Preparation and evaluation of a mesoporous calcium-silicate material (MCSM) from coal fly ash for removal of Co(II) from wastewater

• A mesoporous calcium-silicate material (MCSM) was prepared from coal fly ash.
• The sorption capacity of MCSM for Co(II) was maintained at a high level at pH 2–7.
• A single-chain calcium-silicate-hydrate(I) is the effective component for sorption.
• 76.7% of Co(II) was adsorbed by ion exchange and the rest via surface complexation.
• MCSM is a promising sorbent for efficient removal of toxic metals from wastewater.

The widespread industrial use of cobalt and its salts has raised concerns associated with its efficient removal from wastewater. In this study, a mesoporous calcium-silicate material (MCSM, 733 m2 g−1) was prepared from desilication liquor of coal fly ash and examined for use in adsorbing Co(II) from aqueous solutions. At 2 g L−1 dosage, 109.6–154.8 mg of Co(II) could be removed by 1 g of MCSM in the pH 2–7 within 4 h. The effective component for sorption was found to be a layered single-chain calcium-silicate-hydrate(I), and its negatively charged surface was helpful for Co(II) sorption (pHPZC = 1.6). Before precipitation, 76.7% of Co(II) was efficiently removed via ion exchange with Ca(II) in MCSM, while the rest of Co(II) was probably adsorbed by surface complexation. The sorption followed Langmuir one-site isotherms and the kinetics was controlled by surface and intra-particle diffusion processes. Unlike conventional sorbents or ion exchangers, increasing the MCSM dosage represents a viable and economic option for improving adverse effects from practical wastewater (strong acidity, high Co(II) concentration, and high salinity). More than 98.7% of the Co(II) and metal radionuclides could be removed from the wastewater samples using 15.4 g L−1 of MCSM. The results suggest that MCSM has the potential for use as an effective and low-cost sorbent for removing Co(II), as well as related hazardous metal ions from wastewater. After being used as an sorbent, MCSM is suitable for use as a substitute of cement and disposed by inexpensive solidification/stabilization technique.

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