Abstract
Madagascar is ranked among the largest consumers of rice in the world. The annual per capita consumption of rice in rural Malagasy is 138 kg, and in urban areas 118 kg. Urban households eat 85% of their meals with rice. Rice cultivation is practiced throughout the island. The overall annual rice production is estimated at 4 680 630 t in 2020. For each tonne of paddy milled, 200 kg of rice bales (outer husk of rice) are obtained from husking, which have an energy content equivalent to 60 L of fuel oil. The rice husk contains a non-negligible amount of silica varying between 26% and 88% depending on the extraction methods. Two methods of silica extraction are used: the thermal method and the soft method. The silica content extracted from the rice husk is different in both methods. The extraction was carried out in three varieties of Malagasy rice: Makalioka, Tsemaka and Dista. The percentage of silica obtained varies from 82% to 85%. It was compared to that synthesised by the sol–gel process using the X-ray fluorescence technique and spectrophotometer infrared analysis. This study is of economic and environmental interest: recovery of agricultural waste, reduction of pollution and the circular economy in Madagascar. The extraction of nanometric silicon dioxide, commonly known as silica (SiO₂), from rice bales allows for the transformation of abundant agricultural waste into a material of high added value.