Studies On Preparation And Application Basis Of Pectin/Al₂O₃-ZrO₂ Composite Microsphere

Wastewater with excessive concentration of fluoride is discharged from uranium mine factories, mine extraction, semiconductor factories and so on, which will cause damage to the health of people or animals.Therefore, it is necessary to remove the fluoride from the wastewater.Adsorption has been paid more extensive attention owing to its high removal rate, easy operation, water stability and low cost. However, the removal efficiency of fluoride is limited by adsorbent. Therefore, it is necessary to search for an adsorbent of low cost and good adsorption capacity. Two adsorbents were prepared in this study, one is Al₂O₃-ZrO₂ power adsorbent, the other is pectin/Al₂O₃-ZrO₂ core/shell beads. The adsorption performances of two adsorbents on fluoride were investigated, and the adsorption mechanism and regeneration test were studied, the results are as follows:1. The effect of concentrationof pectin solution, pH and metal ions on the rheological property were investigated. The results are shown that the viscosity of pectin is increased with increasing in the pectin concentration and exhibits the nature of pseudoplastic fluid. The viscosity of pectin is decreased with increasing in the solution pH and pectin gel will formed by adding a certain amount of acid or metal ions.The viscosity of pectin is increased in the following order Zr4+, Al3+ and Ca2+ when the concentration of metal ions is the same. The crosslinking ability of Ca2+ with pectin is the strongest.2. A sorbent of Al₂O₃-ZrO₂ powder was prepared via coprecipitation method, and the molar ratio of Al/Zr, calcination temperature of precursor and adsorption performance on fluoride were investigated.The prepared optimum conditions of adsorbent were Al/Zr molar ratio of 1:4 and calcination temperature of 700 ?. The optimum conditionsfor adsorption were pH of 2, temperature of 25 ?, contact time of 240 min. The experiment data were fitted by Langmuir, Freundlich and kinetic model, and the results showed that the experiment data was better fitted by Langmuir model and pseudo-second-order, the maximum capacity was 114.54mg/g. The sorption process was spontaneous and exothermic from thermodynamic parameters. The adsorption mechanism of Al₂O₃-ZrO₂ powder adsorbent could involve ion-exchange and ligand-exchange based on the results of XRD, EDX,XPS and sorption models.3. A sorbent of pectin/Al₂O₃-ZrO₂ core/shell beads were prepared by coaxial electrostatic spinning device, and the adsorption performance was investigated in batch experiments. Results showed that the prepared optimum conditions of adsorbent were 6 wt% of pectin, 2 wt%of calcium chloride and 3 k V of voltage. The sorption optimum conditions were pH of 2, dose of 0.05 g, temperature of 25 ? and contact time of240 min. Isothermal adsorption models and kinetic model were investigated, and the results showed that the experiment data were better fitted by both Langmuir and Freundlich model and pseudo-second-order model. And the maximum sorption capacity was98.077 mg/g. The adsorption capacity of the adsorbent will be affected by the ions of HCO3- ? PO43- and SO42- coexisting in solution. 90% of volume reduction rate can be reached after the sorbent burning,and 70%of regeneration rate can be reached after four recycling of the sorbent.The adsorption mechanism of pectin/Al₂O₃-ZrO₂ adsorbent was investigated based on the results of XRD, EDX, XPS and sorption models.4. The effect of initial fluoride concentration, flow rate and bed height on dynamic adsorption properties of pectin/Al₂O₃-ZrO₂core/shell bead sorbent were investigated. Results showed thatbreakthrough time and depletion time were decreased with increasing in the bed height, and increased with decreasing in initial fluoride concentration and flow rate.