Study Of Radioactive Methyl Iodide Modified Activated Carbon Adsorption And Desorption Properties

Adsorption filtration method is a common method used for trapping radioiodine because of its high adsorption efficiency,low cost and simple process.Actived Carbon(AC) impregnated by Triethylene diamine (TEDA) is one of the most widely used solid adsorption materials.However,TEDA could sublime easily,which could decrease the adsorption efficiency. The kindling point of impregnated AC could be degenerated as well with the usage of TEDA. Aging,weathering and poisoning of impregnated charcoals may result in lower adsorption efficiency and retention ability,therefore AC for trapping radioiodine should be replaced frequently. A mass of dust may be generated by impregnated charcoals after used for a long time,which could do damage to human and enviroment.In addition,during the process of transportation,reservation and disposal,Iodine could desorb from AC, leading to secondary pollution. Due to these critical problems we face, it is necessary to seek for efficient and widely applicable impregnant. Also, by looking into the desorption mechanism of AC impregnated by TEDA could help improve the property of this kind of adsorption materials.In this paper, the adsorption property of Hexamethylene tetramine (HMTA) impregnated AC and the desorption behavior of AC impregnated by TEDA were researched in order to help develop new kind of impregnant and prevent the secondary pollution caused by Iodine.In the first part of our research, the impacts of a few parameters on the process of locating Iodine by AC containing Hexamethylene tetramine (HMTA) with high flash point and low volatility were tested at27℃and95%-96.5%(RH%).It is shown that HMTA is a highly efficient impregnant with its maximum adsorption efficiency to be94.82%.In the process of preparation of AC impregnated by HMTA,the optimum conditions are:5wt.%impregnant and30min of drying time. Our results also show that the decrement of granularity of AC and concentration of CH3I could improve the adsorption efficiency,whereas the increment of pH and aging of AC play the negative role.The effects of nitrogen flow rate,dipping in water,temperature and K+on the Iodine retention were also discussed in this paper.The results show that the quantities of Iodine released are3.15times when nitrogen flow rates increased from1.4cm/s to21cm/s. Methyl Iodine molecules desorbed after half an hour’s dipping in water, and keep the same at1.5h,2h,3h,4h. Release of Iodine did not happen below80℃. We also find that K+plays a positive role for the retention of Iodine species, for the amount of released Methyl Iodine from AC with0.06KC1is56%of that of AC without KC1.Our preliminary results described in this paper provide some experimental basis for further study of HMTA as an impregnant for capture of radioactive Iodine, as well as guarding against the secondary pollution caused by Iodine.