Carbon adsorbents for the uptake of radioactive iodine from contaminated water effluents: A systematic review

The need to remove radioactive iodine from water extends beyond the liquid radioactive waste treatment in the nuclear industry, as it can also be found in hospital wastewater and reach wastewater treatment plants. However, it remains a challenge affected by diverse iodine speciation, which includes anions and neutral forms. Recent developments in new carbon materials are offering new opportunities to capture radioactive iodine species from aqueous and gas phases. But how are they made, how feasible is their use, and how effective can they be? Do they outperform traditional carbon materials such as activated carbon? This review, for the first time, assesses current developments in preparing adsorbents for removing iodine species, including nanocarbons. Specifically, their synthesis, properties, maximum extraction capacity, and sorption mechanisms are discussed. The most effective biomass-based carbon for iodine removal was found to be chemically activated (with KOH) sunflower hydrochar with highly developed porosity and a surface area >2000 m(2)/g. Its capacity achieved 6.46 g of I-2/g adsorbent. A similar level of uptake was demonstrated by KOHactivated hydrochar made from cellulose diacetate. The range of nanocarbons studied for this application did not outperform biomass-activated carbons. The regeneration of adsorbents, their scalability, current gaps understanding the mechanisms of iodine species uptake, and the need to achieve their practical application have been discussed. The purpose of the review is to extract new knowledge from relatively new carbon nano materials, nanocomposites as well as traditional carbon sorbents that will inform the preparation of effective sorbents for upscaled applications such as the treatment of radioactive effluents from hospitals or liquid radioactive waste produced in the nuclear fuel cycle.