Natural deep eutectic solvent integrated with bulk liquid membrane system for salicylic acid removal from wastewater

Abstract

This work describes an innovative approach for salicylic acid (SA) removal from wastewater using a bulk liquid membrane (BLM) technique incorporated with natural deep eutectic solvents (NADES) as the stripping phase. The preparation of NADES was achieved by mixing of choline chloride (ChCl) as a hydrogen bond acceptor (HBA) with lactic acid (LA) as a hydrogen bond donor (HBD). Screening studies were performed to select the best NADES molar ratio as a stripping agent for SA removal. The impact of various parameters such as the pH of the feed phase, initial concentration of SA, carrier concentration, mixing speed and temperature were investigated. The conductor-like screening model for real solvents (COSMO-RS) is used to analyse the SA removal and molecular interaction. The SA achieves an extraction efficacy of 73 % and a stripping efficacy of 90.28 % under the optimum conditions: HBA: HBD of 1:1, pH 2 of feed, 0.001 M of SA, 4 wt% of carrier concentration, 150 rpm of mixing speed and at 50 ºC. The SA extraction using the NADES-based BLM technique follows the consecutive first-order kinetic model with an extraction (K₁) and stripping rate constants (K₂) of 0.0128 and 0.0627 min⁻¹, respectively. The SA transport mechanism through the NADES-based BLM adheres to the film theory for mass transfer. COSMO-RS confirmed the extraction efficiency through molecular interactions validated by a sigma profile and a sigma potential between the SA molecules and NADES. This study provides a new and cleaner route for using NADES as the stripping agent in the BLM system for water treatment.