Adsorption of lead ions in aqueous solution using silica–alumina nanoparticles M. Medina a , J. Tapia a , S. Pacheco b , M. Espinosa c , R. Rodriguez d, * a DCBI, UAM-Azcapotzalco Av. San Pablo No. 180, Col. Reynosa Tamaulipas, C.P. 02200, México, Mexico b Instituto Mexicano del Petróleo, Eje Central L Cárdenas 152, Apdo. Postal 14-805, C.P. 07730, México, Mexico c Posgrado en Ingeniería UAQ, Cerro de las Campanas S/N, Querétaro, Qro. C.P. 7600, México, Mexico d CFATA, Campus UNAM, Juriquilla, Apdo. Postal 1-1010, Querétaro, Qro C.P. 76230, México, Mexico article info Article history: Received 24 October 2008 Available online 13 January 2010 Keywords: Diffraction and scattering measurements Rayleigh scattering Nanoparticles, colloids and quantum structures Colloids Oxide glasses Aluminosilicates Sol–gel, aerogel and solution chemistry Aerogels Sol–gels (xerogels) Solution chemistry Water Hydration abstract The adsorption of lead ions in aqueous solution on the surface of silica–alumina nanoparticles is reported. The removal of lead ions from simulated industrial wastewater was performed using silica–alumina par- ticles synthesized by the sol–gel method with a molar ratio of 1:1. Small amounts of lead ions were added to the sol until the critical flocculation concentration was reached and the particles flocculated forming aggregates which sediment down, being removed from the sol. The flocculation kinetics was followed using Dynamic Light Scattering that measures the particle size as a function of time. The amount of lead ions adsorbed by the nanoparticles was determined using Atomic Absorption Spectroscopy. The lead con- centration was reduced from 140 ppm to below 10 ppb; this final concentration fulfills the corresponding legislation requirements. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction The environmental pollution produced by lead ions has in- creased in the last decades, becoming an important problem in public health and environmental protection with important eco- nomical repercussions [1]. The increasing levels of lead in the envi- ronment represent a serious threat to human health, living resources and ecological systems, not only by its intrinsic high tox- icity but also by the accumulating effects [2]. Poisoning by lead has been well documented in many areas, mainly in those where Pb pollution has been found more acute [3]. The primary sources of lead pollution arise from industrial effluents, lead smelting areas, deposition of lead mine wastes, mil- itary operations, the use of lead-containing chemical compounds, etc. As a consequence of this, large areas of soil and sediments have been contaminated [4]. Great efforts are made to limit lead con- tamination in wastewater streams and drinking water; these have been stimulated by tough national and international regulations. To meet these regulations, effluents or contaminated water must be treated. The world health organization recommends a maximum lead level, in drinking water where lead pipes are pres- ent, of 50 lgL 1 (50 ppb); if the sample exceeds 100 lgL 1 , ac- tions must be taken to reduce the lead concentration to recommended levels [5]. To reach this goal numerous physical and chemical treatment methods have been designed to remove lead ions from waters and wastewater streams. Different separation techniques including chemical precipitation and separation of pollutants, volatilization, oxidation/reduction reactions, mechanical filtration, ion exchange, membrane separation, selective liquid–liquid extraction, photo- chemical process, flotation and elimination by adsorption on acti- vated carbon, etc., have been applied in the removal of different metal ions in aqueous solutions [6]. From all of these, the physico- chemical methods are the most convenient and widely used for wastewater treatments. These methods are based on the precipita- tion of metal oxides and hydroxides under alkaline conditions, and the subsequent removal of the precipitate by sedimentation and/or filtration; however in these cases the efficiency is far to reach the low values required by the legislation (50 ppb), mainly due to the presence of organic and inorganic complexing agents which difficult the formation of the appropriated insoluble compound, modifying the solubility of the metal oxide and hydroxides [7]. Other methods require expensive facilities and/or are restricted 0022-3093/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2009.11.032 * Corresponding author. E-mail address: rogelior@servidor.unam.mx (R. Rodriguez). Journal of Non-Crystalline Solids 356 (2010) 383–387 Contents lists available at ScienceDirect Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/locate/jnoncrysol