Adsorption of Divalent Heavy Metal Ions from Aqueous Solution by Citric Acid Modified Pine Sawdust

Removal of certain divalent heavy metal ions (Cu2+, Pb2+, and Cd2+) from aqueous solutions by citric acid modified pine sawdust (CA-PS) was investigated in this study. The contribution of the citric acid modification to the increase of adsorption capacity of metal ions is significant. In the mono-component system of Cu2+, the maximum adsorption capacity of CA-PS (0.253 mmol/g or 16.19 mg/g) is more than three times higher than that of B-PS (0.079 mmol/g or 5.06 mg/g). The adsorption kinetics and isotherm of the pretreated pine sawdust (B-PS) and CA-PS can be well elucidated with the pseudo-second order model and the Langmuir model, respectively. The competitive adsorption behavior of Cu2+, Cd2+, and Pb2+ in the binary systems (Cu2++Pb2+, Cu2++Cd2+, and Pb2++Cd2+) were studied, and the preference of adsorption onto CA-PS can be ordered as Pb2+ > Cu2+ > Cd2+. The results showed the possibility of utilizing natural bio-sorbent as cost-effective adsorbent alternative for heavy metal ions removal.