Optimization of protic ionic liquid-assisted chitosan production from shrimp shell waste via response surface methodology for the sustainable recovery of critical metals from spent lithium-ion batteries

The application of protic ionic liquids (PILs) proved to be a viable and sustainable method for chitin extraction from shrimp shell biomass waste. Among the three amin-based PILs investigated for extracting chitin from shrimp shells (Triethylammonium acetate [Tea][Ac], Triethylenetetrammonium acetate [Teta][Ac], and Ethanolammonium acetate [Eth][Ac]), [Eth][Ac] was selected as the optimum option due to its greener characteristics, lower toxicity, biodegradability, and property enhancement. The PIL-extracted chitosan was then used as a biosorbent for the selective adsorption of Co(II), Mn(II), and Ni(II) from the leachate of spent lithium-ion battery (LIB) cathodes, leached with a synergistic mixture of 1.25 M sulfuric acid and 0.55 M citric acid. Chitin extraction parameters (temperature, time, and liquid-to-solid ratio) were optimized using response surface methodology. The optimal conditions (92 °C, 27.8 h, L/S = 16 g/g) resulted in a chitin yield of 56.67 wt.%, with adsorption rates of 82.42 ± 1.65% for Co(II), 35.09 ± 2.63% for Mn(II), and 98.30 ± 0.63% for Ni(II). Adsorption isotherm analysis of the optimal [Eth]-extracted chitosan demonstrated adsorption performance exceeding that of commercial chitosan. FT-IR spectra matched those of commercial chitosan, confirming the preservation of key functional groups, whereas BET analysis indicated a higher specific surface area. Collectively, these results validate a green, waste-biomass-derived adsorbent for the efficient recovery of critical metals from spent lithium-ion batteries while simultaneously valorizing biomass waste. • Ammonium-based ionic liquids were used to extract chitin from shrimp shell waste. • Shrimp shell-derived chitosan treated spent LIBs in a circular economy approach. • [Eth]-extracted chitosan was used as a biosorbent for critical metal recovery. • Optimal extraction chitin conditions were 92 °C, 27.8 h, L/S = 16 g/g. • The adsorption rates were 82% for Co(II), 35% for Mn(II), and 98% for Ni(II).