Characterization of Silica Produced from Rice Husk Ash: Comparison of Purification and Processing Methods

As a byproduct of the combustion of rice husk to generate energy, rice husk ash (RHA) is formed by silica and carbon, apart from small amounts of other constituents. Several treatments can be used to increase the purity of the silica obtained, or even produce pure silica. The present study tested the efficiency of different techniques to obtain silica, characterizing and comparing the silicas obtained from RHA. A literature review was conducted, and then selected techniques were used to produce silica, which was characterized by XRF, XRD, particle sizing, specific weight, specific surface area, total carbon, and SEM. The literature review showed that most techniques include a pretreatment like acid or alkaline leaching followed by thermal treatment to increase the amount of silica produced by reduction of carbonaceous materials. The results showed that it is possible to produce silica from RHA using simple methods, and that these produced silica with purity above 98%. The treatments that afforded the best results were acid leaching followed by thermal treatment at 800oC, and alkaline extraction at low temperature, with silica purity of 99.3% and 99.6%, respectively.