Study of hexavalent chromium sorption by hydrotalcites synthesized using ultrasound vs microwave irradiation
Estudio de la sorcion de cromo hexavalente mediante hidrotalcitas sintetizadas utilizando irradiación de ultrasonido vs microondas
S.P. Paredes-Carrera1*, R.F. Valencia-Martínez2, M.A. Valenzuela-Zapata1, J.C. Sánchez-Ochoa1 and L.V. Castro-Sotelo1
1 Lab. Catálisis y Materiales. SEPI ESIQIE, Instituto Politécnico Nacional, UPALM Zacatenco 07738, México D.F., México. *Corresponding author. E-mail: siviappcar@gmail.com Tel. 57-29-60-00 etx 54224 Fax 57-29-60-00.
]]> 2 SEPI ESIA, Instituto Politécnico Nacional, UPALM Zacatenco 07738, México D.F., México.
Received November 14, 2014
Accepted June 9, 2015
Abstract
The increase of water contamination caused by toxic compounds is a matter of primary concern, the case in point is the state of Guanajuato in Mexico, where one of Ihe main contaminants found in wastewater is Cr(VI), a widely used compound in the tanning process. The development of an efficient technology to remove this substance from water is absolutely necessary. In this work a comparative study of different anionic clays and activated carbon as a reference, was proposed to eliminate this pollutant Hydrotalcites were prepared by the coprecipitation method using ultrasound or microwawe irradiation during the crystallization step. The interlayer compounds were: sulfates, nitrates, chlorides and etoxide-acetylacetonate. The solids were characterized by X-ray diffraction, nitrogen physisorption and scanning electron microscopy with EDS microanalysis. The amount of sorbed Cr(VI) was determined by UV-vis spectrometry. The best option for Cr(VI) removal was the hydrotalcite with chloride as anion in the interlayer. It was found that the sorption was mainly dependent of the interlayer anion and the preparation method and it was not: a function of the specific area. On the other hand the activated carbon is rapidly saturated and its sorptive capacity is practically null.
Key words: hexavalent chromium, hydrotalcites, sorption, synthesis by microwave, synthesis by ultrasound.
Resumen
]]> El aumento en la contaminación del agua es un asunto de gran reelevancia; en Guanajuato México, uno de los principales contaminantes hayados en aguas residuales es el Cr(VI), ya que este compuesto es ampliamente utilizado en el proceso de curtido; de ahí que el desarrollo de tecnologías eficaces para eliminar este tipo de contaminantes es absolutamente necesario. En este trabajo se realizó un estudio comparativo con diferentes arcillas aniónicas, empleando como referencia al carbon activado, el cual permitió proponer un sistema eficaz de eliminación. Las hidrotalcitas se prepararon por coprecipitacion mediante irradiación de ultrasonido y microondas durante la etapa de cristalización. Se utilizaron como aniones de compensación: sulfatos, nitratos, cloruros y una combinación de etóxido-acetilacetonato. Los sólidos se caracterizaron por difracción de rayos-X, fisisorcion de nitrógeno y microscopía electrónica de barrido con microanálisis EDS. La cantidad de Cr(VI) sorbida se determinó por espectrometría UV-vis. La hidrotalcita clorada resultó en la mejor opción para la eliminación del Cr(VI). Se encontró que la sorción es dependiente principalmente del tipo de anión interlaminar seguida por el método de preparación e independiente del área específica. Por otro lado el carbon activado se satura rápidamente y su capacidad de sorción es prácticamente nulo.Palabras clave: cromo hexavalente, hidrotalcitas, sorción, síntesis por microondas y síntesis por ultrasonido.
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Acknowledgements
The authors gratefully acknowledge SECITI-PICSO12-151 and SIP IPN- SIP2014 13 75 proyects for financial support.
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