Total and solid-phase arsenic and adsorption of aqueous arsenic of some selected soils in Taiwan
| Autor: | Huang, Hung-pin, 黃弘斌 |
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| Rok vydání: | 1997 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 85 Arsenic is a metalloid element which is a toxic substance to both animals and plants. Higher content of soil arsenic affects the growth and reduces the production of crops. Higher amount uptake of arsenic by man will cause the symptoms of epidermis disease. For examples, the occurrence of black-foot disease in south-eastern area of this province is generally regarded a relation to higher contents of arsenic in soils and groundwaters. In soil environment, various forms of solid-phase arsenic of total amount of arsenic and the aqueous form of arsenic in soil solution make a thermodynamic equilibrium system. The uptake of aqueous arsenic by crop roots results in the shift of this equilibrium system. The purpose of this study was thus to investigate the difference in application of two extraction methods for total soil arsenic, the distributions of various forms of solid-phase arsenic extracted by two sequential methods, and the adsorption characteristics of aqueous As(III) and As(V) by different soils. Both 9.6 M HCl and alkaline NaOBr solutions were used to extract total arsenic of soils; two sequential procedures recommended by Chao and Sanzolone and by Tessier et al. were used to extract various forms of solid-phase arsenic of soils. In addition, the batch experiment of aqueous As(III) and As(V) adsorbed by 3 kinds of soils was conducted in 0, 1, 2, 4, 8, 12, 16 and 24 hrs of reaction periods. The amounts of total soil arsenic extracted by 9.6 M HCl and by alkaline NaOBr solutions were quite close. Moreover, QA/QC data for these two extraction methods show no great difference in efficiency. However, the extraction by alkaline NaOBr solution was more simple and less time-consuming. For the same soil, the sums of the amounts of various form of solid-phase arsenic extracted by the procedures recommended by Chao and Sanzolone and by Tessier et al. were quite close. In addition, these two sums of the amounts were also quite close to hose of total soil arsenic extracted by 9.6 M HCl and by alkaline NaOBr solutions. The order of the amounts of various forms of solid-phase arsenic extracted by the procedure recommended by Chao and Sanzolone was acid hydrolyzable form (bound to Fe-Mn oxides) > residual form > exchangeable form > organic form soluble form. However, the amounts of various forms of solid-phase arsenic extracted by the procedure recommended by Tessier et al. were mostly residual form and some form bound to Fe-Mn oxides. This clearly indicates that the procedure recommended by Chao and Sanzolone was much more reasonable and suitable than that recommended by Tessier et al. for the extraction of various forms of solid-phase arsenic. The results from the adsorption batch experiment show that the adsorption capability of the soils increased with increasing their amounts of Fe, Mn and Al oxides. In addition, the adsorption of As(V) was stronger than that of As(III) by a same soil. Due to the competition between phosphate and arsenic anion for the adsorption sites on the soils, the soil with high amount of bound phosphate was less capable to adsorb aqueous arsenic. The desorption of arsenic occurred after soils submerged with water in 2 to 3 hrs. This contributed to the increase of concentration of aqueous arsenic in the reaction systems. In the batch experiment, the kinetics analyses of the adsorption of As(III) and As(V) by the soils show that the main reaction was zero order in 0 to 24 hrs and 3rd order in some few reaction periods. |
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