Removing or decreasing Lead concentration of wastewater to the permitted levels before discharging to the environment is important because its bioaccumulation and non-biodegradation. Removal of metal ions from wastewaters has been performed by chemical precipitation, membrane filtration, ion exchange, reverse osmosis, evaporation, electrolysis and adsorption processes. The best treatment choice among these methods depends on heavy metal concentration in the wastewater and treatment costs. Adsorption is widely used for removal of heavy metals from wastewater because of its simplicity and low cost. Many natural and synthetic adsorbents are used for this method. Recently, natural adsorbents have gained importance, and the choice of these materials depends on their availability, cost and adsorption capacity. In this study, removal of Pb(II) from aqueous solutions by adsorption onto dolomite, travertine, blast furnace slag(BFS) and activated carbon(AC) was investigated as a function of initial metal concentration (in the range of 5-100mg/L), initial pH (in the range of 2-6.5), stirring speed (in the range of 50-200 rpm) and adsorbent dosage (in the range of 1-10g/L) in a batch system. The optimum conditions were found by Taguchi approach. The results show that the equilibrium time for dolomite and travertine is 4hr, in BFS is 2hr and for AC is 1hr. Also, sorption data of metals are described by Langmuir, Freundlich and BET models and the equilibrium process is described well by the Freundlich isotherm model. The maximum removal of lead obtained from batch studies was more than 99.8% for BFS (initial concentration: 25mg/L, initial pH: 6.5, stirring speed: 50rpm and adsorbent dosage: 7g/L), 99.9% for dolomite (initial concentration: 25mg/L, initial pH: 6.5, stirring speed: 100rpm and adsorbent dosage: 7g/L) and travertine (initial concentration: 50mg/L, initial pH: 6.5, stirring speed: 100rpm and adsorbent dosage: 4g/L) and ) and 99.7% for AC (initial concentration: 50mg/L, initial pH: 6.5, stirring speed: 100rpm and adsorbent dosage: 10g/L). All of experimental factors was statistically significant on Pb(II) removal for dolomite, travertine and AC, while stirring speed was not statistically significant for BFS. Overall, it can be concluded that the dolomite and travertine and BFS perform well for the removal of Pb(II) ions from wastewaters as a low cost adsorbent.
