Evaluation of carbon nanotubes performance in the lead and cadmium adsorption from refinery wastewater: Process modeling by RSM

Supply of safe drinking water is crucial to human life, and safe drinking water should not impose a significant risk to humans. Although few heavy metals are essential for human health, an excess amount of these metals can have negative effects. The heavy metals are released into the environment through natural process and anthropogenic activities. The industrial processes generate wastes, which are mostly discharged into the environment. Lead (Pb) and cadmium (Cd) are among the heavy metals in surface waters, which may lead to adverse effects such as bone and lungs cancer, chronic headaches, dizziness, chest pain, body weakness etc. Hence, it is necessary to remove such heavy metals from drinking water sources. The aim of present study was to determine the efficiency of multi-walled carbon nanotubes to remove lead and cadmium from refinery wastewater. Batch adsorption experiments were carried out by varying main operational parameters such as pH, initial concentrations of Pb and Cd, carbon nanotubes dosages, and contact time. Experimental design was applied to reduce the number of experiments, save time and cost, determine the main effects of independent variables on response, and determine optimum conditions. Experiments were designed by central composite design (CCD) based on response surface methodology (RSM) using Design Expert, version ۱۱ software. Based on the results pH, initial concentrations of heavy metals, and adsorbent (carbon nanotubes) dosage had main role in adsorption process. The findings demonstrated that the highest adsorption of Pd and Cd from aqueous solution was achieved under optimal conditions (Pb/Cd initial concentration: ۵۰ mg L-۱, pH: ۵,adsorbent dosage: ۰.۲۵ g L-۱, and contact time: ۷۵ min).