Eco-friendly recycling of silicon-rich lye: Synthesis of hierarchically structured calcium silicate hydrate and its application for phosphorus removal.

Silicon-rich lye (SRL), a byproduct generated from pre-treatment of coal-based solid waste (CSW), was considered as a preponderant silicon source to prepare hierarchically nanostructured calcium silicate hydrate (C-S-H). Through the novel mild-causticization synthesis strategy, C-S-H was prepared under optimal caustic process conditions at time of 3 h, temperature of 80 °C, Ca/Si of 1.25:1, and active CaO to obtain a conversion rate of Si up to 97.33 % during the high-value utilization of SRL. The synthesized C-S-H possesses abundant mesoporous structure and massive exchangeable active sites, whose formation is advanced through an appropriate elevation regulation of caustic temperature and time. The silicate chain depolymerization occurs to C-S-H prepared in the highly alkaline system at higher caustic temperature, longer caustic period, especially at existence of massive sodium ions, but it presents higher polymerization degree at more aluminum co-existing. The adsorption capacity up to 119.27 mg/g for C-S-H presents a valid removal performance toward phosphorus in the wastewater than massive present reports. The removal mechanism of phosphorus can be identified as the surface chemisorption and formation of calcium phosphate co-precipitation. This study can provide considerable and potential guidance to the coordinated disposal between industrial solid wastes and wastewater purification.