Cements obtained from rice hull: encapsulation of heavy metals.

Rice hull is an agricultural residue containing organic materials (carbohydrates, cellulose, etc.) and about 10% of silica, as inorganic component. Usually rice hull is burned at the fields generating small silica particles that may cause respiratory and environmental damage. On the other hand, beta-Ca2SiO4 is the second most important component of commercial portland cement. The utilization of beta-Ca2SiO4 brings many environmental benefits, such as reduction of carbon dioxide emissions and the saving of raw materials and energy. This work describes the synthesis of beta-Ca2SiO4 and related cements prepared from rice hull and the insertion of heavy metals (copper and cadmium). The insertion of these metals, chemically bounded to dicalcium silicate may represent a useful method to permanent encapsulation of hazardous chemicals. Silica was obtained from burning rice hull at 600 degrees C. The synthesis was carried out by a combination of sonochemical and solid-state chemical reactions and is completed at 800 degrees C. It was found that copper and cadmium can be inserted into beta-Ca2SiO4 structure in proportions up to 10%.