Statistical physics modeling of phosphate adsorption onto chemically modified carbonaceous clay

In the current study, carbonaceous clay was activated by (I) cetylpyridinium chloride and (II) a mixture of cetylpyridinium chloride with hydrogen peroxide. The raw and modified clays were characterized by FTIR, SEM, zeta potential measurements, and tested as adsorbents for phosphate. Experimental parameters effects including solution pH, shaking time, initial concentration, and adsorbent mass on phosphate adsorption were investigated. The phosphate adsorption kinetics was fitted well by the pseudo-second-order equation. At different temperatures (from 298 to 318 K), phosphate adsorption data were fitted by linear and non-linear forms of different traditional equilibrium models. Theoretical treatment including monolayer, double-layer, and multilayer models were applied for a deeper explanation of the adsorption process. Statistical modeling of phosphate adsorption indicated that monolayer with two energy sites fitted well the experimental data at 298 K. Double-layer with two energies was found to be the best model in describing the phosphate adsorption at 308 and 318 K. Physicochemical parameters governing the interaction mechanism of phosphate adsorption at all temperatures were determined and interpreted. For 298 K, the number of phosphate per site (n) ranged from 1.11 to 1.999 and the adsorbed phosphate amount at saturation (Q(sat)) extended from 10.915 to 21.364 mg g(-1) at 298 K. With rising temperature to 308 and 318 K, then values were found to be less than unity, while the Q(sat) increased from 91.456 to 130.813 mg g(-1), respectively. The calculated adsorption energies (E) in the range of 20-22 kJ mo1(-1) reflected the involvement of dipole bond forces and electrostatic interactions in adsorption process. Thermodynamic parameters indicated that the phosphate uptake was spontaneous and endothermic. (C) 2019 Elsevier B.V. All rights reserved.