Eco-utilization of steel slag: Preparation of Fe-based calcium silicate hydrate and its application in As(V) removal

Arsenic (As), a carcinogenic heavy metal, is a toxic environmental pollutant that threatens human and environmental health. Here, a cost-effective and high-performance Fe-based calcium silicate hydrate (Fe-CSH) was synthesized through a one-step alkaline activation process using steel slag as an in situ Ca and Fe source to treat As(V)-containing solutions. The synthesized Fe-CSH exhibited a flower-like structure with numerous interleaving nanosheets, which provided abundant adsorption sites. More importantly, this compound could remove large quantities of As(V) from wastewater, achieving maximum adsorption capacities of up to 141.5 mg/g at a pH of 5. The adsorption kinetics were consistent with a Langmuir isotherm model and followed pseudo-second-order and intra-particle diffusion kinetics. Thermodynamics analyses indicated that the adsorption process was spontaneous and feasible. XRD, FTIR, SEM, TEM, and XPS analyses indicated that the outstanding adsorption performance of the Fe-CSH could be due to the release of Ca 2+ and OH – from this material. The released Ca 2+ reacted with arsenate ions via coprecipitation, whereas OH – promoted the generation of Fe hydroxide from iron ions, which adsorb As(V) by forming stable bidentate surface complexes. Ultimately, a potential process was proposed for the remediation of As-containing wastewater using hierarchically structured Fe-CSH derived from steel slag. The “trash-to-treasure” strategy implemented for the repurposing of steel slag and the remediation of As-contaminated wastewater are both conducive to sustainable development.