Synthesis of sodium silicate crystals from rice husk ash

Abstract

The rich husk is an agricultural waste of rice cultivation worldwide, which is highly rich in amorphous silica. Rice husk obtained from Dagiri was pyrolyzed at 750ºC to give white ash (RHA) which was further treated with acid (ARHA). The ash was reacted with sodium hydroxide at 90ºC for 2.5 h to produce sodium silicate crystals. Sodium silicate synthesized in the study was characterized for some physicochemical parameters. Their structural and morphological properties were assessed using a Fourier transform infra-red spectrophotometer (FTIR), X-ray diffractometer (XRD) and scanning electron microscope (SEM). The mineralogical composition of the ash and sodium silicate was investigated with energy-dispersive X-ray fluorescence (EDXRF) spectrometer. The sodium silicate produced has a melting point of 61ºC, pH of 12.03 and appeared as brownish–white to clear-white in colour. The RHA and ARHA from XRD investigation showed patterns which match the mineral phase cristobalite, while that of the sodium silicate XRD patterns match the mineral heptahydrate disodium trioxosilicate as the most dominant phase. Rietveld refinement of the XRD pattern for the sodium silicate gave Rwp = 12.81, Rexp = 5.55, χ2 = 5.3274 and GoF = 2.3081 against a dual phase analysis. The crystals synthesized are suitable for use in cosmetic formulations.

Keywords

• acid treated ash
• cosmetic
• crystal structure
• paddy
• silica
• water glass