In particular, at a starting SiO2/Al2O3 (i.e. total SiO2/Al2O3 ratio of the mix including silica and sodium alumanate) of 3.5 mol/mol the degree of reaction of the silica feedstocks (microsilica or silica-rich residue from chlorosilane production) in these previous investigations was only 55%, while the degree of reaction of the rice husk ash at the same starting SiO2/Al2O3 in near 100%.