بررسي كارايي ضايعات كشاورزي در مقايسه با خاك در جذب برخي فلزهاي سنگين

Agricultural Residues in Comparison with Soil as Heavy Metal Sorbents

In present paper two agricultural residues, rice hull,sawdust and a soil sample were examined as sorbents to remove heavy metals Pb(II), Cd(II), Cu(II), Zn(II) and Ni(II) from synthetic solutions. The sorbents were analyzed for some physico-chemical characteristics as CEC, surface area and elemental composition using ammonium acetate method, N2-BET and SEM-EDX respectively. The effect of initial pH and concentration of solutions, type of sorbents, equilibrium time and particle size of sorbents were studied in removal of heavy metals from metal solutions. The sorption experiments were carried out in 1:100 suspensions of sorbent to synthetic solutions. The sorption of the heavy metals from the synthetic solutions was increased with pH for all sorbents, significantly (p< 0.01). pH=5 was selected as the lowest pH with highest mean sorption. At this pH, among the heavy metals, Pb(II) and Cd(II) showed the highest sorption with the average of 0.87 and 0.77 mg/g and then Cu, Zn and Ni, respectively. The increase of metal concentration in the solution increased the sorption. The sorption isotherms of the natural sorbents and the soil sample were best described by the Freundlich model. The highest sorption capacity was observed for the soil sample, followed by the rice hull and the sawdust samples, respectively. The sorption of the heavy metals from the synthetic solutions was increased with increasing of shaking time. Shaking time of 60 minutes was considered as equilibrium time. Decreasing of sorbent particle size increased the sorption. The smallest diameter of particles (<0.5 mm) showed the highest sorption capacity.