Synthesis and characterization of new zeolite materials obtained from fly ash for heavy metals removal in advanced wastewater treatment

• A novel substrates are obtained from fly ash by hydrothermal synthesis at low cost.
• The zeolite type has specific surface ten times higher than raw fly ash.
• Kinetic investigations show fast adsorption of the heavy metals on the new zeolites.
• Removal of heavy metals from wastewater has to be correlated with hydrolysis constant.
• Adsorption of HM follows the pseudo-second order equation, indicating chemisorptions.

Waste management and water quality are two of the main problems that humanity faces nowadays. Increased urbanization and industrialization lead to excessive release of wastes into the environment, including fly ash resulted from coal combustion. Fly ash reuse in developing low cost, efficient adsorbents of zeolite-type could support wastewater treatment according to the concept wastes for waste treatment. The ashes converted in zeolite materials were collected from two Combined Heat and Power Plants (CET Brasov and DEVA) from Romania. The zeolite materials were characterized by AFM, XRD, FT-IR, SEM, BET and surface energy measurements to outline the crystalline and morphology modifications. The zeolite-type substrates were obtained by using the fly ashes modified through hydrothermal processes using a low concentration of NaOH, and were further used for heavy metals removal (Cd2 +, Ni2 +, Cu2 +, Zn2 +, Pb2 +) from synthetic solutions with mono-, bi-, and five-cations. In order to obtain maximum efficiency during the heavy metals removal of the adsorption conditions (contact time, optimum amount of substrate and initial concentration) were optimized. These parameters were further used in the thermodynamic and kinetic modelling of the adsorption processes. Correlated with the surface structure, composition and morphology, the kinetic adsorption mechanisms and the substrate capacities are further discussed.

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