Sorption interactions and behavior of bentonite-lignite based composite toward immobilization of dyes, pharmaceuticals and surfactants

The presence of dyes, pharmaceuticals, and surfactants in the environment results from extensive industrial and societal progress, prompting the need to explore efficient and safe techniques for their removal. Common concentrations in wastewater can range from micrograms to milligrams per liter, which is concerning due to their persistence and potential health impacts. The sustainable approach of using a nonconventional, eco-friendly mineral-organic composite might address this environmental issue. This study focuses on utilizing a composite of bentonite (BEN) and lignite (LIG) as a sorbent for dyes: Rhodamine b (RB), Remazol brilliant blue r (RBBR), pharmaceuticals: ibuprofen (IB), sulfamethoxazole (STX), and surfactant: sodium dodecylbenzenesulfonate (SDBS) from both synthetic solutions and real wastewater. BEN was chosen for its high cation exchange capacity, while LIG was selected for its ability to adsorb both anionic and cationic formsdiverse functional groups. The composite with BEN to LIG ratio of 20:80 (BL 20:80) demonstrated superior sorption capacity. The adsorption performance is quantified, showing removal efficiencies of up to 18.9 mg RBBR/g, 22.8 mg RB/g, 1.77 mg IB/g, 1.47 mg STX/g, and 4.7 mg SDBS/g. Sorption efficiency is influenced by factors such as the initial sorbate concentration, the pH of the solution, the form of sorbates, and the adsorbents textural, physicochemical (point of zero charge pHZPC), ion-exchange capacity, hydrophobicity/hydrophilicity) properties. Generally, STX and RB is favored by slightly acidic conditions (pH 4-7), while RBBR and IB are favored by alkaline conditions (pH >7). The complex physical sorption mechanism includes hydrogen bonding, electrostatic and dispersion forces, as well as π-π interactions. Nuclear magnetic resonance spectroscopy (NMR) suggests that a significant portion of the hydrogen bonding interactions contributes to RB adsorption. The sorption results indicate that the specially-designed mineral composite can effectively remove various chemically distinct organic compounds from real wastewater. Subsequent investigations will focus on the granulated BL 20:80 composite and its applicability in dynamic column systems. This aligns with the ongoing development of purification technologies.