Theoretical and experimental on the thermodynamic, kinetic and phase evolution characteristics of secondary aluminum ash

Abstract

As a kind of hazardous solid waste, the resource utilization of secondary aluminum ash (SAA) has become a worldwide challenge. The powdered Al and AlN contained in SAA will release a significant amount of heat during thermal treatment, making SAA have the potential to be used as a secondary energy resource. The thermogravimetric analysis (TG/DTG) coupled to a Fourier transform infrared spectrometer (FTIR) was carried out to evaluate the thermal degradation behavior and thermodynamic of SAA from room temperature to 1300 °C at three different heating rates (5, 10, 20 °C/min). The activation energy was calculated by model-free methods, showing that the activation energy of SAA during pyrolysis ranged from 39.99 to 552.3 kJ/mol for conversion rate (α) = 0.1–0.4. The FTIR results displayed gas products including O–H, C–H, N–H, and N=O groups. The increase in temperature from 1100 °C to 1500 °C will make the phase intensity of chloride and AlN gradually decrease, while the Al2O3 is opposite. However, submicron-sized aggregates can still be observed in the sintered samples at 1100 °C and 1200 °C. After calcination at 1500 °C for 3 h, the micro morphology of SAA is basically dominated by large granular Al2O3 and spinel, which verifies the possibility of slag as the raw material for ceramics and refractories. This research provides a novel idea of employing SAA as a secondary energy resource as well as the theoretical basis data on thermodynamics.

Keywords

• Secondary aluminum ash
• Kinetic model
• Thermogravimetric analysis
• Thermal treatment