XAFS ANALYSIS OF THE POTASSIUM-SILICA INTERACTION IN RICE HUSKS

The Si K-edge X-ray absorption spectra of three samples obtained from rice husk have been recorded to investigate changes in medium and shor t range order that could explain the drastic differences in surface ar ea of the samples, from 1 to 260 m(2)/g. The recorded differences are similar to those detected in densified silica. where they have been as sociated with changes in medium range order. Similar changes have been observed in K2O-SiO2 glasses where the addition of potassium oxide le ads to the disruption of SiO4 network, and the formation of chain like structure of non-bridging oxygen atoms, as increasing the quantity of potassium oxide. This suggests that this behavior is due to the stron g interaction between silica and the potassium ions contained in the r ice husks, which leads to a dramatic decrease of the specific surface area if K+ ions are not removed before the annealing of the sample. (C ) 1997 Elsevier Science B.V.