Thermodynamics and Kinetics of Pb(II) and Hg(II) Ions Removal from Aqueous Solution by Romanian Clays

Heavy metals cations are released to the environment by natural phenomena and human activities, such as agricultural practices, transport, industrial activities and waste disposal. Because of their high negative impact as environmental contaminants, in this study the removal of Pb(II) and Hg(II) from wastewaters was studied. Clays from Valea Chioarului and Razoare areas - Romania as well as Na-clays were investigated as sorbents. The effect of initial concentration of metal ions - Pb(II) and H(II), temperature and time on removal efficiency was studied. The equilibrium data were fitted with two standard isotherms, the Langmuir and Freundlich models. The Langmuir model was more suitable for these systems. The highest ion exchange capacity based on Langmuir constants was displayed by the Na-exchanged clay: 0.696 mmoles/g for lead and 0.71 mmoles/g for mercury. These amounts of lead and mercury immobilized on solids are high enough to foresee their convenient possibility of separation from wastewaters. A future study concerning the toxic ions form real wastewaters will be necessary in this respect. The kinetic studies showed that the sorption rates could be described by a second-order Lagergren equation.