Manganese removal from aqueous solution using a thermally decomposed leaf

As a significant agricultural and industrial raw material, Mn(II) has been intensively used and widely distributed in the environment. Recent studies indicate that Mn(II) could cause acute toxicity to aqueous livings and human beings. The treatment of Mn(II) contained wastewater is stringent for environmental preservations. This paper attempts to testify the performance of Mn(II) adsorption by a novel adsorbent, natural leaf that was partially decomposed at moderate temperature. The isothermal adsorption shows high prevalence for Mn(II) with adsorption capacity determined at 61-66 mg g−1. Various factors including adsorbent dosage, pH, temperature and equilibration time were investigated regarding the effects on Mn(II) adsorption. It was shown that a rapid equilibration within 30 min could be achieved at pH values as low as 4.0 while an endothermic and spontaneous process could be disclosed with enthalpy change ranged from 13 to 0.78 kJ mol−1 and the entropy change ranged from −35.79 to −11.58 kJ mol−1 from 5 to 55 °C, separately. Spectroscopy study revealed chemisorptions relevant to phosphate, ferrous oxide and carbonate groups, and a physisorption on carbon black, which were main components of the adsorbent. No obvious linkage was observed between Mn(II) adsorption and the amine group which is critical to heavy metal adsorption in previous studies. The proposed preparation method and the basic guidelines regarding the adsorbents' selection seem promising in the engineering practices.