Studies on the treatment of wastewaters containing Cr6+ with ironoxide-silica composite materials prepared by different methods

Abstract

Chromium is found in many forms, but Cr(VI) is known to be carcinogenic to humans. It is important to ensure the removal of Chromium (VI) from aqueous solutions and industrial effluents. Among the known methods for removing chromium from aqueous solutions, adsorption is an important method based on the ability of some porous materials to bind chromium to their surfaces. In order to improve the efficiency of this process a variety of new synthetic materials have been investigated. In the present work a novel method for preparing Fe2O3-SiO2 composite materials is presented. Iron (III) oxide was prepared by electrochemical method. SiO2 was prepared by acid hydrolysis of the tetraethylorthosilicate (TEOS). A relatively slow rate of hydrolysis of the TEOS occurred during the process, which resulted in larger silica particles with a narrower size distribution. This study shows the influence of the type of silica matrix on the structure, size, and distribution of the Fe2O3 particles in the Fe2O3-SiO2 systems. The gels were annealed at 550°C in order to consolidate the matrices. The structural characterization of the synthesised materials was performed by X-ray diffraction, FT-IR, Scanning Electron Microscopy (SEM), EDS and DTA/TGA analysis. The present study introduces a good alternative method for Cr (VI) removal from aqueous solutions by adsorption, allowing the development of newer, lower operational cost, and more efficient technology than other processes already in use. Adsorption was found to be dependent on pH and initial concentration of Cr(VI) solution. Results of adsorption studies suggest that pristine iron oxide and silicon (IV) oxide removes 72.10% and 24.73% respectively. The iron oxide – silicon (IV) oxide composite, prepared in this work, removes 93.88% Cr(IV) from aqueous solution. Therefore, it can be concluded that iron oxide – silicon (IV) oxide composite is a potential adsorbent for adsorption of Cr(VI) from aqueous solution. Studies of the sorption kinetics show that equilibrium adsorption was attained in 20 minutes depending on other experimental conditions. The kinetic data justified Lagergren first-order kinetic equation. Adsorption isotherm study showed that the results fulfilled the Langmuir Model of adsorption isotherm. oxide and silicon (IV) oxide removes 72.10% and 24.73% respectively. The iron oxide – silicon (IV) oxide composite, prepared in this work, removes 93.88% Cr(IV) from aqueous solution. Therefore, it can be concluded that iron oxide – silicon (IV) oxide composite is a potential adsorbent for adsorption of Cr(VI) from aqueous solution. Studies of the sorption kinetics show that equilibrium adsorption was attained in 20 minutes depending on other experimental conditions. The kinetic data justified Lagergren first-order kinetic equation. Adsorption isotherm study showed that the results fulfilled the Langmuir Model of adsorption isotherm.oxide and silicon (IV) oxide removes 72.10% and 24.73% respectively. The iron oxide – silicon (IV) oxide composite, prepared in this work, removes 93.88% Cr(IV) from aqueous solution. Therefore, it can be concluded that iron oxide – silicon (IV) oxide composite is a potential adsorbent for adsorption of Cr(VI) from aqueous solution. Studies of the sorption kinetics show that equilibrium adsorption was attained in 20 minutes depending on other experimental conditions. The kinetic data justified Lagergren first-order kinetic equation. Adsorption isotherm study showed that the results fulfilled the Langmuir Model of adsorption isotherm.