An activated carbon from walnut shell for dynamic capture of high concentration gaseous iodine

In order to capture the high concentration gaseous iodine from off-gas streams under nuclear accident conditions, an advanced activated carbon was prepared by using walnut shell as a raw material and zinc chloride as an activator agent (named WS-ZnCl2). The pore structure and functional groups characteristics of the adsorbent were researched via three techniques including N2 adsorption–desorption isotherms, transmission electron microscope (TEM), and Fourier transform infrared spectroscopy (FTIR). The Brunauer-Emmett-Teller (BET) surface area, the total pore volume and the average pore size of the adsorbent were observed to be 1360 m2/g, 0.68 cm3/g and 2.00 nm, respectively. In addition, the adsorption capacities of the adsorbent to capture gaseous iodine were investigated with static and dynamic experimental adsorption methods. The results of the static experimental adsorption indicated that the gaseous iodine equilibrium adsorption capacity of the walnut shell before and after ZnCl2 activation increased from 606 mg/g to 2374 mg/g at condition of 80 °C and ambient pressure. The dynamic adsorption performance of the adsorbent for capture of gaseous iodine was studied by varying operating parameters, such as temperature, adsorption column height, and the flow rate. More significantly, the maximum dynamic adsorption capacity of the adsorbent for capture gaseous iodine reached a record of 1634 mg/g at 60 °C, 2.2 cm and 250 mL/min. Finally, the importance ranking of the influencing factors on the dynamic adsorption was analyzed by Grey relational analysis (GRA) method. The results showed that adsorption capacity was obviously affected by flow rate, whereas adsorption time was highly influenced by adsorption column height. The adsorbent researched in this paper has potential to capture high concentration gaseous iodine.