Preparation of Cellulose Nanofiber Aerogels from Paper Sludge Waste and Their Use for the Removal of Metal Ions Used in Batteries from Water

Developing cost-effective, bio-based adsorbents for hazardous battery industry effluents is a major environmental challenge. This study isolated cellulose nanofibers (CNFs) from primary paper sludge (PS)—a tissue manufacturing waste—via chemical modification using (2,2,6,6-Tetramethylpiperidin-1-yl)oxyl oxidation (TEMPO oxidation) and ultrasonication to fabricate highly porous aerogels. The PS-CNF aerogels were evaluated for removing battery-related metal ions (Pb2+, Cd2+, Co2+, Mn2+, Ni2+, and Li+). To assess the structural impact of residual kaolin in the sludge, performance was compared against aerogels derived from fiber dust (FD) waste, as well as a commercial resin (Purolite C-100). The PS-CNF aerogels demonstrated superior maximum adsorption capacities of 39.28 mg/g for Pb2+, 29.80 mg/g for Cd2+, 21.05 mg/g for Co2+, 20.19 mg/g for Mn2+, 16.80 mg/g for Ni2+, and 11.33 mg/g for Li+. They consistently outperformed the FD-CNF matrix across the entire series. This enhanced efficiency is attributed to the residual kaolin in the paper sludge, which also acts as a physical spacer, increasing the aerogel’s internal porosity. Adsorption generally followed the Langmuir isotherm and pseudo-second-order kinetics. Furthermore, the PS-CNF aerogels exhibited higher efficiency than the commercial Purolite C-100 cation exchange resin. Ultimately, this work demonstrates the potential of upcycling paper sludge into sustainable, high-performance adsorbents for treating toxic battery effluents.