The results showed that reactions with high NaOH concentration usually resulted in low
SiO2/Na2O (2.0 M NaOH were 0.64 -1.73) and that reactions with low NaOH concentration gave high SiO2/Na2O (0.5 M NaOH were 1.68 -2.92). SiO2/Na2O of 5 min reaction of 0.5 M NaOH by MW 800 W was as high as 2.92, which was higher than confirmed by any report for the reactions between quartz sand and NaOH solution.(7) The result implied that the silicate production from the reaction of rice husk ash and NaOH is worth further investigation for practical applications.