Clinoptilolite based zeolite-geopolymer hybrid foams: Potential application as low-cost sorbents for heavy metals

Clinoptilolite based zeolite-geopolymer foams (abbreviated as CFs) were prepared from natural clinoptilolite and calcined clinoptilolite, using H2O2 solution as pore former through a straightforward process. Natural clinoptilolite and CFs are characterized by analytical techniques including optical microscope, XRF, FTIR, XRD, BET, MIP and SEM. The obtained CFs possesses micropores of zeolite and meso/macropores of geopolymer matrix. The porosities range from 66.7 to 69.5%. Clinoptilolite (partially dissolved) and impurity minerals (montmorillonite, illite and albite) contribute to the formation of geopolymer. CFs shows a good static sorption performance for toxic heavy metals at pH = 5 and sorption time of 24 h. Results show that the adsorption amount of CFs for Cr3+, Pb2+, Ni2+, Cu2+ and Cd2+ in the 50 mg/L working solutions are 6.21 mg/g, 6.11–6.13 mg/g, 5.92–6.07 mg/g, 5.53–5.93 mg/g and 5.44–5.79 mg/g, respectively. In addition, CFs could reach a high removal rate (Cr removal rate >80% and Cd > 60%) for different heavy metals after three cycles. The elimination order of toxic metals is Cr3+ > Pb2+ > Ni2+ > Cu2+ > Cd2+. The sequence is in accordance with Hard-Soft-Acid-Base principle, it is also related to the speciation and the ionic radii of the hydrated metal ions. This research provides a feasible approach for preparation of promising foams sorbent based on natural zeolite for wastewater management. [Display omitted] •Clinoptilolite based zeolite-geopolymer foams (CFs) were successfully fabricated.•CFs possess micropores of zeolite and meso/macropores of geopolymer matrix.•Clinoptilolite and impurity minerals contribute to the formation of geopolymer.•CFs shows high potential adsorption properties for the five studied metal ions.•Sorption selectivity is related to speciation and ionic radii of hydrated metals.