Effects of Elmtree sawdust pretreatments using alkali and alkaline earthmetals (NaCl, KCl, CaCl2, MgCl2 and Elm tree ash) and deashing solutions (water, HCl, HNO3 and aqua regia) before the carbonization process on the porosity of produced activated carbons and Pb (II) and Cr (VI) adsorption were studied. The activated carbonswere characterized by pore size distribution, surface area, FTIR, and SEM-EDX analysies. Based on the results, HCl leaching pretreatment of the biomass increased the activated carbon adsorption capacity of Cr (VI) from 114 to 190mg g−1. The treatment of biomass with alkali and alkali earth metal salts, especiallyMgCl2, remarkably increased the activated carbon adsorption capacity of Pb (II) from233 to 1430 mgg−1. The results indicated that Pb (II) adsorptionwas attributed to both the mesoporous structure of activated carbon and the abundance ofMg on the activated carbon\\\\\\\\\\\\\\\'s surface. On the other hand, the micropores played amajor role in Cr (VI) adsorption capacity. The development of themicro- ormesoporous structure of activated carbons through pretreatment of lignocellulosic precursor could be an approach for providing high performance activated carbons for Pb (II) and Cr (VI) removal from aqueous solutions.

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