Removal of Ni2+ and Cu2+ ions from aqueous solution on to lignite-based carbons

Non-activated lignites were prepared by the carbonization of Egyptian ligni te in a limited quantity of air at 500 degreesC, 700 degreesC and 900 degre esC, respectively. Zinc chloride-activated carbons were also prepared by th e carbonization of lignite with 20 wt%, 40 wt% and 60 wt% zinc chloride in a limited quantity of air at 600 degreesC. The surface areas of the resulti ng samples were determined from nitrogen adsorption studies at 77 K and fro m carbon dioxide adsorption studies at 298 K. The functional acidic groups on the surface were determined by neutralization with aqueous solutions of NaHCO3, Na2CO3 and NaOH, respectively. The sorption of Ni2+ and Cu2+ ions o n the prepared carbons as well as on the as-received lignite (L) were inves tigated. The influence of the time of contact, the initial ion concentratio n and the temperature was studied and the kinetics of the process were inve stigated. Equilibrium sorption isotherms were determined and the results in terpreted by applying the Freundlich and Langmuir equations. The surface area was found to generally increase with increasing carbonizat ion temperature. For activated carbons, the surface area increased with an increase in the amount of zinc chloride used in the activation process. The chemisorption of Ni2+ and Cu2+ ions on lignite-based carbon was found to b e a pseudo-second order process. The acid sites on the surface provide acti ve sites for the chemisorption of Ni2+ and Cu2+ ions and a qualitative rela tionship was found to exist between the maximum sorption capacity of these metal ions and the total surface acidity.