TY - JOUR

T1 - Dissolution kinetics and phase transformations of Autoclaved Aerated Concrete (AAC) in alkaline and acid media without further additives

AU - Hartmann, A.

AU - Pawlas, G.

AU - Petrov, V.

AU - Buhl, J. C.

PY - 2014/5/1

Y1 - 2014/5/1

N2 - The reaction behaviour of autoclaved aerated concrete (AAC) in alkaline solution (4M and 16M NaOH) as well as diluted citric acid (0.5M and 1M C6H8O7) was investigated without addition of further components to the system. The aims of these experimental studies were to estimate the dissolution kinetics of the mineral phases tobermorite, quartz and calcite from AAC in dependence of solvent concentration and to study the time and concentration ruled precipitation of new crystalline and/or amorphous solids during leaching. The kinetic experiments were performed for times up to 20 h. A temperature of 453 K was selected for the experiments under alkaline conditions to reach high dissolution rates of quartz. Acid treatment was performed at 333 K according to the rapid dissolution of tobermorite and calcite in acids at low temperature with the aim of formation of Ca2+ containing solutions beside precipitates with low calcium but high silica content. The conversion of AAC was followed by XRD, FTIR and SEM/EDX-analysis for each leaching experiment. Besides strong dissolution of quartz the whole content of tobermorite was found to remain stable in 4 M NaOH over the investigated reaction period. In contrast tobermorite and quartz were both completely converted into solution in 16 M NaOH. Here a crossover reaction of dissolution of tobermorite and quartz and crystallization of sodium calcium hydrogen silicate NaCaSiO3(OH) could be revealed. The onset of precipitation of this new phase was found to start already after 1 h reaction time. Strong dissolution of tobermorite and calcite hand in hand with the precipitation of new solid material was detected under acid conditions. High background contributions in the XRD diagrams indicate a mostly amorphous character of these precipitates but some weak reflections also show formation of a few amounts of new solid phases like earlandite beside very weak lines of unknown phases. Summarizing all the experimental results it can be stated that important information on the most suitable leaching conditions can be withdrawn in consideration of further converting of the solids and solutions in materials recycling process.

AB - The reaction behaviour of autoclaved aerated concrete (AAC) in alkaline solution (4M and 16M NaOH) as well as diluted citric acid (0.5M and 1M C6H8O7) was investigated without addition of further components to the system. The aims of these experimental studies were to estimate the dissolution kinetics of the mineral phases tobermorite, quartz and calcite from AAC in dependence of solvent concentration and to study the time and concentration ruled precipitation of new crystalline and/or amorphous solids during leaching. The kinetic experiments were performed for times up to 20 h. A temperature of 453 K was selected for the experiments under alkaline conditions to reach high dissolution rates of quartz. Acid treatment was performed at 333 K according to the rapid dissolution of tobermorite and calcite in acids at low temperature with the aim of formation of Ca2+ containing solutions beside precipitates with low calcium but high silica content. The conversion of AAC was followed by XRD, FTIR and SEM/EDX-analysis for each leaching experiment. Besides strong dissolution of quartz the whole content of tobermorite was found to remain stable in 4 M NaOH over the investigated reaction period. In contrast tobermorite and quartz were both completely converted into solution in 16 M NaOH. Here a crossover reaction of dissolution of tobermorite and quartz and crystallization of sodium calcium hydrogen silicate NaCaSiO3(OH) could be revealed. The onset of precipitation of this new phase was found to start already after 1 h reaction time. Strong dissolution of tobermorite and calcite hand in hand with the precipitation of new solid material was detected under acid conditions. High background contributions in the XRD diagrams indicate a mostly amorphous character of these precipitates but some weak reflections also show formation of a few amounts of new solid phases like earlandite beside very weak lines of unknown phases. Summarizing all the experimental results it can be stated that important information on the most suitable leaching conditions can be withdrawn in consideration of further converting of the solids and solutions in materials recycling process.

KW - AAC recycling

KW - Acid treatment

KW - Alkaline leaching

KW - Dissolution kinetics

KW - Hydrothermal behavior of tobermorite

KW - Recrystallization process

UR - http://www.scopus.com/inward/record.url?scp=84907012182&partnerID=8YFLogxK

U2 - 10.5276/JSWTM.2014.97

DO - 10.5276/JSWTM.2014.97

M3 - Article

AN - SCOPUS:84907012182

VL - 40

SP - 97

EP - 109

JO - Journal of Solid Waste Technology and Management

JF - Journal of Solid Waste Technology and Management

SN - 1088-1697

IS - 2

ER -