Optimization, Equilibrium and Kinetic Studies of Basic Red 2 Removal onto Waste Gossypium hirsutum Seeds

Cationic dye - basic red 2 (BR2) was removed from aqueous solutions by sulfuric acid activated waste Gossypium hirsutum seeds (WGSAB). The main and interactive effects of five process variables such as, adsorbent dose (1.25 – 5 g/L), initial dye concentration (100–300 mg/L), contact time (1–3 h),  pH (2 – 12) and temperature (20 – 400C) were investigated via  response surface methodology (RSM) based on Box–Behnken statistical design.  The optimum values of the key variables were estimated using Derringer’s desirability function. The optimal values were found to be at an adsorbent dose 2.41 g, initial dye concentration 150 mg/L, pH 8.69, temperature 33.570C, and contact time 1.42 h with the maximum desirability of 91%. The equilibrium data obeyed Redlich-Peterson isotherm which showed that the WGSAB was heterogeneous and BR2 was adsorbed in multilayers. The kinetic investigation showed that the BR2 was chemisorbed on WGSAB surface following Avrami fractional order kinetics. The thermodynamic parameters revealed that the BR2 adsorption process was spontaneous and endothermic. Regeneration of exhausted WGSAB found to be possible via acetic acid as elutant.