Extraction of home brewed sodium silicate from palm oil fuel ash and its effect on alkali activated materials

Abstract

The development of alternative binders as a replacement for Portland cement is one approach to address the growing demand for cement in the building sector. Alkali-activated materials (AAMs) are gaining popularity as a viable and environmentally friendly alternative to Portland cement-based products. However, the energy-intensive manufacturing process of alkaline activators increases the total embodied energy and greenhouse gas emissions of AAM systems. Waste-derived activators have not only been used to reduce greenhouse gas emissions, but also to recycle wastes into valuable activators that can replace conventional alkali-silicate activators. In this novel investigation, home-brewed silicate (HBS) was extracted from the treated palm oil fuel ash (TPOFA) using the thermochemical method. Combining TPOFA and NaOH with molars of 3 M and 4 M generates an alternate sodium silicate solution. The effect of several parameters, including NaOH molarity (3 and 4 M), temperature (80 °C), and stirring time (5 h) on the dissolution efficiency of silica from TPOFA was studied. In addition, the compressive strength was investigated as part of its mechanical property. The results indicated that after 28 days, compressive strength of 51 MPa was obtained using HBS, while the commercial silicate obtained a compressive strength of 52 MPA. About 82% of the 60.3% SiO2 present in the TPOFA was dissolved by 4 M NaOH with a NaOH:TPOFA ratio of 2. However, a lower amount of 54% was dissolved by 3 M NaOH with a NaOH:TPOFA ratio of 3. When compared to the mortar prepared using commercial sodium silicate, the FTIR measurements revealed a reduction in the intensity in the HBS based mortar. Furthermore, the SiO2 and Na2O contents were found in the HBS solution between 11% and 16.8%, 11.5% and 24%, respectively.