Síntese e caracterização de compósitos de zeólitas magnéticas utilizando caulim para abrandamento de água

Abstract

The present work deals about the synthesis and characterization of magnetic zeolites obtained by hydrothermal route using kaolin from Brazilian Northeast as silicon and aluminum source. By means of the X-ray diffraction technique it was possible to identify zeolite LTA and zeolite P1 as major crystalline phases for each synthesis, with low intensity peaks referent to unreacted quartz present in the kaolin used, which is in accordance to the. FTIR spectra; the nanoparticles were identified as magnetite, with low intensity peaks referent to goethite. In scanning electron microscopy, however, it was not possible to morphologically identify these minor components, while the zeolites showed well defined morphologies, presenting unchanged morphology when in the composites form, but with nanoparticles dispersed over their surface, as expected. From transmission electron microscopy it was observed that the nanoparticles were of ca. 50 nm. Magnetic measurements indicated magnetite presence with superior diameter to critical diameter to superparamagnetic particles and remanent magnetization. Thermogravimetric analyses showed for the composites, lower mass loss than compared to the pure zeolites what may be associated to the improvement of its thermal stability. Granulometric distribution indicated nanoparticles agglomeration in variable sizes, while zeolites formed agglomerates of ca. 10 µm. Water softening was accomplished by using both zeolites, with high efficiency on Ca2+ removal and similar behavior between the zeolite and its respective composite, being the best result observed for zeolite A, with efficiency of 97,95%, reaching equilibrium in the first contact minutes. The dependence on mass studies also showed that zeolite A and its composite presented the best efficiency, whereas zeolite P achieved the same removal levels using corresponding zeolite masses (45 mg). This way, the proposed method for zeolites synthesis proved to be efficient, so that the use of a magnet is capable to attract them, leading their excellent separation from the aqueous medium with its ionic exchange capacity unaffected.