Optimization of alkali treatment of rice husk ash for producing an alternative alkali activator via response surface methodology

Abstract

The geopolymer field is flourishing, as researchers work to lessen the reliance on conventional cements as building materials. However, high price and energy-intensity of commercial alkaline activators hamper the usage of geopolymers. Bio-based waste materials are efficacious in mitigating the environmental concerns for alkaline activators, but the synthesis process of this alternative alkali activator requires further research, especially on the optimization for RHA dissolution parameters. The objective of this study was to optimize the alkali treatment process on rice husk ash (RHA) using response surface methodology. The effect of five factors, i.e., RHA quantity, sodium hydroxide concentration, stirring speed, heating temperature, and heating time on two output responses, i.e., activator alkalinity and silica composition of alternative activators, were investigated. Central composite design provided the combination for an optimum alternative activator, which was 162.5 g of RHA quantity, 3M of NaOH concentration, 350 RPM of stirring speed, 75 °C of heating temperature, and 3.5 h of heating time with R2 > 0.91 of reduced quadratic models. The activator alkalinity (pH) and silica composition (wt%) for alkali treatment processed activator were 12.1 and 20.3, respectively.