Preparation and bloating mechanism of porous ultra-lightweight ceramsite by dehydrated sewage sludge and Yellow River sediments

Abstract

To solve the disposal problems of solid wastes, dehydrated sewage sludge and Yellow River sediments were tested as components for production of ultra-lightweight ceramsite. The effects of Yellow River sediments addition on the characteristics of ceramsite were investigated. Ceramsite with different Yellow River sediments additions was characterized using thermal analysis, X-ray diffraction, morphological structures analyses, pore size distributions and porosity analyses. Chemical components, especially ratios of SiO₂ + Al₂O₃/Flux, were used to explain the glassy shell formation, physical properties and pores distribution of ultra-lightweight ceramsite; physical forces for instance expansion force and frictional resistance which combined with SiO₂ + Al₂O₃/Flux ratios were used to explain the bloating mechanism. Results showed that the maximum addition of Yellow River sediments for making ultra-lightweight ceramsite was 35%. Macropores (between 0.226 μm and 0.554 μm) of ultra-lightweight ceramsite were dominant in the pore structures of ultra-lightweight ceramsite and its porosity was up to 67.7%. Physical force of expansion force was constant with the variation of Yellow River sediments content and physical force of frictional resistance was decreased with the increase of Yellow River sediments addition. The relationship between expansion and frictional resistance could determine the expansion rate of ceramsite. Larger pores inside the ceramsite bodies could be obtained as Yellow River sediments additions ranged from 10% to 30%. Ceramsite with higher Yellow River sediments additions of 40% (SiO₂ + Al₂O₃/Flux ratios ⩽ 4.25) became denser and have lower porosity. Crystal components analysis proved that the sintering process made some components of raw materials transfer into other crystals having better thermostability.

Keywords

yellow river sediments / dehydrated sewage sludge / ultra-lightweight / ceramsite / bloating mechanism

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