輻射元素於天然水及水處理單元中之物質狀態

Abstract

為瞭解核災意外發生時，放射性落塵污染水源的情況下，目前淨水場對放射性銫-137的移除效果及可行的緊急應變措施。本研究以直潭淨水場上游底泥配製之人工高濁水結合黏土，探討直潭淨水場上游底泥對Cs+吸附及混沉處理之移除率，以及黏土作為核災意外應急吸附劑之可行性。 研究結果顯示，直潭淨水場上游底泥對Cs+的吸附能力欠佳，於原水pH7條件下，濁度265NTU的人工原水對1 mg/L Cs+的吸附移除率僅為8.49%，換算成單位底泥Cs+吸附量約為2.97μeq/g。以含15.79μg/L Cs+的直潭低濁度原水作混沉處理，可得20 ~ 75%Cs+移除率，並且在pH6.5 ~ 7.0，明礬加藥量大於0.75 mg/L Al2(SO4)3 as Al下，可得大於40%的Cs+移除率。 於原水常見之pH條件下，6.67g/L高嶺土對1 mg/L Cs+有80%的吸附移除率。將1g/L高嶺土加入濁度130NTU天然原水中，在快混pH8.2，加藥量為0.788 mg/L Al2(SO4)3as Al的混沉條件下，可使Cs+移除率增加。以放射性Cs-137與非放射性Cs-133吸附實驗作比較，發現放射性Cs-137吸附移除率較低，可能原因為動力學同位素效應及離子強度所造成的遮蔽效應。

Nuclear power plants provide about 6% of the world's energy and 13 ~ 14% of the world's electricity needs. Conversely, such as Greenpeace International and NIRS, believes that nuclear power poses many threats to people and the environment. The result of this study has indicated that Cs+ adsorption capacity at pH 7 by upstreamt sediments in the synethic water samples with turbidity of 265 NTU is relatively low,i.e. 8.49% and 2.97 μeqCs+/g for Cs+ adsorption removal ratio and sediment adsorption capacity, respectively. By spiking 15.79 μg/L Cs+ in natural water sample with turbidity of 30 NTU, alum mixing and quiescentsettling at pH6.5 ~ 7.0 for this sample could allow at least 40% reduction for Cs+in the supernatants as alum dosage is greater than 0.75 mg/L as Al. By spiking 1 mg/L Cs+ in synthetic water sample containing 6.67g/L kaolinite, 80% reduction in Cs+can be achieved probably due to adsorption. By spiking 1 mg/L Cs+ in natural water sample with 130 NTU of turbidity,mixing with 1g/L kaoliniteas coagulation aid could obtain better Cs+ removal than without kaolinite at 0.788 mg-Al/L of alum dosage and pH8.2 Radioactive Cs-137 has lower affinity than non-radioactive Cs-133 onto turbidity particles in natural water sample. It might be due to the kinetic isotope effect and shielding effect caused by higher ionic strength in the sample of Cs-137.