Microwave-synthesized CMCAM hydrogels for simultaneous organic and metal removal from mixed oilfield effluent

Managing mixed oilfield effluent is challenging due to its high salinity and organic content. This research develops a microwave-assisted method to produce a carboxymethyl cellulose-grafted polyacrylamide (CMCAM) hydrogels capable of removing multiple pollutants from raw, hypersaline MOE (COD ≈ 20,000 mg/L; TDS ≈ 49,000 mg/L). The best-performing CMCAM 10% formulation achieved 33% COD removal with an adsorption capacity of 1462 mg/g at the optimal adsorbent dosage of 5 g/L. Beyond organic removal, the hydrogel shows strong selectivity for harmful divalent cations, capturing 95.2% of Sr 2+ , 87.8% of Ba 2+ , and 70.9% of Pb 2+ at higher dose of 50 g/L. A notable finding is the “wave-like” non-monotonic kinetic behavior, which challenges the effectiveness of traditional pseudo-second order models in complex multi-solute systems. Mechanistic insights from XPS and FTIR confirm a combined removal mechanism involving hydrogen bonding, electrostatic attraction, and metal coordination. High-resolution SEM images reveal surface colonization by inorganic salts (radial spherulites) and organic compounds (acyclic spheroids). Although thermal regeneration suggests some stubborn “poisoning” ions persist, overall, CMCAM hydrogels are a high-capacity, selective, and sustainable solution for pretreating the industry's most difficult wastewater streams.