Valorization of Posidonia oceanica balls: sustainable simultaneous synthesis of green de-icer and eco-friendly adsorbent for saline water treatment from methylene blue.

Neptune beach balls (NB) are natural waste materials often found along the Mediterranean Sea coasts. NB are originated from the decay of Posidonia oceanica (PO) organs leaving balls of the plant fibers, sand and impurities. Due to upcoming global warming, the accumulation of contaminants-loaded NB among PO wastes, they are expected to intensify, increasing the environmental challenges posed by these eco-wastes. This study presents a novelle sustainable acetic-acid activation strategy for the double valorization of Neptune balls (NB) into an eco-friendly adsorbent and green deicer. The materials were characterized using ICP-OES, FTIR, Raman spectroscopy, XRD, TGA, SEM-EDX, zeta potential, and/or pHPZC analyses. Through a simple and economical treatment process, 84.5% of the cleaned NB waste is transformed into a natural adsorbent. Simultaneously, the circular economy is approached by valorizing the acid activation liquor waste into an environmentally friendly calcium magnesium acetate (CMA) deicer that was recovered with approximately 83% efficiency, as a by-product adding value to the NB valorization process. The natural adsorbent was capable of removing up to 97.5% of MB from freshwater and saline water, with a monolayer MB adsorption capacity of 135 mg g- 1. The MB adsorption is well fitted by the Langmuir and Freundlich models while following the pseudo-second-order kinetics model. MB-multilayer was suggested to be adsorbed primarily by electrostatic attraction. The activated NB has been successfully tested for the removal of MB dye from seawater spiked with MB, while CMA demonstrated better deicing performance compared to conventional sodium chloride salt, highlighting the potential to advance the economic valorization of NB waste, supporting both water treatment and eco-waste management.