Abstract:
Modification of coconut (Cocos nucicera L.) shell activated carbon with an Azo ligand: 1, 2– dihydro-1,5-dimethyl-2-phenyl-4-(E)–(2,3,4-trihydrophenyl)-3H-pyrazol-3-one (DDPTP) and its potentials for the removal of Cd2+, Pb2+ and Ni2+ from polluted water samples were studied. It was activated chemically using CaCO3 as the activating agent. Proximate analysis on the coconut shell showed 8.7 % moisture content, 10.4 % volatile matter, 3.2 % ash content and 77.7 % fixed carbon. The developed adsorbent has bulk density of 0.46 g/cm3, pore volume of 8.0 x 10-3 cm3 and the conductivity was 37.9 µS/cm. Fourier Transform Infrared (FTIR) analysis showed that hydroxyl, carbonyl, amino and azo groups are present on the surface of the adsorbent. Scanning Electron Microscope (SEM) showed the micro-pores in the Modified Coconut Shell Activated Carbon (MCSAC) while Energy Dispersive X-ray Spectrum exposed carbon as the major quantitative element with 57 %. Batch adsorption was carried out and the results obtained showed that, MCSAC adsorbed Pb2+ (98 %), Cd2+ (80 %) and Ni2+ (92.2 %) ions more than un-modified coconut shell activated carbon which adsorbed Pb2+ (79 %), Cd2+ (60.2 %) and Ni2+ (73.6 %) ions from aqueous solutions. The quantity of the metal ions adsorbed increased with increase in initial concentrations, contact time, temperature of carbonization, the degree of treatment of adsorbent and pH for each metal. The percentage removal decreased with increase in particle sizes of the adsorbent. It also increased initially with increase in ligand amount but later decreased. Competitive adsorption of Pb2+, Cd2+ and Ni2+ on MCSAC from their mixed solution showed that the percentage removal of Ni2+ was highest with 80.35 % followed by Pb2+, 71.05 % and Cd2+, 45.10 %. The analysis of adsorption isotherm showed that, adsorption of Ni2+ followed Langmuir isotherm than Cd2+ and Pb2+; Ni2+ and Cd2+ followed Freunlich isotherm than Pb2+; Ni2+ and Pb2+ followed Temkin isotherm than Cd2+. Kinetic studies showed that the sorption of the metal ions can also be described by pseudo-first-order (Pb2+ and Ni2+), pseudo-second-order (Cd2+ and Ni2+) and intra-particle diffusion models for the three metals.
