Comparative Kinetic Study of Removal of Pb2+ Ions and Cr3+ Ions from Waste Water using Carbon Nanotubes Produced using Microwave Heating

A comparative study of the removal of Pb2+ ions and Cr3+ ions was conducted to determine the efficiency of carbon nanotubes (CNTs) produced using microwave heating as an adsorbent in removing heavy metal ions from waste water. Optimization of parameters such as adsorbent dosage, pH value, agitation speed, and agitation time was done using the Design Expert software version 6.0. The statistical analysis revealed that optimized conditions for the highest removal for Pb2+ are at pH 4.0, CNTs dosage of 0.09 g, agitation time and speed of 50 min and 150 rpm respectively. Meanwhile, the highest removal Cr3+ ions was observed at pH 8.0, CNTs dosage of 0.09 g, agitation time and speed of 60 min and 150 rpm respectively. For the initial concentration of 2 mg/L, the removal efficiency of Pb2+ ions and Cr3+ ions were 99.9% and 95.5% respectively. The maximum adsorption capacities of both Pb2+ ions and Cr3+ ions onto the CNT were 15.34 mg/g for Pb2+ ions and 24.45 mg/g for Cr3+ ions. Besides that, the Langmuir and Freundlich constants for the removal of Pb2+ ions were 0.073 and 1.438 L/mg while 0.071 and 1.317 L/mg for Cr3+ ions. The statistical analysis proved that the removal of Pb2+ ions and Cr3+ ions fits the Langmuir and Freundlich isotherm models, and both models obeyed the pseudo-second-order.