a new SCE scheme was set in this study, the sequential fractionations were exchangeable and carbonate-bound(EC), acid-extractable (AE), amorphous Fe/Mn oxyhydroxide (AmFe), crystalline Fe/Mn oxyhydroxide (CyFe), organic matter (OM) and residual (Res). Third, soils were washed with HCl solution by low soil/liquid ratio(S/L), Soil A was 1:2(w/v), and Soil B1 and B2 were 1:1(w/v).The concentration of the heavy metals, phosphorus and other nutrient elements were measure by Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES).
The results show that the portion of heavy metals combined with phosphate in exchangeable fraction is very low. In alkaline contaminated soils, the polluted metals were mainly remained in the EC fraction, while the unpolluted metals in the AmFe fraction. In neutral contaminated soil, the polluted metals were distributed in the order : AmFe >EC>CyFe, while unpolluted metals were remained mainly in the AmFe fraction. The phosphorus was mainly remained in the AmFe and CyFe fractions. The correlations between the concentrations of phosphorus and heavy metals in different fractions extracted by this SCE were significant in soil A. In study on fate of heavy metals in agricultural land(and shall take phosphorus in account, especially the presence of phosphorus at high levels.) In acid-washing study, part of the AmFe form of heavy metals could be extracted by concentrated HCl solutions, but it was hardly to destroy the crystalline Fe/Mn oxyhydroxide so that the heavy metals with CyFe form could not be released by the HCl solution. In the high Pb and Cd contaminated soil (Soil B1), the amount of Pb and Cd in acid leachates did not show the increase with increasing the strength acid. This may indicate that a reprecipitation with phosphate happened during prolonging the extraction period. In the acid washing, a large amount of Ca (neutral soil>42%; alkali soils>63%) was removed, but the part of Mg and K removed were quite low (i.e., less the 10% of the total content). The informations were be worth for remediation of heavy metal polluted soil washed by HCl in fertility management.
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