Removal of heavy metals by adsorbent prepared from pyrolyzed coffee residues and clay

In this work, we investigated the preparation and utilization of coffee residues binding with clay as adsorbent (hereafter called CC-adsorbent) for removal of heavy metal ions in solution. Factors affecting the adsorption such as pyrolysis temperature, weight ratio of coffee-residue to clay and particle size were investigated in the present preliminary study on the adsorption of metal ions. The pyrolysis temperature of 500degreesC, weight ratio of coffee residue to clay of 80:20, and particle size diameter of 4 mm were found to be the suitable conditions in our work. At this condition, the adsorption capacities of the CC-adsorbent for Cd2+, Cu2+, Pb2+, Zn2+ and Ni2+ were determined by the Langmuir isotherm model. The adsorption increased in the order of Cd2+ > Cu2+ > Pb2+ > Zn2+ > Ni2+. The effects of solution pH (8-10) and temperature (30-80degreesC) on the adsorption of Cd2+ were investigated. The Cd2+ adsorption increased with increasing pH and temperature, and remained constant at high pH. The heat of adsorption (DeltaH=-1.11 kcal/g) implied that the adsorption was physical exothermic adsorption. Desorption was easily achieved by leaching with distilled water which gave the recovery yield 88-92%. The functional groups studied by FTIR indicated that hydroxyl, carboxyl and amine groups were the main functional groups. Electrical potential study showed that the CC-adsorbent exhibited negative charge that was favorable to attract metal ion. The surface and pore study implied that the high fraction mesopores in the granular CC-adsorbent contributed to the adsorption capacity. (C) 2003 Elsevier B.V. All rights reserved.