Isotherm, Kinetic and Thermodynamic Terms of Adsorption of Pyrimethamine from Binary Aqueous Solution

The processing of under-utilized sawdust as adsorbent for removing contaminants like pharmaceuticals from aqueous solutions is a sustainable environmental management strategy. In this study, sawdust was carbonized, activated with ZnCl2 and code-named Z-AC. Binary aqueous solutions of pyrimethamine containing paracetamol were treated with Z-AC; and effects of contact time, pH, temperature, adsorbent dose and adsorbate concentration were determined in batch adsorption experiments. The isotherm, kinetic and thermodynamic studies were conducted. The equilibrium was attained at 100 minutes. At pH 2.0 and 7.6, pyrimethamine load on Z-AC were 5.20 and 2.68 mg/g respectively. At 30 oC and 50 oC, pyrimethamine adsorbed were 1.68 and 2.52 mg/g respectively. Z-AC has monolayer adsorption capacity of 4.76 mg/g for pyrimethamine in binary solution. Load of pyrimethamine per unit mass of Z-AC decreased with increased dose of Z-AC. The best isotherm and kinetic fitting were Langmuir (0.98) and pseudo-first order (0.98) respectively. The process was endothermic (+18.5 kJ/mol/K) with increased degree of randomness (+48.52 J/mol/K). The process was feasible at higher temperatures. Higher pH and adsorbent doses de-enhanced the process while increased temperatures enhanced adsorption of pyrimethamine in binary aqueous media. Therefore, Z-AC could be utilized in adsorption process for remediating pharmaceutical contaminated aqueous media. Keywords: pyrimethamine, binary solution, paracetamol, pharmaceuticals, isotherm, thermodynamics