# Removal of Cesium from Radioactive Waste Liquids Using Geomaterials
## 1 Introduction  
With the development of modern science and technology, nuclear energy has been widely applied in industry, national defense, agriculture, medicine, and scientific research. However, radioactive waste liquid has been produced with the rapid development of the nuclear industry. For example, due to the Fukushima Daiichi nuclear power plant accident in Japan in 2011, a significant amount of radioactive material leaked, and a substantial volume of wastewater containing radioactive cesium (Cs) was discharged. As these waste liquids are radioactive and can cause immeasurable harm to the environment and human bodies. Among them, \({}^{137}\)Cs is the most common radionuclide in this type of waste liquid; it produces continuous radioactivity and biological toxicity and has a half-life of about 30 years [1, 2]. \({}^{137}\)Cs mainly releases \(\beta\) and \(\gamma\) rays, which are enriched in human muscles and expose the entire body to radiation. In addition, it may cause cell carcinogenesis, leading to long-term effects and genetic hazards, such as leukemia, infertility, and fetal malformations. The continued harm caused by the nuclear leakage accident at the Fukushima Daiichi Nuclear Power Plant once again sounds the alarm for humankind [3, 4, 5, 6]. Due to this disaster, the removal of radioactive cesium as well as strontium in water has gained considerable attention from many scholars around the world.  
The current removal methods for radioactive cesium mainly include chemical precipitation [7; 8; 9; 10], solvent extraction [11; 12; 13; 14], membrane separation [15; 16; 17; 18], biological treatment [19; 20], and adsorption [21; 22; 23; 24]. The adsorption method is widely used in the removal of radionuclides in water due to its high efficiency, simplicity, high selectivity, and strong adaptability. In recent years, the most versatile inorganic materials that have been used to remove radioactive cesium in water mainly include geopolymers, nano-carbon materials, and metal oxides, among others [25; 26; 27].  
Geomaterial [28] is a type of inorganic cementitious polymer material that has been developed in recent years. It uses calcined clay (metakaolin), volcanic pumice, fly ash, mineral waste slag, and other silico-alumina materials as raw materials. Under the action of the activator, a polymerization reaction occurs to form a three-dimensional, network-like, high-strength dense material that is mainly composed of silicon-oxygen tetrahedrons and aluminum-oxygen tetrahedrons and that has amorphous and quasi-crystalline characteristics.  
With regard to the current problem of the solidification of heavy metal and radioactive waste, this study proposes a practical solution. For our experiments, we used synthetic fly ash-based geomaterials at room temperature, which can overcome some of the consequences of solidified heavy metal and nuclear waste, both locally and abroad. It has the advantages of a low solidification treatment cost, a simple and easy-to-control process, and it can reduce or avoid secondary pollution. This study provides a theoretical basis for the optimization and preparation of adsorption materials with high-efficiency adsorption performance and lays a foundation for the solidification of heavy metal and nuclear waste and their safe adsorption and disposal. It is of great significance to the healthy and sustainable development of the modern economy.