Hot water treatment effect in the elephant grass ashes calcinated at different temperatures

Résumé

In recent years, agro-industrial residues have focused attention in the scientific community as a new source of
pozzolans. In Brazil, for example, one of the wastes generated from agro-industrial activities comes from
elephant grass that is cultivated as biomass for energy cogeneration. This study evaluated the effect of hot
water treatment on the crystalline structure of elephant grass ashes calcinated in two different temperature
(700 and 900°C). To study the chemical structure and the composition of the ashes the X-ray fluorescence
(XRF) and X-ray diffractions (XRD) analyses were carried out. The results achieved in the present work
shown that, elephant grass ashes meet the ASTM C-618 standard, for the minimum sum content of the silica
(SiO2), aluminum (Al2O3) and iron (Fe2O3) oxides, of 50% to be considered as a pozzolanic material. The
presence of an amorphous phase has been detected in all XRD patterns. The ashes calcinated at 700°C
showed lower crystallinity and the treatment with hot water decreased crystallite size, i.e., the material became
more amorphous. On the other hand, the ashes calcinated at 900°C, less reactive, had a lower content of
K2O. Therefore, the hot water treatment was effective to reduce the potassium content in the ashes. Additionally,
it contributed to reduce the crystallite size of silica in the ash calcinated at 700°C, while the effect is
contrary to the ash calcinated at 900°C.
Keywords: Mineral addition, biomass, amorphous formation, potassium leaching, crystallite size.