Interaction of heavy metals with dehydrated carbon

Abstract

Dehydrated carbon material was prepared from date palm leaflets via sulphuric acid treatment. The acid causes dehydration via the removal of water. In addition it causes oxidation to the dehydrated carbon surface. The carbon was tested for the removal of Pb2+, Zn2+, Cu2+, Co2+, Ag+, Pd2+ and Hg2+ from aqueous solution in terms of different pH, time and concentrations and temperature. Optimum pH was found to be in the range of 3-5 for the metals under investigation. Sorption of Pb2+, Zn2+, Cu2+, Co2+ was found fast, reaching equilibrium within ∼ 2 hr while the sorption of Ag+, Pd2+ and Hg2+ (nitrate and chloride media) was slow and required ∼80 hr to reach equilibrium. Activation energy, Ea, for the sorption of Pb2+, Zn2+, Cu2+, Co2+ was 40 kJ/mol indicating a chemically controlled process. Equilibrium sorption capacity was much higher for Ag+, Pd2+ and Hg2+ than for Pb2+, Zn2+, Cu2+, Co2+ with increased uptake, for both metals, by rising the temperature (25-45 °C). Scanning electron microscopy, X-ray diffraction and energy dispersive spectroscopy showed that Ag+ and Pd2+ were reduced to their respective elemental states. For Hg2+, reduction took place to elemental mercury from nitrate media and to Hg2Cl2 from the chloride media. However, no reduction processes were involved in the sorption of Pb2+, Zn2+, Cu2+, Co2+.

Keywords

• heavy metals
• sorption
• reduction
• dehydrated carbon