Resin-Based Technology for the Efficient Removal of Benzocaine from Wastewaters

Pharmaceutical residues continue to increasingly contaminate water systems at a global level, and conventional wastewater treatment plants are unable to completely remove these emergent compounds. This study investigates the benzocaine adsorption from aqueous solutions onto Amberlite XAD-7 (X7) resin, with emphasis on quantitative performance metrics and mechanistic understanding. Adsorption occurred rapidly, reaching equilibrium within 60 min, with a maximum adsorption capacity (Qe) of 140 mg/g and a Langmuir monolayer capacity of 147 mg/g. Experimental parameters strongly influenced X7 performance: resin dosage (0.01–0.05 g) and agitation speed (25–200 rpm) enhanced removal efficiency from 10% to 99.9%, while pH variation (5–9) had a negligible effect, confirming a predominantly hydrophobic, non-ionic adsorption mechanism. Equilibrium data are best described by the Langmuir model (R2 = 0.9920, b = 5.2 L/mg, RL = 0.0003), indicating highly favorable monolayer adsorption, while kinetic behavior is described by the pseudo-second-order (PSO) model. FTIR-ATR analysis confirms benzocaine retention through characteristic shifts in aromatic, amine, and ester bands. TG/DSC measurements prove the thermal stability of X7 and the incorporation of benzocaine within the polymeric matrix. Desorption efficiencies ranged from 40% (NaOH) to 97% (HCl-ethanol mixture), demonstrating that X7 was regenerated under the tested conditions with a single cycle. Overall, X7 exhibits high capacity, robustness, and recyclability, highlighting its strong potential for efficient benzocaine removal from contaminated wastewater.