In vitro biodurability of the product of thermal transformation of cement–asbestos

To safely recycle the product of the thermal transformation of cement–asbestos as secondary raw material,its toxicity potential should be assessed by in vitro biodurability tests. In this work, the acellularin vitro biodurability of the products of transformation of cement–asbestos at 1200 ◦C (named KRY·AS)was tested using both inorganic and organic simulated lung fluids at pH 4.5. The dissolution kineticswere followed using chemical, mineralogical and microstructural analyses. The total dissolution timeestimated from the experiments with inorganic HCl diluted solution is one order of magnitude higherthan that determined from the experiments with buffered Gamble solution (253 days vs. 20 days). Thekey parameter determining the difference in dissolution rate turns out to be the solidus/liquidus ratiowhich prompts a fast saturation of the solution with monosilicic acid. The calculated dissolution rateconstants showed that the biodurability in vitro of KRY·AS is much lower with respect to that of standardchrysotile asbestos (total estimated dissolution time of 20 days vs. 298 days, respectively). This proves alow potential toxicity of this secondary raw material.