We study interlayer cation exchanges between potassium and cesium ions in micaceous clay minerals by ab initio calculations using the density functional theory. The calculations reveal that the cesium exchange is energetically favored when the exchange neighbor sites are preoccupied by cesium, otherwise it is not so. This tendency is explained by the simple halide model, suggesting that the interlayer distance adjusted by serially occupied ion radius has a key role in the exchange stability.

View full abstract

Intercalation behavior of acetylsalicylic acid (ASA) to interlayer of hydrotalcite (HT) was investigated in various organic solvents to synthesize ASA/HT composite. ASA intercalation to the interlayer of HT did not occur in an aprotic solvent like acetone but occurred in a protic solvent like alcohols. In the case of alcohols used for solvent, the intercalation behavior was revealed to depend on the alcohol's type. In the primary alcohol (methanol, ethanol, 1-propanol, 1-butanol, and i-butanol), the acetylsalicylate ions were not intercalated, but the salicylate ions were intercalated into the interlayer of HT because of the complete decomposition of ASA in the solution. Since ASA decomposed partially in the secondary alcohol (2-propanol and 2-butanol), the both acetylsalicylate and salicylate ions were intercalated into the interlayer of HT. On the other hand, the decomposition of ASA was substantially restricted in the tertiary alcohol (tert-butanol) because of the stability of the tertiary alcohol. As a result, the acetylsalicylate ions were found to intercalate into the interlayer of HT over 80 mol% and ASA/HT composite was successfully obtained using tert-butanol as solvent.

View full abstract

We propose a low-pressure sublimation method as a new dry method to remove radioactive Cs from clay minerals. To develop this method, we used thermogravimetric analysis (TGA), thermal desorption spectroscopy (TDS), and X-ray photoelectron spectroscopy (XPS) to study Fukushima vermiculite particles saturated and sorbed with nonradioactive Cs and heated in air and under low-pressure and high-vacuum conditions. The results of low-pressure TGA show a mass decrease due to Cs desorption, which is not observed for TGA conducted with the samples in air. The Cs desorption peak at 680℃ is confirmed by high-vacuum TDS. XPS measurements clarify that, on maintaining the samples at 800℃ for 3 min in high vacuum, approximately 40% of the Cs desorbs from the vermiculite. Furthermore, TDS results show that adding a mixed salt, NaCl-CaCl_2, shifts the Cs desorption peak by 180℃ to lower temperatures. These results demonstrate that the proposed method of low-pressure sublimation with added salts enables Cs decontamination of clay minerals at considerably lower temperatures than those in conventional dry methods.

View full abstract

Caryopilite, Mn^<2+> -rich serpentine group mineral, is a major constituent of the manganese ores in the North Chichibu belt in the Shikoku region, SW Japan. The North Chichibu belt is the Jurassic accretionary complex containing abundant chert beds of Permian-Triassic age and has been subjected to low-grade metamorphism of the prehnite-pumpellyite to pumpellyite-actinolite facies. Caryopilite close to Mn end-member in composition and having 1M polytype commonly occur in the chert-hosted manganese deposits. Greenalite, the Fe^<2+> analogue of caryopilite, has 1T polytype and rarely occurs in some chert-hosted deposits. Fe-rich caryopilite having intermediate composition between caryopilite and greenalite and having 1M polytype occurs in an iron-manganese deposit and a manganese deposit associated with basalt. Manganoan chlorites also occur in these deposits.

View full abstract