Valorization of thermally hydrolyzed sludge with clay for sintering of ceramic tiles

Lei Wen; Lin Lin; Yi-Ang Fan; Yang Luo; Sheng-Shou Ma; Ying Zhou; Chao Yang; Kaimin Shih; Xiao-Yan Li

doi:10.1016/j.scitotenv.2023.162871

Valorization of thermally hydrolyzed sludge with clay for sintering of ceramic tiles

Sci Total Environ. 2023 Jun 15:877:162871. doi: 10.1016/j.scitotenv.2023.162871. Epub 2023 Mar 16.

Authors

Lei Wen¹, Lin Lin², Yi-Ang Fan¹, Yang Luo³, Sheng-Shou Ma¹, Ying Zhou¹, Chao Yang¹, Kaimin Shih¹, Xiao-Yan Li⁴

Affiliations

¹ Department of Civil Engineering, The University of Hong Kong, Pokfulam, Hong Kong.
² Institute of Environment and Ecology, Tsinghua Shenzhen International Graduate School, Tsinghua University, Shenzhen 518055, China. Electronic address: linlin00@sz.tsinghua.edu.cn.
³ Department of Materials, ETH Zürich, Vladimir-Prelog-Weg 5, Zurich 8093, Switzerland.
⁴ Department of Civil Engineering, The University of Hong Kong, Pokfulam, Hong Kong; Institute of Environment and Ecology, Tsinghua Shenzhen International Graduate School, Tsinghua University, Shenzhen 518055, China. Electronic address: xlia@hku.hk.

PMID: 36933740
DOI: 10.1016/j.scitotenv.2023.162871

Abstract

The disposal of wastewater sludge is one of the most challenging environmental problems for large cities. Wastewater sludge may be utilized as a feasible substitute for clay to sinter ceramics, given their similar mineralogical composition. However, the organics in sludge will be wasted, while their release during sintering will leave cracks in the ceramic products. In this research, after the thermal treatment for effective organic recovery, the thermally hydrolyzed sludge (THS) is incorporated with clay for the sintering of construction ceramics. The experimental results showed that a THS dosing ratio up to 40 % can be achieved for mixing with montmorillonite clay to make ceramic tiles. The sintered tiles (THS-40) had an intact shape and structure, and the tile performance was close to that made from single montmorillonite (THS-0), with water absorption of 0.4 % vs. 0.2 %, compressive strength of 136.8 vs. 140.7 MPa, and undetected heavy metal leaching. Further addition of THS would lead to a considerable deterioration of the quality of the tiles to a compressive strength of as low as 5.0 MPa for the THS only product (THS-100). Comparing with the tiles incorporated with raw sludge (RS-40), the THS-40 tiles had a more intact and denser structure with a 10 % improved compressive strength. Cristobalite, aluminum phosphate, mullite, and hematite dominated in the THS-born ceramics, which are typical components of ceramics, and the amount of hematite increased with the THS dosing ratio. Sintering at a high temperature of 1200 °C enabled efficient phase transformation from quartz to cristobalite and from muscovite to mullite, which ensured the toughness and compactness of the THS-born ceramic tiles.

Keywords: Ceramic; Heavy metals; Montmorillonite; Phase transformation; Sludge disposal; Thermally hydrolyzed sludge.