Grafted Amberlite 200C Resin for Enhanced Salicylic Acid Adsorption

Removing relatively concentrated salicylic acid (SA) from pharmaceutical aqueous waste was performed using unmodified and modified commercial cationic exchange resin (Amberlite 200C). The modification of the resin involved grafting functional molecules onto the aromatic ring through classical organic reactions or by irreversible adsorption into the resin’s structure. The nitro group ( $${\text{NO}}_{2}^{ + }$$ ) was synthesized by combining nitric and sulfuric acids and then attached to the resin matrix through nitration. Meanwhile, 2,4-dinitrophenyl hydrazine (DNPH), tributyl phosphate (TBP), and ammonium ( $${\text{NH}}_{4}^{ + }$$ ) were irreversibly adsorbed onto the resin matrix via immersion. Consequently, the unmodified resin achieved a 21% elimination of the initial SA, whereas modified resins significantly increased the elimination yield. Specifically, $${\text{NH}}_{4}^{ + }$$ and DNPH-modified resins achieved SA elimination rates of 51.94 and 41.5%, respectively. However, the use of TBP and $${\text{NO}}_{2}^{ + }$$ modified resins resulted in negligible SA removal. The optimal conditions for operation were determined to be: pH 5.5, temperature 21°C, and a contact time of 20 min.