Relationship between the Presence and Absence of Oxygen at the Time of Carbonization of Rice Hull Charcoal and Adsorption Abilities toward Cesium and Strontium

抄録

  The relationships of adsorption abilities of cesium and strontium in the presence or absence of oxygen in the atmosphere during carbonization of rice hull charcoal was investigated. Rice hulls were carbonized at 400–1000 °C by flowing nitrogen gas containing 100% nitrogen or 3% oxygen. The amount of acidic functional groups was higher with 3% oxygen. The rice hull charcoal carbonized in any atmosphere decreased the amount of acidic functional groups with increase in carbonization temperature. A correlation was found between cesium adsorption rate and acidic functional group content. However, there was no correlation between strontium adsorption rate and acidic functional group content. The specific surface area was largest at 237 cm²/g at 800 °C for charcoal carbonized with 3% oxygen and largest at 124 cm²/g at 600 °C for charcoal carbonized with 0% oxygen. From the measurement results of pore distributions, it was found that the volumes of mesopores were larger in charcoal carbonized in 3% oxygen atmosphere than that carbonized under 0% oxygen. There was a high correlation between the pore volume of mesopores and the adsorption amount of strontium. It seemed that rice hull charcoal carbonized with 3% oxygen had a large adsorption rate of strontium.