Interaction of heavy metals with dehydrated carbon

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, E_a, for the sorption of Pb²⁺, Zn²⁺, Cu²⁺, Co²⁺ was < 17 kJ/mol indicating a diffusion controlled ion exchange process, however, for Ag⁺, Pd²⁺ and Hg²⁺ sorption, E_a 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⁺.