Modeling isotherms, kinetics and understanding the mechanism of phosphate adsorption onto a solid waste: Ground burnt patties

• Grounded burnt patties (GBP), a solid waste is used as an adsorbent for phosphate removal for the first time.
• Approximately 98% phosphate removal efficiency of GBP from phosphate rich aqueous solution.
• Characterization of adsorption behavior of phosphate onto GBP by PIXE, PIGE, FTIR, XRD and SEM.
• No influence of co-existing anions on phosphate adsorption onto GBP.
• Suggestive use of spent adsorbent as a source of phosphorous in agriculture.

The objective of the present study was to investigate the adsorption behavior of grounded burnt patties (GBP), a solid waste generated from cooking fuel used in earthen stoves, as an adsorbent for phosphate removal from aqueous solution. The characterization of adsorbent was done by proton induced X- ray emission (PIXE), and proton induced γ-ray emission (PIGE) methods and the adsorption mechanisms by Fourier transferred infra-red spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis. The effects of adsorbent dose, contact time, initial solution concentration, agitation, etc. on the uptake of phosphate by the adsorbent in batch mode were examined. The equilibrium data were fitted to different types of adsorption isotherms and kinetic models. Freundlich isotherm model and pseudo-second-order kinetic model illustrated best fit to the data. The favorability and spontaneity of the adsorption process are established by the values of experimentally calculated parameters such as separation factor (RL), 0.03, Freundlich exponent (n), 3.57 and Gibb
tm)s free energy change (΢G°), ∧1.32 kJ/mol. The presence of coexisting anions showed no competing effects on phosphate removal efficiency. Breakthrough curves obtained from column study revealed that the lower flow rate and higher bed heights result in longer column saturation time. The results of this study suggested that GBP can be used as a low cost, highly efficient adsorbent for phosphate removal from aqueous solution.

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