Carboxymethyl cellulose/sugarcane bagasse/polydopamine adsorbents for efficient removal of Pb2+ ions from synthetic and undergraduate laboratory wastes

Low-cost eco-friendly adsorbents are important as sustainable alternatives for water treatment. Carboxymethyl cellulose (CMC), polydopamine (PDA) and sugarcane bagasse microparticles (BG) were combined to create new biobased adsorbents that can be molded into desirable shapes and sizes, facilitating their application as filters for the treatment of wastewater. Their efficiency was evaluated towards the removal of Pb2+ ions from synthetic solutions and from an undergraduate laboratory waste containing other 16 metal ions, a case study within a real-world context. The adsorption isotherms of Pb2+ ions on CMC/BG/PDA in the absence and in the presence of Ca2+ and Mg2+ ions fitted better to Langmuir models, yielding maximal adsorption capacity values of 27.4 ± 2.8 mg/g and 25.9 ± 1.8 mg/g, respectively. The ΔHads and ΔSads values of +5.7 kJ/mol and +48.3 J/(K.mol), respectively, indicated interactions between Pb2+ ions and CMC/BG/PDA hydroxyl groups, which were confirmed by XPS spectra. The fixed bed column adsorption studies indicated the highest adsorption capacity (qTh) for Pb2+ ions (20 mg/L) as 70.3 mg/g, which would correspond to the purification of 3.5 L of water by 1.0 g of adsorbent. In the presence of Mg2+ and Ca2+ ions, the qTh for Pb2+ ions (20 mg/L) decreased to 28.3 mg/g due to the competitive adsorption. In the column, CMC/BG/PDA removed 80% of Pb2+ ions from the undergraduate laboratory waste at pH 1.0. The simultaneous removal of the other 16 metal ions from the laboratory waste was larger than 50%. The subsequent flocculation with a polycation removed 98.7% of Pb2+ ions and 90% of other metal ions, disclosing the potential of combining biobased CMC/BG/PDA adsorbents adsorption and flocculation to treat complex wastewater from undergraduate laboratories.