Modification of rice hull and sawdust sorptive characteristics for remove heavy metals from synthetic solutions and wastewater

In this work two modified agricultural residues, rice hull and sawdust were examined as sorbents to remove heavy metals Pb(II), Cd(II), Zn(II), Cu(II) and Ni(II) from synthetic solutions or wastewater samples. To modify their sorptive characteristics, samples were treated with HCl, NaOH and heat. The sorption of the heavy metals from the synthetic solutions was increased with pH and initial concentration. In pH 5, Pb(II) and Cd(II) showed the highest sorption and Cu(II), Zn(II) and Ni(II) showed the following orders, respectively. Sorption capacity of rice hull was higher than sawdust. The modifications changed the sorption capacity of the natural sorbents in the following order base > heat > natural > acid. The sorption isotherms of sorbents were best described by the Freundlich and Langmuir models. The basic treated rice hull and sawdust followed by the heat treated rice hull sorbed the maximum of heavy metals from the industrial wastewater samples. In the column experiment, the synthetic solutions and the wastewater samples gave almost the same results as the suspensions. The recovery of the columns using water and HCl showed positive results. Commercial sorbents removed Pb(II), Zn(II) and Ni(II) a little more than rice hull.