Stabilization and reduction in bioaccessibility of As-contaminated soil through in situ co-precipitation of amorphous Fe oxides

in situ stabilization;amorphous Fe oxides;bioaccessibility;neutralizing agent;X-ray absorption near edge structure;aging;624

University:서울대학교 대학원

关键词: in situ stabilization;    amorphous Fe oxides;    bioaccessibility;    neutralizing agent;    X-ray absorption near edge structure;    aging;    624;   

Others  :  http://s-space.snu.ac.kr/bitstream/10371/160978/1/000000157803.pdf

美国|英语

来源: Seoul National University Open Repository

【 摘 要 】

This study used in situ amorphous Fe oxide synthesis to form Fe-As co-precipitates with high resistance to chemical extraction in As-contaminated soil. Fe oxide was formed by injecting 2% soil mass of iron nitrate and 30% water, and adjusting to neutral pH. Effectiveness was assessed using a five-step sequential extraction and solubility/bioavailability research consortium (SBRC) method. The five-step sequential extraction demonstrated that >50% of extractable As [i.e., sum of SO42- and PO43- extractable As] in original soil samples was converted to less extractable fractions [i.e., oxalate extractable As] after in situ co-precipitation at an L/S ratio of 0.3. Consistent with the solvent extraction results, the SBRC revealed decreased bioaccessibility. In situ stabilization dramatically decreased bioaccessibility from 71.6 to 33.5% and 64.9 to 26.3% in soil samples. X-ray absorption near edge structure (XANES) with linear combination fitting (LCF) confirmed the formation of schwertmannite or ferrihydrite, indicating amorphous Fe oxide precipitation. Aging confirmed that As bound to amorphous Fe oxides decreased but crystalline Fe oxides increased (i.e., transformation of amorphous Fe oxides into more stable crystalline Fe oxides). Consequently, bioaccessibility of stabilized soils was noticeably alleviated. Such increase was consistent with the XANES results showing increased goethite. Overall, in situ co-precipitation of amorphous Fe oxides using As effectively reduced bioaccessibility of As-contaminated soil long-term. Also, the effects of the neutralizing agent on bioaccessibility of As(V) was investigated. SBRC assessed bioaccessibility of Fe oxides synthesized using NaOH or CaO. As the result, bioaccessibility was much lower in that case of being synthesized with NaOH than CaO. Such results were consistent with that Ca-Fe arsenate minerals have high bioaccessibility in previous study. In order to confirm the effects of neutralizing agents, soil sample pH was adjusted to neutral levels using CaO or NaOH when in situ stabilization applied. After stabilization, the fraction of non-specifically and specifically sorbed As(V) was remarkably decreased in both samples. On the other hand, As(V) bound to amorphous Fe oxides increased from 61.2% to 85.4% and to 85.5% in CaO treated soil and NaOH treated soil, respectively. Bioaccessibility was remarkably decreased in the soil sample used NaOH as a neutralizing agent, but not changed significantly when used CaO. Besides, XANES-LCF confirmed that arseniosiderite, a kind of calcium-iron arsenate, was formed in stabilized soils whenCaO used as neutralizing agent. It is reported that labile calcium on neutral pH might form calcium-iron arsenate which has high bioaccessibility. Therefore, it is necessary to use appropriate neutralizing agents to reduce bioaccessibility when applying in situ stabilization through co-precipitation of Fe oxides.