Rice Husk and Bottom Ash Utilization in Production of Porous Glass-Ceramics.

Ceramics, Glasses, and Glass-Ceramics:

Rice Husk and Bottom Ash Utilization in Production of Porous Glass-Ceramics.

Rice husk, an agricultural waste, is abundantly available in many countries. Despite the massive production of rice husk, it is mainly disposed to landfill. In this work, we aim at reducing its landfill by providing a potential application and use for it: rice husk, with its high surface area can serve as an adsorbent in waste water treatment (adsorption of heavy metals e.g. Pb, Zn, Cd). The new rice-husk bearing heavy metals can further get encapsulated within a glass-ceramic structure, making it possible to produce cheap, eco-friendly porous glass-ceramics as insulation materials.

We have used rice husk to adsorb heavy metals Pb and Cd from a prepared simulated waste water. After reaching the adsorption saturation, they were encapsulated inside a glass-ceramic structure. The method is as follows:

Vitrified bottom ashes were mixed with foaming agents in different weight ratios (40:60, 50:50, and 60:40) to prepare a glass matrix for encapsulation of Pb-/Cd-loaded rice husk. It was shown that using 40 wt% vitrified bottom ash with 60 wt% foaming agents leads to a foam glass with the best pore size distribution. Therefore, this batch was further mixed with 5 wt% heavy metal-loaded rice husk and was heat- treated at 750C for 3 hours. it was shown that it is safe to be used as it passes the EN12457-2 leaching test.

Optical images and porosity analysis of 40V60F, 50V50F, and60V40F batches. a) 40V60F has three categories of pores diameters. The smallest pores (D< 5µm) are distributed more homogeneously while the largest pores (D> 20µm) are distributed more heterogeneously b) 50V50F shows similar pore distribution to that of 40V60F, being slightly less porous c) 60V40Fshows very heterogeneous pore distribution. This sample has the largest pores (D > µm) among all. d)Porosity analysis of 40V60F, 50V50F, and 60V40F. The overall porosity of these batches is estimated to be 38%, 34% and 62%respectively.

Compression on glass-ceramic obtained from mixing 5 Wt% loaded rice husk with 40V60F batch. The apparent stress drops at point 1 but, the material is still able to withstand the load. Then, the stress rises again and a second peak can be observed at point 2. After a third broad peak, there is the definite stress drop ,marked as point 3, corresponding to the loss of integrity of the sample, which is reduced in powder. The elastic modulus and compressive strength were measured to be 0.950 ± 0.24 GPa, and 7.5 ±1.9 MPa respectively.

Keywords: circular economy; rice husk; bottom ash; foam glass; glass-ceramics

Contact(s): Debora Fino (debora.fino@polito.it) Elham Sharifikolouei, Francesco Baino, Monica Ferraris (monica.ferraris@polito.it)