Silicate bonded unsintered ceramics of Bayer process waste

Abstract

Sodium silicates are investigated to enhance the strengths of Bayer process muds and develop structural ceramics without sintering. With an impregnation of sodium silicate from 2% to 10% concentration in red mud, the fracture toughness is enhanced from 0.2 to 0.9 MPa. Compression strengths of 25.1 MPa (3628 psi) have been attained with red mud at 10% silicate concentration. Similar enhancements by a factor of 4 to 5 have been obtained for modulus of rupture and Brinell hardness number. It is shown that these properties do not deteriorate in acidic and neutral environment in water, implying stability to weathering conditions. SEM investigations reveal elongated crystal formation, possibly of aluminum and iron silicates in the aggregate. These crystals act like whiskers enhancing the strength. The process is applicable for development of low-cost construction components.