Removal of lead, copper, nickel, cobalt, and zinc from water by a cancrinite-type zeolite synthesized from fly ash

As a low Si/Al ratio zeolite, cancrinite received very scant study in previous studies on the adsorption removal of heavy metals from water. In this study, a cancrinite-type zeolite (ZFA) was synthesized from Class C fly ash via the molten-salt method. Adsorption equilibriums of Pb2+, Cu2+, Ni2+, Co2+, and Zn2+ on ZFA were studied in aqueous solutions and were well represented by Langmuir isotherms. The increase of pH levels during the adsorption process suggests that the uptake of heavy metals on ZFA was subjected to an ion exchange mechanism. It is found that the maximum exchange level (MEL) follows the order: Pb2+ (2.530 mmol g−1) > Cu2+ (2.081 mmol g−1) > Zn2+ (1.532 mmol g−1) > Co2+ (1.242 mmol g−1) > Zn2+ (1.154 mmol g−1). Comparison with previous studies shows that the MEL of ZFA is higher than the commonly used natural zeolites; and it is also comparable to (or higher than) several synthetic zeolites and ion exchange resins. The high MEL of heavy metals on ZFA is attributed to the high cation exchange capacity (CEC) and proper pore size of cancrinite. The pseudo-first-order kinetics suggests that the ion exchange processes were diffusion-controlled.