Zinc oxide coated regenerated spent FCC catalyst for water purification

Abstract

Introduction: Zeolites are microporous aluminosilicates, commonly used as commercial adsorbents and catalysts. As an adsorbent, zeolite can adsorb gram-positive bacteria when compared with gram-negative bacteria (1,2). Ultrafine zinc oxide nanoparticles in colloidal medium is toxic to E. coli bacteria (3). ZnO-coated zeolite adsorbent can effectively remove of humic acid and E. coli from water when compared to zeolite adsorbent (4-5). The spent FCC (SFCC) catalyst is very harmful to the human health by being absorbed mainly into the respiratory tract and lungs due to its tiny particles of size 60-100 micrometer (1). Most of the spent FCC catalysts are currently disposed as landfills, which leads to the wastage of valuable metal resources and the environmental pollution. In this work the spent zeolite catalyst is regenerated and coated with zinc oxide and this zinc oxide coated regenerated spent FCC catalyst (ZOCRSC) is used to remove E. coli from water. Methods: In this work, decoking is done to burning off the deposited carbon by roasting in air at 550°C for 2 hours. Then SFCC catalyst is leached with HCl and oxalic acid. Activated SFCC catalyst, obtained as a leaching residue is separated. Zinc oxide is coated on the regenerated catalyst to develop zinc oxide coated zeolite adsorbents. Coating procedure follows activated catalyst modified by HNO3 and then Zn(NO3)2 solution. To characterize crystal structure of zeolite and ZOCRSC, XRD, SEM, and BET analysis were carried out. The water from the treatment plant after secondary treatment was used for the experiments and the E. coli content was estimated using plate counting technique. ZOCZ is added to the E-coli containing water and after proper mixing the suspension is allowed to settle. Sample is collected from treated water at different intervals for determining E. coli content. The treatment procedure was also done using the spent coated sample, acid activated sample and spent FCC catalyst and are used as a comparison with ZOCZ. Results & Discussions: The XRD pattern shows that the ZOCRSC exhibited similar characteristic diffraction peaks to that of the uncoated samples which indicates that the modification did not affect the mineralogy of the zeolite and in addition it also exhibited similar characteristic diffraction peaks to those of ZnO. Thus, the XRD pattern and the SEM images of ZnO coated spent catalyst and ZnO coated regenerated catalyst shows that coatings of ZnO on zeolites were done effectively. The surface area and pore volume of zinc oxide coated regenerated spent FCC catalyst is determined from BET analysis. The removal of E. coli from water was quantified by plate counting. The E. coli count of the untreated water sample is 560 cfu/ml and treated sample after 30 minutes is less than 1 cfu/ml. Water treated using spent FCC catalyst without any modification did not show any change in the E. coli count. The acid activated catalyst and spent FCC catalyst coated with ZnO reduce the E. coli content in the water to 11 cfu/ml and 6 cfu/ml respectively after 90 minutes. Conclusions: ZnO coated regenerated spent FCC catalyst is developed from waste spent catalysts is utilized for the removal of E. coli from water. The ZOCRSC removes E. coli effectively when compared with spent FCC catalyst coated with ZnO, acid activated catalyst, and spent FCC catalyst in a short period. The spent FCC catalyst coated with ZnO cannot be directly used for treating purpose as it contains various contaminant metals which should not be present in treated water. Keywords: Escherichia coli, Spent FCC catalyst, Zinc oxide, ZOCRSC