Study of hexavalent chromium sorption by hydrotalcites synthesized using ultrasound vs microwawe irradiation

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 the 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.