Biogenic cements from rice hull ash doped with aluminum and iron

This work describes the use of rice hull as starting material for the synthesis of cements doped with iron and aluminum. Rice hull contains about 10–20% of silica along with organic material. In many countries rice hull represents an environmental problem since this material is merely burned at rice fields, rendering suspended silica particles in the air. Dicalcium silicate (β-Ca2SiO4) is the second most important component of Portland cement and presents many environmental advantages over commercial cement. It can be prepared at lower temperatures saving energy and raw-materials. In this work we describe the synthesis β-Ca2SiO4 using silica derived from rice hull ash. Silica was obtained from heating rice hull at 600 °C. Starting materials (silica, calcium oxide, barium chloride, iron or aluminum oxide) were weighed in stoichiometric proportions and aqueous dispersions having water:solid ratio of ≈20:1 were prepared and treated in an ultrasonic bath for 60 min. After this, an intermediate silicate and the excess of calcium hydroxide were obtained. Finally solids were dried, grounded and heated up to 800 °C. It was observed that β-Ca2SiO4 was obtained when dopant concentration was limited to 1%.