Simultaneous adsorption of methylene blue cationic dye and paraquat herbicide on activated lightweight expanded clay aggregate (LECA) as a sustainable and recyclable adsorbent

In recent years, organic dyes and herbicides have become a major source of water pollution threatening human health and the environment. In this study, acid-alkali-activated lightweight expanded clay aggregate (LECA) was used for the binary adsorption of methylene blue (MB) dye and paraquat (PQ) herbicide. The effects of various parameters, including initial dye and paraquat concentration, adsorbent dosage, contact time, solution pH, and temperature, were studied and optimized to maximize single and binary mixture adsorption. In the binary system, MB's maximum adsorption capacity was 37.03 mg/g, which was higher than in the single system (31.74 mg/g). In contrast, PQ adsorption capacity in the binary system was significantly reduced (21.23 to 10.09 mg/g). As a result, MB inhibited PQ uptake in the binary system significantly. Adsorption kinetics and equilibrium isotherms were performed for both single and binary mixtures. Experimental data were simulated using the Langmuir, Freundlich, and Temkin isotherm models in the single system and competitive Langmuir in the binary system. Kinetic study revealed that dye and paraquat herbicide adsorption process followed the pseudo-secondorder model. Moreover, to evaluate the reuse performance of the adsorbents, the adsorption-desorption process of MB and PQ was repeated five times. The study proved that activated LECA can simultaneously remove dyes and herbicides from aqueous solutions as a sustainable and reusable adsorbent.