This paper has investigated the influence of alkali treatment on the acidic functional groups of rice hull charcoal and investigated the relationship between its cesium and strontium adsorption ability. In the alkali treatment, rice hull charcoal carbonized from 400 to 1000 °C was immersed in a basic aqueous solution. The pH of the rice hull charcoal increased after alkali treatment. Furthermore, the alkali treatment of rice hull charcoal carbonized at 400 and 600 °C increased the adsorption of cesium and strontium. In the FTIR results, the OH band of alkali-treated rice hull charcoal was stronger than that of the untreated rice hull charcoal. The mesopore volume of alkali-treated rice hull charcoal increased. The alkali-treated rice hull charcoal showed an increased pH, increased negative charge, and cleaved lactone rings contained compared to the untreated sample. In addition, the valence of acidic functional groups increased, and the adsorption ability of cesium and strontium improved.

The relationship between the potassium content in rice hull charcoal and strontium ion adsorption was investigated. Potassium elution treatment was performed on rice hull charcoal , wherein the rice hull charcoal was stirred with distilled water. The pore distribution and specific surface area of the processed rice hull charcoal were measured. Significant change was not observed in the mesopore volumes of rice hull charcoal subjected to elution treatment for 1 h. The specific surface area increased as the elution time became longer. Based on the result of the pore distribution, it was assumed that the macropores increased. Potassium was eluted at 56.0 mg/L from rice hull charcoal subjected to elution treatment for 3 h. This eluted approximately 83% of potassium content. In the strontium ion adsorption experiment, the adsorption amount of the eluted rice hull charcoal was approximately 40% lower than that of untreated rice hull charcoal. High correlation was observed between the potassium content and the strontium ion adsorption amount. Thus, this paper confirmed that it is possible to show a higher adsorption ability by using rice hull charcoal with high potassium content.