Enrichment and Removal of Heavy Metals Contained in PCB Boards by Multiwalled Carbon Nanotubes for WEEE Directive

摘要

PCB board is an important part of electronic and electrical equipment. In place of piling e-wastes, much of heavy metals in PCB boards percolate into soil, air, river etc. which is a great threaten to environment. In order to removal the hazardous materials for WEEE directive, in this paper, a study on enrichment of lead, cadmium ions by multiwalled carbon nanotubes (MWCNTs) as a solid-phase extraction adsorbent was employed. ICP-OES was used to determine the adsorbed concentrations. Some valuable guidelines can be drawn from the following discussions. MWCNTs has proven to be a promising materials for the removal of contaminants owing to its amazing effects of enrichment, the objective content was concentrated about 50-100 fold, and limit of detection (LOD) The ion exchange or hydrogen binding mechanism canvery well explain the heavy metals such as Pb, Cd adsorptiononto CNTs. Sorption can be modeled by Freundlich isothermsfrom which thermodynamic parameters such as free energychange (△G), enthalpy change (△H), and entropy change (△S)can be calculated. △G<0, △S>0 indicated the process to befeasible and spontaneous nature. △H>0 suggested that theprocess to be an endothermic nature.Enrichment can be influenced by factors as contact time,temperature, pH and initial concentration of adsorbate, etc.Sorption increased with increasing contact time, andtemperature, initial concentration of adsorbate. For each ofanalyte, there is a neutral pH beyond which MWCNTs will beeither positively or negatively charged. Desorption studieshave shown the applicability to regenerate the CNTs used.The process is economically feasible and easy to carry out. Allthose add more credits to MWCNTs for removing pollutantsfrom e-wastes, which is meaningful for complying withWEEE directive.