Zeolites synthesis using as a raw material the aluminium anodizing sludges

There were found, by atomic absorption and scanning electronic microscopy techniques, concentrations in between of 25,3% and 39,45% of aluminium respectively, in the anodized aluminium sludge on an industry that operates in Ecuador. Besides there were identified minor concentrations of Na, Mg, Ca and Si. Therefore the objective of the present research was to investigate, at the laboratory level, the feasibility of using these industrial residues as a source of precursors for the zeolites synthesis. The chemical composition of a fixed 20 g of sludge was adjusted by using a sodium hydroxide solutions in a varying concentrations of 0,5M, 1,0 M, 1,5 M, 2,0 M, 2,5 M and 3,0 M in a mixture with hydrated Na₂SiO₃ in a constant amount added to the raw material. Molar ratio SiO₂/Al₂O was kept constant at 1,24 value, whereas the Na₂O/Al₂O₃; Na₂O/SiO₂ and H₂O/Na₂O were varied as sodium hydroxide solutions changed in concentration. The processes of precursor's dilution, aging and zeolite crystallization were carried out a constant temperature of 100 degrees celsius for a 48 hours reaction time. By the X-ray diffraction technique, the synthesis of the Na-P1 GIS [Na₆(H₂O)₁2] [Si₁0Al₆O₃2] zeolite was identified, with three types of mineralogy. Besides the zeolites ACP-1 and Sodalite Octahydrate were identified. The electronic images show a product with a well-defined morphology. The optimum conditions for the synthesis were the 1.5 M concentration of the caustic soda solution, and molar ratios of 1,24 SiO₂/Al₂O₃; 0,61 Na₂O/Al₂O₃; 2,02 SiO₂/Na₂O; 15,51 H₂O/ Na₂O and 7,68 H₂O/ SiO₂. At higher concentrations of the sodium hydroxide solution, the same zeolites were obtained, as evidenced by X-ray diffractograms, but the electronic images of the products show deformed crystals, possibly due to the excess of sodium hydroxide. (author)