Adsorption of Chromium (VI) from Aqueous Solutions Using Sol-Gel Anionic Clays with Mg/ Al=7
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Adsorption of Chromium (VI) from Aqueous Solutions Using Sol-Gel Anionic Clays with Mg/ Al=7 Ramos R. Esthela1, Gutiérrez O. Norma1, Contreras S. Cesar1, Álvarez R. Javier1 and Fuentes R. Rosalba2. 1 Departamento de Química y 2Departamento de Ingeniería de la División de Ciencias Naturales y Exactas de la Universidad de Guanajuato, Noria Alta s/n, Col. Noria Alta, C.P: 36050, Guanajuato, Guanajuato., México. Email: [email protected] ABSTRACT Anionic clays has been used in the adsorption of anionic species of toxic heavy metals, such as chromium (VI), which is considered to be a dangerous pollutant, due to its deleterious effects on human health such as epithelial irritation and cancer. In this work the removal of chromium in aqueous solutions using anionic clays with Mg/Al=7 was determined. The anionic clays were synthesized by the sol-gel method at pH 10 and 11.5, and were characterized by Xray diffraction, thermal analysis, infrared spectroscopy and N2 adsorption Brunauer-EmmettTeller (BET). By this method, anionic clay containing brucite was obtained. The solids exhibited meso-porosity, high surface areas and thermal stability until 500°C. The data obtained from the adsorption experiments of chromium fitted to the Langmuir adsorption isotherm model and the adsorbent capacity was determined using the Langmuir adsorption equation. The maximum chromium uptake was 45 mg of Cr/g sorbent and 43 mg Cr/g sorbent for anionic clays prepared to pH 10 and 11.5, respectively. The Cr saturation point was attained after eight minutes stirring time. According to chromium adsorption values, the solution pH does not have a significant affect on the adsorption capacity of the anionic clays. INTRODUCTION Chromium exists in the aqueous solution mainly in (III) and (VI) states. In trace concentrations, chromium (III) is non-toxic, and helps the body to control blood-sugar levels, but is toxic to fish when present in water above 5.0 mg/L [1]. On the other hand, chromium (VI) is toxic to mammals and aquatic organisms. Water containing chromium (VI) above 0.05 mg/t [2], is toxic to many plants, aquatic animals and bacteria [3]. Furthermore, Cr (VI) acts as a powerful epithelial irritant and as human carcinogen [4]. In under-developed countries a wide range of industries such as paint and pigment, leather tanning, chrome plating, textile, match, etc. use chromium in their processes and the wastewater containing significant amounts of this metal is pour into superficial water streams [5] Different techniques have been employed for removal chromium (VI) from wastewaters. The most widely used method involves the reduction of chromium (VI) to chromium (III). However, this conventional treatment is expensive and may produce toxic sludge. Sorption process is one of the more effective physical processes that may be used to remove chromium (VI) from wastewaters using traditional sorbets material such as activated carbon [6], zeolites [7] and, metallic oxides [8]. Ion-exchange resin [9] also has been used for chromium removal, but with poor
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