The demand for lithium (Li) is increasing by its pivotal role in energy storage and transportation electrification nowadays. The surge in demand has prompted a global quest for sustainable and cost-effective methods to extract Li from water sources. This thesis centers on valorizing abundant lignocellulosic waste, specifically hazelnut shell waste, abundant in Türkiye starting with the phosphorylation of pristine cellulose, contributing to the development of innovative biosorbents tailored for extracting Li from aqueous solutions. Comprehensive material characterization was conducted using SEM– EDS, FTIR, XPS, BET, XRD, and TGA analyses. Various factors influencing the process, such as biosorbent dosage, initial concentration, temperature, contact time, pH, and coexisting ions were explored. The maximum sorption capacity was determined to be 9.60 mg/g for phosphorylated functional cellulose (FC) and 7.71 mg/g for phosphorylated functional hazelnut shell waste (FHS) at 25°C, by the Langmuir model. Impressively, Li sorption reached equilibrium within a 3-minute, indicating the rapid kinetic properties of biosorbents. Furthermore, FC and FHS were employed in a packed bed column, leading to a threefold increase in sorption capacity under dynamic flow, especially at lower flow rates, regardless of bed height. Remarkably, a mere 15.75 mL of 5% H2SO4 solution was adequate to desorb approximately 100% of Li from the saturated biosorbents. The column data interpreted with theoretical models, affirmed the potential for large-scale implementation of these biosorbents. Preliminary tests on Li recovery from geothermal water using FC and FHS were also conducted to assess their applicability in real brine conditions, with a comparison made to the commercial ion exchange resin, Lewatit® TP 260.