The Effects of Phosphate and Ferric Ions on the Releasing of Arsenic from Arsenic-Contaminated Soil

• Main Authors: HE, FU-RU, 何馥如
• Other Authors: WANG, MEI-SHEUE
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/24g2wm

碩士 === 萬能科技大學 === 環境工程研究所 === 106 === Special geological environment has resulted in arsenic contamination of soils and groundwater in some areas in Taiwan. The purpose of this study was to explore the effects of adding phosphate and ferric iron in soil suspension on the releasing of arsenic from soil, and to evaluate the effects of cultivation of vegetables on the removal of arsenic. Soil samples with arsenic contamination were collected from Dong Shan , and soil samples collected from Daxi were used as background controls. The results of this test showed that shaking for 24 hours was sufficient to achieve equilibration of arsenic release from arsenic contaminated soil. The higher the phosphate concentration in the extracting solution was, the higher the amount of arsenic released. In the absence of phosphate, the arsenic released increased slightly as the concentration of ferric irons in the solution was raised. When both phosphate and ferric iron were present in the solution, the phosphate and ferric iron reacted to each other and lowered their own concentrations, thereby reduced the amount of arsenic released. The results of the planting experiments showed that the water spinach absorbed arsenic in the soil, with the amount depending on the concentration of arsenic in the soil. The form of the arsenic in the soil influences the amount of arsenic accumulated in water spinach. Solubility and mobility of arsenic are higher, and more arsenic can be released into groundwater when there is significantly higher fraction of non-specifically bound As (F1). Planting crops in contaminated soils will lead to absorption of arsenic from pore water by crops and accumulation in plants, which causes threats to human health. The results of sequential extraction analyses of arsenic-containing soil indicate that F3, fraction of arsenic bound to amorphous iron and aluminum oxides, was the most abundant fraction, accounting for 65% to 74% of the total arsenic, followed by F4, fraction bound to crystalized iron and aluminum, with 15% to 25% of the total arsenic, while F2, specifically bound fraction, and F5, residual fraction, were similar with respectively about 4% -6.5% of the total, and at least the F1 phase, non-specifically bound fraction, only 0.1% to 0.2% of the total arsenic content. After planting experiments, regardless of whether there was or was not cultivation of water spinach, the F1 phase of arsenic in the soil was reduced by about half. Therefore, growing water spinach indeed will reduce the soil arsenic content, mostly by removing the arsenic in F1 phase.