Behavior of Metal Impurities on Surface and Bulk of Biogenic Silica from Rice Husk Combustion and the Impact on Ash-Melting Tendency

Highly pure biogenic silica can be obtained from rice husk ash if agglomeration and ash melting during combustion can be avoided. In the present study, the effects of fuel pretreatment and combustion temperature on the properties of the ash samples from rice husk combustion were investigated. In this respect, the chemical compositions of the bulk and outer surface and morphology of the obtained rice husk ash were evaluated. Compositions of the bulk ashes were analyzed with X-ray fluorescence and inductively coupled plasma with optical emission spectroscopy, while surface compositions were obtained from X-ray photoelectron spectroscopy. Images from a scanning electron microscope were used to evaluate the morphologies of the ash samples. Results showed that the concentrations of metal impurities on the surfaces of the ashes were higher than in the bulks. In pretreated rice husk ash samples, the levels of metal impurities decreased considerably on the surfaces. Consequently, ash melting was obviated, and powdery ashes without any agglomeration were obtained.