Eco-utilization of silicon-rich lye: Synthesis of amorphous calcium silicate hydrate and its application for recovering heavy metals

During sustainable high-value utilization of coal-based solid wastes, a kind of characteristic silicon-rich lye (SRL) generated, and its comprehensive recovery and recycling remains an important subject. Through a simple and facile strategy of mild caustic-crystallization method, SRL was favorably utilized through calcium silicate hydrate (C-S-H) synthesis with silicon conversion efficiency over 97.33%. The micro-morphology of C-S-H presented a typical "honeybee hive " like porous structure with numerous exchangeable activity cations and combination sites in the silicate chain structure. The amorphous C-S-H products possessed marvelous recovery abilities for typical heavy metals as Cu (II), Zn (II), and Cr (III) in industrial wastewater with recovery efficiency all above 99.6% in quite a short period. The recovery mechanism of C-S-H toward heavy metals was revealed as calcium ions exchange and interlayer structure combination with SiO4 and AlO4 tetrahedron through the analysis of characterization technologies and DFT simulation calculation. C-S-H synthesized in SRL contributes to achieving valuable resources conversion and recycling for guiding sustainable development of coal-based solid waste comprehensive utilization.