Mesoporous structure of hydrothermally solidified water purification sludge

Abstract

The recycling technology of water purification sludge using hydrothermal treatment was investigated. The sludge was mixed with 0-20mass% of Ca(OH)₂. The mixtures were formed by uniaxial pressing and hydrothermally treated under saturated steam pressure at 220^oC for 10 h. The flexural strength of the specimens increased with amount of added Ca(OH)₂ to 5mass% and reached the maximum value of 13.0MPa. The nanostructures formed through the hydrothermal treatment influenced on the strength development. TEM-EDX results showed the nanostructures consisted of mainly SiO₂ and Al₂O₃ with Ca/(Al+Si)=0.02 and Al/(Al+Si)=0.57. Nitrogen gas adsorption porosimetry showed the specimen had 4-7 nm mesopores. The high specific surface area of 157m²/g suggests an application as a self-humidity conditioning material.