Sustainable Thermochemical Extraction of Amorphous Silica from Biowaste

Swapna Banoth,V Suresh Babu,S Ojha,K Rakesh,G Raghavendra

doi:10.1007/s12633-021-01293-z

Swapna Banoth, V Suresh Babu + Show 3 more

Open Access

https://doi.org/10.1007/s12633-021-01293-z

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Abstract

The objective is to utilize zero wastage rice hull material which contains silica as a major component in amorphous form and is used as reinforcement material for various applications. Burning of rice hull (RH) under controlled condition after removal of metal ions leads to white silica of high purity. An inexpensive method for extraction of amorphous silica by thermochemical treatment (pyrolysis process) is performed. Pyrolyzed biomass at four different temperatures is observed for treated and untreated rice hull. Calcination of the rice hull at 600ºC in a muffle furnace turns it into white amorphous silica. In this research, HCl was used to retrieve silica from the rice hull. Extracted silica was characterized by X-ray diffraction analysis, which indicates that the silica is in amorphous form, and displayed a strong broad peak at 22.32º and 21.52˚ (2θ). The FTIR data revealed the existence of peaks at 4000 cm− 1& 400 cm− 1 showing the presence of siloxane and silanol groups. UV-Visible (absorption) band maxima was demonstrated at 367 nm, photoluminescent (emission) spectra displayed a short peak at 453 nm and a sharp intensity peak at 488 nm is comparable with amorphous nano-silica. Less amount of silica appeared at the inner surface of rice hull fiber revealed by SEM analysis. Other element traces were absent, high purity of amorphous silica is observed by EDS.

Highlights

Rice hull is the waste biomass and good source for the production of silica about 50%-90%, majorly cultivated crop in the world [1,2]
Synthesized Silica is characterized by X-ray diffraction analysis, which indicates that the silica is amorphous form, it displayed a strong broad peak at 22.32o and 21.52 ̊ (2q)
Verities of sources are available for the synthesized amorphous silica, among them one of the simple and good sources is rice hull, which has a large amount of silica up to 22%

Summary

Introduction

Rice hull is the waste biomass and good source for the production of silica about 50%-90%, majorly cultivated crop in the world [1,2]. Verities of sources are available for the synthesized amorphous silica, among them one of the simple and good sources is rice hull, which has a large amount of silica up to 22%. The metal impurities, i.e. Fe, Mn, Na, Ca, K and Mg, which effect the color and purification of the SiO2 are removed by the pre-treatments with inorganic acids like HCl, H2SO4 or HNO3 before combustion [6]. Two forms of SiO2 occur in nature Amorphous and crystalline. Opal is the amorphous form of silica and crystalline occurs in three forms namely cristobolite, quartz and tridymite. At different temperatures and heat treatment crystalline form of silica is obtained [7]

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