DEHYDRATION OF NATURAL GAYLUSSITE (NA2CA(CO3)(2)CENTER-DOT-5H(2)O) AND PIRSSONITE (NA2CA(CO3)(2)CENTER-DOT-2H(2)O) AS ILLUSTRATED BY FTIR SPECTROSCOPY

The FTIR spectra of natural gaylussite (Na2Ca(CO3)(2) . 5H(2)O) and pi rssonite (Na2Ca(CO3)(2) . 2H(2)O) are reported between 400 and 4000 cm (-1), and the effect of heating up to 500 degrees C on the mid-infrare d spectra of quenched reaction products is investigated. Upon heating, the hydrated carbonates lose their crystallisation water and transfor m directly to Na2Ca(CO3)(2). The mid-infrared spectrum of Na2Ca(CO3)(2 ) is reported for the first time and the absorption bands are assigned to specific vibrational modes. Under the chosen conditions, dehydrati on temperatures are between 60 degrees and 90 degrees C for gaylussite , and between 110 degrees and 200 degrees C for pirssonite. Gaylussite and pirssonite are heated up to 360 degrees C directly or as prepared KBr pellets. Depending on the experimental conditions chosen, differe nces in the FTIR spectra of quenched carbonates are observed. A short Na-K exchange between (dissolved) KBr and Na2Ca(CO3)(2) in a self-gene rated water-steam atmosphere within the prepared KBr pellets is suppos ed to be the reason for different FTIR spectra and formation of (Na,K) (2)Ca(CO3)(2) solid-solutions is suggested. No cation exchange is obse rved upon heating gaylussite and pirssonite dispersed in KBr pellets t o temperatures below the dehydration temperature.