Removal of Cu(II) and Ni(II) from aqueous solution by lignite-based humic acids

The removals of Cu(II) and Ni(II) metal ions from an aqueous solution were investigated by using humic acids (HAs) in a batch arrangement. HAs were prepared by using alkaline extraction, following sedimentation and acidic precipitation from three Turkish lignites: Ilgin, Beysehir, and Ermenek. The interactions of Cu(II) and Ni(II) with solid HAs and influence of three parameters (initial metal concentration, solution pH and temperature) on the removal of metals were studied. Adsorption equilibrium was achieved in about 120 min for Cu(II) and Ni(II) ions. The sorption of Cu(II) and Ni(II) on the surface of HAs depended strongly on the pH, and increased with increasing of pH and the initial concentration of metal. The sorption of Cu(II) was higher than that of Ni(II) for HAs. The equilibrium relationship between adsorbent and adsorbate is described by adsorption isotherms at a fixed temperature 35C, at pH 4.0. The Langmuir adsorption isotherm was used to describe observed sorption phenomena. It was observed that the maximum adsorption capacity of Cu(II)/g was 0.27 mmol for Ilgin (HA1) and Beysehir (HA2), 0.19 mmol for Ermenek (HA3) and that of Ni(II)/g was 0.28 mmol for HA1, 0.24 mmol for HA2, 0.18 mmol for HA3 at pH 4.1, respectively. More than 80% of Cu(II) was removed by HA1 and HA2 and 58% by HA3, 82% of Ni(II) was removed by HA1, 71% by HA2 and 52% by HA3 from aqueous solution. The adsorption of Cu(II) and Ni(II) was higher between pH 4.1 and 5.1 for all HAs, and maximum sorption was observed at pH 4.1. The increase in temperature caused a slight decrease in the value of the equilibrium constant (Kc) for the sorption of metal ions. Adsorption isotherms and kinetics data of Cu(II) and Ni(II) ions removed by HAs are presented and discussed.