- 學位論文
核設施附近土壤中銫與鍶之遷移
Transportation of Cesium and Strontium in Soils Nearby Nuclear Facilities
摘要
污染土壤中放射性核種的來源可能來自核子試爆後大氣沉降、核燃料操作過程的疏失，例如蒸發池、液態儲存槽、掩埋場的洩漏，或是核能生產過程中意外的洩漏或釋出。如果棄置不顧，這些污染土壤不但將立即危害人類健康而且會持續造成環境風險。因此環境中放射性核種的化學與生物交互作用將變的相當重要。本研究目的將針對鄰近核設施土壤中銫與鍶之遷移與轉化進行研究，其中包含銫和鍶吸附動力學、吸附能力、土壤中的傳輸、釋放機制以及評估油菜對銫累積的能力。 為了能夠清楚了解放射性核種外洩事故發生時，洩漏至土壤後，土壤對核種之緩衝之能力，因此分別選定具代表性之土壤進行研究。土壤採樣地點可分為四個地區，分別是鄰近核能研究所、鄰近第三核能發電廠、第一核能發電廠以及蘭嶼暫時貯存廠四個地區之土壤進行試驗。 實驗結果顯示在本研究中，短晶距三氧化物(尤其是與有機鍵結鐵鋁氧化物) 影響對銫和鍶的最大吸附量。根據所有方程式飾配結果，二級速率方程式具有較佳的擬合結果，因此本實驗中選用二級速率方程式來計算速率常數。土壤反應組成顯著的與銫和鍶的最大吸附量有關，也因此影響銫和鍶的動力吸附。 線性與非線性吸附參數導入Lt與Kt土壤中銫和鍶傳輸行為。 由統計分析結果，ARE、ME、RMSE及CV 值顯示MT3DMS 傳輸模式對銫和鍶在土柱中傳輸模擬良好。 最好的預測是由Freundlich 非線性遲滯因子。 應用Freundlich 非線性遲滯因子至一維延散擴散傳輸模式中能獲的良好的預測結果並能評估化合物在土註中傳輸的命運。 磷酸銨誘發137Cs 從污染土壤釋放的動力學可由 two-constant rate equation 描述。 由1 M NH4H2PO4 溶液(pH 4.0)造成污染土壤中137Cs 釋出的速率常數較1 M NaCl 溶液(pH 4.0)抽出高。 然而(NH4)2SO4 、NH4Cl及 KCl 溶液抽出卻有相同的趨勢。低分子量有機酸的分泌會增加氫離子濃度。 H+ 能質子化破烈邊緣的氫氧基及氧原子或是弱化礦物表面的 Mg-O, Fe-O, and Al-O 鍵。 低分子量有機酸是一種強力的錯合配位基，它能與礦物的 OH 及 OH2 基交換並與表面陽離子形成錯合如 Al、Fe及Mg。合併磷酸根與質子誘導效應是控制土壤黏土礦物中銫釋出制磷酸銨溶液中的主要機制。 施用磷酸銨肥料至土壤中會促進 137Cs 釋放並因此增加植物吸收、遷移至地下水以及進入食物鏈的機會。 Lt與Kt土壤中根圈土壤中低分子量有機酸總量與油菜中銫累積量有關。 Lt與Kt土壤影響油菜根圈中低分子量有機酸的量表示土壤中的化學及生物性質能控制根圈土壤有機酸的量與種類。 一般來說揮發性有機酸 (如乙酸、丙酸及丁酸) 的貢獻佔兩種土壤根圈總有機酸的67.8 % 至 87.3 %。 然而Kt根圈土壤中較Lt根圈土壤中有較高的有機酸含量。 更多的銫會從土壤中釋放並增加油菜對銫的吸收。 對於調控根-土壤動態機制的更進一步的研究是必要的並且可以降低放射性元素污染食物鏈。
並列摘要
Abstract Radionuclide-contaminated soils were contaminated either through accidental spillage or leakage, deposition of airborne material during nuclear testing and incinerator processing, or plume development from evaporation ponds, liquid-storage tanks, and burial grounds and, operation of nuclear facilities. If left untreated, these contaminated soils may represent not only an immediate danger to human health, but also a chronic environmental hazard. Therefore, it is very important for interacting between chemical and biological of radionuclide in the environment. These objectives are focusing on transportation and transformation of cesium and strontium in the soils nearby nuclear facility, including kinetics and isotherm of cesium and strontium, transportation in the soils, release mechanism, and capacity of cesium accumulation in the rape. Soil sampling was separated to four sites, including Institute of Nuclear Energy Research, the Third Power Plant, the First Power Plant, and Lan-Yu Storage Plant. The data indicate that among components of the subtropical and tropical soils studied, short-range ordered sesquioxides especially Al and Fe oxides complexed with organics play an important role in influencing their capacity and dynamics of Cs and Sr adsorption. Both linear and nonlinear equilibrium-controlled sorption parameters were examined to describe the Cs+ and Sr2+ transport behavior in the red and iron-rich calcareous soils. From statistical analysis, the ARE, ME, RMSE and CV values revealed that MT3DMS simulated well with the Cs+ and Sr2+ transportation in soil column. The best predictions and measurements were obtained from Freundlich nonlinear retardation factors. Application of Freundlich nonlinear retardation factors to the one-dimensional advection-dispersion transport equation with an explicit. The kinetics of the NH4H2PO4-induced 137Cs release from the contaminated soils can be described by a two-constant rate equation. The rate-coefficient values of 137Cs release from contaminated soil in 1 M NH4H2PO4 solution (pH 4.0) were much higher than that of the 1 M NaCl solution (pH 4.0). However, it showed a similar desorption trend in (NH4)2SO4 and NH4Cl, and KCl solutions. The combined effect of phosphate and proton was the major mechanism of 137Cs release from contaminated soils in NH4H2PO4 solution. Application of NH4H2PO4 fertilizer to soil is recommended to promote 137Cs release from soil, and thus also increase opportunity for plant uptake, migration to groundwater and entry into the food chain. The amounts of LMWOAs present in the rhizosphere soils were co-related to Cs accumulation in rape grown in the Lt and Kt soils. Lt and Kt soils affected the total amount of LMWOAs exudates found in the rhizosphere soil of rape, indicating that chemical and biological properties of soils can alter the composition and quantity of organic acids in the rhizosphere soils. Generally, volatile acids (i. e. acetic, propionic, and butyric acids) contributed for 67.8 % to 87.3 % of the total LMWOAs in the rhizosphere of both soils. However, the Kt soil contains higher total LMWOAs in the rhizosphere soils than that of the Lt soil. More Cs was released from soils and led to increased Cs uptake by rape. Further understanding of the basic mechanisms regulating root-soil dynamics is essential for reducing the contamination of food chain with radioelements.