Production process of zeolite X using alum sludge issued from drinking water treatment plants
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Production process of zeolite X using alum sludge issued from drinking water treatment plants F. Espejel-Ayala, R. M. Ramírez Z. Instituto de Ingeniería, Coordinación de Ingeniería Ambiental, Universidad Nacional Autónoma de México, Cd. Universitaria, Coyoacán 04510. México, D. F., México. ABSTRACT The present work describes a patent applied for registration at the IMPI (Instituto Mexicano de la Propiedad Industrial) of a production process of zeolite X using as raw materials alum sludges issued from drinking water treatment plants. Sludge sample was collected in a water drinking plant located northern Mexico City. The sample was dried and then physicochemical and microbiological analyses were carried out (metal content, main oxides content, mineralogical analysis, helminth eggs content, fecal coliforms). In accordance with its characterization, two main steps of the zeolites production process were performed: 1) alkaline fusion of alum sludge-NaOH mixture for increasing the dissolved precursor’s content and 2) alkaline hydrothermal treatment. Spherical particles of zeolite X were identified by SEM and XRD respectively. The best synthesized zeolite showed a CEC=2.11 meq/g, value being similar to the data reported for clinoptilolite (the most commonly zeolite used for water treatment in the removal of heavy metals). Thus, the synthesized zeolite X in this work can be used for the same purpose. INTRODUCTION Zeolites are aluminosilicates belonging to the tectosilicate group. They are formed by [SiO4]4- y [AlO4]5-tetrahedrons [1]. Structural arrangement of tetrahedrons produces the formation of porosity of molecular size and also of a great surface area. These characteristics allow zeolites can be used as selective adsorbents for the removal of certain molecules (heavy metals, ammonium, nonpolar molecules, etc). The crystalline lattice of [AlO4]5- tetrahedrons shows sites with excessive negative charge, thus metallic positive ions and protons can be added to equilibrate the lack of positive charge. This fact confers them exchange ionic properties for the removal of heavy metals and ammonium from wastewater [2]. Among these materials, zeolite X, having a general formula Na2Al2Si3.3O10.67H2O, is used as detergent builder, heterogeneous photo degradation catalyst and in the adsorption of SO2, CO2 and NH3 [3, 4]. Due to the high production costs of zeolite X, the use of raw economical materials has been studied [5]. This could also mitigate the environmental problems associated to disposal of industrial wastes, such as alum sludges (AS) generated in drinking water treatment plants. AS are usually disposed in landfills, however, some attempts have been made to reuse them for producing some industrial materials. For example, Ramírez Zamora, [6] assessed alum AS to be used as raw material to produce mortars and to elaborate fired bricks. On the other hand, in South Korea, You et al. [7] carried out synthesis trials of zeolite A and hydroxisodalite using sludge generated in drinking water treatment plants. However, currently an
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