The need for the development of sustainable, efficient, and green radioactive waste disposal methods is emerging with the saturation of spent nuclear waste storage facilities in the Republic of Korea. Conventional radioactive waste management methods like using cement or glass have drawbacks such as high porosity, less chemical stability, high energy consumption, carbon dioxide production, and the generation of secondary wastes, etc. To address this gigantic issue of the planet, we have designed a study to explore the potential of alternative materials having easy processability, low carbon emissions and more chemical stability such as ceramic (hydroxyapatite, HAP) and alkali-activated materials (geopolymers, GP) to capture the simulated radioactive cobalt ions from the contaminated water and directly solidify them at low temperatures. Physical and mechanical properties of HAP alone and 15wt% GP incorporated HAP (HAP-GP- 15) composite were studied and compared. The surface of both materials was fully sorbed with an excess amount of Co(II) ions in the aqueous system. Co(II) sorbed powders were separated from aqueous media using a centrifuge machine operating at 5,000 RPM for 10 minutes and dried at 100°C for 8 hours. The dried powders were then placed in stainless steel molds, and shaped into cylindrical pellets using a uniaxial press at a pressure of 1 metric ton for 1 minute. The pellets were sintered at 1,100°C for 2 hours at a heating rate of 10°C/min. Following this, the water absorption, density, porosity, and compressive strength of the polished pellets were measured using standard methods. Results showed that HAP has a greater potential for decontamination and solidification of Co(II) due to its higher density (2.65 g/cm3 > 1.90 g/cm3), less open porosity (16.2±2.9% < 42.4 ±0.9%) and high compressive strength (82.1±10.2 MPa > 6.9±0.8 MPa) values at 1,100°C compared to that of HAP-GP-15. Nevertheless, further study with different constituent ratio of HAP and GP at various temperatures is required to fully optimize the HAP-GP matrix for waste solidifications.

Coal briquette ash is an inorganic and non-combustible material. Although coal briquette ash is mainly composed of SiO2, Al2O3, and is an acceptable raw industrial material (containing Fe2O3, K2O, MgO, CaO, TiO2, and Na2O), it is merely considered waste and is exploited as a building material for concrete admixtures and bricks. Because mullite (3Al2O3 2SiO2), which coal briquette ash contains, is a stable compound with a crystalline structure, it plays essential roles in its fracture strength and bending strength. This study serves the purpose of developing environmentally friendly, economical clay bodies through the use of coal briquette ash as a substitute for kaolin to provide Al2O3 and SiO2. We also investigated the seed effects during sintering process by feeding mullite directly into clay bodies. The results show that in 1,300°C heat, a mixture of 40% coal briquette ash, 40% feldspar/limestone (8 : 2), and 20% clay indicates a fracture strength value of 525 kgf/cm2, an absorption rate of 0.72%, burning shrinkage of 11.5%, and an average bending strength of 0.6 cm, which is superior to other clay bodies. The addition of coral briquette ash in clay bodies promoted mullite formation and grew as mullite acted as a seed. In addition to the developing clay bodies, it can also make an oatmeal-colored glaze to widen the spectrum of its usability. This study will help resolve waste problems, reduce environmental pollution, and raise economic value by using coal briquette ash as a raw material for ceramics. Clay bodies made with coal briquette ash are expected to continuously contribute to the development of the ceramics industry with upcycling effects.