Preparation of pervious concrete with 3-thiocyanatopropyltriethoxysilane modified fly ash and its use in Cd (II) sequestration

Heavy metal contamination is an important environmental issue. Heavy metal removal by cementitious materials would be an efficient method because of their large-scale exposure to rainwater and groundwater. In this study, 3-thiocyanatopropyltriethoxysilane (TCPS)-modified Fly ash (T-FA) beads were prepared and incorporated into pervious concrete. The functionalized pervious concrete was used to sequester Cd (II) from solution, utilizing the chelating property of the thiocyanate on TCPS. TCPS molecules were chemically bonded onto FA beads after alkali activation, which was confirmed by IR spectroscopy. IR shows the vibration of Si OH and the asymmetric vibrations of CH2 and CN on TCPS. In addition, 29Si NMR spectroscopy identifies a new peak at −47.22 ppm assigned to T2[RSi(OSi)2OH]. T-FA beads can efficiently remove Cd (II) when immersed and stirred in a CdCl2 solution. An equally significant sequestration capacity was demonstrated when T-FA beads were incorporated in pervious concrete. Cd (II) concentrations were reduced from 300 to 15.86 ppm when a 100 × 100 × 100 mm3 T-FA-loaded concrete specimen was exposed to a 5 L CdCl2 solution.