Chromates Removal Using Hydrotalcite-Like Compounds of Mg/Al = 2 And 7: Effect of Textural, Thermal and Structural Prope
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Chromates Removal Using Hydrotalcite-Like Compounds of Mg/Al = 2 And 7: Effect of Textural, Thermal and Structural Properties E. Ramos1*, N. L. Gutiérrez1, C. A. Contreras1, M. T. Olguín2 1
Departamento de Química de la División de Ciencias Naturales y Exactas, Campus Guanajuato de la Universidad de Guanajuato, Noria Alta s/n, Col. Noria Alta, C.P: 36050, Guanajuato, Guanajuato., México. *Email: [email protected] 2 Instituto Nacional de Investigaciones Nucleares, Carretera México-Toluca s/n, km 36.5, La Marquesa, Coyoacán México, C.P: 52750, México.
ABSTRACT Hydrotalcite-like compounds (HLC’s) are a type of ionic lamellar solids with divalent and trivalent metal cations, and exchangeable inorganic and organic anions in the interlamellar space. Interest in HLC arises from the wide applications, where thermal, structural and textural properties and as well as sorption capacity are the properties interested in. HLC are used to removal dangerous metallic anionic, such as Chromium (VI). In this study, Mg/Al - HLC’s were synthesized by sol-gel method. Effect of Mg/Al was probed to show the effect on their structure, morphology, physical properties and sorption capacity. The materials were characterized by Xray diffraction, Fourier transform infrared spectroscopy, textural analysis and thermal analysis. Sorption profiles were investigated using batch method at initial concentration different to was determinate model and kinetic sorption capacity such as maximum removal capacity to equilibrium. Was find values of 428 and 127 mg chromates/g HLC’s to Mg/Al = 2 and 7 respectively, equivalent to 125 and 57 mg of chromium /g HLC’s in la little time of one minute. Keywords: absorption, ion-exchange material, porosity, sol-gel, texture, waste management INTRODUCTION Hydrotalcite-like compounds are a type of anionic clays who present lamellar structure. These layers present at residual positive-charge produced for some trivalent metallic atoms have been replaced at divalent atoms in brucite-like structure. The cationic charge of sheets is compensated by hydrated anions between the interlamellar spaces. The HLC’s can be represented by the general formula [M2+1-xAl3+x(OH)2](An-)x/n•mH2O. M2+ and M3+ are any divalent (Mg2+, Ni2+, Zn2+, Co2+, Fe2+, etc.) and trivalent (Al3+. Cr3+, Fe3+, etc.) metallic atoms, respectively. An- is any atom and compound anionic (CO32-, SO42-, Cl-, OH-, NO3-, etc.). The x and 1-x are the molar ratio between both cationic metals, equivalent to x = M3+/(M2+ + M3+). The most common HLC’s known is hydrotalcite, which contain Mg2+ and Al3+ as metallic atoms, and carbonate as anion of compensation who are in general preferred. Lamellar structure are stable thermally until 400-500 °C where collapse due to dehydration, dehydroxylation and decarbonation formed then mixed oxides, which are commonly able to recover the lamellar structure by means of “memory effect” that consisting in t o leave the HLC’s in contact with an anion aqueous solution [1]. HLC’s are conventionally synthesized by coprecipitation of m
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