# Sorption of \({}^{137}\)Cs and \({}^{90}\)Sr on Organic Sorbents
## 1 Introduction  
Ensuring the safety of nuclear legacy facilities involves not only the disposal of high-activity waste in underground storage facilities, but also the isolation and reclamation of millions of tons of intermediate and low-level waste placed in near-surface storage facilities [1, 2]. The main problem for many such facilities is the proximity of rivers and other watercourses, which gives rise to the need to use waterproofing [3] and filtration barriers for effective sorption of radionuclides.  
Wastewater treatment with a low content of heavy metals using organic sorbents is known to be an efficient and relatively cheap method, and is used as an alternative to synthetic resins and other more expensive materials [4, 5, 6, 7]. The advantage of organic sorbents is the ability to utilize the waste material by incineration, which can significantly reduce the volume of waste of the first and second classes.  
High-moor peat is formed on high moors and waterlogged areas as a result of decomposition of plant debris. The main peat-forming agents in such bogs are sphagnum masses [8].  
Coal is a combustible mineral, which mainly consists of organic matter, converted in the process of lithtification under the influence of temperature and pressure.  
Shungite are quite rare rock and distributed in the northwestern part of Russia. It usually contains more than 30% of the so-called shungite substance with the admixture of terrigenous and clayey material. It is in fact a polymorphic modification of carbon, which occupies an intermediate position between anthracite and graphite. Shungite consists of molecular structures with different allotropy, connected by amorphous carbon. Shungites are formed from organic bottom sediments of a high level of carbonatization with a fullerene content of 1 ppm to 10 ppm. The study of shungite began more than 150 years ago, which is associated with its special properties. Currently, shungites are used in various fields: as catalysts, in construction, as fire- and acid-resistant materials, in medicine, in the chemical industry, in metallurgy, etc. [9; 10; 11].  
The sorption properties of peat, hard and brown coal are primarily determined by the composition and number of functional groups which, under certain conditions, are capable of interacting with metals. The mechanisms of metal sorption on shungite remain unclear. Most of the published works provide data on the sorption of metals on shungite containing up to 70% of impurity minerals, mainly clayey [11; 12], which probably determines the high sorption properties of such shungite rocks. In this work, sorption experiments were carried out on enriched monomineral shungite, consisting of 99% pure shungite.  
The purpose of this study was to investigate the sorption properties of the natural organic sorbents with various degrees of lithification in relation to the \({}^{137}\)Cs and \({}^{90}\)Sr radionuclides. Experiments were carried out under identical conditions over a wide pH range. A detailed study of the mineral composition and functional groups of the studied sorbents made it possible to establish the regularities and some mechanisms of sorption of Cs (I) and Sr (II) on organic sorbents.