Versatile use of droplet coagulation: Shaping fine-grained SiO2 and Al2O3 waste streams into monodisperse microspheres

Elsevier, Sustainable Materials and Technologies, Volume 14, December 2017, Pages 19-28
J. Pype, B. Michielsen, S. Mullens, V. Meynen


The versatile use of droplet coagulation to recycle complex waste resources (fly ash FA, rice husk ash RHA and alum sludge AS) was investigated. Monodisperse microspheres were shaped, creating higher impact on the applicability of the waste resources. In order to obtain a suspension with appropriate rheological properties, pre-processing was required for the AS powder in contrast to the RHA and FA powders. Furthermore, the impact of the shaping process and waste stream properties on the calcination and sintering was determined and correlated to the microstructure of the sintered spheres. The porosity of the sintered AS microspheres was significantly lower (4%) as compared to the FA (50%) and RHA (67%) microspheres. Consequently, the crushing strength of the sintered microspheres varied for the different waste resources. Due to the enhanced densification, the highest crushing strength (185 MPa) was obtained for the AS microspheres.