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Removal of lead(II) from aqueous solution by adsorption onto manganese oxide-coated carbon nanotubes1.IntroductionLead is attracting wide attention of environmentalists as one of the most toxic heavy metals. The sources of lead release into the environment by waste streams are battery manufacturing, acid metal plating and finishing, ammunition, tetraethyl lead manufacturing, ceramic and glass industries printing, painting, dying, and other industries [1,2]. Lead has been well recognized for its negative effect on the environment where it accumulates readily in living systems. Lead poisoning in human causes severe damage to the kidney, nervous system, reproductive system, liver and brain. Severe exposure to lead has been associated with sterility, abortion, stillbirths and neo-natal deaths [3].Out of the wastewater treatment methods involving lead,precipitation, coagulation–sedimentation, reverse osmosis, ion exchange, cementation, and adsorption onto activated carbon,adsorption is considered quite attractive in terms of its efficiency of removal from dilute solutions, economics, and handling [4,5]. Various adsorbents such as activated carbon, iron oxides, filamentous fungal biomass and natural condensed tannin havebeen explored [6]. EPA drinking water standards for lead are 0.05 mg/l, but a level of 0.02 mg/l has been proposed and is under review [4]. Increasingly stringent standard on the quality of drinking water has stimulated a growing effort on the exploiture of new high efficient adsorbents. So the necessity to exploit new high efficient adsorbents is great. Carbon nanotubes (CNTs), a novel kind of carbon, were first reported by Iijima in 1991 [7]. CNTs can be thought of as cylindrical hollow micro-crystals of graphite. Because of relatively large specific area, CNTs have attracted researchers’ interest as a new type of adsorbent and offer an attractive option for the removal of metals, fluoride, organic pollutants, and radionuclide 243Am(III) [8–11]. CNTs can also be used as supports for adsorption materials. Aluminum and iron oxide-coated CNTs for metal removal have been proved successful for the enhancement of treatment capacity [12,13]. Compared to Fe or Al oxides, Mn oxides have a higher affinity for many heavy metals and it was coated on activated carbon, zeolite, and sand for metal ions removal [14–18]. Based on these observations, a composite adsorbent, Mn oxide-coated CNTs (MnO2/CNTs), was proposed to adsorb Pb(II) from aqueous solution. The effect of dose of MnO2, pH and the kinetic adsorption process and adsorption thermodynamics of Pb(II) on MnO2/CNTs were studied. |
