Utilização de resíduos aluminosilicatos como catalisadores foto-Fenton e adsorventes no tratamento de efluentes

Abstract

The management of Water Treatment Plant (WTP) sludge and coal fly ash waste is one of the biggest problems faced by many sanitation and thermoelectric companies, with landfill being the main destination of these materials. In parallel, textile effluents are potential polluters of water resources, so the removal of these contaminants from wastewater is extremely important. This work evaluated the utilization of WTP sludge and thermoelectric coal fly ash (raw materials, calcined and modified by alkaline fusion) as photo-Fenton catalysts and adsorbents in the removal of dyes present in industrial effluents. In the photo-Fenton reaction, WTP sludge calcined at 600°C and coal fly ash was used for degradation of amaranth red dye and procion red, respectively. In the adsorption, the WTP sludge calcined at 600 ºC was also used in the removal of red dye 97 and the coal fly ash after alkaline fusion in the adsorption of crystal violet dye. Both materials presented in their chemical composition high contents of silicon oxides (45.10 and 65.50%), aluminum (36.65 and 23.94%) and iron (12.65 and 4.10%). It was observed in the X-ray diffraction (XRD) of the two materials that the main crystalline phase was quartz. Both materials have mesoporous structures, with average pore diameters of 13.2 and 34 nm and surface areas of 60.2 and 0.50 m² g-¹ , respectively. Through scanning electron microscopy (SEM) analysis with EDS, the iron oxide was homogeneously distributed on the solid surface of these materials. The optimum conditions of the photo-Fenton reaction of the WTP sludge defined by RCCD were pH 2.8, amount of H2O2 5.5 mmol L-¹ and mass of catalyst 0.75 g L-¹ , with 97% decolorization efficiency after 30 min and 98% of TOC at 420 min. The best conditions of fly ash were mass: 0.6 g L-¹ ; pH 3 and H2O2 4 mmol L1 with decolorization efficiency of 93.6% of procion red dye at 60 min photo-Fenton reaction and 43% of TOC at 240 min. The WTP sludge adsorption kinetic experimental data were best fitted to the pseudo-second order model and the equilibrium data to the Langmuir model, with the maximum adsorption capacity of 4957 mg g-¹. In the tests with simulated effluent the removal was 74.4 %. Through the characterizations it was analyzed that the alkaline fusion of fly ash provided an amorphization of the material and considerable improvement in the textural properties because the modified fly ash (MFAAF) showed high pore volume (0.154 cm³ ) and surface area (65.40 m² g -¹). The pseudo-second order kinetic model fitted best to the kinetic experimental data with maximum adsorption capacity 77.60 mg g-¹ and the Freundlich model, to the equilibrium data. From the results obtained, it was concluded that the WTP sludge and coal fly ash are alternative catalysts in the photo-Fenton reaction and efficient adsorbents to treat textile effluents.