Synchrotron X-ray microtomography, electron probe microanalysis, and NMR of toluene waste in cement

Synchrotron X-ray microtomography shows vesicular structures for toluene/ce ment mixtures, prepared with 1.22-3.58 wt% toluene. Three-dimensional imagi ng of the cured samples shows spherical vesicles, with diameters ranging fr om 20 to 250 mu m; a search with EPMA for vesicles in the range of 1-20 mu m proved negative. However, the total vesicle volume, as computed from the microtomography images, accounts for less than 10% of initial toluene. Sinc e the cements were cured in sealed bottles, the larger portion of toluene m ust be dispersed within the cement matrix. Evidence for toluene in the ceme nt matrix comes from Si-29 MAS NMR spectroscopy, which shows a reduction in chain silicates with added toluene. Also H-2 NMR Of toluene-d(8)/cement sa mples shows high mobility for all toluene and thus no toluene/cement bindin g. A model that accounts for all observations follows: For loadings below a bout 3 wt%, most toluene is dispersed in the cement matrix, with a small fr action of the initial toluene phase separating from the cement paste and fo rming vesicular structures that are preserved in the cured cement and quant itatively imaged with tomography. Furthermore, at loadings above 3 wt%, the abundance of vesicles formed during toluene/cement paste mixing leads to m acroscopic phase separation (most toluene floats to the surface of the ceme nt paste).