Removal of Heavy Metals from Polluted Solutions by Zeolitic Adsorbents: a Review

The usage of zeolites in wastewater treatment has been extended in the two recent decades. This review investigates recent developments on the zeolite usage in the removal of heavy metals from polluted solutions. Various databases were used to search, evaluate, combine and analyze. The number of specific publications based on keywords linked with zeolite usage used in searching engines was more than 1000. However, about 200 publications passed the criteria set. The synthesis methodology for the production of zeolitic adsorbents, the modification of natural zeolites and their effect on the removal of heavy metals are described. Furthermore, the capacity of adsorbents to remediate polluted solutions and identify optimum conditions are reported and compared. The maximum adsorption capacity among heavy metals was for Pb(II) for all types of zeolite adsorbents (27.70 mg/g for chloride-modified zeolite, 113 mg/g for Fe-modified zeolite, 653 mg/g for surfactant modified zeolite, 808 mg/g for synthesized zeolites and 909.09 mg/g for nanozeolite). Cr(IV), Cu(II), Ni(II), Zn(II) and Co(II) were other heavy metals having good adsorption capacities on synthesized zeolites. According to the literature review, the adsorption of heavy metals by synthesized and nanozeolites is the most efficient.