Hydrotalcite and hydrocalumite as resources from waste materials of concrete aggregate and Al-dross by microwave-hydrothermal process

Abstract Hydrotalcite (HT) and hydrocalumite (HC) were synthesized from active MgO, CaO and Al 2 O 3 in the presence of K 2 CO 3 using microwave-hydrothermal (M−H) process at 100 °C/1 h. The above active oxides were prepared via HCl leaching of dolomite (fine waste of concrete aggregate) and Al-dross waste, precipitated as hydroxides and then activated by calcination. The prepared materials were characterized via XRD, FTIR and TEM. Results showed that chemical recycling of Al-dross and dolomite wastes produced aluminum, magnesium and calcium hydroxides from which their active oxides produced at 600, 900 and 1000 °C, respectively. The M−H treatment of MgO/Al 2 O 3 (4:1) slurry of the active oxides for 1 h at 100 °C resulted in Mg 2 Al(OH) 7 in amorphous plate-like shape while the CaO/Al 2 O 3 (4:1) slurry under the same conditions provided semi-crystalline multi-phases. These phases were identified through X-ray diffraction (XRD) analysis as Katoite [Ca 3 Al 2 (OH) 12 ] and calcium aluminum hydroxides [Ca 2 Al(OH) 7 ·3H 2 O]. In the presence of K 2 CO 3 , MgO/Al 2 O 3 and CaO/Al 2 O 3 slurries produced nano-sized crystalline hydrotalcite or hydrocalumite as deduced from XRD, FTIR and TEM results.